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RETARDERS      FOR      CONCRETE,     AND     THEIR 
EFFECTS      ON      SETTING      TIME       AND 
SHRINKAGE 


DECEMBER      1972   -  NUMBER     51 


BY 


YASUHIKO     YAMAMOTO 


JHRP 

JOINT  HIGHWAY  RESEARCH  PROJECT 

PURDUE    UNIVERSITY     AND 

INDIANA    STATE    HIGHWAY     COMMISSION 


TECHNICAL  REPORT  STANDARD  TITLE  PAGE 


1.     Report  No. 


1.     Government  Accession  No. 


3.     Recipient's  Catalog  No. 


4.    Title  and  Subtitle 

RETARDERS  FOR  CONCRETE,  AND  THEIR  EFFECTS 
ON  SETTING  TIME  AND  SHRINKAGE 


5.     Report  Date 

December  1972 


6.     Performing  Organization  Code 


7.     Author(s) 

Yasuhiko  Yamamoto 


8.     Performing  Organization  Report  No. 

JHRP-51-72 


9.     Performing  Organization  Name  and  Address 

Joint  Highway  Research  Project 
Civil  Engineering  Building 
Purdue  Universit 


10.     Work  Unit  No. 


11.    Contract  or  Grant  No. 


We 


roue  university 

st  Lafayette,  Indiana  47907 


HPR-l(lO)  Part  II 


12.     Sponsoring  Agency  Name  and  Addres* 

Indiana  State  Highway  Commission 
100  N.  Senate  Avenue 
Indianapolis,  Indiana   46204 


13.     Type  of  Report  and  Period  Covered 

Interim  Report 


14.     Sponsoring  Agency  Code 


15.     Supplementary  Notes 

Prepared  in  cooperation  with  Federal  Highway  Administration  and 
U.  S.  Department  of  Transportation 


16.  Abstract 

Sixty- five  pure  chemicals  and  three  proprietary  retarders  were 
tested  in  the  penetration  test  for  setting  time  at  concentrations 
at  or  around  0.1%  of  the  cement.   The  most  effective  retarders  had 
several,  closely-grouped  oxygen  atoms  in  hydroxyl,  carboxyl ,  or 
carbonyl  groups.   Some  of  the  retarders  were  used  in  the 
fabrication  of  0.2  x  0.2  x  4-in.  bars  of  cement  paste,  which 
were  subsequently  oven-dried  and  the  shrinkage,  non-evaporable 
water  content,  and  specific  surface  of  the  paste  was  determined. 
The  retarders  caused  a  change  in  the  shrinkage  that  was  paralleled 
by  a  change  in  the  specific  surface  of  the  paste. 


The  contents  do  not  necessarily  reflect  the  official  views  or 
policies  of  the  Federal  Highway  Administration.   This  report  does 
not  constitute  a  standard,  specification,  or  regulation. 


17.  Key  Words 

Concrete,  retarders,  shrinkage, 
mi  cros tructure 


18.    Distribution  Statement      The     contents     Qf     tnig 

report  reflect  the  views  of  the 
author  who  is  responsible  for  the 
facts  and  the  accuracy  of  the  data 
presented  herein. * 


19.    Security  CloniC  (of  this  report) 


20.    Security  ClaisiC  (of  this  page) 


21*  No.  of  Paget 


181 


22.    Price 


Form  DOT  F  1700.7  (8-69) 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

LYRASIS  members  and  Sloan  Foundation;  Indiana  Department  of  Transportation 


http://www.archive.org/details/retardersforconcOOyama 


Interim  Report 

RETARDERS  FOR  CONCRETE,  AND  THEIR  EFFECTS  ON  SETTING 
TIME  AND  SHRINKAGE 


TO:    J.  F.  McLaughlin,  Director 

Joint  Highway  Research  Project 

FROM:   H.  L.  Michael,  Associate  Director 
Joint  Highway  Research  ProjeC 


December  28,  1972 
Project:   C-36-47L 
File:   4-6-12 


The  attached  Interim  Report  titled  "Retarders  for 
Concrete,  and  Their  Effects  on  Setting  Time  and  Shrinkage" 
is  submitted  on  the  HPR  Part  II  Research  Study  "Effect  of 
Retarders  on  Volume  Changes  in  Portland  Cement  Concrete". 
The  Report  has  been  authored  by  Mr.  Yasahiko  Yamamoto  under 
the  direction  of  Professor  W.  L.  Dolch. 

The  purpose  of  this  work  was  to  gain  some  insight  into 
effective  molecular  structure  of  retarders  and  to  examine  the 
shrinkage  behavior  of  cement  pastes  as  affected  by  the 
addition  of  retarders.   Principle  findings  include  a 
determination  that  effective  in  retarder  molecules  are 
hydroxyl,  carbonyl  and  carboxyl  groups  and  that  retarders 
cause  a  moderate  increase  in  the  shrinkage  of  cement  paste. 

The  Report  is  submitted  in  partial  fulfillment  of  the 
objectives  of  this  Study.   It  will  also  be  forwarded  to  the 
ISHC  and  FHWA  for  their  review,  comments  and  acceptance. 

Respectfully  submitted, 

Harold  L.  Michael 
Associate  Director 

HLM:ms 


cc:   W.  L.  Dolch 

R.  L.  Eskew 

W.  H.  Goetz 

M.  J.  Gutzwiller 

G.  K.  Hal lock 

R.  H.  Harrell 


M.  L.  Hayes 

C.  W.  Lovell 

G.  W.  Marks 

R.  D.  Miles 

J.  W.  Miller 

G.  T.  Satterly 


C.  F.  Scholer 

M.  B.  Scott 

J.  A.  Spooner 

N.  W.  Steinkamp 

H.  R.  J.  Walsh 

E.  J.  Yoder 


Interim  Report 

RETARDERS  FOR  CONCRETE,  AND  THEIR  EFFECTS  ON  SETTING 
TIME  AND  SHRINKAGE 


by 


Yasahiko  Yamamoto 
Graduate  Instructor  in  Research 


Joint  Highway  Research  Project 

Project  No.:   C-36-47L 

File  No. :   4-6-12 


Prepared  as  Part  of  an  Investigation 

Conducted  by 

Joint  Highway  Research  Project 

Engineering  Experiment  Station 

Purdue  University 

in  cooperation  with  the 

Indiana  State  Highway  Commission 

and  the 

U.S.  Department  of  Transportation 
Federal  Highway  Administration 

The  contents  of  this  report  reflect  the  views  of  the  author 
who  is  responsible  for  the  facts  and  the  accuracy  of  the  data 
presented  herein.   The  contents  do  not  necessarily  reflect  the 
official  views  or  policies  of  the  Federal  Highway  Administration 
This  report  does  not  constitute  a  standard,  specification,  or 
regulation. 


Purdue  University 
West  Lafayette ,  Indiana 
December  28,  1972 


Ill 


ACKNOWLEDGEMENTS 

The  writer  wishes  to  express  deep  appreciation  to  his 
major  professor,  Dr.  W.  L.  Dolch,  for  his  kind  guidance  and 
understanding  during  the  course  of  this  work.   Dr.  S. 
Diamond  and  Dr.  C.  F.  Scholer  should  be  also  appreciated 
for  their  valuable  suggestions  and  helps. 

The  discussion  with  Mr.  D.  N.  Winslow  was  helpful  and 
meaningful  in  solving  many  difficulties.   Some  technical 
phases  of  this  work  were  done  by  the  assistance  of  Mrs. 
T.  R.  Brendel.   The  writer  is  thankful  to  them  and  also  to 
many  other  people  who  have  helped  him  in  many  respects 
toward  the  accomplishment  of  this  work. 

This  research  was  sponsored  by  the  Indiana  Highway 
Department  and  administrated  by  Joint  Highway  Research 
Project  of  Purdue  University.   The  writer  wishes  to  thank 
the  authorities  for  the  support  of  this  work. 

Finally,  the  writer  is  thankful  to  Dr.  M.  Kokubu  and 
Dr.  H.  Okamura,  professor  and  associate  professor,  re- 
spectively, University  of  Tokyo,  Japan,  for  their  continu- 
ous encouragement  in  pursuing  the  advanced  degree  in  the 
United  States. 


TABLE  OF  CONTENTS 

Page 

LIST  OF  TABLES vii 

LIST  OF  FIGURES viii 

ABSTRACT xiii 

CHAPTER  I  -  INTRODUCTION   1 

CHAPTER  II  -  REVIEW  OF  LITERATURE  6 

Interaction  of  Retarder  with  Cement  6 

Effective  Molecular  Structure  of  Retarder  and 

Retardation  Mechanism  13 

Drying  Shrinkage  of  Paste,  Mortar,  and  Concrete 

as  Affected  by  Retarders 17 

CHAPTER  III  -  MATERIALS 21 

Admixtures 21 

Cement 2  7 

Sand 2  9 

Water 2  9 

CHAPTER  IV  -  EXPERIMENTAL  WORK 30 

A  -  Setting  Time  Measurements 30 

General  Remarks  30 

Apparatus 31 

Container 31 

Penetration  Resistance  Apparatus   31 

Mixer 31 

Preparation  of  Mortar  Specimens  33 

Mixing  Proportions  and  Size  of  Batch 33 

Mixing  Procedures  33 

Casting  and  Storage  of  Specimens   34 

Penetration  Test  Procedure   34 


TABLE  OF  CONTENTS,  cont. 

Page 

B  -  Measurement  of  Shrinkage  of  Cement  Pastes  ...  35 

General  Considerations   35 

Apparatus 36 

Mold  for  Cement  Paste  Specimens 36 

Gauge  Studs  and  Length  Comparator  36 

Mixing  Apparatus   38 

Preparation  of  Cement  Paste  Specimens  40 

Mixing  Proportion  and  Concentration  of  Retarders  40 
Mixing,  Casting,  and  Curing  of  Cement  Paste 

Specimens 42 

Measurements  of  Length  and  Weight,  Method  of 

Drying 44 

C  -  Determination  of  Degree  of  Hydration  of  Cement 

Pastes 46 

Loss  on  Ignition  Test 46 

Derivation  of  Equations  for  Determining  Non- 

Evaporable  Water  and  Evaporable  Water  47 

Assumptions 47 

Notation 48 

Derivation  of  Equations  50 

Reduction  of  Data 51 

D  -  Surface  Area  Measurements  of  Cement  Pastes   .  .  52 

General  Remarks 52 

Apparatus  and  Procedures  of  Measurement  53 

E  -  Scanning  Electron  Microscope  Observation   ...  54 

General  Procedures   54 

CHAPTER  V  -  RESULTS 56 

Infrared  Spectra  of  Commercial  Retarders  ....  56 
Non-Evaporable  Water  Content  of  Fully  Hydrated 

Cement  Paste   56 

Result  of  Setting  Time  Experiments   59 

Commercial  Retarders   59 

Pure  Chemicals 66 

Effects  of  Retarders  on  the  Drying  Shrinkage  of 

Cement  Paste  at  Various  Stages  of  Hydration  .  .  72 


TABLE  OF  CONTENTS,  cont, 


VI 


Page 


Drying  Shrinkage  of  Mature  Cement  Pastes  When 

Dried  at  50%  Relative  Humidity 7  9 

Water  Content  of  Cement  Pastes 84 

Specific  Surface  Area  of  Cement  Pastes   87 

Scanning  Electron  Microscopy  of  Cement  Pastes  .  .  96 

CHAPTER  VI  -  DISCUSSION 109 

Molecular  Structure  of  Retarders   109 

Effect  of  Retarders  on  the  Hydration  of  Cement   .  12  8 
Effect  of  Retarders  on  the  Shrinkage  of  Cement 

Pastes 143 

CONCLUSIONS 153 

LIST  OF  REFERENCES 155 

APPENDICES 

Appendix  A:  Correction  Curve  for  Warping  of 

Cement  Paste  Bars 161 

Appendix  B:  Summary  of  Setting  Time  Experiments 

When  Pure  Chemicals  Were  Added 163 

Appendix  C:  Shrinkage  of  Vacuum  Oven-Dried  Cement 

Pastes  at  Various  Stages  of  Cement  Hydration   .  169 

VITA 181 


LIST  OF  TABLES 

Table  Page 

1.  List  of  Chemicals 22 

2.  List  of  Commercial  Retarders 27 

3.  Composition  and  Properties  of  Lab  Cement 

No  319 28 

4.  Concentration  of  Retarders  Added  to 

Cement  Pastes  41 

5.  Non-Evaporable  Water  Content  of  Bottle  Hydrated 
Cement  (W/C  =10) 58 

6.  Summary  of  Relative  Initial  Setting  Time  of 
Mortars  When  Pure  Chemicals  Were  Added   ....    6  7 

Appendix 
Tables 

7.  Summary  of  Relative  Setting  Time  of  Mortar 
Samples  When  Pure  Chemicals  Were  Added   ....   164 


Vlll 


LIST  OF  FIGURES 

Page 
Figure  3 

1.  Calibration  Curve  for  Proctor  Penetrometer 

(ASTM  C403) 32 

2.  Mold  for  Cement  Paste  Specimens,  Cement  Paste 
Sample,  and  Paste  Caster   

3.  Length  Comparator  39 

4.  Apparatus  for  Drawing  Mixing  Solution  from 

Funnel  into  Mixing  Container   43 

5.  Schematic  Diagrams  of  Cement  and  Cement  Paste  .    49 

6.  Infrared  Spectra  of  Commerical  Retarders   ...    57 

7.  Penetration  Resistance  vs  Elapsed  Time  for 

Mortar  with  Retarder  L 60 

8.  Penetration  Resistance  vs  Elapsed  Time  for 

Mortar  with  Retarder  A 61 


9.   Penetration  Resistance  vs  Elapsed  Time  for 

Mortar  with  Retarder  S 62 

10.  Effect  of  Concentration  of  Retarder  L  on 

Setting  Time  of  Mortar 63 

11.  Effect  of  Concentration  of  Retarder  A  on 
Setting  Time  of  Mortar   

12.  Effect  of  Concentration  of  Retarder  S  on 
Setting  Time  of  Mortar   

13.  Penetration  Resistance  vs  Elapsed  Time  for 

Mortar  with  1, 3-Dihydroxy-2-Butanone   73 

14.  Concentration  of  Admixture  vs  Relative  Initial 
Setting  Time  of  Mortar  (No.  1)   74 

15.  Concentration  of  Admixture  vs  Relative  Initial 
Setting  Time  of  Mortar  (No.  2)   75 


IX 


LIST  OF  FIGURES,  cont. 
Figure  Page 

16.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Hydration  (Commercial 
Retarders)   76 

17.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 

at  Various  Stages  of  Hydration  (Pure  Chemicals)    77 

18.  Shrinkage  vs  Drying  Time  for  Mature  Cement 
Pastes  When  Dried  at  50%  Relative  Humidity 
(Commercial  Retarders)   80 

19.  Shrinkage  vs  Drying  Time  for  Mature  Cement 
Pastes  When  Dried  at  50%  Relative  Humidity 

(Pure  Acid  Chemicals) 81 

20.  Shrinkage  vs  Weight  Loss  of  Mature  Cement 
Pastes  When  Dried  at  50%  Relative  Humidity 
(Commercial  Retarders)   82 

21.  Shrinkage  vs  Weight  Loss  of  Mature  Cement 
Pastes  When  Dried  at  50%  Relative  Humidity 

(Pure  Acid  Chemicals) 83 

22.  Non-Evaporable  Water  vs  Evaporable  Water  of 

Cement  Pastes  (Commercial  Retarders)   85 

23.  Non-Evaporable  Water  vs  Evaporable  Water 

of  Cement  Pastes  (Pure  Chemicals)  .......    86 

24.  Non-Evaporable  Water  vs  Curing  Age  of 

Cement  Pastes  (Commercial  Retarders)   88 

25.  Non-Evaporable  Water  vs  Curing  Age  of 

Cement  Pastes  (Pure  Chemicals)   89 

26.  Specific  Surface  Area  of  Vacuum  Oven-Dried 
Cement  Pastes  When  Expressed  on  the  Basis  of 

Total  Ignited  Weight  of  Sample  (No.  1)   .  .  .  .    90 

27.  Specific  Surface  Area  of  Vacuum  Oven-Dried 
Cement  Pastes  When  Expressed  on  the  Basis  of 

Total  Ignited  Weight  of  Sample  (No.  2)   ....    91 

28.  Specific  Surface  Area  of  Hydrated  Portion  of 
Vacuum  Oven-Dried  Cement  Pastes 

(Commercial  Retarders)   93 


>: 


LIST  OF  FIGURES,  cont. 

Figure  Page 

29.  Specific  Surface  Area  of  Hydrated  Portion  of 
Vacuum  Oven-Dried  Cement  Pastes 

(Pure  Chemicals  -  No.  1)   94 

30.  Specific  Surface  Area  of  Hydrated  Portion  of 
Vacuum  Oven-Dried  Cement  Pastes 

(Pure  Chemicals  -  No.  2)   95 

31.  Unhydrated  Cement  Grains  (X5000)   97 

32.  Cement  Paste  With  No  Admixture  (X3000) , 

Age:  1  min 97 

33.  Cement  Paste  With  No  Admixture  (X9000) , 

Age:  1  min 98 

34.  Cement  Paste  With  Calcium  Lignosulfonate 

(X5000)  ,  Age:  1  min 98 

35.  Cement  Paste  With  Citric  Acid  (X3000) , 

Age:  1  min 99 

36.  Cement  Paste  With  Sucrose  (X5000)  , 

Age:  1  min 9  9 

37.  Cement  Paste  With  No  Admixture  (X5000) , 

Age:  5  min 101 

38.  Cement  Paste  With  Calcium  Lignosulfonate 

(X5000)  ,  Age:  5  min  .  . 101 

39.  Cement  Paste  With  Citric  Acid  (X3000) , 

Age:  5  min 102 

40.  Cement  Paste  With  Sucrose  (X5000) , 

Age:  5  min 102 

41.  Cement  Paste  With  Citric  Acid  (X3000) , 

Age:  10  min 103 

42.  Cement  Paste  With  Citric  Acid  (X8000) , 

Age:  10  min 103 

43.  Cement  Paste  With  Citric  Acid  (X3000) , 

Age:  3  0  min 104 


XI 


LIST  OF  FIGURES,  cont. 

Figure  Page 

44.  Cement  Paste  With  Citric  Acid  (X3000) , 

Age:  1  hr 104 

45.  Cement  Paste  With  No  Admixture  (X5000) , 

Age:  1  hr 106 

46.  Cement  Paste  With  Sucrose  (X3000) , 

Age:  30  min 106 

47.  Cement  Paste  With  No  Admixture  (X2000) , 

Age:  12.5  hr  (degree  of  hydration:  24%)  ....   107 

48.  Cement  Paste  With  Glycolic  Acid  (X2000) , 

Age:  15.5  hr  (degree  of  hydration:  26%)  ....   107 

49.  Cement  Paste  With  Retarder  A  (X2000) , 

Age:  14  hr  (degree  of  hydration:  18%) 108 

50.  Cement  Paste  With  Retarders  (X2000) , 

Age:  13  hr  (degree  of  hydration:  20%) 108 

51.  Retardation  Ability  vs  Complexing  Ability 

of  Chemicals 135 

52.  Effect  of  Continuous  Vacuum  Oven-Drying  on 
Shrinkage  of  Cement  Pastes   145 

53.  Effect  of  Continuous  Vacuum  Oven-Drying  on 

Weight  Loss  of  Cement  Pastes 146 

Appendix 
Figures 

54.  Correction  Curve  for  Warping  of  Cement  Paste 

Bars 162 

55.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(No  Admixture)   17  0 

56.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Retarder  L)   171 

57.  Shrinkage  of  Vacuum  Oven  Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Retarder  A)   172 


LIST  OF  FIGURES,  cont. 

Figure  Page 

58.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Retarder  S)   173 

59.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Glycolic  Acid)  174 

60.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Sucrose) 175 

61.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 
(3-Hydroxy-2-Butanone)   17  6 

62.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 
(Hydroquinone)   177 

63.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 
(CaCl2-2H20)   178 

64.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(Effect  of  Concentrations  of  Citric  Acid)  .  .  .   179 

65.  Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 

(effect  of  Water-Cement  Ratio)   180 


Xlll 


ABSTRACT 

Yamamoto,  Yasuhiko.   Ph.D.,  Purdue  University, 
December  1972.   Retarders  for  Concrete,  and  Their  Effects 
on  Setting  Time  and  Shrinkage.   Major  Professor:  W.  L.  Dolch. 

The  main  purposes  of  this  work  are  to  gain  some  insight 
into  effective  molecular  structure  of  retarders  and  to 
examine  the  shrinkage  behavior  of  cement  pastes  as  affected 
by  the  addition  of  retarders. 

A  total  of  sixty  five  organic  chemicals  were  tested 
for  their  retarding  abilities  by  means  of  setting  time 
experiment  on  mortar  specimens  by  the  penetration  method. 
The  chemicals  were  added  mostly  at  the  concentration  of 
0.1%  of  cement  by  weight.   Three  commercial  retarders  that 
are  chemically  classified  in  the  three  principal  categories 
were  also  tested  at  several  concentrations.   The  mix  pro- 
portions of  the  mortars  were  kept  constant;  water-cement 
ratio  and  sand-cement  ratio  being  0.5  0  and  2.75,  respective- 
ly.  The  effectiveness  of  the  chemicals  as  retarders  was 
judged  by  comparing  the  initial  setting  time  of  a  sample 
with  that  of  a  control  sample  without  the  admixture. 
Effect  of  the  concentration  of  admixture  was  studied  for 
the  commercial  retarders  and  some  chemicals.   These  results 


XIV 


were  discussed  in  connection  with  the  effective  molecular 
configurations  of  retarders  and  possible  retardation 
mechanisms. 

Small  cement  paste  bars  (1/5  x  1/5  x  4  in.)  were  pre- 
pared for  shrinkage  measurements.   Admixtures  used  in  this 
part  include  five  chemicals  that  were  found  to  be  retarders 
in  this  work,  the  three  commercial  retarders,  and  CaCl-^H-O 
(accelerator) .   Concentration  of  each  retarder  was  selected 
in  such  a  way  that  it  gave  50%  of  additional  retardation 
compared  with  a  control  mortar.   Water-cement  ratio  was 
fixed  at  0.40.   Drying  of  the  samples  was  conducted  in  a 
vacuum  oven  at  105  to  110°C  for  2  4  hours.   Shrinkage  was 
compared  at  various  degrees  of  cement  hydration;  the  ages 
of  samples  were  as  early  as  lOhr  after  mixing  to  8  months, 
at  which  time  90%  or  more  of  the  cement  was  hydrated. 

Determinations  of  specific  surface  area,  non-evaporable 
and  evaporable  water  contents,  and  scanning  electron  micro- 
scopic observation  were  made  on  cement  paste  samples  to 
explore  whether  or  not  some  changes  were  induced  in  the 
cement  hydrates  by  the  addition  of  retarders. 

The  following  are  main  findings  in  this  research. 
1.   Hydroxyl,  carbonyl,  and  carboxyl  groups  are  all 
effective  in  retarder  molecules.   Strong  retarder  molecules 
contain  many  of  these  groups  in  such  a  way  that  the  oxygen 
atoms  are  constrained  to  approach  each  other  closely. 


XV 


Substitution  of  other  more  weakly  electronegative  groups 
for  these  groups  results  in  greatly  reduced  effectiveness. 

2 .  Retarders  cause  a  moderate  increase  in  the  shrink- 
age of  cement  pastes  at  ages  when  more  than  about  half 
hydration  is  attained  in  about  4  days.   At  lesser  ages  the 
shrinkage  may  be  increased  or  decreased. 

3.  When  cement  paste  are  severely  dried  of  all  their 
evaporable  water,  they  exhibit  shrinkage  behavior  that 
shows  a  minimum  at  about  half  hydration  and  a  maximum 
earlier.   A  similar  change  is  observed  in  the  specific 
surface  area  of  the  hydrated  cement.   Some  cause  and  effect 
relationship  exists  between  these  quantities. 


CHAPTER  I  -  INTRODUCTION 

Retarders  are  classified  as  type  B  or  type  D  chemical 
admixtures  for  portland  cement  concrete  in  ASTM  Designation 
C494.   Their  primary  function  is,  as  the  name  implies,  to 
retard  the  setting  time  of  concrete.   Many  problems  of  hot 
weather  concreting,  mass  concrete,  multi-lift  concreting, 
continuous  placement,  and  others  have  been  helped  by  the 
use  of  retarders  (1,  2)*. 

As  a  secondary  effect,  many  retarders  reduce  the  water 
requirement  to  produce  a  concrete  of  desired  workability  and 
produce  a  concrete  of  higher  strength  with  equal  cement  con- 
tent.  Some  retarders,  additionally,  produce  many  small  air 
bubbles,  much  the  same  as  those  produced  by  air-entraining 
agents  in  concrete  mixtures.   Hence,  the  use  of  retarders  is 
also  beneficial  to  other  properties  of  concrete  such  as 
workability,  strength,  and  durability  (3) . 

Commercial  retarders  are  classified  chemically  into 
three  categories: 

1.  lignosulfonic  acids  and  their  salts 

2.  hydroxycarboxylic  acids  and  their  salts 

3.  carbohydrates  (sugars) 


*  Numbers  in  parenthesis  refer  to  references  at  the  end  of 
this  paper. 


When  these  retarders  are  added  to  concrete  mixtures, 
some  kind  of  physical  and/or  chemical  reaction   takes  place 
in  such  a  way  to  retard  the  setting  time.   Little  is  known 
of  what  the  effective  molecular  structures  of  the  retarders 
are  and  how  the  retardation  mechanism  proceeds. 

As  will  be  shown  in  Chapter  II,  the  most  widely  be- 
lieved theory  of  the  retardation  mechanism  is  the  so-called 
"coating  theory".   The  idea  of  the  theory  is  basically  as 
follows:   As  soon  as  retarders  are  added  they  are  adsorbed 
at  the  solid-water  interface  of  cement  grains  or  their 
hydration  products.   The  sorbed  retarder  molecules  block 
or  delay  further  contact  of  the  unhydrated  cement  with 
water  and  therefore  retard  the  hydration  of  the  cement. 

The  effective  molecular  structure  of  retarders,  then, 
has  to  be  of  such  a  configuration  that  the  coating  is  most 
efficiently  attained.   Most  workers  believe  that  large 
chain  molecules  with  many  hydroxyl  groups  are  essential  to 
effective  retarders.   The  -OH  groups  are  for  bonding  with 
cement  grains,  presumably  by  hydrogen  bonding  to  surface 
oxygen  atoms. 

However,  owing  to  the  variety  of  both  the  compounds 
in  portland  cement  and  molecular  structures  of  retarders, 
it  is  difficult  to  imagine  that  the  theory  mentioned  above 
is  the  only  mechanism  for  the  retardation. 

Some  workers  have  reported  that  retarders  increase 
the  shrinkage  of  concrete  (4).   On  the  other  hand,  other 


workers  observed  no  increase  in  shrinkage  with  the  addition 
of  retarders  (3) .   Because  the  shrinkage  behavior  of 
concrete  is  extremely  complex  and  is  influenced  by  many 
factors,  it  is  not  surprising  to  see  this  discrepancy. 
Yet,  it  is  of  importance  to  establish  basic  information  as 
to  whether  retarders  really  change  the  shrinkage  behavior 
of  concrete  and,  if  they  do,  how  much  the  change  is  and  how 
it  should  be  considered  in  practice.   If  sound  aggregates 
are  used  in  concrete,  change  in  shrinkage  behavior  of  the 
concrete  can  be  attributed  to  that  of  the  cement  paste  in 
the  concrete.   Therefore  a  detailed  study  on  cement  paste 
should  provide  such  information. 

Hardened  cement  paste  consists  of  capillary  pores, 
cement  gel,  and  unhydrated  cement  grains  (5) .   Each  of  them 
has  a  certain  role  in  the  shrinkage  behavior  of  cement 
paste.   The  extent  to  which  these  phases  exist  and,  there- 
fore, the  structure  of  the  cement  paste  depends  on  the 
degree  of  hydration.   Since  retarders  change  the  rate  at 
which  a  cement  hydrates,  a  consideration  of  the  magnitude 
of  these  phases  is  appropriate  when  drying  shrinkage  of 
retarded  cement  paste  is  compared  with  that  of  unretarded 
paste. 

Additionally,  there  is  evidence  that  the  morphology  of 
hydrated  C,A*  is  altered  significantly  by  the  addition  of 


The  usual  abbreviations  are  used  through  the  paper: 
C  =  CaO,  S  -  Si02,  A  =  A1203,  H  =  H20. 


lignosulf onate ,  a  constituent  of  some  retarders  (6).   So 
there  is  some  possibility  that  retarders  also  change  the 
specific  surface  or  crystal  habit  of  the  hydration  products 
of  cement  paste  and  thereby  induce  different  shrinkage 
behavior  of  the  paste. 

Hence,  what  seems  important  and  necessary  is  to  examine 
the  effect  of  retarders  on  the  structure  of  the  hydration 
products  at  various  hydration  stages  and  to  interpret  the 
observed  shrinkage  behavior  of  cement  pastes  in  these  terms. 

An  alternate  hypothesis,  based  on  the  coating  theory, 
is  that  retarders  act  merely  by  changing  the  rate  of,  or 
time  of  initiation  of,  the  hydration  reaction.   A  combina- 
tion of  the  kinetic  and  the  structural  change  theories  is, 
of  course,  also  possible. 

The  present  paper  discusses  the  results  of  experiments 
undertaken  to  gain  information  on  the  action  of  retarders. 
By  means  of  setting  time  experiments  on  mortar  specimens, 
many  chemicals  were  examined  for  their  effects  as  retarders. 
Possible  effective  molecular  structures  of  retarder  mole- 
cules are  discussed.   Small  cement  paste  bars  were  made 
with  and  without  retarders.   Their  shrinkages  were  measured. 
The  results  are  compared  at  various  degrees  of  hydration  of 
the  cement,  ranging  from  as  early  as  10  hours  after  mixing 
with  water  to  8  months  of  age,  at  which  time  the  pastes 
were  almost  mature. 


Determination  of  evaporable  and  non-evaporable  water 
contents,  measurement  of  specific  surface  area,  and  scann- 
ing electron  microscopic  observations  were  conducted  to 
examine  the  properties  and  the  structure  of  the  cement 
pastes. 


CHAPTER  II  -  REVIEW  OF  LITERATURE 

Interaction  of  Retarder  with  Cement 
Blank,  Rossington  and  Weinland  (7)  observed  that  the 
adsorption  from  aqueous  solutions  of  salicylic  acid  and 
calcium  lignosulf onate  on  C2S  and  C~S  was  negligibly  small 
and  showed  the  following  order  of  the  adsorption  on  the 
cement  compounds  from  aqueous  solution  in  10  to  15  minutes, 
calcium  lignosulf onate: 

C3A  >  C.AF  >  Type  I  portland  cement  >  C3S,  C„S  >  0 
salicylic  acid: 

C3A  >  C4AF  >  TyPe  x   Portland  cement  >  C2S  =  C3S  =  0 
The  adsorption  on  the  compounds  from  ethyl  alcohol  solution, 
however,  was  in  the  following  order  for  salicylic  acid: 

C3S  >  C2S  >  Type  I  portland  cement  >  C^A  =  C.AF  =  0 
From  these  results,  they  suggested  that  the  negligible  ad- 
sorption on  C2S  and  C~S  in  aqueous  solution  is  probably  a 
result  of  the  competitive  adsorption  of  water,  and  that 
certain  modified  properties  of  cement  due  to  admixture  addi- 
tion are  a  result  of  the  preferential  adsorption  of  the 
admixture  by  C,A  and  C,AF ,  thereby  rendering  them  inactive 
and  allowing  the  main  cementing  compounds  (C..S  and  C„S) 
to  control  the  hydration  reaction. 


Seligmann  and  Greening  (8)  showed  that  one  gram  of 
C^A  could  remove  99%  of  the  sugar  from  5  cc  of  a  1%  sucrose 
solution  within  7  minutes.   The  presence  of  gypsum  or 
calcium  hydroxide  did  not  interfere.   C^A  also  sorbed 
considerable  calcium  lignosulf onate ,  whereas  C^S  and  C.AF 
sorbed  little.   It  may  be  added  that  a  rough  calculation 
using  these  results  showed  that  the  sugar  adsorption  on 
unhydrated  C-.A  corresponded  to  a  uniform  coverage  of  about 
150  molecular  layers.   The  result  is  unrealistic,  and  it 
would  be  adequate  to  suppose  that  the  sucrose  was  adsorbed 
by  the  hydration  products  of  C~A  instead  of  or  in  addition 
to  the  unhydrated  material  as  Diamond  (9)  observed  with 
salicylic  acid. 

Stein  (10)  observed  that  monomer  organic  anions 
exerted  a  relatively  small  influence  on  C,S  hydration,  but 
a  pronounced  effect  on  C,A  hydration  by  forming  calcium 
double  salts  with  C^A,  similar  to  ettringite.   Hansen  (11) 
has  a  similar  concept  that  the  hydration  of  C,A  is  retarded 
by  chemisorbing,  rather  than  adsorbing,  lignosulonate . 
The  chemisorption  results  from  the  formation  of  double 
salts  between  the  lignosulfonate  and  calcium  ions  in  the 
surface  of  cement  minerals. 

Mielenz  and  Peppier  (12)  ,  however,  pointed  out  that 
formation  of  compounds  isostructural  with  sulf oaluminates 
and  containing  such  large  anions  as  lignosulfonate  would 
be  impossible.   They  suggested  that  retardation  of  C-.A 


hydration  by  materials  like  lignosulf onates  may  better  be 
explained  in  terms  of  adsorption  of  lignosulf onate  upon 
C,A  grains  or  precipitation  of  insoluble  calcium  ligno- 
sulfonate  around  the  grains  of  C^A. 

The  hydration  of  C-.A  is  widely  believed  to  proceed 
in  two  steps  in  the  absence  of  gypsum: 

2C-.A  +  (n+8)H  •>  C0AH0  +  C.AH   ;  metastable  phase 
J  z   o     4   n      / ,        ,  . 

(hexagonal) 

C0AH0  +  C.AH   ■*  2C_AH_  +  (n-4)H  ;  stable  phase 

(cubic) 

Daugherty  and  Kawalewski  (13)  examined  the  effect  of  many 

chemicals  on  the  relative  amount  of  hydration  products  of 

C-,A  by  quantitative  x-ray  diffraction  analysis.   They  found 

that,  in  general,  organic  acids  permitted  the  hydration  of 

C-.A  to  proceed  to  C-,AHfi  while  sugars  and  their  derivatives 

blocked  the  hydration  reaction  at  metastable  C~AH8  and 

C.AH  .   However,  all  the  sugars  and  sugar  derivatives 

examined  accelerated  the  initial  hydration  of  CUA  at  the 

concentration  level  of  0.25  mole  %  relative  to  C,A.   They 

speculated  on  the  retardation  mechanism  of  C-.A  hydration: 

"In  concentrations  of  0.3  mole  %  or  less  relative  to 
C3A  the  organic  materials  complex  or  chelate  with 
available  calcium  ions  (and  other  cations)  in  solution 
and  on  the  surface  of  the  CoA.   These  reactions  might 
affect  the  rates  of  solution  of  C3A  and  the  solution, 
precipitation  or  nucleation  of  the  hydration  products 
in  a  manner  which  accelerates  hydration. 

After  the  available  calcium  is  tied  up,  the 
organic  material  is  adsorbed  on  the  surface  of  C^A. 
This  adsorption  may  be  chelation  with  calcium  in  the 
C3A,,  complexation,  or  surface  adsorption  depending 
upon  the  type  of  organic  molecule 


Organic  compounds  with  more  insoluble  calcium 
salts  would  be  expected  to  form  more  closely  packed, 
more  impervious  sheaths  around  the  C^A.   This  might 
prevent  H20  from  further  attacking  the  C3A.   The 
organic  layers  could  prevent  the  intermediate  products, 
C2AHs  an<^  c4AHn/  from  transforming  to  C^AHg. 
Retardation  of  hydration  would  be  the  result." 

Young  (6)  made  similar  observation  with  lignosulf onate 
by  measuring  refractive  indices  of  the  hydration  products 
of  C^A.   Lignosulfonate  stabilized  C4AH13  and  C^AHg  with 
respect  to  C,AHg .   When  gypsum  was  present,  the  formation 
of  ettringite  was  not  affected  by  the  addition  of  ligno- 
sulfonate, and  the  final  hydration  products  were  low  sulfo- 
aluminate,  C„AHR ,  and  C.AH..-..   Another  interesting  observa- 
tion by  Young  is  that  there  was  no  evidence  of  the  trans- 
formation of  C_AH0  and  C.AH,  _.  to  C0AH,  when  C-.A,  even  in 
the  absence  of  lignosulfonate,  hydrated  at  low  temperature, 
say  less  than  30°C. 

Diamond  (14,  15)  analyzed  salicylate  bearing  precipi- 
tates observed  in  the  C^A  (or  C,AH,)  -  salicylic  acid-water 
system.   They  were  amorphous  salicylate-aluminum  complexes 
and  did  not  contain  calcium. 

Because  the  C^A  and  C,S  phases  in  cement  are  responsible 
for  early  hydration  of  the  cement,  the  papers  introduced  so 
far  give  an  impression  that  the  C\A  is  mainly  concerned 
with  the  retardation  mechanism  when  retarders  are  added. 
Forbrich  (16),  however,  demonstrated  that  salicylic  acid 
delayed  the  time  of  maximum  heat  generation  due  to  hydra- 
tion of  C3S  by  8  to  10  hr  relative  to  a  reference  mixture, 


10 


and  that  calcium  lignosulf onate  shifted  the  peak  more  than 
27  hours.   On  the  other  hand,  the  hydration  of  C3A  with 
12%  gypsum  interground  was  accelerated  by  the  addition  of 
salicylic  acid,  but  was  retarded  remarkably  when  calcium 
lignosulf onate  was  added. 

Polivka  and  Klein  (17)  examined  the  setting  time  of 
many  cements  influenced  by  various  admixtures  and  showed 
that  retarders  are  more  effective  when  used  with  cements  of 
low  alkali  and  low  C,A.   Forbrich  (16)  also  showed  that 
cements  low  in  C,A  and  high  in  C,S  were  the  ones  retarded 
to  the  greatest  degree  by  either  calcium  lignosulf onate  or 
salicylic  acid. 

Bruere  (18)  showed  that  delayed  addition  of  retarders 
(citric  acid  and  calcium  lignosulf onate)  produced  a  con- 
siderably longer  setting  time  of  cement  paste.   This  effect 
was  much  greater  in  pastes  made  from  ordinary  portland 
cement,  which  had  a  high  C^A  content,  than  in  pastes  made 
from  low  heat  cement,  which  had  a  low  C^A  content.   Dodson 
and  Farkas  (19)  observed  the  same  result.   Bruere  suggested 
that  this  effect  was  due  to  competition  between  the  gypsum 
in  the  cement  and  organic  retarders  to  combine  with  or 
adsorb  on  C3A  surfaces  and  explained  further: 

"When  cement  is  pre-mixed  with  water  for  a  few  minutes, 
gypsum  has  ample  time  to  dissolve  and  coat  the  C3A. 
Consequently,  when  the  retarder  is  added  to  the  pre- 
mixed  paste,  the  C3A  is  unable  to  adsorb  it  and  a 
large  amount  of  retarder  is  available  to  retard  the 
silicate  hydration  reactions." 


11 


Seligmann  and  Greening  (8)  examined  the  effects  of 

sucrose  and  lignosulf onate  on  the  hydration  of  various 

cement  constituents  by  x-ray  diffraction  and  observed  that 

sucrose  accelerated  the  reaction  between  gypsum  and  C^A; 

but  lignosulf onate  had  little,  if  any,  acceleration  effect. 

Lignosulf onate  inhibited  the  release  of  Ca (OH) 2  from  C,S 

and  also  suppressed  the  release  of  alkali  into  the  liquid 

phase.   The  alkali  is  supposed  to  react  chemically  with 

the  retarder  to  destroy  its  hydration  inhibiting  effect. 

They  concluded: 

"Materials  that  cause  retardation  of  set,  such  as 
sucrose  or  lignosulf onates,  can  also  produce  a  large 
initial  acceleration  of  the  hydration  reactions.   This 
acceleration  may  be  caused  by  inhibition  of  lime 
release  by  the  silicates  phases  or  by  increased 
reactivity  of  the  C3A  with  gypsum,  resulting  from  the 
very  high  sorption  of  the  additive  in  the  C3A  surface. 
The  early  acceleration  and  high  sorption  can  be  avoided 
by  delayed  addition  of  the  retarder;  the  retarding 
effect  is  then  markedly  increased." 

Kalousek  et  a_l.  (20)  analyzed  extracts  from  various 

clinkers  at  7  minutes  and  2  hr  after  mixing  and  observed 

that  sucrose  was  the  only  added  material  (the  others  being 

gypsum,  CaCl- ,  calcium  acetate,  fluosilicic  acid,  TDA, 

tannic  acid,  and  triethanolamine)  that  increased  the 

basicity  of  the  extract.   This  was  observed  not  only  by 

increased  extraction  of  alkali,  but  also,  to  a  greater 

extent,  by  almost  complete  conversion  of  dissolved  sulfate 

to  insoluble  products.   Thus  sucrose  accelerated  the  early 

hydration  involving  the  alumina-bearing  constituents  of  the 

clinkers. 


12 


Tamas  (21)  assumed  that  retarders  would  behave  in  the 
opposite  manner  to  calcium  chloride  and  suggested  that 
retarders  formed  an  adsorbed  layer  on  the  grain  of  cement 
silicates,  causing  de-activation  of  the  reaction  between 
the  silicate  phase  and  water.   He  also  suggested  the 
possibility  of  the  formation  of  insoluble  compounds  between 
retarders  and  the  aluminates  in  cement. 

An  interesting  result  was  shown  by  Ramachandran  (22) . 
He  examined  the  adsorption  and  desorption  isotherms  of 
calcium  lignosulf onate  from  both  aqueous  and  non-aqueous 
solutions  on  C3S  ,  hydrated  C3S,  and  lime.   It  was  the 
hydrated  CUS,  but  not  C,S,  that  was  responsible  for  a 
perceptible  amount  of  adsorption  of  calcium  lignosulf onate 
from  the  aqueous  solution.   Because  the  adsorption  was 
irreversible,  he  suggested  surface  complex  formation 
(chemisorption)  involving  the  silicate  surface,  calcium 
lignosulf onate,  and  water. 

It  appears  that  silicate  phases  in  portland  cement  can 
not  be  neglected  in  considering  the  interaction  between 
retarders  and  cement  and,  therefore,  the  retardation 
mechanism  in  cement  paste.   Long  ago,  Steinour  (23)  said, 
"Indeed,  in  cements  with  good  contents  of  gypsum  in  which 
setting  is  due  to  hydration  of  tricalcium  silicate,  it  is 
logical  to  assume  that  in  order  to  obtain  further  retarda- 
tion it  is  the  reaction  of  the  silicate  that  must  be  slowed 
up." 


13 


From  the  review  of  literature  in  this  section,  the 
following  summary  of  information  is  meaningful: 

1.  C~A,  C.AF,  hydrated  C,S  ,   and,  possibly,  hydrated 
CUA  adsorb  retarders  from  solution. 

2.  Retarders  that  have  chemically  different  structures 
act  differently  in  their  effects  on  cement  hydra- 
tion. 

3.  Not  only  the  aluminate  phase  but  also  the  silicate 
phase  in  cement  plays  a  significant  role  in  the 
setting  process. 

4.  Retarders  are  more  effective  when  they  are  added 
to  cement  of  low  C-.A  and  low  alkali  content. 

Effective  Molecular  Structure  of  Retarder  and 
Retardation  Mechanism 

Hansen  (24)  found  that  most  of  the  organic  compounds 
that  retarded  the  hydration  of  oil  well  cements  had  a  common 
structural  feature  of  the  H-C-OH  group.   He  later  suggested 
that  large  anions  of  retarders  could  react  by  ionic  bonding 
with  the  calcium  ions  in  the  surface  of  cement  minerals 
and  that  OH  groups  react  by  hydrogen  bonding  with  oxide  ions 
of  the  minerals.   Thus  the  organic  compounds  block  the 
contact  of  cement  granules  with  water  molecules  and  so 
inhibit  hydration  (11) . 

Steinour  (25)  showed  that  retarders  characterized  by 
undissociated  OH  groups  retarded  B-C-S  hydration.   Because 
these  retarders  are  effective  at  small  concentrations,  and 


14 


because  the  OH  groups  can  form  hydrogen  bonds,  he  assumed 
that  they  retard  the  hydration  of  cement  by  an  adsorption 
mechanism  (23,  26). 

Taplin  (27)  added  a  large  number  of  inorganic  and 
organic  chemicals  to  cement  paste  to  find  out  the  effective 
molecular  structure  of  retarders.   He  found  that  the  group 
HO-C-C=0  was  usually  present  in  organic  substances  that 
retard  the  hydration  of  portland  cement,  and  that  the 
effective  molecules  usually  contain  at  least  two  oxygen 
atoms  each  bound  to  a  single  but  different  carbon  atom  in 
such  a  way  that  the  oxygen  atoms  can  approach  each  other. 
However,  there  were  some  exceptions.   He  also  showed  that 
location  and  arrangement  of  OH  groups  in  molecules  changed 
the  retardation  power  widely.   His  proposed  retardation 
mechanism  is  the  adsorption  of  these  chemicals  (i)  on  the 
surface  of  clinker  minerals  so  as  to  protect  them  from 
attack  by  water  and  (ii)  on  the  surface  of  a  coherent  coat- 
ing of  hydration  products  so  as  to  prevent  transport  of 
materials  to  or  from  the  clinker  surface. 

Danielson  (28)  made  cement  pastes  with  thirteen 
different  organic  calcium  salts  and  measured  the  setting 
time  of  the  pastes.   He  concluded  that  the  retarding  capa- 
cities of  the  salts  were  related  to  the  characteristics  of 
the  added  molecule  in  a  way  that  suggests  a  confirmation  of 
the  hypothesis  proposed  by  Hansen  and  many  other  workers, 
namely  that  retardation  is  due  to  adsorption  of  the  mole- 
cules on  cement  grains. 


15 


Previte  (29)  measured  the  end  point  of  the  dormant 
period  in  the  course  of  hydration  of  cement  paste  by  iso- 
thermal calorimetry  and  showed  that  saccharides  of  larger 
molecular  weight  generally  were  more  powerful  as  retarders 
when  they  were  added  on  an  equimolar  basis.   However,  the 
rate  of  alkaline  degradation  was  another  factor  affecting 
the  set  retardation  effectiveness.   He  concluded  that  the 
effect  of  alkalinity  in  the  aqueous  phase  of  hydrating 
cement  reduces  the  set  retardation  efficiency  of  alkaline- 
degradable  saccharides. 

Bruere  (30)  examined  why  the  dissaccharide  a,    a- 
trehalose  had  been  found  to  possess  only  weak  retarding 
ability,  while  all  other  sugars  studied  were  powerful  set- 
retarders.   Only  a,  a-trehalose  failed  to  produce  any 
trace  of  cuprous  oxide  in  boiling  Fehling's  solution  at 
all  alkali  concentrations  used,  whereas  all  the  other 
sugars  produced  significant  amounts  of  cuprous  oxide  in  the 
test  solution.   He  postulated  that  the  latter  could  hydro- 
lyse  significantly  in  the  highly  alkaline  conditions  in 
cement  paste  to  produce  reducing  sugars  that  in  turn  could 
be  converted  to  saccharinic  acids  containing  the  HO-C-C=0 
group,  and  thus  he  supported  Taplin's  theory  even  in  the 
case  of  saccharides. 

But  according  to  Daugherty  and  Kawalewski  (13)  , 
a,  a-trehalose  is  a  powerful  retarder  for  the  hydration  of 
C-jA,  and  it  retards  the  hydration  to  the  same  extent  as 


16 


sucrose.   They  also  found  that  OH  groups  tend  to  retard  the 
hydration  of  C,A  and  carbonyl  (C=0)  groups  tend  to  accele- 
rate the  hydration  of  C^A,  but  the  a-hydroxyl  carbonyl 
(HO-C-C=0)  group  itself  did  not  appear  to  be  important. 

Koide  (31)  stated  that  carboxyl  (COOH)  group  has  always 
retarded  the  hydration  of  CA  (the  principal  component  of 
high-alumina  cement) .   The  effect  was  especially  marked  when 
the  group  was  contained  in  a  chelating  compound  (example; 
EDTA)  that  produce  sexadendates  of  high  stability. 

In  a  review,  Young  (32)  postulated  that  organic  re- 
tarders  adsorb  on  calcium  hydroxide  nuclei  in  cement  pastes 
and  poison  their  future  growth.   Retardation  is  the  result 
of  this  delayed  formation  of  calcium  hydroxide.   He  further 
explained  that  higher  levels  of  calcium  hydroxide  super- 
saturation  are  required  to  overcome  the  effects  of  the 
retarders . 

Summarizing  this  section,  most  workers  believe  that  the 
retardation  of  cement  hydration  is  a  result  of  the  adsorp- 
tion of  the  retarder  molecules  on  the  surface  of  cement 
grains  or  hydration  products.   The  adsorption  may  be  by 
hydrogen  bonding.   However  not  much  is  known  of  the  effect 
of  the  molecular  structure  of  the  retarders.   The  different 
results  for  a,  a-trehalose  found  by  different  workers 
indicate  that  the  behavior  of  retarders  in  cement  paste 
may  not  necessarily  be  the  same  as  that  in  pure  compound 
systems. 


17 


Drying  Shrinkage  of  'Paste,  Mortar,  and  Concrete 
as  Affected  by  Retarders 

When  retarders  (or  water  reducing  admixtures)  are 
added  to  concrete,  the  subsequent  drying  shrinkage  is 
generally  thought  to  increase  (4,  33).   On  the  other  hand, 
Wallace  and  Ore  (3)  examined  the  test  results  reported  by 
many  field  laboratories  and  concluded  that  these  admixtures 
neither  increase  nor  decrease  the  shrinkage  of  concrete. 
This  uncertainty  of  the  effect  of  retarders  on  the  shrinkage 
of  concrete  arises  from  the  many  complicated  factors  that 
affect  shrinkage  (34,  35).   Tremper  and  Spellman  (4) 
demonstrated  that  the  cumulative  effects  of  some  factors 
on  shrinkage  could  be  expressed  by  the  product,  not  the 
sum,  of  individual  effects.   Hence,  the  true  effect  of 
retarders  on  the  shrinkage  of  concrete  has  to  be  examined 
carefully  so  that  indirect  influences  are  avoided.   How- 
ever, only  a  few  papers  have  been  published  concerning  the 
shrinkage  behavior  as  affected  by  retarders. 

Danielson  (28)  observed  that  the  shrinkage  of  cement 
paste  in  an  atmosphere  of  6  0%  R.H.  was,  in  general,  increas- 
ed by  the  admixtures  studied.   The  increase  was  consider- 
able when  benzonate  and  salicylate,  which  were  the  only 
aromatic  salts  examined,  were  added. 

Tremper  (36)  dried  mortar  specimens  that  were  4  days 
old  for  4  days  in  an  atmosphere  of  50%  R.H.   At  low  SO^ 
contents  of  the  cement,  the  admixtures  (lignosulf onate  and 
hydroxylated  carboxylic  acid)  increased  drying 


18 


significantly.   At  higher  S03  contents  the  trend  was  re- 
versed, and  in  most  cases  the  drying  shrinkage  decreased 
relative  to  that  of  mortars  containing  no  admixture.   Thus 
he  suggested  that  the  optimum  gypsum  content  in  cement 
should  be  increased  to  minimize  the  shrinkage  when  ad- 
mixtures are  added. 

In  cement  paste,  gypsum  reacts  with  C3A  and  forms  the 
high-sulfate  form  of  calcium  sulfoaluminate  hydrate 
(ettringite)  in  early  stages  of  hydration.   This  reaction 
is  known  to  be  expansive.   According  to  Lerch  (37)  ,  for 
cements  of  low  alkali  content,  those  of  high  C^A  content 
require  larger  additions  of  gypsum  to  give  minimum  subse- 
quent shrinkage  than  do  those  of  low  C3A  content.   For 
cements  of  the  same  C3A  content,  those  of  high  alkali 
content  require  larger  addition  of  gypsum  than  do  those  of 
low  alkali  content.   Therefore,  the  observation  by  Tremper 
could  be  related  to  some  modified  rate  of  hydration  of 
the  cement  caused  by  the  retarders. 

Another  conceivable  cause  could  be  changes  in  the 
structure  of  the  hydration  products.   Young  (6)  observed 
that  no  new  hydrate  was  formed  in  C,A  hydration  by  the 
addition  of  calcium  lignosulf onate,  but  a  modification  of 
the  crystal  habit  of  the  usual  hydrates  took  place; 
acicular  structures  were  formed  instead  of  hexagonal 
plates  of  C-AHg  and  C.AH,3.   When  gypsum  was  present,  the 
formation  of  high  sulfoaluminate  was  not  affected  by  the 


19 


admixture.   However,  the  final  hydration  products  (low 
sulfoaluminate,  C„AH  ,  and  C.AH..-)  were  changed  from  their 
usual  hexagonal  plate  form. 

Danielson  (28)  examined  the  properties  of  cement  paste 
affected  by  organic  admixtures  at  an  age  of  28  days.   The 
amount  of  combined  water  and  the  total  heat  of  hydration 
were  not  altered  significantly  by  the  admixtures.   The 
compressive  strength  was  also  either  unaffected  or  some- 
what lowered.   The  reduction  in  Young's  modulus  was  un- 
expectedly small  compared  with  the  reduction  in  compressive 
strength  for  all  the  pastes  to  which  dibasic  salts  were 
added.   He  attributed  this  result  to  a  modified  structure 
of  hydration  products. 

On  the  other  hand,  Seligmann  and  Greening  (8)  showed 
that  sucrose  and  lignosulf onate  did  not  affect  the  nature 
of  the  hydration  reaction  of  cement;  only  the  rate  was 
influenced.   Prior  and  Adams  (1)  mentioned  that  differ- 
ential thermal  analysis  studies  of  hydrated  cement  at  the 
ages  of  7  and  2  8  days  showed  no  significant  change  in  the 
identity  or  proportion  of  the  hydration  products  of  cement 
with  the  addition  of  lignosulf onates. 

By  means  of  a  scanning  electron  microscope,  Schwiete, 
Ludwig,  and  Sieler  (38)  examined  the  morphology  of  the 
hydration  products  of  cement  pastes  at  the  ages  of  1,  7, 
14,  and  28  days.   There  was  no  difference  observed  among 
them  regardless  of  the  addition  of  different  kinds  of 


20 


retarders.   These  workers  also  confirmed,  by  means  of 
x-ray  diffraction,  that  retarders  changed  only  the  rate 
of  hydration  of  the  cement. 


21 


CHAPTER  III  -  MATERIALS 


Admixtures 


A  total  of  sixty-five  chemicals  were  tested  in  the 
setting  time  experiments  to  examine  the  effects  of  the 
molecular  structure  of  the  retarders.   They  included  a 
variety  of  organic  chemicals  -  many  aliphatic  compounds, 
aromatic  compounds,  chelating  agents,  dyes  and  others. 
About  one  half  were  organic  acids.    Their  names,  chemical 
formulae,  and  producer's  names  are  listed  in  Table  1. 

The  three  commercially  available  proprietary  retarders 
L,  A,  and  S  were  used  throughout  the  work.   Each  represents 
one  of  the  three  main  categories  of  organic  retarders,  i.e., 
calcium  (also,  sodium  or  ammonium)  lignosulf onates ,  hydroxy- 
carboxylic  acids,  and  carbohydrates,  respectively.   Since 
the  commercial  retarders  were  supplied  in  solution  form, 
their  solids  content  was  determined  by  oven-drying  in  the 
usual  way.   Density  and  amount  of  solid  content  of  each 
commercial  retarder  are  shown  in  Table  2.   It  should  be 
noted  that  concentrations  of  all  retarders  are,  hereafter, 
discussed  in  terms  of  weight  of  the  solid  component  per  unit 
weight  of  cement  in  the  mixture. 


22 


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27 


Table  2  -  List  of  Commercial  Retarders. 


Retarders 

Density 

Residue* 

(g/cc) 

(g/cc) 

Name 

Chemical  Classification 

L 

Calcium  Lignosulf onate 

1.147 

0.370 

A 

Hydroxycarboxylic  Acid 

1.152 

0.413 

S 

Carbohydrate  (Sugar) 

1.175 

0.376 

*Weight  of  residue  was  obtained  by  oven-drying  retarder 
at  110°C. 


In  the  shrinkage  experiments,  five  reagent  grade 
chemicals  that  had  been  found  to  be  retarders  were  selected 
and  used  along  with  the  three  commercial  retarders.   The 
pure  compounds  were  glycolic  acid,  citric  acid,  3-hydroxy- 
2-butanone,  sucrose,  and  hydroquinone.   Reagent  grade 
calcium  chloride  was  also  included  to  investigate  the 
effects  of  an  accelerator. 


Cement 
The  cement  used  was  an  ASTM  Type  I,  Lab.  No.  319,  the 
properties  of  which  are  shown  in  Table  3.   Since  a  great 
number  of  setting  time  measurements  on  mortar  specimens 
were  conducted  for  more  than  a  year,  some  cements  had 
changed  slightly  during  storage,  and  it  was  found  that  the 
cements  thus  partially  hydrated  and  possibly  carbonated 
had  slower  setting  properties.   This  difficulty  was 


28 


Table  3  -  Composition  and  Properties  of  Lab  Cement  No.  319 

Compound  Composition 

c3s 

C2S 

C3A 

C4AF 

CaSO. 

Total       96.94 


Chemica 

1  Analysis 

(%) 

sio2 

21.64 

A1203 

5.29 

Fe2°3 

2.19 

CaO 

65.36 

MgO 

0.92 

so3 

2.40 

Na20 

0.08 

K20 

0.41 

Lo  s  s  on 

Ignition 

1.80 

Free  Lime         1.08 

Insoluble  Residue  0.25 

Physical  Tests 

Normal  Consistency (ASTM  C187)  24.5  (%) 

Expansion (ASTM  C151)  0.136  (%) 
Setting  Time;  Gilmore (ASTM  C266) : 

Initial  2:55 

Final  4:15 

Fineness;  Blaine (ASTM  C2 04)  3870  (cm2/g) 

Paste  False  Set(ASTM  C451)  93.5  (%) 

Air  Entrained (ASTM  C185)  8.3  (%) 
Compressive  Strength (ASTM  C109) : 

1  day  1550  (psi) 

3  day  3130  (psi) 

7  day  4600  (psi) 

28  day  6450  (psi) 

Tensile  Strength (ASTM  C190) : 

1  day  205  (psi) 

3  day  345  (psi) 

7  day  430  (psi) 

28  day  520  (psi) 


56. 

.03 

19. 

.86 

10. 

.31 

G. 

.66 

4, 

,08 

29 


overcome  by  running  a  blank  test  on  a  plain  mortar  as  a 
control  once  a  month  or  whenever  cement  was  taken  from  a 
new  sack. 

For  shrinkage  measurements  of  paste  samples  and  for 
some  chemical  experiments  only  one  sack  of  cement  was 
selected  and  stored  in  sealed  glass  bottles. 

Sand 
The  sand  used  in  the  preparation  of  mortar  specimens 
for  setting  time  determinations  had  a  specific  gravity  of 
2.63,  1.33%  absorption,  and  a  fineness  modulus  of  2.26  and 
2.45  for  the  two  lots  used.   These  were  masonry  mortar 
sands  with  more  than  99%  passing  the  No.  8  sieve,  because 
it  was  thought  that  large  sand  particles  might  result  in 
erroneous  penetration  values  when  a  small  needle  was  used. 
In  use,  these  sands  were  oven-dried  for  24  hr   at  110°C 
and  stored  in  a  temperature  controlled  room  at  21°C. 

Water 

In  the  setting-time  experiments,  tap  water  was  used  to 
prepare  the  mortar  specimens.   The  water  was  put  in  a  poly- 
ethylene bottle  and  stored  in  the  same  temperature 
controlled  room. 

Deionized  or  distilled  water  was  used  for  all  of  the 
other  experiments  in  this  paper.   These  include  chemical 
analyses  and  preparation  of  cement  paste  specimens. 


30 


CHAPTER  IV  -  EXPERIMENTAL  WORK 

A  -  Setting  Time  Measurements 

General  Remarks 
The  setting  times  were  determined  by  the  Proctor 
penetration  method,  ASTM  Designation:  C403.   This  method 
involves  obtaining  a  mortar  sample  by  wet-screening  concrete 
to  remove  the  coarse  aggregate  and  is  time-consuming  and 
requires  large  amounts  of  materials.   It  has  been  shown  (39) 
that  the  setting  time  of  concrete  can  be  determined  from 
that  of  a  directly-mixed  mortar  if  the  mortar  is  made  with 
the  same  water-cement  ratio,  sand-cement  ratio ,   and  materials 
as  the  concrete.   Therefore,  it  was  decided  to  measure  the 
penetration  resistance  of  directly-mixed  mortar  as  the 
method  of  evaluating  chemicals  as  retarders.   Mix  pro- 
portions corresponding  to  those  of  a  practical  concrete 
were  chosen  for  the  mortar.   Initial  setting  time  and  final 
setting  time  are,  according  to  C403,  defined  as  the  elapsed 
times  to  reach  penetration  resistances  of  500  psi  and  4000 
psi,  respectively.   This  definition  has  been  used  in  this 
work. 

All  materials  were  stored  in  a  temperature-controlled 
room  at  21°C,  and  all  operations  were  conducted  in  the  same 
room. 


31 


Apparatus 

Container 

One-gallon  cardboard  containers,  with  a  diameter  of 
6.75  in.,  were  used  to  contain  the  mortar;  this  represents 
a  slight  modification  of  Method  C403. 

Since  the  containers  are  not  as  rigid  as  metal  con- 
tainers, it  was  suspected  that  the  value  of  penetration 
resistance  might  vary  with  the  location  that  was  probed  in 
the  surface  of  the  sample.   However  preliminary  experiments 
showed  that  the  differences  among  the  measurements  were 
negligibly  small  if  the  test  was  conducted  within  a  circle 
located  1  inch  in  from  the  side  of  the  container. 

Penetration  Resistance  Apparatus 
A  hand- loaded  Proctor  apparatus  was  used.   The  spring 
was  calibrated  by  means  of  a  platform  scale.   The  calibra- 
tion curve  is  shown  in  Figure  1. 

Mixer 

A  model  A200  Hobart  Mixer  was  used.   The  slow  speed 
was  determined  to  revolve  the  paddle  at  a  rate  of  94  rpm, 
with  a  planetary  motion  of  47  rpm.   The  medium  speed  re- 
volved the  paddle  at  a  rate  of  180  rpm,  with  a  planetary 
motion  of  90  rpm. 

Total  capacity  of  the  mixing  bowl  was  20  liters,  and 
an  optimum  mix  volume  was  felt  to  be  about  7  liters. 


32 


• 

IPO 

100 

- 

/ 



80 

/ 

■ — ■ 

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i 

fiO 

OU 

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/ 

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p 

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7 

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20  40  60  80  100 

Reading    on  Rod,Pe(lb) 


120 


Figure  1  -  Calibration  Curve  for  Proctor  Penetrometer 
(ASTM  C403) 


33 


Preparation  of  Mortar  Specimens 

Mixing  Proportions  and  Size  of  Batch 
Constant  mix  proportions  were  maintained  throughout 
the  experiments.   The  water  to  cement  ratio  was  0.50,  and 
the  sand  to  cement  ratio  was  2.75,  by  weight.   These  are 
typical  of  ratios  used  in  concrete  mixtures.   The  mortar 
thus  proportioned  was  plastic  and  workable.   Since  the  sand 
was  oven-dried,  the  actual  water  to  cement  ratio  of  the 
mortars  was  a  little  lower  than  0.50. 

In  preliminary  experiments  it  was  found  that  three 
values  of  penetration  resistance  from  three  samples  had  a 
range  of  less  than  5%  of  the  average  value,  in  every  case. 
It  was  therefore  determined  to  prepare  a  mix  of  6*2/3 
liters,  and  two  test  samples  were  prepared  from  this  batch. 

The  reagent  chemicals  used  as  admixtures  were  added 
at  a  concentration  of  0.1%  of  the  cement  by  weight  in  most 
cases,  although  sometimes  others  were  used  to  determine  the 
influence  of  concentration.   For  the  three  commercial 
retarders,  various  concentrations  were  tested  depending 
on  each  manufacturer's  suggested  dosage. 

Mixing  Procedures 
The  admixture  was  added  to  the  mixing  water  and  stirred 
until  dissolved  completely.   Some  relatively  insoluble  sub- 
stances required  heating  for  dissolution.   The  solution 
thus  prepared  was  placed  in  the  mixing  bowl,  and  the 


34 


cement  was  added.   They  were  mixed  at  the  slow  speed  for 
3  0  seconds.   The  mixing  operation  was  interrupted  for  about 
5  sec  during  which  time  the  sand  was  added.   Mixing  was 
resumed  at  slow  speed  for  30  sec  and,  then  for  1  min  at 
medium  speed.   Then  the  mixing  was  stopped  for  1  minute. 
During  this  period,  all  the  mortar  on  the  blade  of  the 
mixer  and  the  wall  of  the  bowl  was  scraped  down  with  a 
spatula.   The  mixture  was  again  mixed  at  medium  speed  for 
an  additional  1  minute.   Mortars  thus  prepared  had  flow 
values  of  110  to  140%,  according  to  ASTM  Method  C87, 
depending  on  the  admixture  used. 

Casting  and  Storage  of  Specimens 
The  mixed  mortar  was  placed  in  the  two  containers  and 
was  compacted  by  rodding  2  5  times.   The  surface  of  the 
specimen  was  then  approximately  leveled  with  a  trowel,  and 
the  side  of  the  container  was  tapped  lightly  with  the 
tamping  rod.   The  distance  between  the  finished  surface  of 
the  mortar  sample  and  the  top  edge  of  the  container  was 
approximately  1  inch.   The  sample  and  container  were  covered 
with  a  damp  cloth,  and  the  lid  was  placed  on. 

Penetration  Test  Procedure 
ASTM  C4  03  was  followed  exactly.   Six  to  seven  penetra- 
tion resistance  determinations  were  made  on  most  specimens. 
Some  samples  did  not  reach  the  final  setting  time  within 
24  hr;  in  such  instances  the  test  was  stopped  after  24  hr, 


35 


mainly  because  there  was  no  location  left  for  further 
penetration  measurements  on  the  surface  of  the  sample. 

A  needle  was  selected  for  each  penetration  of  such  a 
size  that  the  load  on  it  was  between  40  and  90  lb,  a 
range  in  which  the  most  reliable  values  were  obtained. 

B  -  Measurement  of  Shrinkage  of  Cement  Pastes 

General  Considerations 

Because  of  the  impermeability  of  cement  paste  and  its 
consequent  slowness  of  drying,  it  was  desired  to  use  small 
specimens  for  the  shrinkage  experiments  to  minimize  both 
the  time  to  reach  drying  equilibrium  and  the  moisture  (and 
therefore,  strain)  gradients  within  the  specimen.   Homo- 
geneity and  reproducibility  are  required  for  such  small 
specimens. 

A  possibly  troublesome  effect  with  small  specimens  is 
carbonation  of  the  cement  paste  by  reaction  with  atmos- 
pheric CO„ ,  which  can  induce  more  shrinkage  than  drying  (35) 
Another  consideration  is  that  cement  paste  continues  to 
hydrate  for  a  comparatively  long  period  of  time.   This  con- 
tinued hydration  changes  the  structure  of  the  paste  and, 
therefore,  affects  the  shrinkage  behavior.   Since  many  re- 
tarders  modify  the  early  hydration  of  cement,  this  effect 
of  continued  hydration  is  of  significant  importance  in  this 
study.   With  these  considerations  in  mind,  the  following 
apparatus  and  techniques  were  employed. 


36 


Apparatus 

Mold  for  Cement  Paste  Specimens 
A  special  mold  was  made  of  Teflon  so  that  the  paste 
specimens  could  be  demolded  without  using  any  parting  medi- 
um, such  as  oil.   Thus  the  surfaces  of  the  specimens  were 
free  from  any  contamination,  so  that  uniform  drying  could 
be  attained.   The  mold  is  shown  in  Figure  2  together  with 
a  cement  paste  specimen. 

A  total  of  ten  specimens  could  be  made  at  one  casting. 
The  size  of  the  specimen  was  1/5  x  1/5  x  4  inch.   A  small 
hole  was  made  through  the  centers  of  the  opposite  end 
blocks  to  accommodate  the  gauge  studs  for  the  length  change 
measurements. 

Some  specimens  had  to  be  demolded  at  about  7  to  10  hr 
after  casting.   In  these  cases  a  thin  polyethylene  sheet 
was  placed  between  the  teflon  mold  and  the  specimen.   In 
spite  of  this  effort,  about  half  of  the  specimens  were 
broken  on  demolding. 

Gauge  Studs  and  Length  Comparator 
Gauge  studs  were  needed  to  measure  the  length  changes 
of  the  cement  paste  bars.   The  studs  used  were  the  ends 
clipped  from  empty  ball-point  pen  refills  made  of  stainless 
steel.   These  were  inserted  in  the  end  blooks  with  the 
ball-portion  outward  so  that  after  casting  about  3  mm  of 
the  shaft  was  embedded  in  the  paste  specimen.   The  ball 


37 


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38 


portions  proved  to  be  ideal  as  gauge  studs  and  showed  no 
deformation,  to  0.0001  in.,  within  themselves. 

The  length  comparator  is  shown  in  Figure  3.   All 
elements  except  the  base  plate  were  stainless  steel.   The 
dial  gauge  provided  a  maximum  stroke  of  0.3  in.,  and  the 
smallest  subdivision  was  0.0001  inch.   Since  the  length  of 
the  cement  paste  bars  was  4  in.,  a  length  change  of  0.0025% 
could  be  determined.   A  standard  bar  was  also  made  of  stain- 
less steel  to  compensate  the  effects  of  temperature  fluctua- 
tion on  the  gauge  distance  of  the  apparatus.   It  was  enclosed 
in  a  rubber  tube  to  eliminate  heat  transfer  from  the  hand 
to  the  bar  during  handling. 

Mixing  Apparatus 
A  vacuum  mixing  container  was  made  from  stainless  steel 
tubing.   A  stainless  steel  plate  was  welded  to  one  end  of 
the  tube,  and  a  circular  slit  was  made  on  the  other  end  to 
accommodate  an  O-ring.   The  O-ring  provided  the  seal  between 
the  container  and  the  lid.   The  lid  was  attached  to  the 
container  by  means  of  four  clamping  screws.   On  the  side  of 
the  container  was  inserted  a  vacuum-tight  stainless-steel 
needle  valve,  through  which  the  container  was  evacuated 
and  through  which  a  measured  amount  of  water  was  introduced 
into  the  container.   The  inside  dimension  of  the  container 
was  3x4  inch.   The  size  was  so  determined  that  a  paste 
made  from  lOOg  of  cement  could  be  mixed  efficiently  and 


39 


Figure  3  -  Length  Comparator 


40 


uniformly  by  a  shaking  action.   The  shaking  action  was 
provided  by  a  Red  Devil  paint  shaker. 

Preparation  of  Cement  Paste  Specimens 

Mixing  Proportion  and  Concentration  of  Retarders 
It  was  desirable  to  use  a  water-cement  ratio  as  close 
as  possible  to  that  normally  used  in  concrete  mixtures.   A 
ratio  of  0.40,  however,  was  found  to  be  the  maximum  allow- 
able for  a  cement  paste  to  be  mixed  and  cast  without  experi- 
encing a  significant  amount  of  bleeding;  this  ratio  was 
employed  throughout. 

The  three  commercial  retarders  (L,  A,  and  S)  and  five 
pure  chemicals  (citric  acid,  glycolic  acid,  hydroquinone, 
3-hydroxy-2-butanone,  and  sucrose),  each  representing  a 
certain  group  of  retarders,  were  used.   Their  concentrations 
were  determined  on  the  basis  of  the  results  of  setting  time 
experiments  on  mortars.   The  relationship  between  concentra- 
tion of  retarder  and  initial  setting  time  of  the  mortar 
containing  it  was  plotted  and  the  concentration  that  gave 
50%  of  additional  retardation  to  a  reference  mortar  contain- 
ing no  admixture  was  established  from  the  curve.   The  values 
obtained  are  given  in  Table  4.   Additionally  calcium 
chloride  dihydrate  (CaCl2 • 2H20) ,  an  accelerator  of  set,  was 
used  at  a  concentration  of  1%  of  the  cement  by  weight. 


41 


Table  4  -  Concentration  of  Retarders  Added  to  Cement  Pastes, 


Retarder 

Concentration 
(percent  of  cement) 

Commercial  Retarders 

L 
A 
S 

0.260 
0.065 
0.100 

Pure  Chemicals 

Citric  Acid 

Glycolic  Acid 

Hydroquinone 

3-Hydroxy-2- 
Butanone 

Sucrose 

0.050  (0.076)* 

0.135 

0.080 

0.400 

0.050 

*  This  is  the  concentration  which  gives  100%  of  additional 
retardation  to  a  reference  mortar.   Others  give  50% 
of  additional  retardation. 


42 


Mixing,  Casting,  and  Curing  of  Cement 
Paste  Specimens 

The  cement  was  placed  in  the  mixing  container.   The  lid 
was  attached  and  the  four  clamping  screws  were  tightened. 
The  container  was  evacuated  on  an  aspirator  for  10  to  15 
minutes.   During  this  time,  8  0  ml  of  deionized  water  were 
poured  into  a  graduated  separatory  funnel  and  the  required 
amount  of  admixture,  if  necessary,  was  dissolved  in  it. 
The  evacuated  mixing  container  was  closed  with  the  needle 
valve  and  then  was  removed  from  the  aspirator.   The  solution 
was  then  drawn  from  the  funnel  into  the  container  by  open- 
ing the  valve.   The  valve  was  closed  again  when  the  required 
amount  of  the  solution,  4  0  ml  in  most  cases,  had  been 
introduced  into  the  container.   The  apparatus  is  shown  in 
Figure  4. 

The  container  was  then  placed  on  the  shaker  and  shaken 
for  5  minutes.   This  method  yielded  an  extremely  uniform 
paste  mixture  that  contained  no  entrained  air. 

After  the  shaking  the  paste  was  removed  from  the  con- 
tainer and  placed  in  a  "cake-decorator"  type  of  apparatus 
made  of  a  pyrex  glass  tube  with  a  squeezable  ball  attached 
to  one  end  (Figure  2) .   The  cement  paste  was  cast  in  the 
mold  from  the  paste  caster.   First  the  bottom  of  one  gauge 
stud  was  filled;  and  the  upper  part  next.   The  other  end 
was  then  filled  in  the  same  way,  and  the  rest  of  the  mold 
was  filled  continuously  from  one  end  to  the  other.   The 
paste  was  cast  slightly  above  the  surface  of  the  mold,  and 


43 


Figure  4  -  Apparatus  for  Drawing  Mixing  Solution  from 
Funnel  into  Mixing  Container 


44 


was  later  sliced  off  at  the  time  of  demolding  to  eliminate 
any  effects  of  either  bleeding  or  carbonation.   The  mold 
was  then  placed  on  a  vibrating  table  (paper  jogger)  and 
was  vibrated  briefly.   This  general  technique  produced  uni- 
form specimens  with  a  minimum  amount  of  bleeding.   Finally, 
the  specimens  in  the  mold  were  covered  with  damp  cloths 
arranged  so  that  they  did  not  come  in  direct  contact. 

The  specimens  that  were  tested  at  an  age  of  4  days  or 
later  were  demolded  at  2  days.  The  other  specimens  were 
demolded  at  7  to  22  hr  after  the  mixing  depending  on  the 
kind  of  admixture  added  or  the  desired  age  of  specimens. 
The  specimens  were  then  immersed  in  closed  containers  in 
a  saturated  calcium  hydroxide  solution. 

Measurements  of  Length  and  Weight, 
Method  of  Drying 

At  the  desired  age  the  specimens  were  measured  for 
length  change,  weight  change,  and  degree  of  hydration.   The 
specimen  was  taken  from  the  curing  bottle  and  was  placed 
in  the  length  comparator  in  the  standard  manner .   The 
length  was  recorded  in  the  wet  state.   After  the  measure- 
ment, the  sample  was  returned  in  the  storage  bottle. 

Shortly  thereafter,  the  sample  was  again  taken  from 
the  bottle,  the  studs  and  the  body  of  the  paste  bar  were 
wiped  with  tissue  paper,  and  the  weight  was  measured  rapidly 
on  an  analytical  balance,  to  the  nearest  0.1  mg. 


45 


The  specimen  was  then  dried  in  a  vacuum  oven  controlled 
at  105  to  110 °C,  which  was  continuously  evacuated  on  a 
vacuum  pump.   This  was  a  severe  drying  condition  and  un- 
realistic for  concrete  in  the  field.   It  was  used  to  shorten 
the  time  of  drying,  to  eliminate  carbonation,  and  to  mini- 
mize the  effects  of  continuing  hydration  of  the  cement.   At 
the  end  of  the  drying  time  the  specimen  was  taken  out  of 
the  oven  and  was  cooled  to  room  temperature  in  a  desic- 
cator over  anhydrous  magnesium  perchlorate. 

The  specimen  was  then  weighed.   The  length  change  was 
measured  with  the  Ames-dial  comparator.   This  sequence  was 
based  on  the  observation  that  the  weight  of  the  dried 
sample  was  very  sensitive  to  exposure  to  air,  whereas  the 
length  was  not  especially  so.   Some  very  young  specimens 
had  warped  longitudinally.   However,  deflection  at  mid- 
length  (due  to  warping)  was  less  than  0 . 5  mm  for  most 
specimens.   Calculation  showed  that  errors  caused  by  such 
a  warping  were  less  than  an  experimental  error  of  length 
measurement,  and  no  correction  was  made.   Only  four  speci- 
mens warped  more  than  0.5  mm  at  the  center;  they  were 
corrected  for  lengths,  using  the  curve  shown  in  Appendix  A. 
Shrinkage  was  calculated  with  respect  to  the  water-saturated 
length. 

After  all  measurements,  the  specimen  was  broken  into 
three  approximately  equal  lengths.   The  middle  third  was 
used  immediately  for  the  determination  of  non-evaporable 


46 


water,  and  the  other  two  portions  were  stored  in  a  vial 
out  of  contact  with  air. 

Some  relatively  mature  paste  specimens  were  tested 
after  drying  in  air  of  50%  relative  humidity  at  room  temper- 
ature.  These  specimens  were  placed  in  a  desiccator  over  a 
saturated  salt  solution  of  Mg(NO_)2.   A  chemical  sorbent 
for  CO-  was  also  placed  in  the  desiccator,  which  was  then 
evacuated.   Changes  of  length  and  weight  were  measured  at 
various  times  in  the  same  manner  described  above. 

C  -  Determination  of  Degree  of  Hydration  of  Cement  Pastes 

Loss  on  Ignition  Test 
The  degree  of  hydration  of  the  cement  in  the  paste 
was  determined  by  measuring  the  amount  of  chemically  com- 
bined, or  non-evaporable,  water.   Direct  determinations 
were  made  by  the  Penfield  method  (4  0) ,  which  has  certain 
drawbacks.   It  was  decided  to  conduct  a  loss  on  ignition 
test  and  to  calculate  the  amount  of  non-evaporable  water 
from  the  result.   The  derivation  of  the  equation  used  is 
shown  in  the  next  section. 

The  loss  on  ignition  was  determined  in  the  usual  way, 
using  approximately  lg  samples  of  the  crushed,  oven-dry 
paste  in  platinum  crucibles.   The  heating  was  in  a  muffle 
furnace  to  constant  weight  at  about  1050°C. 


47 


Derivation  of  Equations  for  Determining  Non-Evaporable 
Water  and  Evaporable  Water 

Loss  on  ignition  has  sometimes  been  considered  a 
measure  of  the  degree  of  hydration  of  cement  paste.   But 
this  idea  is  misleading.   Even  an  unhydrated  cement  has  a 
loss  on  ignition  of  around  1%,  because  the  loss  on  ignition 
includes  not  only  non-evaporable  water,  but  also  carbon 
dioxide  from  carbonated  compounds. 

In  hardened  cement  paste,  most  bulk  water  is  evaporable 
at  relatively  low  temperature.   However,  some  water  mole- 
cules are  sorbed  on  cement  gel  with  a  differentiating 
degree  of  bond  strength.   As  a  result  the  distinction  be- 
tween chemically-combined  (non-evaporable)  water  and 
physically  sorbed  (evaporable)  water  is  possible  only  on 
an  empirical  basis.   In  this  study,  therefore,  they  were 
defined  as  follows: 

"Evaporable  Water":        Water  lost  from  a  sample  during 

vacuum  oven  drying  at  105-110°C 
for  24  hours. 

"Non-Evaporable  Water":     Water  remaining  in  a  sample  dur- 
ing vacuum  oven  drying  of  2  4  hr 
at  110°C  and  lost  on  drying  at 
about  1050°C. 

Assumptions 
In  the  derivation  of  these  equations  it  was  assumed 
that  chemically  combined  water  or  carbon  dioxide  (due  to 
inadvertent  exposure  to  atmosphere)  in  the  "dry"  cement 
are  not  lost  on  vacuum  oven  drying  to  110 °C  and  that  any 
further  carbonation  during  mixing,  curing,  and  drying  of 


48 


the  paste  is  negligible.   In  any  case  the  pastes  prepared 
for  this  study  had  carbonated  only  slightly. 

Notation 

Schematic  diagrams  for  "dry"  cement  and  for  cement 

paste  are  shown  in  Figure  5.   The  notations  are: 

We     :   weight  of  evaporable  water  in  cement  paste 

Wn*    :   weight  of  chemically  combined  water  after 
mixing 

Wn    :   total  weight  of  non-evaporable  water  in 
cement  paste 

Wc     :   total  weight  of  cement 

Wee    :   weight  loss  of  cement  when  dried  in  the 
vacuum  oven  for  24  hr  at  110°C 

Wclw   :   weight  of  chemically  combined  water  in 
cement  before  mixing 

Wclc   :   weight  of  chemically  combined  carbon  dioxide 
in  cement  before  mixing 

Wcl    :   (Wclw  +  Wclc) 

Wch    :   weight  of  cement  hydrated  in  cement  paste 

Wcu    :   weight  of  cement  unhydrated  in  cement  paste 

Wei    :   ignited  weight  of  cement  at  1050°C 
(=Wch  +  Wcu) 

Wl     :   total  weight  loss  on  ignition  of  cement 
before  mixing 

Wli    :   weight  loss  on  ignition  of  cement  paste  after 
being  dried  in  the  vacuum  oven  for  24  hr 
at  110°C 

Wss    :   weight  of  water  saturated  surface  dry  cement 
paste 

Wod    :   weight  of  the  same  sample  after  dried  in  the 
vacuum  oven  for  24  hr  at  110°C 


49 


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50 


Derivation  of  Equations 

Immediately  obtainable  relations  are, 

Wc  =  Wei  +  Wcl  +  Wee  =  Wei  +  Wl   (1) 

Wcl  =   Wclc  +  Wclw  (2) 

Wss  =   Wei  +  Wcl  +  Wn*  +  We        (3) 

Wod  =   Wei  +  Wcl  +  Wn*  (4) 

Wli  =   Wn*  +  Wcl  (5) 

From  eq.  (5) , 

Wli  m   Wn*  +  Wcl   .    Wn*_  =  Wli  _  Wcl .,. 

Wei  "     Wei  Wei   Wei   Wei 

Combining  eqs.  (3)  and  (4),  and  dividing  by  Wei, 

We   _  Wss  -  Wod  __  Wss  -  Wod   Wod 
Wei      Wcl    "    Wod    x  WcT 


i   Wss    ^    \          ,  t  L  Wcl  x  Wn*  x  ._, 

=   (  rr-j  -  1  )   X   (  1  +  - — r  +  rr — i-  )   (7) 

Wod               Wei  Wei            ' 
Substituting  eq .  (6)  into  eq .  (7)  , 

We   =  ,  Wss  _  Wli        . 

WcT    (  Wod    X  )  (  X  +  WcT  >  (8) 


We  =  We    Wei  _  We     (Wc-Wl) 


Wc    Wei   Wc    Wei     Wc 


=(Wss_l)  (  !  +  Wli  }  (1_W1}  ( 

v  Wod   x  ;  K    •"•   WcT  ;  l  x   Wc  ;      ^' 


Dividing  both  terms  of  eq.  (2)  by  Wei, 


Wcl 
Wcl  " 

Wclc 
Wei 

L  Wclw 
+  Wei 

# 

Wclw 

Wcl   Wclc 

Wei 

Wc  i   Wc  i 

Wcl 
WcT 

Wc lc    Wc 
Wc    Wei 

(10) 


51 


Since  Wn  =  Wn*  +  Wclw, 

Wn   _  Wn*  +  Wclw 
Wci  "     Wci 

Substituting  eqs.  (6)  and  (10)  into  eq.  (11) , 


(11) 


Wn 
WcT 

Wli   Wclc    Wc 
WcT    Wc   x  WcT 

Wli 
WcT 

Wn 
Wc 

Wn    Wci   Wn   ,, 
WcT  x  Wc    WcT  u 

Wl 
Wc 

W£l£  (1  +  ^K)—    (12) 
Wc   VJ-   WcT;    vxz; 


)       (13) 

It  should  be  noted  that  Wci  includes  also  the  part  of 
cement  which  has  been  carbonated  before  mixing  with  water 
and,  therefore,  is  not  available  for  hydration.   Calcula- 
tion, however,  showed  that  the  true  Wn/Wci  and  Wc/Wci  did 
not  differ  by  more  than  1%  from  the  calculated  values  from 
eqs.  (8)  and  (12).   Because  the  experimental  error  of  loss 
on  ignition  test  amounts  to  the  calculative  error,  no 
further  consideration  was  made. 

Reduction  of  Data 
The  following  equations  were  derived  and  used  to 
reduce  loss  on  ignition  data  in  this  study. 

Wn  _  Wli  _  Wclc  ,,    Wl  .  ,.. 

WcT   WcT    Wc   u   WcT  u  ' 

Wn  _  Wn   M    Wl.  nt-v 

Wc"  "  WcT  (1   Wc0  (15) 

We  _  ,Wss  _  ..  n    Wli,  n  _  Wl.   ,,,. 

Wc"  "  (Wod    1}  (1  +  WcT5  (1   Wc"5  (16) 


52 


Wli/Wci  can  be  determined  directly  from  the  loss  on 
ignition  test,  as  can  Wl/Wci  and  Wl/Wc.   Wclc/Wc  was 
determined  by  a  common  method  (41) .   The  value  of  Wl/Wc 
varied  from  0.0196  to  0.0203  during  the  shrinkage  study. 
(Wclc/Wc)  x  (  1  +  Wl/Wci  )  ranged  only  from  0.01091  to 
0.01092.   Wss  and  Wod  were  obtained  from  the  specimens  used 
for  the  length  change  measurements.   In  calculating  Wss  and 
Wod,  the  weight  of  the  gauge  studs  was,  of  course,  sub- 
tracted from  the  total  weight  of  the  specimen.   Degree  of 
hydration  was  expressed  by  dividing  Wn/Wci  of  a  sample  by 
that  of  fully  hydrated  cement  paste. 

D  -  Surface  Area  Measurements  of  Cement  Pastes 

General  Remarks 
Water  vapor  and  nitrogen  are  the  two  gases  commonly 
used  for  measuring  the  surface  area  of  a  solid  by  the 
adsorption  method.   These  gases,  however,  give  surface 
areas  of  a  different  order  of  magnitude  for  cement  paste. 

Typical  BET  surface  areas  of  a  mature  cement  paste  by  water 

2  2 

vapor  and  by  nitrogen  sorption  are  2  00  m  /g  and  2  0  m  /g, 

respectively.   Because  the  surface  area  is  one  of  the 

important  factors  of  a  model  of  cement  paste  structure 

there  has  been  a  critical  controversy  between  some  workers 

concerning  the  value  of  surface  area  and  the  method  of 

measuring  it  (42,  43,  44,  45).    This  controversy  is  yet 


53 


unresolved.   In  this  study,  since  only  relative  values  were 
needed,  the  water  vapor  adsorption  value  was  chosen. 

Apparatus  and  Procedures  of  Measurement 
Four  glass  desiccators  were  prepared  with  solutions  of 
glycerin  and  deionized  water  to  control  the  vapor  pressure 
of  water.   The  relative  humidities  ranged  from  10  to  32  per 
cent.   The  concentration  of  glycerin  in  the  solution,  and 
hence  the  relative  humidity,  was  determined  by  the  measure- 
ment of  the  refractive  index  of  the  solution.   Approximately 
1  liter  of  each  solution  was  placed  in  the  desiccator  and 
continuously  stirred  with  a  magnetic  stirrer. 

The  cement  paste  samples,  which  had  been  vacuum-oven 
dried  for  the  shrinkage  measurements,  were  ground  in  a 
mortar  and  pestle  so  that  most  passed  a  No.  60  sieve.   The 
powdered  samples  were  placed  on  watch  glasses  and  were  re- 
dried  in  the  vacuum  oven  for  an  additional  hour  at  110 °C. 
After  drying,  the  samples  were  placed  in  weighed  weighing 
bottles.   Lids  were  placed  while  the  samples  were  still  hot. 
The  bottles  were  cooled  to  room  temperature  in  a  desiccator 
and  weighed.   The  weight  of  the  sample  was  about  lg. 

The  bottles  were  placed  in  the  desiccator  of  the  lowest 
humidity  and  their  lids  were  removed.   The  desiccator  was 
closed  and  evacuated  on  a  vacuum  pump.   Adsorption  was 
allowed  to  continue  for  48  hours.   Then  the  desiccator  was 
opened,  and  the  bottles  were  covered  with  the  lids.   They 
were  weighed  and  replaced  in  the  desiccator  of  the  next 


54 


lowest  humidity,  and  the  process  was  repeated.   The  refr- 
active index   of  the  solution  was  tested  after  the  bottles 
were  taken  out  of  the  desiccator,  and  the  temperature  was 
recorded. 

The  adsorption  isotherms  were  interpreted  in  the  usual 
way  by  the  BET  Theory  (46,  4  7).    The  rectified  form  of  the 
equation  was  used  and  the  data  were  analyzed  by  least 
squares;  the  calculation  was  made  by  a  computer.   Specific 
surface  area  was  expressed  on  the  basis  of  ignited  weight 
of  the  cement  paste  sample. 

E  -  Scanning  Electron  Microscope  Observation 

General  Procedures 

The  model  JSM-U3  scanning  electron  microscope,  Japan 
Electron  Optics  Laboratory  Co.  Ltd.,  was  used  for  the 
observation  of  the  samples. 

At  the  desired  age,  the  sample  was  oven-dried  at  110°C 
and  mounted  on  a  brass  sample  holder.   The  sample  was  stored 
in  a  desiccator  over  anhydrous  magnesium  perchlorate  until 
the  mounting  glue  dried.   It  was  necessary  to  coat  the 
sample,  usually  only  with  carbon,  to  get  a  clear  image. 
The  sample  was  then  placed  in  the  microscope  and  the  image 
of  the  sample  was  first  observed  on  a  TV  screen  at  a 
relatively  low  magnification.   Various  locations  of  the 
sample  were  viewed  in  detail  by  changing  the  magnification, 


55 


and  a  desired  representative  area  was  determined  on  the 
screen.   Then  the  image  was  switched  from  the  TV  screen  to 
the  probe  screen  of  the  microscope  and  examined  further  in 
detail.   Finally,  photomicrographs  were  taken  with  a 
Polaroid  camera.   The  scanning  speed  at  this  time  was 
slowed  down  to  50  seconds. 


56 


CHAPTER  V  -  RESULTS 

Infrared  Spectra  of  Commercial  Retarders 
The  three  commercial  retarders  were  representative  of 
the  three  main  categories  in  current  use.   To  identify  them 
more  precisely,  a  small  amount  of  each  was  oven-dried  at 
110 °C,  and  KBr  pellets  were  made  and  infrared  spectra 
obtained  in  the  usual  way  with  a  Beckman  DK-10  spectrophoto- 
meter.  Figure  6  shows  the  results.   The  interpretations  of 
individual  absorption  band  follow  the  assignments  given  by 
Halstead  and  Chaiken  (48)  .   That  marked  L  is  a  ligno- 
sulfonate  retarder,  A  is  a  hydroxycarboxylic  acid  retarder, 
and  S  is  a  modified  sugar  or  carbohydrate,  probably  with 
some  other  materials  in  it  that  remain  unidentified. 

Non-Evaporable  Water  Content  of  Fully  Hydrated 
Cement  Paste 

The  non-evaporable  water  content  of  fully  hydrated 

cement  was  needed  to  calculate  the  degree  of  hydration  of 

the  cement  paste  samples.   The  value  was  determined  by 

hydrating  the  cement  as  follows:  45  g  of  the  cement  and 

450  ml  of  distilled  water  were  placed  in  a  clean  16-ounce 

glass  bottle  and  a  lid  was  placed  on  it  with  a  teflon  sheet 

as  a  lid-liner.   The  bottle  was  rotated  continuously  on  a 


57 


Figure  6  -  Infrared  Spectra  of  Commercial  Retarders 


58 


roller  mill  for  10  days.   The  mixing  was  then  changed  to 
magnetic  stirring  until  the  time  of  test.   At  this  time 
the  sample  was  vacuum  filtered  on  paper,  and  the  residue 
was  placed  in  the  vacuum  oven  at  105  to  110°C.   Loss  on 
ignition  of  the  oven-dry  sample  was  then  determined  by 
furnace  drying  at  1050°C. 

The  results  of  the  determination  conducted  at  hydration 
times  of  4  and  10  weeks  are  shown  in  Table  5.   Most  of  the 
cement  had  hydrated  in  4  weeks;  only  a  little  further 
hydration  was  observed  from  4  weeks  to  10  weeks.   Hence, 
the  values  at  the  age  of  10  weeks  were  employed  as  those 
of  the  fully  hydrated  cement  in  this  work. 


Table  5  -  Non-Evaporable  Water  Content  of  Bottle- 
Hydrated  Cement  (W/C  =  10)  . 


Age 
(weeks) 

Loss  on  Ignition 
Wli/Wci  (%) 

Non-Evaporable  Water 
Wn/Wci  (%) 

4 
10 

19.81 
20.59 

18.72 
19.50 

59 


Result  of  Setting  Time  Experiments 

Commercial  Retarders 

Figures  7 ,  8 ,  and  9  show  the  results  of  setting  time 
experiments  for  the  three  commercial  retarders  when  they 
were  used  at  different  concentrations,  expressed  as  weight 
percent  of  the  retarder-solids  based  on  the  cement.   In 
these  figures,  values  of  penetration  resistance  are  plotted 
against  elapsed  time  after  initial  contact  of  the  cement 
with  mixing  water  (plus  admixture) .   The  general  expectation 
that  the  higher  the  concentration  of  retarder ,  the  longer 
the  setting  time,  is  apparent.   However,  it  is  noteworthy 
that  the  retarders  A  (hydroxycarboxylic  acid)  and  S  (carbo- 
hydrate)  tend  to  accelerate  the   initial  hydration  of 
cement  when  they  were  added  at  the  highest  concentration 
whereas  the  retarder  L  (lignosulfonate)  retards  all  stages 
of  the  hydration  evenly  up  to  4000  psi  even  at  higher 
concentration . 

In  order  to  compare  the  effects  of  concentration  of 
retarders  at  different  penetration  levels,  Figures  10,  11, 
and  12  were  made  from  the  same  results.   It  is  observed 
that  relative  retardation  of  the  mortars  is  smaller  at 
higher  penetration  resistances.   This  is  an  important  and 
necessary  property  for  properly  retarded  concrete.   Another 
interesting  point  is  that  the  increases  in  setting  time  at 
the  penetration  resistance  levels  of  500,  1000,  and  4000 
psi  are  in  close  agreement  and  the  retardation  at  500  psi 


60 


4000 


6  8 

Elapsed  Time  (hr) 


Figure   7    -   Penetration  Resistance  vs  Elapsed  Time   for 
Mortar   with  Retarder   L 


61 


4000 


1000 


-     500 


in 

a 


a> 

u 

c 
o 

4- 

</> 
0) 

a: 


0) 

c 


6        8 
Elapsed  Time  (hr) 


Figure  8  -  Penetration  Resistance  vs  Elapsed  Time  for 
Mortar  with  Retarder  A 


62 


/                ' 

/ 

4000 

1               / 

/ 

/X 

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/  /  / 

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-    y 

is 

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i 

i 

1 

1 

1 

6  8 

Elapsed  Time  (hr) 


10 


Figure  9  -  Penetration  Resistance  vs  Elapsed  Time  for 
Mortar  with  Retarder  S 


63 


0.40 


0.30 


;£ 


0.20 


S 

o 

c 
o 


0.10 


100 


130  160  190 

Relative   Retardation  (%) 


220 


Figure  10  -  Effect  of  Concentration  of  Retarder  L  on 
Setting  Time  of  Mortar 


64 


0.15 


0.10 


c 

o 

c 
o 

O 


0.05 


100 


130  160  190 

Relative  Retardation  (%) 


210 


Figure  11  -  Effect  of  Concentration  of  Retarder  A  on 
Setting  Time  of  Mortar 


65 


£ 

c 
o 
u 


0.15 


0.10 


0.05 


100 


130  160  190 

Relative  Retardation  (%) 


220 


Figure  12  -  Effect  of  Concentration  of  Retarder  S  on 
Setting  Time  of  Mortar 


66 


level  appears  to  be  a  mean  retardation  in  the  resistance 
range  of  100  to  4000  psi.   Since  initial  setting  time 
corresponds  approximately  to  the  last  time  when  revibra- 
tion  of  concrete  can  be  made,  the  result  would  indicate 
that  initial  setting  time  is  a  practical  and  convenient 
standard  point  for  evaluating  retarders. 

Manufacturer's  suggested  dosages  are  also  shown  in 
each  figure  by  a  shaded  range.   These  dosages  produce  in- 
creases in  setting  time  of  roughly  30  to  90%  for  all  the 
retarders.   The  resulting  range  of  retardation  is  typical 
of  that  of  concrete  (49) .   This  result  implicitly  affirms 
the  adequacy  of  the  penetration  resistance  test  as  con- 
ducted on  mortar  specimens  in  this  work.   In  the  same 
figures,  it  should  be  noted  that  the  lignosulf onate  retarder 
(L)  required  more  than  twice  as  much  dosage  as  the  others 
(A  and  S)  did  to  obtain  a  certain  amount  of  retardation. 

Pure  Chemicals 
Table  6  summarizes  the  initial  setting  times  of  mortar 
specimens  incorporating  many  chemicals  at  a  concentration 
of  0.1%  of  the  cement  by  weight.   For  some  of  the  chemicals 
that  were  found  to  be  a  weak  or  ineffective  retarder  at  a 
concentration  of  0.1%,  other  results  of  tests  at  a  con- 
centration of  0.5%  are  also  shown.   T500  is  defined  as 
the  initial  setting  time  of  each  sample  relative  to  that 
of  a  control  sample,  and  was  obtained  as  follows:   A 
relationship  between  elapsed  time  and  penetration  resistance 


67 


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71 


was  drawn  for  each  sample  in  the  same  way  as  was  done  for 
the  commercial  retarders,  and  an  initial  setting  time  was 
determined.   This  time  was  then  expressed  in  terms  of  a 
percentage  of  that  of  an  appropriate  control  sample  without 
admixture.   In  the  same  way,  T50,  T100,  and  T4  0Q0,  which 
are  relative  setting  times  at  the  penetration  resistance 
of  50,  100,  and  4000  psi,  respectively,  were  determined. 
They  are  to  be  found  in  Appendix  B.   A  tendency,  similar 
to  that  observed  with  the  commercial  retarders,  was  noted 
-  namely  the  relative  setting  time  at  500  psi,  T500,  is 
about  the  same  value  as  the  corresponding  T100  and  T4000. 
T50  is  different  from  the  other  relative  setting  times  for 
some  chemicals.   If  T50  is  smaller  than  the  others,  it 
indicates  that  the  chemical  accelerated,  relatively  speak- 
ing, the  very  early  hydration  of  cement.   The  ratio 
T500/T50  was  used  for  this  indication  in  Table  6,  i.e.,  the 
larger  the  ratio  the  more  the  reactions  were  relatively 
accelerated.   Strong  retarders  such  as  tartronic  acid, 
d-tartaric  acid,  mucic  acid,  gluconic  acid,  2-ketoglutaric 
acid,  citric  acid,  sucrose,  and  2 ,4 ,6-trihydroxybenzoic 
acid  have  large  values  of  T500/T50. 

Again,  calcium  lignosulf onate  is  not  a  strong  re- 
tarder.   Glycolic  acid,  methyl  glycolate  and  a-hydroxyacet- 
amide  are  strong  retarders  at  higher  concentrations.   Only 
l,3-dihydroxy-2-propanone  showed  an  unusual  setting  when 
it  was  added  at  the  rate  of  0.5%.   It  accelerated  early 


72 


hydration  of  the  cement  to  reach  a  penetration  resistance 
of  2  00  psi  in  2  hr ,  but  extremely  retarded  the  later 
hydration.   This  behavior  was  similar  to  that  observed  in 
the  hydration  of  a  Type  I  cement  clinker  without  any  gypsum 
addition  (Figure  13) . 

Figures  14  and  15  show  the  effects  of  concentration  of 
admixture  on  the  relative  initial  setting  time  of  mortar 
specimens.   It  is  seen  that  strong  retarders  can  delay  the 
setting  of  mortars  almost  indefinitely  even  at  a  relatively 
low  concentration  while  some  other  chemicals  accelerate  the 
setting  when  added  at  higher  concentration. 

The  results  seem  to  divide  themselves  into  two  groups. 
In  Figure  14,  whatever  the  magnitude  of  the  retardation, 
additional  increments  of  concentration  produced  an  in- 
creasingly larger  relative  retardation,  i.e.,  the  curves 
are  concave  downward.   In  Figure  15,  on  the  other  hand 
the  opposite  is  true;  the  instances  showed  less  additional 
effect  at  higher  concentrations.   Indeed,  sometimes  the 
effect  was  reversed. 

Effects  of  Retarders  on  the  Drying  Shrinkage  of 
Cement  Paste  at  Various  Stages  of  Hydration 

Figures  16  and  Figure  17  show,  respectively,  the 
shrinkage  of  the  cement  paste  bars  as  affected  by  the 
addition  of  commercial  retarders  and  selected  pure  chemi- 
cals when  the  pastes  were  dried  in  a  vacuum  oven  at  105 
to  110°C  for  24  hours.   The  shrinkage  values  were  plotted 


73 


4000 


4  6 

Elapsed    Time   (hr) 


Figure   13   -  Penetration   Resistance  vs  Elapsed   Time   for  Mortar 
with   1, 3-Dihydroxy-2-Butanone 


74 


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against  the  degree  of  hydration  of  the  samples,  determined 
as  previously  explained.   For  clarity,  data  points  are  not 
shown  in  the  figures.   They  are  to  be  found  in  Appendix  C. 
For  citric  acid,  however,  data  points  only  are  shown  in 
Figure  17  because  of  the  lack  of  enough  points  to  draw  a 
complete  curve. 

At  the  degree  of  hydration  of  about  50%,  which  roughly 
corresponds  to  an  age  of  2  days,  all  the  samples  shrank 
practically  an  equal  amount,  approximately  0.8%.   The 
cement  paste  alone,  with  no  admixture,  always  had  a  smaller 
shrinkage  than  the  others  at  this  point  and  at  most  later 
ages.   At  the  degree  of  hydration  of  85  to  90%,  the  rate 
of  increase  in  shrinkage  was  reduced  for  all  pastes  except 
that  with  calcium  chloride. 

When  the  degree  of  hydration  was  between  2  0  and  4  5% 
the  shrinkage  behavior  of  the  samples  was  changed  signifi- 
cantly.  All  hydroxycarboxylic  acids  such  as  retarder  A, 
glycolic  acid  and  citric  acid  increased  the  shrinkage 
considerably.   Sucrose  had  an  effect  about  equal  to  that  of 
these  acids,  but  the  carbohydrate  retarder  (S) ,  conversely, 
minimized  the  shrinkage.   The  cement  paste  with  lignosulfo- 
nate  retarder  (L)  shrank  more  or  less  in  the  same  way  as 
did  the  cement  paste  with  no  admixture,  but  showed  less 
shrinkage  at  early  ages.   Addition  of  3-hydroxy-2-butanone 
or  hydroquinone ,  which  have  no  acid  group,  but  only  hydroxy 1 
or  carbonyl  groups,  resulted  in  a  smaller  shrinkage  of 


79 


cement  paste  at  this  early  age.   Calcium  chloride  increased 
the  shrinkage  at  all  stages  of  hydration  and  showed  the 
largest  shrinkage  of  all  hydrations  higher  than  50%. 

When  either  the  concentration  of  citric  acid  was  in- 
creased enough  to  result  in  a  relative  retardation  of  200% 
or  the  water-cement  ratio  of  plain  paste  was  changed  from 
0.40  to  0.43,  the  shrinkage  of  the  pastes  was  practically 
unchanged.   These  results  are  to  be  found  in  Appendix  C. 

Drying  Shrinkage  of  Mature  Cement  Pastes 
When  Dried  at  5  0%  Relative  Humidity 

Shrinkage  of  10-months-old  (i.e.  almost  mature)  samples 
was  measured  over  a  period  of  50  days  in  an  atmosphere  of 
50%  relative  humidity.   The  results  are  shown  in  Figures  18 
and  19.   Each  data  point  is  the  average  of  two  separate 
measurements.   The  range  of  duplicate  measurements  was 
usually  within  3%  of  the  average.   The  commercial  retarders 
and  most  of  the  chemicals  of  the  hydroxycarboxylic  acid  type 
increased  the  shrinkage  consistently.   However,  all  the  ad- 
mixtures also  increased  the  degree  of  hydration  of  cement 
paste  at  this  age,  and  the  samples  did  not  reach  the  same 
degree  of  hydration.   Instead,  there  is  a  tendency  that  a 
sample  of  higher  degree  of  hydration  shrinks  more,  as 
would  be  expected. 

The  relationships  between  shrinkage  and  weight  loss 
of  the  samples  are  shown  in  Figures  20  and  21.   If  the 


80 


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Weight  Loss  (%) 


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Figure  20  -  Shrinkage  vs  Weight  Loss  of  Mature  Cement  Pastes 
When  Dried  at  50%  Relative  Humidity 
(Commercial  Retarders) 


83 


Weight   Loss    (%) 
2  4  6 


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o    i  Glycolic    Acid 
x     •  Citric    A**'^ 

•    :  Tartaric 
A   :  Ketomal 

Acid 
onic  Acid 

Figure  21  -  Shrinkage  vs  Weight  Loss  of  Mature  Cement  Pastes 
When  Dried  at  50%  Relative  Humidity 
(Pure  Acid  Chemicals) 


84 


weight  loss  in  these  figures  is  replaced  by  drying  time  in 
Figures  18  and  19,  the  relative  position  of  each  data  point 
in  both  sets  of  figures  appears  to  be  the  same.   This 
similarity  may  be  caused  either  by  differences  in  the 
amount  of  hydration  products  produced  or  some  change  in 
the  structure  of  the  cement  paste  induced  by  the  addition 
of  the  retarders.   The  cement  paste  with  retarder  S,  how- 
ever, showed  extraordinarily  large  shrinkage  when  a  certain 
amount  of  weight  was  lost.   In  this  case,  some  changes  in 
composition  or  structure  of  hydration  products  would  be 
more  expectable. 

Water  Content  of  Cement  Pastes 
Figures  22  and  23  show  the  relationship  between  evapo- 
rable  water  and  non-evaporable  water  contents  of  cement 
paste  samples.   These  water  contents  are  expressed  in  per- 
centage of  original  (i.e.  dry)  weight  of  cement,  for  ease 
of  comparison.   The  original  water-cement  ratio  of  the 
samples  was  0.40.   The  reason  why  the  sum  of  Wn  and  We  is 
greater  than  this  is  the  increased  water  content  brought 
about  by  self-desiccation  and  the  efficient  curing  of 
these  samples. 

Each  cement  paste  with  a  certain  admixture  shows  its 
own  relation  in  some  different  way  from  others.   However, 
as  indicated  for  the  plain  cement  paste  by  solid  lines, 
the  data  point  could  have  scattered  in  a  wide  range  if  more 
measurements  had  been  made.   Yet,  most  of  the  points  fall 


85 


15 


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40 


Figure  22  -  Non-Evaporable  Water  vs  Evaporable  Water  of 
Cement  Pastes  (Commercial  Retarders) 


86 


c 


35 
We/Wc  (%) 


Figure  23  -  Non-Evaporable  Water  vs  Evaporable  Water  of 
Cement  Pastes  (Pure  Chemicals) 


87 


in  the  region  that  the  two  lines  for  the  control  samples 
enclose.   This  could  indicate  that  retarders  do  not  change 
the  structure  of  cement  paste  significantly. 

In  Figures  24  and  25,  the  non-evaporable  water  content 
is  plotted  against  curing  time  of  the  samples.   The  solid 
line  represents  the  relation  for  the  cement  paste  without 
admixture.   It  can  be  seen  that  retarded  degree  of  hydration 
of  a  cement  by  the  addition  of  retarders  at  the  concentra- 
tion that  results  in  relative  set  delay  of  150%  seems  to  be 
recovered  completely  in  2  to  4  days.   After  that,  even  some 
increase  in  the  degree  of  hydration  is  observed  for  most 
pastes  with  retarders. 

Specific  Surface  Area  of  Cement  Pastes 
The  results  of  the  water  vapor  adsorption  experiments 
were  used  to  calculate  the  specific  surfaces  of  the  paste 
samples.   The  calculation  was  done  by  means  of  the  BET 
theory  in  the  usual  way  and  with  the  assumption  of  a  unit 
area  for  the  water  molecule  of  10.6  A  .   The  results  are 
shown  in  Figures  2  6  and  27,  on  a  basis  of  the  ignited 
weight  of  the  total  sample.   The  values  shown  are  averages 
of  two  measurements,  which  agreed  to  about  10%.   As  is 
expected,  the  larger  the  degree  of  hydration,  the  higher 
the  specific  surface  area,  and  the  relation  is  almost  linear. 
However,  there  is  no  quantitatively  noticeable  difference 
observed  among  cement  pastes  with  different  admixtures. 


88 


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Figure  26  -  Specific  Surface  Area  of  Vacuum  Oven-Dried 

Cement  Pastes  When  Expressed  on  the  Basis  of 
Total  Ignited  Weight  of  Samples  (No.  1) 


91 


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CaCl2-2H20 


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Figure  27  -  Specific  Surface  Area  of  Vacuum  Oven-Dried 

Cement  Pastes  When  Expressed  on  the  Basis  of 
Total  Ignited  Weight  of  Samples  (No.  2) 


92 


When  specific  surface  area  was  expressed  in  terms  of 
ignited  weight  of  the  hydrated  portion  of  the  sample, 
rather  than  the  total  sample,  interesting  curves  were 
obtained.   They  are  shown  in  Figures  28,  29,  and  30.   These 
curves  are  similar  to  those  of  the  shrinkage  results,  shown 
previously.   The  samples  that  showed  larger  shrinkage  at 
earlier  age  have  also  hydration  products  with  larger  surface 
areas  at  this  age.   At  the  degree  of  hydration  of  about  5  5 
to  60%  where  the  shrinkage  curves  showed  a  minimum,  curves 
for  surface  area  also  show  it,  for  the  most  part.   Maximum 
specific  surface  area  is  attained  when  85  to  90%  of  cement 
is  hydrated,  except  for  the  sample  with  calcium  chloride, 
and  the  surface  area  is  reduced  to  some  extent  on  further 
hydration.   In  the  shrinkage  curves,  the  rate  of  increase 
in  shrinkage  was  also  reduced  at  this  degree  of  hydration. 
The  cement  paste  with  calcium  chloride  showed  a  strong  in- 
crease in  shrinkage  at  this  stage  and  does  so  also  in  the 
surface  area  curve.   The  curves  for  sucrose  and  saccharide 
retarder  (S)  have  a  similar  trend  after  more  than  35%  of 
the  cement  is  hydrated.   At  earlier  ages,  however,  sucrose 
increases  surface  area  of  hydration  products  remarkably 
as  it  did  also  the  shrinkage  of  cement  paste  containing  it. 
The  only  exception  was  the  relatively  young  cement  pastes 
with  3-hydroxy-2-butanone;  they  had  hydration  products  of 
higher  surface  area,  but  shrank  less  than  the  others. 


93 


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Scanning  Electron  Microscopy  of  Cement  Pastes 
Unhydrated  cement  grains  seen  through  the  scanning 
electron  microscope  are  shown  in  Figure  31.   Cement  graim 
of  various  sizes  ranging  from  0.1  to  more  than  15  microns 
can  be  seen.   Their  surface  texture  looks  smooth  at  this 
magnification.   Figures  32  -  50  show  pictures  of  hydrated 
cement  pastes.   Samples  for  Figures  32  -  46  were  cast  on 
glass,  and  the  surface  that  faced  the  glass  was  observed 
after  its  removal  by  drying  shrinkage.   Concentrations  of 
additives  in  these  samples  are  those  that  yield  a  relative 
retardation  of  200%  in  mortars.   Figures  47  -  50  are  photos 
of  broken  surfaces  of  samples  that  had  been  used  for  shrink- 
age measurements.   Age  shown  is  elapsed  time  or  curing  time 
before  the  sample  was  started  to  be  dried  in  the  oven. 

At  an  elapsed  time  of  1  min,  addition  of  retarders 
resulted  in  remarkable  differences  in  the  morphology  of 
the  hydration  products.   This  can  be  seen  in  Figures  32  - 
36.   When  no  admixture  was  added,  hydration  products  were 
observed  on  the  surfaces  of  the  grains.   With  calcium 
lignosulf onate  added,  the  appearance  of  the  product  was 
changed;  some  particles  were  long  and  some  were  spherical. 
Their  frequency  seemed  to  be  lower  and  their  size  larger. 
When  citric  acid  was  added,  many  needle-like  crystals  were 
seen.   The  needles  were  mostly  observed  to  grow  in  a  way 
so  that  several  radiated  from  a  point  located  either 
between  large  cement  grains  or  sometimes  from  small  grains 


97 


Figure  31  -  Unhydrated  Cement  Grains  (X5000) 


t   i 1 


Figure  32  -  Cement  Paste  with  No  Admixture  (X3000) 
Age:   1  min 


98 


Figure  33  -  Cement  Paste  with  No  Admixture  (X9000) 
Age:   1  min 


Figure  34  -  Cement  Paste  with  Calcium  Lignosulfonate  (X5000) 
Age:   1  min 


99 


Figure  35  -  Cement  Paste  with  Citric  Acid  (X3000) 
Age:   1  min 


Figure  36  -  Cement  Paste  with  Sucrose  (X5000) 
Age :   1  min 


100 


of  cement.   EDAX  analysis  showed  that  these  needles  were 
composed  of  some  silica,  alumina,  and  sulfur  and  a  large 
amount  of  calcium.   It  should  be  noted  in  the  same  figure 
that  the  surfaces  of  most  of  the  cement  grains  remained 
relatively  unchanged.   In  the  sample  containing  sucrose 
irregularly  shaped  and  rounded  hydration  products  were  seen 
on  the  surfaces  of  cement  grains. 

Photos  of  cement  pastes  at  the  age  of  5  min  are  shown 
in  Figures  37  -  40.   More  hydration  had  occurred  in  all 
samples.   Most  of  the  cement  grains  were  covered  with  hydra- 
tion product  in  the  case  of  neat  cement  paste,  and  a  hexa- 
gonal plate,  which  is  probably  a  lime  crystal,  can  be  seen. 
The  cement  paste  with  calcium  lignosulf onate  still  retained 
some  rod-like  projections.   The  long  needles  observed  in 
the  1  minute  citric  acid  sample  tended  to  be  fewer  and 
seemed  to  be  precipitated  on  the  surfaces  of  the  cement 
grains. 

Figures  41  -  44  show  that  the  long  needles  observed  in 
citric  acid  samples  at  early  ages  disappeared  as  time 
elapsed.   In  the  10  minute  sample,  it  is  seen  that  most  of 
the  shortened  needles  were  gone  or  transformed  into  rounded 
products  on  the  cement  grains.   These  round  products  look 
like  those  observed  in  1  minute  samples  containing  calcium 
lignosulf onate  or  sucrose.   In  30  minute  and  1  hour  samples 
containing  citric  acid,  no  needle  was  seen,  and  the 


101 


Figure  37  -  Cement  Paste  with  No  Admixture  (X5000) 
Age:   5  min 


Figure  38  -  Cement  Paste  with  Calcium  Lignosulf onate  (X5000) 
Age :   5  min 


102 


Figure  39  -  Cement  Paste  with  Citric  Acid  (X3000) 
Age:   5  min 


iL.    i  & 


Figure  40  -  Cement  Paste  with  Sucrose  (X5000) 
Age:   5  min 


103 


Figure  41  -  Cement  Paste  with  Citric  Acid  (X3000) 
Age:   10  min 


Figure  42  -  Cement  Paste  with  Citric  Acid  (X8000) 
Age:   10  min 


104 


Figure  43  -  Cement  Paste  with  Citric  Acid  (X3000) 
Age:   30  min 


Figure  44  -  Cement  Paste  with  Citric  Acid  (X3000) 
Age:   1  hr 


105 


transformed  products  continued  to  spread  over  the  surface 
of  the  cement  grains. 

Figure  45  is  a  photo  of  a  cement  paste  with  no  ad- 
mixture after  1  hour.   Cement  grains  appear  to  be  covered 
by  many  grainy  hydration  products.   The  sucrose-containing 
sample  at  30  min  is  shown  in  Figure  46  and  is  similar  to 
the  1  hour  sample  containing  citric  acid. 

Figures  47  -  50  show  broken  surfaces  of  cement  pastes 
with  and  without  retarders  at  ages  of  about  half  a  day. 
The  degree  of  hydration  is  also  indicated.   No  noticeable 
difference  is  observed  among  the  figures. 

No  photo  is  shown  for  cement  pastes  older  than  these 
samples  in  this  thesis,  because  there  was  no  notable 
difference  observed  regardless  of  the  presence  of  retarders, 
Additionally,  at  ages  later  than  4  days,  strong  growth  of 
lime  crystals  obscured  the  observation. 


106 


Figure  45  -  Cement  Paste  with  No  Admixture  (X5000) 
Age:   1  hr 


Figure  46  -  Cement  Paste  with  Sucrose  (X3000) 
Age:   30  min 


107 


Figure  47  -  Cement  Paste  with  No  Admixture  (X2000) 
Age:   12.5  hr 
(degree  of  hydration:   24%) 


Figure  48  -  Cement  Paste  with  Glycolic  Acid  (X2000) 
Age:   15.5  hr 
(degree  of  hydration:   26%) 


108 


Figure  49  -  Cement  Paste  with  Retarder  A  (X2000) 
Age:   14  hr 
(degree  of  hydration:   18%) 


>~\.    *  i 


Figure  50  -  Cement  Paste  with  Retarder  S  (X2000) 
Age:   13  hr 
(degree  of  hydration:   2  0%) 


109 


CHAPTER  VI  -  DISCUSSION 

Molecular  Structure  of  Retarders 

One  of  the  purposes  of  this  study  was  to  gain  more 

understanding  of  the  aspects  of  molecular  structure  that 

make  a  substance  an  effective  retarder.   The  previous  work 

of  others  (27)  has  shown  that  organic  retarders  frequently 

contain  hydroxyl  groups  and  that  one  of  these  is  frequently 

in  the  a  position  (i.e.,  on  the  carbon  atom  adjacent)  to  a 

carbonyl  group  as,  for  example,  in  glycolic  acid, 

CH2(OH)C02H,  or 

CHo-C-0H 
i  ^  ii 

OK   O 

It  is  true  that  most  of  the  strong  retarders  used  in 
this  work  do  have  this  structure.   Those  with  relative 
retardations  of  more  than  200%  when  tested  at  0.1%  con- 
centration (by  weight  of  the  cement)  are: 

Tartronic  acid     HO-C-CH-CO_H 

OH 

Tartaric  acid     HO-C-CH-CH-CO-H 

*       l   l     * 
OH  OH 

Mucic  acid      HO-C-CH-CH-CH-CH-CO-H 
*   I   I    I   I     z 
OH  OH  OH  OH 

Gluconic  acid      CH--CH-CH-CH-CH-CO-H 
I  *    l   I   I   l     * 
OH   OH  OH  OH  OH 


110 


Citric  acid 


Pyrogallol 


CO^H 
H02C-CH2-C-CH2-C02H 
OH 


Gallic  acid 


2 ,4 ,6-Trihydroxybenzoic  acid 


C02H 


HO 


^^ 


OH 


Sr 


Sucrose      CCH,  .  Oc-0-C,,Hn  ,Oc 
6  11  5     6  11  5 


Pyruvic  acid     CHo-C-C0oH 
J  II    2 

0 
and  a-Ketoglutaric  acid     H02C-CH2-CH2-C-C02H 


Of  these,  all  are  acids  except  sucrose  and  pyrogallol 

In  connection  with  the  latter  compound  it  should  be  noted 

that  hydroquinone 

OH 


OH 


Ill 


almost  fell  into  the  class  of  compounds  listed  above,  with 

its  relative  retardation  of  198%,  and  is  also  not  an  acid. 

The  compounds  listed  above  contain  hydroxyl  groups,  usually 

many  of  them,  and  almost  always,  at  least  in  aliphatic 

compounds,  there  is  one  in  the  a  position  to  the  C  =   0 

of  the  carboxyl  group.   The  only  exceptions  to  these 

generalizations  are  the  last  two  compounds  in  the  list, 

pryuvic  acid  and  2-ketoglutaric  acid.   These  two  have  a 

carbonyl  group  in  the  a  position  to  the  carboxyl  group. 

This  carbonyl  group  perhaps  hydrates,  to  some  extent,  in 

solution  to  form  a  2,2-dihydroxyl  compound  stabilized  by 

the  strong  electron-withdrawing  tendency  of  the  adjacent 

carboxyl  group.   Another  example  of  this  condition  is 

glyoxylic  acid,  which  exists  as  the  hydrate,  even  in  the 

solid  state.   So  these  a-carbonyl  compounds  may  qualify 

with  respect  to  the  hydroxyl  group  criterion,  even  though 

it  is  not  apparent  from  the  conventional  formula. 

The  importance  of  the  hydroxyl  group  is  further 

emphasized  by  the  changes  that  occur  when  it  is  exchanged 

for  other  groups.   The  relative  retardation  (T500)  of 

glycolic  acid 

CH--CO„H 
OH 

is  127%,  a  moderately  strong  retarder  and  the  simplest 

example  of  an  a-hydroxy  acid.   But  if  the  hydroxyl  group 

is  exchanged  for  a  sulfhydryl  group,  forming  mercaptoacetic 


112 


acid 

CH,.-C0oH 
SH 

the  T500  drops  to  113%  and  for  glycine 

CHo-C0-H 
I  l         2 
NH2 

it  is  100%,  indicating  no  retarding  action  at  all. 

On  the  other  hand,  the  presence  of  the  hydroxyl  group 

in  the  a   position  to  the  carboxyl  group  is  not,  in  itself, 

sufficient  for  a  compound  to  be  a  retarder.   This  conclusion 

is  drawn  from  the  insignificant  retarding  abilities  of 

lactic  acid 

CH-.-CH  -CO_H 
OH 

a-hydroxybutyric  acid     CH3-CH2-CH-C02H 

OH 


and  mandelic  acid, 


-CH-C02H 


all  of  which  are  a-hydroxycarboxylic  acids. 

If  the  reason  for  the  frequent  efficacy  of  an 
a-hydroxy  acid  as  a  retarder  is  the  activation  of  the 
hydroxyl  group  in  the  3,4  position  with  respect  to  the 
double  bond,  then  other  compounds  with  a  similar  structure 
should  behave  similarly.   Allyl  alcohol 

CH0=CH-CH0 

Z  I  2. 

OH 


113 


has  no  retarding  ability;  neither  does  2-butene-l, 4-diol, 

CH~-CH=CH-CH0 
OH         OH 

but  both  have  hydroxyls  activated  by  the  double  bond.   On 

the  other  hand,  a  carbonyl  group  does  seem  to  have  some 

effect,  even  if  it  is  not  part  of  a  carboxyl  group,  as  in 

3-hydroxy-2-butanone 

CH,-C-CH-CH0 
3  ii  I     3 

0  OH 

which  has  a  T500  of  only  107%  at  a  concentration  of  0.1% 

but  173%  at  a  concentration  of  0.5%.   Another  example  is 

1, 3-dihydroxy-2-propanone 

CH--C-CH- 
I  2  II  l  2 

OH   0  OH 

which  has  a  value  of  125%  at  0.1%,  but  seems  to  act 

atypically,  with  a  value  of  97%,  i.e.  slight  acceleration, 

at  0.5%  concentration.   The  curve  is,  however,  unusual. 

See  Figure  13.   These  last  two  examples  cannot  be  said  to 

be  strong  retarders,  although  there  is  some  action. 

The  presence  of  many  hydroxyls  is  not,  of  itself, 

sufficient  to  confer  retarding  abilities  on  a  molecule,  as 

is  shown  by  the  result  that  glycerine 

CH--CH-CH0 
I  2  I  I  2 
OH   OH  OH 

and  pentaerythritol 


114 


OH 

l 
CH0 

I  * 

H0-CHo-C-CHo-0H 

Z     |     z 

CH0 
i  * 
OH 

do  not  retard.   Sometimes,  however,  strong  retarders  have 

only  hydroxyls  as  functional  groups,  as  has  already  been 

shown  by  the  examples  of  hydroquinone  and  pyrogallol. 

It  is  possible  to  have  good  retardation  without  the 

presence  of  the  alcoholic  hydroxyl  group,  as  with  1,2,3- 

propanetricarboxylic  acid 

CH-  —  CH  —  CH- 
I  ^  I  I  * 
C02H    C02H   C02H 

which  had  a  T500  of  139,  a  value  higher  than  that  of 

glycolic  acid.   At  the  same  time,  it  should  be  recognized 

that  if  the  hydroxyl  is  not  absolutely  necessary,  it  is 

usually  helpful  in  promoting  retarding  ability  of  a 

molecule;  if  the  tertiary  hydrogen  in  the  above  compound 

is  replaced  by  a  hydroxyl  group,  giving  citric  acid,  the 

retarding  ability  is  greatly  promoted. 

Other  good  examples  of  this  effect  involve  the 

dicarboxylic  acids.   The  acids  malonic,  succinic,  glutaric, 

and  adipic  have  only  slight  retarding  ability  at  0.1% 

concentration,  although  if  five  times  as  much  is  used, 

malonic  and  succinic  acids  have  a  respectable  action.   But 

the  addition  of  hydroxyls  greatly  increases  the  retarding 

ability.   At  a  concentration  of  0.1%  succinic  acid 


115 


H02C-CH2-CH2-C02H 

has  a  T500  of  only  110%.   The  addition  of  only  one  hydroxyl 

to  make  malic  acid 

H02C-CH2-CH-C02H 
OH 

causes  a  great  increase  in  a  T500  of  198%.   A  second 

hydroxyl  gives  tartatic  acid 

H0-C-CH-CH-C0oH 
2.        |    |      2 

OH  OH 

which  has  a  T500  of  254%  and  is  a  powerful  retarder. 

Glutaric  acid 

H02C-CH2-CH2-CH2-C02H 

has  a  T500  of  also  only  110%,  but  2-ketoglutaric  acid 

H0oC-CH--CHo-C-C0„H 
0 

which  may,  as  previously  mentioned,  exist  as 

OH 
I 
H02C-CH2-CH2-C-C02H 

OH 

in  solution,  has  a  T500  of  292%,  one  of  the  highest  values 

measured.   A  similar  effect  is  observable  with  pyruvic  acid 

CH-,-C-C0oH 
.3  ||    2. 


or 


OH 
I 
CH„-C-C0oH 
3  |    2 


OH 


116 


which  is  a  strong  retarder  with  a  T500  of  207%,  whereas 

the  mono-hydroxy  counterpart,  lactic  acid 

CHo-CH-C0_H 
j  l     Z 

OH 

has  no  retarding  ability  at  all  at  0.1%  concentration  and 

not  much  at  0.5%  (T500  =  118%). 

Sometimes,  however,  more  hydroxyls  seem  to  be  too 

much  of  a  good  thing.   For  example,  dihydroxytartaric  acid 

OH  OH 

I    I 

H0~C  -  C  -  C  -  C0oH 

OH   OH 

is  not  as  good  a  retarder  (T500  =  166%)  as  tartartic  acid 
(T500  =  254%) ,  although  it  is  still  a  strongly  active  sub- 
stance.  The  same  effect  is  observed  with  the  hydroxy 
devivatives  of  malonic  acid, 

H02C-CH2-C02H 
which  has  a  T500  of  only  102%.   Addition  of  one  hydroxyl 
group  gives  tartronic  acid 

H02C-CH"C02H 
OH 

which  is  a  powerful  retarder  with  a  T500  of  278%.   A 

second  hydroxyl  gives  the  hydrate  of  ketomalonic  acid 

OH 
I 

H0oC-C-C0oH   +   Ho0  >    H0_C-C-C0oH 

Z       ||     Z  Z  Z  Z 

0  OH 

which  is  still  a  strong  retarder,  with  a  T500  of  154%,  but 
is  not  nearly  so  strong  as  tartronic  acid. 


117 


From  the  above  it  is  apparent  that  the  hydroxyl  group 
is  frequently  found  in  retarder  molecules  and  is  frequently 
a  to  a  carbonyl,  but  that  this  structure  alone,  or  the 
plain  hydroxyl  alone,  is  not  sufficient  in  itself  to  confer 
a  high  retardation  ability  on  a  molecule. 

Influences  of  molecular  structure  are  observable  also 

with  respect  to  the  different  retarding  abilities  of 

position  isomers.   Salicylic  acid,  which  has  been  recognized 

as  a  set  retarder  for  some  time,  has  a  T500  of  122%.   It 

is  o-hydroxybenzoic  acid. 

C02H 


0 


But  the  meta  and  para  isomers 


and 


OH  "OH 

had  practically  no  retarding  ability.   Of  the  three 
dihydroxybenzenes,  resorcinol,  the  meta  isomer, 

OH 


is  not  a  retarder,  but  the  ortho  isomer,  catechol 

OH 

OH 


118 


is  a  fairly  good  retarder,  with  a  T500  of  127%,  and  the 
para  isomer,  hydroquinone , 


Nr 


is  better  yet,  with  a  T500  of  198%.   It  is,  of  course, 

usual  for  ortho  and  para  isomers  to  be  alike  in  chemical 

properties  and  different  from  the  meta  compound.   Another 

example  is  the  trihydroxybenzenes.   Phloroglucinol, 

1,3 ,5-trihydroxybenzene, 

OH 


HO 


k^H 


has  a  T500  of  131%,  a  fairly  good  retarder,  but  pyrogallol, 

1,2 ,3-trihydroxybenzene  , 

OH 
/%,  OH 


^^ 


OH 


is  much  stronger,  with  a  T500  of  239%. 

From  this  discussion  certain  generalities  can  be 
inferred  empirically  with  respect  to  the  molecular 
structures  that  characterize  retarders.   They  are  frequently 
carboxylic  acids,  but  need  not  be  necessarily.   They 
frequently  contain  many  hydroxyl  groups,  but  need  not 
necessarily.   The  hydroxyl  is  frequently  in  the  a  position 


119 


to  the  carboxyl.   And  some  compounds  containing  most  of 
these  features  are  not  especially  good  retarders. 

All  the  really  strong  retarders  used  here  are  highly 
oxygenated  substances.   The  oxygen  atoms  can  be  in  hydroxy 1, 
carboxyl,  or  carbonyl  groups;  all  seem  to  be  effective, 
although  some  are,  no  doubt,  more  so  than  others.   The 
oxygen  atoms  are  also  usually  fairly  well  spread  out  across 
the  molecule.   That  is,  significant  portions  of  the  molecule 
devoid  of  oxygens  seem  to  lessen  the  retarding  ability  as, 
for  example,  with  the  dicarboxylic  acids,  lactic  acid,  and 
a-hydroxybutyric  acid.   The  strong  retarders,  furthermore, 
usually  contain  several  oxygen  atoms  that  can,  by  virtue  of 
their  location  on  the  chain  and  rotations  about  single 
bonds,  approach  each  other  closely  and  form  a  "cluster"  of 
oxygen  atoms.   In  this  connection,  it  should  be  remembered 
that  chain  structures  are  kinked  at  tetrahedral  angles,  so 
the  usual  formula  as  written  is  not  a  particularly  clear 
indication  of  the  real  spatial  relationships  in  the 
molecule. 

The  foregoing  notions,  of  course,  merely  repeat  to 
some  degree  the  older  postulates  of  Hansen  (24)  ,  Steinour 
(25),  and  especially  Taplin  (27). 

Deserving  perhaps  of  special  comment  is  the  seemingly 
great  strength  of  the  a-carbonyl  group.   All  substances 
tested  that  have  carbonyls  adjacent  to  carboxyl  groups  - 


120 


pyruvic  acid,  ketoraalonic  acid,  and  2-ketoglutanic  acid, 

were  strong  retarders. 

One  can  go  a  little  further  and  say  "Why  oxygen?" 

Why  will  not  other  groups  function  just  as  well?  But  it 

seems  that  the  oxygen  atom  is  one  form  or  another  is  almost 

uniquely  required  for  the  retarding  action.   For  example, 

glycolic  acid 

CHo-C0oH 
OH 

is  a  fairly  good  retarder,  but  mercaptoacetic  acid,  glycine, 

and  monochloroacetic  acid  in  which  the  hydroxyl  has  been 

exchanged  for  -SH,  -NH2 ,  and  -CI,  respectively,  are  all 

poor  or  completely  ineffective  as  retarders. 

The  properties  of  the  oxygen  atom  that  seem  most  likely 
to  be  of  consequence  are  its  high  electronegativity,  its 
consequent  ability  to  participate  in  strong  hydrogen  bond- 
ing with  other  electronegative  atoms,  its  small  size,  and 
its  presence  in  the  molecules  of  both  the  liquid  phase  of 
concrete  and  the  surfaces  of  the  anhydrous  cement  minerals 
and  of  their  hydration  products. 

It  may  be  that  one  important  function  of  the  highly 
electronegative  oxygens  is  to  bring  about  electron  shifts 
in  the  retarder  molecules  and  induce  charge  polarizations 
that  could  determine  the  adsorption  characteristics  of 
the  molecules  on  the  charged  solids  present. 


121 


For  example,  consider  the  differences  between  glycolic 

acid, 

CH~-C0oH 
OH 


lactic  acid, 


and  pyruvic  acid, 


CH0-CH~C09H 
OH 


CHo-C-C0oH 
J  ii    I 


0 

It  should  first  be  emphasized  that  in  the  relatively 
highly  basic  medium  of  cement  paste  or  concrete  (about 
pH=12.5)  the  carboxyl  hydrogen  atoms  of  all  these  weak 
acids  will  be  dissociated,  leaving  the  anion  as  the  species 
really  present  in  the  aqueous  phase. 

In  glycolic  acid  it  can  be  postulated  that  small  local 
positive  charges  are  generated  on  the  carbons  or  the 
hydrogens  by  the  polarizing  power  of  the  various  oxygens. 
Lactic  acid  is  an  extremely  weak  retarder,  regardless  of 
the  fact  that  it  has  only  a  methyl  group  attached  to  the 
second  carbon  in  place  of  the  one  hydrogen  atom  of  glycolic 
acid.   On  the  contrary,  pyruvic  acid  which  has  one  oxygen 
attached  to  the  second  carbon  by  a  double  bond,  instead  of 
the  hydroxyl  group  of  lactic  acid,  retarded  the  hydration 
of  cement  strongly.   As  has  already  been  noted,  the  pyruvic 
acid  may  hydrate  in  aqueous  solution  to  give  the  dihydroxy 
compound  with  both  groups  on  the  alpha  carbon  atom. 


122 


In  pyruvic  acid  the  double  bonded  oxygen  or  the 
oxygens  in  the  hydroxyl  groups,  as  the  case  may  be,  may 
pull  the  electrons  around  the  third  carbon  toward  the  second 
carbon  and  polarize  the  hydrogen  atoms  on  the  third  carbon 
atom.   This  trend  may  be  further  promoted  by  the  oxygens 
in  the  acid  group.   This  kind  of  polarizing  effect  on  the 
hydrogens  in  the  methyl  group  would  be  expected  little 
for  the  lactic  acid  molecule,  although  the  hydrogen  of  the 
second  carbon  could  be  subjected  to  the  effect,  mainly  by 
the  double  bonded  oxygen  in  the  acid  group  and  partially 
by  the  oxygen  in  the  hydroxyl  group. 

When  one  hydrogen  of  the  third  carbon  of  lactic  acid 
is  replaced  by  another  methyl  group,  the  result  is  a- 
hydroxybutyric  acid,  which  was  not  a  retarder.   However, 
if  the  end  methyl  group  of  lactic  acid  or  a-hydroxybutylic 
acid  is  replaced  by  an  acid  group,  the  strong  retarders 
tartronic  acid  and  malic  aaid,  respectively  are  made. 
Possibly  all  the  hydrogens  of  the  latter  two  chemicals 
could  have  the  aforementioned  polarizing  effect.   Hence, 
it  appears  that  perhaps  the  movement  of  electrons  should 
be  considered  in  seeking  the  effective  molecular  structure 
of  retarders. 

The  question  of  the  relative  locations  of  hydrogen 
atoms  and  atoms  of  high  electronegativity  (usually  oxygen) 
arises  next.   The  dicarboxylic  acid  compounds  -  malonic, 
succinic,  glutaric  and  adipic  acids  -  have  an  acid  group 


123 


at  each  end  of  the  molecule,  but  no  hydroxy 1  groups.   The 
former  two  are  weak  retarders  when  added  at  relatively  high 
concentrations,  while  the  latter  two  are  not  retarders  at 
all.   If  the  differences  in  retardation  powers  of  these 
chemicals  are  caused  by  the  polarizing  effects  of  the 
carboxyl  groups  on  nearby  hydrogens,  the  result  would 
indicate  that  at  most  only  two  hydrogens  attached  to  the 
second  carbons  could  have  the  influence  to  some  extent. 
Following  this  logic,  it  can  be  concluded  that  the 
greater  retarding  abilities  of  the  compounds  in  which 
hydroxyl  or  carbonyl  groups  lie  along  the  chain  between 
the  acid  groups  (tartronic,  ketomalonic,  malic,  tartaric, 
dihydroxytartaric,  2-ketoglutaric,  and  mucic  acids)  are 
due,  at  least  partly,  to  the  increased  polarization  effects 
of  these  groups  on  the  other  atoms  in  the  chain,  effects 
which  are  lacking  in  the  simple  acids. 

For  the  oxygen  in  the  hydroxyl  group,  the  extent  of 
this  effect  is  found  by  comparing  the  above  result  and  the 
molecular  structures  of  the  chemicals  already  referred  to. 
Lactic  acid  was  an  extremely  weak  retarder.   3-Hydroxy- 
propionic  acid  and  a-hydroxybutyric  acid  were  not  retarders. 
Hence,  the  hydroxyl  oxygen  atom  could  have  this  effect  on 
only  the  one  hydrogen  atom  attached  to  the  same  carbon. 
The  hydrogen  atom  in  the  hydroxyl  group  would  be,  of 
course,  also  polarized. 


124 


If  these  ideas  are  applied  to  the  glycine  molecule, 
the  reason  why  it  is  not  a  retarder  may  be  also  explained. 
The  nitrogen  of  glycine  has  two  hydrogens  bonded  to  it, 
but  it  has  lower  electronegativity  than  oxygen.   Therefore, 
the  nitrogen  may  not  have  enough  ability  to  polarize  even 
one  hydrogen  bonded  to  the  second  carbon  atom.   Additionally, 
the  polarizing  effect  per  hydrogen  which  is  bonded  directly 
to  the  nitrogen  would  be  less  than  half  of  that  of  the 
hydrogen  in  hydroxyl  group,  and  the  resulted  polarization 
might  not  be  strong  enough  to  permit  the  substance  to  act 
as  a  retarder.   The  small  retarding  ability  of  mercapto- 
acetic  acid,  compared  with  glycolic  acid,  can  be  also 
explained  by  the  considerably  lower  electronegativity, 
therefore  the  polarizing  effect,  of  sulfur  than  oxygen. 
The  discussion  so  far  given  is  confined  to  several 
chemicals.   The  idea  can  be  generalized;  that  is,  the 
molecular  configuration  of  effective  retarders  is  that 
atoms  in  the  molecule  are  arranged  in  such  a  way  to 
polarize  as  many  hydrogen  atoms  as  strongly  as  possible. 
Oxygen  atoms  are  mainly  responsible  for  the  polarizing 
process  because  of  their  high  electronegativity  and  low 
valence.   However,  it  should  be  noticed  that  the  effective 
configuration  does  not  necessarily  require  carboxylic  acid 
groups.   If  the  idea  is  correct,  it  should  be  able  to  be 
generalized,  at  least  somewhat.   The  modest  retarding 
abilities  of  1, 3-dihydroxy-2-propanone 


125 


I  2  II  I  ' 
OH   O  OH 

and  3-hydroxy-2-butanone 

CH^-CH-C-CH- 
J  I   II    3 
OH  0 

are  examples  of  such  generalization. 

The  rationality  of  these  ideas  is  further  supported 
by  the  fact  that  the  electrogenativities  of  hydrogen, 
carbon,  sulfur,  nitrogen,  and  oxygen  are  2.1,  2.5,  2.5, 
3.0,  and  3.5,  respectively.   The  larger  the  difference  in 
electronegativity  between  two  atoms,  the  more  ionic  is  the 
bond.   Therefore,  stronger  polarizing  effect  would  be 
expected  for  O-H  combination  than  for  N-H  or  S-H 
combination. 

These  ideas  are,  furthermore,  subject  to  semiquanti- 
tative verification.   For  example,  2 , 4-pentanedione 

CH-.-C-CH^-C-CH-, 
J  II    l    ,|    J 

0      0 

and  ethyl  acetoacetate 

CH,-C-CH0-C-0-C0Hc 
3  ||    2  ||     2  5 

0      0 
are  both  mild  retarders,  as  would  be  expected  from  the 
strong  polarizations  of  only  the  methylene  hydrogens. 
Generally,  little  retardation  is  expected  unless  more  than 
two-thirds  of  the  hydrogens  in  a  molecule  are  polarized 
evenly  throughout  the  molecule  and  the  polarizing  effect 
is  strong  enough. 


126 


However,  it  should  be  noticed  that  the  relative 
effectiveness  of  some  compounds,  e.g.  tartaric,  dihydroxy- 
maleic,  and  dihydroxytartaric  acids,  can  not  be  explained 
by  these  ideas.   Also,  ketomalonic  acid  should  have  been 
a  stronger  retarder  than  tartronic  acid,  because  the  middle 
double  bonded  oxygen  of  ketomalonic  acid  will  be  opened 
in  water  and  will  form  two  hydroxyl  groups.   These  apparent 
contradictions  were  probably  caused  by  the  many  other 
physical  and  chemical  influences  of  chemicals  in  cement 
paste. 

What  has  been  said  previously  has  dealt  with  the 
aliphatic  compounds  tested.   The  aromatic  compounds  also 
show  many  of  the  same  features,  as  well  as  interesting 
effects  of  structural  isomerism  mentioned  earlier.   The 
strong  aromatic  retarders  are  all  highly  oxygenated  and  the 
strongest  retarders,  gallic  acid 


pyrogallol 


and  2,4 ,6-trihydroxybenzoic  acid 


127 


OH 
all  have  groups  of  oxygen  atoms  that  approach  each  other 

closely.   In  this  connection,  it  should  be  recalled  that 

most  of  the  hydrogen  atoms  of  strong  aliphatic  retarders 

are  polarized  strongly  by  many  oxygen  atoms  and  that  these 

oxygen  atoms  are  usually  located  in  such  a  way  that  they 

also  approach  each  other  closely. 

Benzoic  acid  is  not  a  retarder,  nor  is  its  meta  or 
para  hydroxy  acid,  but  salicylic  acid  is  a  moderate  re- 
tarder.  Since  the  hydroxy  group  of  salicylic  acid  is 
located  on  the  second  carbon  from  the  acid  group,  it  might 
seem  that  it  would  be  analogous  to  the  non-retarding 
3-hydroxypropionic  acid.   But  the  latter  is  a  much  more 
flexible  molecule  with  configurations  in  which  the  hydroxyl 
and  carboxyl  are  relatively  removed  from  each  other, 
whereas  in  salicylic  acid  the  two  groups  are  constrained 
to  proximity  and  also  tied  together  by  their  intramolecular 
hydrogen  bond. 

The  trihydroxybenzenes  are  good  retarders,  but  pyro- 
gallol,  in  which  the  hydroxyls  are  in  adjacent  positions 
on  the  ring,  is  a  much  stronger  retarder  than  is  phloro- 
glucinol,  in  which  they  are  separated.   Converting  either 
to  its  acid  improves  the  retardation  ability  still  further. 


128 


Gallic  acid  (3 , 4 , 5-trihydroxybenzoic  acid)  is  an  even 
stronger  retarder  than  is  2 , 4 , 6-trihydroxybenzoic  acid. 

The  three  dihydroxybenzenes  present  an  apparent 
exception  to  the  generalization  involving  contiguous 
hydroxyls  or  oxygen  atoms.   The  ortho  isomer,  catechol,  is 
a  fair  retarder,  while  the  meta  isomer,  rescoicinol,  is 
not  active  at  all.   But  the  para  isomer,  hydroquinone,  in 
which  the  hydroxyls  are  separated  to  their  greatest  extent, 
is  the  best  of  all,  with  a  T500  of  198%. 

The  findings  of  this  study  agree  generally  with  those 
of  Steinour  (25,  26)  with  respect  to  the  importance  of 
hydroxyl  groups  and  of  Taplin  (27)  with  respect  to  the 
importance  of  the  hydroxyl  adjacent  to  a  carbonyl  group. 
But,  as  mentioned  earlier,  glycerin  and  pentaerythritol 
are  not  retarders  in  spite  of  many  hydroxyl  groups. 
Propanetricarboxylic  acid  is  a  good  retarder  with  no 
alcoholic  hydroxy  groups;  citric  acid  is  very  strong  with 
only  one.   Lactic  and  mandelic  acids  fulfill  Taplirfs 
criteria,  yet  they  are  not  good  retarders,  and  so  on. 
There  are  so  many  exceptions  that  it  is  clear  the  older 
generalizations  must  leave  out  important  aspects  of  the 
problem. 

Effect  of  Retarders  on  the  Hydration  of  Cement 
In  an  effort  to  explain  some  of  the  ways  in  which 
retarders  influence  the  hydration  of  portland  cement, 


129 


some  facts  concerning  the  process  need  to  be  reviewed 
briefly. 

The  principal  active  components  of  portland  cement  at 
early  stages  of  hydration  are  CUS  and  C^A.   Through  the 
hydration  of  C^S,  calcium  silicate  hydrate  is  formed  and 
lime  is  released  into  solution  in  the  form  of  Ca++  and  OH  . 
C,A,  on  the  other  hand,  reacts  with  sulfate  and  calcium 
ions  from  the  solution  to  form  ettringite,  C,A-  3CS  'H-.- . 
In  a  heat  evolution  curve  of  cement  hydration,  the 
initial  rapid  hydration  is  followed  by  a  dormant  period, 
perhaps  a  couple  of  hours  long,  and  the  second  heat 
generation,  which  is  mainly  due  to  additional  hydration  of 
C,S,  occurs  at  the  end  of  the  dormant  period  (37,  50). 
According  to  Verbeck  (50) ,  the  initial  setting  time  of 
cement  paste  lies  somewhere  between  the  end  of  the  dormant 
period  and  the  time  when  the  maximum  peak  of  the  second 
heat  generation  is  reached.   Previte  (2  9)  obtained  the  same 
result. 

Powers  (5)  has  discussed  the  details  of  the  processes 
he  considered  to  be  taking  place  up  to  the  decline  of  the 
heat  evolution  rate  after  the  second  peak.   This  is  the 
period  in  which  we  are  interested  from  the  standpoint  of 
the  setting  process  and  the  influence  of  retarders  thereon. 

The  dormant  period  is  thought  to  be  due  to  a  great 
diminution  of  the  hydration  reaction  brought  about  by  a 
coating  of  hydration  products  that  limits  the  access  of 


130 


water  to  the  underlying  anhydrous  grains.   For  the  C~A  the 
coating  is  presumably  ettringite.   For  the  C~S,  with 
which  we  are  more  concerned  here,  the  coating  is  an 
initially-formed  C-S-H  gel.   Powers  (5)  considered  the 
reality  of  these  ideas  to  be  substantiated  by  various 
electron  microscope  studies  of  the  appearance  of  the  paste 
soon  after  mixing  (52). 

Powers  considered  the  end  of  the  dormant  period  and 
the  beginning  of  the  second  heat  evolution  peak  to  be 
caused  by  a  breakup  of  the  coatings  of  hydration  products 
that  would  allow  an  increase  in  the  rate  of  hydration  to 
take  place.   Indeed,  if  the  dormant  period  is  caused  by 
such  a  coating,  its  removal,  at  least  partially,  is 
logically  necessary  for  an  increase  in  the  hydration.   The 
reason  given  for  the  breakup  of  the  coating  is  the  genera- 
tion of  an  osmatic  pressure  by  the  concentration  difference 
between  the  solutions  outside  the  coating  in  the  bulk 
aqueous  phase  and  inside  the  coating  adjacent  to  the 
anhydrous  cement  minerals. 

In  his  recent  review,  Young  (32)  has  classified  the 
various  possible  modes  of  action  of  retarders  into  four 
categories.   These  are  (i)  adsorption,  (ii)  complexation, 
(iii)  precipitation,  and  (iv)  nucleation.   The  applicability 
of  the  results  of  the  present  study  to  these  ideas  will  be 
discussed  in  reverse  order. 


131 


One  possible  action  is  an  influence  on  the  nucleation 
of  crystalline  calcium  hydroxide,  changing  the  time  at 
which  macroscopic  lime  crystals  are  observed,  which  is 
about  the  same  time  as  initial  set.   If  this  inhibition  of 
crystallization  and  consequent  supersaturation  of  lime  in 
solution  can  inhibit  further  reaction  of  cement  with  water, 
then  it  may  be  important  to  the  setting  process.   Young 
(32)  considers  this  as  perhaps  the  most  important  mode  of 
action  of  retarders.   It  is  well-known  that  small  amounts 
of  some  dyes,  surfactants,  and  other  solutes  can  profoundly 
influence  the  habit  and  growth  rate  of  crystalline  phases 
(53) .   The  most  recent  study  of  this  effect  in  the  phases 
of  interest  here  is  that  of  Berger  and  McGregor  (54)  who 
found  that  some  of  the  substances  studied  here  altered  the 
crystal  size  and  habit  of  the  CH  formed  during  C-.S  hydra- 
tion.  They  used,  however,  concentrations  ten  times  those 
usually  used  in  this  study. 

The  only  results  developed  here  that  apply  directly 
to  this  aspect  are  those  in  which  the  four  dyes  were 
tested.   These  dyes  were  selected  from  the  list  of  Buckley 
(53,  p.  558)  as  being  substances  that  strongly  modify  the 
habit  of  some  growing  crystals.   They  show  some  influence 
on  the  habit  of  CH  grown  slowly  by  interdif fusion  of  the 
ions  (55) .   The  change  in  the  habit  would  have  been  caused 
by  the  effect  that  Young  called  "adsorption  of  organic 
compounds  on  the  calcium  hydroxide  nuclei".   But  they  show 


132 


negligible  action  as  retarders.   This  is,  of  course,  no 
proof  that  the  substances  that  were  strong  retarders  did 
not  act  in  this  way. 

The  precipitation  idea  is  that  retardation  is  brought 
about  by  some  precipitation  of,  for  example,  the  calcium 
salt  of  the  retarder  substance  on  the  surface  of  the 
anhydrous  grains.   Young  places  no  great  importance  on 
this  idea.   The  applicability  of  this  idea  to  the  data  of 
this  study  is  referred  to  next  in  the  discussion  of 
complexation . 

The  complexation  theory  envisages  the  combination  of 
the  agent  as  some  sort  of  complex,  most  likely  with  calcium 
or  aluminum.  It  is  true  that  many  of  the  substances  tested 
form  complexes  of  greater  or  less  stability  with  calcium 
or  other  metal  ions.   Furthermore,  two  of  the  substances 
that  complex  calcium  strongly,  ethylene  diamine  tetracetic 
acid  (EDTA)  and  nitrilotriacetic  acid  (NTA)  are  fairly  good 
retarders,  although  the  larger  dosage  of  EDTA  did  not 
result  in  as  great  an  increase  in  retardation  as  was  the 
case  for  the  better  retarders  (Figure  15) .   Young  (32) 
pointed  out,  there  is  no  correlation  between  the  stability 
constants  of  the  calcium  complexes  of  these  substances  and 
their  potency  as  a  retarder. 

Any  effect  may  even  be  in  the  opposite  direction. 
The  review  of  literature  in  Chapter  II  showed  the  retarders 
(lignosulfonate,  sucrose,  salicylic  acid)  generally 


133 


accelerated  the  very  initial  hydration  of  cement,  but 
retarded  subsequent  hydration  and  transformations  of  some 
hydration  products.   The  reason  for  the  initial  accelera- 
tion of  cement  hydration  due  to  the  addition  of  retarders 
has  to  be  sought  in  some  changes  in  ion  concentration  in 
the  aqueous  phase  of  cement  paste.   A  few  minutes  after 
mixing  cement  with  water,  ions  in  the  solution  of  cement 
paste  would  be  saturated  or  supersaturated  with  respect  to 
possibly  each  ion  concentration.   Any  consumption  of  these 
ions  would  accelerate  the  hydration  of  the  phases  that  can 
supply  the  ions  into  the  solution.   The  consumption  could 
be  attained  by  any  process  such  as  precipitation  or 
crystallization  of  hydration  products,  or  complex  forma- 
tion of  the  ions  with  some  chemicals. 

It  should  be  recalled  that  molecules  of  strong  re- 
tarders contain  many  highly  electronegative  groups  such  as 
hydroxyl,  acid,  and  carbonyl.   These  groups  could  complex 
metal  ions  in  the  aqueous  phase  of  cement  paste  (13,  56) . 
Whatever  the  states  of  the  complexes,  this  complex  forma- 
tion would  accelerate  the  hydration  of  cement  paste, 
especially  in  the  very  early  stages  of  the  hydration, 
because  more  free  organic  molecules  are  available  for 
complexing. 

As  a  rough  indication  of  the  complexing  ability  of 
these  materials  under  the  conditions  present  in  a  cement- 
itious  system,  the  following  test  was  performed.   A 


134 


0.124M  NaOH  solution,  which  has  an  alkalinity  equivalent 
to  the  aqueous  phase  of  the  usual  cement  paste,  was  prepared. 
In  100  ml  of  the  solution,  0.2g  of  the  retarder  chemical  was 
dissolved  in  a  beaker.   This  gave  a  concentration  in  the 
solution  equal  to  that  in  a  0.5  w/c  paste.   The  solution 
was  continuously  stirred  by  a  magnetic  stirrer  and  was 
titrated  with  a  0.5M  CaCl2  solution  until  the  first 
precipitate  was  detected.   The  result,  volume  of  CaCl- 
solution  necessary  to  give  a  precipitate,  was  plotted  in 
Figure  51  against  the  relative  initial  setting  time  of  the 
corresponding  mortar  specimen  (w/c=0.50)  in  which  the 
retarder  has  been  added  at  a  concentration  of  0.1%  of  the 
cement. 

In  the  blank  test,  the  first  precipitate  of  Ca(OH)_ 
was  observed  when  the  calcium  chloride  solution  consumed 
was  0.9,  1.1,  0.9,  1.0,  0.8,  1.0,  and  0 . 9  ml  for  several 
tests,  the  average  being  0.94  ml.   The  chemicals  that 
required  more  CaCl2  solution  for  the  titration  that  this 
blank  amount  must  have  complexed  some  calcium  ions  in  the 
solution.   The  chemicals  which  show  stronger  complexing 
ability  such  as  sucrose,  gluconic  acid,  citric  acid,  and 
catchol  would  presumably  induce  more  acceleration  during 
the  initial  hydration  of  the  cement,  as  mentioned  earlier. 

When  some  other  chemicals  were  added,  on  the  other 
hand,  precipitates  were  observed  earlier  than  in  the  case 
of  the  blank  solution.   These  precipitates,  presumably, 


135 


+-> 

■H 


Cn 

c 

■H 

X 

<u 

H 

a, 
E 
o 
u 

> 

4J 


•H 

< 

C 

H 
"J 

yt 

rrj 

-p 
Pi 


m  q-  ro  c\j  — 

(|tu)   uoudjjij.  JOi    papaaN    uojjnios  2iddo 


136 


are  not  lime,  but  are  insoluble  calcium  salts  or  complexes 
of  these  chemicals.   Calcium  lignosulfonate  would  fall  in 
this  category  (19) . 

In  any  event,  Figure  51  shows  that  many  substances  of 
strong  "complexing"  ability,  as  evidenced  by  the  consumption 
of  a  relatively  large  amount  of  the  CaCl-  solution,  are 
also  strong  retarders.   But  there  are  also  many  exceptions 
and  the  results  are  only  qualitative.   Also,  as  implied 
earlier  in  this  section,  any  such  agreement  may  be  acci- 
dental if  the  main  effect  of  complexation  is  to  accelerate 
the  very  early  reactions. 

The  discussion  so  far  has  emphasized  the  importance 
of  the  C-jS  and  has  made  little  mention  of  the  aluminates. 
In  a  cement  that  is  normally-retarded  with  gypsum,  the 
formation  of  ettringite  acts  to  retard  the  otherwise  too- 
rapid  reaction  of  the  C~A.   The  aluminates,  and  especially 
the  hydrated  aluminates,  have  been  shown  to  react  with 
certain  retarders  to  form  adsorbed  phases  and/or  complexes 
(7,  9,  14,  15).   Such  reactions  may  change  the  rate  of 
consumption  of  various  species,  e.g.  sulfate,  and  are 
important  and  complicated  in  their  own  right.   But  for 
the  purposes  here,  it  is  considered  that  the  main  influence 
of  the  aluminates  is  to  tie  up  more  or  less  of  the  ad- 
mixture in  one  way  or  another  and  so  make  less  of  it 
available  to  do  whatever  it  does  in  connection  with  the 
silicate  hydration  process.   The  extent  to  which  this 


137 


occurs  with  most  of  the  retarders  used  in  this  study  has 
not  been  investigated.   It  is,  however,  known  that  re- 
tarders would  be  more  effective  when  used  with  cement  of 
low  C3A  (16,  17) . 

After  and/or  during  the  initial  acceleration  of  cement 
hydration,  retarders  have  to  act  in  some  way  to  retard 
subsequent  cement  hydration.   Change  in  ion  concentration 
in  the  aqueous  phase  of  cement  paste  would  probably  not  be 
concerned  with  the  retardation  mechanism  any  more.   Hence, 
the  mechanism  has  to  be  sought  in  direct  interaction  between 
remaining  anhydrous  cement  grains  or  hydration  products  of 
cement  and  retarder  molecules  or  complexes  thereof. 
Additionally,  the  interaction  must  proceed  in  such  a  way 
that  the  effective  molecular  structures  of  retarders  are 
most  efficiently  utilized  for  the  retardation. 

The  adsorption,  or  "coating",  theory  was  the  earliest 
put  forward  to  account  for  the  influence  of  retarders  on 
cement  hydration.   It  was  assumed  that  the  retarder  in  some 
way  became  affixed  to  the  cement  grains  and  prevented  their 
contact  with  the  water  in  the  same  way  that  the  ettringite 
on  the  C^A  and  the  calcium  silicate  hydrate  on  the  sili- 
cates were  presumed  to  act.   This  idea  is  consistent  with 
the  results  of  calorimetric  experiments  that  showed  re- 
tarders to  extend  the  dormant  period,  i.e.  delay  the  onset 
of  the  second  heat  evolution  peak  and  spread  it  out  over 
a  longer  time  and  with  a  smaller  maximum  value  of  heat 


138 


release  rate  (10,  16,  57) .   These  results  were  for  both 
Portland  cements  and  C~S.   Although  the  experiments  were 
not  extensive  in  terms  of  the  admixtures  used,  they  form 
the  basis  for  the  belief  that,  whatever  else  they  may  do, 
retarders  delay  set  by  delaying  the  chemical  reactions 
between  cement  and  water. 

Several  possible  ways  in  which  retarders  might  form 
such  a  coating  or  film  have  been  suggested. 

Hansen  (11)  suggested  that  the  surfaces  of  C,S  (and 
C~A)  would  be  principally  Ca++  or  0   ions,  because  these 
are  larger  and  more  numerous  than  ions  of  silicon  and 
aluminum  and,  therefore,  the  latter  would  be  screened  by 
the  former.   Organic  acids  could  presumably  be  attached 
by  ionic  attraction  between  Ca  ions  in  the  surface  and  the 
anionic  carboxylate  groups.   Another  suggested  possibility 
(25)  involves  the  fact  that  most  retarder  molecules  contain 
hydroxyl  groups,  which  are  known  to  form  hydrogen  bonds 
with  highly  electronegative  atoms  such  as  oxygen  atoms  in 
the  surfaces  of  the  cement  grains.   Such  bond  could  also  be 
a  mode  of  attachment  of  the  retarder  molecule. 

Young  (32)  has  also  suggested  that  the  attachment 
could  be  via  some  complex  between  surface  atoms  and  the 
retarder  molecules. 

The  work  done  by  Blank  et.  al  (7) ,  however,  showed 
that  adsorption  of  retarders  on  C\S  from  aqueous  solution 
was  negligible.   Recently  the  same  result  was  obtained  with 


139 


more  realistic  concentrations  of  materials  by  Diamond  (9) . 
These  results  cast  considerable  doubt  on  any  mechanism  of 
retardation  that  involves  adsorption  of  the  agent  on  the 
anhydrous  C.,S. 

On  the  other  hand  Ramachandran  (22)  showed  that  it  was 
hydrated  C.,S,  not  C3S,  that  was  responsible  for  a  percept- 
ible amount  of  adsorption  of  calcium  lignosulfonate  from 
an  aqueous  solution.   Diamond  (9)  obtained  the  same  result 
with  salicylic  acid.   The  details  of  the  surface  structure 
of  the  C-S-H  gel  are  unknown.   Only  speculation  can  be 

o 

based  on  analogies  with  the  structure  of  11  A  tobermorite 
(58)  with  which  the  gel  is  thought  to  have  many  similarities, 
It  seems  safe  to  say  that  the  surface  is  probably  composed 
of  either  oxygens  or  hydroxide  groups  and  is  partly  covered 
with  calcium  ions  abstracted  from  the  solution  phase  that 
give  it  an  overall  net  positive  charge. 

The  formation  of  a  discrete  film  of  retarder  molecules 
on  the  anhydrous  minerals  is  conceivable.   Indeed,  the 
difficulty  lies  in  the  idea  of  too  thick  a  film.   If  one 
assumes  a  concentration  of  retarder  of  0.1%  of  the  cement, 

a  molecular  weight  of  100,  and  a  coverage  per  molecule  of 

°2  2 

50  A  ,  then  a  cement  with  a  fineness  of  3000  cm  /g  would 

have  a  layer  of  retarder  ten  molecules  thick,  which  is 

unrealistic  in  light  of  the  known  processes  of  adsorption 

from  solution. 


140 


If  one  considers  the  situation  of  adsorption  on  the 
hydrated  phases,  the  results  are  more  believable.   Some 
dispute  exists  concerning  the  thickness  of  the  hydrate 
layer  covering  the  cement  grains  during  the  dormant  period. 
Estimates  range  from  several  angstroms  to  several  hundred 
(59) .   If  one  assumes  5%  of  the  cement  is  hydrated  during, 

or  at  the  end  of,  the  dormant  period,  and  if  the  specific 

2 
surface  of  the  hydrated  product  is  2  00  m  /g,  then  the 

retarder  would  be  sorbed  on  only  25%  of  this  material. 

It  was  found  in  this  work  that  the  chemicals  effective 
as  retarder  have  molecular  configurations  in  which  most  of 
the  hydrogen  atoms  around  a  molecule  are  strongly  polarized 
by  many  electronegative  groups.   Stronger  polarization  of 
hydrogen  atoms  would  lead  to  stronger  adsorption  on  charged 
surfaces  of  the  hydration  products  of  cement.   More  numer- 
ous polarized  hydrogen  atoms  would  result  in  more  efficient 
coverage  of  the  molecules  on  the  hydration  products. 

Further,  the  most  efficient  retarders  have  several, 
and  usually  many,  oxygens  closely  grouped  and  so  constrained 
either  by  frequency  along  the  chain  or  rigidity  of  a  ring 
structure.   These  oxygens  can  be  in  hydroxy 1,  carbonyl, 
or  carboxyl  groups.   These  groups  can  participate  in  bond- 
ing to  surfaces  of  the  hydration  products  by  hydrogen  bond- 
ing to  surface  oxygens  in  the  solid  hydrate  or  by  ionic 
attraction  to  calcium  sorbed  on  the  surfaces.   A  close 
grouping  as  well  as  a  large  number  of  such  groups  in  the 


141 


retarder  molecule  would  presumably  lead  to  stronger  bond- 
ing of  the  molecule  to  the  solid. 

The  questions  still  remains  of  the  mode  of  action  of 
retarder s.   Assuming,  as  seems  likely,  that  they  are  sorbed 
out  of  solution  onto  the  initially-formed  C-S-H  gel,  how 
do  they  thereby  delay  the  hydration  and  set? 

In  view  of  the  probability  of  less  than  a  monolayer 
being  formed  on  the  solid  hydrate  surfaces,  it  seems  un- 
likely that  the  sorbed  molecules  act  as  a  physical  barrier 
to  the  passage  of  water  inward  to  the  unreacted  minerals. 
There  could,  of  course,  be  some  kind  of  partial  "plugging" 
action  that  could  retard  the  passage  of  some  water, 
especially  since  the  good  retarders  have  a  highly  oxygen- 
ated structure  that  could  exert  some  binding  influence  on 
adjacent  water  molecules  by  hydrogen  bonding  and  thus 
generate  an  effectively  larger  structure  with  a  better 
blocking  action. 

Another  possibility  may  be  more  likely.   At  least  it 
satisfys  the  known  facts.   As  previously  mentioned,  if  the 
dormant  period  is  caused  by  a  "coating"  of  C-S-H  gel  on 
the  silicate  surfaces  (the  aluminates  being  controlled  by 
the  gypsum) ,  then  this  coating  must  partially  break  up 
for  increased  reaction  to  occur  and  bring  about  the  onset 
of  the  second  heat  peak.   Whatever  the  force  impelling  the 
breakup  of  the  coating,  if  the  coating  is  mechanically 
stronger  it  would  resist  the  breakup  longer,  and  when  it 


142 


occurred  it  would  be  less  extensive  and  result  in  a  "milder' 
second  heat  peak.   Such  a  result  would  be  consistent  with 
the  observed  calorimetric  data.   So  it  is  postulated  that 
the  retarder  molecules  sorb  on  the  initially  formed  hydrate 
material  and  that  some  of  the  molecules  will  sorb  in  areas 
where  the  gel  particles  are  already  in  close  contact  and 
are  coherent.   The  molecular  structure  of  good  retarder s  is 
such  that  they  have  regions  (the  highly  oxygenated  or 
charged  parts  of  the  molecule)  that  can  sorb  over  a  large 
part  of  the  molecule  and  that  presumably  do  so  relatively 
strongly.   If  they  sorbed  onto  two  adjacent  gel  particles 
the  resulting  bonding  would,  according  to  elementary 
calculations,  result  in  a  considerable  increase  in  the 
resistance  to  rupture  by  whatever  forces  ultimately  break 
up  the  coating.   No  doubt  many  of  the  molecules  would  sorb 
on  only  the  surface  of  one  particle  of  gel,  but  some  of 
the  pore  spaces  are  so  small,  even  in  a  mature  gel,  that 
it  is  reasonable  to  envisage  such  a  bridging  action  of  the 
retarder  molecule  and  a  consequent  increase  in  the  mechani- 
cal strength  of  the  coating.   It  is  recognized  that  this  is 
only  a  postulate,  which  requires  much  more  work  to  estab- 
lish or  refute,  but  at  least  it  fits  most  of  the  known 
facts. 

From  the  discussion  of  the  retardation  mechanisms 
above,  it  appears  that  strong  retarders  not  only  accelerate 
the  initial  hydration  of  cement  by  removing  possibly  more 


143 


calcium  ions  or  other  metal  ions  from  the  aqueous  phase  of 
cement  paste,  but  also  have  molecular  configurations  that 
can  either  cover  or  bridge  the  hydration  products  on  cement 
grains  more  efficiently.   Even  if  a  chemical  has  an  ap- 
parently effective  molecular  structure,  it  may  not  act  as 
strongly  as  expected  unless  it  can  accelerate  the  initial 
cement  hydration  and  unless  the  molecular  adsorption  on 
the  hydration  products  on  cement  grains  proceeds  effici- 
ently.  Examples  may  be  mucic,  dihydroxy tartaric  or 
dihydroxymaleic,  and  ketomalonic  acids  that  are  consider- 
ably weaker  retarders  than  gluconic,  tartaric,  and  tar- 
tronic  acids,  correspondingly,  regardless  of  their  similar 
molecular  structures.   These  are  the  chemicals  that  seem 
to  have  precipitated  when  only  little  CaCl-  was  added  in 
alkaline  solution  (Figure  51) .   Either  only  a  little  complex 
formation  or  less  efficient  action  for  adsorption  would  be 
expected  for  these  chemicals. 

Effect  of  Retarders  on  the  Shrinkage  of  Cement  Pastes 
As  shown  in  Figures  16  and  17,  the  addition  of  retar- 
ders altered  the  shrinkage  of  cement  paste  significantly  at 
earlier  ages  and  increased  the  shrinkage  to  some  extent  at 
later  ages,  when  the  samples  were  dried  in  the  vacuum  oven 
for  2  4  hours.   However,  the  general  trend  of  the  relation 
between  degree  of  cement  hydration  and  shrinkage  was  the 
same  for  all  the  samples.   An  early  peak  of  shrinkage 
occurred  at  about  2  5%  hydration  of  the  cement,  and  then  the 


144 


shrinkage  decreased  to  a  minimum  of  0.7-0.8%  at  about  60% 
hydration.   Thereafter  the  shrinkage  increased  parabolically 
as  the  paste  became  more  mature. 

It  would  be  normally  expected  that  a  longer  period  of 
cement  hydration  would  induce  larger  shrinkage  of  cement 
paste,  because  larger  amounts  of  C-S-H  gel,  which  is  the 
component  causing  the  shrinkage,  are  produced.   The  in- 
creased shrinkage  can  be  also  explained  by  the  reduction  of 
the  amount  of  unhydrated  cement  grains,  which  act  as  a 
"microaggregate"  and  restrain  the  shrinkage  of  the  cement 
gel  (60) .   The  latter  idea  is  similar  to  the  shrinkage- 
restraining  action  of  aggregates  in  concrete  (61) . 

However,  these  ideas  do  not  explain  the  existence  of 
the  first  peak  observed  in  most  of  the  shrinkage  curves. 
Part  of  the  effect  could  be  due  to  the  slightly  greater 
"efficiency"  with  which  the  young  and  immature  pastes  were 
dried  by  being  in  the  vacuum  oven  for  a  constant  time  of 
24  hours.   The  pastes  continued  to  loose  a  little  water  and 
to  shrink  appreciably  when  they  were  kept  in  the  oven  for 
longer  times;  this  effect  was  greater  for  the  more  mature 
pastes  (Figures  52  and  53) .   Also,  the  less  mature  pastes 
probably  had  a  considerably  lower  elastic  modulus  than  the 
more  mature  ones,  an  effect  that  would  result  in  greater 
deformations  for  a  given  driving  force  of  shrinkage.   It 
should  be  noted  here  that  the  data  points  were  closely 
grouped  about  the  curves  and  that  the  effects  being 


145 


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described  are  real,  rather  than  the  result  of  experimental 
variability. 

According  to  Powers  (62)  ,  menisci  in  which  hydrostatic 
tension  develops  can  not  form  at  humidities  below  about 
45%,  and  all  the  evaporable  water  in  cement  paste  at  45% 
R.H.  exists  as  adsorbed  water  on  the  solid  phases.   In 
explaining  the  shrinkage  of  cement  pastes  at  humidities 
below  the  vapor  pressure  at  which  menisci  vanish,  Mills 
(63)  ascribed  the  shrinkage  to  the  reduction  of  swelling 
pressure  in  gel  water  which  is  adsorbed  on  the  cement  gel. 
Verbeck  and  Helmuth  (35) ,  on  the  other  hand,  said  that 
water  held  by  cement  paste  below  30%  R.H.  is  not  "adsorbed 
water"  but  rather  is  in  a  state  similar  to  that  of  inter- 
layer  water  in  clays.   So  there  is  some  question  about  the 
exact  state  of  the  water  in  pastes  at  relatively  low 
humidities.   However,  it  is  known  that  only  those  water 
molecules  that  are  held  tightly  by  the  solid  phase  are  left 
when  the  paste  is  severely  dried.   Therefore,  the  measured 
shrinkage  should  be  directly  related  to  the  properties  of 
the  solid  phases,  and  especially  of  the  hydration  products. 
Since  the  amount  of  unhydrated  cement  is  constant  at  a 
certain  degree  of  hydration,  it  appears  that  the  observed 
difference  in  shrinkage  due  to  the  addition  of  retarders 
has  to  be  attributed  to  some  modification  of  the  properties 
of  the  hydration  products. 


148 


According  to  other  workers,  retarders  do  not  alter  the 
composition  or  identity  of  the  hydration  products,  but 
change  only  the  rate  of  cement  hydration  (1,  8).   The 
scanning  electron  microscope  did  not  show  any  noticeable 
difference  among  the  hydration  products  of  cement  pastes 
with  and  without  retarders  after  more  than  2  0%  of  the  cement 
hydrated.   Therefore,  the  only  conceivable  modifications  by 
retarders  would  be  either  some  morphological  changes  in  the 
microstructure  of  the  hydration  products  or  a  difference  in 
the  relative  amounts  of  hydration  products  produced  from 
each  compound  of  cement,  or  both.   Whatever  the  reason  is, 
specific  surface  area  measurement  on  the  hydration  products 
should  reveal  some  of  the  evidence,  because  the  shrinkage 
would  have  been  caused  by  removal  of  water  molecules  from 
their  surfaces. 

As  shown  in  Figures  28,  29  ,  and  30,  the  retarders,  in 
fact,  changed  the  specific  surface  areas  of  the  hydration 
products,  and  the  change  was  frequently  closely  related  to 
the  shrinkage  behavior  of  corresponding  cement  paste.   For 
example,  those  retarders  which  induced  the  larger  shrinkage 
at  earlier  ages  increased  the  specific  surface  area  at  the 
ages  and  the  subsequent  change  was  also  similar  to  that  in 
shrinkage.   The  consistently  larger  shrinkage  of  the  cement 
paste  with  calcium  chloride  would  be  well  explained  by  the 
consistently  larger  specific  surface  area  of  the  hydration 
products. 


149 


It  is  of  interest  to  note  that  for  the  control  paste 
with  no  admixture  the  minimum  in  the  shrinkage  curve  coin- 
cided well  with  that  in  the  surface  area  development  curve, 
at  about  60%  hydration.   The  maximum,  however,  occurred 
somewhat  earlier  for  the  shrinkage  curve,  at  25%  as  opposed 
to  45%  for  the  surface  area.   They  would  not,  of  course,  be 
expected  to  be  exactly  similar,  because  of  changing  second- 
ary affects,  such  as  the  elastic  modulus. 

For  the  commercial  retarders,  it  may  be  significant 
that  at  later  ages  all  admixtures  gave  pastes  of  slightly 
higher  shrinkages  than  the  control,  whereas  all  except  S 
gave  slightly  smaller  areas.   For  the  pure  chemicals  the 
relationship  is  equally  mixed.   At  intermediate  maturities 
of  the  paste,  near  the  minimum  shrinkage,  many  of  the  pure 
compounds  resulted  in  significantly  larger  specific 
surfaces,  while  causing  only  a  small  increase  in  the 
shrinkage. 

For  the  younger  pastes,  one  would  expect  a  closer  cor- 
respondence between  shrinkage  and  specific  surface  because 
their  structures  are  less  influenced  by  later,  secondary, 
processes.   This  seems  to  be  the  case  for  A  and  S,  although 
L  gave  a  somewhat  higher  surface,  but  slightly  smaller 
shrinkage.   All  the  pure  chemical  gave  pastes  of  higher 
surface  area  in  the  immature  pastes,  and  all  also  gave 
higher  shrinkage  except  3-hydroxy-2-butanone  and  hydroquinone, 
It  may  be  significant  (Figure  25)  that  hydroquinone  seems  to 


150 


have  been  atypical  in  that  it  did  not  slow  down  the  hydra- 
tion rate,  as  determined  by  W ,  but  did  retard  the  set. 
When  the  sample  bars  were  demolded,  the  one  containing 
hydroquinone  seemed  to  have  a  hardened  core  and  a  still- 
soft  exterior.   The  reasons  for  this  anomalous  behavior  are 
not  known.   The  unusual  shape  of  the  curve  for  sucrose 
should  also  be  noted. 

In  all  matters  involving  the  specific  surface  area,  it 
should  be  remembered  that  different  batches  of  samples 
hydrate  somewhat  differently,  even  though  the  mixing  and 
curing  conditions  were  as  similar  as  possible.   The  data 
for  the  control  pastes  were  obtained  from  five  different 
batches,  and  they  show  such  a  variability.   Therefore 
caution  should  be  observed  in  drawing  conclusions  from  small 
variations  in  this  parameter. 

In  general,  however,  at  the  younger  ages  the  shrinkage 
behavior  changes  in  a  manner  similar  to  the  specific  sur- 
face, which  is  logical. 

It  should  be  recalled,  that  the  adsorption  process  of 
retarder  molecules  is  not  necessarily  the  same  for  all  the 
retarders.   Such  differences  may  have  caused  kinetic  changes 
in  the  subsequent  hydration  of  each  cement  compound  in 
these  samples. 

Retarders  also  increased  the  shrinkage  of  mature  cement 
pastes  (10  months  old)  when  the  samples  were  dried  at  50% 
R.H.   (Figure  18  and  19).   Menisci  can  exist  in  small  pores 


151 


of  the  pastes  in  this  case,  and  the  drying  would  be  equiva- 
lent to  a  severe  condition  for  normal  concrete  members  in 
the  field.   In  interpreting  these  kinds  of  shrinkage  data, 
however,  one  can  not  forget  that  the  delayed  hydration  of 
cement  due  to  the  addition  of  retarders  normally  recovers 
in  2  to  3  days,  and  retarders  rather  accelerate  the  sub- 
sequent hydration  (see  Figures  24  and  25) .   Then,  it  would 
be  apparent  from  the  previous  discussion  that,  if  the 
comparison  is  made  at  an  equal  age,  retarders  generally  in- 
crease the  shrinkage  of  older  cement  paste.   The  comparison 
at  an  equal  age  would  have  a  practical  meaning.   But  the 
result  may  not  be  necessarily  caused  by  the  modified 
property  of  hydration  products  by  retarders  but  could  be 
caused  simply  by  the  difference  in  the  degree  of  cement 
hydration. 

The  relationships  between  shrinkage  and  weight  loss  of 
the  same  samples  revealed  that  the  relation  was  more  or  less 
the  same  as  that  of  the  control  sample  for  all  of  the 
samples  except  for  the  sample  with  retarder  S.   Hence,  it 
can  be  said  that  the  observed  increase  in  the  shrinkage  of 
the  samples  are  mostly  caused  by  the  difference  in  the 
degree  of  cement  hydration,  for  drying  at  50%  R.H. 

Although  the  determination  of  evaporable  water  content 
of  cement  paste  was  made  carefully  as  possible,  the 
results  scattered  in  a  relatively  wide  range,  and  no  infor- 
mation was  obtained  as  to  why  only  retarder  S  increased 


152 


the  shrinkage.   It  should  be  recalled  that  retarder  S  in- 
creased the  specific  surface  area  of  the  hydration  products 
remarkably  at  later  stage  of  the  hydration.   Presumably, 
the  effect  of  this  increased  specific  surface  area  would 
have  remained  even  at  the  intermediate  humidity.   This 
would,  in  turn,  indicate  a  possibility  that  the  modified 
property  of  hydration  products  by  retarders  may  affect  the 
shrinkage  of  cement  paste  in  a  relatively  severe  drying 
condition. 


153 


CONCLUSIONS 

The  following  conclusions  seem  reasonable.   They  are 
based  on  the  materials  used  and  the  tests  performed. 

1.   Strong  retarders  have  a  molecular  composition  that 
includes  many  oxygen  atoms  constrained  to  approach  each 
other  closely.   Hydroxyl,  carboxyl,  and  carbonyl  are  all 
effective,  and  carbonyl  seems  especially  strong  in  its 
influence.   Many  a-hydroxy  acids  are  retarders,  but  the 
presence  of  other  groups  can  exert  a  strong  effect  reducing 
the  retarding  action.   The  oxygen-containing  groups  can  be 
presumed  to  exert  polarizing  influences  that  could  con- 
tribute to  relatively  strong  adsorption  onto  the  solid 
surfaces  of  concern. 

2.  More  weakly  electronegative  atoms  on  the  molecule 
do  not  have  the  same  effect  as  oxygens. 

3.  When  cement  pastes  are  strongly  dried  of  all  their 
evaporable  water,  they  exhibit  shrinkage  behavior  that 
shows  a  minimum  at  about  half  hydration  and  an  earlier 
maximum.   This  behavior  is  also  exhibited  by  the  change  in 
specific  surface  area  of  the  hydrated  cement;  the  hydrate 
gains  appreciable  surface  area  between  about  60%  and  80% 
hydration,  and  thereafter  remains  relatively  unchanged. 


154 


Some  cause  and  effect  relationship  exists  between  the 
specific  surface  area  of  a  paste  and  its  shrinkage  poten- 
tial, although  other  factors,  such  as  restraint  by  un- 
hydrated  cement,  are  probably  also  operative. 

4.  Retarders  cause  a  moderate  increase  in  the  shrink- 
age of  cement  pastes  at  ages  greater  than  about  half  hydra- 
tion. At  lesser  ages  the  shrinkage  may  be  either  increased 
or  decreased. 

5.  The  changes  in  shrinkage  brought  about  by  retarders 
can  be  partially  ascribed  to  those  brought  about  in  specific 
surface  areas  of  the  hydrated  cement,  but  other  effects, 
probably  related  to  the  chemical  species  present,  are  also 
important. 


LIST   OF    REFERENCES 


155 


LIST  OF  REFERENCES 


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160 


(54)  R.  L.  Berger  and  J.  D.  McGregor,  "Influence  of  Ad- 
mixtures on  the  Morphology  of  Calcium  Hydroxide 
Formed  During  Tricalcium  Silicate  Hydration"  Cement 
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(55)  W.  L.  Dolch,  Private  Communication. 

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(57)  H.  N.  Stein,  "Influence  of  Some  Additives  on  the 
Hydration  Reactions  of  Portland  Cement  I.  Non-Ionic 
Organic  Additives"  Journal  of  Applied  Chemistry, 
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(58)  H.  F.  W.  Taylor,  "The  Chemistry  of  Cement",  Vol.  I, 
Academic  Press,  1964,  pp.  187-189. 

(59)  K.  Fujii  and  W.  Kondo,  "Hydration  of  Tricalcium 
Silicate  in  a  Very  Early  Stage"  Proceedings  of  Fifth 
International  Symposium  on  the  Chemistry  of  Cement, 
Tokyo,  1968,  Vol.  II,  pp.  362-371. 

(60)  G.  Verbeck,  "Shrinkage  of  Concrete  -  Applied  Research 
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(61)  G.  Pickett,  "Effect  of  Aggregate  on  Shrinkage  of 
Concrete  and  Hypothesis  Concerning  Shrinkage" 
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Vol.  52,  No.  5,  Jan.  1956,  pp.  581-590. 

(62)  T.  C.  Powers,  "Physical  Properties  of  Cement  Paste" 
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(63)  R.  H.  Mills,  "Effects  of  Sorbed  Water  on  Dimensions, 
Compressive  Strength  and  Swelling  Pressure  of  Hardened 
Cement  Paste"  Highway  Research  Board,  Special  Report 
90,  1966,  pp.  84-111. 


APPENDICES 


APPENDIX   A 


161 


APPENDIX  A 


Correction  Curve  for  Warping  of  Cement  Paste  Bars 


162 


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APPENDIX   B 


163 


APPENDIX  B 


Summary  of  Setting  Time  Experiments  When 
Pure  Chemicals  were  Added 


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164 


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APPENDIX   C 


169 


APPENDIX  C 


Shrinkage  of  Vacuum  Oven-Dried  Cement  Pastes 
at  Various  Stages  of  Cement  Hydration 


The  following  abbreviations  are  used  in  this  part. 

h:   hour(s) 
d:   day(s) 
m:   month (s) 

Each  data  point  is  the  average  of  two  separate  measurements, 
The  range  of  duplicate  measurements  was  usually  about  1%  of 
the  average. 


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181 


VITA 


Yasuhiko  Yamamoto  was  born  on  May  1,  1943  in  Korea. 
He  is  a  citizen  of  Japan. 

After  completing  early  education  at  Kofu  First  High 
School  in  Yamanashi  prefecture,  he  entered  Yamanashi 
University  where  he  received  B.S.C.E.  degree  in  March  1966 

In  April  1966,  he  became  a  graduate  student  of 
University  of  Tokyo  and  received  M.S.C.E.  degree  in  March 
1968.   He  continued  his  study  at  the  same  university 
toward  Doctor  of  Science  degree  until  he  came  to  the 
U.S.A.  to  study  at  Purdue  University  in  September  1969.