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Full text of "Retarders for Concrete and Their Effects on Setting Time and Shrinkage : Interim Report"

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 Q f tn ig 

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 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 

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 
(CaCl 2 -2H 2 0) 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 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 - Si0 2 , A = A1 2 3 , H = H 2 0. 



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 C 2 S 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: 

C 3 A > C.AF > Type I portland cement > C 3 S, C„S > 
salicylic acid: 

C 3 A > C 4 AF > T yP e x Portland cement > C 2 S = C 3 S = 
The adsorption on the compounds from ethyl alcohol solution, 
however, was in the following order for salicylic acid: 

C 3 S > C 2 S > Type I portland cement > C^A = C.AF = 
From these results, they suggested that the negligible ad- 
sorption on C 2 S 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 •> C AH + C.AH ; metastable phase 
J z o 4 n / , , . 

(hexagonal) 

C AH + 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-,AH fi while sugars and their derivatives 

blocked the hydration reaction at metastable C~AH 8 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 H 2 from further attacking the C3A. The 
organic layers could prevent the intermediate products, 
C 2 AHs an< ^ c 4 AH n / 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,AH g . 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„AH R , and C.AH..-.. Another interesting observa- 
tion by Young is that there was no evidence of the trans- 
formation of C_AH and C.AH, _. to C AH, 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 C 3 S 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 C 3 A 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 C 3 A surfaces and explained further: 

"When cement is pre-mixed with water for a few minutes, 
gypsum has ample time to dissolve and coat the C 3 A. 
Consequently, when the retarder is added to the pre- 
mixed paste, the C 3 A 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 C 3 S , hydrated C 3 S, 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 S0 3 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 C 3 A 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 C 3 A content. For 
cements of the same C 3 A 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 

c 3 s 

C 2 S 

C 3 A 

C 4 AF 

CaSO. 

Total 96.94 



Chemica 


1 Analysis 






(%) 


sio 2 




21.64 


A1 2 3 




5.29 


Fe 2°3 




2.19 


CaO 




65.36 


MgO 




0.92 


so 3 




2.40 


Na 2 




0.08 


K 2 




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 (cm 2 /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 

















• 


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100 


- 










/ 





80 










/ 


■ — ■ 

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i 


fiO 








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/ 




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p 


?o 




/ 


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\ 


II 






/ 
/ 















| | 


I 


I 


i 


i 





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 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 



4 




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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 (CaCl 2 • 2H 2 0) , 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 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 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 . 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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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 Wc (15) 

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

Wc" " ( Wod 1} (1 + WcT 5 (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 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 



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



62 







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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 
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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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78 



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 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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Q T> 
•H 

o) e 

> 3 

QJ 
t7> <D 

<a > 

^ -H 
C -P 
•H (0 

rH rH 

x: a) 

i 

en 



•H 



82 



Weight Loss (%) 



% 0-2. 
o 

3C 
C 



0.3 



0.4 



o ; 


i 


4 


S 


9 


i 


i 


l 


i 




- 


• 

• ■ 


• 






- 


• • • 

• 


1 *>. • 

>• xo 

• 




- 














• .* No Admixture 
x : Retarder L 










o : Retarder 
• : Retardei 


■ A 
- S 





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



83 



Weight Loss (%) 
2 4 6 






S. 0.2 

o 

it 
c 



in 



0.3 



0.4 



1 


I 


1 


I 




- 


1* 

X 


°i o 






- 








- 










• : No Admixture 

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 



o 

c 



\ 

o 


\°* • \ 


Orininnl 


- 


\ •• \ 
\ *• \ 

\ ° \ 

\ # \ 


W/C*40% 

• 


- 






\ 

\ • *\ 

\ \ x 
\ o ^ 

V\ i 






- 


w • [no MumixTure 
x .'Retarder L 
o : Retarder A 
• : Retarder S 


\f \. 

* •• 

\°\ 

1 1 1 1 


1 1 




i i i i 



30 



35 
We/Wc (%) 



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 




O 
CM 



iO o 



m 



0) 

u 

cn 
■H 
Pq 



89 




o 



0> 
< 



03 
OJ 

+J 
03 

05 

4J 
G 

o 

S-i 
0) 

u 
o 

0) 

en 

c 

•H 

M 

U 

> 

U 

0) 
4-1 

nj 

s ~ 

OJ rH 



> 

W oj 

I u 

c 3 

o & 

I 



u 

Cn 
•H 



90 







• 


: NO 


Admixture 










250 






: Retarder L 
: Retarder A 










o 












• 


Retarder S 






• O 


5 200 




A 


Citric Acid 

Citric Acid 
(200% Relative 

Retardation) 






» 

,**** 

* 






Specific Surface Area 

O oi 
O O 


— 












• 
• 

« x * 








• 


• • 

• 

1 








X* 

• 


w • 

X 

o 






•so 




X 












o 











i 




i 


1 


1 


l 



20 40 60 

Degree of Hydration (%) 



80 



100 



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 



300 



250 



o»200 



o 
o 

CO 



o 
CO 



150 



100 



50 



No Admixture 

Glycolic Acid 

Sucrose 

3- Hydroxy -2- Butanone 

Hydroquinone 

CaCl 2 -2H 2 



0*# 



O 



V 



•a, o 






A o 



V 



20 40 60 

Degree of Hydration (%) 



80 



100 



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 




2 -i < w 

X 

'5 *- i» u 

t t> D b 

TJ P T) TJ 

o a* at a* 

zcKtt: 



TT 



o • 
I 

II I 

* o • 



8 



j i i 



>> 



0> 

l_ 

Q 



O 
O 



(B/ lu) D9JV dOD^jns Di^pads 



o 


o 


O 


m 


o 


lO 


CM 


CM 





r 

0) 

■H 

u 
a 
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c 

0) 

> 

o 

g 



id 
> 

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a 

o 

■H 

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S-i 

O — 
a< en 

P U 
rfl (0 
l-i -P 

t> a) 
>.« 

rH 
4-1 rtj 

O H 

O 
(0 >-i 
QJ d) 



o 

0) u 
o — 
(0 

<+-! U) 

^ a) 
p -p 
co en 

rfl 
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(Jl 




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96 



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, 

CH 2 (OH)C0 2 H, or 

CH o -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 
H0 2 C-CH 2 -C-CH 2 -C0 2 H 
OH 



Gallic acid 




2 ,4 ,6-Trihydroxybenzoic acid 



C0 2 H 



HO 



^^ 



OH 



Sr 



Sucrose C C H, . O c -0-C,,H n ,O c 
6 11 5 6 11 5 



Pyruvic acid CH o -C-C0 o H 
J II 2 


and a-Ketoglutaric acid H0 2 C-CH 2 -CH 2 -C-C0 2 H 



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 = 

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,.-C0 o H 
SH 

the T500 drops to 113% and for glycine 

CH o -C0-H 
I l 2 
NH 2 

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 CH 3 -CH 2 -CH-C0 2 H 

OH 



and mandelic acid, 




-CH-C0 2 H 



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 

CH =CH-CH 

Z I 2. 

OH 



113 



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

CH~-CH=CH-CH 
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-CH 
3 ii I 3 

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 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-CH 
I 2 I I 2 
OH OH OH 

and pentaerythritol 



114 



OH 

l 
CH 

I * 

H0-CH o -C-CH o -0H 

Z | z 

CH 
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 * 
C0 2 H C0 2 H C0 2 H 

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 



H0 2 C-CH 2 -CH 2 -C0 2 H 

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

to make malic acid 

H0 2 C-CH 2 -CH-C0 2 H 
OH 

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

hydroxyl gives tartatic acid 

H0-C-CH-CH-C0 o H 
2. | | 2 

OH OH 

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

Glutaric acid 

H0 2 C-CH 2 -CH 2 -CH 2 -C0 2 H 

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

H0 o C-CH--CH o -C-C0„H 


which may, as previously mentioned, exist as 

OH 
I 
H0 2 C-CH 2 -CH 2 -C-C0 2 H 

OH 

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

measured. A similar effect is observable with pyruvic acid 

CH-,-C-C0 o H 
.3 || 2. 



or 



OH 
I 
CH„-C-C0 o H 
3 | 2 



OH 



116 



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

the mono-hydroxy counterpart, lactic acid 

CH o -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 - C0 o H 

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, 

H0 2 C-CH 2 -C0 2 H 
which has a T500 of only 102%. Addition of one hydroxyl 
group gives tartronic acid 

H0 2 C-CH"C0 2 H 
OH 

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

second hydroxyl gives the hydrate of ketomalonic acid 

OH 
I 

H0 o C-C-C0 o H + H o > H0_C-C-C0 o H 

Z || Z Z Z Z 

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. 

C0 2 H 









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 

CH o -C0 o H 
OH 

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

and monochloroacetic acid in which the hydroxyl has been 

exchanged for -SH, -NH 2 , 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~-C0 o H 
OH 



lactic acid, 



and pyruvic acid, 



CH -CH~C0 9 H 
OH 



CH o -C-C0 o H 
J ii I 





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 

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 



and ethyl acetoacetate 

CH,-C-CH -C-0-C H c 
3 || 2 || 2 5 


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 CaCl 2 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 . 9 ml for several 
tests, the average being 0.94 ml. The chemicals that 
required more CaCl 2 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 2 iddo 



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 C 3 A (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 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 C 3 S, 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 



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147 



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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(2) R. C. Mielenz, "Water-Reducing Admixtures and Set- 
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156 



(9) S. Diamond, "Interactions Between Cement Minerals and 
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Dec. 1961, pp. 482-492. 

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(14) S. Diamond, "Interactions Between Cement Minerals and 
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(15) S. Diamond, "Interactions Between Cement Minerals 
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(16) L. R. Forbrich, "The Effect of Various Reagents on the 
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Vol. 37, Nov. 1940, pp. 161-181. 

(17) M. Polivak and A. Klein, "Effect of Water-Reducing 
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1960, pp. 124-139. 

(18) G. M. Bruere, "Importance of Mixing Sequence When 
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157 



(19) V. H. Dodson and E. Farkas, "Delayed Addition of Set 
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(2 0) G. L. Kalousek, C. H. Jumper, and J. J. Tregoning, 
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(21) F. C. Tamas, "Acceleration and Retardation of Portland 
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(22) V. S. Ramachandran, "Interaction of Calcium Ligno- 
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(23) H. H. Steinour, Discussion of the paper by W. C. 
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(25) H. H. Steinour, Discussion of the paper by W. C. 
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(28) U. Danielson, "Studies of the Effect of Simple Organic 
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158 



(30) G. M. Bruere, "Set-Retarding Effects of Sugars in 
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(31) S. Koide, Discussion of the paper by K. E. Daugherty 
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(32) J. F. Young, "A Review of the Mechanisms of Set- 
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(33) R. C. Mielenz, "Use of Surface-Active Agents in 
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(34) A. M. Neville, "Hardened Concrete: Physical and 
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159 



(42) R. F. Feldman and P. J. Sereda, "A Model for Hydrated 
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Inc., 1951, p. 571. 



160 



(54) R. L. Berger and J. D. McGregor, "Influence of Ad- 
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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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163 



APPENDIX B 



Summary of Setting Time Experiments When 
Pure Chemicals were Added 



Setting times are expressed in terms of T50, T100, 
T500, and T4000 which are the relative retardations at the 
penetration resistances of 50, 100, 500 and 4000 psi, 
respectively, to the retardation of plain mortar with no 
admixture. 



164 





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(U 


W 



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. 



170 



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171 



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173 




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174 




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175 




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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.