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THE EFFECT OF ALKALI UPON PORTLAND CEMENT

A DISSERTATION

SUBMITTED TO THE FACULTY

OF THE OGDEN GRADUATE SCHOOL OF SCIENCE

IN CANDIDACY FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY

BY

KARL THEODOR STEIK

Private Edition, Distributed By

THE UNIVERSITY OF CHICAGO LIBRARIES

CHICAGO, ILLINOIS

Reprinted from UNIVERSITY OF WYOMING BULLETIN, No. 122

"dniwrsitp of Gbicago

THE EFFECT OF ALKALI UPON PORTLAND CEMENT

A DISSERTATION

SUBMITTED TO THE FACULTY

OF THE OGDEN GRADUATE SCHOOL OF SCIENCE

IN CANDIDACY FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

DEPARTMENT OF CHEMISTRY

BY

KARL THEODOR STEIK

Private Edition, Distributed By

THE UNIVERSITY OF CHICAGO LIBRARIES

CHICAGO, ILLINOIS

Reprinted from UNIVERSITY OF WYOMING BULLETIN, No. 122

BULLETIN NO. 122

DECEMBER, 1919

UNIVERSITY OF WYOMING

AGRICULTURAL EXPERIMENT STATION

Cement in different stages of disintegration.

THE EFFECT OF ALKALI UPON PORTLAND CEMENT— II

Bulletins will be sent free upon request. Address : Director of Experiment Station, Laramie, Wyoming.

713

UNIVERSITY OF WYOMING

Agricultural Experiment Station

LARAMIE, WYOMING

BOARD OF TRUSTEES

Officers

ALEXANDER B. HAMILTON, M. D President

W. C. DEMING, M. A.... .'.. Vice President

C. D SPALDING Treasurer

F. S. BURRAGE, B. A Secretary

Executive Committee

A. B. HAMILTON C. P. ARNOLD C. D. SPALDING

Members Term

Appointed Expires

1911 .....ALEXANDER B. HAMILTON, M. D... 1923

1911 LYMAN H. BROOKS .1923

1913 CHARLES S. BEACH, B. S ! 1. .1923

1913 C. D. SPALDING. 1921

1914. MARY N. BROOKS. .1925

1915... ....... J. M. CAREY, LL. B V. 1921

1918 .C. P. ARNOLD, M. A 1919

1919 . ...E. W. CROFT, M. D 1925

1919 W. C. DEMING, M. A.. 1925

KATHARINE A. MORTON, State Superintendent of Public Instruc- tion Ex Officio

A. NELSON, Ph. D. , . .... Ex Officio

% STATION STAFF

A. ^NELSON, Ph. D. President

A. D. FAVILLE, M. S.. . . . . . . .... .-". -.-. . . . : . \ .....'... Director

F. S. BURRAGE, B. A Secretary

O. A. BEATH, M. A Research Chemist

C. ELDER, D. V. M Assistant Veterinarian

J. C. FITTERER, M. S., C. E Irrigation Engineer

F. A. HAYS, Ph. D Associate Animal Husbandman

F. E. HEPNER, M. S Research Chemist

J. A. HILL, B. S Wool Specialist

E. H. LEHNERT, D. V. S Veterinarian

P. T. MILLER, M. A Associate Station Chemist

E. C. O'ROKE, M. A Assistant Parasitologist

J. P. POOLE, A. M Botanist and Horticulturist

J. L. ROBINSON, M. S Assistant Agronomist

*J. W. SCOTT, Ph. D . .Parasitologist

K. T. STEIK, M. A Engineering Chemist

A. F. VASS, Ph. D Associate Agronomist

MARION V. HIGGINS Librarian

F. M. LONG.. ..Clerk

*On leave.

The Effect of Alkali Upon Portland Cement-II

KARL STEIK

INTRODUCTION.*

Of the salts which constitute the so-called "alkali", the fol- lowing were used in the determination of their effect on Portland cement: The sulfates of sodium and magnesium, chlorides of sodium and magnesium and the carbonate of sodium. The nitrates occur only in very small quantities and therefore are not detri- mental to any extent in regard to the cement problems. Cases are mentioned in the literature where concrete is supposed to have been damaged by water which had percolated through gypsum beds, therefore, effects of solution of calcium sulphate, too, were investigated.

In the Western States the number of different salts present in the so-called "alkali" varies according to local conditions. The two most abundant and frequent salts are the sulfates of sodium and magnesium. The carbonate of sodium is present in the black alkali. The concentration of the salts in waters varies accord- ing to the localities and seasons of the year. Some of the alkali lakes are filled with saturated solutions during dry seasons and in many of them solid deposits occur on the lake bottoms.

Experiments were conducted with solutions of only one salt at different concentrations in order to determine the effect of each salt separately. Solutions were also used which contained two, three and four different salts at different concentrations. In order to determine the relative merits in regard to resisting the action of alkali, neat cement and mortars of different concentration were used. For comparison, several brands of cement were tried, but most of the experiments were carried out on "Ideal" cement. In all cases the amount of solution per gram of cement or mortar was the same.

Experience showed that the reaction of alkali on neat Port- land cement was very slow ; consequently, for the purpose of ob-

*A progress report on this problem was made in Bulletin 113 of the Wyoming Station. Much of the work outlined on the following pages appeared in the earlier publication but is included at this time to round out and complete the final report.

4 Wyoming Agricultural Experiment Station. Bui, 122

taining more marked results, some experiments were conducted with solutions kept at temperature of boiling water during eight hours a day for eighteen months. In connection with these ex- periments, the effect of periodical wetting and drying was tested and also the effect of treating the cement with large quantities of hot distilled water.

CHEMICAL CHANGES

The chemical reactions which take place between the con- stituents of the alkali were judged from the reaction products. In solutions of sodium sulfate, or magnesium sulfate singly or combined, deposits of crystalline calcium sulfate were obtained as shown in Figures I and 2. In dilute solutions, single crystals were more likely to form, as in Figure i ; in more concentrated solutions crystalline rosette-like aggregates were formed, as in Figure 2.

Fig. 1.

On cement kept in water, crystalline and amorphous deposits of Ca(OH)., — calcium hydroxide — were obtained, as shown in Figures 3 and 4. The surfaces of cement kept in a solution of sodium carbonate were either entirely or partially covered with amorphous calcium carbonate, CaCO;!, as shown in Figure 5.

Dec.

Effect of Alkali Upon Portland Cement — //.

The magnesium hydroxide which was formed in solutions of magnesium sulfate was amorphous, and, usually, mixed with amorphous calcium sulfate. Deposits of crystalline magnesium hydroxide were obtained on surfaces of cement kept in hot solu- tions of magnesium chloride. The crystals formed small nodules, as shown in Figure 6.

Wyoming Agricultural Experiment Station. Bui. 122

Fig. 4.

Dec. 1919 Effect of Alkali Upon Portland Cement— II.

Fig. 5.

Fig. 6.

Besides these products of reaction, one more was obtained from cement which was kept in a 5 per cent solution of sodium chloride. This solution was not changed during the entire time of experiments and the crystals appeared after a period of about 3 years. In other cases, fresh solutions were used after each testing of the compression and tension strength of the cement. The crystals, after cleaning off the adhering matter from their surfaces, gave the following analytical results: SiO,, 40.14 per

8

Wyoming Agricultural Experiment Station. Bui. 122

cent; A12O3, 31.48 per cent; FeL,O:!, o.n per cent; CaO, 10.09 per cent; 'Na2O, 14.13 per cent; Cl, 4.32 per cent. Figure 7 shows these crystals.

Fig. 7.

Dec.

Effect of Alkali Upon Portland Cement— II.

From the above results, it appears that the following re- actions took place in different solutions used :

Ca(OH)2 + MgSO4 + aq. -» CaSO4.2H2O + Mg(OH)2 + aq. ; Ca(OH)2 + Na2CO;t + aq. -» CaCO, + 2NaOH + aq.

The analysis of the calcium sulfate crystals gave the follow- ing, showing it to be CaSO4.2H,O : Water, 21.0% ; CaO, 32.5% ; SO,,, 46.3%.

PHYSICAL CHANGES.

The reaction of sodium and magnesium sulfates produced characteristic changes, which were especially apparent in the case of mortars. From the appearance of the mortar, it was possible

Fig. 9.

IO

Wyoming Agricultural Experiment Station. Bui. 122

to tell which of the salts had been acting. Figure 8 shows the cracks formed on a i 14 mortar which was immersed in a solution of sodium sulfate. Notice that every cu'be in the set has been affected in the same manner. In figure 9 is demonstrated the effect of a magnesium sulfate solution on T 14 mortar. The solu- tion of sodium sulfate and the solution of magnesium sulfate were of the same normality. Figure 10 also shows the effect of magnesium sulfate, but at a somewhat earlier stage than in figure 9. The little clumps of needles are crystals of calcium sulfate.

As the concentration of cement in the mortar increases, the cracks appear nearer the edges of the briquets and cubes and thin layers gradually fall off, as shown in figure n. In figure 12, from left to right is shown a cube as it looks when the first layer is nearly off, the thickness of the layer and the cube with first layer removed.

Cement which was immersed in o. 5 N. sulfuric acid showed

Fig. 10.

Dec. 1919 Effect of Alkali Upon Portland Cement — //.

i i

the same kind of results as cement in a solution of sodium sulfate. In this experiment the acid was renewed when it became neu- tralized. The effects of hydrochloric acid of the equivalent con-

12

Wyoming Agricultural Experiment Station. Bui. 122

centration of the sulfuric acid used were somewhat different.. In- stead of parallel cracks produced along the edges of cubes, as •in case of sulphuric acid, minute cracks in large numbers, were produced all over the surfaces. Figures 13 and 14 repr_esent_jhe results of the action of sulfuric and hydrochloric acid respec- tively.

Fij?. 13.

Dec. /p/p Effect of Alkali Upon Portland Cement — //.

Fig. 14.

Figure 15 shows the results produced by the following treat- ment : The cubes were covered with distilled water and warmed on a water-bath. The water was allowed to evaporate and the cement dried. Then it was covered with water again and the process repeated. After a sufficient length of time cracks were formed which extended from edge to edge. No cracks were formed on cubes which were treated in the same way, except that they were always covered with water. Consequently the cracking was due to alternate wetting and drying of the cement.

In order to test the alkali resisting quality of mortars with varying proportions of sand, mortars were made up containing as many as 10 parts of sand to one part of cement. Figure 16 shows a comparison between neat cement and mortars of different dilu- tions which were placed in a normal solution of sodium chloride and sodium sulfate.

14 Wyoming Agricultural Experiment Station. BuL 122

Dec. /p/p Effect of Alkali Upon Portland Cement — //. 15

Top row left to right: Neat cement in distilled water; neat cement which was heated on water bath and was periodically either covered with water, or dry ; the next ones are in order : neat cement ; i :i ; 1:2; 1:3; 1:4; 1:5; i :6, and i 7 mortars, all in a normal solution of normal sodium chloride and sodium sul- fate for a period of 6 months. Notice the characteristic cracking produced by sodium sulfate. All specimens, except the first and third show the effects of treatment. The neat cement in the solution looks as well as the neat cement in distilled water.

Fig. 17.

1 6 Wyoming Agricultural Experiment Station. Bui. 122

Figure 17 represents the effects produced in a normal solu- tion of magnesium chloride and magnesium sulfate. Except for the first cube on the left in the top row, which is neat cement in distilled water, the following cubes from left to right had composi- tions: neat cement; i :i ; 1:2; 1:3; 1:4; 1:5; 1:6; 1:7. Dur- ing the entire period of 6 months the specimens were not dis- turbed, but even then the i 7 mortar had crumbled away. Notice the bulging which is characteristic of the action of magnesium sulfate.

In figure 18 cubes 15, 17 and 19 are i :i, i :2 and i 13 mortars respectively, placed in a' normal solution of sodium chloride and sodium sulfate. Numbers 16, 18 and 20 have the same respective

Fig. 18.

composition as the ones above, but these were in a normal solu- tion of magnesium chloride and magnesium sulfate, for a period of 6 months. Notice how the cubes in the solution of magnesium salts have expanded and, judging from appearance, have disinte- grated more. Numbers i and 9 are neat cement in distilled water. All the above illustrations go to show that as the sand

Dec. 1919 Effect of Alkali Upon Portland Cement-^II. i?

content of the mortar increases, its resistance against the action of alkali decreases.

Of the different brands of cement only two were claimed to be alkali-resisting, the "Iron ore" cement, and the "Alkali-proof" cement. In regard to the first one, it was impossible to tell from the appearance whether or not it had been affected. The first five briquets and cubes in figure 19 were made of "alkali-proof" cement. It is apparent that a 5 per cent magnesium sulfate solu- tion (first) and a 5 per cent sodium carbonate solution (second) had some deteriorating effects. Briquet marked 59 was coated with Toch's No. 232 R. I. W. ; the next to the right was coated with Toch's No. 44 R. I. W. This coating was almost gone after 24 months, after which the above picture was taken.

Fig. 19.

CHANGES IN STRENGTH OF NEAT CEMENT AND MORTARS.

The tables on the following pages set forth clearly some of the results obtained in the cement investigational work. Addi- tional detailed data may be found in Wyoming Bulletin 113.

1 8 Wyoming Agricultural Experiment Station. Bui. 122

TABLE I — Showing the Average Strength of Cement Blocks Before

14

SOLUTION

Neat Ideal in various solutions:

(1) In distilled water for comparison.

Distilled water

(2) In solutions of jingle salts.

(a) 7 days in water before immersion.

Sol. 1, NaCl, 5 per cent

Sol. 2, MgSO4, 5 per cent

Sol. 3, Na2S04, 1 per cent

Sol. 4, Na2SO4, 5 per cent

Sol. 5, Na2S04, 10 per cent

NaOH 5 per cent

(b) 14 days in water before immersion.

Sol. 4, Na2SO4, 5 per cent

Sol. 1, NaCl, 5 per cent

Sol. 6, Na2COs, 5 per cent

Sol. 7, NaHCOs, 5 per cent

Sol. 8, NaCl, 7 per cent

(c) 14 days in water and 3 months in air before im>-

mersion.

Sol. 8, NaCl. 1 per cent

Sol. 6, Na2CO3, 5 per cent

(3) Neat Ideal in solutions of mixed salts.

(a) 7 days in water before immersion.

Sol. 11, CaClo, MgCl, 1.33 per cent each

Sol. 10, NaCl, Na2SO4, MgCl2, MgSOi, 1.25 per cent each -

(b) 3 months in water before immersion.

Sol. 10, (See No. 16)

(c) 48 hours in damp oven before immersion.

Sol. 10, NaCl, Na2SO4, MgCl2, MgSO«, 1.25 per cent each

(4) Neat Ideal to show effects of titn>tion.

In water. Titrated with H2SO4*

Sol. 14 NaCl, Na2SO4, 2.5 per cent each. Titrated

weeklyt

In water. Titrated dailyj

Sol. 4, Na2SO4, 5 per cent. Titrated weekly§

Before immersion

Com- press

Ibs. 7826

6745

7939 8827 7708 8031 5802

10815 8950 9663 9453

11700

5791 10467

5723 8552 7090

4035

7162 4760 6174

Ten- sion

Ibs. 494

284 664 455 588 688 594

525 662 423 437

774 712

400 337 455

340 32«

261

387 276

Dec. 1919 Effect of Alkali Upon Portland Cement — //. 19

and After Being in Salt Solutions for Various Periods.

After being in solution:

12 months	24 months	30 months	40 months	84 months
Com- press	Ten- sion	Com- press	Ten- sion	Com- press	Ten- sion	Com- press	Ten- sion	Com- press	Ten- sion
Ibs.	Ibs.	Ibs.	Jbs.	Ibs.	Ibs.	Ibs.	Ibs.	Ibs. Ibs.
7145	716	9560	7-15	10907	677	9877	678	16970	252
9675 11615 10687 8457 11577 8685	994 482 400 644 660 905	10185 11310 10712 7045 11597 9965	1017 289 -,03 716 409 920	10452 10030 10282 6482 11265 8515	910 651 725 701 280 920	7527 8073 9047 6523 11460 7383	747 612 698 632 377 768	13057 9472 11742 8525 13887 16107	197 202 231 297 350
9342 8597 10660 8942 9922	669 5500 905 10295 830 10327 847 8882 779 11390	297 j-46 717 757 948	4415 8030 9907 9750 10217	655 762 720 729 892	5050 10393 12270 9503	455 "685 712 793	4325 "15375 " 10632 16017	305 629 " 220
8740 11540	619 701	9215	;49	8505 11235	640 672	7950 10833	593	11052 10732	231 332
7837 11167 10355	336 802 916	8860 8300 . 7680	844 849 794	7960 8120 8085	797 745 807	8703 7850 7553	672 773 860	10147	282 120 34
5252
10440	297	9880	1105	7325	1131	7920	1175	10100	211
9622	726	10165	P67	10650	679	10640	255
12570 10240 10522	581 475 902	11330 10565 9885	876 836 804	10827 12100 9287	720 821 860	10020 10607 9660	980 805 740	13380 16600	371 214

2O

Wyoming Agricultural Experiment Station. Bui 122

TABLE II — Showing Change of Strength of Cement Blocks During a Period

Same Cement at the

		1
d S3	SOLUTION	1	2 months
js M «.		Comp.	Tens'n	Ave.	Comp.
	I. Neat Ideal in various solutions:	%	%	%	%
	(1) In distilled water for cu-mparisou.
15	Distilled water	—8.7	+44.8	+18.0	+35.1
	(2) In solutions of jingle salts.
	(a) 7 days ?n water before immersion.
1	Sol. 1, NaCl, 5 per cent	+43.4	+250 0	+146 7	+5 2
2	Sol. 2, MgSO4, 5 per cent	+46.3	-27 is	+9^2	—2.' 6
3	Sol. 3, Na2SO4, 1 per cent	+21.0	—12.0	+5.5	+0.2
4	Sol. 4, .Na2SO4, 5 per cent	+9.7	+9.5	+9.6	—16.6
5	Sol. 5, Na2S04, 10 per cent	+44.1	—4.0	+20.0	+0.2
3S	5 per cent NaOH	+49.6	+52.3	+50.9	+14. 7
	(b) 14 days in water before immersion.
6	Sol. 4, Na2SO4, 5 per cent	—13.6	+4.8	—4.4	—41.1
7	Sol. 1, NaCl, 5 per cent	—3.9	+72.3	+34 2	+19 7
8	Sol. 6, Na2CO3	+10.3	+25.3	+17.8	— 3J
9	Sol. 7, '\7aHCO3, 5 per cent	—5.4	+100.2	+47.4	—0.6
12	Sol. 8, NaCl, 1 per cent	—15.1	+78.2	+31.5	+14.7
	(c) 14 days in water and 3 months in air
	before immersion.
10	Sol. 8, NaCl, 1 per cent	+50.9	—20.0	+15.4'	+5.4
11	Sol. 6, NTa2CO3, 5 per cent ;	+20.2	—1.5	+9.3
	(3) Neat Ideal in solutions of mixed salts.
	(a) 7 days in water before immersion.
17	Sol. 11, CaCl2, Mg€l2, NaCl, 1.33 per
	cent each	+36.9	—16.0	+10.4	+13.0
10	Sol. 10, NaCl, Na2S04, MgCI2,
	MgSO4, 1.25 per cent earn	+30.5	-j-137.9	+84.2	-25.6
	(b) 3 months in water before immersion.
11	Sol. 10, NaCl, Na2S04, MgCl2,
	M?;S04, 1.25 per cent each .'	+46.5	+101.3	+73.9	—25.7
	(c) 48 hours in damp oven before im-
	mersion.
33	Sol. 10, NaCl, Na2S04. MgCl2,
	M2rSO4, 1.25 per cent each	4-158.7	—12.3	+73.2	—5.3
	(4) Neat Ideal to show effects of titration.
37	In water. Titrated with H2SO4*	+81.9	+133.7	+107.8	+5.6
43	Sol. 14, NaCl, Na«S04, 2.5 per cent each.
	Titrated weeklyf	+74 6	+122 3	+98 4	- -9 4
39	In water. Titrated dailyj	+115J	+22^7	+68.9	+s!i
15	Sol. 4, Na2S04, 5 per cent. Titrated
	weekly§ .	+70.3	+226.8	+148.5	—6.0

*Titrated daily; water changed weekly. t Water not changed.

tWater changed after each test for strength. iWater changed after each test for strength.

Dec. /p/p Effect of Alkali Upon Portland Cement — //.

21

in Salt Solutions Expressed as Per Cent, Computed on the Strength of the Last Preceding Test.

After being in solution:

24 mon Tens'n	ths	30 months	40 months	84 months
Ave.	Comp.	Tpns'n	Ave.	Comp.	Tens'n	Ave.	Comp.	Tens'n.	Are.
% +4.0	+19.5	+14.1	—9.1	+2.4	—20.2	+0.1	—10.0	+71.6	—62.8	+4.4
+2.3 —40.0 +101.0 +11.1 —38.0 +1.5	+3.7 —21.3 +50.6 —2.7 —18.9 +8.1	+2.6 —11.2 —4.0 —7.9 —2.8 -4.5	—10.5 +125.2 —10.0 —2.0 —31.5 0	—3.9 +57.0 —7.0 —4.9 —17.1 —2.2	—27.9 —19.5 —11.9 -J-0.6 —7.1 -15.3	—16.8 —5.9 —3.7 —9.8 +34.6 —16.5	—22.3 —20.9 —7.8 —4.6 +13.7 —15.9	+73.4 +17.2 +29.7 +30.6 +21.1 -118.1	—73.8 —66.9 —66.9 —53.0 —7.1	—0.1 —29.8 —18.6 —11.2 +7.0
—55.6 —6.5 —13.6 —10.6 +21.6	—48.3 —19.7 +6.6li —22.0 —8.3 || —4.0 —5.6 +9.7 +18.6 —10.2 I	+123.9 —9.9 +0.4 —3.7 —5.9	+52.1 —15.8 —1.8 +3.0 —8.0	+14.3	—30.5	—8.1	—14.3	—33.6	—33.6
+4.9 +25.8 —6.9	—4.8 —2.3 —11.1	0 +11.7 —9.0	+47.3 —13.3 +68.5	—72 '.2	•™— —1.8
+21.0	+13.2	-7.7 —2.6	—14.5 —4.1	—11.1 —3.3	—6.5 —5.3	—7.3 —18.1	—6.9 —11.7	+39.2 +5.9	—61.0 —31.6	—0.9 —18.3
+151.1	+82.0	—10.0	—5.5	—11.8	+8.5	—15.6	—3.5	+20.0	—58.0	—19.0
—5.8	—9.9	—2.1	—12.2	—7.7	—3.3	+3.7	+0.2		—84.4
—13.3	—19.5	+5.2	•H.i	+3.4	—6.5	+6.5	0	—23.4	—18.0	—36.3
+272.0 —12.4 +.50.7 +76.0 —10.8	+133.3 —3.9 +20.6 +34.5 —8.4	—5.6 +4.7 —4.4 +14.4 —6.0	+2.3 +1.7 —17.8 —1.7 +6.9	—1.6 +3.2 —11.1 +6.3 +0.4	+8.1 —0.1 —7.4 —12.3 +4.0	+3.9 —62.4 +22.2 —1.9 —13.9	+6.0 —31.2 +7.4 —7.1 —4.9	+27.5	—82.0	—27.2
+33.5 +56.5 &L'	—62.1 —73.4	— w'.s —8.4

22

Wyoming Agricultural Experiment Station. Bui. 122

TABLE III — Showing the Strength of Cement Blocks Before and After

of Cement Blocks in Water

Lab No.	SOLUTION	Before Immersion	12
d .U	Tension	Average	d S 0 O
15 1 2 3 4 5 38 6 7 8 9 12 10 11 17 16 14 33 37 43 39 45	I. Neat Ideal in various solutions: (1) In distilled water for comparison. Neat Ideal. In distilled water (2) In solutions of single salts, (a) 7 days in water before immersion. Sol. 1, NaCl, 5 per cent	% 100 86.1 101.4 112.7 98.4 102.6 74.1 138.1 114.2 123.5 120.8 149.5 74*0 133.7 73.1 109.3 90.6 51.6 65.0 91.5 68.2 78.8	% 100 57.4 134.4 92.1 119.0 139.2 120.2 129.1 106.3 134.0 85.6 95.7 156.7 144.1 81.0 68.2 92.1 68.8 66.0 52.8 78.3 55.8	% 100 71.7 117.9 102.4 108.7 120.9 97.1 133.6 110.2 128.8 108.2 122.6 115.3 138.9 77.0 88.7 91.3 60.2 65.5 72.1 73.2 67.3	% 100 135.4 162.5 149.5 118.0 162.2 121.5 130.7 120.3 149.2 125.4 138.8 122.3 161.5 109.6 156.1 144.9 146.1 134.6 175.0 143.3 147.1
Sol 2, MgSO4, 5 per cent
Sol. 3, Na2SO4, 1 per cent Sol 4 Na2SO4 5 per cent
Sol. 5, Na2SO4, 10 per cent 5 per cent NaOH
(b) 14 days in water before immersion. Sol. 4, Na2SO4, 5 per cent Sol 1, NaCl, 5 per cent
Sol. 6, Na->CO3, 5 per cent Sol. 7, NaHCO3, 5 per cent
Sol 8 NaCl 1 per cent
(c) 14 days in water and 3 months in air before immersion. Sol. 8, NaCl, 1 per cent Sol. 6, Na2CO3, 1 per cent (3) Neat Ideal in solutions of mixed salts, (a) 7 days in water before immersion. Sol. 11, CaCl2, MgCl2, NaCl, 1.33 per cent each Sol. 10, NaCl, Na2S04, MgCl2, MgSO4, 1.25 per cent each
(b) 3 months in water before immersion. Sol. 10, NaCl, Na2S04, MgCl2, MgSO4, 1.25 per cent each
(c) 48 hours in damp oven before immersion. Sol. 10, NaCl, Na2SO4, MgCl2, MgSO4, 1.25 per cent each (4) Neat Ideal to show effects of titration. In water. Titrated daily with HoSO4* Sol. 14, NaCl, Na2SO4, 2.5 per cent each. Titrated weeklv with H2SO4f
In water. Titrated daily with H2SO4J Sol. 4, Na2SO4, 5 per cent. Titrated weekly with H2S04t

*Water changed weekly. tSolution not changed. $Water changed after each test for strength.

Dec. 1919 Effect of Alkali Upon Portland Cement — //.

Given Periods in Salt Solutions Expressed as Per Cent of the Strength for a Similar Length of Time.

After being in solution:

month 1 z d	s	24 months	30 months	40 months	84 months
a £ 0	jt 1	\\	a £ 0	a o 1	1 i	a £ o	3 5	I	a I	o a d 9 EH	tt C3
— :		°	"£	~			—
100	100	100 100	100	100	100	100	100	100	100	100	too	100
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Dec. 1919 Effect of Alkali Upon Portland Cement— II. 29

DISCUSSION OF THE DATA.

The chief reacting substance in the cement is lime, in the form of calcium hydroxide. It may be formed either from the hydration of the calcium oxide present in the clinker, or may be formed during the setting of cement. With the sulfate salts of sodium and magnesium it forms calcium sulfate, CaSO4.2H2O, and sodium hydroxide with the former and magnesium hydroxide with the latter. The ratio of the molecular volume of calcium sulfate formed in the reaction to the molecular volume of calcium hydroxide is as 1.98:1. The sodium hydroxide formed in re- action with sodium sulfate remains in solution. In the case of magnesium sulfate, the ratio of the molecular volume of calcium sulphate, plus the magnesium hydroxide formed in the reaction to the molecular volume of calcium hydroxide originally in the cement is as 2.78:1. In Bulletin 81 of Montana Experiment Sta- tion, the disintegration of cement is ascribed as being due to this formation of compounds with larger molecular volumes, causing expansion and consequent cracking. Another theory, similar to the above, is held by several experimenters. According to this theory, tricalcium-aluminium sulfate is formed, and this then causes the expansion and disintegration of cement. In Tech- nologic Paper No. 12 of the Bureau of Standards, by Messrs. Bates, Phillips, and Wig, data is produced to disprove this theory.

Turning to the data given in tables i and 2, based on an 84 month period of action, we find that the changes in com- pression strength and changes in tension strength do not always go parallel ; one may increase while the other may decrease, and vice versa. The 5% solution of sodium sulfate affected the compression strength more than any other solution of one salt only, cement thus treated having only 25.4% of the com- pression strength of cement in distilled water for the same length of time. The next lowest compression strength was shown by cement in following solutions: Magnesium sulfate (557%)> sodium bicarbonate (62.6%), sodium chloride (76.8%), and sodium carbonate (90.5%). The solution of sodium sulfate was used in 3 different concentrations: i%, 5% and 10%, and the compression strength of cement kept in these solutions was 69.1%,

30 Wyoming Agricultural Experiment Station. Bui. 122

$0.2% and 81.8% respectively at the end of 84 months. It also appears that cement which has been in ordinary or distilled water for a longer period was affected more strongly, thus cement 14 days in water before immersion in a 5% solution of sodium sul- fate only had a compression strength equal to 25.4%.

It is a noticeable fact that the compression strength after 84 months is rather high in most cases, but that the tension strength is low, even for cement which was kept in distilled wrater. On the average, it is only 50 per cent of the tension strength which the cement had before immersion. This difference between com- pression and tension strength becomes more noticeable when considering the effects of solutions which contained more than one salt. In the case of solution No. 10, which contained the sulfates and chlorides of sodium and magnesium, when the ten- sion strength of cement, which was in water 14 days and 3 months before immersion in solution, was only 120 and 34 Ibs. respective- ly. The tension strength of cement which was only 48 hours in a damp oven before immersion in solution No. 10 at the end of 84 months still was 211 Ibs., thus showing again that younger cement is less affected.

The compression and tension strength of cement in different sets recorded in the table was not the same for all sets before immersion in solutions. Regardless of what the strength was before immersion, in all cases the maximum was reached some- time during the experiment, and this maximum is very nearly the same. In every case recorded, even in the case of cement which was in water 3 months previous to immersion in a solution, the compression as well as the tension strength always increased after the immersion in a solution until the maximum was reached. If the formation of molecules which have larger volumes than the original compounds of set cement is the cause of the disintegration of cement, then this would be more pronounced soon after im- mersion, for then the formation of CaSO.4.2H2O would be faster than it would be later. Consequently, the decrease of strength should be most noticeable during the reaction. The tacts do not show this to be true. The progress of the formation of hydrated calcium sulfate from lime and sodium sulfate can be followed by determining the amount of sodium hydroxide formed in the re-

Dec. 1919 Effect of Alkali Upon Portland Cement — //. 31

action. This was done by titrating the solution to neutral with sulfuric acid. The procedure was carried on until no more sodium hydroxide was formed, which was after 24 months. At this time the cement should be the weakest. Figure 20 represents graphically the change of compression strength and the amount of acid required to neutralize the sodium hydroxide formed, the neutralizing being done every day. Instead of the expected de- crease of strength during this reaction, there was an increase.

Fig. 20.

Besides, the cement in magnesium sulfate solution should have a lower strength than cement in sodium sulfate solution. The results show that this is not the case. This does not mean that the formation of reaction products, which have larger molecular volumes than the reagents in the cement, does not contribute towards disintegration. But it is not the chief cause or the only cause of disintegration.

In tables 6, 7 and 8 are given the strength values of cement kept in solution at the temperature of boiling water. The results

32 Wyoming Agricultural Experiment Station. Bui. 122

after a period of 18 months are characteristic. The set which was completely disintegrated is the one which was in a solution of magnesium chloride, while the cement in a solution of magnesium sulfate had an average compression strength of 9775 Ibs., and cement in a solution of sodium sulfate, 6122 Ibs. Noteworthy is the fact that cement kept in solution containing both magnesium chloride and sulfate still had a strength of 2365 Ibs., and cement in a solution containing magnesium sulfate and sodium chloride, 4797 Ibs. Evidently the solution of sodium chloride did not pro- duce any bad effect, since the strength of cement in it was 12735 Ibs., while the strength in hot distilled water was only 10922 Ibs. These results suggest the following questions: Why did mag- nesium chloride have the strongest disintegrating effect? Why did the solution of magnesium chloride containing also magnesium sulfate produce a slower decrease in strength than the solution containing magnesium chloride alone ? Why was the strength of cement kept in the solution of magnesium sulfate containing also sodium chloride 50 per cent less than the strength of cement in the solution of magnesium sulfate alone, although the solution of sodium chloride did not produce any bad effects ?

The answer to the first question is the fact that magnesium chloride in solution undergoes hydrolysis, the result of which is the formation of hydrochloric acid. It is then this hydrochloric acid which attacks the cement. The hydrolysis of magnesium chloride in solution goes on to a lesser extent when magnesium sulfate is also present in solution. For this reason the disinte- grating effect of a solution containing both salts is less severe for equal periods.

When magnesium sulfate and sodium chloride are dissolved together in water, the solution contains 4 salts instead of two. This may be expressed by the following equation: MgSO4+ 2Na€l*=$MgCl2+ Na,SO4. The magnesium chloride thus pro- duced hydrolizes and the result of this reaction is the formation of hydrochloric acid: MgCl2+H2O±?Mg(OH)2+HCl. As the dydrochloric acid reacts with the components of the cement, it is being removed, so to speak, and the result of this is that the above reactions gradually progress toward the right.

Dec. 1919 Effect of Alkali Upon Portland Cement — //. 33

Results analogous to those obtained in hot solutions were also obtained from experiments on mortars with various propor- tions of sand. Again, the magnesium chloride solution had the most rapid disintegrating effect and other solutions in the same order as above. But the results in this table show also that as the proportion of sand in the mortar increases the disintegration is hastened. The data in these tables are in agreement with con- clusions from figures 16, 17 and 18. Although for numbers 60, 61 and 62 the strength after 18 months in solution is higher than the strength which the mortars had before immersion, neverthe- less there is a decided decrease of strength after the maximum had been reached.

The data recorded in table 9 were meant to give a compari- son of the resistance to action of alkali by i :i mortars prepared with cements of different brands. The comparison of sets 22 and 23 is interesting. Apparently the presence of sodium car- bonate in the solution counteracted the disintegrating effect. No. 22 in a solution containing sodium carbonate, sulfate and chloride after 84 months had higher compression strength (11830 Ibs.) than the cement No. 60 in solution of sodium chloride and sulfate had, after 18 months (7612 Ibs). The same is also true for tensile strength. These results are graphically represented in figures 21 and 22 for compression and tension strength respec- tively.

The cements, of brands tried, do not show very much differ- ence in compression strength. The "Alkali-proof" cement had the lowest compression, below normal, while the others did not show any decrease. The tensile strength of all of them, although still higher than the tensile strength of cement in distilled water, show distinctly a decrease after the maximum had been reached. It is noteworthy that the cements which were made up with solutions of sulfuric acid of various concentrations and also kept in the above solution (containing sodium carbonate, sulfate and chlo- ride) had normal compression strength, but the tensile strength also had decreased during the last period. The cement which w^s mixed with a solution containing one per cent of sulfuric acid and di-sodium-hydrogen phosphate, at the end of 84 months in the above solution had normal compression strength and the

34

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Effect of Alkali Upon Portland CYimW— //. 35

a solution was used for mixing which contained an organic sub- stance, a distinctly inferior cement was obtained. The results with the " Alkali-proof" cement are represented in table 10. It is evi- dent that its tensile strength suffered greatly after the maximum had been reached, regardless of what the solution was. Here, too, a comparison between the results in this table and No. 51 in table 9 distinctly show that the solution which contained sodium car-

.ie was less harmful.

For testing out the value as surface protectors against the action of alkali of different commercial paints recommended as waterproofers, t :^ mortar was covered with them. The mortar of each set received 2 coatings of some one paint. After 24 months in a solution of sodium carfaonate-sul fate-chloride the paints were off. Tint the paints after that did no* offer resist- ance to penetration of solutions is shown by the marked dyf^my of tensile strength during the last period of 60 months. Although ico C paint was off after 12 months, some of the "yfl^K of the paint must have had a beneficial effect as ptoteclofs, since in this even the tensile strength did not decrease liming the las* period of 50 months.

In actual practice cement fuequently is only periodically ex- posed to the action of alkali. This change of conditions from wet and dry itself has a deteriorating effect on the cement. in set Ho. ?i the cement was periodically wet and dry and the result was that its compression strength was 2$% less than that off cement which was under water constantly. Ttae solvent effect of large volumes of water also conies in pb\\ as seen Iran No, 72, This cement was trailed with 3 liters of *i^ distilled water even? day daring a period of i& months and the result is uhat its com- pression strength at the end of tthiis period was 3*-$% less than the compression strength of cement which was undtef the conditbr- >i nhat the water never was cliinffji. In

the dismtegration of cement is Kne result of aH the causes combined, and besides it is aocetetmled % fimjung and

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36 Wyoming Agricultural Experiment Station. Bui. 122

until a maximum is reached. During this period the reaction between the salts and the calcium hydroxide takes place and if any bad effects are produced from these reactions, they are not marked by a decrease in the strength of the cement. The cause of this may be that the increase in strength during this period is greater than the decrease. The calcium sulfate or calcium car- bonate, as the case may be, increases the density of cement and makes it less pervious to the solutions. Besides, the calcium sul- fate has a binding value, which may reach 200-300 Ibs. This was tried out on halves of a broken briquet ; they were cemented to- gether and it took that much force to full them apart. When the compounds of the cement other than the calcium hydroxide are attacked, then the decrease of strength begins to show. As the table of analyses shows, the extent of chemical changes is com- paratively small. What the changes may be can to some extent be judged from the analysis of the crystals shown in figure 7. The effect of magnesium chloride is more marked than the effect of the other salts because the hydrochloric acid formed due to hydrolysis reacts with the fundamental compounds of cement. In the case of chlorides, the calcium chloride formed is removed from the cement, while in the case of sulfates, the calcium sulfate is deposited. The experiments with equivalent solutions of hydro- chloric and sulfuric acids show that the former is more harmful. After 6 months the strength of cement in hydrochloric acid de- creased 22%, in sulphuric acid only 16%. The difference may be due to the fact that the calcium sulfate formed makes the cement less permeable. That the mortars are more rapidly de- stroyed than the neat cement is to be expected. For the same jweight, they contain less of the reacting material, but expose as much surface to the action of solutions as neat cement. Conse- quently, a greater proportion of their cement content has been jreached in shorter time. The effects from the reactions are augmented by the dissolving action which increases the porosity of cement, by the friction of particles carried in suspension, by the wearing away of the weakened surface layers, thus exposing deeper layers of cement, and, finally, by the formation of cracks due to uneven expansion and contraction, through which the solu- tion also penetrates deeper into the cement. Any process which

Dec. ip/p Effect of Alkali Upon Portland Cement — //. 37

will make the cement less porous and less permeable to the solu4 tions will also increase its resistance to the action of alkali. In this connection, attention may be called to the behavior of cement which was not mixed with water but with solutions containing ions forming insoluble calcium salts. Results with oxalic acid (5%) used for mixing the cement and which, after setting, was put in a hot solution of N. sodium sulfate and N. sodium chlo- ride were as follows : Compression strength before immersion, 8502 ; after 6 months in solution, 10742 ; after 12 months, 10280, and after 18 months, 13685 Ibs. Cement mixed with a solution of magnesium flouride had a compression strength before immersion 6087 Ibs ; after 6 months in the above sodium-chloride-sulfate solution, 9499 Ibs., and after 18 months, 15580. Since these sub- sta'nces and also the sodium phosphate and sulfuric acid are not very expensive, their solutions could be used in cement practice.

The results with a hot saturated calcium sulfate solution are not recorded in the tables. The compression strength of cement varied as follows: Before immersion, 7240; after 6 months, 9452; 12 months, 8745 ; 18 months, 11710.

Evidently the calcium sulfate solution did not have any bad effect upon the strength of cement.

38 Wyoming Agricultural Experiment Station. Bui. 122

SUMMARY

Cement put in solutions of salts which constitute the "alkali" sets as well as in water.

In solutions of sodium sulfate, or magnesium sulfate CaSO4. 2H.,O is formed and NaOH and Mg(OH)a respectively.

A solution of magnesium chloride had the greatest disinte- grating effect, due to the action of hydrochloric acid produced by the hydrolysis of this salt.

A sodium sulfate solution was more harmful than a solution of magnesium sulfate, other conditions being equal.

The presence of sodium chloride in solutions of sulfates of sodium and magnesium increased their harmful effect on cement.

A five per cent solution of sodium sulfate had a stronger effect than either the i per cent or 10 per cent solutions.

The presence of sodium carbonate in solutions of the other salts retards the disintegrating effects.

Compression strength and tensile strength are not affected in the same degree ; tensile strength decreases more rapidly in all solutions, even when compression strength increases.

Solutions of calcium sulfate had no bad effects

Water-proofing paints offer protection only for short periods

The "iron-ore" cement resisted the action of sodium car- bonate-sulfate-chloride solution ; the other cements tried had somewhat lower tensile strength.

The mixing of cement in weak solutions of sulfuric acid, di-sodium phosphate, magnesium flouride and oxalic acid is of ad- vantage and increases the alkali resisting qualities.

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