JULY 15, 1936
ANALYTICAL EDITION
The experiments outlined in Table IV again indicate the quality of the results obtained with the improved method in the experimental room. However, experiments carried out in such a test room can yield good results only if (1) the atmosphere ii3 uniformly mixed, (2) the test room is sufficiently tight so that there will be no appreciable flow of atmosphere from the test room to the outside, or vice versa, during the course of the test, and (3) the surface of the interior of the test room does not react with any constituent of the atmosphere tto be tested. The experiments can become highly unsatisfactory if any of these conditions is not fully satisfied. The thermal decomposition method with the slight modifications given accounts for a t least 97.3 per cent of carbon tetrachloride vapor present in air, down to a concentration of 10 p. p. m., and probably lower. Since absorption in distilled water will give recoveries of almost this degree, the method is suitable for development of continuous automatic indicating equipment based on electrical conductivity. It is believed that the chemical method described, as well as the
263
electrical method suggested, is generally applicable to the quantitative determination of vaporized halogenated hydrocarbons other than carbon tetrachloride in air. It is planned to conduct further tests in this field in order to confirm this conclusion.
Literature Cited (1) Am. Pub. Health Assoc., “Standard Methods for the Examination of Water and Sewage,” 7th ed., New York, 1933. (2) Fieldner, A. C., Katz, S. H., Kinney, S. P., and Longfellow, E. S., J . Franklin Inst., 190, 543 (1920). (3) Nuckolls, A. H., Underwriters’ Laboratories’ Report, Miscellaneous Hazard No. 2375 (November 13, 1933). (4) Palmer, P. E., and Weaver, E. R., BUT.Standards Tech. Papers 249 (1924). (5) Robbins, B. H., J. Pharmacol., 37, 212 (1931). (6) Robbins, B. H., and Lamson, P. D., J. Pharmacol., Proc., 31, 220 (1927). (7) Smyth, H. F., Jr., J.I d . Hug., 9, 338 (1929). RECEIVED March 31. 1936
Determining the Resistance of Portland Cement to Sulfate Waters An Accelerated Test R. W. STENZEL, Metropolitan Water District of Southern California, Banning, Calif.
is e c o n o m i c a l l y feasible. A The present active interest in the manunumber of specifications have years many investigations facture of Portland cements which will prorecently been written with a rehave been made On the resistduce concretes highly resistant to the acstriction of this nature, notably ance of Portland cement conthose of t h e M e t r o p o l i t a n crete to corrosive salt waters. tion of natural waters has created a need for The conclusions regarding the a reliable but short-time laboratory test to Water District of Southern California @), and of the Bureau actively c o r r o s i v e constituent determine this resistance. The slab-warpof R e c l a m a t i o n (S), and the therein have almost ing test herein proposed is believed to give a r e s u l t s of t e s t s have shown been that the sulfate ion is reliable indication of the probable resistthat this procedure has been primarily responsible for the reactioru leading to the evenance of the cement to sulfate-bearing r e a s o n a b 1y we 11 justified. tual disintegration of the conwaters, and compares favorably with longNevertheless, it is not to be presumed that a similar sulfateCrete. It is likewise now genertime tests of concrete cylinders made from resis tance-compound-composiagreed that even the most the same cement. It has the merit of bedense p r a c t i c a1 combinations tion r e l a t i o n s h i p will necesing completed within 28 days, so that it is of aggregates and cement will sarily hold for other geographical not resist the corrosive suitable for acceptance test purposes. areas where the raw materials action ofhighly sulfated natural and m a n u f a c t u r i n g practice waters. It is only by the use of a cement which does not mav be somewhat different. Therefore it is desirable to have a reliable short-time test which will directly measure the readily react with sulfates that long life of an exposed consulfate-resistance of a cement and whose results will be crete structure is to be expected. The preponderance of experimental evidence indicates that, available by the time the usual 28-day strength tests are completed. One such test has been incorporated in the speciif the cement is made under conditions obtaining in the best fications (7) for the Fort Peck Dam, Montana, but no data modern practice of manufacture, its resistance to sulfate regarding the results of its use and comparison with actual action can be reasonably well deduced from its chemical concrete tests have been published. composition. The method is to compute the hypothetical The slab-warping test which is here described has been compound composition from the results of the usual chemical applied to Portland cements having a wide variation in analysk;, as proposed by Bogue ( I ) , and then from the perchemical composition, and has been found to give a good centage of the sulfate-sensitive compounds to estimate its correlation with long-time compressive strengths of the corprobable resistance. The tricalcium aluminate is widely regarded as the source of all evil in the family of cement responding mortar and concrete cylinders. Since it is fundamentally an expansion test, it must be used with caution compounds in most of those properties which tend to make on cements other than the Portland variety, such as cements concrete less durable, and indeed its properties-i. e., those with pozzuolanic admixtures, and it is not applicable to highof the pure compound-fully warrant these suspicions. Therefore the present practice in consumer specifications, when a alumina cements in which sulfate disintegration may proceed high Bulfate-resistance is desired, is to specify a composition without external volume changes. The test consists in casting a neat-cement specimen 5 x which will make the percentage of this compound as low as
D
U R I N G t h e p a s t few
VOL. 8, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
264
FIGURE1. APPARATUS ENSEMBLEFOR MOLDINGCEMENT SLABS
with wet cloths to prevent any water's dripping upon the surface. After storage for 16 to 20 hours, the rubber gasket is removed and the specimens are carefully scraped with a stiff steel spatula until their surfaces are level with that of the brass mold. The last few scrapings should be done with special care to avoid any gouging or other impairment of the surface, and are usually best done by drawing the spatula in a vertical position toward the operator. There should be no pressure of the flat part of the blade against the surface, such manipulation having the effect of glazing it and therefore introducing a possible variation. Immediately after scraping, the mold and slabs are placed in a covered pan of fresh distilled water and allowed to cure in this way for 3 days. At the end of that period the mold is stripped from the slabs, which are replaced in the water. On the seventh day the slabs are removed, and the bottom surface (unscraped surface) and sides are quickly dried with a towel and then painted with a coat of adherent waterproof Daint, such as Goodrich acid seal primer No. 8. The top sk-facemust never be allowed to become drv and the Drocess should be carried out as expeldii,iously as possibfe. The dabs are then placed face down upon a wet cloth in the moist room (protected from water spray) for about 2 hours. Any moisture is then quickly wiped from the painted side and a brush coat of hot beeswax and paraffin (50-50) is applied. They are replaced in the pan of water for a t least 15 minutes, then removed and marked with the template to define the position of the spherometer legs. The initial spherometer reading is then taken and recorded, and the slabs are placed in a 10 per cent sodium sulfate solution (100 grams of anhydrous salt per liter of water). Subsequent readings may be taken a t periods of 3,7, 13, 17, and 21 days after immersion, but the 7-day and 21-day readings a t least must be obtained.
11.25 X 0.32 cm. (2 X 4.5 X 0.125 inch) from a sample of the cement to be tested, using a water-cement ratio of 0.40 for m o s t c e m e n t s . After the cement has obtained its final set, the top surface is scraped and the specimen immersed in water for 7 days. It is then coated with an impervious material on the bottom, and immersed in a 10 per cent solution of sodium sulfate. Because of attack (and therefore expansion) on only one face, the specimen will tend t o warp, the extent of the warping beFIGURE2. SPHEROMETER FOR MEASURING SLABWARPING ing used as an indication of the extent of the attack. Figure 1 shows the apparatus used in preparing the specimens, consisting principally of a gang brass mold, a rubber gasket for increasing the depth of the specimens, a mixing cup, and a spherometer. Figure 2 shows in more detail the spherometer used for measuring the extent of the warping in the slabs.
The susceptibility of the cement to attack by sulfate solution is indicated by the difference in the spherometer readings between the 21-day and the 7-day period. With each group of slabs there should be made a control slab of a cement whose warping curve has been well established. If the
Procedure The brass mold is first prepared by coating it with a thin layer of oil, such as a mixture of paraffin and motor oil, to prevent adhesion of the specimen to the form, and the rubber gasket is cemented on the mold with rubber cement. For each slab to be prepared, 100 grams of cement are weighed out and mixed with distilled water (from a pipet) to give the required water-cement ratio. This ratio is standardized at 0.40 by weight for a cement having a normal consistency of 22.5 per cent. If the normal consistency of the cement to be tested is greater or less than this by more than one unit, then for each unit greater than 23.5 or less than 21.5 the water-cement ratio is increased or decreased by 0.005 unit, respectively. The water and cement, which should be within 5' of 21' C. (70" F.), are mixed preferably in a round-bottomed cup which has an opening in the bottom-from which the cement paste may be drawn while it is still being stirred. The stirring should be done in such a manner that no air is incorporated during the process, and should have a duration of about 2 minutes after initial mixing. At the end of this time, if the mixture is entirely homogeneous, the paste is allowed to flow into the mold, the stirring being continued until the form has been filled to the to of the rubber gasket. The paste is spread evenly in the form wit! a spatula, using a slight tapping on the bottom to facilitate escape of any entrained air bubbles. Any excess paste is struck from the surface with the spatula, and the adjacent form is then filled in a similar manner with the next mixture. Unless these operations are performed in a moist room, they should be done as rapidly as possible to avoid any evaporation during the process. As soon as the preparation of the specimen is completed, the mold is placed in a moist room a t 21" C. (70' F.) and protected
i
io
M
PERIOD OF IMMERSION-
d
4b
DAYS
FIGURE3. EFFECTOF WATER-CEMENT RATIO ON WARPING OF NEAT-CEMENT SLABS (D68cement)
readings on this slab are out of line with its predetermined values, a faulty technic may be suspected and the test should be repeated. The test is of course essentially an index of the amount of expansion produced in the cement by the sulfate Bttack. From geometrical considerations it is easily seen that for
‘col 90-
Y 8
a 80-
E970-
0
265
ANALYTICAL EDITION
JULY :L5,1936
Y 40
io
-0
30
40
FIGURE4. WARPING OF SLABS IN 10 PERCENT SODIUM SULFATE SOLUTION
OR!lPD OF IMMERSION-DAYS FIGURE 5. WARPING OF SLABSIN 10 PER CENT SODIUM SULFATE SOLUTION
small values the deflection is about four times as great as the expansion in the top fibers, thus magnifying the expansion effect. The effect of the water-cement ratio on the degree of warping of the slabs is shown in Figure 3. The sensitivity of the test to this ratio is rather high, so that care must be exercised in the proportioning. Test results on various types of cement in 10 per cent sodium sulfate are shown graphically in Figures 4, 5, and 6. Figure ‘7 shows comparable specimens in magnesium sulfate. The curves, which have been drawn through the observed points and are in no way idealized, indicate that the warping is a regular, continuous process, at least until large cracks begin to appear. In order to obtain a numerical value from the curves, the difference between the 21-day and the 7-day readings has arbitrarily been chosen as the slab-warping index to indicate the relative resistance of the specimens to sulfate attack.
The chemical composition of the cements tested is shown in Table I, in which are also given the 7- to 21-day index and the compressive strength index of 7.5 X 15 cm. (3 X 6 inch) concrete cylinders made from the same cement, after 6 months’ exposure in 10 per cent sodium sulfate solution. This index is the per cent disintegration of the specimen measured by the ratio of the strength of the cylinders in the solution to those cured in a moist room for the same period, subtracted from unity. Thus 20 per cent disintegration indicates that the compressive strength of the sulfate-exposed cylinder is 80 per cent that of the corresponding moist cured specimen, at 6 months. In the case of the MWD specimens the slabs were not made from the same lot of cement, but from other lots from the same mill having a similar composition. The compounds are computed by the method of Bogue (I), no account being taken of any free lime present. The last two columns of Table I show that with the exception of the “blended” cement E, the slab-warping index is
“1
1 90
u,
I
/
3
3 80
3
70
p o P
$50
!40
k 330 @
%20
a
10 0
0
FIGURE 6. WARPING OF SLABS IN 10 PERCENT SODIUM SULFATE SOLUTION
10
20
PERIOD OF IMMERSION-
30
40
DAYS
FIGURE 7. WARPING OF SLABS IN 10 PERCENT MAGNESIUM SULFATESOLUTION
INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE I. DISINTEGRATION OF CONCRETES AND NEATCEMENTS IN 10 PERCENTSODIUMSULFATE SOLUTION Compressive Strength Index;
%
Cement NO.
Type
Cas
CIS
CsA CiAF
DisintegraSlab- tion Warp- at ing 'Six Index Months
Fineness Sq. om./
In./ 1000
8.
S A D68 46N B C 66D D 14s 51s E 50W 63 6W 9w 47W
Commercial Laboratory MWD specif. 68 MWD specif. 79 Laboratory Laborat ory MWD specif. 79 Laboratory MWD specif. 79 MWD specif. 79 Laboratoryblended MWD mecif. 79 Commefcial sulfate resistant MWD specif. 79 MWD sulfate resistant MWD sulfate resistant
49 53 51 37 60 54 52 40 46 51
23 23 22 32 15 23 21 34 26 21
10 12 10 6 8 9 6 8 6 6
7
48 32 29 26
8 8 18
1.3 11 13 14 13 14
17 16 15
1 00 100 100 92 46 52 100 33 21 50
11 11
0 7
20
20
18
2200
B with 20 per cent admixture
52
29
7
5
1860
60
13 36
2 6
16 5
I900 2000
39
46
4
5
2000
9 4 2
46
38
4
4
2000
1
46
2 0 ,
*'O 0
VOL. 8, NO, 4
nearly the same and are definitely in the same relative order, which indicates that, at least so far as this test is concerned, the influence of the positive ion is of minor consequence in comparison to the activity of the sulfate ion. The curve for a 10 per cent solution of sodium chloride in Figure 7 shows the negligible effectof this salt upon the highly sulfate-susceptible D68 cement. The degree of reproducibility of the test during the period of its use in this laboratory has been good. An indication of this is seen in the curve for cement D68 which appears in Figures 3 and 6, each of which represents a different slab made at different times, from the same sample of cement. The same is true for the curves of 9W in Figures 4 and 6, and for E in Figures 4 and 5. While the position of the curves on the ordinate scale sometimes varies from one test to another, the slopes themselves are usually constant, so that the warping index (which measures the slope) can be reasonably well reproduced. In this connection i t has been found that long storage (a year or more) of a cement sample causes it to show markedly lower attack than originally. No tests have been made with concretes to find whether the aged cement would behave similarly in such a specimen, so that caution must be exercised in making the test on other than fresh cements The test has also been applied to natural soils which were suspected as potentially corrosive to concrete structures. The method was to saturate the soil with water, adding a little excess, and to immerse the slabs in the resulting mud. A soil having a sodium sulfate content of 380 p. p. m. showed only a slight attack, while one having 5000 p. p. m. showed a warping index of 19, using the susceptible cement D68. There are, of course, many other applications in which the slab-wayping test might prove fruitful, such as a study of the corrosivity of natural waters, of the effects of other salts and salt concentrations, and of the temperature influence on rate of attack. I
OF SODIUM AND MAGNESIUM SULFATE TABLE 11. COMPARISON ACTION
Cement D68 46N 66D 519 50W 9w 47w
Warping Index In 10% I? 10% sodium sulfate magnesium sulfate 35 24 18 13 10
4
..
generally parallel to the compressive strength index, the displacements of 66D and 515 being due to the fact that cement from different lots of the same mill was used for these comparisons. It appears that cements with an index of 10 or less may be regarded as highly resistant to sulfate action, while those above 10 will be proportionately more susceptible. A survey of the properties given in Table I indicates that no one compound can be held to be solely responsible for a lack of sulfate-resistance of the cement. In agreement with the results of other investigators (2,4, 6), the sulfate-resistance is roughly inversely proportional to the tricalcium aluminate content, but it is evident that some of the other compounds and the fineness also exert an influence. It is interesting to note, for example, that cements 14s and 6W, which are similar except for percentage of the aluminoferrite compound, have considerably different sulfate-resistant characteristics, although the tricalcium aluminate content is the same for both. The higher tricalcium silicate contents also tend to make the cement less resistant and, as is to be expected, the coarser cements are somewhat inferior to the finer cements. More extended comparisons than these are, however, not warranted, since most of these cements were made in commercial milk, and a fine distinction in compound composition is an extrapolation to ideal equilibrium conditions which can hardly be expected to obtain in this case. Nevertheless, the general dependence of the cement resistance on chemical composition for products from several different sources tends to justify recent trends of specifying compound limits when sulfate-resistance is of primary consideration. Resistance of cements to solutions other than sodium sulfate is also of interest, and Figure 7 shows the curves for a 10 per cent solution of magnesium sulfate. Table I1 compares the warping index for the two solutions; the values are
Acknowledgment This work represents a portion of the results of investigations conducted by the Metropolitan Water District of Southern California in connection with the construction of the Colorado River Aqueduct. The laboratory a t Banning is under the direction of Lewis H. Tuthill, testing engineer, reporting in matters of investigation and research to Julian Hinds, assistant chief engineer. F. E. Weymouth is chief engineer and general manager. Acknowledgment is made to E. C. Reid and the laboratory staff at Banning for their generous cooperation.
Literature Cited Bogue, IND.ENB.CHEM., AnaI. Ed., 1, 192 (1929). Bogue, Lerch, and Taylor, IND.ENG.CHEM.,26,1049 (1934). Bureau of Reclamation, Xpecifications 648, All-American Canal Project, 1935. Gonnerman, Proc. Am. SOC.Testing Materials, 34, 244 (1934). Metropolitan Water District of Southern California, Specifications for Sulfate-Resistant Cement, 1935. Thorvaldson, Wolochow, and Vigfusson, Can. J. Research, 6, 485 (1932). U. S.Engineers Office, Specifications for Cement, Fort Peck Dam Project, 1934. RECEIVPJD April 15, 1936.
