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86-/ f ,, 6/ A 0 K A A A bl AKAAEMMM HAYK CCCP PROCEEDINGS of the ACADEMY of SCIENCES of the USSR !2 2 3'3 6 1956 IN ENGLISH TRANSLATION REACTION OF CALCIUM SIUCATES WITH SILICA IMRUO HH3ROTHF8MAL HARDanHU Yu. M. Butt et al PLEASE INDICATE RETENTION CONSULTANTS BUREAU, INC. RETAIN r YEARS 'T'rtJ/JSA/f-Tyo/J DISCARD *n tgtncy for the inierprtt .i RETURN TO LIBRARY ASARCO, Centrol Research Deportment ASARCO ALV 0005617 REACTION OF CALCIUM SILICATES WITH SILICA DURING HYDROTHERMAL HARDENING Yu. M. Butt, L. N. Rashkovich and S. G. Danilova (Presented by Academician P. A. Rebinder, October 15, 1955) One method of intensifying hardening of cement materials is autoclave treatment. During this treatment it is possible to add to the cement significant amounts of ground quartz sand without lowering the strength of the article. However, the reactions of sand with cement have been Insufficiently studied; therefore, selection of the optimum mineralogical composition of the cement and autoclaving regime for the preparation of articles of high strength cannot be satisfactorily made. TABLE 1 Results of the ChemicalAnalysis of the Raw Mixtures and the Autoclaved'Samples (in <7o) Samples with tricalcium silicate Samples with dicalclum silicate ( 6 -form) 8 tech, atm,, 8 hours 16 tech, atm., 8 hours 8 tech, atm., 8 hrs 16 tech, atm.,8 hrs. Content Content in auto- Content Content in auto Content in Content Content in of cry claved samples of cry clayed samples autoclaved stalline Free Free stalline Free Free IK samples silica in SiO, CaO silica SiO, CaO Free the raw mixture in the S raw -8j .1EPml;xture a aotn 2Vo SiO, eg ig ao 3 - o- &S. of cry autoclaved stalline samples silica in Free the raw SiO, mixture J--1 -GaO o 5.28 10.17 20.17 29.91 40.00 49.94 72.47 89.79 13,38 12,74 3.98 11.86 12.27 7.91 10.37 12.15 16.02 8.93 10.77 ;22.75 6.03 9,27 31.85 3.63 7.81 ,39.13 0.78 5.84 '58.23 5.0C .82.9 2.44 0 13.65 12.19 0 3,18 5.24 3.83 12.52 11.95 5.11 3.15 4,58 10.01 7.19 10.90 11.91 10.09 6.20 4.35 20.37 14.34 9.12 10.78 20.16 13.7C 5.06 29.71 20.60 3.81 8.8C 29.90 21.93 5.44 39.93 25.30 0.62 7.75 39.84 30.00 4.75 49.81 31.60 0.05 5.16 49.99 39.81 4.72 69.56 54.35 6.85 70.00 61.77 1.13 90.00 32.35 2.16 90.00 85.90 0.69 0 5.00 2.98 10.11 4.22 30.11 1(To7 39.82 26.43 49.63 39.31 6.92 6.36 7.49 7.28 6.86 5.84 In recent years, Kalousek [1, 2], by means of x-ray and thermal analysis, succeeded in identifying two new phases in hardened porland cement containing sand. According to his data, the first of these -- the ahydrate of dicalcium silicate -- decreases the strength of the articles, and the second -- a hydrosilicate with a basicity of 0.9 -- increases strength. Below are presented the results of an investigation of the reactions of crystalline silica with the basic minerals of portland cement clinkers, di- and tricalcium silicates. .1I ASARCO ALV 0005618 The calcium silicates (with Impurities of the order of 3 "7) used in the experiments were synthesized by means of repeated calcinations, and the finely ground quartz sand was treated, after grinding, with hydrochloric acid. The samples, 1.41 x 1.41 x 1,41 cm cubes, were prepared from soft paste. After a day in the molds, the samples were removed and placed in the autoclave where they were soaked for 8 hours at 8 or 16 technical atmospheres. The strength was determined 12 hours after the end of the soaking. The data are presented In Figure 1. kS/cM* Figure 1. Strength of samples of mixtures of calcium silicates with sand after hydrothermal treatment. 1) samples of 3CaO SiC^ with sand, soaked 8 hours at 8 technical atm.; 2) the same soaked 8 hours at 16 tech, atm.. 3) samples of 8 -2CaO SiOj with sand, soaked 8 hours at 8 tech, atm.; 4) the same soaked 8 hours at 16 tech. atm. Figure 2. Differential thermal analysis curves of samples of tricalcium silicate (C3S) and added sand. Samples soaked 8 hours at 16 technical atmospheres. The differential thermal analysis curves are presented in Figures 2 and 3. All curves were recorded at a constant rate of temperature rise (20* per minute). The endothermic effect at 450' corresponds to the ot-hydrate of dicalcium silicate; the exothermic effect at about 800' corresponds to the hydrosilicate with a basicity of 0.9 (according to the data of Kalousek). The endothermic effects at 550 and 575' relate, re spectively, to the dehydration of calcium hydroxide and a polymorphic transformation of quartz. On the basis of these data and the analytical data (Table 1), the mechanism of the reaction of clinker minerals -- silicates -- with sand during hydrothermal treatment is as follows. Tricalcium silicate. Hydration of pure tricalcium silicate (without added sand) at temperatures up to 200' always leads to the formation of the ct-hydrate of dicalcium silicate [3, 4], In samples with sand, the coexistance of the following compounds (besides unreacted sand) Is possible; undecomposed tricalclum silicate, calcium hydroxide, the ct-hydrate of dicalcium silicate, and the hydrosilicate with a basicity of 0.9 . From the results of the chemical analysis (Table 1) it is possible to calculate the content of these compounds in the samples. Graphs corresponding to such calculations (for oneregim*) ate presented in 1 34 ASARCO ALV 0005619 Figure 4. Note that the content of these compounds were calculated on the basis of calcium silicates, not of the hydrosilicates. As seen from a comparison of Figures 1 and 4, the minimum strength of the sample corresponds to the maximum content of the oc-hydrate, and maximum strength corresponds to the maximum content of the slightly basic silicate. The increase in strength with small additions of sand can be associated with an acceleration of the hydrolysis of tricalcium silicate. Figure 3. Differential thermal analysis curves of samples of dicalcium silicate (8 -CjS) with sand additions. Samples soaked 8 hours at 16 technical atmospheres. Figure 4. Composition of cements in samples of tricalcium silicate with added sand, soaked 8 hours at 16 tech. atm. (in weight "fr of the total sample). 1) undecomposed trlcalclum silicate; 2) free calcium hydroxide; 3) a-hydrate of dicalcium silicate; 4) hydrosilicate with a basicity of 0.9. Dicalcium silicate ( 8 - modification). Hydration of this compound under the conditions of the ex-' periment can lead to the formation of several hydrates of dicalclum silicate [4]. It is not possible to cal culate the amount of each of them and also of the unreacted starting material. However, it is possible to calculate the total amount of compounds with a oasiclty of 2, both hydrated and unhydrated, and also the hydrosilicate with a basicity of 0.9. The results of the calculations (for samples autoclaved 8 hours at 8 tech, atm.) are presented In Table 2. From a comparison of these data with Figure 1, it is seen that maximum strength corresponds to maximum content of slightly basic hydrosilicate. The decrease in strength with small additions of sand is associated with the formation of large amounts of a-hydrate (Figure 3). Thus maximum strength of the samples prepared from each of the clinker materials - silicates -- corresponds to the maximum content in these samples of calcium hydrosilicate with a basicity of 0.9; the latter, in turn, depends on the amount of crystalline silica added. The optimum amount of this addition depends on the type of silicate, on the autoclaving regime, and, evidently, on fineness of grinding of both the silicate and the sand. .( 35 ASARCO ALV 0005620 TABLE 2 Content of Dicalcium Silicates (total) andsilicate with a Basicity of 0.9 in Samples of g -2CaO SiOj (in %) Crystalline silica in the original material 0 5.11 10.09 20.16 29.90 ' 39.84 49.99 70.00 90.00 Dicalcium silicates in the autoclaved mixtures 96.82 86.40 77,70 62.90 51.10 32.15 27.90 12.90 2.44 Slightly basic silicate (hydrosilicate) in the autoclaved mixtures 0 5.85 11.74 18.35 21.50 27.29 27.57 24.20 11.95 It is interesting to note that an increase in pressure, that is, an increase in temperature, lowered the possible maximum strength of the samples and, moreover, decreased the optimum amount of sand. In our experiments, the possible maximum strength of the samples of B -2CaO SiC^ with sand were higher than the strengths of the samples of 3CaO SiOj with sand by a factor of approximately 2.5. It is also pointed out that the strength of the samples of pure 8-2CaO SiOj was lower than that of the samples of pure 3CaO SiQj when the hydrothermal treatment was carried out at 8 tech, atm., and higher when the treatment was at 16 tech. atm. It should be stressed that it was established in this work that both the dicalcium and the tricalcium silicates become bonded to the sand during autoclaving. The strength of the samples of B-dicalcium silicate and sand (optimum composition) were higher than the strength of the samples of tricalcium silicate and sand. Although the results obtained on the clinker materials cannot be transferred directly to sandy Rsrtland cements, they do confirm that, by changing the dosage of sand and the autoclaving reglme.it is possible to obtain concrete and ferroconcrete articles from belite clinkers with the addition of sand which are not inferior to articles made from cement from alite clinkers. Received September 12, 1955 LITERATURE CITED [1] G. L. Kalousek, M. Adams, J. Am. Concrete Inst., 23, 1, 77 (1951). [2] G. L. Kalousek, J. Am. Concrete Inst., 25, January, 365 (1954). [3] L. Heller, H. F. W. Taylor, J. Chem. Soc., 3, 2535 (1952). [4] W. C. Hansen, J. Am. Concrete Inst., 24, No. 9, 842 (1953). 36 ASARCO ALV 0005621