Title: Hydration Products Formed in Cement Pastes at 25 to 175 C
Author(s): George L. Kalousek and Milton Adams
Publication: Journal Proceedings
Appears on pages(s): 77-90
Keywords: no keywords
Research described indicates the chemical nature of a new potential hydration product of cements responsible for the high strength of steam cured cement, products. Differential thermal analysis was used in studying hydration products of cement and related solids at temperatures between 25 and 175 C. Additions to the cement included gypsum and finely ground quartz. The trisulfate form of calcium sulfoaluminate and presumably the analogous sul-foferrate were found as t,hc initial RsOs-bearing hydrates at temperatures be-tween 25 and 100 C, but these transformed to the related solid solution of the SO3-bearing solids. The latter then converted to phase X. At 100 C these consecutive reactions appeared to be complete in 3 to 4 hours, and in-creasingly longer time was required for completion as the temperature was lowered. The solid solution formed in greater abundance at about 70 to 100 C than at lower temperatures. The hydrogarnem were not found in any sample of cement hydrated at temperatures between 25 and 175 C. Samples of pure converted initially to hydrogarnets in the presence of water, but with periodic regrinding of the solids it was found that in the interval between about 3 and 6 months the initial product was transformed completely into which probably contained some integrally bound and a gel. Experimentation on the synthesis of phase X indicated that, this solid may be a gel consisting of all the oxide constituents of cement. Lime, silica and ferric oxide are required constituents for the format.ion of this phase. Ground silica added to the cement in an amount of about 8 to 10 percent appcnrcd to combine with all the hydrolytic at 175 C, the reaction product being the crystalline dicalcium silicate hydrate discovered by Thor-valdson and Shelton. The total amount, of this phase was estimated to be about one-third to one-half of the reaction products. Further additions of silica reacted in turn with this compound and at about 40 to 45 percent addi-tion the new product of reaction approached in composition a molar ratio of about 1.0 and is characterized in thermal analysis by a pronounced exoithermic peak at 840 = 5 C.