Hydration of Portland Cement Compounds R. H. Rogue
and
William Lerch
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Portland Cement Association Fellowship, National Bureau of Standards, Washington, D. C. This paper presents the results of an investigation on the reactions which take place when the compounds of cement, individually and collectively, are gaged with water in proportions similar to those used with cements in concrete. There have been studied the chemical nature of the reactions of hydrolysis and hydration, the rate of the reactions, the nature of the reaction products, the physical structure of the hardened specimens, and the compressive strengths and other physical characteristics of the materials. A general theory has been developed which permits an understanding of the chemical and physical mechanism of the hardening process. The effects of the aluminates on the silicates is indicated both in the absence and in the presence of a retarder.
Rotaby Cement Kiln
Portland cement is gaged with a sufficient amount of water to form a plastic paste, it stiffens in the course of a few hours. This phenomenon is spoken of as the initial set (2). Subsequently it becomes hard, and more or less rapidly acquires marked resistance to rupture by either compressive or tensile stresses. A certain arbitrarily defined degree of hardness, sufficient to bear a given light weight without indentation, is spoken of as the final set (2). The hydrolytic reactions of the cement compounds in an In that investigaexcess of water have been reported (14)· tion the products of the reactions were determined when a condition of equilibrium had been attained. The reactions that take place when a cement paste sets and becomes hard may, however, attain a condition of arrested progress, or apparent equilibrium, long before true equilibrium is reached. During the setting and hardening, several forces compete for the available water—the physical forces of adsorption and capillarity, and the chemical forces of hydrolysis and hydration. Furthermore, the reaction products of one compound with water may greatly influence the nature or rate of the reactions of the other compounds with water, or the reaction products may themselves interact with other compounds in the system. The chemical reactions which determine the setting and hardening of Portland cement can be more completely understood through the examination of the behavior of the compounds of the cement, individually and collectively, when gaged with water in proportions similar to those used with cements in concrete. That has been the objective in this investigation. Seven compounds that may occur in Portland cement have been investigated, individually, with and without gypsum, and in various combinations. The chemi-
cal nature of the reactions of hydrolysis and hydration, the rate of the reactions, the nature of the reaction products, the compressive strength and other physical characteristics of the materials have been studied. The literature on the reactions of set has been reviewed by one of the authors in a previous publication (5).
WHEN
Materials
Investigated
The cement compounds used in this investigation were those which comprise the major constituents of a wellburned Portland cement clinker and, in addition, 5-3 calcium alumínate, dicalcium ferrite, and gamma dicalcium silicate. In the tables, abbreviations are used for the compounds as follows: Cement Compounds CaS for 3Ca0-Si02 8 C2S for 8 2CaO SiOí
C3A for 3Ca0 Al203 C
