STUDIES ON THE RATE OF HYDRATION OF HARDENED CEMENT PASTES

Abstract

The rate of hydration of hardened cement pastes can be well expressed by means of the volume of hydrates in unit volume of hardened pastes. This is calculated by the following formula, Vh=l(1+1/sp)mwhere, Vh: the volume of hydrates in unit volume of the pastes.l: weight of cement in the pastes.m: amount of combined water in the pastes in wt. per unit wt. of used cement.p: amount of water necessary for perfect hydration in wt. per. unit wt. of used cement.s: specific gravity of used cement.From author's experiment, the following results are ascertained.(1) Under earlier age than 28 days, increase in the rate of hydration of the pastes of a fixed water cement ratio is proportional to logarithm of the age. The state of increase is approximately the same within the limits of water cement ratio from 0.4 to 1, 0, but in the case of 0.3 water cement ratio, increase of the rate of hydration is somewhat smaller than other cases at longer age than 28 days.(2) In the case larger water cement ratio taan 0.4, the rate of hydration decreases as initial water cement ratio increases, and also it decreases linearly as true water cement ration (total water contents in hardened pastes) increases.(3) The rate of hydration is not the same as varieties of cement, and the difference between them is remarkable especially in earlier ages.(4) The effect of low temperature curing on the rate of hydration is more considerable, earlier the age, and larger the amount of water used. The rate of hydration is remarkably accelerated by not water curing even in a short time.For example, the pastes of 0.3, 0.4, 0.5, 0.65, 1.0 water cement ratio which had been cured in hot water of 99°C and 70°C during six hours after one day ordinary curing, have been all accelerated about to 70% as compared with ordinary curing.