Hydration of ultrafine and ordinary Portland cement at early ages

Experimental results of a quantitative of the hydration of ultrafine and ordinary Portland cement pastes were presented in this paper. The degree of hydration of cement pastes was determined based on the determination of non-evaporable content. The purpose of this study was to explore the mechanism of the effects of particle size distribution on hydration kinetics of cement. The data obtained from test indicate that at each age before 7 days, the non-evaporable water content of the ultrafine cement paste was higher than that of the ordinary cement paste. The fineness has a great effect on early 7 days hydration. In the later age, the rate of hydration slows down and diffusion of silicate ions through layers of existing products becomes the rate-limiting process. The porosity of ultrafine cement paste is lower thod than of ordinary cement paste. The difference in porosity of two cement paste is most pronounced at early ages before 14 days. A general reduction in porosity with increasing in age is observed from test results. The ultrafine cement consistently produces higher gel/space ratios at all seven testing ages. At an age of 1 day, the ordinary Portland cement achieves 79% of its fine counterpart.