Research on hydration mechanism of ultrafine fly ash and cement composite

Abstract

In order to adjust the hydration process of ultrafine fly ash and cement composite (UFAC) and provide a theoretical basis, the hydration mechanism of UFAC under normal curing was systematically analyzed by hydration heat, X-ray diffraction (XRD), thermal gravity/differential thermal gravity (TG/DTG), non-evaporable water, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and mechanical tests. The content of ultrafine fly ash (UFA) in UFAC is 25% and 50%, respectively. Comparing with cement, in the early hydration stage (before 3 days), UFAC paste showed a higher hydration rate, while fly ash and cement composite (FAC) paste showed a lower hydration rate. The cumulative hydration heat of UFAC paste was less than that of cement paste during the early hydration stage. In the hydration process of 3–360 days, more non-evaporable water was determined in UFAC paste than in cement paste and FAC paste. At 360 days, UFAC paste showed finer pore structure. After 90 days, UFAC mortar showed higher mechanical strength comparing with cement mortar.