An assessment method of hydration degree of Rice husk ash blended cement considering temperature effect

Abstract

Rice husk ash (RHA) has been considered as a suitable cement mineral additive. A key issue in the study of RHA blended cement is to evaluate the contribution of RHA to hydration kinetics. Although numerous methods have been given to assess the hydration degree of blended cement, there are still some controversial aspects, such as the effect of temperature is not well considered. Therefore, this study aims at developing a method for evaluating the hydration degree of blended cement which can consider the influence of temperature. The key of this method is to adopt a hydration kinetic model of nonevaporable water (NEW) to determine the ultimate NEW content of blended cement when it is completely hydrated. In the hydration kinetic model, the Arrhenius equation is introduced to reflect the relationship between hydration rate and temperature, and the inversion phenomenon between ultimate NEW and temperature is considered simultaneously. Furthermore, the hydration process of portland cement pastes containing RHA (two types of RHA: RHA-1 from the factory and RHA-2 by controlled combustion) is analyzed by this assessment method. It is found that the effect of temperature on RHA cement is similar to that of ordinary Portland cement (OPC), which has an inversion phenomenon between hydration degree and temperature. Under the same temperature, the hydration degree of RHA cements is lower than that of OPC, while the difference in hydration degree gradually decreases with the progress of hydration. Moreover, according to the fitting results of the model when m = 3, the addition of RHA could reduce the apparent activation energy (Ea) of blended cement, the Ea values of OPC, RHA-1 cement and RHA-2 cement are 37.64 kJ/mol, 35.39 kJ/mol and 34.18 kJ/mol, respectively.