The study on the hydration process of cement-based materials is of significance since it determines the development of the macro-properties. The hydration process of high-volume fly ash (FA)-cement based materials is quite special and needs systematic study. In this study, the hydration heat release of cement paste with high volume FA were measured with isothermal calorimetry at different temperatures. The full-width at half-maximum (FWHM) value of the exothermic peak and the cementitious index (CMI) of FA were used comprehensively to evaluate the influence of FA on cement hydration. It was found that increasing the FA content and water-binder ratio retarded the hydration process for paste but did not show obvious effects on the hydration of cement. The CMI values show that raising the temperature intensified the retarding effect of FA on cement hydration during the induction period, but promoted the subsequent hydration process. According to the normalized heat release to cement, and the change of CMI values with temperature, new evidence was found that FA may not act as nucleation sites during the hydration process of cement. The result can be better explained by the topochemical reaction mechanism.

In this study, the tensile creep (TC) of high-strength concrete (HSC) containing 30 wt% fly ash was measured at early ages to investigate the applicability of creep prediction models for concrete containing FA, and to provide ideas to study the prediction model of concrete creep containing other SCMs in the future. The TC values obtained from the experiment were compared with the predicted values of six TC models. Then the accuracy of different models was evaluated by the ratio of predicted values to experimental values. Finally, the applicability of these models to the TC of HSC with fly ash was discussed at an early age. By comparison, it was found that when the loading age was 1d, 2d, and 3d, the ZC model (ZC are the initials for the word “Self-developed” in Chinese), which is a rheology-based model for TC, proposed by Yang.Y et al. agreed with the experimental values. The predicted values of the other five models deviated significantly from the tested ones. When the loading age was 5d and 7d, the calculated results of the ACI 2009R model were more accurate. Compared with the other five models, the time dependency of the paste with fly ash was considered in the ZC model, and parameter q of the ZC model was introduced in order to characterize the influence of fly ash on the paste at early ages. Therefore, this paper demonstrated both theoretically and experimentally that the ZC model can better predict the early-age TC of HSC with fly ash.