The early hydration and rheological characteristics of cement paste containing co-combustion fly ash

Abstract

In this study, the early hydration and rheological characteristics of cement paste containing co-combustion fly ash (CCFA) were studied by using isothermal calorimetry, low-field NMR (LF-NMR), and rheological tests, and the differences between CCFA/cement system and the traditional binding system made with coal fly ash (CFA) were analyzed. The results indicate that co-combustion fly ash has a retarding effect on the early hydration of the cement. This effect becomes more pronounced as the dosage of fly ash increases from 10% to 30%. Additionally, the early hydration rate of samples containing CCFA was found to be faster compared to samples with CFA, even when the same admixture was used. The T2 spectrum analysis reveals that fly ashes primarily influence the early hydration characteristics by affecting the consumption of capillary water. As the admixture of fly ash increases, there is a reduction in moisture loss. The pattern of moisture evolution exhibits a strong correlation with the heat of hydration. At 72 h, the relaxation characteristics of both CCFA and CFA samples were found to be similar. Moreover, the rheological properties of the cement paste are influenced by factors such as the type and admixture amount of fly ash, as well as the degree of hydration. With an increase in the amount of fly ash blending, the rheological properties exhibit an increase as well. Specifically, CCFA samples display higher plasticity compared to CFA samples, even when the same admixture amount is used. The results of different analytical methods in the study were consistent.