The Performance Of Fly Ash During The Hydration Process Of Complex Binder

Fly ash has been widely utilized in concrete in recent years as a kind of active mineral admixture. The physical and chemical activity of fly ash, which respectively refer to morphological plus micro-aggregate effect and pozzolanic reactivity, act differently on the performance of complex cementitious materials. Studying on their separate effects is essential to the much more reasonable utilization in practical projects. Therefore, experiments were carried on several series of complex binders, containing fly ash or ground inert quartz powder with various water-binder ratio and replacement percent, in order to discuss the different roles the physical and chemical activity of fly ash play during the hydration of cementitious materials. Moreover, these binders were prepared under two different curing temperatures.There were mainly the contrastive investigations, including the compressive strength measurements of mortars and pastes, determination of chemically combined water, and other microcosmic analysis methods such as XRD, MIP and SEM. Conclusions were made on performance of fly ash on hydration process of complex binders, based on results from these experiments.Binders with fly ash show obvious better mechanical and hydration performance as well as microstructure than the ones with ground inert quartz powder, especially in the later hydration process. The former ones have potential strength development, higher cement hydration degree and better pore distribution, due to the chemical activity of fly ash in later hydration process. Furthermore, these favorable performances become more prominent with the higher replacement percent of fly ash.The curing temperature is significant to effects on binders resulted from the chemical activity of fly ash, not only enhances the performance degree of chemical activity, but also advances the time that the chemical activity starts to react. Binders with fly ash under high curing temperature display quite high strength and hydration degree in the very early hydration, and their microstructures seem much better than the ones with inert admixture. Accordingly, it is concluded that the chemical activity of fly ash play more important role under higher curing temperature, which alsoprove that the chemical activity has great value in use.The change of water-binder ratio has less evident effect on the chemical activity of fly ash. However, it is proved that high strength of binders with fly ash equal to cement binders can be obtained by adjusting the water-binder ratio, even when the replacement reaches 50%.