Properties prediction of fly ash blended concrete using hydration model

Fly ash is an industrial by-product from coal combustion and has been widely used as mineral admixture in normal and high strength concretes. Owing to the pozzolanic reaction between calcium hydroxide and fly ash, compared with Portland cement, the hydration of concrete containing fly ash is much more complex. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of concrete containing fly ash. Similar to the hydration reaction of cement, fly ash activity is divided into three processes: an initial dormant period, a phase-boundary reaction process and a diffusion process. The mutual interactions between the cement hydration and fly ash reaction are considered through the available calcium hydroxide amount and available capillary water amount in the system. The properties of hardening fly ash blended concrete, such as the reaction degree of fly ash, chemically bound water, calcium hydroxide, and compressive strength, are determined from the contributions of cement hydration and fly ash pozzolanic reaction. The evaluated results show good accordance with the experimental results.