Study on hydration characteristics and mechanism of recycled powder-cement binary and multivariate systems

In this paper, the effects of recycled powder content, fly ash content, and different mixing ratios of recycled powder and fly ash on the hydration process of cement were systematically studied by isothermal calorimetry, and the evolution of its mechanical properties was explored. Additionally, a variety of modern analytical testing techniques were used to quantitatively characterize the content of hydration products and the evolution of microstructure. The results showed that the recycled powder can accelerate the early hydration rate, while the fly ash reduces the early hydration heat release rate and delays the hydration process. Both recycled powder and fly ash can reduce the total heat of hydration. The increase of recycled fine powder and fly ash content leads to a decrease in mechanical properties. In the ternary system, when the total substitution rate of recycled powder and fly ash is 30%, and the rate of the two is 1:1, the mechanical properties are optimal; with the increase of the content of recycled powder and fly ash, the content of hydration products of the specimen decreases and the porosity increases. When the ratio of recycled fine powder and fly ash is 1:1, the content of hydration products of the specimen increases, the pore size is refined, and the porosity decreases, which indicates that there is a synergistic effect between recycled fine powder and fly ash.