Effect of recycled concrete powder with different sizes on the properties of cement paste

In this paper, the effects of recycled waste concrete powder (RP) with different content and particle size on the hydration process of cement paste were explored, and the evolution of its mechanical properties and setting behaviour was also discussed. The nucleation characteristics of RP were analysed by means of hydration kinetics and microstructure images. The results indicated that with the increase of RP content, the fluidity of paste decreased continuously. Moreover, the smaller the particle size, the greater the fluidity decreased. The large RP had a retarding effect, while RP with small particle size would accelerate the setting process. RP can not only significantly increase the early strength, but also have an obvious improvement effect on the later strength. The effect of RP on the hydration process depended largely on its particle size. Only if the particle size was small enough would RP have an obvious nucleation effect. The influence of RP on the hydration kinetics of cement was mainly reflected in the nucleation and crystal growth stage. After the nucleation of hydration products, the effect of RP on the phase boundary reaction and diffusion process was relatively small.