Effect of Particle Size on Hydration Kinetics and Microstructure Development of Recycled Brick Powder-Cement Pastes

With the advancement of urbanization and the transformation of the old city, the production and stock of construction waste in China are ever increasing, with waste clay bricks accounting for 50%~70%. It has been found that recycled brick powder has the potential as a supplementary cementitious material, but it can lead to a significant reduction in the mechanical properties of cement-based materials. In order to explore the effect of particle size on the activity of recycled brick powder and the hydration kinetics of cement, this study prepared recycled brick powder with different particle sizes by high-energy ball milling. The physical and chemical properties and hydration activity of recycled brick powder were characterized. The effect of particle size of recycled brick powder on the hydration process, microstructure and mechanical properties of recycled brick powder-silicate cement system was analyzed. Based on the Krstulovic-Dabic model, the hydration kinetic parameters of the system were obtained to realize the quantitative evaluation of the hydration process. The results show that with the decrease of the particle size of the recycled brick powder, the lattice distortion of the silicon-aluminum mineral becomes larger and the surface binding energy decreases, resulting in an increase in its hydration activity. The early hydration of recycled brick powder mainly plays a physical filling role, which can accelerate the early hydration of recycled brick powder-cement system and improve the hydration degree of crystallization nucleation and crystal growth→phase boundary reaction→diffusion process. With the decrease of particle size of recycled brick powder, the starting time of pozzolanic reaction is advanced and the degree of pozzolanic reaction is higher. Finally, the later strength of cement mixed with 30% fine-grained recycled brick powder exceeds that of pure cement. This paper lays a foundation for the efficient application of recycled brick powder in cement-based materials.