Study on the effect of particle size on the basic characteristics of RCP and hydration kinetics of slurry
Cuizhen Xue, Guangjin Tian, Yunsheng Zhang, Zhe Wang, Hongxia Qiao, Li Su
Abstract
Aligned with national strategies promoting green, low-carbon, and environmental protection initiatives, this study aims to mitigate the issues of substantial construction waste accumulation and low recycling rates. Additionally, it seeks to address bottlenecks such as the limited reactivity of recycled concrete powder (RCP) and the lack of comprehensive theoretical research. To achieve these objectives, RCP samples with varying particle sizes were prepared using a mechanical grinding method. The study examines how particle size affects the characteristics, surface binding energy , and hydration reactivity of RCP. This examination elucidates the mechanism by which particle size influences the hydration process and properties within the cement-RCP cementitious material system. The hydration kinetics parameters of the system are analyzed and its hydration process is quantitatively characterized based on the Krstulovic-Dabic model. The results show that with the decrease of particle size, the fine particle content in RCP increases, the particle angularity and surface binding energy decreases, the lattice distortion worsens while the hydration reactivity increases. The addition of RCP reduces the hydration heat release rate , cumulative heat release and hydration degree. It also delays the appearance of the exothermic peak . In the early stage of hydration, RCP mainly plays the role of physical filling and crystal nucleation. The hydration process of the cement-RCP system consists of three stages: nucleation and crystal growth (NG), interactions at phase boundaries (I), and diffusion (D). As the RCP particle size decreases, the hydration rate, hydration heat release and hydration degree increase, and the slurry microstructure after hydration is relatively uniform. These research findings can lay a sound theoretical and technical foundation for the production as well as high-value and efficient application of RCP in cement-based materials.