Compact Filling Effect and Property Evolution Law of Cement-Recycled Brick Powder Cementitious Material System
摘要
In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste, this study crushed and ground the waste red bricks to produce recycled brick powder (RBP) with different fineness, used the Andreasen model to explore the influence of RBP on the compact filling effect of cementitious material system based on the basic characteristics of RBP. The influence of grinding time (10, 20, 30 min) and content (0%, 5%, 10%, 15%, 20%) of RBP on the macroscopic mechanical properties of cementitious materials was investigated. We analyzed the significant impact of RBP particle characteristics on the compressive strength of the specimen with the aid of grey entropy theory, and revealed the influence mechanism of RBP on the microstructure of cementitious materials by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results show that the fineness of RBP after grinding is smaller than that of cement. The fineness of recycled brick powder increases gradually with the extension of grinding time, which is manifested as the increase of <3 µm particles and the decrease of >18 µm particles. Compared with the unitary cement cementitious material system, the particle gradation of the RBP-cement binary cementitious material system is closer to the closest packing state. With the increase of RBP content and grinding time, the compactness of the binary cementitious system gradually decreases, indicating that the incorporation of RBP reduces the mechanical strength of the specimen. The results of grey entropy show that the specific surface area D(0.1) and <45 µm particles are the significant factors affecting the mechanical properties of cementitious materials mixed with RBP. RBP mainly affects the macroscopic properties of cementitious materials by affecting the internal compactness, the number of hydration products and the pore structure. The results of SEM show that when the RBP content is less than 15%, the content of C-S-H in cement paste increase, and the content of Ca(OH)2 decreases, and the content of C-S-H decreases and the content of Ca(OH)2 increases when the RBP content is more than 15%. The NMR results show that with the extension of grinding time, the pore size of micropore increases gradually, that of middle-small pores decreases gradually, and that of large pores remains unchanged. With the increase of RBP content, the micropores first decrease and then increase, and the middle-small pores and large pores gradually decrease. In summary, the compactness of cementitious material system can be improved by adjusting the fineness of RBP. Considering the performance of cementitious materials and the utilization rate of RBP, it is recommended that the grinding time of RBP is 20 min and the content is 10%–15%.