The pile-up of massive construction waste causes serious challenges to environment and engineering practice. In order to promote the reuse rate of construction waste bricks, the effects of the content and fineness of construction waste brick powder and of brick powder-silica flour mixture on the strengths of cement mortar were experimentally investigated. Based on the test results, the significance of the particle characteristics of brick powder on mortar strength was analyzed by grey entropy method. The experimental results show that the early strength of cement mortar decreases due to the addition of brick powder; the reduction is, however, not significant when the content of brick powder is less than 10%; the 28 d strength of cement mortar increases with a proper content of brick powder. The grey entropy analysis indicates that the particle characteristics have strong influence on the activity of brick powder and mortar strength; the strength is significantly dependent on specific surface area and the fraction of particles smaller than 20 μm. Fine brick powder and silica flour can improve the macroscopic strengths of cement mortar by affecting the type and quantity of hydration products and the structure of interfacial transition zone between cement paste and sand.

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The construction and demolition wastes have increased rapidly due to the prosperity of infrastructure construction. For the sake of effectively reusing construction wastes, this paper studied the potential use of construction waste composite powder material (CWCPM) as cementitious materials in small-scale prefabricated concretes. Three types of such concretes, namely, C20, C25, and C30, were selected to investigate the influences of CWCPM on their working performances, mechanical properties, and antipermeability and antifrost performances. Also the effects of CWCPM on the morphology, hydration products, and pore structure characteristics of the cement-based materials were analyzed. The results are encouraging. Although CWCPM slightly decreases the mechanical properties of the C20 concrete and the 7 d compressive strengths of the C25 and C30 concretes, the 28 d compressive strength and the 90 d flexural strength of the C25 and C30 concretes are improved when CWCPM has a dosage less than 30%; CWCPM improves the antipermeability and antifrost performances of the concretes due to its filling and pozzolanic effects; the best improvement is obtained at CWCPM dosage of 30%; CWCPM optimizes cement hydration products, refines concrete pore structure, and gives rise to reasonable pore size distribution, therefore significantly improving the durability of the concretes.

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