Abstract: The waste clay brick contains a large amount of active mineral components such as SiO₂ and Al₂O₃. After crushing and grinding, recycled brick powder (RBP) can be prepared. By improving the pozzolanic activity of RBP through effective excitation methods, RBP can be applied to engineered cementitious composite (ECC) as part of cementitious materials, which has great economic and environmental benefits. By analyzing the activity index, microstructure and XRD pattern of RBP after physical excitation, the optimum physical excitation time of RBP was determined. On this basis, the recycled brick powder-engineered cementitious composite (RBP-ECC) was prepared with RBP after active excitation. The flexural, compressive, uniaxial tensile and four-point bending tests were carried out to study the influence of RBP replacement rate on the mechanical properties of RBP-ECC. The results show that the strength indexes of RBP-ECC decrease with the increase of RBP replacement rate after physical excitation, while the ultimate tensile strain and mid-span deflection increase gradually, up to 5.22% and 55.53 mm, respectively. When the RBP replacement rate is 20% (mass fraction), the bending toughness index of RBP-ECC increases the most, which is about 59% higher than that of benchmark ECC. Each strength index of RBP-ECC has a lower decline, but still can maintain high strength and toughness. The strength, toughness and sustainability indexes of RBP-ECC were comprehensively considered, and 20% was selected as the best brick powder replacement rate of RBP-ECC, and microscopic analysis of RBP-ECC fiber-matrix interface under this replacement rate was carried out. The results show that there are fiber pull-out failure modes and fiber breaking failure modes in RBP-ECC at 20% RBP replacement rate, and RBP-ECC shows higher tensile toughness and suitable tensile strength compared with benchmark ECC.

Key words: ECC, recycled brick powder, active excitation, brick powder replacement rate, mechanical property, failure mode