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The recycled brick micropowder was formed after crushing and ball milling and waste clay bricks have great potential activity. It can replace some percentage of cement in the preparation of concrete through activation effects of excitation, and thus, reutilization of waste products is the objective of this study. This study analyzed the activation effects of mechanical excitation, chemical excitation, and high-temperature excitation on the activity of regenerated brick powder. The correlation between different excitation methods and the activity index was fitted, and the microstructure and mechanism of action of the material were analyzed and revealed using SEM and XRD techniques. The results show that after using mechanical excitation, chemical excitation, and high-temperature excitation to activate the brick powder, the activity index of the material was improved to varying degrees, and there is a good correlation between different excitation modes and the activity index. The study shows that the 45 min mechanical excitation of ball milling and the high-temperature excitation of 800 have better effects, with the highest activity index reaching 71%, and the highest activity index in the chemical excitation mode is 65%. Considering the excitation effect, energy consumption, economy, and practical operation feasibility, it is recommended to use the ball milling 45 min excitation method as the best activation method for the recycled brick micropowder.

This study investigates the potential use of Yellow River sand (YRS) sourced from the lower reaches of the Yellow River in China as a sustainable and cost-effective substitute for quartz sand in Engineered Cementitious Composites (ECC). With an annual accumulation of approximately 400 million tons in this region, YRS presents a substantial resource. ECC specimens with 100% YRS replacement with quartz sand were subjected to various curing methods: natural, steam, standard, and sprinkler. Extensive mechanical testing including flexural, compressive, uniaxial tensile, and four-point flexural tests was conducted. Additionally, Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimetry (MIP) analyses investigated microscopic mechanisms influencing macroscopic mechanical properties. Finally, the mechanical properties of the YRS-ECC test block after 14 days of standard curing and the traditional sand ECC test block were compared and analyzed. The results indicate that ECC specimens with 100% YRS substitution under natural curing show an optimal ultimate tensile strain of more than 4%, providing the best resistance to the reduction in ultimate flexural load and deflection due to aging. Steam curing enhances flexural and compressive strength, achieving an ultimate flexural load of 5 kN and a maximum deflection of 4.42 mm at 90 days. SEM analysis revealed lower C-S-H gel density under natural curing and higher under steam curing, enhancing fiber pull-out in steam-cured specimens. The MIP tests demonstrated that natural curing had the highest porosity (32.86%) and average pore size (51.69 nm), whereas steam curing resulted in the smallest average pore size, with 44% of pores under 50 nm. Compared with traditional sand, it is found that the ultimate bending load and deflection of YRS-ECC are 5.7% and 9.4% higher than those of traditional sand ECC, respectively, and its ultimate tensile strength and strain are also improved. These findings highlight YRS as a sustainable alternative to natural sand in ECC, with natural curing proving the most effective for superior mechanical performance, including tensile strain, crack resistance, and durability. [ABSTRACT FROM AUTHOR]

Recycled brick powder (RBP) is a kind of solid waste material with pozzolanic activity, which can partially replace cement as a cementitious material to prepare concrete. In this paper, ultra-high-performance concrete (UHPC) was prepared by RBP. The effects of different RBP contents as a mineral admixture on the mechanical properties and microstructure of UHPC were studied by experiments. The results show that RBP has a certain weakening effect on the compressive strength development of UHPC. The compressive strength of UHPC decreases with the increase in the replacement rate of RBP, but the 28 d compressive strength of each group of specimens is not less than 140 MPa. The flexural toughness and tensile strain of RBP UHPC increased first and then decreased with the increase in brick powder replacement rate and reached the maximum at 40% and 30%, respectively. The material exhibits good strain-hardening characteristics. In addition, the incorporation of RBP can improve the bond strength between steel fiber and matrix and the ultimate bond strength reaches the maximum when the substitution rate is 40%. From the perspective of nano-scale characteristics, the RBP not only fills the pores as micro-aggregate, but also participates in the secondary hydration reaction to further optimize the pore structure of UHPC. [ABSTRACT FROM AUTHOR]