Mechanical, microstructural, and load–displacement performance of sustainable concrete incorporating recycled brick waste coarse aggregate

The increasing generation of construction and demolition waste has created significant environmental challenges for the construction industry. Among these wastes, brick debris produced from demolished masonry structures represents a considerable portion that is often disposed of in landfills. Recycling such materials in concrete production can contribute to sustainable construction and reduce the consumption of natural aggregates. This study experimentally investigates the mechanical performance and load–deflection behavior of concrete incorporating crushed brick waste as a partial replacement for natural coarse aggregate. Five concrete mixtures were prepared with brick waste coarse aggregate (BWCA) replacement ratios of 0%, 10%, 15%, 20%, and 25% by volume of natural gravel. The fresh and hardened properties of concrete were evaluated through slump, compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity (UPV), and load–deflection response obtained from flexural tests. The experimental results showed that workability decreased with increasing BWCA content due to the high-water absorption and porous nature of brick aggregates. Moderate replacement levels improved certain mechanical properties. The mixture containing 10% BWCA exhibited the highest compressive strength, with an increase of approximately 15% compared with the control mixture. Splitting tensile strength also showed slight improvement at lower replacement ratios, while flexural strength gradually decreased as BWCA content increased. UPV measurements indicated acceptable internal quality for all mixtures. SEM observations confirmed that moderate BWCA incorporation enhanced matrix densification and aggregate–paste bonding, whereas higher replacement ratios increased porosity and weakened microstructures. The results suggest that a moderate replacement level of approximately 10% BWCA provides a favorable balance between mechanical performance and sustainability, making it a viable alternative for partially replacing natural coarse aggregates in concrete production.