Yuanzhen Liu

Cracks that appear during the initial setting and hardening stage of concrete can compromise the durability and service life of structure. The focus of this study was on the crack-resistance properties of recycled aggregate concrete (RAC) doped with basalt fibre (BF) reinforcement to enhance its early-stage crack resistance. By investigating the relationship between recycled fine aggregate (RFA) content and BF volume fraction, intrinsic connections among mechanical properties, drying shrinkage and the crack resistance of RAC were revealed. The results showed that incorporating BF at 0.2% by volume significantly enhanced the RAC's mechanical properties, regulated drying shrinkage and reduced early-stage cracking. The improvement became more pronounced with higher contents of RFAs. For the mix with 100% RFA, the addition of BF at 0.25% by volume reduced the total crack area per unit area of test specimens by 85.4% and decreased the maximum crack width by 60.1%. Combining grey correlation theory with the microhardness distribution at the RFA–mortar interface, the correlation ranking for crack resistance in RAC was found to be drying shrinkage strain > flexural–compressive ratio > tensile–compressive ratio > splitting tensile strength. BF locally reinforces cement paste, leading to a relatively uniform stress distribution. During cracking, BF effectively dissipates energy, mitigating the cracking risk associated with high contents of RFAs.

Recycled aggregate concrete incorporating glazed hollow beads (GHBRC) achieves the dual objectives of energy conservation and emission reduction by combining recycled coarse aggregate with glazed hollow bead aggregate, aligning with the construction industry’s “dual-carbon” goals for the development of low-carbon concrete. This study systematically investigates the flexural performance of GHBRC beams to establish calculation formulas for ultimate limit state bearing capacity and serviceability limit state verification. Six full-scale GHBRC beams were tested under simply supported conditions with two-point symmetric mid-span loading. Three critical variables (concrete composition, longitudinal tensile reinforcement ratio, and stirrup reinforcement configuration) were examined. Experimental results indicate that GHBRC beams exhibit failure modes consistent with conventional concrete beams, confirming the validity of the plane section assumption. At identical reinforcement ratios, GHBRC beams demonstrated a 3.1% increase in ultimate bearing capacity and an 18.78% higher mid-span deflection compared to ordinary concrete beams, highlighting their superior deformation performance. Building on methodologies for conventional concrete beams, this study recalibrated key short-term stiffness parameters using a stiffness analytical method and proposed a computational model for mid-span deflection prediction. These findings provide theoretical and practical foundations for optimizing the structural design of GHBRC beams in alignment with sustainable construction objectives.