Study on axial tensile mechanical properties of alkali‐activated slag full recycled aggregate concrete

Abstract To investigate the axial tensile mechanical properties of alkali‐activated slag full recycled aggregate concrete (ASFRC), direct axial tensile tests were conducted on 56 prismatic specimens (40 mm × 40 mm × 300 mm) across 14 groups. The effects of water‐to‐binder ratio (0.4, 0.5, 0.6), recycled coarse/fine aggregate replacement ratio (0%, 50%, 100%), and steel fiber type (straight, single‐hooked, double‐hooked) and volume fraction (0.4%, 0.8%, 1.2%) on axial tensile strength, tensile elastic modulus, and peak tensile strain were systematically examined. The results show that the axial tensile strength and tensile elastic modulus of ASFRC decrease with increasing water‐to‐binder ratio, while the peak tensile strain first increases and then decreases. As the w/b ratio increases from 0.4 to 0.6, the axial tensile strength and tensile elastic modulus of natural aggregate specimens decrease by 29.1% and 17.9%, respectively, while the corresponding reductions for recycled aggregate specimens are 27.7% and 16.5%. The axial tensile strength and tensile elastic modulus decrease with increasing recycled coarse/fine aggregate replacement ratio, whereas the peak tensile strain first decreases and then increases. When the recycled coarse aggregate (RCA) replacement ratio increases from 0% to 100%, the axial tensile strength and tensile elastic modulus decrease by 7.5% and 4.4%, respectively; for recycled fine aggregate, the corresponding reductions are 3.1% and 2.6%. The axial tensile properties first improve and then decline with increasing steel fiber volume fraction, with an optimum at 0.8%, at which the axial tensile strength, tensile elastic modulus, and peak tensile strain increase by 34.4%, 19.6%, and 66.9%, respectively. Among the three fiber types, single‐hooked steel fibers provide the most pronounced reinforcement. Regression analyses establish conversion relationships between axial tensile strength and cube compressive strength ( R 2 >0.90), as well as between tensile and compressive elastic moduli ( E t = 1.65 E c ), with prediction errors within ±10%, providing design‐oriented formulas for ASFRC structural applications. Microstructural analyses reveal that these macroscopic trends are closely associated with the densification of C‐A‐S‐H gels at lower water‐to‐binder ratios, the porous nature of recycled aggregate interfacial transition zones, and the bridging effect of steel fibers.