This study investigates the early-age bond behavior between steel reinforcement and lightweight alkali-activated concrete (LWA-AAC) using pull-out tests and modeling. Deformed and plain steel bars with different diameters were embedded in two LWA-AAC matrices to examine the effects of curing age, matrix strength, confinement, and bar surface geometry. The bond of plain bars is governed primarily by adhesion and friction and shows weak dependence on matrix strength or confinement. In contrast, the bond strength of deformed bars increases with curing age and matrix strength, while reduced confinement promotes a transition from ductile pull-out to brittle splitting failure. This confinement-sensitive transition highlights the dominant role of matrix tensile capacity in controlling bond stability in LWA-AAC. Compared with lightweight ordinary Portland cement (OPC) concrete, LWA-AAC exhibits more brittle bond behavior, characterized by smaller peak slip, steeper post-peak softening, and lower residual bond stress. Existing OPC-based bond models show limited applicability to LWA-AAC due to differences in failure mechanisms and confinement sensitivity. New empirical models incorporating matrix tensile strength and geometric confinement are proposed to predict bond parameters and bond–slip responses, providing a mechanism-informed basis for the design of reinforced LWA-AAC structures.
Lyu et al. (Wed,) studied this question.