Bond behavior between cementitious grout and deformed steel bars after freeze–thaw cycles

A reliable bond between cementitious grout and deformed steel bars is essential for effective load transfer and composite action. With the growing use of cementitious grout jackets for strengthening RC structures in cold regions, a comprehensive understanding of their bond behavior is critical for evaluating the load-bearing capacity and performance evolution of strengthened structures under freeze–thaw conditions. Accordingly, establishing the bond stress–slip model between cementitious grout and deformed steel bars is of great importance for both theoretical analysis and numerical simulation. This study conducts local bond–slip tests to examine the effects of steel bar diameter and cover thickness on bond performance under freeze–thaw cycles. The results reveal that as the c/d ratio decreases, the failure mode shifts from pullout to splitting failure. Specimens exhibiting pullout failure show significantly higher peak bond strength and slip compared to those with splitting failure. The peak bond strength decreases rapidly with increasing freeze–thaw cycles, while higher c/d ratios mitigate the rate of degradation. After 240 freeze–thaw cycles, the peak bond strength is reduced by 24.6 to 51.9%. Peak slip remains relatively unaffected by freeze–thaw cycles and is primarily influenced by rib spacing and c/d. To account for the combined influence of c/d and stirrup ratio, a confinement coefficient K is introduced. Based on this, a bond–slip model incorporating freeze–thaw effects and confinement is proposed, and its reliability is validated.