Experimental investigation of bond performance between BFRP and different strength recycled-aggregate concrete

In recent years, there has been a large number of studies on recycled-aggregate concrete as a potential solution to the problem of a scarcity natural resources. This study investigated the bonding performance of a new reinforcement material employed in medium and high-strength recycled aggregate concrete. The pull-out test was carried out by employing basalt fiber-reinforced polymer (BFRP) bars with different diameters (12, 14, and 20 mm) in medium and high-strength concrete with different ratios of recycled coarse aggregate replacement (0, 25, 50, 75, and 100%). Based on the concrete bond damage, the failure modes were identified, the corresponding bond mechanism was analyzed and the bond stress–slip characteristics were summarized. The effect of each parameter on the failure mode, bond strength, and the bond-slip curve between recycled-aggregate concrete and BFRP bars was evaluated. Results indicated that as the diameter of the BFRP bar increased, the failure mode was shifted, the uneven distribution of bond stress became more pronounced, and the bond strength showed a decreasing trend. Two distinct situations of medium to high-strength concrete with very different relative bond strengths at different replacement ratios were found. The relative bond strength of medium-strength concrete increased at first and then decreased with the increase of the replacement ratio of recycled coarse aggregate. A non-linear relationship between the bond strength of recycled concrete and its compressive strength was found. The two-stage model was proposed to describe the bonding behaviour more accurately between BFRP bar and medium to high-strength recycled aggregate concrete.