Experimental study on bonding performance of GFRP bars-recycled aggregate concrete under sulfate attack environment

The sufficient bonding performance between glass fiber reinforced polymer (GFRP) bars-concrete is essential for the composite section's integrity. In addition, sulfate attack is one of the primary causes of concrete damage, which will inevitably lead to a decline in bonding performance between GFRP bars and recycled aggregate concrete (RAC). This paper uses the GFRP bar-RAC pull-out test to study the effect of recycled aggregate (RA) replacement rate and RAC protective layer thickness on bonding performance under continuous sulfate im-mersion. The results indicated that as the sulfate attack time increases, the bond strength of various GFRP bars -RAC specimens rises and then decreases. At the same time, as the RA substitution ratio grows, the specimen requires less time to reach its peak of bond strength, and the bond strength decreases rapidly in the later stages of erosion. When the erosion age reaches 360 days, the bond strength of specimens with recycled RA rates of 0%, 25%, 50%, and 100% drops by 12.93%, 15.18%, 17.99%, and 28.22%, respectively, compared to those without erosion. Since sulfate attacks RAC from the outside, the bond strength of the specimen with a thin protective layer thickness decreases faster after long-term erosion. Through the fitting analysis of the variation law of bond strength of 7 groups (147) specimens, a prediction model of GFRP bars-RAC bond strength is developed, considering the influence of RA substitution ratio and protective layer thickness under continuous sulfate im-mersion. The ratio of all predicted values to experimental values ranges between 0.94 and 1.133. It provides reliable guidance for the GFRP bar-RAC structure's durability design.