Bond durability of sand coated and ribbed basalt FRP bars embedded in high-strength concrete

Abstract

This study examines the bond durability behavior of basalt fiber-reinforced polymer (BFRP) bars in harsh environments. The effects of surface treatment, concrete compressive strength, exposure type, and period of exposure on bond strength were examined through an experimental program. The results of 42 pull-out samples show that the bond strength of sand-coated bars was not significantly affected by concrete compressive strength. However, specimens with high-strength concrete achieved most of or above their maximum bond strength after the descending stage, while those with normal-strength concrete showed a decrease in bond strength to an approximately constant value with continuous slip. Ribbed bars had significantly higher bond strength than sand-coated bars and were less affected by the surrounding environments. After 9 months, the bond strength retentions for sand-coated bars were 29.43, 63.93, and 67.43%, and 66.10, 94.94, and 80.44% for ribbed bars under the exposure to the 50 °C seawater, sulfuric acid, and freeze–thaw cycles, respectively. The failure in sand-coated bars was governed by a complete delamination of the outer surface from the core of the bar, whereas the ribbed bars failed due to bar rupture and interlaminar shear failure between bar layers. Both BPE and CMR models correlated well with experimental findings of the sand-coated bars, but CMR was more accurate for ribbed bars.