Influence of sand coating intensity on bond properties between basalt fibre-reinforced polymer bars and concrete

Basalt fibre-reinforced polymer (BFRP) bars, which do not corrode, offer promising advantages in terms of the durability and sustainability of concrete structures. Their use helps to reduce environmental impact and ensure long-term efficiency. The present work deals with the influence of the intensity of sand coating on a BFRP bar’s bond with concrete. The bond properties were determined through pull-out tests. Experimental investigations were carried out on BFRP bars with a diameter of 12 mm, which were helically wrapped and sand-coated with quartz sand. Visual assessment revealed that the amount and distribution of the sand coating varied greatly from sample to sample. There was a need to evaluate both the amount of sand coating and its effect on bond properties such as initial adhesion, bond strength, and slip at bond strength. We developed a method to determine the proportion of coated surface based on automatic computer processing of photographs of the part of the rebar in contact with the concrete. The results confirm a large scatter in the proportions of the sand-coated surface, highlighting the necessity to standardize the surface treatment of such rebars. Statistical analysis of the pull-out test results showed that the proportion of sand-coated area had no statistically significant effect on the mean bond strength between the basalt reinforcement and the concrete, for both normal and high-strength types, at a standard significance level of 5%. In addition, the average and characteristic bond strengths are lower for high sand-coated helically wrapped bars compared to bars that are low sand-coated and helically wrapped, in both NSC and HSC. However, the sand coating intensity of the helically wrapped BFRP bar had a statistically significant influence on mean initial adhesion and stiffness. The scatter of the results for all investigated bond parameters of the pull-out test was significantly higher for bars with a higher sand coating. • Innovative method for determining sand coating on FRP rebars. • Sand coating intensity of BFRP bars ranged from 0 to 60%. • Significant scatter of bond strength for high sand-coated bars, for both NSC & HSC. • Lower characteristic bond strength for high sand-coated bars. • Regulation for sand-coated FRP bars’ surface treatment is needed.