Deterioration of bond performance between BFRP bars and coral aggregate concrete incorporating slag-based geopolymers under seawater corrosion environments

Abstract

The utilization of durable geopolymers instead of ordinary Portland cement (OPC) for developing geopolymer-based seawater coral aggregated concrete (GPCAC) in coastal constructions contributed to the improved marine resource utilization and the reduced CO2 emissions and construction costs. Thus, this study investigated the durability of GPCAC and its bond performance with basalt fiber-reinforced polymer (BFRP) bars under seawater drying-wetting cycles, and cement-based CAC was also selected as a comparison. The bond characteristics and degradation mechanisms of slag-based GPCAC and cement-based CAC specimens were compared and analyzed under different seawater exposure condition. Experimental results revealed that both GPCAC and CAC specimens demonstrated various degrees of degradation in bond strength, whereas their initial bond stiffness exhibited a slight increase owing to the hygroscopic expansion of the superficial epoxy resin of BFRP bars, after being exposed to seawater environmental attacks. This degraded bond strength was primarily attributed to the existence of corrosive ions (i.e., SO42-, Mg2+, and Cl-) in seawater and free OH- in concrete capillary pores. These compounds chemically reacted with the slurry hydration products and the resin matrix, which resulted in the decreasing of concrete strength, the hydrolysis of the resin matrix, the deterioration of fibers, and fiber-resin interface debonding. Compared with CAC specimens, GPCAC specimens achieved better resistance to seawater attacks owing to the more dense and stable reaction products formed by geopolymers compared to OPC. After being subjected to 60 °C seawater attacks for 12 months, approximately 4.9% and 12.0% reductions in the bond strength were reported for GPCAC and CAC specimens, respectively. Finally, the residual bond strength of both GPCAC and CAC specimens was predicted after being served in seawater erosion conditions for 50 years.