Towards Sustainable Concrete Infrastructure: Durability of Full-Scale BFRP Dowel Bars Under Seawater and Alkaline Exposure

Basalt fibre-reinforced polymer (BFRP) dowel bars offer a corrosion-resistant alternative to steel dowels for jointed concrete infrastructure, particularly in aggressive marine environments. However, the durability of full-scale BFRP dowels remains insufficiently understood because their shear-dominated behavior differs from that of conventional small-diameter FRP reinforcement. This study investigates the durability of 25-mm epoxy-based BFRP dowel bars exposed separately to artificial seawater and alkaline solution at 60 °C under accelerated continuous-immersion conditions. Mechanical performance was evaluated through flexural strength, transverse shear strength, and interlaminar shear strength (ILSS), while chemical and microstructural changes were examined using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS). At the common 2- and 4-week exposure durations, seawater caused greater flexural-strength losses (10.0% and 11.5%) than alkaline exposure (1.3% and 8.5%), whereas alkaline exposure caused greater reductions in transverse shear strength (7.3% and 8.3% vs. 2.5% and 5.5%) and ILSS (7.0% and 10.0% vs. 1.3% and 2.4%). FTIR and SEM/EDS observations provided complementary evidence of matrix modification and fibre–matrix interfacial deterioration. Overall, the investigated BFRP dowel system showed limited mechanical degradation under the accelerated conditions, indicating promising material-level durability performance within the investigated exposure durations.