Alkaline aging effects on thermal stability and apparent interlaminar shear strength of GFRP/epoxy/graphene bars

Abstract Composite materials are increasingly used in civil construction as alternatives to traditional materials. Pultruded glass fiber-reinforced polymer (GFRP) bars stand out for their corrosion resistance, and the addition of graphene enhances polymer performance. This study evaluated the durability of GFRP/epoxy/graphene bars exposed to a pH 13.5 alkaline solution at 60 °C for 60 and 90 days. Microstructural, thermal, chemical, and mechanical analyses were performed using SEM, DSC, TGA, MCC, FTIR, and short-beam shear testing. After 90 days, the glass transition temperature decreased by 3.42 °C, FTIR indicated significant changes in O–H groups while C–H bands remained stable, and apparent shear strength decreased by 15.67%. These results demonstrate that the composite maintains substantial structural performance under aggressive alkaline conditions, providing valuable insights for its use in reinforced concrete applications requiring durability and corrosion resistance.