There is a continued process to implement innovative materials to enhance the sustainability and durability of the built infrastructure. Technologies developed over the last two decades have facilitated the use of glass fiber reinforced polymer (GFRP) composites as internal reinforcement bars (rebars) for concrete structures, which have proven to be an alternative to traditional steel reinforcement due to significant advantages, such as magnetic transparency and, most importantly, corrosion resistance, equating to durability and structural life extension. This study evaluates the durability of three different available and most commonly used GFRP rebar types, based on exposure to aggressive environments, such as those experienced in coastal areas. For that, the specimens were expose to high pH seawater solution (that simulates the alkalinity of the concrete exposed to seawater), at 60 °C for different periods of time: 45, 90, and 180 days. The durability of these GFRP rebars was assessed by testing four different physio-mechanical properties, including: tensile strength, elastic modulus, and transverse and horizontal shear strength. Preliminary results show that the resilience of the GFRP rebars after being exposed to high pH seawater at high temperature, varies considerably among the three different types. The tensile strength was the most affected physio-mechanical property.