Durability of GFRP rods in water and alkaline solution

Corrosion of steel reinforcement in concrete structures is a critical problem that designers, contractors and owners have to face everywhere. The corrosion resistance of Fibre Reinforced Polymers (FRP) bars makes them attractive for the replacement of steel reinforcement if it can be ensured that their mechanical and physical characteristics remain stable over time under service conditions. The durability of Glass FRP (GFRP) materials used in construction is related, among the other things, to the conditions within concrete. Several studies have suggested that the high alkalinity of the cementitious environment and thermal variations act as a catalyst for stress corrosion mechanisms driven by the exchange of alkali metal ions (Na+ and K+). This research was focused on long-term properties of a new GFRP rebar that was developed using a polyester resin and E-glass fibres. The physico-mechanical properties were investigated in order to measure the retained properties and to observe the causes of damage and possible strength reduction. Tensile tests according to provisions of ACI 440K, ASTM D4475 short beam shear test, gravimetric measurements were performed after immersion in water and alkaline solution at 50°C. Experimental results showed a small amount of mechanical and physical damage; retained longitudinal and transverse properties were high, according to the small amount of absorbed fluid. A theoretical comparison is also presented herein. The analytical prediction that was made using a model based on a correlation between absorption behaviour and retained mechanical properties overestimated the mechanical properties after accelerated aging.