Durability of FRP Reinforcement

 Glass fiber reinforced polymer (GFRP) materials are sensitive to salt water. If salt

water comes to contact with the glass fibers it will attack them and can destroy them in a

short period of time. It is not unusual for a GFRP bar to lose approximately 50% of its

strength once the fibers are exposed. Even though GFRP reinforcing bars have an epoxy

coating that provides protection against such attack, cracking of the epoxy protective

layer can allow saltwater to penetrate and destroy the fibers. It is therefore dangerous to

use GFRP bars for such applications. On the other hand carbon fibers are immune to

attack by saltwater and therefore well suited for marine structures. Even in the case of

cracking in the matrix material of carbon fiber reinforced polymer (CFRP) bars their

strength will not be compromised. Micelli and Nanni (2004) tested both GFRP and CFRP

rods for durability in various environments and reported problems with GFRP rods but no

problems were unveiled for the CFRP rods. Jansons et al. (2002) exposed carbon FRP

composites to salt water at elevated temperatures with no noticeable changes to the

strength and modulus of the composites. Myers et al. (2002) tested both glass and carbon

FRP rods in tension after alkali exposure or a combined effect of Ultra Violet (UV)

radiation, high temperature cycles and high moisture (environmental cycles). Although

the environmental cycles did not have any effect on the tensile strength of neither the

glass nor the carbon rods, the alkali exposure had a significant impact on one of the glass

rod types. A reduction in the tensile strength of 41% was observed after alkali exposure

for 42 days at a temperature of 60 C. No significant loss of tensile strength was reported

for the carbon rods. Carbon fibers are not influenced by alkaline environments even when

in direct contact, while glass fibers will deteriorate once they come into contact with such

an environment (Malvar 1998).