Key Findings: Assessment of GFRP Properties White Paper

Key Findings: Assessment of GFRP Properties White Paper
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White Paper by by David Trejo, PhD


There has been significant development in the design and use of GFRP reinforcing bars. This

report provides an overview of the literature on the properties, characteristics, and performance

of GFRP bars. This literature review indicates that when compared with steel reinforcement,

GFRP reinforcing bars exhibit lower modulus of elasticity values, lower ductility, and lower barconcrete

bond. The literature also indicates that structures reinforced with GFRP can exhibit

larger deflections and larger crack widths. GFRP bars are also lighter than steel bars and are

non-conductive and non-magnetic, which provide some potential benefits for specific situations.

However, one characteristic that has not achieved consensus in the engineering community is

the durability of GFRP when embedded in concrete. In the large majority of cases concrete has a

high relative humidity within its pore system and this moisture consists of a high pH solution.

When GFRP reinforcing bars are embedded in concrete, the composite surrounding the glass

fibers is supposed to protect the glass fibers from potential deterioration. However, the high pH

pore solution can penetrate this composite material. As the high pH pore solution penetrates

the composite it eventually reaches the glass fiber and these fibers are susceptible to etching

and leaching. This etching and leaching of the glass fibers in the GFRP can result in loss of bond

between the glass fibers and composite material or can result in weakening of the glass fibers.

Both debonding and loss of glass fiber strength result in loss of strength in GFRP reinforcing

bars. Loss of strength in GFRP reinforcing bars has been reported throughout the literature.

Unlike steel reinforcement, which when corroded exhibits signs of degradation (e.g., rust stains

or concrete delamination), when GFRP degrades there are no visual signs of this degradation.


Some recent research indicates that GFRP reinforcing bars embedded in field structures do not

exhibit degradation or loss of strength. However, these research studies contained no direct

measurements of the residual tensile strength of GFRP reinforcing bars. Although indirect

measures of GFRP degradation are improving, direct measurements of GFRP reinforcement

degradation provide a clear and unambiguous measure of performance. Because the literature

indicates that GFRP reinforcing bars do lose strength with time and because degrading GFRP

bars provide no visible warning of this degradation, the engineering community must move

forward in using this reinforcement with caution.