Bond of FRP bars in air-entrained concrete : experimental and statistical study

The combined use of Fibre Reinforced Polymer (FRP) and Air-Entrained Concrete (AEC) can be an alternative to traditional steel-reinforced concrete as this system is less affected by the corrosion of the reinforcement and by the freeze-thaw cycles induced concrete degradation. However, the viability of this system hinges on the bond performance of the reinforcing bars. A total of 236 pull-out specimens were prepared and tested to study the effect of air-entraining admixtures (AEA) on the bond behaviour of FRP bars to concrete with varying compressive strengths. Failure modes and bond stress-slip curves were reported and discussed. The bond energy, calculated as the area under the bond stress-slip diagram, was also analyzed. The experimental peak bond stresses (bond strength) were compared to the theoretical ones characterized by the formula proposed for steel bars by the Model Code 2010. In addition, the statistical significance of the effect of AEA on bond characteristics was determined, yielding a reduction factor to account for the effect of AEA on bond strength. The test results show that the bond strength of FRP bars in AEC was statistically significantly lower than in normal concrete. However, the decrease is sufficiently small that could be accounted for, during the design stage, by merely increasing the reinforcement development length.