Effect of Construction Contaminants on the Bond-Slip Behaviour of GFRP Reinforcing Bars

Abstract

Glass fibre-reinforced polymer (GFRP) reinforcing bars are an attractive alternative to conventional steel bars in reinforced concrete (RC) bridge construction due to their non-corrosive properties. With advances in production and quality control, GFRP reinforcing bars are an economical alternative for steel reinforcement in many bridge components, particularly in the substructure and at joints. However, gaps remain in the design and construction of GFRP reinforced concrete. including the impact of surface contamination on GFRP reinforcing bars. During construction, construction activities are frequently carried out in close vicinity to exposed GFRP reinforcing bars, which can damage and contaminate their surface. Existing standards, such as CSA S807 and CSA S806, do not provide guidance on how contamination affects performance or how to treat contaminated GFRP reinforcing bars. In Ontario, exposed GFRP reinforcement contaminated by concrete splatter is required to be replaced, leading to costly delays and waste. This study evaluates the impact of surface contamination on GFRP bond behaviour using pullout specimens. 13M and 20M ribbed GFRP bars, and 12M and 20M sand-coated GFRP bars were tested with surface contamination from two common materials used in concrete placement: form oil and concrete splatter. Additionally, non-destructive inspection methods are used to investigate potential differences in ultrasonic pulse velocities associated with different surface contaminants and corresponding bond strength outcomes, and to establish the potential correlation between the contamination effects identified in the pullout and tests those obtained from the non-destructive testing measurements. The results demonstrated that the form oil contamination reduced bond strength and UPV considerably. This suggests that UPV is an effective method for predicting bond loss caused by the form oil contamination. Nevertheless, the concrete splatter contamination exhibited no clear correlations between the pullout test and the Ultrasonic test. Therefore, preventive measures should be applied for the form oil contamination from GFRP reinforcement, and immediate removal is required if detected. Concrete splatter contamination should be removed as a precautionary measure. Furthermore, comparison to the test data showed that the mBPE model yielded a slightly conservative estimate of experimental bond behaviour, while the CMR model tended to under-predict the bond slip response. The experimental bond stresses exceeded the ACI 440 and CSA S806 predictions for all bar sizes and contamination groups.