Abstract
This paper presents experimental and numerical investigations about the effects of elevated temperatures on the bond behaviour between concrete and carbon fibre reinforced polymer (CFRP) strips installed according to the near-surface mounted (NSM) technique. Firstly, single-lap shear tests were performed on concrete prisms strengthened with CFRP strips inserted into slits pre-cut in the concrete cover and bonded with an epoxy-based adhesive. The specimens were heated up to the target temperature (from 20 to 270 ℃, measured in the adhesive) and then loaded up to failure while the temperature was maintained constant. The experimental results show that with increasing temperatures (i) the bond strength is significantly reduced, and (ii) the failure mode changes from CFRP tensile failure at 20 ℃ and 50 ℃ to adhesive failure in the CFRP-adhesive interface at higher temperatures. Secondly, a numerical procedure was developed to calibrate (based on the experimental results) the local bond vs. slip laws at different elevated temperatures. Overall, both the stiffness and maximum bond stress of the obtained laws decrease with increasing temperatures; in addition, the predicted load vs. slip curves fit well the experimental counterparts.
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It was not possible to define a higher bonded length due to geometric limitations of the test setup.
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For high values of slip at the free end, the targets dots used for the video extensometer were lost – the free end of the strip entered in the adhesive and the targets detached from the CFRP.
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Acknowledgments
The authors wish to acknowledge FCT (projects PTDC/ECM-EST/1882/2014 and PTDC/ECI-EGC/30611/2017) and CERIS for funding the research, Secil and Unibetão for supplying the concrete, S&P Clever Reinforcement Ibéria for supplying the CFRP strips and adhesive. The first author also wishes to thank the financial support of FCT through the scholarship SFRH/BD/145256/2019.
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Azevedo, A.S., Firmo, J.P., Correia, J.R., Tiago, C. (2022). Influence of Elevated Temperatures on the Bond Between CFRP Strips and Concrete Using the NSM Technique – Definition of Local Bond vs. Slip Laws. In: Ilki, A., Ispir, M., Inci, P. (eds) 10th International Conference on FRP Composites in Civil Engineering. CICE 2021. Lecture Notes in Civil Engineering, vol 198. Springer, Cham. https://doi.org/10.1007/978-3-030-88166-5_25
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