Bond properties between smooth carbon fibre-reinforced polymer bars and ultra-high performance concrete modified with polymeric latexes and fibres

Abstract

This paper assesses the benefits of styrene-butadiene rubber (SBR), steel fibres (SF), and polypropylene fibres (PPF) to mitigate the brittle failure and drop in bond properties due to smooth surface geometries of carbon fibre-reinforced polymer (CFRP) bars embedded in ultra-high performance concrete (UHPC). A ready-to-use UHPC was employed to determine the bond stress vs. slip properties of CFRP and deformed steel bars. Test results showed that the incorporation of SBR is beneficial to alleviate up to 20% the detrimental effect of smooth CFRP geometry, which was attributed to enhanced adhesion along the spiral wounds. The ultimate bond improved by 45% and 87% when 1% of either PPF or SF was added, respectively, given the fibre bridging effect that limits the formation of radial cracks. Also, the ductility improved with fibre additions, reflecting their beneficial role for better transmitting the stresses along the cementitious matrix. The experimental bond strengths determined from the UHPC-Steel specimens are 3- and 3.5-times higher than those computed from EC2 and ACI 318-19 code provisions, respectively. Yet, such ratios dropped to 1.3- and 1.5-times for the CFRP bars, given their lower shear and lug indices that reduced the interaction with surrounding UHPC.