Bond performance of CFRP bars embedded in UHPFRC incorporating orientation and content of steel fibers

Abstract

The bond behavior of carbon fiber-reinforced polymer (CFRP) bars embedded in ultra-high-performance fiber-reinforced concrete (UHPFRC) is a pivotal factor affecting the performance of CFRP bar-reinforced UHPFRC structures. The present investigation delves into the bond performance of CFRP bars in UHPFRC by conducting tests on thirty-six pullout specimens. In these tests, the effects of steel fiber orientation, steel fiber content, and CFRP bar diameter were considered. The results revealed that specimens with 12 mm-diameter CFRP bars primarily failed in a splitting-pullout mode, whereas those with 10 mm- and 8 mm-diameter CFRP bars exhibited pullout failure. It was observed that specimens containing 45° oriented steel fibers have the maximum bond strength (∼35.30 MPa), as the cracks within UHPFRC were more effectively constrained. The bond strength was found to increase with an increase in steel fiber content, attributed to the improved cracking resistance of UHPFRC. The average bond strengths of specimens with fiber contents of 2% and 2.5% are respectively increased by 10.66% and 14.52% compared to those with a fiber content of 1.5%. The bond strength increases with the increase in CFRP bar diameter, owing to the greater rib height and rib height-to-inner diameter ratio of larger-diameter CFRP bars. Finally, a theoretical model was developed to predict the bond strength, with an average ratio of predicted results to experimental results of 0.93 and a standard deviation of 0.176.