Bond performance between surface-modified bamboo bars and concrete under pull-out loading

Abstract

Bamboo is abundant, eco-friendly, and cost-effective, making it an excellent alternative to traditional building materials with limitations such as resource scarcity, pollution, and increasing price. Additionally, bamboo has excellent strength and durability, and can be used to replace steel bars. In this study, central pull-out tests were conducted on forty bamboo bars embedded in concrete specimens to study the bonding performance at the interface between bamboo bars and concrete. The test variables included surface modification (unmodified, epoxy mortar (EM)-modified and polyurethane (PE)-modified), equivalent diameter (d), and development length (L). The results indicated that (1) the specimens with PE-modified bamboo bars mainly exhibited bamboo bar pull-out failure, whereas the specimens with EM-modified bamboo bars primarily underwent tensile failure of the bamboo bar; (2) the bond stress‒slip curve had four stages: micro-scale slip, slip, descending, and residual stages; (3) the average peak bond stress (τ0) of the specimens with EM-modified bamboo bars was the highest; (4) τ0 decreased with increasing L and d values; and (5) the largest strain values were observed near the loading end. Finally, bond stress-slip constitutive models suitable for pull-out specimens with PE-modified bamboo bars with different L values were obtained by fitting test data. The findings of this study broaden the application of bamboo bars in the concrete structures.