Experimental and theoretical investigation on bond performance between surface-modified bamboo scrimber bars and concrete

With the aim of facilitating the adoption of eco-friendly bamboo scrimber bars as an alternative to the widely used steel bars in concrete structures, center pull-out tests were conducted on 75 specimens to investigate the bond performance between bamboo scrimber bars and concrete. Two innovative modification methods were employed, including the sand coating modification method with varying particle sizes and a newly proposed method involving wrapping with basalt fiber bundles, with a focus on the impact of bundles spacing on bond strength. Additionally, other influence factors, including the concrete compressive strength, development length, and equivalent diameter of bamboo scrimber bars, were investigated. The test results show that compared to unmodified bamboo scrimber bars, those modified with sand and basalt fiber bundles show increases in bond strength of 5.50-5.96 times and 4.82-6.15 times, respectively. The bond strength was most significantly influenced by the development length, which decreases with increasing development length. Besides, specimens with development length less than 75 mm mainly exhibit pull-out failure, while those with development length equal to 75 mm primarily occur concrete splitting failure. Furthermore, a bond strength prediction formula and a bond stress-slip constitutive model for the interface between bamboo scrimber bars modified with sand coating and concrete were established, which show great agreement with the test results.