Bond Behaviour of Steel Bars Embedded in Low Strength Concrete

Abstract

This paper aims at investigating bond behavior of steel bars embedded in low strength concrete compared to those embedded in normal strength concrete. The bond behavior of steel bars was studied using bar pull-out tests on 12 cubic specimens. The influence of bar diameter and concrete compressive strength on bond behaviour of embedded steel bars were investigated in this study. The load-slip behavior of all specimens was recorded during the test. The test result showed that the load-slip behavior of all specimens agreed well with the test report in literature. The splitting failure occurred in low strength concrete specimens when cracks in the surrounding concrete were caused by wedging action of the lugs of the steel bar. Failures occurred suddenly with the formation of the longitudinal cracks. For normal strength concrete specimens, the average peak axial load was significantly higher than those of low strength concrete specimens. The test results revealed that bond strength of the embedded steel bars was significantly dependent on compressive strength of concrete. It was noticed that when the strength of concrete is very low, the bond strength seems not to be proportional to square root of concrete strength (fc’) as recommended by design provisions. The test results also showed that the size of steel bar has less influence on bond strength of steel bars compared to concrete compressive strength. In addition, the ACI code (ACI 308-08) was also used to calculate the bond strength of the test specimens. It was found that the experimental-to-design ratios were higher than 1.0 for all cases.