# The Influence of Interlock Loss between Rebar and Concrete on Bond Performance of RC Member
## 6 Conclusions and Suggestions  
In this paper, the authors tried to separate out the multiple factors of bond deterioration and focused on the interlock, which is a dominant factor in the bond components. To evaluate the effect of change in the interlock condition on load-bearing mechanism and bond performance of RC beams with different interlock condition, experimental and analytical investigations were conducted. Furthermore, the finite element analysis as case studies that simulated interlocking conditions that were expected to occur due to rebar corrosion was performed. From these investigations, the conclusions are summarized as follows:  
1. Bond between round bar and concrete was significantly low compared with deformed bar with interlock. It was confirmed that whether interlock can work or not was a dominant factor for a sound bond rather than chemical adhesion or friction effects. Section loss of rebar caused reduction of contact area between a lug and concrete, but interlock can be maintained until some lug height was lost. 2. When bond performance between rebar and concrete as an entire member was focused, as long as a part of surface remained interlocked, slip and pull-out of rebar did not occur even if some region in rebar lost interlock completely. Thus, bond performance was insensitive even though the section loss ratio increased due to corrosion. As long as the section loss ratio was lower than approximately 20%, stress can be transferred by interlock, and the bond of an entire member can be maintained in an almost sound state. 3. Stirrups can strongly suppress the relative displacement of main rebar against concrete in axial direction and for the detachment. As a result, this affected crack location and kept an interlock between the concrete and main rebar, as long as a certain degree of roughness on rebar surface remains even after a corrosion crack was formed along rebar or cover concrete is lost. This study focused on interlock effects, which are a dominant component of the bond between rebar and concrete. Interlock deteriorated with section loss. However, when considering bond deterioration by actual rebar corrosion, corrosion crack also affects bond deterioration. Some points still need more consideration for understanding the correspondence between the actual corrosion condition and bond deterioration. It may be possible to evaluate a bond condition by residual interlocking and to assume an almost sound bond until the corrosion ratio reaches the point where the interlock between lugs and concrete is significantly lost. Figure 18 shows a conceptual diagram of the relationship between the corrosion process and interlock condition alteration focusing on local interlocking around a lug. At first, after the onset of rebar corrosion, a sound bond is maintained until cracks occurin the surrounding concrete while chemical adhesion is lost due to corrosion product (Stage 2). When corrosion cracks occur, bearing strength of the concrete contacted with lugs is reduced. However, as long as the interlock persists, relative displacement between rebar and concrete can be suppressed (Stage 3). If the interlock is lost owing to serious section loss, the stress transfer will be completely lost (Stage 4). As far as the influence of section loss alone on the bond is concerned, Stage 4 is achieved in 25% section loss. However, when the rebar is actually corroded, the same state of Stage 4 can occur at a lower corrosion ratio due to corrosion cracks, which causes the geometry change of the concrete surface around rebar and the reduction of bearing strength. When considering bond not on a meso scale but on a macro scale as a RC member, due to non-uniform corrosion in axial direction various local interlock conditions can be mixed. Figure 19 shows the interlocking condition of the entire corroded steel bar. Even if some regions reach Stage 4, as long as the other parts are corroded to a smaller degree, interlocks in these regions can maintain the bond of an entire member.