Experimental Investigation of the effect of super-plasticizer additive on the concrete-steel bond strength using pull-out test

The bond between concrete and reinforcing steel is essential for the composite action in reinforced concrete structures. In the present study, the effects of super-plasticizer additive on the steel-concrete bond strength is experimentally investigated. A total of 18 pullout samples are prepared in two concrete mix design cases, including ordinary and high-strength concrete. The used steel bars are of diameters 8, 10 and 12 mm, which are embedded inside the concrete in a length five times the rebar diameter. The steel-concrete bond strength is evaluated using direct pullout test method with the universal testing machine. Besides preparing the pullout specimens, 5 standard cube samples of concrete are casted to examine the concrete compressive strength and dimensions of the hardened concrete cubes. The specimens are tested at the 42-day ages and the slip-force curves are obtained using the pullout test. The maximum force and the corresponding slip, bond stress and other important parameters are determined and discussed for the different studied conditions. The results indicate that the rebar-concrete bond strength decreases by increasing the rebar diameter and the super-plasticizer additive has an important effect on the bond strength. For instance, the average bond strength for the concrete mix containing superplasticizer is 2.3 time of that for the normal concrete.