Interface between steel rebar and concrete, studied by electromechanical pull-out testing

The interface between concrete and steel rebar was evaluated by electromechanical pull-out testing, which involved measuring the shear bond strength and contact electrical resistivity of each sample. The bond strength was increased by steel rebar surface treatment (acetone, water, ozone or sand blasting, with ozone being most effective and acetone being least effective), polymer addition to concrete (methylcellulose or latex), increase in water/cement ratio of concrete (particularly from 0.45 to 0.50), and decrease in curing age (particularly from 14 to 7 days). The origins of these effects are rebar cleansing for acetone treatment, rebar surface oxide film formation for water and ozone treatments, rebar surface roughening for sand blasting, polymer interface layer formation for polymer addition, and decreased interfacial void content for water/cement ratio increase and for curing age decrease or both treatments but, in addition, epoxy systems involved economic advantages. An experimental procedure for epoxy resin deposition was developed; various parameters, such as the nature of the curing agent used to harden the epoxy prepolymer, the deposition process, the amount of coating, the ratio between the epoxy prepolymer and the curing agent and the curing temperature were investigated. Data show that only the three first parameters had a significant influence on the mechanical properties. In all cases, an improvement in tensile properties was obtained for epoxy-coated composites but in lower proportions compared to silane-treated composites. However, the impact characteristics worsened.