Modeling the bond strength of reinforced concrete with oil polluted rebars

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November, 2015
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The serviceability and ultimate strength of reinforced concrete structures is greatly influenced by the strength of the bond mechanism between steel and concrete. The bond ensures that the structure maintains its state of equilibrium under any giving load. This study examined the basic influence of used engine oil on bond strength at the steel–concrete interface and subsequently develops models for predicting it. Ninety (90) concrete specimen of dimension 150 x 150 x 150mm with rebar inserts were used. Three (3) grades of concrete (C15, C20, C25) were designed. The loss adhesion and the decrease in the frictional resistance was evaluated using pullout test specimens with different levels of rebar oil pollution. The results revealed that used engine oil coating has adverse (negative) effect on the bonding action between concrete and steel reinforcement. It forms a layer on the concrete-steel interface which impairs the gripping of the steel bar within the concrete-steel interface and consequently gives rise to a weakened bond. The loss in bond strength was higher for mild steel than for high tensile steel. Finally, using the regression analysis tool pack in Microsoft excel (2010 version) the relationship between the dependent variable (bond strength) and the independent variables (degree of oil pollution and concrete compressive strength) was established for two grades of steel (Mild steel and high tensile) as follows: τ_Msteel = 0.2699f_cu – 1.8451 X_P and τ_Hsteel = 0.3105f_cu – 1.5939 X_P. From the findings it was concluded that the use of oil as formwork releasing agent on construction site should be carefully carried out to ensure that the bars are free from oil. Moreover, designers should factor the effect of oil in the design of the ultimate bond strength of reinforced concrete structures in situation where oil is used on the construction site.
A thesis submitted to the Department of Building Technology in partial fulfillment of the requirements for the award of the Degree of Master of Philosophy in Building Technology.
Bond strength, Concrete, Used engine oil, Compressive strength, Mild steel, High tensile steel, Steel-concrete interface