Optimization of the effect of corrosion on bond behaviour between steel and concrete

Abstract

This research program consists of laboratory study of corrosion phenomenon in reinforced concrete and further analytical study of the experimental results obtained by Amleh (2000). The laboratory study examined the influence of increasing levels of corrosion on the progressive deterioration of bond between the steel and concrete and determined the extent to which the various water to cement (w/c) ratio in concrete mixtures influence the corrosion of the steel reinforcement as well as the chloride ion penetration. The influence of corrosion on the bond characteristics of the reinforcing bars in pullout test specimens made with two different w/c ratios and two different concrete cover thicknesses were investigated using control specimens to study the effect of the concrete cover ratio and the concrete compressive strength. The two w/c ratios were 0.47 and 0.37, with two concrete cover thicknesses of 40 mm and 65 mm. Hence, the effect of w/c ratio on different parameters like rate of corrosion, compressive strength and the effect of concrete cover thickness on the corrosion rate were studied. An accelerated electrochemical corrosion procedure was used to develop four levels of corrosion including no corrosion to complete corrosion, with over 25 percent steel bar weight loss due to corrosion, with wide longitudinal cracks. This research study clearly indicated that the bond stress-slip response of the embedded bar in the pullout specimen, was adversely affected by the width of the crack, and the level of corrosion. The crack width was found to develop faster and longer in specimens with lower compressive strength and as a result the maximum bond strength in the pullout test is affected signifcantly by the number and size of cracks, and thus, the level of corrosion. For a given crack width due to corrosion, it is observed that the available bond strength is higher for larger concrete cover thicknesses than for smaller cover thicknesses. Certainly, the quality of concrete in terms of its permeability is equally important for the corrision protection. A relationship between the effect of w/c ratio on chloride ingress was developed to count for the deterioration in bond stress, and the induced current used in corroding the speciments of Amleh (2000) and of this investigation program were incorporated to consider for the lack of chloride lot content measured due to the shorter immersing time in this investigation and the high current used to force the specimens to corrode in the accelerated corrosion process.