Corrosion Of Steel In Cracked Reinforced Concrete Pipes

ABSTRACT Reinforced concrete pipes are commonly used for culvert and storm drainage applications and are intended to last for several decades. The effect of cracks on corrosion of embedded reinforcing ~3/16 in (~4.75 mm) diameter steel wires was investigated. Cracks having a nominal width of 0.02 and 0.1 inch (~ 0.5 and ~2.5 mm) were induced by 3-point bending on the interior surface of quadrants extracted from 18inch (45 cm)-diameter concrete pipes. Two types of concrete pipes were examined and referred to as Z-type and R-type with average interior concrete covers of 1.2 and 0.7 inch (30.5 and ~17.8 mm) respectively. The Z-type contained higher cement content whereas the R-type had a 20 % fly ash replacement. The cracked specimens along with controls were tested under both continuous and 1 week-dry/1 week-wet cyclic exposures to 500 ppm chloride solution for periods of 115 days and 7 cycles respectively. Open circuit potential and electrochemical impedance measurements were performed. Electrochemical test results were calibrated using data obtained from destructive examination of wire corrosion. Data analysis showed that corrosion current increased as the crack width-to-cover ratio increased for both types. Corrosion-based projection models indicated strongly enhanced performance for the 0.02-inch (~0.5 mm) cases compared to the 0.1-inch (~2.5 mm) cases. INTRODUCTION Reinforced concrete pipes (RCP) are widely used in installations requiring service over a period of many decades, so only extremely slow deterioration with time can be accepted. Concrete cracks are often revealed by inspections conducted on recently placed pipes. In-place RCP cracks can degrade pipe performance by decreasing structural strength and dimensional stability, permitting leaks and marginally increasing hydraulic resistance, and by allowing premature corrosion of steel reinforcement.^{1- 3} At the bottom of such cracks bare steel is likely to be directly exposed to water which, if renewed regularly by flow, would eventually have a pH close to that of the environment.