Non-destructive monitoring of incipient corrosion in reinforced concrete with top-bar defect using a combination of electrochemical and ultrasonic techniques

Abstract

Top-bar defect in reinforced concrete (RC) leads to the formation of interfacial voids underneath the reinforcements at an elevation of 300 mm or more. Rebars with top-bar defects show earlier corrosion initiation, faster corrosion rate and a different pattern of corrosion, compared to those without. This paper proposes combined electrochemical and ultrasonic methods for monitoring incipient corrosion in RC. An RC wall structure is cast vertically aiming to create top-bar defect. The specimens were subjected to accelerated chloride-induced corrosion. Simultaneously, they have been monitored with half-cell potential method (HCP), linear polarisation resistance method (LPR), ultrasonic guided waves (GW) and ultrasonic imaging (UI). The pros and cons of the four techniques are determined and discussed. The results are correlated and calibrated with the state of corrosion. Key milestones of the corrosion mechanism such as corrosion initiation and crack initiation can be successfully identified and the progression of bar deterioration, steel-concrete interfacial debonding and cracking propagation have been traced.