Microscopic Assessment of Corrosion-Induced Cracking in Reinforced Concrete Using the Damage Rating Index

Abstract

Corrosion of embedded reinforcement remains one of the most critical deterioration mechanisms compromising the longevity and serviceability of reinforced concrete (RC) structures. The Damage Rating Index (DRI), a microscopic technique that has been employed for assessing concrete damage induced by internal swelling reactions, has not yet been applied to the assessment of reinforcement corrosion-induced damage. This study investigates the applicability and sensitivity of the DRI protocol in evaluating corrosion-induced cracking in the RC. A series of cylindrical RC specimens with two water-to-cement ratios (0.4 and 0.54) and a range of concrete cover-to-rebar diameter ratios were subjected to accelerated corrosion to achieve a target reinforcing steel mass loss of 5% embedded.

Microscopic examination and DRI quantification were conducted on polished sections of concrete, focusing on two key deterioration features: cracks in the cement paste (CCP) and cracks with reaction products in the cement paste (CCP-RP). The findings demonstrate that the DRI effectively captures variations in damage pattern and severity as a function of mixture design and cover depth. An extended DRI approach, incorporating normalized crack densities and area-based analyses, further substantiated the sensitivity of the method. A corrosion damage classification model was proposed, integrating DRI counts, normalized crack areas, and visual observations to define five progressive levels of deterioration. The results establish the DRI as a viable diagnostic tool for quantifying microstructural damage due to reinforcement corrosion, marking the first demonstration of its application beyond internal swelling reactions and underscoring its potential as a broader framework for structural durability assessment.