Quantifying movements of corrosion products in reinforced concrete using x-ray attenuation measurements

Corrosion of steel reinforcement, embedded in concrete, may substantially degrade concrete structures due to the expansive nature of corrosion products. Expansion of corrosion products cause tensile stresses to develop and cracks to form in concrete. Extensive research has focused on corrosion-induced damage of concrete, typically by monitoring and quantifying the formation of cracks in concrete surrounding corroding reinforcement. Based on the type of experimental data numerous corrosion-induced damage models have been developed. One common conclusion from these models is that a certain amount of corrosion products move into the concrete without generating tensile stresses and cracks in the concrete. Typically, corrosion products are thought to occupy pores, interfacial defects, and/or air voids located near the concrete-steel interface and stresses develop only after filling of these pores. Further, the amount of corrosion products the concrete can accommodate is directly related to model predictions of time-tocracking. While some have attempted to measure the size of the region where corrosion products are accommodated using destructive and invasive approaches, additional techniques are needed to more accurately assess this vital parameter. This paper describes the use of x-ray attenuation measurements to monitor and quantify the movements of reinforcement corrosion products into mortar surrounding corroding reinforcement. Corrosion is induced by application of direct current to the embedded reinforcement. X-ray attenuation measurements are also capable of detecting cracks. Therefore, this approach provides a direct measurement of the amount and location of reinforcement corrosion products required to induce cracking. Results of a parametric investigation on the impact of water-to-cement ratio (0.30, 0.40, and 0.50) and corrosion rate are presented. Results from this non-destructive experimental approach should provide further insights for the modelling of reinforcement corrosion and corrosion-induced damage of concrete structures.