Corrosion of reinforcement in concrete : electrochemical chloride extraction

Abstract

In recent decades, some reinforced concrete buildings have come to be regarded as culturally significant due to their architectural or social importance. Such structures include buildings, infrastructure, and disused industrial facilities. Unfortunately, many of these sites are vulnerable to damage from the effects of concrete carbonation and corrosion of embedded steel bars, particularly in coastal structures. To address this issue, a study was undertaken on the Fire Control Tower (1938) in Fort St. Elmo in Valletta, Malta. The project's objective was to assess the applicability and performance of Electrochemical Chloride Extraction (ECE) on historic reinforced concrete structures exposed to a marine environment (air-borne salts). A comprehensive appraisal was conducted to investigate the degradation processes and ascertain the cause of the deterioration. The assessment included a visual inspection supplemented with photogrammetry and non-destructive testing (NDT). Various NDT techniques were employed, including Cover Metre, Ultrasonic Pulse Echo, Resistivity, Schmidt Hammer, Thermal Camera, Ground Penetrating Radar (GPR) and Half-Cell Potential. The research involved examining two locations, one facing the sea and one facing the land, to ascertain chloride's presence and predict its accumulation on concrete surfaces and within its structure under different exposure conditions. An electrochemical chloride extraction system was implemented for 24 days as a temporary solution, using synthesized pore solutions as electrolytes and with an applied current density of 1A/m2 . Additionally, cores were extracted to assess the efficiency of the treatment in removing harmful chlorides from the structure, with a comparison between cores from treated and untreated areas. Material testing was conducted to assess if the ECE had any effects on the electrochemical properties of the materials. Materials analysis conducted on extracted cores included; carbonation, density, vacuum saturation porosity, and compressive strength. The study results indicate that ECE treatment was successfully applied to the historic concrete structure, and no further damage was done to the structure and can be considered a viable and practical approach to mitigating the damage caused by chloride accumulation on concrete surfaces.