Assessment of carbonation and corrosion in a 50-year-old reinforced concrete building

This paper presents an investigation conducted on a 50-year-old structure in a composite climactic zone of India. The study comprises two parts, one covering the comparison of long-term natural and short-term accelerated carbonation while another revealing insight into the structure's durability and potential concerns. Mineralogy, pore solution, and transport properties comparison of natural and accelerated carbonated concrete samples highlight similar modifications, demonstrating the representative nature of accelerated carbonation at 3% carbon dioxide concentration. However, accelerated carbonation led to the preferred precipitation of calcite and a higher degree of C-S-H carbonation. Core strength and carbonation depth measurements indicate that the carbonation coefficient shows a high variation within the structure due to micro-climatic conditions, and there is a need to consider carbon dioxide concentration greater than 400 ppm for residential buildings. Additional investigations based on half-cell potential, surface resistivity, and corrosion rate measurement highlighted that moisture availability is the main deterioration-controlling factor during the propagation phase. Also, it was realized that during an inspection, if different non-destructive measurements fall in the middle range, it becomes inconclusive to ascertain the severity of corrosion. In such situations, visual inspection of the reinforcement is imperative. Finally, the authors recommend collecting data on carbon dioxide concentration and the moisture state of different locations in the structure during structural inspection.