Phase composition and Durability Assessment of 50-year-old Reinforced Concrete subjected to Natural and Accelerated Carbonation

Abstract This paper presents an investigation conducted on a 50-year-old structure in a composite climactic zone of India. The study comprises of two parts, one covering the comparison of long-term natural carbonation and short-term accelerated carbonation, while another reveals 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. Accelerated carbonation did, however, lead to preferred precipitation of calcite and higher degree of C-S-H carbonation. Additional investigations including core strength, carbonation depth measurements, half-cell potential analysis, resistivity, and corrosion rate measurements were also carried out. Findings from structural investigation indicate that carbonation coefficient shows a high variation within the structure and moisture is found to be main factor influencing the corrosion rate. Based on the results, recommendations on additional measurements are made, to better understand variations in carbonation rate. Visual inspections are seen to become crucial in the propagation phase, especially when half-cell potential and surface resistivity lie in the inconclusive range.