Service-life prediction of recycled coarse aggregate concrete under natural carbonation: A time-dependent reliability analysis

Abstract

Carbonation is a phenomenon that involves several uncertainties associated with concrete properties and environmental factors. However, most existing studies have adopted a deterministic approach to deal with this phenomenon, which can lead to misinterpretations. This study aimed to carry out a probabilistic analysis of natural carbonation with data collected for over 30 months of recycled coarse aggregate (RCA) concretes and natural coarse aggregate concretes (NCA), used as reference. The probabilistic analysis showed that the cover depth collected in field presented a normal distribution behavior, in this way, random variables were generated to sample cover depth values to be used in time-dependent Monte Carlo simulations. A computational algorithm was developed in MATLAB to evaluate the probability of the carbonation depth (xc) overcoming cover depths (cd) of 15-, 20-, 25-, 30-, 35-, and 40-mm, usual values in structural design. The simulations showed that the RCA anticipated the probability of failure (xc ≥ cd) by up to 100 months compared to natural coarse aggregate (NCA) concrete. The results indicated that the total replacement of NCA by RCA requires increases of up to 1.4 in cover depth to perform equivalently to the reference concrete (with NCA). Moreover, regardless of the type of aggregate and w/c ratio, with the cover depth established in the Brazilian standard for urban environments, the evaluated concrete did not reach the minimum service life of 50 years established for structural elements of reinforced concrete. The methodology applied in this paper can be used to predict the service-life considering failure due to carbonation using the statistics response of experimental data.