Model for practical carbonation depth prediction for high volume fly ash concrete and recycled aggregate concrete

The reuse of industrial residue streams such as fly ash (FA) or waste materials such as recycled concrete aggregate (RCA) can be beneficial both from an economic and an ecological point of view. Extensive research, investigating different properties of these concrete types, has been carried out so far. However, durability remains a key property ensuring sustainable application of these materials in the construction sector that still needs more research to be fully understood. The main objective of this study was to evaluate the application of widely used models for carbonation depth prediction—defined for ordinary Portland cement concrete with natural aggregate (NAC)—to high volume FA concrete (HVFAC) and recycled aggregate concrete (RAC). The research presented in this paper was conducted in two steps. First, an experimental programme was designed to provide better understanding of the influence of different CO2 concentrations on the carbonation process kinetics in HVFAC, RAC and NAC. This was performed using accelerated carbonation tests (CO2 concentrations of 1%, 2%, 4% and 16%) and natural carbonation tests (duration 21 and 48 months). Furthermore, a database of previously published results of HVFAC and NAC carbonation depths was made in order to analyse the application of carbonation depth prediction defined by Tuutti and given in the fib Model Code 2010. It was shown that the existing models, providing the relationship between accelerated test results and natural carbonation depth, are applicable to NAC and RAC but not to HVFAC. Modifications of the above mentioned models were proposed in order to enable a more accurate and reliable prediction of the HVFAC carbonation depth under natural exposure conditions