New insights into diffusion and reaction of CO₂ gas in recycled aggregate concrete

The diffusion and reaction mechanisms of gas in natural aggregate concrete cannot be directly used for modelling the gas behavior in recycled aggregate concrete due to its inhomogeneity. Thus, the inhomogeneity of CO₂ diffusivity in RAC is simulated for the first time using the multi-path modelling theory proposed herein. The diffusion and reaction models of CO₂ in each path are then established. The carbonation depth in each path is determined. The reliability of theoretical maximum and average values of carbonation depths in different paths is further verified by experimental data. The results showed that there were five kinds of CO₂ diffusion paths in recycled aggregate concrete and their carbonation depths showed a noteworthy difference. Besides, the developed theoretical model can predict the maximum value, weighted and mathematic average values of carbonation depths with reasonable accuracy, and the model in this study was more accurate than those in the literature.