Carbonation dominates the acid intake of recycled concrete aggregate subjected to intermittent leaching

• Carbonation dominates the acidity intake of the in-situ recycled concrete aggregate (RCA).
• The volume of effluent plays a secondary role on the alkali consumption of the field RCA.
• Open-grade drainage course is efficient to delay the toxic species leaching from the RCA.

Recycled concrete aggregate (RCA) is being encouraged to use as substitute materials of the virgin aggregate for the pavement materials. RCA used in road layers is submitted to intermittent leaching. The leachant neutralizes the alkali of the RCA and the leaching intermission promotes the carbonation of the RCA’s residual mortar. Both processes introduce acid to the RCA, releasing the pH-dependent toxic constituents of the RCA to the local aquifer. In this study, the acid intake caused by the leachant renewal and leachate decantation is calculated and compared with the acid intake induced by the carbonation during the leaching intermission. It is found that carbonation dominates the acid intake of the leached RCA layer while the renewal-decantation process acts only secondary role. The use of open-graded RCA base overlain by a dense pavement is recommended to reduce the carbonation rate of the RCA and to retard the leaching pH-dependent toxic elements to the local aquifer.