CO2 uptake by fine fractions of CDW

Abstract

Current concrete recycling consists of crushing waste concrete and use it again as aggregate for new concrete, according to specifications which are based on local regulations in different countries. Construction and demolition waste recycling is generally limited to the use of the coarser fraction as aggregate for new concrete. The quality of RCA is lower than that of natural aggregates, due to presence of residual mortar: for this reason, when dealing with concrete recycling, a differentiation between coarse (nominal size > 5 mm) and fine aggregates (maximum size < 5 mm) is generally done. While coarse recycled concrete aggregates (CRCA) are commonly used in partial replacement of natural aggregates in concrete, fine recycled concrete aggregates (FRCA) are less useful as aggregates in concrete as they can be highly detrimental for what concern strength, workability and durability. The problem with FRCA is mainly related to the presence of hydrated cement pastes and unreacted clinker phases. Interestingly, these phases are valuable materials when carbon uptake is considered. Interaction of cement pastes with environmental CO2 is a well-known phenomenon that has always been undesired due to the bad consequences on reinforcement bars. Only recently, the attention of scientific community moved into the direction of considering this interaction a resource in the environmental CO2 reduction: it is estimated that almost the half of CO2 emitted during clinker processing is reintroduced in the cement during its service life. In this paper, the potential CO2 uptake by carbonation of different simulated CDW is evaluated.