Improvement of Recycled Cement Powder Characteristics from C&D Wastes by Accelerated CO2 Curing and/or Heat Treatment

Huge quantities of construction and demolition waste are produced each year, and about a third of this is concrete. With growing interest in circular economy, there is a need to examine how this can be applied to end-of-life concrete. While there is a potential market for recycled coarse aggregate, the reuse of fine aggregate and recycled concrete powder is more limited. However, recycled concrete powder constitutes up to 10% of the mass of crushed end-of-life concrete, and comprises almost 80% hardened cement paste. This calcium- and silicon-rich paste is ripe for reactivation. This study has examined the latent hydraulic behaviour of recycled concrete powder and investigated how various treatment methods can produce an effective supplementary cementitious material. Heat treatment and carbonation, either in isolation or combined has been used to produce materials with activity indices approaching unity at 20% replacement. The performance of these materials has been understood via detailed characterization by thermal analysis, XRD and FTIR. It has proven possible to produce effective supplementary cementitious materials from waste recycled concrete powder, thus finding a use for this end-of-life material and potentially reducing cement’s carbon footprint.