Durability of concretes bearing construction and demolition waste as cement and coarse aggregate substitutes

Abstract

Concrete combining ground recycled masonry aggregate (GR-RMA) as a partial cement replacement and coarse mixed recycled aggregate (MRA), both sourced from construction and demolition waste (CDW), was analysed for durability. The analysis consisted in indirectly characterising pore system permeability based on key water transport indicators. Concretes were prepared with 25%–50% MRA and/or 25% GR-RMA. The findings showed that, irrespective of the MRA content, in 28 d materials bearing 25% GR-RMA total water absorption was 5.7%–7.1%, porosity 3.5%–5.8%, depth of penetration of water under pressure 3.6%–4.6% and capillary water absorption 3.2%–4.9% lower than in concretes manufactured with conventional cement and MRA. Those values were directly attributable to the lower connectivity of the pore structure in the new concretes, which translated into higher electrical resistivity. All the concretes prepared with both 25% GR-RMA and 25%–50% MRA exhibited depth of water penetration under pressure of <30 cm, total water absorption of <4.2% and sorptivity of <0.4 mm min−0.5, ensuring their impermeability to aggressive external agents. According to a multi-criterion analysis also conducted, optimal mechanical efficiency, durability and environmental impact were attained for materials bearing 25% GR-RMA and 25% MRA. The conclusion drawn from those findings is that the lower quality of MRA than conventional aggregate may be suitably offset by using supplementary cementitious materials (SCMs) in the respective cement in conjunction with such recycled mixed waste to obtain more eco-efficient concretes with properties that ensure their impermeability throughout their service life.