Utilization of powders and fine aggregates from the recycling of construction and demolition waste in the 3D printing of Portland-based cementitious materials

This paper analysed the possibility of using recycled powders (<75 µm) and recycling fine aggregates (<1.18 mm) obtained during the crushing and grinding of concrete waste (CoW), ceramic waste (CeW) and red clay brick waste (RCBW) when designing cementitious pastes and mortars for 3D printing. The effects of the type of powder (CoW-powder, CeW-powder and RCBW-powder) and of the liquid/solid (L/S) ratio on the mixture properties in the fresh and hardened states were studied. In the fresh state, the level of flowability (mini-slump), flow index (flow table), buildability and setting time characteristics of the cementitious pastes were evaluated. In addition, the rheological behaviour was analysed through a rotational rheometer. In the hardened state, the compressive strength was determined at 3, 7, 28 and 90 days. The effects of the type of recycled fine aggregate (RFA − CoW, RFA − CeW and RFA − RCBW) were evaluated for mortars with a cement:aggregate ratio of 1:0.5. Based on the results obtained, the most suitable mixtures were selected to carry out 3D printing tests on a laboratory scale. From the 3D printing of beam-type specimens, it was possible to determine the flexural and compressive strengths (28 days) of the selected mixtures. The results obtained validated the possibility of using recycled powders (CoW, CeW and RCBW) to replace 30 % of ordinary Portland cement (OPC) and to incorporate 100 % recycled fine aggregates in the design of cementitious materials (pastes and mortars) for 3D printing. In this regard, the recycled powders and recycled fine aggregates increase the buildability and thixotropy of cementitious mixtures. With an adjustment in the L/S (liquid/solids) ratio, their application in 3D printing becomes feasible. This alternative for the use of powders and fine aggregates from construction and demolition waste (CDW) could be considered a contribution towards the sustainability of the sector and the implementation of a circular economy.