Closing the loop in lime-based renders: circular design, material properties and cradle-to-cradle LCA

The massive extraction of virgin raw materials has intensified the focus on the circular economy of building materials. As a Cradle-to-Cradle approach for lime-based construction materials (LBCM) is lacking, this study evaluates the environmental impact and feasibility of creating a fully recycled second-life render (SL) through a closed-loop upcycling process for first-life renders (FL). A second-life binder was thermally activated (900, 1000, 1100, 1200 °C), and its microstructure, compressive strength, and thermal conductivity were investigated. SL had up to 33% open porosity (FL 29%), compressive strength ranged from 2.5 to 3.4 MPa (FL 4.4 MPa), and thermal conductivity from 1.002 to 1.107 W/mK (FL 1.231 W/mK). SL and FL resistance against sulfate attack was equivalent, per RILEM TC 271-ASC recommendation. Environmental impact indicators confirm that the second-life render can reduce CO2 emissions by up to 55%. This research highlights sustainability gains through circular practices in the life cycle of LBCM.