Rendering Mortars Incorporating Construction and Demolition Waste: Effects on Mechanical Properties, Color Characteristics and Microbial Anti-Adherence Capacity

The paper presents experimental results regarding the valorization of construction and demolition waste and fly ash in rendering mortars based on Portland cement and lime. The binder was partially replaced (50 wt.%) with concrete waste and/or fly ash, while the natural aggregate (quartz sand) was completely substituted with recycled aggregate consisting of brick and concrete waste obtained from demolition activities. This replacement led to a reduction in mortar mechanical strength, while increasing the capillary water absorption coefficient. However, mortars containing fly ash exhibited the lowest water absorption coefficients among the waste-containing formulations and the smallest reduction in mechanical performance. The color differences observed among the individual raw materials were substantially reduced after their incorporation into the mortars. Following accelerated carbonation, all mortars showed good anti-adherent capacity against C. albicans, S. aureus and E. coli, mainly associated with their residual alkalinity, while porosity-related effects on microbial colonization were limited. Overall, the results demonstrate the feasibility of producing rendering mortars incorporating high levels of construction and demolition waste as binder and aggregate replacements, while maintaining acceptable mechanical, colorimetric, and antimicrobial performance, thus supporting resource conservation and circular economy principles in the construction sector.