Analysis of Lime Mortars Modified with Polymeric Waste Aggregates as a Circular Economy Strategy for Sand Replacement

Currently, plastic waste is a major environmental problem. In line with circular economy principles, plastics’ non‑biodegradability, high volume and health impacts demand end‑of‑life recovery and recycling solutions. This study evaluates the use of plastic aggregates from medium‑voltage cable waste in hydraulic lime mortars as a circular alternative to linear “take–make–dispose” practices. Substituting natural sand with secondary plastic aggregates conserves primary mineral resources, closes material loops for post‑consumer plastics, and situates this strategy higher in the waste hierarchy than landfilling or energy recovery. The research evaluates the replacement of natural sand with these secondary raw materials and its influence on the physicochemical and mechanical performance of mortars. Replacement levels up to 100% of the aggregate were assessed, achieving reductions in apparent density of hardened mortars of up to 30.8%. Mechanical properties were monitored at 28, 90, and 180 days, revealing a progressive gain in strength over time and showing how increasing plastic aggregate content reduces flexural and compressive strength. This mechanical evolution was correlated with changes in mineralogical composition through thermogravimetric analysis and X‑ray diffraction, quantifying the gradual transformation of portlandite into calcite. The results demonstrate that plastic waste from electrical installations can be successfully incorporated into non‑structural lime‑based materials, providing a valorization route for this waste stream. The study strengthens the circularity of construction products and helps reduce the consumption of natural raw materials in the building sector, offering insights for the design of sustainable mortars and contributing to a more circular management of plastic waste in construction.