Mechanical and Hygrothermal Evaluation of Eco-Friendly Cement Mortar Incorporating Upcycled Low-Density Polyethylene

This study examined the mechanical and hygrothermal response of cement mortars in-corporating recycled low-density polyethylene (LDPE) as a partial replacement of fine ag-gregate at levels of 2.5%, 5.0%, and 7.5% by weight of sand. A reference mixture without polymer was also prepared. The experimental program included determining density, workability, and compressive strength at 7 and 28 days. Based on the mechanical results, the formulation containing 2.5% LDPE was selected for further hygrothermal assessment in 1:5 scale chambers coated with conventional and modified mortars. The incorporation of LDPE progressively decreased both density and compressive strength. At 28 days, the reference mortar reached 5.243 MPa, whereas the mixture with 2.5% LDPE attained 1.461 MPa. Hygrothermal monitoring showed no substantial improvement in indoor tempera-ture regulation; however, the LDPE-modified coating maintained higher indoor relative humidity than the conventional system during the test period. These results indicate that recycled LDPE can be incorporated into cement-based mortars at low replacement levels for exploratory non-structural applications. However, the resulting decrease in mechani-cal strength restricts its wider applicability and highlights the necessity for further verifi-cation to satisfy performance standards tailored to specific applications.