Screed Mortars Containing Recycled Plastic Waste: Influence on Physical Properties and Durability

Screed mortars are extensively used in construction, yet their durability and environmental footprint remain key challenges. This study evaluates the effects of partially replacing natural sand with polymeric waste aggregates (25–55% by volume) on the mechanical, hygric, and deformation-related properties of cementitious screed mortars. The proposed material solution, protected under patent ES2973008, results in a significant reduction in density of up to 26.87% while decreasing natural aggregate consumption by as much as 55%, improving workability and ease of application. Experimental results indicate reductions in flexural and compressive strength with increasing polymer content; however, the obtained strength levels remain suitable for self-leveling mortars and applications subjected to pedestrian traffic or light loads. In contrast, the incorporation of polymeric aggregates leads to marked improvements in durability-related parameters, including reductions in drying shrinkage of up to 25.2%, Young’s modulus of up to 73%, capillary water absorption of up to 72.34%, and water vapour permeability of up to 6.53%. These combined effects reflect a pronounced increase in elastic deformation capacity, dimensional stability, and resistance to moisture ingress, thereby reducing susceptibility to shrinkage-induced cracking and freeze–thaw damage. Overall, the results demonstrate that polymeric waste incorporation enables the development of lighter, more crack-resistant, and more durable screed mortars, achieving a favourable balance between mechanical performance and long-term durability while contributing to sustainability and circular economy objectives.