Mortar with Substituted Recycled PET Powder: Experimental Characterization and Data-Driven Strength Predictive Models

The physical and mechanical characteristics of a novel mortar that uses recycled PET powder as a replacement for natural sand are examined in this paper. This study specifically looks at the impacts of replacing recycled polyethylene terephthalate (PET) powder in place of fine aggregates in mortars. To create five distinct mortar mixes, recycled PET powder was substituted in varying proportions (0%–30% by volume of the sand). The investigation focuses on the physical and mechanical characteristics of the material, including density, slump, water absorption, ultrasonic pulse velocity, flexural and compressive strength, and microstructural and interface characterization. Results reveal that the substitution of recycled PET powder reduces slump, compressive strength, ultrasonic pulse velocity, dry and wet density, and slump, whereas flexural strength and fracture energy exhibit the reverse tendency. The slump variation indicates the controllable workability of the mortar in the fresh state. The latter feature is quite important for the application of such a material where flowability is a dominating parameter, e.g., 3D printing. Two data-driven models for the compressive and flexural strength reduction factors as a function of the substitution ratio based on symbolic regression techniques are proposed using the findings of this study in conjunction with data from the literature.