Sustainable interlocking floor tiles from recycled PP/HDPE, fly ash, and jute fiber: Characterization, performance optimization, and techno-economic assessment

Plastic-waste accumulation and the growing demand for affordable, durable construction materials require scalable valorization pathways that integrate performance, manufacturability, and economic viability. This study developed injection-molded interlocking floor tiles from recycled polypropylene/high-density polyethylene (rPP/rHDPE; 80:20 within the polymer fraction), fly ash (FA), jute fiber (JF), and sodium silicate (SS). Twenty-one formulations were manufactured using a purpose-designed CNC-machined die and evaluated through standardized tensile, compressive, flexural, Izod impact, Shore D hardness, seven-day water absorption, and chemical exposure tests, complemented by FTIR, FESEM–EDX, response surface methodology (RSM), ANOVA, multi-response ranking, and scenario-based cost analysis. Among the experimentally tested formulations, Sample 19, containing 80 wt% rPP/rHDPE, 10 wt% FA, 6 wt% JF, and 4 wt% SS, achieved the highest equal-weight normalized score of 0.72. It exhibited a tensile modulus of 1.61 GPa, tensile strength of 38.68 MPa, compressive strength of 68.20 MPa, flexural modulus of 0.97 GPa, flexural strength of 42.40 MPa, impact strength of 37 kJ /m², hardness of 57.38 Shore D, water absorption of 0.31%, and chemical-exposure mass change of 0.64%. FTIR indicated that constituent integration was governed primarily by physical interactions rather than new covalent bonding, whereas FESEM–EDX revealed a predominantly continuous polymer-rich matrix with dispersed inorganic phases, together with localized voids, fiber pull-out, and agglomeration. RSM–ANOVA identified the recycled-thermoplastic fraction as significant across all responses, while revealing response-specific contributions from FA, JF, and SS together with significant interaction and nonlinear effects. Multi-response optimization predicted an optimum composition of 75.14 wt% rPP/rHDPE, 15 wt% FA, 5 wt% JF, and 4.85 wt% SS, with an overall desirability of 0.749. The corresponding predicted tensile, compressive, and flexural strengths were 30.19, 73.24, and 46.58 MPa, respectively, together with an impact strength of 34.2 kJ /m², hardness of 60.78 Shore D, water absorption of 0.38%, and chemical-exposure mass change of 0.56%. Under the stated production assumptions, the estimated installed cost was BDT 63.79 ft⁻² (USD 0.52 ft⁻²), approximately 41.9% below the ceramic-flooring benchmark. These findings establish proof-of-concept manufacturability and composition-dependent performance for circular flooring applications; however, independent confirmation of the model-predicted optimum and service-relevant durability testing are required before commercial qualification.