Abstract Global cement production reached approximately 4.1 billion metric tons in 2023, while global plastic production climbed to 413.8 million metric tons, projected to reach 590 million metric tons by 2050. This growth underscores the need for sustainable construction materials that can simultaneously divert plastic waste from landfills and reduce demand for virgin aggregates. Controlled Low-Strength Material (CLSM), or flowable fill, offers a promising platform by incorporating large volumes of industrial by-products. This study investigates the use of Recycled Plastic Coarse Aggregates (RPCA) produced from High-Density Polyethylene (HDPE), Low-Density Polyethylene (LDPE), PP (Polypropylene) and mixed plastic waste via a semi-mechanized process as a full replacement for natural coarse aggregates in CLSM. Low-, medium- and high-strength mixes were prepared with Portland cement, fly ash, M-sand and pond ash, and their fresh, hardened and in-service properties were evaluated. Results showed that RPCA-based CLSM achieved flow values of 590–620 mm, wet density reductions of ~ 30%, compressive strength up to 13.4 MPa at 28 days span both excavatable (≤ 8.3 MPa) and structural fill (> 8.3 MPa) CLSM categories as per ASTM D6103, with all low- and medium-strength mixes meeting typical excavatability requirements, shrinkage as low as 0.032%, permeability reductions of 9–15%, and thermal conductivity reductions of ~ 90% leading to a 92% increase in thermal resistivity relative to natural aggregate mixes. An integrated machine learning approach was employed to predict compressive strength from 252 experimental data points using Decision Tree, Random Forest and XG Boost regressors. XG Boost achieved the best performance with R 2 =0.97, MSE 0.08 and MAE = 0.12, outperforming the other models. SHAP analysis revealed that curing age and pond ash content were the most influential variables, followed by fine aggregate and RPCA proportion. This combined experimental–computational framework demonstrates that RPCA-based CLSM can deliver measurable environmental and performance gains while enabling data-driven mix optimisation for sustainable infrastructure applications. Overall, the proposed RPCA-based CLSM aligns with the United Nations Sustainable Development Goals by promoting responsible consumption and production (SDG 12), fostering industry innovation and resilient infrastructure (SDG 9), supporting sustainable cities and communities (SDG 11), and contributing to climate action through material efficiency and reduced embodied energy (SDG 13).
Karthik et al. (Fri,) studied this question.