Stabilization of compressed earth blocks using recycled thermoplastics: experimental study of key parameters

The construction sector is a major contributor to global resource depletion and environmental pollution, particularly due to its reliance on energy-intensive and water-demanding materials such as cement and fired clay. Moreover, the increasing accumulation of plastic waste and the growing scarcity of freshwater resources present critical sustainability challenges. These intersecting issues highlight the urgent need for innovative, low-carbon, and water-efficient building materials. Among sustainable construction approaches, earth construction offers a viable solution by utilizing natural, locally available materials with minimal environmental impact. This study introduces a cement-free, low-water alternative through the development of recycled thermoplastic-stabilized Compressed Earth Blocks (CEBs) incorporating shredded recycled plastic with heat application. The experimental program comprised 54 mix-designs composed of soil, sand, gravel, lime, water, and plastic, with lime content fixed at 10%. Key variables included plastic content (5%, 10%, 15%), water content (10%, 12.5%, 15%), soil-to-sand ratio (1:1 and 1:1.25), and gravel proportion (5%, 15%, 25%). The blocks were tested for dry compressive strength (DCS), wet compressive strength (WCS) (i.e., following water immersion), and thermal conductivity. The 1:1 soil-to-sand ratio yielded the best performance, achieving a maximum dry strength of 9.93 MPa, wet strength of 4.08 MPa, and minimum thermal conductivity of 0.27 W/m·K. Statistical analysis showed that plastic content had the strongest influence on DCS, while the soil-to-sand ratio governed WCS. Water content was the most influential factor affecting thermal conductivity, whereas the remaining variables showed weak or non-significant effects. The selection framework produced three high-performing mixes (10% lime, 10% water, 10% plastic) with gravel contents of 5%, 15%, and 25%. These mixes advanced through successive performance thresholds, resulting in a refined set of combinations exhibiting strong structural, improved durability, and thermal characteristics. A preliminary economic assessment indicated that the proposed blocks are cost-competitive with conventional concrete bricks. However, this assessment is limited to raw material costs and does not include life-cycle cost or environmental impact analysis. The study avoids cement usage and incorporates recycled plastic waste, although no quantitative assessment of carbon reduction or environmental performance was conducted.