Thermal insulation and mechanical performance of sustainable rammed earth walls incorporating construction and demolition waste and calcium oxide

The construction industry must reduce its environmental footprint and use sustainable materials with low energy and carbon emissions. Conventional masonry and concrete are reliable, durable, and widely used construction materials, but they use up natural resources and produce a considerable amount of CO₂ emissions. Rammed earth (RE) is a sustainable material and an environmentally friendly construction method that is less energy intensive and exhibits good thermal performance; however, its strength is a limitation for larger structural projects. To address these challenges, this study presents an experimental evaluation of the thermo-mechanical, environmental, and economic performance of stabilized rammed earth (RE) walls incorporating construction and demolition waste (CDW) and calcium oxide (CaO) as sustainable stabilizing additives. This research aims to enhance the structural integrity, thermal insulation, and sustainability of RE systems by partially replacing natural soil with CDW (10-30%) and CaO (2-6%). Seven mix designs were designed and tested for compaction properties, unconfined compressive strength (UCS), thermal conductivity, embodied energy, CO₂ emissions, and thermal behavior under simulated hot climate conditions with varying relative humidity. The optimal mixture, CDW30-C2 (30% CDW and 2% CaO), achieved a peak UCS of 9.3 MPa at 28 days, the lowest thermal conductivity (0.88 W/m·K), moderate embodied energy (705.27 MJ/m³), and reduced carbon emissions (177.73 kg/m³), offering a high strength-to-impact efficiency. To validate its practical applicability, a full-scale RE wall was constructed using the CDW30-C2 mixture and subjected to thermal insulation tests in a controlled climate chamber at 40-80% relative humidity. The findings demonstrated a time lag of up to 90 min and a decrement factor of 0.85, indicating favorable thermal inertia and effective moderation of heat transfer. The synergistic effects of CDW particles enhanced mechanical interlocking and matrix densification, while CaO contributed to pozzolanic reactivity and void filling. Compared to conventional fired brick and concrete, the optimized RE mix demonstrated competitive performance with significantly lower environmental impact. These findings demonstrate the viability of CDW-CaO stabilized rammed earth as a climate-resilient, low-carbon, and resource-efficient building solution for sustainable construction.