Life cycle carbon emissions and thermal performance of unfired bricks for sustainable construction materials

This study evaluates the environmental impacts and thermal performance of fired and unfired bricks incorporating Para Rubber Latex (PRL). Samples were collected from eight traditional and small-scale production sites in Ayutthaya provinces, Thailand. A cradle-to-gate Life Cycle Assessment (LCA) was conducted with measurement-based thermal analysis of 1 × 1 m wall panels under hot-humid climate conditions. Fired bricks exhibited total emissions of approximately 474.54 gCO₂e per brick, with the firing stage (Module A3) contributing 53.86.%, dominated by biogenic CO₂ released from rice husk combustion. In contrast, unfired bricks emitted only 336.56 gCO₂e per brick, mainly from transportation and cement use (Module A2), accounting for 88.77 % of total emissions—an 29.07 % reduction compared to fired bricks. PRL incorporation induced favorable microstructural modification, forming a continuous polymer film that reduced pore connectivity, leading to lower water absorption and enhanced thermal insulation. The PRL5 % mixture achieved balanced performance, improving compressive strength by 3.0 % while maintaining low thermal conductivity. Thermal analysis revealed that fired brick walls, with higher thermal conductivity (1.12 W/m·K), experienced faster and greater internal temperature fluctuations (ΔT_in=10.0°C). Unfired bricks, with lower conductivity (0.4253 W/m·K), maintained better thermal stability, maintaining a time lag of under one hour. For a 10 m² wall, unfired bricks reduced average heat loss by up to 78.81 % and lowered CO₂ emissions over fourfold compared to fired bricks. Overall, unfired rubberized bricks—especially those with 2.5–5 % rubber latex (PRL2.5–PRL5)—demonstrate strong potential as low-carbon, energy-efficient alternatives for sustainable building applications.