Sustainable Poured Earth Construction Using Tropical Soil and Local Wood Residue Extracts

French Guiana faces high population growth and requires affordable local building materials. Poured earth construction primarily uses local soils and could offer a cost-effective and eco-friendly solution. However, achieving easy casting and fast hardening requires additives, which can increase the economic and environmental costs when using imported industrial chemicals. Recent advancements highlight the promise of combining tannin, a polyphenolic wood extract, with sodium hydroxide (NaOH) and ferric oxides for easy pouring and fast hardening. Importantly, the tannin-iron interaction enhances water resistance, addressing a major drawback of earth-based materials. This study evaluated five local wood residue extracts and compared them to commercial Chestnut tannin to fluidify and improve the water resistance of a local soil. Extracts were obtained through microwave-assisted water extraction and analyzed by infrared spectroscopy and total phenolic content. Results revealed that each wood extract showed different structures and amounts of phenolic content, resulting in different effects on the soil's fluidity and water resistance. Notably, the extract from Wapa, abundant in the forests of northern South America, showed the highest phenolic content and could improve soil fluidity similar to Chestnut. Additionally, Wapa significantly improved water resistance, resulting in a 79% reduction in mass loss, compared to only a 43% reduction achieved with Chestnut. This study underscores the potential of locally sourced tannin extract for sustainable poured earth construction with tropical soils.