Résumé
Tropical regions like French Guiana need local building materials to cope with high population growth and the high cost of imported cementitious materials. Poured earthen construction could represent a local, cost-effective, and ecologically friendly alternative. To ensure good workability and facilitate pouring, the use of dispersants to deflocculate clay particles is an effective strategy that reduces water demand and increases the material's density and strength. Natural organic dispersants can replace industrial ones while reducing costs and carbon footprint. It is currently unknown how organic dispersants could improve the workability, physical and mechanical properties of the iron-rich lateritic soils present in French Guiana. Here, different potential dispersants were evaluated at constant water content on a lateritic soil-based mortar: citric acid, sodium carbonate, tannins, tannins+sodium hydroxide (tannins+NaOH), tannins+sodium carbonate (tannins+Na2CO3). These dispersants were compared to industrial sodium hexametaphosphate (NaHMP). Three types of tannins were tested: hydrolyzable tannins from oak and chestnut, and condensed tannins from acacia. This study shows that all formulations improved workability and mechanical strength but only tannins+NaOH or Na2CO3 had a strong dispersant effect comparable to NaHMP. Furthermore, tannins+NaOH or Na2CO3 decreased the mortar's density without impacting strength, which may result from reactions between the soil's iron oxides and tannins, as observed by infrared spectroscopy (FTIR). Altogether, these results show that the addition of organic dispersant is an appropriate strategy to improve the fresh and hardened properties of lateritic soils. Particularly, tannins combined with sodium carbonate may represent an eco-friendly dispersant for poured earth in regions with iron-rich lateritic soils.