A comparative study of metakaolin-based geopolymers with immobilised organic liquids: vegetable oil, mineral oil, and organosilicon liquids

Eco-friendly geopolymers have demonstrated highly effective in immobilising organic liquid wastes, even outperforming Portland cement-based materials. To evaluate the feasibility of reusing liquid waste-containing geopolymers, this study systematically investigated the effects of immobilising three categories of organic liquids, i.e., vegetable oil, mineral oil, and organosilicon liquids, on the strength, wettability, water absorption, multi-scale pore structure, and chemical composition of metakaolin-based geopolymers (MKGs). Results indicate that mixing 18 % vegetable oil has minimal impact on the early-age (3 and 7 d) compressive strength but reduces long-term (28 d) strength by 29.2−34.9 %. Vegetable oil generally exists as small spherical droplets (10−50 μm) within the MKG matrix, acting as hydrophobic fillers that reduce the water absorption rate by 78.0−83.2 %. In contrast, mineral oil with low dosages of <4 % enhances the 28-d compressive strength by up to 20.4 %. Mineral oil tends to aggregate into larger droplets (20–100 μm) due to poor dispersion. Organosilicon liquids markedly improve hydrophobicity of MKG, with water transport inhibition varying based on the functional groups of organosilicons and the microstructure of MKG matrix. This work reveals the effects and underlying mechanisms of various organic liquids on the reaction and properties of MKG, providing guidance for assessing their engineering applicability, durability, and functionality, and promoting the full utilisation of available resources.