Mechanical behavior, mineralogy, and microstructure of alkali-activated wastes-based binder for a clayey soil stabilization

This paper evaluated the mechanical and microstructural behavior of a clayey soil stabilized by an alkali -activated binder composed of two residues (sugarcane bagasse ash and hydrated eggshell lime) and sodium hydroxide. The sugarcane bagasse ash, an agro-industrial waste, contains high aluminosilicates content (64.74 % silica and 13.25 % alumina), needed for alkali-activation processes; calcium additions from the lime (72.90 % calcium oxide) allow curing at room temperatures. An experimental design analyzed the mechanical behavior of soil-alkali activated binder, and soil-Portland cement mixtures. Unconfined compressive strength (UCS), tensile strength (STS), stiffness (G0), durability (accumulated loss of mass, ALM), and matric suction tests, and XRD and SEM-EDS investigations were performed. Statistical analysis showed a higher influence of the dry unit weight over the binders' mechanical results. In addition, binders presented similar mechanical results for mixtures cured in room temperature (23 degrees C) (e.g., UCS around 5 MPa for high density-high binder content samples with 30 % moisture content, and STS around 0.6 MPa for high density-high binder content samples with 28 % moisture content). For both binders, the lowest ALM was 1.63 % for high density-high binder content samples. The porosity/binder content index was a reliable parameter when evaluating soil stabilization. XRD and SEM analysis of alkali-activated samples showed, respectively, an amorphous hump attributed to disordered structures (C-S-H and (C,N)-A-S-H) and soil particles embedded in a cementitious matrix. Higher temperature (40 degrees C) and curing period (28 days) resulted in a denser structure.