Effect of soil mineralogy on the performance of Rice husk ash and wood ash (RHAWA) as Agrowaste-based alkali-activated Binders/modifiers in soil stabilisation

Soil stabilisation is crucial for enhancing the strength and bearing capacity of earth roads, particularly in regions where soils lose stiffness when saturated with moisture. Traditional stabilisers like Portland cement have been used, but emerging technologies such as alkali activation offer promising alternatives. However, the high energy requirements of alkali activators raise concerns about their environmental impact. This study investigates the feasibility of using agro/industrial wastes as alkali activator replacements for soil stabilisation and the effect of mineralogy on the performance of the binders. Materials from various regions were sourced, including wood ash and rice husk ash from Fursa rice mill, Kano, and kaolin from Bokkos, Plateau State in Nigeria. Soil samples from Abuja were also collected. Characterisation of source materials determined geotechnical properties and mineralogical/elemental oxide compositions. Initial trials determined optimal mix ratios for developing waterproofing binders. Optimised mixes were then introduced into soils at varying proportions (0-15% by dry weight) at moisture contents corresponding to the optimum moisture content of respective soils. Unconfined compressive strength tests were conducted after 24 hours and 7 days of curing at room temperature, both in dry and soaked conditions. Two-way ANOVA analysis revealed that the mineralogical composition of soils significantly influenced the strength and density of treated soils at a 5% confidence level. Additionally, alkali-activated modifiers significantly improved soil strength, with curing time showing minimal effect on soil behaviour. These findings underscore the potential of utilising waste materials for developing sustainable soil stabilisation solutions, aligning with the global transition toward a circular economy as well as showing the significance of mineralogy on the performance of the binder.