Use of binder based on palm oil fuel ash for stabilization of tropical clay soils

• The optimal POFA calcination temperature is 850 °C, enhancing reactivity with 70 % POFA-30 % lime. • The 70 % POFA-30 % lime mix exhibits the highest reactivity among the studied combinations. • The POFA-lime binder reduces soil plasticity and enhances compaction properties. • Stabilized soil achieves 0.5 MPa UCS with 10 % POFA-lime, comparable to 6 % Portland cement. This study evaluates the use of palm oil fuel ash (POFA), a waste product generated during palm oil production, as a stabilizing binder for tropical soils. The raw materials were characterized through chemical composition analysis (XRF), mineralogical composition (XRD), and morphology (SEM). It was determined that the optimal calcination temperature for POFA is 850 °C, significantly enhancing its reactivity. The calcined POFA was mixed with hydrated lime in ratios of 30:70, 50:50, and 70:30 to determine the best combination as a binder. Clayey soil was stabilized using binder proportions of 6 %, 8 %, 10 %, and 12 % (POFA and lime). For reference, an Ordinary Portland Cement (OPC) was used in the same proportions. The impact of the binder on soil plasticity, optimum moisture content for compaction, and maximum dry density were analyzed. Additionally, mechanical performance was evaluated under dry and capillary-saturated conditions. The results indicate an increase in the soil’s compressive strength, reaching 0.50 MPa with 12 % binder (POFA and lime), compared to 0.14 MPa for untreated soil and 0.60 MPa for soil–cement with the same binder proportion. These findings demonstrate that adding POFA with hydrated lime significantly improves the soil’s physical and mechanical properties, presenting itself as a viable and efficient alternative to traditional cement.