Effect of cow bone ash on the geotechnical properties and microstructure of lateritic soil for road pavement applications

Flexible pavements require stable subgrade and subbase layers, yet lateritic soils commonly used in tropical regions may possess inadequate strength, bearing capacity, and moisture resistance in their natural state. Conventional stabilizers such as cement and lime are effective but costly and carbon-intensive. Meanwhile, abattoir waste, particularly cow bones, creates environmental problems in many developing countries. Converting cow bones into ash (CBA) offers a dual benefit by reducing waste and providing a calcium-rich, pozzolanic-type additive for soil stabilization. This study therefore evaluated cow bone ash (CBA), a calcium-rich abattoir-waste derivative, as a sustainable additive for improving lateritic soil properties and microstructure. Cow bones were calcined to produce CBA, which was mixed with lateritic soil at 0, 2, 4, 6, 8, and 10% by dry soil mass. Index properties, consistency limits, compaction characteristics, California bearing ratio (CBR), unconfined compressive strength (UCS), hydraulic conductivity, volumetric shrinkage, and microstructural characteristics were evaluated. One-way analysis of variance (ANOVA) at a 95% confidence level was used to determine the statistical significance of CBA effects. The untreated soil was classified as A-2-6(2) under AASHTO and SC under USCS, indicating a not highly plastic fine-grained lateritic material of limited suitability for pavement foundations without improvement. CBA reduced the liquid limit and plasticity index, indicating flocculation, reduced clay activity and improved workability, while the plastic limit initially increased with increasing CBA content, reaching a peak at 6–8% CBA, before decreasing at 10% CBA. Although maximum dry density decreased from 1.87 to 1.66 g/cm 3 (11.2%), optimum moisture content increased from 13.7% to 26.0% (89.8%), and mixtures containing up to 6% CBA retained acceptable compaction characteristics for subbase applications. At the optimum 6% CBA content, soaked CBR, unsoaked CBR, and 7-day UCS increased by up to 333%, 167%, and 103%, respectively. ANOVA confirmed the significance influence of CBA on the lateritic soil properties. Hydraulic conductivity and volumetric shrinkage of the treated soil also decreased, while the improvement in microstructure of the treated soil was confirmed from its fewer interconnected pores and a denser matrix. CBA is therefore a promising sustainable stabilizer for lateritic pavement materials.