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June 6, 2026Open Access

Modeling the effects of rice husk ash and cassava peel ash on the California bearing ratio (CBR) of Agbani soils

Key Points

This study aims to explore the effects of rice husk ash and cassava peel ash on the California Bearing Ratio of Agbani lateritic soils.
Collected soil samples from fifteen locations in Agbani, Nigeria.
Blended soils with varying proportions of rice husk ash (0-25%) and cassava peel ash (0-35%).
Used multiple linear regression modeling to predict CBR based on ash content.
Untreated soil had a CBR of 21.59%.
Peak CBR of 33.69% achieved with 70% soil, 25% RHA, and 5% CPA.
Regression model showed strong predictive performance (R² ≈ 0.92), with CPA more influential on CBR than RHA.

Abstract

Lateritic soils commonly used for road construction in southeastern Nigeria often exhibit low bearing capacity and high plasticity, necessitating stabilization before use as pavement subgrade or sub-base materials. The use of conventional stabilizers such as cement and lime is associated with high cost and environmental concerns, motivating the exploration of sustainable alternatives. This study investigates the effects of rice husk ash (RHA) and cassava peel ash (CPA), individually and in combination, on the California Bearing Ratio (CBR) of lateritic soil obtained from Agbani, Enugu State, Nigeria. Soil samples collected from fifteen locations were blended with varying proportions of RHA (0-25 %) and CPA (0-35 %), producing fifteen representative mix designs. Laboratory testing included index properties, compaction characteristics, and CBR determination. Multiple linear regression (MLR) modeling was employed to develop predictive relationships between CBR and RHA-CPA contents. Results show that the untreated soil exhibited a low CBR of 21.59 %, while stabilization with agro-waste ashes significantly improved bearing capacity, with a peak CBR of 33.69 % achieved at a mix ratio of 70 % soil, 25 % RHA, and 5 % CPA. The developed regression model demonstrated strong predictive performance ( R 2 ≈ 0.92), with CPA exhibiting a more statistically significant influence on CBR than RHA. The findings confirm the technical viability of RHA-CPA blends as sustainable stabilizers for lateritic soils and provide a quantitative tool for preliminary pavement design.

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