article · Journal of Energy Environmental & Chemical Engineering
Expansive soils, like Agbede soil in Nigeria, are typically unsuitable for engineering due to high plasticity and low load-bearing capacity. This study investigated groundnut shell ash (GSA) and rice husk ash (RHA) as sustainable alternatives to conventional stabilisers. Laboratory tests showed that untreated Agbede soil was highly plastic clay. Incorporating GSA and RHA, individually and blended, significantly improved the soil's engineering properties. Plasticity was reduced, compaction characteristics improved, and strength, measured by California Bearing Ratio and Unconfined Compressive Strength, increased markedly. Microstructural analysis confirmed the formation of cementitious compounds. The research concludes that GSA and RHA are effective, sustainable stabilisers for expansive soils, with an optimal blend of 10% GSA and 10% RHA making the soil suitable for highway subgrade applications.
Many construction projects face challenges with unstable soils, leading to costly and less durable infrastructure. This research offers a sustainable solution by transforming problematic soils into suitable building foundations using agricultural waste. It helps reduce construction costs and environmental impact by utilising readily available by-products.
This research provides an applied solution for soil stabilisation in civil engineering, particularly for highway subgrade construction. Potential users include construction companies, road builders, and infrastructure developers seeking cost-effective and environmentally friendly materials. The identification of an optimal blend suggests this technology is ready for further field trials and potential adoption in construction practices, offering a pathway for agricultural waste valorisation.
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Expansive soils in Nigeria, such as Agbede soil, are generally unsuitable for engineering applications due to their high plasticity, volumetric instability, and low load-bearing capacity. Although conventional stabilizers like cement and lime are effective, their high cost and environmental impacts necessitate the exploration of sustainable alternatives. This study evaluates the geotechnical performance of Agbede soil stabilized with groundnut shell ash (GSA) and rice husk ash (RHA), individually and in blended proportions, as eco-friendly and cost-effective stabilizing agents. Laboratory investigations were carried out in accordance with BS 1377 (1990) standards and included particle size distribution, specific gravity, Atterberg limits, Standard Proctor compaction, California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), and microstructural analysis using Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX). The natural Agbede soil was classified as a highly plastic clay with a plasticity index (PI) of 32%, a maximum dry density (MDD) of 1.85 g/cm 3 , and low strength characteristics, confirming its inadequacy for direct use in highway subgrade construction. The incorporation of GSA and RHA resulted in progressive improvement of the soil’s engineering properties. Plasticity was significantly reduced, with the PI decreasing to 14% at a 15% GSA content. Compaction characteristics improved, as the MDD increased to a peak value of 1.92 g/cm 3 at 10% GSA, while the optimum moisture content (OMC) decreased from 14.3% for the untreated soil to 13.5%. Strength performance improved markedly, with CBR values increasing from 7% to 21% for GSA-treated soil and reaching up to 24% for blended GSA–RHA mixtures. Similarly, UCS values increased from 120 kN/m² in the untreated soil to 280 kN/m² at 15% GSA. SEM/EDX analysis confirmed the formation of cementitious compounds, particularly calcium silicate hydrates, which enhanced inter-particle bonding and reduced pore spaces. The study concludes that groundnut shell ash and rice husk ash are viable, sustainable, and effective stabilizers for expansive soils. Their application significantly improves strength, durability, and overall geotechnical performance while contributing to agricultural waste management. An optimal blend of 10% GSA and 10% RHA was identified as providing a balanced combination of mechanical performance and constructability, making the stabilized soil suitable for subgrade and other highway engineering applications.
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DOI: 10.11648/j.jeece.20261103.11
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