Multi-Criteria Evaluation of XL-Terrasil and Metakaolin Geopolymer for Subgrade Improvement in Rural Roads of Ondo State, Nigeria

Abstract

Weak lateritic soils in tropical regions present significant challenges for road construction due to their poor load-bearing capacity and high compressibility. This study evaluated the effectiveness of XL-Terrasoil (XL) and Metakaolin (MTK) in stabilizing weak lateritic soils from three locations in Ondo State, Nigeria, to enhance their suitability for subgrade applications. A laboratory-based experimental approach was adopted. Soil samples were collected from failed road sections and subjected to stabilization, XL -Terrasil and Metakaolin was incorporated into the soil as percentage of its dry weight with dosages set at (0.5%–2.5%) for XL- Terrasil and (2%–10%) for Metakaolin, while the control samples without additive (0% Dosage) was prepared for base line comparison. Tests performed include compaction, unconfined compressive strength (UCS), California Bearing Ratio (CBR), permeability, and microstructural analyses (XRF, SEM-EDX, and XRD). The untreated soil samples exhibited poor engineering properties: Location 1 had UCS of 180 kPa and CBR of 6.5%; Location 2 showed UCS of 165 kPa and CBR of 12%; while Location 3 had UCS of 195 kPa and CBR of 18%. Stabilization with 1% XL improved UCS to 340 kPa (90% increase), while 6% MTK further enhanced UCS to 420 kPa (133% increase). Similarly, soaked CBR improved to 30% with 1% XL and 40% with 6% MTK. Permeability reduced significantly, with 6% MTK decreasing hydraulic conductivity to 8.0 × 10?? m/s (65% reduction). Microstructural analyses confirmed improved bonding between grainsand better crystallinity, silica -alumina promote cohesion and decrease plasticity particularly in MTK-treated samples. The study concluded that Metakaolin outperforms XL-Terrasoil in improving soil strength, durability, and permeability, making it the preferred stabilizer for sustainable subgrade applications in tropical road construction