Chemical Characterisation of Laterite Soils in Nasarawa State and Their Potential as Road Construction Materials

Laterite soils are abundant across the North Central Nigerian plateau and represent a widely used but variably characterised material for road subbase and base construction. This study chemically characterises laterite deposits from five locations in Nasarawa State and evaluates their suitability as road construction materials based on chemical, mineralogical, and engineering parameter correlations. Soil samples were collected from natural exposures at designated locations, chemically analysed by X-ray fluorescence for major oxides, and characterised by X-ray diffraction for mineral phase identification. Index properties including Atterberg limits, specific gravity, particle size distribution, California bearing ratio, and compaction characteristics were determined following BS 1377 methods. The relationship between chemical composition parameters and engineering properties was assessed by Pearson correlation analysis. Results indicate that the iron oxide content of laterite, ranging from 18 to 47 percent across sampled locations, correlates strongly with California bearing ratio values, with iron-rich samples showing superior bearing capacity. Aluminium oxide content showed a positive correlation with plasticity index, indicating that high aluminium laterites require stabilisation before use in pavement courses. Two of five sampled laterite sources met criteria for direct use as subbase material, while three required either lime or cement stabilisation. The study provides a chemical-engineering database for laterite resources in Nasarawa State and recommends geochemical mapping of the state's laterite belt to support road infrastructure planning. Keywords: laterite soils, chemical characterisation, road construction, Nasarawa State, California bearing ratio