Characterisation of Laterite Deposits for Road Construction Material in Kebbi State, North West Nigeria

Laterite is the primary road construction material used for rural road subbase and base course construction across much of North West Nigeria, yet material quality varies significantly between borrow pit locations. This study characterises laterite deposits from selected borrow pits in Kebbi State, North West Nigeria, for their suitability as road construction material. Bulk samples were collected from six borrow pits across Birnin Kebbi, Argungu, and Bagudo Local Government Areas. Laboratory tests performed in accordance with Nigerian General Specifications for Roads and Bridges include grain size analysis, Atterberg limits, compaction tests, California Bearing Ratio determination, and free swell index. Results indicate considerable variation in geotechnical properties between locations. Three sites meet specifications for subbase material, while two meet base course requirements. One site produces laterite that exceeds plasticity index limits and is unsuitable for road use without lime stabilisation. California Bearing Ratio values range from 38 to 126 percent, with the highest values from samples with lower fines content. The study maps the spatial distribution of qualifying borrow pits and assesses their estimated extractable volumes. This information is designed to assist Kebbi State Ministry of Works and Infrastructure in selecting construction materials for the ongoing rural road improvement programme. Keywords: laterite, road construction, Kebbi State, California Bearing Ratio, borrow pits.