Strength Properties of Laterite Soil Stabilised with Ordinary Portland Cement for Road Base Construction in Kwara State

Laterite soils, while abundant across North Central Nigeria, often exhibit CBR values and plasticity indices that render them unsuitable for road base layers without stabilisation. This study investigates the strength improvement of laterite soil from Kwara State through Ordinary Portland Cement stabilisation for road base application. Laterite samples were collected from four borrow pit sites in Ilorin East LGA and subjected to classification tests including Atterberg limits, particle size distribution, and specific gravity. Cement was added at 0, 3, 6, 9, and 12 percent by dry weight of soil, and specimens were compacted and cured for 7 and 28 days before CBR, Unconfined Compressive Strength, and indirect tensile strength testing. Results show that untreated laterite has a soaked CBR of 8 percent, below the 30 percent minimum for road base under Federal Roads Design Manual specifications. With 9 percent cement addition and 28-day curing, soaked CBR reaches 46 percent and UCS reaches 1.84 N/mm2. Atterberg limits show consistent reduction in plasticity with increasing cement content. The 9 percent cement addition is identified as the optimal treatment level, offering the best balance of strength improvement and economic efficiency. The study concludes that cement-stabilised laterite from Kwara State is suitable for road base layers at 9 percent cement content and recommends this specification for rural road programmes in the North Central zone.

Keywords: laterite stabilisation, cement treatment, road base, CBR, Kwara State