BITUMEN STABILIZED LATERITIC SOIL REINFORCED WITH GRANITE POWDER AND RECYCLED STEEL FIBER AS BASE MATERIAL IN ROAD CONSTRUCTION

This study investigates the geotechnical suitability of laterite soil from Ogbogoro, Obio-Akpor Local Government Area, Rivers State, Nigeria, stabilized with bitumen, granite powder, and recycled steel fiber (RSF) from vulcanized tyres, for flexible pavement use. The natural laterite was classified as a high-plasticity soil (plasticity index 26.91%), confirming the need for stabilization. A compaction test with bitumen contents of 0-10% was used to select an optimum binder content (OBC) of 6%, giving a favorable combination of maximum dry density and reduced optimum moisture content. Specimens prepared at the OBC were reinforced with RSF (0-3%, 0.5% intervals) and granite dust (0-30%, 5% intervals) and evaluated through water absorption, unsoaked and soaked California Bearing Ratio (CBR), and indirect tensile strength (ITS) tests. Water absorption decreased progressively with RSF content up to 2%, beyond which it rose slightly due to fiber clustering. Both unsoaked and soaked CBR improved substantially with RSF and granite dust addition, peaking at 2% RSF with 20% granite dust, an improvement of about three times the plain bitumen-stabilized soil. Indirect tensile strength followed a similar trend, rising consistently with RSF up to 2% before declining at higher fiber dosages. The results indicate that a blend of 2% RSF and 20% granite dust with bitumen-stabilized laterite gives the best composite strength and moisture-durability performance, and that combining these waste-derived materials offers a technically sound, environmentally beneficial option for subgrade and sub-base construction in tropical lateritic terrains.