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

Abstract

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.