Geotechnical Behaviour of Steel Slag–Lateritic Soil Reinforced with Shredded Plastic Waste for Road Foundations

Abstract

This study assessed the eco-friendly use of plastic wastes on the geotechnical features of steel slag-stabilized lateritic soil from Imota, Lagos state, Nigeria. Steel slag and plastic bottles constitute major environmental wastes that have been posing serious disposal challenges. Steel slag is a known pozzolanic material, its incorporation into lateritic soil along with shredded plastic would reduce the environmental pollution caused by both wastes, and improve the soil properties.  The soil, classified as A-6 or CL, is a poor subgrade material. It was treated with 8-24% steel slag, and 20% slag addition yields the optimal strength improvement. Waste plastic strips at 1, 2, 3 and 4% by weight were subsequently introduced to the optimised sample. Sieve analysis, consistency limits, California bearing ratio (CBR) and unconfined compressive strength (UCS) tests were performed on the natural and stabilized soil samples. Results demonstrated that 2% of plastic strip inclusion produced optimal improvements. This combination reduced the plasticity index (PI) of natural soil from 15 to 7%, compared to 10% with slag stabilization alone. The CBR increased from 1% for the natural soil to 24% for the combined mix, surpassing the 16% achieved with slag alone. Similarly, the UCS value reached 320 kN/m² in the combined mix, compared to 270 and 80 kN/m² for slag stabilization and natural soil, respectively. This new optimal mix of the soil is suitable for application as a sub-base layer for low-traffic roads having satisfied the minimum specified 20% CBR value. This research demonstrates that incorporating plastic strips from waste bottles into slag-stabilized lateritic soil can significantly enhance its geotechnical properties, offering a sustainable approach to soil improvement using waste materials.