Enhancing the Stability of Expansive Soils with Copper Slag and Cement: A Comprehensive Study on Environmental Impact and Durability

IJEP 46(6): 591-600 : Vol. 46 Issue 6 (June 2026)

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Gunnam Sanijya1,2, Bala Murugan R.1* and Samatha Chowdary Ponduri2

1. Annamalai University, Department of Civil Engineering, Annamalai Nagar, Chidambaram – 608 002, Tamil Nadu, India
2. R V R and J C College of Engineering, Department of Civil Engineering, Chowdavaram, Guntur – 522 019, Andhra Pradesh, India

Abstract

Stabilizing expansive subgrade soils remains a significant challenge in geotechnical and transportation engineering, especially when constructing low-volume roads in areas with poor soil quality. This study explores effective, long-lasting methods to improve black cotton soil (BCS) using copper slag (CS), an industrial byproduct and ordinary Portland cement (OPC). We combined six proportions of CS (2%, 4%, 6%, 8%, 10% and 12%) with fixed amounts of OPC (2%, 4%, 6% and 8%) to examine their effects on the strength, durability and environmental impact of the stabilized soil. Full testing included standard proctor compaction, unconfined compressive strength (UCS), free swell index (FSI), freeze–thaw resistance, wet–dry durability and the toxicity characteristic leaching procedure (TCLP). Results showed that increasing CS content significantly enhanced soil strength and volume stability. The UCS steadily increased with more CS, reaching a peak of 1.89 MPa after 90 days of curing at 8% OPC and 12% CS—over 340% higher than untreated soil. The free swell index decreased by more than 80%, indicating a substantial reduction in the soil’s tendency to swell. Durability tests under cyclic environmental conditions confirmed that the stabilized samples remained structurally sound despite repeated drying and soaking. Additionally, TCLP results indicated that the leachate levels of heavy metals, such as Cu, Pb and Zn stayed well within USEPA limits, demonstrating that copper slag use is environmentally safe. These findings suggest that copper slag is a promising, sustainable material for soil stabilization that can enhance performance while adding value to waste materials used in infrastructure development.

Keywords

Copper slag stabilization, Black cotton soil, Unconfined compressive strength, Swelling reduction, Freeze-thaw durability

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