Assessing the Effects of Motor Oil, Gypsum, and Sodium Chloride on the Behavior of Lime-improved Grey High Plasticity Clay

Abstract

This study evaluates the effects of motor oil (MO), gypsum (CaSO₄·2H₂O), and sodium chloride (NaCl) as additives on the geotechnical properties of Grey High Plasticity Clay (GS) improved with 0, 4, and 8% lime (L). Each additive was incorporated into GS at 0, 2, and 4% by dry weight. Unconfined compressive strength (UCS) tests were performed on specimens compacted at their optimum moisture content (OMC) and maximum dry density (MDD) after 7, 30, and 120 days of curing. Results indicated that the plasticity index (PI) of GS decreased with the addition of additives, whether used alone or combined with lime. The introduction of any additive into natural or lime-improved GS enhanced soil classification, with gypsum and NaCl exhibiting a more pronounced effect. Additionally, MDD decreased while OMC increased as lime content rose, due to cation exchange reactions leading to clay particle flocculation. However, MDD increased with higher additive contents, whereas OMC decreased with increasing MO and NaCl but rose with gypsum. UCS values improved significantly with any additive, particularly after 120 days of curing. Microstructural analysis via scanning electron microscopy (SEM) revealed the formation of cementitious compounds and/or ettringite in GS samples improved with lime alone or in combination with gypsum, contributing to strength enhancement.