Effect of Humic Acid on Physical and Engineering Properties of Lime-Treated Organic Clay

Abstract

The study of lime stabilisation has been established for a long time and its implementation in geotechnical engineering has improved regularly. The present work deals with the stabilisation of organic clay using hydrated lime, which resulted in three favourable combinations of artificial organic clay. The idea of using artificial organic clay is to reduce possible inconsistencies that may happen during testing and to ensure the repeatability of the results of the test. This is vital for comparative study that involves varying additive contents and curing periods. Due to the complex nature of natural soils, a series of experiments was carried out using the manufactured kaolin which represents the clay mineral and different commercial humic acid contents (0.5%, 1.5%, and 3%), which are the main constituents of organic matter that impede the lime stabilisation process. The amount of hydrated lime (5%, 10% and 15% based on dry weight of soil) was taken beyond the initial consumption of lime (ICL) value. Results are presented in three aspects: (1) behaviour of physical properties, (2) shear strength development and (3) microstructure changes due to shear strength. Results produced by physical testing show that the presence of humic acid has a drawback effect on untreated and limetreated organic clay. The decrease in specific gravity value is accompanied by a decrease in dry density and strength of kaolin prepared with higher humic acid content. Plasticity of untreated organic clays also decreases with increased humic acid content. Some notable increases in shear strength at 7 days curing period were observed in the limetreated sample for up to 5% lime content. However shear strength of lime-treated organic clay decreased at longer curing periods. A slight decrease in shear strength occurred for samples treated with 0.5% and 1.5% humic acid. The significant decrease in shear strength can be observed at 3% humic acid content. Thus it can be concluded that lime stabilisation is not effective with the presence of more than 1.5% humic acid at longer curing periods. A microstructure analysis was carried out on untreated and limetreated specimens at OLC (5%) with 1.5% and 3% humic acid content at a 14 days curing period, which represent the duration of the modification process. The findings reveal that the fabric of untreated organic clay for both specimens prepared at different humic acid contents reveals no apparent aggregations. More pore spacing was clearly observed for lime-treated clay minerals with 1.5% humic acid than for 3% humic acid soil structure. Flocculating structure was more visible at lower humic acid contents with particles dispersed by large openings.