Stabilization of Expansive Soil using Leather Industry Waste Ash

Abstract

Expansive clays are one of the most widely found soil types across the globe, known for their low strength and high swelling behavior. Numerous studies have been conducted in the past few decades to stabilize such soils using various additives. The traditional stabilizers, such as cement and lime, not only prove to be quite costly due to their high industrial demands but also result in the exhaustion of available natural resources. The current study is a novel effort based on the distinct addition of two different wastes originating from the leather industry in ash form, namely limed leather waste ash and blue leather waste ash. These can be utilized as potential stabilizers to enhance soil strength and reduce the swell-shrink characteristics of expansive clays. The effects of the waste ashes on the properties of expansive soil are analyzed at both macro and micro levels. The macro-level studies are based on the characterization of the chemical nature of the waste ashes and their effects on the consistency, mechanical properties, and swelling properties of the soil in uncured and cured states, with an observation period of up to 28 days. Meanwhile, the micro-level studies aim to examine the changes in surface structure, particle bonding, and chemical nature of the soil at the microscopic level with increased contact period with the stabilizers in the presence of moisture. The study also involves the refinement of the blue leather waste ash through the use of a secondary stabilizer called microfine slag, to optimize its use in the stabilization of expansive soil. The optimum contents of the waste stabilizers are determined based on their most desirable effects on the properties of expansive soil. A one-dimensional rainfall simulated leachate study has been carried out over a pavement model stabilized with leather waste ashes in crude and refined form, to evaluate the possible impact of ash treatment on the water table. It is found from the study that the waste, when used in ash form, is capable of substantially improving the compaction and strength characteristics of the expansive soil. There is a comprehensive increase in soil strength through curing, with up to a 600% increase in the UCS and almost a 400% increase in the CBR of the soil. A significant reduction of 70-80% in the swelling properties of the soil is observed with the addition of LLWA. Although BLWA alone does not have a significant impact on the swell characteristics of the soil, the same is achieved through the addition of MFS to BLWA, resulting in an equivalent effect on the volumetric expansion of the clay. The SEM and XRD results are used to explain the microstructural changes in the soil, as well as the agglomeration and generation of silicate gel compounds responsible for the increase in the strength of the soil-ash mixture at different curing levels. The generation of different types of chemical compounds, including CSH and CASH, is ascertained to exist in various isomeric forms at different phases through the microanalysis. The analysis of leachate samples clarifies that the toxic metals are mostly contained in the soil, and hence the application of the waste has a minimal effect on the groundwater quality. The leaching pattern of different elements in the soil-waste mix is also explained. The utilization of the waste, besides treating the problematic soil, will also solve the dumping issue of the waste itself and reduce the environmental hazards produced by these wastes.