Sustainable Stabilization of NaOH-Contaminated Expansive Soil using Calcium Lignosulfonate: Mechanical and Microstructural Insights

Abstract

 The structural stability and long-term performance of any civil engineering infrastructure are contingent on the geotechnical properties of foundation soil. The chemical intrusions into soil alter its properties by tending to its behavioral changes. Industrial alkali spills into the ground are one of the emerging problems which necessitate a broad study to evaluate the impact of alkali induced behavioral changes in a soil. Black cotton soil (BCS) which exhibits weak characteristics within water saturation and deteriorates more with chemical interactions. The present work is focused on the mechanism of the BCS when exposed with alkali solution and amendments in the alkali included BCS treated with Calcium Lignosulfonate (CLS) of 0.5%, 1% and 2%. The alkali solution used in the study was 2N NaOH. A comparative analysis is done between the untreated BCS, BCS added with 2N NaOH solution to identical to that of 2N NaOH-added BCS treated with CLS. The prepared soil specimens were cured for a period of 1, 3, 7, 14, 28, 56 and 90 days and were tested for evaluating the plasticity characteristics and unconfined compressive strength (UCS). Wetting and drying cycles were performed on BCS with same combinations of 2N NaOH and CLS under 7, 28, 56 and 90 days curing to understand the durability performance. XRD and FESEM analysis were performed to analyze the mineralogical and morphological evidences. The BCS added with 2N NaOH demonstrated a progressive tendency in plasticity and reduced durability under wetting and drying cycles. There is a noticeable reduction in the UCS with 2N NaOH.  Adding 1% of CLS to 2N NaOH included BCS has improved the plasticity, UCS and durability by enduring more wetting and drying cycles under long-term curing. Microstructure studies revealed clear transformation of montmorillonite-rich BCS into a stabilized geopolymer - matrix by long-term alkali activation under CLS stabilization.