Utilization of bioethanol industry recycled waste for sustainable soil improvement: A win-win application

Abstract

Abstract Dispersive soils are a common problematic soil that may pose engineering distress if not adequately taken care of. On the other hand, the stabilization of problematic soils with waste materials has recently gained more interest from an environmental and sustainable point of view. Hence, this study utilized sulfur-free lignin (SFL), which is a bioethanol-based by-product, to improve dispersive silt clay and investigated the stabilization effectiveness considering combine impacts of water and freeze-thaw (F-T). The SFL was added to five sample groups ranging from 3 to 15%. Then, a series of experiments was performed to study the water stability of the SFL stabilized soil from a mechanical, chemical and micro-structural point of view. The results reveal that the dispersive soil moisture resistance can be significantly improved with addition of SFL and low content SFL (3%) is slightly better than high content (15%) under no cyclic F-T. This is attributed to the increased cation exchange capacity (CEC) owing to the exchangeable sodium ions used during the pretreatment process of bioethanol. Nevertheless, the high content SFL stabilized samples exhibit superior water stability characteristics when considering the adverse effects of F-T\xa0cycles. According to X-ray fluorescence analysis (XRF), no new elemental composition was found indicating that SFL does not bring chemical contamination risk to the soil. However, the organic matter content increases with SFL content. Scanning electron microscopy (SEM) provided visual evidence that the formation of physical bonds and denser soil structure due to SFL, is responsible for the improvements observed. In addition, cracks in the soil matrix caused by F-T\xa0cycles were also observed. Overall, utilization of the studied SFL shows good potential to improve the engineering performance of dispersive soils.