Physicochemical properties of carbonized grass (CG): Implications for soft clay improvement

Abstract

In global environmental governance, effectively and sustainably treating soft clay remains a key challenge. The production of traditional soil stabilizers, like cement, not only consumes vast non-renewable resources but also poses issues related to high energy consumption and environmental burdens. Hence, there is an urgent need to identify sustainable alternatives. This study introduces carbonized grass (CG) prepared from waste cutting grass as a sustainable material, experiments on soft clay and research on its physical and chemical properties, and adds wood charcoal (WC) and carbonized cow dung compost (CC) as controls. The study assesses the impact of carbonization temperature (500–1000 °C) on the water absorption properties of WC, CC, and CG. Using CG produced by a homemade dry distillation gasifier (SDDG) as raw material, it is added directly or together with calcined oyster shell waste (COS) into the soft clay, and a cone penetration test is conducted. The impact of different initial moisture contents (30%, 50% and 70%) of soft clay and the blending amounts of CG and CG-COS on the strength of the samples was studied, and an evaluation formula was proposed. Test results showed that CG exhibited a significant advantage in stabilizing high-moisture clay compared to CC and WC. After 28 days, the incorporation of CG significantly reduces the amount of COS (about 40%). Employing Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS), the physical and chemical properties of the samples were analyzed. The analysis confirmed CG's unique honeycomb structure, acting as nucleation sites between particles. Additionally, its strong water absorbency aided in shortening the distance between particles, promoting the bonding of hydrated calcium silicate (C-S-H) with soil particles, leading to an improvement in sample strength. The results showed that improving soft clay with CG-COS significantly reduces the use of traditional stabilizers while leading to a substantial increase in soil strength. Additionally, this approach contributes to a noteworthy reduction in greenhouse gas emissions. Therefore, recycling cutting grass for CG preparation as a substitute for conventional soil stabilizers emerges as a green and viable method.