# A Comprehensive Review on Clay Soil Stabilization Using Rice Husk Ash and Lime Sludge
## 1 Introduction
### Sustainable Stabilizers
RHAcontains amorphous silica, and if fine RHA particles become airborne during handling or mixing, there is potential for inhalation. Prolonged inhalation of silica dust may pose health risks, such as respiratory issues or lung disease, caused by silica exposure. Therefore, wearing protective masks, using dust suppression techniques, and handling RHA in controlled environments can minimize health risks [65]. RHA contains a high percentage of silica, which can be released as airborne particulate matter during handling or processing. Inhalation of silica dust can cause respiratory issues, including lung damage. It may also contain organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) or volatile organic compounds (VOCs), which can harm the environment and human health [66]. LS can contain heavy metals like chromium, lead, cadmium, and nickel, so improper disposal or release of LS into the environment can contaminate soil and water bodies. Line in LS is mildly caustic, and direct skin or eye contact can cause irritation or burns. Proper safety measures, such as wearing gloves, goggles, and protective clothing, should be in place for workers handling lime sludge. Additionally, the fine particles of LS can become airborne during handling, potentially causing respiratory irritation if inhaled. However, proper dust control and protective equipment can manage these risks effectively [67]. Line sludge has high alkalinity due to its calcium hydroxide content. Discharging untreated lime sludge into water bodies can increase pH levels, affecting aquatic organisms and disrupting the ecosystem's natural balance [68]. LS often contains elevated levels of nutrients, particularly phosphorus. When released into water bodies, it can contribute to eutrophication, leading to excessive algae growth, oxygen depletion, and harm to aquatic life [69]. Proper management practices should be followed to mitigate the potential environmental impact of RHA and LS. This includes appropriate storage, transportation, and disposal methods to prevent the release of impurities into the environment. Additionally, environmental regulations should be followed, and treatment techniques should be employed to minimize the impact on ecosystems and human health. Past studies have explored the effectiveness of clay soil stabilization using eco-friendly alternative materials, including RHA and LS [70]. However, this review bridges research gaps by comprehensively analyzing laboratory test results (UCS, CBR, Mr, and Proctor tests) on RHA and LS as soil stabilizers to promote the reuse of agricultural and industrial byproducts. By identifying optimal proportions for specific applications like structural foundations and roadways, we provide engineers and researchers with precise data to enhance stabilization solutions tailored to project needs. Additionally, it provides an in-depth evaluation of sustainability and cost factors, highlighting its unique contribution to promoting sustainable practices in civil engineering to support the shift toward greener construction. By evaluating lifecycle factors, such as energy use and waste reduction, along with cost savings from locally sourced byproducts, valuable insights for policymakers and stakeholders are provided. This study provides a strong foundation for future studies by offering precise guidelines and test result analyses. It encourages further exploration of RHA and LS in combination with other additives and supports regional case studies that address local soil and waste availability, paving the way for more tailored and effective soil stabilization strategies. To conclude, this review aims to assess the efficacy of clay soil stabilization using rice husk ash (RHA) and lime sludge (LS) to determine the optimum quantity of RHA and LS to be used based on comprehensive geotechnical tests, as well as research on cost-effectiveness and sustainability.