# A Comprehensive Review on Clay Soil Stabilization Using Rice Husk Ash and Lime Sludge
## 4 Cost and Sustainability Evaluation
### Sustainability Evaluation  
Life cycle assessment (LCA) is a comprehensive method to evaluate the environmental impacts of all stages of a product's life and plays a vital role in assessing sustainability. Conducting a comprehensive LCA for stabilizing clay soils using RHA and LS involves evaluating environmental impacts across various stages, including material extraction, processing, transportation, application, and end-of-life scenarios. Existing studies provide insights into their environmental benefits compared to traditional stabilizers like OPC and lime. Summarized results from various studies are provided in Table 5.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Materials** & **Cost Savings** & **Findings** & **Source** \\ \hline RHA + Natural Lime (NL) & 17\% reduction in earthwork costs, 39\% savings in subgrade construction costs & RHA with 2\% NL effectively stabilized clay soils, offering lower costs than traditional techniques & [126] \\ RHA + Lime & Reduced cost compared to OPC or lime stabilization & RHA as an agricultural waste & \\ RHA + Lime & Estimated 25\% cost reduction compared to OPC & Higher performance with RHA–lime mixture, utilizing industrial waste at lower costs & [72] \\ RHA + Lime & Approximately 30\% cheaper than using OPC & Optimal mix of 8\% RHA and 5\% lime reduced costs due to local availability of RHA and less & [128] \\ RHA + LS & Significantly lower material costs compared to OPC or LS stabilization & RHA and LS provided sustainable alternatives with good performance characteristics at lower cost thresholds & [129] \\ \hline \hline \end{tabular}
\end{table}
Table 4: Cost evaluation for clay stabilization using RHA and LS versus traditional stabilizers.  
These studies highlight the advantages of using RHA and LS for clay soil stabilization, providing specific data on material quantities, transportation distances, energy usage, and emissions factors.  
To sum up the cost and sustainability evaluation, the adoption of sustainable materials such as rice husk ash and lime sludge, despite offering substantial environmental and economic benefits, is often constrained not by their quality or performance but by shortcomings in legislative frameworks at both national and EU levels. These materials are frequently classified as waste rather than valuable raw materials, subjecting them to restrictive regulations that limit their potential for reuse and valorization. Additionally, the absence of specific standards tailored to their properties and applications creates uncertainty, making it difficult for industries to incorporate them into industrial applications confidently. Lengthy and inconsistent regulatory approval processes further compound  
\begin{table}
\begin{tabular}{c c c c c} \hline
**LCA Aspect** & **RHA + LS Stabilization** & **Traditional Stabilizers (Lime/OPC)** & **Findings** & **Source** \\ \hline \multirow{6}{*}{Carbon Emissions} & \multirow{6}{*}{\(\sim\)30–50\% reduction compared to OPC stabilization} & \multirow{6}{*}{High emissions from production (\(\sim\)800–1000 kg CO\({}_{2}\)/ton for OPC)} & RHA and LS are  
these challenges, creating barriers to innovation and increasing adoption costs. To address these issues, transparent and harmonized end-of-waste criteria must be established, allowing rice husk ash and lime sludge to be officially recognized as resources rather than waste. Developing EU-wide standards and certification processes tailored to these materials would ensure consistent quality and streamline their integration into industrial applications. Furthermore, legislative incentives, such as subsidies, tax benefits, and grants, could encourage industries to adopt these sustainable materials, driving the transition toward a circular economy. By resolving these legislative challenges, policymakers can unlock the full potential of rice husk ash and lime sludge, reducing waste, promoting resource efficiency, and advancing sustainability goals across multiple sectors.