# A Comprehensive Review on Clay Soil Stabilization Using Rice Husk Ash and Lime Sludge
## 3 Laboratory Tests
### Standard Proctor Compaction Test  
Assessing the compaction characteristics of soils for stabilization purposes is commonly used in geotechnical engineering. Different studies were reviewed to determine the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) of stabilized soil samples using the standard Proctor compaction test [98; 105; 106; 107; 108; 109; 110; 111; 112]. The results from the literature show that the OMC of soil samples increases and the MDD of soil samples decreases as the LS and RHA content increases in soil stabilization processes. During the pozzolanic reaction, the hydration of LS and RHA particles occurs, forming cementitious compounds such as CSH and CASH gels. This reaction consumes water, necessitating a higher water  
\begin{table} \begin{tabular}{c c c c c c c c c} \hline
**Source** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **So\({}_{3}\)** & **Na\({}_{2}\)O** & **LOI** \\ \hline
[99] & 92.25 & 0.06 & 0.56 & 0.45 & 0.03 & - & 0.26 & 6.39 \\
[100] & 95.03 & 0 & 0.13 & 0.08 & 0.25 & 0.02 & 0.05 & 4.33 \\
[101] & 70.85 & 1.19 & 0.69 & 0.12 & 0.53 & - & 0.25 & 26.1 \\
[102] & 40.74 & 5.78 & 0.18 & 0.15 & 0.41 & 0.28 & 2.03 & - \\ Mean & 74.72 & 1.76 & 0.39 & 0.20 & 0.31 & 0.15 & 0.65 & 12.27 \\ SD & 25.10 & 2.74 & 0.28 & 0.17 & 0.22 & 0.18 & 0.93 & 12.02 \\ \hline \end{tabular} 
\begin{tabular}{c c c c c c c c} \hline
**Source** & **CaO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **So\({}_{3}\)** & **Na\({}_{2}\)O** & **LOI** \\ \hline
[99] & 92.25 & 0.06 & 0.56 & 0.45 & 0.03 & - & 0.26 & 6.39 \\
[100] & 95.03 & 0 & 0.13 & 0.08 & 0.25 & 0.02 & 0.05 & 4.33 \\
[101] & 70.85 & 1.19 & 0.69 & 0.12 & 0.53 & - & 0.25 & 26.1 \\
[102] & 40.74 & 5.78 & 0.18 & 0.15 & 0.41 & 0.28 & 2.03 &content to maintain an appropriate moisture level for the reaction to take place, leading to an increase in the OMC of the soil. Simultaneously, adding LS and RHA also influences the soil particle arrangement. The cementitious compounds formed help to fill void spaces and enhance the development of a more compacted soil structure, leading to an increase in the MDD of the soil. The analyzed results show that increasing the LS percentage in the soil sample from 5% to 10% resulted in a sudden decrease in the MDD value. Deploying RHA alone as an admixture in clay soil samples results in an increase in the OMC and a decrease in the MDD due to the lower density of rice husk ash compared to the expansive soil. Similarly, incorporating LS as a binding material with RHA and the soil sample also leads to an increase in the OMC and a decrease in the MDD value. In this context, the decrease in the MDD value can be attributed to the lower density of lime sludge compared to the expansive soil. To clarify the results obtained from the literature, the variation in OMC and MDD based on different admixtures is shown in Figures 2-7. Methodological differences can impact the findings when comparing different results across different studies on clay soil stabilization using green alternative materials. These differences, such as clay mineralogy, soil gradation, soil preparation, curing duration, and environment, may influence the measured variations in results between studies. However, for the sake of simplicity, when comparing the results, methodological differences are not considered. Figure 4: Effect of RHA and LS in OMC [98; 111; 112]. Figure 5: Effect of RHA in MDD [105; 106]. Figure 6: Effect of LS in MDD [108; 109]. The results of the analysis of the drawn graphs from the standard Proctor compaction tests are provided below. Figure 2 demonstrates that with the increase in the percentage of RHA content added to the clay soil samples, the OMC of the soil increases. This increase in OMC with higher RHA content is due to RHA's porous and lightweight nature, which absorbs more water and requires higher moisture for compaction. Moreover, adding 10-20% of RHA content significantly increases the OMC of the soil samples.