# Effect of Mineral Additives on the Behavior of an Expansive Soil for Use in Highway Subgrade Soils
## 4 Results and Discussion
### Physical-Mechanical Properties
#### 4.1.2 Determining the Lime and Natural Pozzolans Dosage  
Table 3 presents the liquid limit, plastic limit, and plasticity index of the stabilized BCS. The lime-stabilized BCS presents a marginal decrease in liquid limit, which decreased from 64.3% to 58.3% on the addition of 9% lime. However, the liquid limit of BCS stabilized with VA, and combined additives presented a rapid decrease with increasing additive content. With the addition of 25% VA and the combination of 3% lime + 20% VA, the liquid limit of the stabilized BCS decreased from 64.3% to 51.6 % and 46.6%, respectively. Similar behavior was observed by [PERSON] et al. [19] using lime, cement, and artificial pozzolan as soil additives. However, lime-stabilized BCS presented an obvious decrease in plasticity index due to the increase of the plastic limit. The plasticity index of lime-stabilized BCS decreased from 30.7% to 8.3% on the addition of 9% lime. The plasticity indices of BCS stabilized with 25% VA and the combination of 3% lime + 20% VA were 22.7% and 22.2%, respectively.  
Figure 3: Influence of lime and VA content on the optimal moisture content (OMC) and maximum dry density (MDD) of BCS.  
The variation of the California bearing ratio (CBR) with dosages of stabilizers is presented in Figure 4. The lime increases the CBR of the BCS from 4.7% to 25.2% and decreases the expansion ratio of the BCS from 3.1% to 0.3% with the addition of lime from 1% to 9%. The BCS stabilized with VA presents a poor result compared with the lime. VA increases the CBR of BCS from 2.2% to 4.5% and decreases the expansion ratio of BCS from 2.6% to 2.1% with the addition of VA from 10% to 25%. The CBR of BCS presents a rapid increase with the use of the composite stabilizer. The CBR of BCS stabilized by composite stabilizer is 24.7% with the addition of 3% lime + 15% VA, and the stabilization effect is similar to that of 9% lime.  
According to JTG D30-2015 (Chinese standard) [37], the liquid limit and the plasticity index of subgrade soils must be less than 50% and 26%, respectively. The CBR of the clay must meet the requirements presented in Table 4. The VA-stabilized BCS can only be used as roadbed materials for a low-volume road. The lime-stabilized BCS, as a roadbed material, can pave a high-grade road, and BCS stabilized with only 3% lime can meet the highest CBR requirement. For this target, the least amount of composite stabilizer required is 1% lime + 15% VA. Considering the requirement of the Atterberg limits, BCS stabilized with 3% lime + 15% VA is well suited as a roadbed material.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Traffic Classification** & \begin{tabular}{c} **Depth Under** \\ **Pavement (M)** \\ \end{tabular} & \begin{tabular}{c} **Expressway/First-Class** \\ **Highway** \\ \end{tabular} & \
\begin{tabular}{c} **Second-Class** \\ **Highway** \\ \end{tabular} &
\begin{tabular}{c} **Third-/Fourth-Class** \\ **Highway** \\ \end{tabular} \\ \hline Any Level ofTraffic & 0.0–0.3 & 8\% & 6\% & 5\% \\ Light/Medium Traffic & 0.3–0.8 & 5\% & 4\% & 3\% \\ Heavy/Very Heavy Traffic & 0.3–1.2 & 5\% & 4\% & - \\ \hline \hline \end{tabular}
\end{table}
Table 4: Minimum CBR of roadbed materials [37].  
Figure 4: Influence of stabilizer content on the California bearing ratio (CBR) and expansion ratio of BCS.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **Liquid Limit (\%)** & **Plastic Limit (\%)** & **Plasticity Index (\%)** \\ \hline Untreated soil & 64.3 & 33.6 & 30.7 \\
1\% lime & 65.6 & 35.7 & 29.9 \\
3\% lime & 68.1 & 41.9 & 26.2 \\
6\% lime & 63.4 & 45.8 & 17.6 \\
9\% lime & 58.3 & 50.0 & 8.3 \\
10\% VA & 58.2 & 30.6 & 27.6 \\
15\% VA & 56.5 & 31.5 & 25.0 \\
20\% VA & 55.1 & 30.3 & 24.8 \\
25\% VA & 51.6 & 28.9 & 22.7 \\
1\% lime + 15\% VA & 58.4 & 30.5 & 27.9 \\
1\% lime + 20\% VA & 59.4 & 32.2 & 27.2 \\
3\% lime + 15\% VA & 49.2 & 25.4 & 23.8 \\
3\% lime + 20\% VA & 46.6 & 24.4 & 22.2 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Atterberg limits of unstabilized and stabilized BCS.