# Natural Para Rubber in Road Embarnment Stabilization
## 3 Preliminary Study of RSS as Reinforcing Materials
### CBR Testing  
CBR testing was carried out and compared under four testing conditions, which were lateritic soil E1 non-reinforcement (E1), lateritic soil E2 non-reinforcement (E2), lateritic soil E1 with RSS reinforcement (E1-RSS), and lateritic soil E2 with RSS reinforcement (E2-RSS), respectively. The standard for the CBR testing method, namely, ASTM D1883 [33], was tested based on the condition of OMC at maximum dry density, which was obtained from conducting the modified compaction test [34]. The maximum dry density of E1 and E2 was 1.86 g/cm\({}^{3}\) at the OMC of 14.00%. A CBR under non-reinforcement conditions (E1 and E2) with lateritic soils E1 and E2 were mixed with tap water until reaching homogeneity. The soil samples were transferred into CBR molds (cylindrical molds with a 152.4 mm inner diameter and a height of 177.8 mm) in sequential order with five equal-sized soil sample amounts reaching up to the top edge of the mold. Each layer of soil sample was compacted with 56 blows using a 10.00 lbf (44.48 N) rammer, which was dropped from a 457.2 mm height. After compaction, the perforated base plate and spacer disk were taken out. The molds containing compacted soil samples were weighed and recorded. A disk of coarse filter paper was placed on the top of the soil sample prior to overturning the CBR mold. In penetration testing, a steel penetration piston with a 50 mm diameter proving ring \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Percent Passing by Weight (\%)**} \\ \cline{2-7}
**Sieve Size** & \multicolumn{6}{c}{**Standard of DH-S 205/2532**} & \multicolumn{6}{c}{**In This Research**} \\ \cline{2-7}  & **Grade A** & **Grade B** & **Grade C** & **Grade D** & **Grade E** & **Grade E1** & **Grade E2** \\ \hline
2\({}^{\prime\prime}\) (50.00 mm) & 100 & 100 & - & - & - & - & - \\
1\({}^{\prime\prime}\) (25.00 mm) & - & - & 100 & 100 & 100 & 100 & 100 \\
3/8\({}^{\prime\prime}\) (9.50 mm) & 30–65 & 40–75 & 50–85 & 60–100 & - & - & - \\ No. 10 (2.00 mm) & 15–40 & 20–45 & 25–50 & 40–70 & 40–100 & 70 & 75.67 \\ No. 40 (0.425 mm) & 8–20 & 15–30 & 15–30 & 25–45 & 20–50 & 31 & 37.10 \\ No. 200 (0.075 mm) & 2–8 & 5–20 & 5–15 & 5–20 & 6–20 & 6 & 13.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Grain size distributions for lateritic soil. Figure 2: Grain sizes distribution of E1 and E2. was inserted at the center point for penetration. Load measurements corresponding to deformation at every 0.64 mm (0.025 in) were taken to calculate the bearing capacity of the lateritic soils E1 and E2. A CBR test under reinforcement conditions (E1-RSS and E2-RSS) followed the same preparation procedure with non-reinforcement conditions (E1 and E2). On the other hand, the RSS with an aperture size of 20 mm \(\times\) 20 mm was cut as a circular shape and placed between layers 2 and 3 of the soil samples in the CBR mold, as shown in Figure 3.  
To determine the effect of RSS reinforcement on the CBR of lateritic soil, E1 (CBR = 64.53%) and E2 (CBR = 40.56%) were representative of lateritic soil in the cases of high CBR and low CBR, respectively. By considering the effect of RSS-reinforced lateritic soil with a high CBR value, E1 and E1-RSS were compared as shown in Table 2. The CBR value in the case of E1-RSS (CBR = 64.31%) was lower than the case of E1 (CBR = 64.53%). This result showed that in cases with RSS reinforcement, the CBR of the lateritic soil was decreased by 0.34%. Meanwhile, E2 and E2-RSS were compared to determine the effect of RSS-reinforced lateritic soil on a low CBR value. The CBR value in the case of E2-RSS (CBR = 49.95%) was higher than the E2 case (CBR = 40.56%), with a percentage difference of 23.15% as presented in Table 2. Therefore, the RSS was strongly recommended to improve the strength of lateritic soil, which had low CBR values.