## 3 Strength Test  
### Unconfined Compressive Strength  
After formation, the cylinder specimen was cured for 1, 3, 7, 14, 28, 60, and 90 days under standard curing conditions. Next, according to the selected cement content and aggregate, on the basis of the Chinese Test Methods of Materials Stabilized with Inorganic Binders for Highway Engineering (JTG E51-2009) [36], unconfined compressive strength tests were carried out at different curing times and with different cement content on the MTS. Five parallel tests were performed at each curing time. The variation pattern was described by a logarithmic equation, and the strength test carried out at different curing times were fitted by Equation (1). Figure 2 shows the fitting results of the unconfined compressive strength, where \(R^{2}\) is the correlation coefficient of fitting.  
\[S_{c}=a+bln(t+c) \tag{1}\]  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Projects** & **Test Results** & **Technical Requirement [20]** \\ \hline Content of flat and elongated & 13.8\% & \(\leq\)20\% \\ particles in coarse aggregate (\%) & 22.5\% & \(\leq\)30\% \\ Less than 0.6 mm particle Liquid & liquid limit \(\leq\)27\% & 26.5\% \\ limit/plastic index & plastic index \(\leq\)8 & 6.2 \\ Content of soft stone (\%) & 1.2 & \(\leq\)3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Technical indicators of aggregate.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Sieve Size** & **26.5** & **19** & **16** & **13.2** & **9.5** & **4.75** & **2.36** & **1.18** & **0.6** & **0.3** & **0.15** & **0.075** & **Total** **Content (g)** \\ \hline Aggregate & 1036.8 & 622.1 & 553 & 829.5 & 1451.5 & 829.5 & 483.8 & 345.6 & 241.9 & 172.8 & 103.7 & 241.9 & 6912.1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The aggregate content of cylinder specimen.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Sieve Size** & **26.5** & **19** & **16** & **13.2** & **9.5** & **4.75** & **2.36** & **1.18** & **0.6** & **0.3** & **0.15** & **0.075** & **Content (g)** \\ \hline Aggregate & 4247.9 & 2565 & 2280 & 3420 & 5984.9 & 3420 & 1995 & 1425 & 997.5 & 712.5 & 427.5 & 997.5 & 28499.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The aggregate content of large-scale beams specimen.  
where \(S_{c}\) is the compressive strength; \(t\) is the curing time; and \(a\), \(b\), and \(c\) are the fitting parameters.  
From the fitting results, it can be noted that  
1. The Chinese Specification for Design of Highway Asphalt Pavement (JTG D50-2017) [37] has stipulated that the unconfined compressive strength of the cement-stabilized gravel base layer for 7 days under special traffic conditions is 5.0-7.0 MPa and that of the subbase layer is 3.0-5.0 MPa. From the existing test, an unconfined compressive strength at 7-day could meet the requirements.
2. The unconfined compressive strength of cement-treated aggregate base materials monotonously increased with the curing time and cement content. The effect of the cement content on the strength of the cement-treated aggregate base material is larger than the curing time. For example, the strength at a curing time of 90 days and 5% cement content was approximately 1.6 times higher than that of 3% cement content at a curing time of 90 days (from 9 to 14 MPa). The strength of the cement-treated aggregate base material is affected by the curing time significantly, but much less than the cement content. At 1-14 days, the unconfined compressive strength of cement-treated aggregate base materials rapidly increased, with a growth rate of \(\sim\)1.6 times (from 6 MPa to 10 MPa). At 14-28 days, the unconfined compressive strength growth rate decreased by 1.2 times (from 10 to 12 MPa). After 28 days, the unconfined compressive strength approached stability. Therefore, the cement-treated aggregate base should be maintained for about 28 days after being paved.