## 4 Results and Discussion
### The Modulus of Three In-Service Pavements  
Table 4 summarizes the average concrete slab modulus and average subgrade layer modulus at each measurement location of three in-service concrete pavements, as the SASW method can measure the modulus of each layer of the pavement. For a more detailed and clear analysis, the moduli are visualized in Figure 7, where the color blue represents data from Section II, the color red represents data from Section I, and the color yellow represents data from Section III. The circles covering the point data represent the average modulus range of the three concrete pavement sections. Additionally, the horizontal axis of Figure 7 shows the subgrade modulus of the concrete pavements, while the vertical axis shows the concrete modulus of the pavements. From the comparison, it is obvious that both the concrete layer modulus and subgrade layer modulus in Section II are the lowest. The concrete layer modulus at Section III is the highest, while the subgrade modulus at Section I is the highest.  
Figure 5: Correlation relationship between FWD modulus and compressive modulus.  
Figure 6: Correlation relationship between SASW modulus and FWD modulus.  
In this research, pavement Section III performs better than the other two pavements, although the initial performance conditions of the three pavements are different. Meanwhile, it is recommended to conduct further detection research on the pavement Section II to monitor the damage degree of the surface and subgrade layer in order to carry out the pavement maintenance in a timely manner. In addition, due to the presence of measurement locations with relatively low concrete layer modulus in Section I, it is also recommended to  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pavement Section** & \multicolumn{6}{c}{**Elastic Modulus (MPa)**} \\ \hline  & Location & X1 & X2 & X3 & Y1 & Y2 \\ \cline{2-7}  & Concrete Layer & 43,291 & 34,075 & 34,958 & 49,675 & 46,224 \\  & Subgrade & 7135 & 7825 & 8081 & 8490 & 8137 \\ \cline{2-7}  & Location & Y3 & Z1 & Z2 & Z3 & M \\ \cline{2-7}  & Concrete Layer & 46,996 & 46,433 & 47,363 & 42,591 & 45,881 \\  & Subgrade & 8507 & 8870 & 7445 & 7968 & 8423 \\ \cline{2-7}  & Location & L & N & & & \\ \cline{2-7}  & Concrete Layer & 44,956 & 48,131 & & & \\ \cline{2-7}  & Subgrade & 9005 & 9170 & & & \\ \hline  & Location & AA & BA & CA & DA & \\ \cline{2-7}  & Concrete Layer & 40,861 & 39,218 & 39,131 & 40,254 & \\  & Subgrade & 6501 & 7096 & 6640 & 6992 & \\ \hline  & Location & JX-1 & JX-2 & JX-3 & JX-4 & JX-5 \\ \cline{2-7}  & Concrete Layer & 46,352 & 48,462 & 47,457 & 42,912 & 46,419 \\  & Subgrade & 8734 & 7820 & 9117 & 7958 & 8396 \\ \cline{2-7}  & Location & JX-6 & JX-7 & JX-8 & JX-9 & JX-10 \\ \cline{2-7}  & Concrete Layer & 45,227 & 50,514 & 50,735 & 55,867 & 50,737 \\  & Subgrade & 8802 & 7798 & 6997 & 7122 & 7299 \\ \cline{2-7}  & Location & A & B & C & D & E \\ \cline{2-7}  & Concrete Layer & 47,922 & 49,196 & 41,020 & 44,843 & 46,246 \\ \cline{2-7}  & Subgrade & 7519 & 6315 & 6855 & 7481 & 7213 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The summary of concrete modulus from the SASW method.  
Figure 7: The modulus of the concrete layer in three pavements was measured by the SASW method.  
perform continued monitoring of this pavement section to avoid obvious damage to the pavement, such as surface cracking. The asphalt overlay of these three concrete pavements needs to be carefully designed according to completely different structural conditions.