# Development of Bonded Natural Stone Pavement Using Ultra-Rapid-Hardening Mortar
## 4 Results and Discussion
### Rut Depth Measurement and Visual Inspection  
To obtain rut depth data, the transverse profile logger recorded the transverse profiles of surface layers using high-quality single point laser sensors with a measuring range and tolerance of \(\pm\)100 and \(\pm\)0.5 mm, respectively. Figure 5 shows the logged transverse profiles of the testing pavements. Additionally, the blue and red lines indicate the measurements taken before and after the APT, respectively, and the black boxes show the driving wheel paths. The rut depth measurements were recorded by measuring the depth differences of surface courses at wheel paths during the APT. Figure 4: Transverse profile logger. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Pavement Construction** & **Bearing Capacity (MN/m\({}^{3}\))** & **Recommended (MN/m\({}^{3}\))** \\ \hline Asphalt pavement & 474 & \\ Concrete block pavement & 463 & \(\geq\)294 (Asphalt) \\ Bound stone pavement A & 501 & \\ Bound stone pavement B & 518 & \(\geq\)196 (Concrete) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Bearing capacity of sub-base course. Figure 5: Transverse profiles of testing pavements. In the case of asphalt pavement, the maximum rut depth was 16.0 mm and the rut depth measurements at various points ranged from 13.0 to 16.0 mm. As shown in Figure 5a, significant ruts were discovered at wheel paths and an upward movement inevitably occurred in the middle of two-wheel tracks. This was because the asphalt pavement was a flexible pavement and the wheel loads induced severe horizontal stresses on the surface course during the APT. Consequently, the lateral movement of asphalt led to the ascendance at the gap between driving paths. For the concrete block pavement, as shown in Figure 5b, the maximum vertical deflection of surface paves caused by the accumulation of wheel load was 4.5 mm at the wheel paths. Additionally, there were plenty of steep fluctuations along with the logged profile. These occasional fluctuations represented the joints filled with sand and the depth of the joints notably increased at the end of the APT. Although an inclined movement of the surface developed in the asphalt profile, a small amount of rutting difference was discovered due to the disconnected surface course. Regarding bound stone pavement A (Figure 5c), the greatest rut depth difference at the wheel paths was 3.0 mm. The rutting indicated that it was generated by the loss of adhesive strength between the stone elements and joint mortar. Moreover, the induced wheel load was directly transferred throughout the dislodged stone elements to bedding and base courses. Due to the flexible base course, the laying mortar affected the rutting of surface elements. Finally, the maximum rut depth in bound stone pavement B (Figure 5d) was 1.5 mm, and it showed a smaller value compared to bound stone pavement A. The deeper stone paves and different material of base courses used in both stone pavements influenced the bearing capacity of these pavement structures. As a result of conducting a visual inspection after the accelerated simulation, there was partial damage in numerous places and loss at the top of joint mortar in the wheel travelling sections. Owing to the defeat of joint material, a deeper rut depth at joints was logged compared to the original measurements. The distinctive deterioration was not recognized further in this type of pavement, excluding the loss in the joint mortar. Figure 6 shows plotted data of rut depth measurements depending upon the number of cumulative ESALs. As illustrated in the graph below, rutting continuously increased over the ESALs. The largest and smallest rut depths were measured in bound stone pavement B and asphalt pavement, respectively. Bound stone pavement A showed relatively greater rutting compared to stone pavement B. In this circumstance, the different application of material types of base courses would lead to the difference.