# Preventive Maintenance Decision-Making Optimization Method for Airport Runway Composite Pavements
## 3 Results and Discussion
### Maintenance Benefits of Preventive Maintenance Maintenance Technologies
#### 3.2.2. Deterioration Rate Reduction  
Figure 6 shows the deterioration rates of _PCI_ before and after the five types of preventive maintenance, as well as the _DRR_ of each technology. The vertical dashed line represents the year of maintenance, and the solid line is divided into two parts by this dashed line. The left part is the deterioration rate of _PCI_ before maintenance, which was calculated according to the difference of _PCI_ in continuous years, whereas the right part is the deterioration rate of _PCI_ without maintenance, which was predicted according to the tendency of the fitting curve. The dashed line represents the _PCI_ deterioration rate after maintenance. The _PCI_ in each year was calculated according to the performance data in the LTP database. The _DRR_ is the relative difference between the _PCI_ deterioration rates immediately before and after maintenance [40].  
Figure 5: _PJ_ versus _PCI\({}_{b}\)_ of sections treated with five different preventive maintenance technologies. (**a**) Crack sealing; (**b**) Crack filling; (**c**) Fog seal; (**d**) Thin HMA overlay; (**e**) Hot-mix recycled AC.  
Figure 6: Deterioration rate of _PCI_ versus year of AC overlay of sections treated with various preventive maintenance technologies. (**a**) Crack sealing; (**b**) Crack filling; (**c**) Fog seal; (**d**) Thin HMA overlay; (**e**) Hot-mix recycled AC.  
Figure 6a,b show the deterioration rates of _PCI_ and _DRR_ of representative sections after crack sealing and crack filling, respectively. The _DRR_ of all 61 sections is small, or 0.01 in order of magnitude. Furthermore, the tendency of the deterioration rate of _PCI_ after crack sealing or crack filling is similar to that without maintenance. Therefore, crack sealing and crack filling rarely influence the deterioration rates of the _PCI_ or _DRR_ of composite pavement.  
Figure 6c shows the deterioration rates of _PCI_ and _DRR_ of representative sections treated with fog seal. The average _DRR_ of the 21 sections treated with fog seal is approximately 0.2. After 2 years of maintenance, the _PCI_ deterioration rate increases to that just before maintenance, indicating that the fog seal has an influence on the _DRR_ for 2 years after maintenance. The deterioration rate of _PCI_ declines by 20% in the year of fog seal maintenance, and that after \(n\) (_n_ = 1, 2) years of maintenance is approximately equal to that (2 - _n_) years before maintenance.  
Figure 6d shows the deterioration rates of _PCI_ and _DRR_ of representative sections treated with a thin HMA overlay. The average _DRR_ of the 19 sections treated with a thin HMA overlay is approximately 0.7. After 3 years of maintenance, the deterioration rate of _PCI_ increases to that just before maintenance, indicating that thin HMA overlay has an influence on the _DRR_ for 3 years following maintenance. The deterioration rate of _PCI_ declines by 70% in the year of HMA maintenance, and the deterioration rate of _PCI_ after \(n\) (_n_ = 1, 2, 3) years of maintenance is approximately equal to that (3 - _n_) years before maintenance.  
Figure 6e shows the deterioration rates of _PCI_ and _DRR_ of representative sections treated with hot-mix recycled AC. The average _DRR_ of the 19 sections treated with hot-mix recycled AC is approximately 0.8. After 4 years of maintenance, the deterioration rate of _PCI_ increases to that just before maintenance, indicating that hot-mix recycled AC has an influence on the _DRR_ for 4 years after maintenance. The deterioration rate of _PCI_ declines by 80% in the year of hot-mix recycled AC maintenance, and the deterioration rate of _PCI_ after \(n\) (_n_ = 1, 2, 3, 4) years of maintenance is approximately equal to that (4 - _n_) years before maintenance.