## 4 Results and Discussion
### Spring-Thawing Clogging Model of OGFC Based on the Mistcherlich Growth Model
It can be seen that the gravelly clogging materials had the least influence on the permeability coefficient of COF-OGFC, which is because the large-size clogging materials are more easily embedded in the open pores of the surface and do not easily enter the pavement to form an accumulation. Moreover, the gap between the clogging materials embedded in the open pores of the surface is larger, which has little influence on the permeability of COF-OGFC. The full-scale clogging materials have the greatest influence on the permeability coefficient of COF-OGFC. This is because the large-size clogging materials are embedded in the interconnected pores, and the small-size clogging materials accumulate and fill the remaining pores, resulting in the complete blockage of the permeability path of COF-OGFC. The effect of powdery clogging materials on the permeability coefficient of COF-OGFC is also small. This is because the two-phase mixture containing the powdery clogging materials and the water flow can smoothly flow out of the pavement surface along the interconnected pores. The powdery clogging materials do not easily form an intrusion in the interconnected pores, and only the accumulation formed by powdery clogging materials has little effect on the permeability coefficient of COF-OGFC. The porosity of COF-OGFC with different clogging materials is shown in Figure 14.  
Figure 14 shows that the porosities of COF-OGFC with powdery clogging materials, sandy clogging materials, gravelly clogging materials and full-scale clogging materials were reduced to 90%, 53%, 97% and 57% of the initial value after 20 cycles. This also indicates that powdery clogging materials and gravelly clogging materials have little effect on the porosity of OGFC, which is consistent with the permeability test results. The main reason for this is that the clogging materials with a larger  
Figure 14: Porosity of COF-OGFC with different clogging materials. Figure 13: Permeability coefficient of COF-OGFC with different clogging materials. size or smaller size cannot remain in the interior of the COF-OGFC, and sandy clogging materials are easily retained in the permeable pavement due to the proper size. The dry weight of COF-OGFC with different clogging materials is shown in Figure 15.  
It can be seen from Figure 15 that, as the cycles increase, the dry weight of COF-OGFC with different clogging materials increases. The increase in the dry weight of COF-OGFC with sandy clogging materials and full-scale clogging materials was quite obvious. After 20 cycles, the dry weight of COF-OGFC with sandy clogging materials and full-scale clogging materials increased by 148.27 g and 90.26 g, respectively. The dry weight change of COF-OGFC with powdery clogging materials and gravelly clogging materials was not significant, and after 20 cycles, the dry weight of COF-OGFC with powdery clogging materials and gravelly clogging materials increased by 37.73 g and 5.64 g, respectively. However, compared with the permeability coefficient and porosity index, the dry weight of COF-OGFC with powdery clogging materials changes more obviously, which may be due to the fact that the clogging materials with a small size can easily enter the pavement under the hydraulic gradient and dynamic water scouring, and the infiltrated clogging materials can only be attached to uneven grooves in the pores or in semi-connected pores. The accumulation of small-size clogging materials only causes a significant change in dry weight and does not affect the porosity and permeability coefficient of COF-OGFC. The dry weight of COF-OGFC with full-scale clogging materials was 1359.57 g after 16 cycles and 1320.96 g after 20 cycles. The dry weight of COF-OGFC with full-scale clogging materials suddenly decreased, but the porosity and permeability coefficient indexes did not fluctuate abnormally, and still increased steadily.