# Study on Noise Reduction with Paving Different Low Noise Pavement Materials
## 2 Experimental Setup of Testing Lanes
### Combination of Low Noise Pavements  
According to the structure of low noise pavement and implementation of pavement, three types of low noise pavement structures are set up in this experimental section according to lanes and pavement structures, with a total of four types of pavement combination forms, as plotted in Figure 1. They are summarized as follows:  
* Type I: The laying range is from K159+100 to K159+400, with a total of 300 m in length. Both the inner lane and the outer lane use a 2.5 cm PUC-10. The PUC-10 mainly uses fine particle size aggregates to increase the smoothness of the pavement and thus to reduce the noise generated by tire vibration, and it also has some sound absorption ability at the same time. Due to the thickness issue, compared with PAC-13, the peak frequency of PUC-10 is much higher, while the absorption coefficient of the peak value is slightly lower.
* Type II: The laying range is from K159+400 to K159+700, with a total of 300 m in length. The inner lane and the outer lane use a double-layer porous asphalt pavement, where the bottom layer uses 4.5 cm PAC-13 and the top layer uses 2.5 cm PUC-10. The double-layer porous pavement has the noise reduction performance of both single-layer porous asphalt pavement and thin-layer asphalt pavement, which is shown as follows: First, within the effective frequency range, there are two peaks of sound absorption coefficient, so the noise absorption effect is more obvious [24]; Second, the top layer has a fine particle size with a lower value of mean profile depth (MPD), and thus it can reduce the vibration and the noise caused by the contact between the tire and the pavement [25]; Third, the absorption layer of double porous pavement is thicker, and the first effective absorption peak frequency can be lower.
* Type III: The laying range is from K159+700 to K160+700, with a total of 1000 m in length. The inner lane uses a 2.5 cm PUC-10, and the outer lane uses 4.5 cm PAC-13+2.5 cm PUC-10 double-layer asphalt pavement. This combination considers that the inner lane is mainly used for light vehicles, while the outer lane is mainly used for heavy ones. The top layers of the combination use fine particle size aggregates to  
Figure 1: Combinations of pavement structures for the experimental section.  
reduce the noise generated by tire vibration [26]. Compared with light vehicles, the tire/road noise generated by heavy vehicles is more dominant at lower frequencies than light vehicles, and the engine noise of heavy vehicles also has more contributes, so double-layer porous asphalt pavements are used in the outer lane. After considering the drainage requirements of road cross-sectional pavement structure, the construction convenience, and the double-layer porous pavement sound absorption capability, the emergency lane also uses double-layer porous asphalt pavement.
* Type IV: The laying range is from K160+700 and K161+300, with a total of 600 m in length. Both the inner lane and the outer lane use a single-layer porous asphalt pavement 4.0 cm PAC-13. PAC-13 is the most widely used pavement to mitigate noise in China nowadays, which can reduce traffic noise by absorbing tire/road noise.  
From Figure 1, one can get that this paper studies four types of pavement materials. The first one is ECA-10, which is used in the experimental section before road maintenance, and the second and third ones are PUC-10 and PAC-13, respectively. The last one is the combination of PUC-10 and PAC-13. The reason for choosing PAC-13 is that it is one of the most widely used materials for porous asphalt pavement in China because of its efficiency in reducing traffic noise by absorbing the tire/road noise. Compared with PAC-13, PUC-10 can absorb the tire/road noise and reduce the vibration between the tire and the ground simultaneously. Moreover, the peak frequency of PAC-10 in noise absorption is often much higher than that of PAC-13, and thus PUC-10 can be expected to be more suitable to absorb the tire/road noise of light vehicles.