2.1. Test Sections
This study was performed based on the pavement engineering of the Yancheng-Jingjiang Expressway in Jiangsu Province, China, a two-way 4-lane highway. The engineering section was located in the downstream direction K162+700-K157+000, with a length of about 5.7 km. In the tested section, there were four types of asphalt pavement structures: (1) Easy compact asphalt (ECA) concrete was used as the top layer, with SMA-13/AC-20/AC-25 asphalt mixture courses underneath in order. (2) Thin-layer porous asphalt overlay with a maximum nominal aggregate size of 10mm (PUC-10) was paved as the top layer, and SMA-13/AC-20/AC-25 asphalt layers underneath were in order. (3) Porous asphalt with a maximum nominal aggregate size of 13mm (PAC-13), with AK-13/AC-20/AC-25 asphalt layers underneath in order. (4) Two-layer porous asphalt with PUC-10+PUC-13, with AC-20/AC-25 asphalt layers underneath in order. Schemes of those pavement structures are shown in
Figure 1, with thickness for each layer of different structures. Porous asphalt mixtures are shown in
Figure 2.
To understand the medium-term service performance of porous asphalt and determine influence of service property of porous asphalt on tire/pavement noise, the service performance indicators of porous asphalt were tracked and observed continuously for 7 years, namely from 2015 to 2022.According to the “Highway Performance Assessment Standards” (JTG 5210-2018), Multifunctional High-Speed Highway Condition Monitor (GB/T 26764) and Specifications of Automated Pavement Condition Survey (JTG/T E61-2014) of China, cracking and other information collecting system (CiCS) of multifunctional automatic pavement detection vehicle and friction coefficient meter were used as automatic detection equipments to detect the indicators of DR, RD, IRI, SFC, and sensor measured texture depth (SMTD). The tire/pavement noise data were also collected by OBSI test in 2022.
According to the
Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering (JTG E20-2011) of China, the characteristics of different road surface mixtures were measured. The gradation and performance indicators of asphalt mixture on the pavement surface are shown in
Table 1 and
Table 2, respectively. Among the four pavement structures, the biggest difference lies in the gradation and porosity of the surface asphalt mixture, which lead to various performances between mixtures.
2.3. Characteristic Indexes
IRI is an important indicator in pavement design, construction acceptance, and maintenance, which reflects the comfort of drivers and passengers and the safety and durability of the pavement. Vehicles traveling on rough pavements will generate additional vibrations, accelerating damage to vehicles and pavements. The higher the IRI was, the worse the smoothness of the pavement surface was. The IRI was detected and analyzed by the CiCS vehicle. The longitudinal section data on the tire tracks were continuously measured by the high-speed laser rangefinder and the accelerometer, and the data errors caused by vehicle bumps were effectively eliminated by the self-developed inertia compensation scheme. The resolution of the laser sensor is 0.05mm. With the support of the positioning data of the integrated control system, the IRI was obtained in real-time through the on-board data acquisition and processing software.
RD is for evaluating road performance. Rutting is a form of damage to asphalt pavement, manifested as a concave surface within the range of the asphalt pavement wheel track, sometimes accompanied by a raised edge of the wheel track. The deeper the RD was, the stronger the bumpiness and vibration of the car during driving. It will impact the vibration noise of the road surface/tires. The RD was detected and analyzed by the CiCS vehicle. Based on the high-resolution and high-frequency sampling frequency of the sensor camera and the sub-pixel data analysis algorithm, the laser image rutting meter was applied to acquire pavement cross-section curves at a fixed sampling interval and calculate the pavement RD values by matching the rutting model to the acquired pavement curves.
SFC is an indicator that characterizes the anti-sliding performance of pavements, directly related to the safety of driving, and is a key quality control indicator during the construction and operation of highways. The SFC was detected and analyzed by the Mu-Meter MK6 friction coefficient meter. Continuous and uninterrupted detection ensured a certain thickness of water film on the pavement surface. An SFC value was output every 10 m, with a detection speed of 50 km/h. The MK6 used the sophisticated tilting tire principle to measure the loads generated by the tires as they passed over the pavement surface, with the tire at an angle of 7.5° to the direction of travel.
DR was detected and analyzed by the CiCS vehicle. The two-dimensional pavement damage detection system was mainly used to detect and recognize pavement diseases. The damage to the road surface can significantly impact the vibration and noise of the road surface/tires.
SMTD was detected and analyzed by the CiCS vehicle. The three-line construction depth was obtained through the pavement wear detection system by adding one laser rangefinder at the left, middle, and right positions behind the vehicle platform (the rangefinders at the left and right positions were shared with the roughness system).
According to the industrial standards of “Highway Performance Assessment Standards” (JTG5210-2018) of China, the values of the indicators DR, RD, IRI, and SFC were converted into the PCI, RDI, RQI, and SRI. The calculation formulas are as follows.
(1) PCI
The value of PCI ranged from 0 to 100, and a greater value represented a better pavement condition. The calculation formula of PCI is given as follow:
The DR of asphalt pavement was calculated based on the following formula:
Where, means the percentage (%) of the sum of the converted areas of various pavement damages to the area of surveyed pavement;
Ai - area of damaged pavement of type i (m2);
A - area of surveyed pavement (the product of the surveyed length and the effective pavement width) (m2);
wi - weight of the pavement damage of type i, referring to the corresponding specification;
i- individual type of damage in item i considering the degree of damage (mild, moderate, and severe);
a0 and a1 are constants, for expressways, a0=15.00, a1=0.412.
(2) RDI
The value of pavement RDI ranged from 0 to 100, and a greater value represented a better pavement condition. The relationship between RDI and RD is as follows:
Where, =10.0,=40.0
(3) RQI
The RQI is calculated based on the formula below:
Where and are constants, for expressways, =15.00, =0.412.
Where, =35.0, = 28.8, = -0.105
(5) TCS
The total number of transverse cracks in the detected section was recorded, and the average value of the transverse crack spacing (TCS) per kilometer was obtained by:
Where, n is total number of transverse cracks in the detected section