The temperature segregation refers to the pavement quality difference caused by the uneven paving temperature of asphalt mixture, and the pavement life with severe segregation can even be reduced by 50%. Some common early-stage pavement problems, such as serious partial rut depth, cracks, local oil spilling, pit groove, mud pumping, surface damage, loosening, uneven structural depth of new asphalt concrete pavement, are related to temperature segregation. In the paving process, asphalt concrete should be controlled within a certain temperature limit. If the temperature is too low, the asphalt will be hard to compact and if the temperature is too high, the asphalt will age easily. In order to improve the quality of pavement construction and reduce the occurrence of early-stage problems, it is necessary to reduce the occurrence of temperature segregation. Therefore, it is necessary to detect the temperature of the mixture in real-time during construction.
Using thermal imaging device to detect temperature segregation has natural advantages. By determining the best shooting distance, the infrared thermal imager can detect the temperature of the outbound and inbound, paving, and each link of the asphalt mixture and can determine the temperature segregation of asphalt mixture during construction.
The void phenomenon of asphalt concrete pavement is a common hazard. It refers to the discontinuous contact phenomenon of the pavement structural layer, which is usually manifested as the gap caused by the separation of the concrete surface layer and subgrade or asphalt layer. At the same time, the existence of the void is one of the causes of other hazards of asphalt concrete pavement. A large number of theories and experiments have proved that the local void phenomenon of asphalt concrete pavement foundation exists for real, especially the cement concrete pavement constructed by the asphalt mixture. According to the observation results of the road test, it is proved that there are a lot of voids under the cement concrete slab caused by mud pumping at the joint edge and slab foot of cement concrete pavement. Therefore, it can be inferred that similar situations will occur in asphalt concrete pavement.
The effect of asphalt concrete pavement slab bottom void is very serious. The stress state of asphalt concrete pavement with voids is similar to that of the cantilever structure. Under the action of moving load, excessive deflection deformation and tensile stress will be produced, which will reduce the fatigue life of the pavement, and make the pavement be forced into repair or reconstruction in a short term. Secondly, after the asphalt concrete pavement bottom disengages, the faulting of slab ends, fracture and other problems of the pavement will appear one after another, resulting in a poor driving experience of vehicles, serious loss of vehicles, increase of transportation costs, and sometimes even leading to serious traffic accidents.
When the asphalt pavement is in use, the surface water seeps into the pavement naturally through cracks or voids, or passively enters into the pavement structure due to some other factors. Due to the existence of these infiltration water, the asphalt on the aggregate surface will be emulsified or peeled off, which will make the asphalt mixture structure loosened, and even form more serious mud pumping and pit hazards. If the pavement water seepage is not found in time, it will accelerate the development of functional hazards to structural hazards. Therefore, it is very important to detect and evaluate the permeability of asphalt pavement quickly and accurately in the early stage.
At present, some scholars learn the relationship between porosity, permeability coefficient, and surface temperature difference, and conclude that the permeability of asphalt pavement has a good correlation with surface temperature difference, which provides a theoretical basis for evaluating the water permeability of pavement with thermal imaging core technology. By analyzing the correlation between surface temperature field and water permeability, Li Zhidong and relative staff developed an infrared differential thermal detector for asphalt pavement water permeability and concluded that it is feasible to use infrared temperature-measuring technology to detect pavement temperature difference and then evaluate the water permeability of asphalt. The infrared thermal imaging technology can identify and evaluate the water permeability of the pavement, which is of great significance to prevent the further deterioration of the pavement.
The infrared thermal imaging technology is widely used in road engineering. Besides the detection function of road construction and maintenance, it is also of great use in daily road monitoring. In the sunny morning, the ordinary monitoring systems are adequate for monitoring the road, but it can't function in the weather of rain, snow, haze or when the light is too weak at night. Infrared thermal imaging technology can eliminate the influence of the external natural environment. It uses an infrared detector to transform the target and background on the road into a gray image coordinate system and reflects the information in the visual field through the size of the gray value. The radiation temperature of walking people, animals and other creatures in the scene is higher than the radiation temperature of the object, the gray level of the image is relatively high, and the background presented in the image is brighter; the lower the radiation temperature, the smaller the gray level of the image, the darker the background presented in the image.