| The twelfth five-year guideline of the China presents the idea of Green which relates with the establishment of resource saving and environmental friendly society, keeping the recycle and protection of resource and environment. Due to the exceptional performance of porous asphalt mixture on drainage, skid resistance, noise reduction, complementarities of ground water etc., the application of porous asphalt mixture in pavements has gradually become an important technology trend. However, due to its different structure from conventional dense-graded asphalt mixtures, that is strength only provided by internal friction angle of coarse aggregate and weak bounding from less binder between aggregates, durability problem has been a big issue for the further application of porous asphalt mixtures, especially for cold regions. Until now, on the durability of porous asphalt in cold regions, researchers at home and abroad mainly focus on the excessive wear caused by tires with nails, as well as the economical and environmental issues by spreading much de-icing salt. But due to the inconsistent research purposes and methods in the past, there are still many issues to be clarified for freeze-thaw durability in adverse seasons. In this paper, theoretical analysis and experimental verification are combined to study the freeze-thaw properties of porous asphalt mixture; furthermore, based on the analysis of interface behaviors, technical measures are proposed to improve freeze-thaw durability. The whole study can provide a theoretical support for its application in seasonal frozen regions.Firstly, damage characteristics of porous asphalt mixtures under freeze-thaw cycles were analyzed. For the complexity of material properties, frozen loading and damage mode, the research methods were determined by a simpler mode. Consequently, the micro-macro analytical methods and corresponding test procedures were proposed. For the macroscopic freeze-thaw mechanical test, a comprehensive analysis on the influence of test conditions on freeze-thaw durability was presented, and two kinds of testing process including different water-saturated conditions and test time were developed at last. For micro level, test method on evaluation of interfacial adhesion performance is provided based on analysis of the asphalt and aggregate interface state. Through the analysis of interfacial system, it was found that the thickness of asphalt film affected interfacial performance badly. And then, the effectiveness of evaluating interfacial performance between asphalt and aggregate with proposed interface system is verified.Secondly, factors affecting on frost resisting performance and evaluation of porous asphalt mixtures were discussed. Based on the attenuation rule of strength and physical properties, the freeze-thaw damage process could be divided into three phases, and among that the interfacial performance would behave rather important. Considering the asymmetrical distribution characteristics of percent of air voids, it is believed that the critical location of porous asphalt mixtures in freeze-thaw cycles lie in the inner structure. Reasonable permeability coefficient considering frost resisting performance in cold region was proposed based on the relationship between the permeability coefficient and porosity of porous asphalt mixture. Then, factors which influence the indoor frost resistance evaluation were analyzed. It was found that uniaxial compression mode is more suitable to the evaluation on frost resistance of porous asphalt pavement in China. Based on the asphalt hardening law during freeze-thaw test, correction method for indoor freeze-thaw test results was established.A viscous-elastic-plastic damage model of porous asphalt mixtures was constructed, and then the stress-strain curves under uniaxial compression modes at freeze-thaw temperature (-10~20℃) were fitted. The rationality of model was validated through parameter analysis including elastic modulus, relaxation time, shear modulus and bulk modulus etc.. The attenuation behavior under multiple freeze-thaw cycles was analyzed with the model. It was concluded that the freeze-thaw will cause to decrease of modulus, enlarge of relaxation time and internal friction angle, increase of bulk volume, and debonding between asphalt and aggregate.To further, the interface bonding performance between two kinds of asphalt and aggregate was discussed. Firstly fatigue loading with low frequency was applied to interfacial system to simulate the effect of temperature cycling. Interface fatigue damage model was established and used to predict fatigue lives. The final test results indicated that rubber asphalt exhibit better fatigue lives. The decrease of temperature and use of basalt could improve the fatigue lives above the 0℃. Aging had an important effect on the fatigue performance. Furthermore, the monotonic test was introduced. And the critical strain energy density (CSED) was determined based on the stress-strain curve. The master curve of CSED at different temperature could be got based on time temperature correspondence, and so the fracture behavior at lower temperature could be predicted. Comparison and analysis of the results from fatigue and cracking tests show that there is a good relationship between these two tests, and a simpler critical strain energy density in cracking test is proposed to evaluate interface performance under the freeze-thaw load. Meanwhile, the CSED results at different temperature and load rates show the same change trend on the effect of rubber asphalt and aging. However, it is found that long-term aging had negative effect on the interfacial performance at lower temperature.Based on the above experiment results, a simpler low-temperature adhesion test was proposed, and interfacial bonding properties between different aggregate and binder at low temperatures were studied. The modified asphalt, especially rubber asphalt had a good effect on the interfacial performance. It was also found that the adhesion between asphalt film and aggregate determined the damage mode. The feasibility of replacing mechanical test with it was analyzed compared to mechanical properties of the interface bonding. Then two kinds of typical asphalt and aggregate combinations were chosen to prepare porous asphalt mixtures, and the freeze-thaw durability was studied. Preliminary analysis shows that freeze-thaw durability of porous asphalt mixtures can be characterized by the interface bonding properties between asphalt and aggregate. Finally, the effect of healing on the interfacial bonding performance was investigated. It is believed that healing of viscoelastic materials has a positive effect on the freeze-thaw durability of asohalt mixtures.
|
PDF Full Text Request