Fracture Mechanisms Of Binder-Aggregate System And Its Effect On Properties Of Asphalt Mixtures

Asphalt pavement was widely used in modern highway construction strategy. But because of the higher load condition and worse serving environment, raveling, surface stripping and cracking were always occurred in asphalt pavement. These require a deeper research on fracture mechanisms of binder-aggregate system to enhance the lifetime of asphalt pavement. Referring to domestically and overseas development trend, through a great deal tests, including aggregate-asphalt adhesion, asphalt mortar, asphalt mixture, fracture mechanisms of binder-aggregate system and its effect on properties of asphalt mixtures were discussed in this research.Firstly, based on Dynamic Mechanic Analyzer (DMA), special sandwich sample, aggregate-asphalt-aggregate, were designed and monotonic and dynamic tests with force-control modes were conducted. With failure surface image analysis, the effect factors, including aggregate, bitumen, temperature, stress, stress loading mode, on the mechanical performance of the asphalt mix and aggregate-asphalt adhesion were discussed. Results indicate that failure life of adhesion properties of binder-aggregate system was decreasing with the increase of loading stress. Aging could enhance the adhesion property shortly while watering decrease, the property decreased sharply when the specimens were subjected to both ageing and watering at the same time. Both adhesive fracture mode and cohesive fracture mode were observed in the failure of binder-aggregate, the ratio of adhesive fracture tend to enhance with the increase of temperature.Secondly, using Dynamic Shear Rheometer (DSR), the shear fatigue properties of asphalt mortar were conducted, varies experiments were compared under different temperature, stress and aging. This was designed to evaluate the adhesion properties and fracture mechanisms of aggregate-binder adhesion in asphalt mixture. Results show that aging decrease the failure life of binder significantly, stress and temperature can affect it remarkable.Then, Direct Tensile Tester (DTT) and Indirect Tensile Test (ITT) were taken on asphalt mixture by Electro-Hydraulic Servo-controlled Testing System and Digital Master-Loader under different strain rate and temperature. The effects of temperature and stain loading rate on adhesion property of aggregate-binder system were analyzed. Furthermore, it can be used to validate the experiment results of the DMA and the DSR test. Using these there parts tests, the fracture mechanisms of aggregate-binder adhesion were worked out. Fracture mode was got from the image analysis on failure surface of single aggregate-asphalt and in asphalt mixture. Results show that indirect tension stress decrease while fracture energy increase with the increase of temperature, it has the contrary relation to loading stress-rate. the Both adhesive fracture mode and cohesive fracture mode were observed in the failure of asphalt mixture, adhesive fracture tend to accrue in 0℃. At high strain loading rate, the main fracture mode in failure surface was adhesive failure between aggregate and asphalt/binder, while adhesive failure at low strain loading rate.This research indicated that it has a good relation between aggregate-asphalt adhesion, shear mechanism of binder and fracture properties of asphalt mixture.