Preparation And Characterization Of High-Performance Epoxy Asphalt

As one of polymer modified asphalts, high-performance epoxy asphalt is the shorted form of epoxy modified asphalt. For epoxy asphalts, a thermosetting network will be formed when epoxy reacts with curing agents in the asphalt, in which the continuous phase is a cured epoxy and the discontinuous phase is a mixture of asphaltic materials. Therefore, the thermoplastic properties of the asphalt in the cured epoxy networks with high temperature and low temperature resistant, mechanical, adhesive and water and solvent resistant properties will be improved remarkably. Epoxy asphalt was first developed by Shell Oil Company in the late 1950's as a jet fuel and jet blast resistant specialty pavement for airfield applications. Since 1967, epoxy asphalt has been widely used as the wear surface on long-span orthotropic steel deck bridges. In 2000, China successfully applied imported epoxy asphalts in the pavement of steel deck of the Second Nanjing Yangtze River Bridge. Since then, more than thirty long-span orthotropic steel deck bridges have been paved with epoxy asphalts in China, including some world-famous bridges, such as Sutong Bridge, Hangzhou Bay Bridge and Zhoushan Xihoumen Bridge. The price of imported epoxy asphalt is very high, which is more 10-fold of ordinary asphalt. Thus, development of domestic epoxy asphalt is of great economic and social importance.In present thesis, based on the researches on the influence of curing agents, compatibilizers, tougheners and viscosity modifiers on the mechanical properties and viscosity of epoxy modified asphalts, high-performance epoxy asphalts were prepared. The ratios of epoxy resin and asphalt with curing agents and other modifiers for domestic epoxy asphalt adhesive and binder are 1:4.40 and 1:5.70, respectively, which are close to those ratios of U. S. epoxy asphalt (1:4.45 and 1:5.85). The tensile strength and elongation at break of epoxy asphalt adhesive and binder at 23℃were 9.57 MPa,3.83MPa and 343%, 588%, respectively, which are close to those of U. S. epoxy asphalts. The viscosities of domestic epoxy asphalt adhesive and binder those increase to 1000 mPa.s at 121℃were 34 min and 57 min, which exceed those of the technical requirement of U. S. epoxy asphalts (20min and 50min). Furthermore, different to imparted products, the viscosity of domestic epoxy asphalts can be adjusted as the actual requirement. The Marshall stabilities, flow values at 60℃and percent air voids of uncured and cured domestic epoxy asphalt concretes all exceed the technical requirements of imported epoxy asphalts.In this thesis, the cure behaviors, glass transition temperatures (Tg), damping behaviors, thermal stabilities and morphologies of U. S. and domestic epoxy asphalt adhesives and binders were compared by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and laser scanning confocal microscopy (LSCM).DSC isothermal curing results revealed that all DSC curves showed sigmoidal forms, indicating the cure reaction of epoxy asphalt adhesives and binders were autocatalytic. The cure rates of domestic epoxy asphalt adhesive and binder were faster than those of U. S. epoxy asphalts. Moreover, the cure heats of domestic epoxy asphalts were higher than those of U. S. epoxy asphalts. Epoxy asphalt adhesives and binders were fully cured for 4h at 121℃. However, it took 1Oh to obtain the fully-cured pure epoxy resin, suggesting the addition of asphalt catalyzed the cure reaction of epoxy resin.Also, DSC results showed that all cured epoxy asphalt adhesives and binders showed a glass transition and the intrinsic melting peak of asphalt disappeared. These results indicated that good compatibility between epoxy resin and asphalt. DSC results showed that the Tgs of cured epoxy asphalt adhesives and binders were between those of cured pure epoxy resins and pure asphalts. Furthermore, the Tgs of cured domestic epoxy asphalt adhesive and binder were lower than those of U.S. epoxy asphalt, suggesting better low temperature properties for domestic epoxy asphalt than those of imported epoxy asphalts. All those results above agreed well with the results of DMA.DMA results showed that the storage moduli of cured epoxy asphalt adhesives were greater than that of those of cured epoxy asphalt binders. tanδ-temperature curves of epoxy asphalt adhesives and binders showed not only a glass transition peak (αtransition) but also a smallβtransition peak, attributed to the Tg of the asphalt confined by the crosslinking networks of epoxy. Both domestic and imported epoxy asphalt adhesives and binders had very high tanδpeak values, which was known as damping coefficient, at the range of 1.46-1.66. The temperature range of tanδ>0.3 for epoxy asphalts were all at about 40℃. Furthermore, the areas of tanδ-temperature curves (TA) for epoxy asphalt adhesives and binders were between 38K and 47K. All those results discussed above showed that epoxy asphalt had good damping properties.TGA results indicated that the thermal stability of asphalt decreased with the addition of epoxy resin. In addition, the thermal stability of asphalt was greater than that of cured pure epoxy resin. Differential thermogravimetry (DTG) results showed that the process of thermal degradation of asphalt was significantly modified with the addition of epoxy resin.Observation of LSCM found that phase separation took place when the U.S. epoxy asphalt adhesive and binder were completely cured. Asphalts aggregated with diameters from several micros to 20μm were uniformly dispersed in the continuous phase formed by the crosslinked epoxy networks. Nevertheless, much denser phase separation formed in the cured domestic epoxy asphalts with several greater aggregates, which contained structure of phase separation of epoxy and asphalt. Due to the formation of phase separation, epoxy asphalt had good toughness.All the results discussed above have good theoretical directions for the explanation of the interaction mechanism, preparation and application of epoxy asphalts.