Research On Design Of Epoxy Asphalt Mixture Based On Fatigue Performance

Epoxy asphalt is asphalt mixed with resin. The hardening reaction occurs with the resin to form irreversible agent which fundamentally changes the thermoplastic performance of the conventional asphalt and other thermoplastic modified asphalt. Epoxy asphalt was applied extensively on long-span bridges, especially on deck paving of steel box girder bridges due to its advanced performance. The research and application on epoxy-asphalt deck paving of steel box girder bridges started late in China and most of the work was mainly conducted on viscosity-temperature curves of asphalt epoxy. While few studies were conducted on its rheology properties. The design of epoxy-asphalt mixture was mainly based on Marshall tests and the optimum asphalt content was determined by volume parameters. There has been a consistent understanding on mechanism, location, development law of fatigue cracking inside the pavement. However, there is no further research conducted on the fatigue performance and fatigue equations of the epoxy-asphalt mix. Moreover, it lacks systematic research on the factors of the asphalt content and grading. Based on current research accomplishments, the following researches were conducted as for the application of epoxy-asphalt mixture on the deck paving of long-span steel bridges through the combination of technology research, theoretical analysis and laboratory tests.The research was mainly conducted on the pavement performance of epoxy mix such as the low-temperature fatigue, high temperature stability, Marshall parameters and so on. While it is lack of viscoelastic property research. The Rheology property research was conducted as for different stresses, strains and time based on dynamic viscoelastic mechanics. The results revealed the creep compliance of the epoxy-asphalt is about 4 orders of magnitude lower than that of the traditional asphalt. Complex modulus decreased with decreasing frequency (the temperature is increasing) and tend to be stable together with storage modulus. While it exhibited some characteristics of viscosity for high frequency (low temperature). Each viscoelastic parameter was far larger than that of the traditional asphalt and modified asphalt and it has good capacity to resist flow and deformation.The main mechanical parameters of epoxy-asphalt mix such modulus and strength gained through experiments were analyzed and discussed. As for dynamic modulus test, the loading test mode was similar to the real state, and the real material stress and strain process under loading was simulated under through dynamic loading test. It was a more suitable modulus for the mechanical analysis on the deck paving comparatively. As for the epoxy-asphalt mix paving under the common temperature, the modus values for mechanical analysis vary between 500～15000Mpa. The maximum tensile strainεB under 15℃was recommended as its limited tensile strain considering the consistency of safety and failure mode. Epoxy-asphalt mixture is a viscoelastic material which is totally different from the traditional asphalt and modified asphalt. The master cure of the epoxy-asphalt mix was got for 40℃and its shape tends to be an"s"style just like the traditional asphalt. However, the magnitude level span was more narrow than the traditional asphalt which indicated relaxation range of epoxy-asphalt mix was relatively lower and its viscoelastic span was more narrow.Based on Finite Element Method (FEM), the mechanical performances and application requirements were analyzed as for deck paving of long-span steel bridges and the sensitivity analysis was conducted on the systematic parameters. The shearing stress within the steel bridge deck paving was analyzed and the results revealed the shearing strength around the paving/bonding layer interface was around 0.5~1.6MPa when the paving modulus varied between 500 and 15000MPa. The epoxy-asphalt could meet the shearing strength requirements of the bonding layer either for high or low temperatures which should be taken for an optimum choice. The results from the paving modulus analysis revealed the modulus change was not in a linear relationship with the horizontal strain change. When the paving modulus was increased from 500MPa to 5000MPa, the horizontal strain was decreased obviously. However, when the paving modulus was around 5000~6000MPa, the paving modulus had an insignificant impact on the horizontal strain. The largest tensile strain inside the structure surface of deck paving with epoxy-asphalt mix was around 300～400μεand the fatigue failure wouldn't occur under such strain levels. Therefore, mix design should be conducted to solve the fatigue problems confronted with epoxy-asphalt mix. The effect of deck depth on the pavement surface is more significant than the stiffener depth. The integrated optimum design should be conducted economically and technically on the deck depth and stiffener depth. Impact toughness (the area of the load-displacement curve under the impact loading) was proposed as the parameter to evaluate the fatigue performance of the epoxy-asphalt mix based on principles of fracture mechanics and energy. The fatigue performance increased with impact toughness value. The epoxy-asphalt mix design was conducted based on the volume parameters. The asphalt contents were changed while controlling the mix volume indices to observe its pavement performances. The analysis revealed the impact toughness had a linear relationship with residual fatigue modulus which indicated the fatigue performance and the correlation was very good. The impact toughness of the epoxy-asphalt mix can be used for the parameter to evaluate its fatigue performance. The three bending test can be applied for evaluating the mix fatigue performance under the impact loading.