| Warm mix asphalt(WMA)technology can significantly reduce the production and construction temperature of asphalt mixture,thusing reducing the emission of asphalt smoke and the aging effect of asphalt.Therefore,warm mix asphalt and mixture technology is an important way to realize the clean application of asphalt materials because of solving the limitations of high energy consumption,air pollution and serious aging of asphalt of hot mix asphalt mixture during production and construction.The warm mix agent has an important effect on the pavement performance of warm mix asphalt.Therefore,an in-depth study about the effect of warm mix agent on the performance of asphalt and asphalt mixture has important guiding significance for the promotion of warm mix asphalt technology.In this paper,the conventional performance analysis method,rheology evaluation method,contact angle test and molecular dynamics simulation method are used to study the effect of organic viscosity-reducing warm mix agent and surfactant warm mix agent on the performances of asphalts.The action mechanism of reducing the mixing temperature of asphalt mixture with surfactant warm mix agent is discussed by surface energy and tribology theories.The performance of warm mix asphalt mixtures are evaluated systematically.The main research points are as follows:The conventional performance of asphalts was comprehensively tested and analyzed.The effect of the content of warm mix agents on the conventional performance of 70 asphalt and high viscosity asphalt was obtained.Results show that the organic viscosity-reducing warm mix agent can reduce the penetration,ductility and high temperature viscosity of asphalts,increase the softening point and kinetic viscosity at 60°C of asphalts,and make the asphalts hard and brittle.Under the condition of low content,surfactant warm mix agent has little effect on the penetration,softening point,ductility and viscosity-temperature relationship of asphalts.The rheological properties of warm mix 70 asphalt and warm mix high viscosity asphalt were tested by dynamic shear rheometer(DSR)and bending beam rheometer(BBR).The effect of warm mix agents on the viscoelastic properties of asphalts was obtained,and the relationship between the amount of warm mix agents and the rheological properties of asphalts was expounded.Results show that the organic viscosity-reducing warm mix agent can increase the modulus,rut factor G*/sinδand zero shear viscosity of asphalts when the temperature is lower than its melting point.That means the organic viscosity-reducing warm mix agent can improve the high temperature deformation resistance of asphalts,but also increase the temperature sensitivity and creep stiffness S of asphalts,and reduce the m value,which may be harmful to the low temperature performance of asphalts.For the surfactant warm mix agent,it can reduce the asphalt modulus and rutting factor G*/sinδin a certain temperature range,increase the cumulative deformation of AH-70,thus the high temperature denaturation resistance of AH-70 is reduced.However,it can reduce the creep stiffness S of AH-70 at the same time,and increase the m value,which means the low temperature performance of AH-70 is improved.The effect of surfactant warm mix agent on the high and low temperature performance of high viscosity asphalt is more complex,due to the influence of modifier in high viscosity asphalt system.It is not that the higher the content of warm mix agent is,the better the performance of high viscosity asphalt is,and there is the best content of surfactant warm mix agent.The contact angle tester was used to test the surface tension and the contact angle variation of warm mix asphalts on the aggregate surface and the calculation model was constructed to quantitatively describe the spreading rate of warm mix asphalts.Results show that the spreading speed of asphalt on different types of aggregate surface is different under the condition of high temperature.The contact angle of asphalts on the aggregate surface shows a power function y=Ax~b relation with time under different temperature conditions.The surface tension of asphalts decreases linearly with the increasing temperature.Organic viscosity-reducing warm mix agent can increase the spreading rate of asphalts,and surfactant warm mix agent can significantly reduce the surface tension of asphalts,thus reducing the contact angle of asphalts on the surface of aggregate and improving the wettability of asphalt.Therefore,the surfactant warm mix agent has more application advantages.The friction process of warm mix agent on the interface between asphalt film and aggregate was simulated by molecular dynamics simulation,and the effect of warm mix agent on the parameters of friction system was analyzed to find the action law of agent.Results show that an increase in the shear rate leads to an increase in the temperature of the lubricating film of warm mix asphalt.There is a stable working region of asphalt lubricating film in a certain range of shear rate,and the surfactant warm mix agent can increase the stable working area of the lubricating film,reduce the shear stress of the asphalt lubricating film,effectively improve the lubricity of the asphalt,as a result,the asphalt mix temperature can be reduced.In order to verify the real performance of the surfactant warm mix agent in the application,comprehensive tests were carried out on the performance of AC-13,SMA-13 and PA-13 asphalt mixtures.Results show that when the mixing and compaction temperature of warm-mix mixture is 30°C lower than that of the corresponding hot-mix asphalt mixture and the content of warm mix agent is between 0.2wt%and 0.35wt%,and the voidage of the warm-mix asphalt mixtures can meet the requirement of the target voidage.Warm mix agent can slightly reduce the performance at high and low temperatured and water damage resistance of AC-13 and SMA-13,but slightly improve the high and low temperature performance of PA-13 asphalt mixture.The pavement performances of the three types of asphalt mixtures all meet the requirements of pavement design. |
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