Experimental Research On High-temperature Viscoelastic Properties Of Rubber Asphalt

As a kind of material with excellent road performance, rubber asphalt has been widely applied in the high-grade asphalt pavement in our country due to its outstanding advantages of energy-saving, noise reduction and environmental protection. Simultaneously, because the rubber powder dosage of rubber asphalt is so high that its structure is complex, it’s too difficult to reflect its mechanical characteristics at high temperatures using conventional methods for evaluating high-temperature properties of rubber asphalt. Therefore, it is necessary to adopt viscoelastic theoretical analysis method and describe its changing rule of high-temperature viscoelastic properties from different angles, which has vital significance for evaluating high-temperature performance of rubber asphalt comprehensively and accurately.In this study, high-temperature viscoelastic mechanical behavior of rubber asphalts of different modification methods, different dosage and different aging state are comprehensively analyzed by using conventional tests, dynamic tests and creep tests. And the relationships between high-temperature viscoelastic parameters with temperature, frequency, stress and other test factors are identified.Firstly, base asphalt of DongHai70#, rubber powder of HongLei60mesh bias tire and connection agent TOR are selected as raw materials to design and prepare rubber asphalt of two modification methods, seven kinds of dosages. And conventional indicators of high-temperature properties including softening point and60℃dynamic viscosity are tested. Researches show that:the two indicators has good correlation and that with the increase of the rubber powder dosage, softening point and60℃dynamic viscosity of unaged and RTFOT (Rolling Thin Film Oven Test) samples of TOR rubber asphalt and common rubber asphalt present increasing trend and that softening point and60℃dynamic viscosity of TOR rubber asphalt of different dosage are greater than that of common rubber asphalt and that softening point and60℃dynamic viscosity of samples after RTFOT aging are basically greater than that of unaged rubber asphalt of the same dosage and the same modification method.Secondly, dynamic mechanical analyses on rubber asphalt are carried out within the high temperature range by using dynamic viscoelastic mechanical theory. Linear viscoelastic range of rubber asphalt is determined from strain sweep tests. Changing rules of phase angle δ, complex modulus G*and anti-rutting factor G*/sinδ are acquired from temperature sweep tests. Through frequency sweep tests phase angle master curves and complex modulus master curves are acquired using time-temperature equivalence principle. Researches show that with the increase of temperature, the phase angle of rubber asphalts gradually decrease while the complex modulus and anti-rutting factor have the trend of dramatical decline. The high-temperature viscoelastic parameter G*/sinδ has the relationship "lg(G*/sinδ)=A·T+B" with temperature T. And|A|can reflect the temperature sensitivity of rubber asphalt within the scope of high temperature. The smaller|A|is, the smaller temperature sensitivity is. Frequency and temperature have equivalent effect on the influence on the high-temperature viscoelasticity of rubber asphalt. The high-temperature viscoelasticity of rubber asphalt of18%rubber powder dosage performs best.Finally, high-temperature viscoelasticity of rubber asphalt is analyzed taking advantage of creep test. Zero Shear Viscosity (ZSV) of rubber asphalts is achieved by fitting from static creep test data and creep stiffness Gv of rubber asphalts is achieved by fitting from repeated creep recovery test data. And the two high-temperature viscoelastic indexes are used for evaluating high-temperature viscoelasticity of rubber asphalt. Researches show that with higher dosage of rubber powder or smaller loading stress, Zero Shear Viscosity fitted from static creep test data is much smaller. Creep stiffness Gv fitted from repeated creep recovery test data indicates that the high-temperature viscoelasticity of rubber asphalt performs best when the dosage of rubber powder is at15%～18%range. Creep stiffness of rubber asphalt presents a trend of "increase firstly and then decrease" with the increase of stress and creep stiffness Gv reaches the maximum value at the stress level of100Pa.The research results above for provide a necessary basis for evaluating the high-temperature viscoelasticity of rubber asphalt accurately and lay a good foundation for exert its advantage on high-temperature performance.