Research On The Rheological Characteristics Of Nano Montmorillonite Modified Bitumen And Its Mixtures

With the development of highway construction, it has emphasized the importance of pavement performance and durability. One of the basic ways is to improve the properties of the materials used for the pavement.In recent years, using nano montmorillonite (OMMT) to modify the bitumen has become a new subject all over the world. The advantages of OMMT are that it can inhibit the ageing process and improve the high-temperature stability of bitumen, thus extending the service life of bituminous pavement. There are some reports on the preparation and mechanical properties of OMMT modified bitumen. However, the researches on the rheological characteristics of OMMT modified bitumen are still very little, especially for the OMMT modified bitumen mixtures. It is thus very significant to study the rheological characteristics and road performance of OMMT modified bitumen and its mixtures due to the obvious influences of rheological characteristics on the road performance of pavement.This paper investigated the rheological characteristics of OMMT modified bitumen and its mixtures, established the rheological model for both modified bitumen and mixtures, and explored the road performance of OMMT modified bitumen mixtures. The main conclusions are as follows:(a) The effects of OMMT content, temperature and loading frequency on the rheological characteristics of OMMT modified bitumen are studied using the dynamic shear rheometer (DSR). The results showed that the addition of OMMT increased the viscosity and complex shear modulus, and at the same time decreased the phase angle of bitumen, which indicated that OMMT could enhance both the stiffness and elasticity of bitumen. Therefore, the resistance of permanent deformation at high temperature and fatigue cracking at low temperature were improved for the addition of OMMT. The master curves of complex shear modulus were obtained by adopting the time-temperature equivalence principle. Such master curves of OMMT modified bitumen proved that the stiffness was enhanced more significantly at low loading frequency.(b) The viscoelastic characteristics of OMMT modified bitumen and its mixtures were investigated by creep test. The results showed that OMMT decreased the total deformation of bitumen and mixtures during loading period, and simultaneously increased the elastic deformation of bitumen and mixtures, which led to the reduction of permanent deformation for bitumen and mixtures.(c) The rheological modulus of OMMT modified bitumen and its mixtures was established. The results indicated that two-term Burgers model could be used to describe the viscoelastic characteristics for OMMT modified bitumen, which revealed that both the elastic and viscous behaviors of bitumen could be affected by OMMT. The mechanical parameters increased at 20℃and 0℃but decreased at-10℃. The revised Burgers model was more suitable for describing the viscoelastic properties of OMMT modified bitumen mixtures. The model demonstrated that the retardant viscoelastic and viscous properties of bitumen mixtures could be improved with addition of OMMT, but the improvement of elastic behavior was somewhat weakened due to the framework of aggregates.(d) The dynamic modulus of OMMT modified bitumen mixtures was studied and the results showed that the frequency dependence and temperature dependence were remarkable for dynamic modulus and phase angle of OMMT modified bitumen mixtures. With the increase of temperatue or the decrease of frequency, the dynamic modulus of mixtures decreased and the phase angle increased. The dynamic modulus master curves of OMMT modified bitumen mixtures could be obtained by adopting the time-temperature equivalence principle. Such master curves of OMMT modified bitumen mixtuers proved that the dynamic modulus increased while the phase angle decreased, and the amplitude of variation of dynamic modulus was decreased in the whole working frequency or temperature range.(e) The fatigue properties of OMMT modified bitumen mixtuers were investigated by the indirect tensile fatigue test. The results showed that using OMMT could increase the fatigue life of OMMT modified bitumen mixtures at 5℃, and the improvement was even more significant at low loading stress.(f) The rutting test results indicated that the addition of OMMT enhanced the high-temperature stability of bitumen mixtuers, and the resistance to permanent deformation of OMMT modified bitumen mixtures could be improved.