Effect Of Desulfurization Degree On Rheological Properties Of Reclaimed Rubber Modified Asphalt

With the widely application of desulfurized rubber asphalt,it is of great necessity to understand the complex relationship between the overall mechanical properties of desulfurized rubber asphalt and the properties of each component material from a meso-scale perspective to ensure its excellent mechanical properties while minimizing SO₂ emissions during the production process.In view of this,this paper used three kinds of Mooney viscosity desulfurized rubber powder to prepare asphalt,and the rheological properties of desulfurized rubber asphalt are investigated comparatively through laboratory tests and a variety of meso-mechanical models.Firstly,laboratory tests,including high temperature multiple stress creep recovery（MSCR）test,linear amplitude sweep（LAS）test and bending beam rheometer（BBR）test,are conducted to study the rheological properties of desulfurized rubber asphalt.Then,finite element software COMSOL was used to simulate the swelling of desulfurized binder powder in asphalt and analyze the relevant factors affecting the degree of swelling of binder powder.Subsequently,the dynamic modulus of the matrix asphalt and the desulfurized rubber powder were obtained by frequency sweep（FS）test,combined with the time-temperature equivalence principle and the corresponding mathematical model.The master curves of general rubber asphalt and desulfurized rubber asphalt were also established to compare their dynamic mechanical properties,as well as the master curves of different degrees of swelling of rubber powder to investigate the influence of the degree of swelling on their mechanical properties.Finally,the mechanical parameters of desulfurized rubber powder and asphalt,i.e.,modulus,Poisson’s ratio and their volume fractions,were applied to the meso-mechanical model.By comparing the laboratory test results,the meso-mechanical model suitable for desulfurized rubber asphalt was selected to guide the actual production control of desulfurized rubber asphalt.The main findings of the study are as follows.（1）In MSCR test,the desulfurized rubber asphalt mixed with 40 Mooney viscosity desulfurized rubber powder（ML40MA）presents excellent resilience,but its J_nr is larger than ML60MA,and the R value is the opposite,which indicates that the high temperature performance index of desulfurized rubber asphalt is more sensitive to the degree of desulfurization.The effect of the degree of desulfurization of binder powder on the fatigue resistance of asphalt at medium temperature has a clear pattern,with the increase of the degree of desulfurization of binder powder,the fatigue damage rate of asphalt gradually decreases and the fatigue life increases.M value,T_c,mandΔTc of ML40MA are the largest,and the desulfurized rubber asphalt mixed with 40 Menny viscosity desulfurized binder powder has the best low temperature crack resistance.（2）The type and size of binder powder affect the swelling of binder powder in asphalt,mainly in the time of"flat valley"characteristic of desulfurized binder powder.The increase of desulfurization degree makes the structure of powder contain more simple long chains,and it is easier to swell.The desulfurized rubber powder with 40 Mooney viscosity starts to show a"flat valley"at2500s.While the size of powder affects the interaction between powder and asphalt to a certain extent,the specific surface area of 0.15mm powder is the largest,and its concentration changes rapidly with time and takes the lead in reaching a"flat valley"at 2000s.（3）The generalized Sigmoidal model establishes a good fit for the dynamic modulus master curve of desulfurized rubber asphalt in the full temperature domain.The dynamic modulus of desulfurized rubber asphalt is higher than that of matrix asphalt at low frequencies and lower at high frequencies,implying that the addition of desulfurized rubber powder improves the high and low temperature performance of asphalt,and it increases with the increase of desulfurized rubber powder degree.The dynamic modulus master curve of desulfurized rubber with different degree of swelling and desulfurization showed significant differences,and the increase of swelling and desulfurization of desulfurized rubber would make the slope of the main curve of dynamic modulus more inclined,and the master curve of desulfurized rubber after 20h swelling obviously showed the same"S"shape as asphalt.（4）The MT model and TLB model have higher accuracy in predicting the modulus of desulfurized rubber asphalt in the high frequency region.Since the modulus of desulfurized rubber asphalt at high temperature is more dependent on the desulfurized binder powder,and these two models have their own limitations,resulting in larger deviation of their prediction results in the low frequency range.（5）Based on the grey correlation method,a comprehensive performance indicator was established to characterize the high and low temperature performance of desulphurized rubber asphalt.The comprehensive performance indicator value of desulphurized rubber powder with 60 Mooney viscosity was the largest.Therefore,it is suggested to control Mooney viscosity to 60 in actual production,when the comprehensive performance of the prepared desulfurized rubber asphalt is the best.In summary,the middle and low temperature performance of desulfurized rubber asphalt prepared by 40,60,80 Menny viscosity desulfurized binder powder are improved with the increase of desulfurization degree.Therefore,in order to minimize the SO₂ emissions,the rubber powder can be pre-treated with desulfurization.In the scope of this study,it is recommended to use 60 Menney viscosity of desulfurized rubber powder for the preparation of rubber asphalt in high temperature areas,which has the optimal performance.