Study On Properties Of Crumb Rubber/SBS Composite Modified Asphalt Based On Rheological Characteristic

Styrene-butadiene-styrene(SBS)copolymers and crumb rubber(CR)have been widely used as the asphalt modifiers to improve the properties of asphalt.However,many issues emerged when the two modifiers were used alone.For instance,the cost of SBS modified asphalt is high and the storage stability of CR modified asphalt is poor.In this context,CR/SBS composite modification technology was developed.The use of CR/SBS composite modified asphalt can fully take the advantages of SBS copolymer and CR,which can not only solve the issues encountered in the application of CR modified asphalt and SBS modified asphalt,but also ensure the economic benefits of modified asphalt while obtaining the excellent properties.Although the CR/SBS composite modified asphalt has been applied in the road engineering,the existed researches mainly focus on the preparation process and the formula optimization of CR/SBS composite modified asphalt,as well as the performance evaluation of the resulting asphalt mixture.Consequently,the quality and performance control of CR/SBS composite modified asphalt is still empirical.Moreover,the occurrence of pavement diseases is closely related to the rheological behavior of asphalt binder.Generally,the excellent rheological properties of asphalt binder help to delay the occurrence of pavement diseases.Therefore,an in-depth research on the rheological characteristic of CR/SBS composite modified asphalt is of great significance for the prevention and alleviation of the pavement diseases.In view of this,the rheological method is used to investigate the properties of conventional wet and Terminal Blend(TB)CR/SBS composite modified asphalts in this thesis,which provides guidance for the production and application of CR/SBS composite modified asphalt.The main research results of this thesis are as follows:The influences of CR particle size,SBS structure,CR content,and SBS content on the rheological properties and storage stability of conventional wet CR/SBS composite modified asphalt were investigated using CR with various particle sizes and SBS copolymers with various structures as modifiers.The results show that the CR with larger particle size benefits the anti-rutting and fatigue resistance,while the CR with smaller particle size benefits the low temperature anti-cracking and storage stability.The SBS copolymers with lower styrene content are beneficial to the rheological properties and are more stable during the storage process.Increasing the CR content can improve the rheological properties and storage stability.Increasing the SBS content can enhance the rheological properties,and there is the optimum SBS content to achieve the best storage stability.The differences in the rheological parameters among the base asphalt and different modified asphalts are compared,revealing the synergistic modification effect of CR and SBS copolymers and giving a quantitative description of the mutual substitution of these two modifiers.The thin film oven test and pressurized aging vessel test were used to simulate the aging of asphalt during the construction and the service life.The rheological and morphological characterizations were performed on the neat asphalt as well as modified asphalt before and after aging.The rheological index for evaluating the anti-aging properties of composite modified asphalt was proposed,revealing the influences of CR and SBS contents on the antiaging properties.The results show that the influence of thermal oxidative aging on the rheological properties varies with asphalt binders,and the long-term aging has a greater effect on rheological properties of all binders.The evaluation index of anti-aging property was defined by the rheological parameters,and was used to compare the anti-aging properties of the neat and modified asphalts.It can be found that polymers cannot improve the resistance of asphalt to the short-term aging,while CR can improve its resistance to long-term aging.The sequence of anti-aging properties of modified asphalts is: CR modified asphalt > CR/SBS composite modified asphalt > SBS modified asphalt.The short-term aging promotes the dispersion of SBS copolymers.The long-term aging causes the degradation of SBS copolymer and CR,thus destroying the cross-linked structure of the polymers,and reducing the particle size of the rubbers in the asphalt.An increased CR content can improve the anti-aging properties of the composite modified asphalt,while an increased SBS content impairs its anti-aging properties.Based on the rheological tests and fluorescence microscopic observation,the degradation process of CR and the properties of TB CR/SBS composite modified asphalt were studied.The results show that the CR powders undergo three stages during the degradation process,including the swelling and partial degradation,rapid degradation,and completion of the degradation.A kinetic model is proposed to quantitatively describe the degradation process of CR in the asphalt.TB CR/SBS composite modified asphalts show the much better conventional and rheological properties than base asphalt,and have good storage stability.Although increasing SBS content can improve the properties of TB composite modified asphalt,the effect of CR on the properties of composite modified asphalt is always greater than that of SBS copolymer.The results of fluorescence microscopic observation reveal the dispersion characteristics of rubbers and SBS copolymers,explaining the reasons for the changes in the workability,storage stability,and rheological properties from a microscopic point of view.Moreover,the asphalt composition also affects the degradation of CR and the properties of TB composite modified asphalt.Low asphaltenes and high saturates contents benefit the degradation of CR and storage stability,while high asphaltenes and aromatic contents benefit the conventional indicators and rheological properties.