Study On Road Performance Of The Silica Fume/SBS Composite Modified Asphalt Mixture

Silica fume is widely used in construction,chemical industry,rnetallurgy and other areas because of its abundant reserves,low cost,large specitic surface area,small thermal conductivity,thermal stability and strong adsorption capacity.This paper relies on the Science and Technology Project of Heilongjiang Provincial Transportation Department" Research on the application technology of silica fume/SBS composite modified asphalt mixture".In this paper,silica fume and SBS are used as modifiers to modify asphalt.Through indoor tests,the performance of silica fume/SBS composite modified asphalt mortar is analyzed,the mechanism of composite modified asphalt is explored,and the pavement performance of silica fume/SBS composite modified asphalt mixture is evaluated.The main contents and conclusions of this paper are as follows:(1)In this paper,the effects of SBS content,silica fume content,ratio of filler asphalt and kind of filler on the properties of composite modified asphalt mortar are analyzed through cone penetration test,softening point test,Brookfield viscosity test,dynamic shear rheometer test and bending beam rheometer test.The anti-aging property of composite modified asphalt is studied by rolling thin film oven test.The results show that:The cone penetration of the composite modified asphalt mortar decreases with the addition of SBS,while the softening point,viscosity and elastic recovery performance are improved significantly.With the addition of silica fume,the high temperature performance of the composite modified asphalt mortar is improved obviously,the low-temperature performance is enhanced initially and then weakened,and the tempurature sensitivity is reduced.The optimum content of SBS is 4%,and the optimum content of silica fume is 7%.Increasing the ratio of filler asphalt promotes the high-temperature performance of the asphalt mortar.However,it will damage the low temperature cracking resistance of asphalt mortar;using cement and lime instead of mineral powder can improve the viscosity and high temperature performance of asphalt mortar,and lime is better;Adding silica fume can improve the anti-aging performance of SBS modified asphalt.(2)The modification mechanism of composite modified asphalt is analyzed by scanning electron microscopy test and infrared spectroscopy test.The thermal stability of composite modified asphalt is investigated by thermogravimetric test and differential scanning calorimetry test.The results show that:The micromorphology of silica fume is an amorphous sphere.It has the characteristics of small particle size,large specific surface area and strong adsorbability.Its unique micro-voids can absorb some light components in asphalt and establish a new colloidal equilibrium system,which further enhances the combining ability between SBS particles and matrix asphalt.Thus the physical and mechanical properties are changed.During the process of composite modification,there is only physical miscibility between SBS,silica powder and asphalt,and no chemical reaction is carried out Silica fume particles,SBS particles and matrix asphalt are well blended into a uniform and stable system after composite modification and the thermal stability of modified asphalt is farther improved.(3)The mix design of silica fume/SBS composite modified asphalt mixture is carried out.The effects of aging,temperature and water on the high temperature performance of silica fume/SBS composite modified asphalt mixture with different gradations are studied by conventional rutting test and immersion rutting test.At the same time,trabecular bending test,immersion Marshall test and freeze-thaw splitting test are carried out to evaluate the low temperature cracking resistance and water stability of the composite modified asphalt mixture.The results show that:The addition of silica fume improves the high temperature performance of composite modified asphalt mixture obviously.The optimum asphalt-stone ratio determined by Marshall test is about 0.3%larger than the corresponding asphalt-stone ratio when the dynamic stability of rutting test is maximum.The dynamic stability of silica fume/SBS modified asphalt mixture increases after aging.With the increase of rolling times of specimen,the dynamic stability increases initially and then decreases.The existence of water will will greatly reduce the dynamic stability of ratting specimens.The dynamic stability of mixture decreases with the increase of temperature.Silica fume has little effect on the low temperature performance of composite modified asphalt mixture.The addition of silica fume enhances the water stability of mixture.