Study On Detoxification Of Coal Tar Pitch And The Road Performance Of Coal-Petroleum Based Blended Asphalt

Coal tar pitch is the residue of coal tar distillation extraction fraction,once widely used in road building,construction and other fields,and has the advantages of good adhesion,anti-aging,corrosion resistance,etc.when used as road building materials.However,with the in-depth understanding of carcinogens such as polycyclic aromatic hydrocarbons in coal tar pitch and the requirements of environmental protection,the application of coal tar pitch has been strictly limited,except for a few for the manufacture of carbon black,electrode materials,most as waste disposal.Some studies have shown that the blending of coal tar pitch with petroleum asphalt can prepare a comprehensive performance than a single asphalt mixture,but there is a lack of systematic research on the road performance of blended asphalt.Therefore,it is very important to find an effective method to remove carcinogenic PAHs from coal tar pitch and to systematically study the road performance of coal-petroleum based blended asphalt.In this paper,the research of single detoxification and compound detoxification technology was carried out based on the method of chemical modification,and the best detoxification technology scheme for coal tar pitch was established.On this basis,the rheological properties of coal-petroleum-based blended asphalt under different aging conditions were investigated using a dynamic shear rheometer,and their fatigue properties were analyzed in combination with viscoelastic continuum damage theory.The main conclusions obtained are as follows:(1)The changes of representative carcinogen benzo[a]pyrene(Ba P)in coal tar pitch before and after modification were analyzed using UV-Vis spectrophotometer.The results showed that all the selected modifiers could effectively reduce the Ba P content,and the detoxification effect was from high to low: polyurethane monomer >trioxymethylene > polyethylene glycol > divinyl benzene > epoxy resin,in which 10%polyurethane monomer catalyzed by p-toluenesulfonic acid reacted with coal tar pitch at 150℃ for 1.5h at 300r/min,which could reduce Ba P by 78.33%.Ba P content was reduced from 2.88% to 0.62% of the original coal tar pitch.Trioxymethylene was also able to achieve a Ba P reduction rate of 74.56% under its optimal reaction conditions.(2)Through the seven-factor three-level orthogonal experiment design,the Ba P reduction rate in coal tar pitch was analyzed by polar difference analysis,and it was found that the most significant reaction conditions affecting the test results were the experiment temperature.The optimal ratio and reaction conditions of the compound modifier are: 6% polyurethane monomer + 10% trioxymethylene + 8% polyethylene glycol,reaction temperature of 150 ℃,reaction time of 1.5h,stirring speed of100r/min,catalyst of 5% p-toluenesulfonic acid,and the Ba P reduction rate reached82.16% under this condition.(3)The technical properties of coal-petroleum based blended asphalt was evaluated using the penetration performance system and SHRP system.The penetration system showed that coal tar pitch can significantly improve the asphalt consistency and resistance to shear damage,but adversely affects the low temperature performance and temperature sensitivity of asphalt.SHRP system results showed that coal tar pitch can improve the asphalt high-temperature performance and elastic response ratio,the improvement rate gradually decreased with the increase of coal tar pitch admixture,when the coal tar pitch admixture of 20% or 30% can improve a high-temperature grade.(4)The viscoelastic properties and fatigue resistance of coal-petroleum based blended asphalt under three conditions of unaged,RTFOT and RTFOT-UV aged were systematically investigated by dynamic shear rheometer.The results showed that coal tar pitch will significantly improve the high temperature deformation resistance and fatigue resistance of asphalt;In terms of fatigue resistance,30% coal tar pitch dosing is recommended for thick layer asphalt pavement,and 20% dosing is recommended for thin layer asphalt pavement;RTFOT has a significant effect on the performance of asphalt,the addition of coal tar pitch will reduce the asphalt’s resistance to UV aging.