Study on the aging properties of coal direct liquefaction asphalt-road modified asphalt

Coal direct liquefaction asphalt(DCLA)is a by-product of the coal direct liquefaction process,which is composed of about50%asphalt and 50%solid particles.The road modified asphalt(DCLA-modified asphalt)is prepared by adding DCLA as the basic modifier with SBS polymer.The asphalt composition has a direct influence on the properties of asphalt,which is reflected in the performance of modified asphalt pavement.Therefore,it is more important to study the aging performance of modified asphalt.In this paper,the aging test of DCLA modified asphalt was simulated by rotary film heating test(RTFOT)and the aging characteristics of DCLA-modified asphalt were studied to establish the relationship between its microscopic properties and macroscopic properties,which provided a theory for improving the life of DCLA-modified asphalt pavement and increasing the amount of DCLA in the modified asphalt.By analyzing the molecular weight,FTIR,oxygen content of modified asphalt before and after aging and DCLA-modified asphalt raw materials,it was found that the aging of DCLA modified asphalt was not a single reaction,but a comprehensive result of many reactions,such as oxidation of active sub-stances,volatilization of light components,aggregation of asphalt molecule and fracture of SBS molecule.The results indicate that the DCLA-modified asphalt average molecular weight decreases from 13 865 g/mol to 11 983 g/mol,the oxygen content increases from 0.9%to 1.3%,the SK90 average molecular weight increases from 1 906 g/mol to 2 068 g/mol,and the SBS average molecular weight decreases from 41 482 g/mol to 20 647 g/mol.The performance of aged DCLR-road modified asphalt is affected by the asphaltene and resin.Asphaltene can improve the aging resistance but reduce the ductility of modified asphalt.In order to meet the JTG F40—2017 I-D standard,that is,the 5℃ductility is not less than 20 cm,and the asphaltene content in the modified asphalt system can't exceed 12.9%,the residual penetration ratio is 72%.Resin can improve the low temperature ductility of modified asphalt,but resin is an unstable substance and is easily oxidized by air,which is reflected in the FTIR of carbonyl ■ and sulfoxide ■.When the resin in the system is 28%,the aging ductility rate can be reduced by 70%.It is an effective way to improve the properties of aged modified asphalt by controlling the asphaltene content and reducing the resin reactivity in raw materials.