Study On Modification Mechanism And Road Performance Of Polyphosphate And Polyurethane Composite Modified Asphalt

The frequent occurrence of rutting,cracking,and other diseases on asphalt pavements poses a significant challenge to their road performance and subsequent maintenance.Researchers often modify asphalt to improve the disease resistance of asphalt pavements.Previous studies have shown that a new high-performance modifier,polyurethane,can significantly improve the low-temperature cracking resistance of asphalt,while polyphosphoric acid(PPA),as an important modifier in the research of acid modified asphalt,can not only significantly improve the high-temperature performance of asphalt,but also cooperate with polymer modifiers to improve the comprehensive performance of composite modified asphalt.Therefore,this article attempts to use PPA and thermoplastic polyurethane elastomer(TPU)to composite modify asphalt.The preparation scheme of the composite modified asphalt is determined through orthogonal experiments and gray correlation theory.Based on Jamming theory,the modification mechanism and performance changes are analyzed.Finally,the asphalt mixture is tested to explore the improvement of disease resistance,and the following conclusions are obtained:(1)Through three index tests of asphalt,the content range of modifier PPA and TPU in base asphalt was studied,and the conclusion was reached that the content of PPA should not exceed 0.8% and the content of TPU should not exceed 3%.(2)The range and variance analysis of orthogonal tests determined that the preparation scheme of PPA/TPU composite modified asphalt was 0.6% PPA+3% TPU,and the TPU content as a significant influencing factor reduced the degree of improvement of the softening point of the composite modified asphalt by PPA.(3)The result of grey correlation degree shows that the correlation between the content of PPA and the softening point is the highest,and the content of TPU is the most sensitive to the low-temperature performance and high-temperature storage stability.When optimizing the high-temperature performance of PPA/TPU composite modified asphalt,it was found that reducing the content of TPU is more effective in improving the high-temperature performance than increasing the content of PPA.Therefore,the optimized preparation scheme of composite modified asphalt is 0.6%PPA+2.5% TPU.(4)The infrared spectrum analysis shows that the modification mechanism of PPA/TPU composite modified asphalt is chemical modification.The dynamic shear rheological test shows that the rheological properties of the composite modified asphalt are significantly improved.The differential scanning calorimetry test shows that the glass transition temperature of the composite modified asphalt is reduced by85% compared to the base asphalt.The scanning electron microscope and thermogravimetric analysis indicate that the change in microstructure reduces the thermal stability.(5)The thermal movement of PPA can effectively increase the volume fraction of the system and promote the microphase separation of TPU to accelerate the Jamming transition of the composite modified asphalt.The overall distribution of the system is more uniform,regular,and orderly,enabling it to have better flow performance compared to the matrix asphalt in the Jammed state.(6)The optimal asphalt stone ratio of composite modified asphalt mixture in AC-13 gradation is 4.5%.The rutting,trabecular,and Marshall tests indicate that the interaction of PPA and TPU improves the high-temperature rutting resistance and low-temperature cracking resistance of composite modified asphalt mixture,but the improvement effect on water stability performance is not satisfactory.