Study On The High Temperature Performance Of Composite Modified Hard Asphalt Mixes

In order to improve the high temperature stability performance of special heavy-duty roads in hot summer areas of China,it is necessary to consider the high temperature climate,traffic load and pavement materials,etc.It is difficult for a single modified asphalt mixture to meet the requirements of asphalt pavements in extreme high temperature and heavy-duty areas in terms of performance,so it is necessary to improve the high temperature rutting resistance of asphalt pavements by means of composite modification.This paper uses SBS modified asphalt as the base asphalt,and selects the commonly used medium surface AC-20 asphalt mixture as the research object,the high modulus agent(HMA),lake asphalt(TLA)and rock asphalt(BRA)are modified with SBS modified asphalt,to prepare three kinds of composite modified hard asphalt and mixture,to study its high temperature performance,for the composite The high temperature performance of the modified hard asphalt mixes was studied to provide a basis for the largescale application of the modified hard asphalt mixes in the hot summer areas of China.Firstly,the reasonable dosage range of the three modifiers and the preparation process of the three composite modified hard bitumen were clarified,and the penetration,softening point,ductility and Brinell rotational viscosity of different composite modified hard bitumen were investigated.The results show that compared with TLA or BRA,HMA has the greatest effect on the high temperature performance of SBS modified asphalt,no matter which modifier is added,it will cause a certain degree of damage to the low temperature performance of SBS modified bitumen and the addition of HMA has a greater effect on the low temperature performance of asphalt,and the three asphalt modifiers have a great effect on the 135℃ and 175℃ Brinell viscosity of SBS modified asphalt.Secondly,frequency scan tests and multi-stress repetitive creep recovery tests were used to evaluate the effects of modifier dosing,test temperature and load level on the viscoelastic properties and high temperature performance of the composite modified hard asphalt.The results show that the optimum dose of HMA,TLA and BRA modifiers is 20%,25% and 8%respectively.Compared with SBS,TLA+SBS and BRA+SBS asphalts,HMA+SBS asphalt has lower temperature sensitivity,smaller phase angle and excellent elastic properties.HMA+SBS asphalt has a greater improved rutting factor than TLA+SBS asphalt and is more resistant to extreme high temperatures.HMA+SBS asphalt is more resistant to repeated load deformation at high stress levels,while asphalt blended with TLA or BRA has better elastic recovery properties.Once again,the water stability,high temperature and low temperature performance of different composite modified hard asphalt mixes were investigated by using water immersion Marshall tests,freeze-thaw splitting tests,60℃ and 70℃ rutting tests and low temperature semi-circular bending tests.The results show that the water stability and high temperature performance of different composite modified hard asphalt mixes are significantly improved compared to SBS modified asphalt mixes,with HMA+SBS asphalt mixes performing best in terms of high temperature performance and water stability.Finally,the dynamic modulus test and the dynamic creep test were used to study the dynamic mechanical properties of different composite modified hard asphalt mixes under high temperature conditions and to evaluate the viscoelastic properties and high temperature creep properties of different composite modified hard asphalt mixes.The results show that the dynamic modulus of the three composite modified hard asphalt mixes is excellent at different test temperatures,and the HMA+SBS asphalt mixes still have high dynamic modulus under high temperature conditions,and the addition of HMA modifier has the greatest enhancement effect on the elastic properties of the mixes,while the addition of TLA is slightly better than BRA.The HMA+SBS asphalt mix has the highest rheological counts under repeated high temperature and heavy loads,and shows optimum high temperature stability against extreme external conditions.