Study On Dynamic Modulus Of Asphalt Mixture Under Complex Stress State

Since Specifications for design of highway Asphalt Pavement in 2017,the design parameters of asphalt pavement in China have gradually changed from static to dynamic,The code only recommends the dynamic modulus of asphalt mixture under uniaxial compression at 20℃ and 10HZ.The material is a temperature-sensitive and obviously stress-dependent composite material,so the dynamic modulus in the simple stress state,single temperature and load frequency is obviously inconsistent with the actual use state of the asphalt pavement.Therefore,in this paper,the compression and tensile dynamic modulus tests are systematically carried out for various mixtures of upper,middle and lower layers commonly used in engineering under complex stress conditions,and a dynamic modulus prediction model considering multiple test conditions and parameters is established within the allowable error range.The main research contents are as follows:(1)Three asphalt mixtures AC-13+SBS,AC-20+SBS,AC-25+70#were tested for dynamic modulus under plane isostatic/axial compression and plane isostatic/axial tension at different temperatures and frequencies.The Arrhenius equation was used to calculate and solve the displacement factors under different stress states,and a unified conversion model between time-temperature-stress states in tension and compression was established.(2)According to the dynamic modulus test results,the improved k-θ model,the improved Witzack-Uzan model and the improved AASHTO 2002 dynamic modulus prediction models are established.On the basis of comparing the accuracy and characteristics of each model,the improved AASHTO 2002 model with clear physical meaning,small error and easy to use is finally selected.Based on the relationship between the dynamic modulus of AC-13,AC-20 and AC-25 graded asphalt mixtures,and on the basis of the prediction model of the dynamic modulus of AC-13 asphalt mixture under triaxial tensile and compressive stress conditions,the dynamic modulus of AC-20 and AC-25 asphalt mixtures is fitted by multiple forms.A unified dynamic modulus prediction model for tensile and compressive modulus of AC asphalt mixture is proposed.(3)The static resilient modulus tests of the above three kinds of mixture were carried out under the condition of plane isobaric/axial compression and plane isobaric/axial tensile stress.The law of the static modulus decreasing with the increase of confining pressure was revealed and the prediction model of the static modulus changing with the confining pressure was established.The static modulus under different stress states is substituted into the corresponding dynamic modulus prediction model and the main curve model to solve the corresponding dynamic modulus load frequency and verify it.Finally,according to the experimental data of dynamic modulus,the improved AASHTO2002 dynamic modulus prediction model is verified to verify the scientificity and effectiveness of the model.