Research On Modulus And Strength Features Of Asphalt Mixture Under Different Stress States

Strength and stiffness are important parameters of asphalt pavement structure design.The strength index can reflects the ability to resist the resistance of asphalt pavement structure.As a kind of stiffness index,the modulus can reflect the mechanical response level of asphalt pavement structure.Currently,the asphalt pavement structural parameters are obtained mostly by laboratory tests.However,the stress states of different test methods are different.Even if at the same stress level,the strength and modulus will be of great difference,which will lead to the randomness of the design parameters of the asphalt pavement structure.In order to overcome the arbitrariness of the parameter value,on the one hand,the test conditions for obtaining material parameters should be able to simulate the real stress state of pavement;on the other hand,it is necessary to study the difference and unity of strength and modulus under different stress states.Therefore,the strength and modulus of asphalt mixture under different stress states are tested in this paper.The formula for calculating the tensile and compression modulus of four point bending is deduced,which is based on the difference of tension and pressure.Based on Hooke law in two-dimensional stress state,the calculation formula of splitting tensile and compression modulus of resilience is deduced.And the two kinds of formulae have been applied to the calculation of dynamic and static modulus,which has important reference for analyzing the difference of tensile and compression modulus in different stress states.Based on the dynamic and static resilient modulus tests of different stress states under the stress control mode,the variation rules of static resilient modulus with loading rate and the variation of dynamic modulus with temperature and loading frequency are obtained.The results show that:among them,the uniaxial compression modulus>splitting modulus>direct tensile modulus>bending modulus;The difference and unity of the three compression modulus and tensile modulus are related to the loading rate.The three kinds of compressive modulus are close to each other when the loading speed is from 0.3MPa/s to 0.4MPa/s.When the loading frequency is high and the temperature is low relatively,the dynamic modulus of splitting is close to that of uniaxial compression.When the loading frequency is low and the temperature is high relatively,the dynamic modulus is close to that of the direct tensile dynamic modulus.Under the condition of low temperature and high frequency,the overall stiffness of asphalt mixture becomes larger,and the splitting specimen mainly shows its compressive deformation ability.On the contrary,the splitting specimen mainly shows its ability of tensile deformation.The experimental results show that the four intensities with the loading rate varies as power functions,and firstly the strength increases quickly with the loading rate,then gradually tends to be gentle.With the loading increasing,the direct tensile strength and the indirect tensile strength are close to each other by the study on strength test and failure deformation under different stress states and different loading velocity.It is found that the nature of uniaxial compression test is tensile failure,and the strength under different stress states is unified based on the tensile strain at the time of initial cracking by study on the failure characteristics of strength test under different stress states.