Effect Of Humidity On Viscoelasticity And Fatigue Cracking Performance Of Asphalt Mixtures

With the great development of road construction,the proportion of asphalt pavement is getting higher and higher.As a typical viscoelastic material,the basic properties of asphalt mixtures are affected by the service environment,not are the same,but are dynamic.Therefore,in the process of asphalt pavement design,we must face up to the factors that affect the basic performance of asphalt mixtures and clarify the rules of influence,so as to give guidance to the design of asphalt pavement.Existing research on the basic performance of asphalt mixtures focuses on factors such as temperature and liquid water environment,and often ignores the gaseous water（ie,humidity）factor.Gaseous water is the"culprit"that causes water damage to asphalt mixtures.Therefore,it is necessary to clarify the influence of humidity on the basic performance of asphalt mixtures,and to give suggestions for guiding the selection of materials and improving the basic properties of materials.Therefore,this paper takes humidity as the key factor for the research,and designs appropriate test methods to obtain the non-destructive viscoelastic properties and fatigue performance of asphalt mixtures under four humidity conditions,and analyzes the influence of humidity on the basic performance of asphalt mixtures.The main research results are as follows;（1）In terms of non-destructive viscoelastic properties,a master curve of viscoelastic parameters at a reference temperature of 20°C and a reference humidity of 0.35 g/m³ was constructed.Based on the time-temperature-humidity equivalent principle,the temperature and humidity were established in this paper.The relationship model of temperature and humidity（ΔT/ΔH=C₂/C₃）is related to the ratio of the main curve shift parameters C₂ and C₃,and the ratio has nothing to do with the selection of reference temperature and reference humidity.Provides a method of non-destructive viscoelastic properties.（2）Based on the constructed viscoelastic parameter master curve,this paper quantifies the effect of humidity on nondestructive viscoelastic characteristics.First of all,under the condition of constant frequency（f=10Hz）,the effect of temperature on the viscoelastic properties of asphalt mixture is greater than that of humidity,which shows that the modulus decreases more and the phase angle increases more.On the other hand,when the humidity is increased from 0.35g/m³ to 17.27g/m³ under high temperature（50°C）conditions,the decrease in modulus is significantly greater than under low temperature（5°C）conditions,indicating that higher temperatures will exacerbate humidity adverse effects.The degree of decrease in the modulus reflects the ability of the asphalt mixture to resist water damage.As a result,the water stability of the diabase SBS modified asphalt mixture is found to be worse than that of the limestone SBS modified asphalt mixture.Secondly,when the temperature is constant（T=20℃）,the viscoelastic properties of the asphalt mixture are also changed to different degrees by the influence of humidity and frequency.It was found that the viscoelastic properties of asphalt mixtures were less affected by frequency than humidity.In the range of13.04～26.08Hz（vehicle speed 60～120km/h）,using the viscoelastic characteristics under 2%relative humidity as the reference property,the humidity pair is quantified by dynamic modulus ratio,storage modulus ratio and loss modulus ratio.The degree of influence of viscoelastic properties of asphalt mixtures.Among them,the dynamic modulus decreases the most,and the strength decreases greatly,which is not conducive to the asphalt pavement’s resistance to deformation;the loss modulus decreases the second,the storage modulus decreases the least,the elastic properties are weakened,the viscosity properties are enhanced,and the asphalt mixture performance is more likely to transition to the damage stage.Then produce disease easily.（3）In the study of fatigue characteristics,the modified Paris formula is used as a model to evaluate the fatigue characteristics,and the parameters of the modified Parris formula model are determined by the fitting results of the dissipated virtual strain energy and the apparent stress amplitude.It is proposed to use lg A+n as the evaluation index,and lg A+n is proportional to the damage density increase after 600cycles of loading,which confirms the rationality of the evaluation index.Based on the research of nondestructive viscoelastic properties,this paper uses the theory of elastic layer system to analyze the degree of life reduction of asphalt mixture due to the decrease of modulus.It was found that the fatigue life was reduced by more than 55%～60%due to humidity.Therefore,a certain modulus safety factor should be introduced in the pavement structure design process to offset the adverse effects caused by humidity;research based on fatigue characteristics found that the evaluation index lg A+n generally increases with humidity,but the maximum increase occurs when the relative humidity increases from 2%to 50%;the increase in damage density also has an increasing trend,and the relative humidity increases from 2%to50%and from 80%The increase was greatest at 100%.Therefore,it is shown that the two processes of water vapor transition from gaseous water to liquid water under the condition of high humidity significantly affect the fatigue performance of asphalt mixture.