Study On The Fatigue Test Of The Asphalt Mixtures Based On The Combined Beam With Large Size

In 2016,the Ministry of Transport issued the " 13th Five-Year Highway Maintenance and Management Development Program" to clarify the green,low-carbon,recycled highway development prospects,and long-term performance of the highway has a close relationship with the design of the pavement structure along with the asphalt pavement fatigue which is always one of the research priorities of pavement structure design.In order to provide a test method to study the influence factors of fatigue behavior of asphalt pavement structure,the relationship between the fatigue performance of asphalt mixture and asphalt pavement structure is studied.The fatigue tests of asphalt mixture beam specimen were compared.Based on the concept of considerable cross section of composite beam of elastic theory,the bending test of large-size composite beams was developed considering the existing four-point bending fatigue test method.On this basis,the experimental indexes of the bending fatigue test were studied and the fatigue life prediction of asphalt mixture with large-size composite beams.The test method can characterize the surface layer structure of asphalt pavement,and provide a new way to study the influence of pavement structure on highway surface fatigue performance,so as to provide references for asphalt pavement structure design and material design.First,the comparison of the fatigue tests of the asphalt mixture beam specimen was carried out.The difference and connection of the three kinds of asphalt mixture beam test were analyzed from the experimental principle,the test specimen making and the fatigue test variable.Secondly,based on the concept of relative cross section of material mechanics elasticity theory,the bending stress model of single and large material beams under the bending test is established.Considering the material weight and temperature,the influence of material modulus,layer thickness and beam height on the bending stress were analysed;then the bending test method of the large-size composite beam of asphalt mixture was studied,and the basic requirements of the test were studied,and the large-size beam forming method was established as well as the fatigue test of the large-size composite beams of the asphalt mixture.Finally,the variability analysis and fatigue life prediction of the asphalt mixture were completed.The statistical analysis of the test data and the verification of the mechanical response model were carried out,and the estimation equation of bending fatigue life of the asphalt mixture were established..The main conclusions of this paper are as follows:(1)The fatigue test principles of asphalt mixture beam test are different,and four-point bending fatigue test has obvious advantages;beam specimen laboratory and field production have their own characteristics,and on-site production has stronger presentation of the actual highway surface performance,which is suitable for Large-size composite beam production;according to different sources,fatigue test variables can be divided into test variables,test machine load variables and variables of test specimen of fatigue process,and the relationship between variables is clear.(2)Using the concept of reference modulus,the mechanical response model of composite beam is suitable for the mechanical calculation of single and multiple materials asphalt mixture beam in pure bending.The large-size composite beam bending test can consider the effect of the material temperature without weight The maximum bending stress decreases with the increase of the modulus ratio of the upper and lower layers(0.6?1.6),and the logarithm of the two kinds of asphalt mixture composite beams is reduced after the beam size and loading method are determined.The maximum bending stress decreases with the increase of the thickness ratio between the upper and lower materials(the ratio of 1.0 to 1.6 in the modulus ratio).With the length and width of the beam fixed as well as the ratio of height and modulus,and the maximum bending stress of the two kinds of composite beams is the maximum bending stress,which is nonlinearly reduced with the increase of beam height.It is suggested to use the load control mode to carry out the bending test of large-size composite beams.(3)In order to verify and improve the bending mechanics response model of large-size composite beam of asphalt mixture based on elastic mechanics,the selection of test pavement structure,site preparation,site construction parameter determination and large-size composite beam are completed to obtain 22 beams The results show that the basic fatigue load(16.0?,8.344KN)of the composite beam,the compressive modulus of the upper and lower layers and the fatigue life under the different load ratio(0.15/0.2/0.5)of the composite beams are determined by the four-point bending test of the composite beam,the uniaxial compression test of the core and the four-point bending fatigue test of the composite beam.(4)The bending response model of large size composite beams of asphalt mixture based on elastic mechanics was validated and perfected.The length and width cutting ability of the composite beam are different,and the size of the composite beam has different distribution rules,which show that the length distribution is more uniform,the thickness is concentrated,and the layer thickness ratio has the normal distribution characteristic;The relationship between the test load and the analytical load of the bending test is built with the deflection of the third-point of 2.5mm and 1.5mm.It is proved that the analytical strain of the bending mechanics response model is significantly correlated with the experimental strain linearity,the correlation coefficient is 0.9484;the fatigue whole life prediction of the asphalt mixture is Nf1=0.0082(?1')-1.991,whose the correlation coefficient is 0.785,and the fatigue half life prediction of the asphalt mixture is Nf2=1×10-6(?2')-2.928,whose the correlation coefficient is 0.911,and the fatigue life error of the control group is within 76%.Compared with the four-point bending fatigue test of the beam,this test can reduce the error of the fatigue life test with the same batch,the prediction accuracy of the whole life prediction of lare-size beam mixture and small-size beam mixute are similar.