The Experiment Research On Load Shear Performance Of Asphalt Overlay On Old Concrete Pavement

How to control the initiation and development of the reflective cracking in Asphalt Concrete Overlay (ACO) is a great challenging in the Road Engineering. At the present, the asphalt concrete overlay has researched many years, but the progress is slow. It still have no well-known rational method of design now, and there is a lot effectiveness of asphalt concrete overlay structure had been satisfied, the research of our country is still in an early stage of exploring and experimental trial. If the Old Portland Cement Concrete Pavement (OPCCP) exist obvious relative displacement, the bilateral shearing effect of traffic load is the prime reason for the appearance of the reflective cracking. So, it is necessary to simulate the effect of shear load in the laboratory.The paper uses SST( Superpave shear test)which was developed by the Introduction of Stratagem Highway Researching Plan in America(SHRP).According to the RSCH research on 5 kinds of bituminous mixtures,it demonstrated that the RSCH can comparatively well evaluate the influence of graduation,asphalt binder and shear stress on mixture's shear performance. The analysis on the test suggests that the index related to RSCH test can reflect the patterns of the share deformability in vertical direction of asphalt mixture in the beginning and stability process of the RSCH very well. Furthermore, the paper putting forwards using logarithm theory(The fitting equation is:γ=A Ln(N)+B) to fitting the shear stain and the times of repeated shear of asphalt mixture. In the early stages of the repeated shear test,the shear strain increased dramatically. When the test is in a stable stage, the growth rate of shear strain is slow. This stage can use a line to fit the actual situation (The fitting equation isγ= k N+ b)."k"is the slope of the line. Smaller the"k", indicates lower sensitivity of the load on shear strain."b"is the intercept of the line. Bigger the"b", indicates the asphalt mixture has a greater need for entering shear stability phase, and it has stronger shear deformation of the adaptive capacity.Through the full-scale test, GSOG-20 and AC-20 asphalt material were laid on the Old Portland Cement Concrete Pavement. According to the test, we can compare the two material and structure's capacity on preventing the reflective cracking in asphalt cement overlay. What's more, we can get the relation of the deflection difference and the times of the load on the pavement. According to fatigue damage double logarithmic equation, using shear strain based on the control of asphalt mixture fatigue performance standards axle load conversion formula, that the asphalt overlay seams with the deflection poor standard axle load changes in the number of the laws, through on a log-linear regression equation form of the experimental data obtained in various joints overlay deflection poor standard axle load with the cumulative number of changes of the index equation form.