Measurement Of HMA Displacement Field And Analysis On Flow Rutting

In recent years, the early rutting of asphalt pavement has been worsen by the combined effects of continus high temperature in summer, heavy loads and canalized traffic. Recent survey indicated that the most prevailing type of rutting in freeways of our country was plastic shear flow rutting. This type of rutting is characterized by concave-down displacement under wheel and ridge deformation at both sides of track. There is an increasing trend of such kinds of rutting. Strategies was undertaken to lessen rutting in the middle and underside layers of pavement by strengthen the middle layer material. It resulted in the new arising problems of swelling of the pavement surface.The characters of permanent deformation for HMA indoor evaluating experiment approach and the present literatures on prediction of rutting are specified in this study. The limitations of present measurement approach for HMA indoor evaluating are indicated. The inadaptation of the theory method which largely focus on the vertical deformation are outlined in HMA shear flow deformation evaluation.Based on the measurement of HMA sample deformation field under varied mechanical status and analysis of plastic flow rutting, major conclusions of this research are summarized as follows.(1) The system composing, software and hardware and measurement precision and error of the digital imaging processing measurement system are introduced in this paper. The method to reduce the errors is also formulated. As a result, the demand precision acquired by theory could be met under normal measurement conditions.(2) A set of experiments of indirect tensile test, Marshall test and uniaxial compression test are attempted to determine sample displacement field. In the studies the lateral deformations show more sensitivity and capability to reflect the initialization and proceeding of partial deformation. The different mechanical status from compression, elastic deformation to plastic flow stages are reflected in the procedure of destroy under varied loads of HMA samples. The lateral deformation is advanced as the evaluating criteria for HMA.(3)The most important parameter reflecting the lateral deformation is Poisson's ratio. From IDT, the Poisson's ratios of HMA at different temperatures are measured and investigated The regular of variety for Poisson's ratio is determined as followed: Poisson's ratio is stable and could be a constant at low temperature and small load. It becomes the function of temperature and stress at high temperature or large load. The Poisson's ratios of HMA even exceed 0.5 under some loading conditions.(4)Based on the experiment and theory analysis for HMA Displacement field, the 3-D pavement structure is built to simulation rutting by Finite-Element-Method (FEM) to reason the formation of plastic flow rutting. The range of Poisson's ratio is enlarged in this analysis of HMA. The developing tendency of the horizontal deformation of the upper, middle and sub layer of asphalt pavement are described with lateral deformation as the evaluating criteria. Factors which are impacted on the developing tendency of the deformation of the upper, middle and sub layer of asphalt pavement are considered: the structural formation and the different layers composition of pavement. The tendency of lateral (horizontal) displacement in AC pavement also reflects the condition and limits of the different material of varied structural composition in resistance for the lateral rutting causing by insufficient stability. The lateral displacement method and the shear theory method are contrast and validated by both theory and experiment. The two methods are corresponding in reflection the shear deformation in asphalt pavement.(5)The pavement mechanical analysis by shear theory and the lateral displacement tendency by lateral displacement method show the following facts: the structural composition significantly impacts on distribution of the lateral displacement, structural shear stress and strain in pavement. The behavior of accentuating only on middle layer while ignoring the coordination of the composition of the pavement structure may induce the stress centralizing on surface layer of pavement. The optimum range of the structural module composition for surface and middle layers is present to prevent tendency of insufficient stability in lateral and minish the shear stress of asphalt pavement. The concept of cooperation composition in design is advanced.(6) By applicant of the digital imaging measurement system, the usage of IDT becomes more widely than with the traditional method. The deformation measurement of the core sample is largely simplified by imaging measurement method. The accuracy and effect of Marshall Test in evaluating high temperature stability are improved by the technique.