Study On Modulus Of Asphalt Pavement Structure

The current design methods for asphalt pavement structure，stiffness modulus whichrepresented by static creep modulus or dynamic modulus is one of the importantparameters of asphalt pavement structure in the process of analysis. However, static creepmodulus or dynamic modulus cannot thoroughly describe the stiffness modulus of asphaltlayer which under the movement of vehicles. Literature review shows that dynamicresilient modulus could represent the stiffness modulus of asphalt pavement structure morereasonably. Both dynamic modulus and dynamic resilient modulus could be obtained bylaboratory tests. For these tests, it is important to applied the accurate waveform on the testspecimen.The main difference between dynamic modulus and dynamic resilient modulus is theresting time between loading cycles is needed for the dynamic resilient modulus tests,while it is not expected for the former one. Whether dynamic or dynamic resilient modulus,The loading waveforms are simulations of vertical compressive stress-pulse in asphaltlayer of pavement structure. In the current method of AASHTO test, the haversine loadingwaveform is input to get the dynamic modulus, which is practically inaccurate. The verticalcompressive stresses are varied along the depth so that the wave-form and wavelength ofvertical compressive stress-pulse are different at different depth in asphalt pavement.Therefore, sinusoidal (haversine) loading wave form is not well enough to represent thevertical compressive stress-pulse. Vertical compressive stress-pulse relies on reasonablevertical tire-pavement contact pressure (TPCP) and calculation model.This paper firstly utilized ANSYS and BISAR establish calculation model,respectively, make comparison of the vertical compressive stress between the results byANSYS and BISAR that assure the three dimensional finite element program is reliable;Secondly, a three dimensional finite element program incorporating measured verticalTPCP as well as the horizontal force was utilized for calculating the vertical compressivestress-pulse of different depths in asphalt concrete (AC) layers with the different combinations of layer thickness and modulus of AC by the proposed finite element model.The stress-pulse waveforms at different positions are obtained, which is followed by theformulas derivation of its wave-length and loading time. The stress-pulse waveforms atdifferent positions are obtained, which is followed by the formulas derivation of itswave-length and loading time. On basis of these works, different functions are adopted tosimulate the stress-pulse waveforms. Finally, the differences between the dynamic modulusand dynamic resilient modulus are studied by laboratory tests with the resting time takeninto consideration.