Back analysis of the multilayer cylindrical HMA samples – height reduction method

Although the complex modulus is one of the most basic properties used in pavement analysis and design, its accurate measurement for existing pavement layers has always been a challenging task. When samples cut out from the pavement asphalt layers are used for the hot mix asphalt (HMA) complex modulus tests, they are performed separately for each layer. This paper describes an original method for determining the complex moduli of individual asphalt layers. The new idea is tested by applying uniaxial loading–unloading cycle tests to the HMA specimens combined of multiple layers. It was observed that changing the thickness ratios in samples' layers, allows obtaining the sets of load and displacement values (F, u), which effectively enlarge the database needed for the back analysis. For now, the conducted analysis presented in the paper focused on numerical modelling of HMA specimens. The simulated numerical testing conditions were based on viscoelastic parameters of asphalt concrete samples whose values were determined in real laboratory tests. In the case of noisy results of laboratory test simulations with a stochastic Gaussian process, by applying multiple cuts and changing sample's height, the determined values of stiffness moduli of the individual layers do not vary from the reference values by more than 10%.