Mechanistic Asphalt Overlay Design Method for Heavy Duty Pavements
Last modified: 2017-02-28
The current Hungarian overlay design manual was developed in the 1990s and no major review has been conducted since then. Therefore the technological and material advances e.g. modified binders and mixes, high modulus mixes, use of reclaimed asphalt pavements, asphalt grids and nets, compromises with local resources, changes in traffic loading and volume, cannot be incorporated in the calculations and the design method is considered outdated in many ways. The current methodology enables two options for the asphalt overlay design, the deflection and the pavement condition criteria. There are cases when the overlay is necessary primarily due to the condition of the asphalt layer(s), and not due to the lack of structural capacity. In such cases, i.e. when a thick existing asphalt layer is to be strengthened – primarily at highways and heavily trafficked roads – the difference between the two methods may be considerable, implying there is an error in either method, or the special circumstances require special considerations. In this paper a researcher group at the Budapest University of Technology and Economics presents a new, mechanistic approach for overlay design. The proposed method is based on statistical analysis of Falling Weight Deflectograph (FWD) measurements, followed by the determination of the analytical input parameters either by laboratory tests or back-calculation of FWD data. Then the strains at the bottom of the asphalt layers are calculated using Odemark’s transformation and the method of equivalent thicknesses. The required asphalt overlay thickness is calculated based on the allowable strains and the strains calculated for varying thicknesses. The proposed method is presented using FWD measurements, core test results and traffic loads of a motorway in service. The method, followed by field calibration, may be an answer to the problems presented, as analytically incorporating the parameters of each material, and taking into account the remaining life of the existing pavement.
deflections; strains; overlay; method of equivalent thicknesses