Master Curves for Stiffness Asphalt Concrete

Abstract

The present paper discusses a methodology and tries to construct the stiffness master curves for asphalt mixture. In asphalt pavements the stiffness modulus of asphalt concrete increases with decreasing temperature and increasing loading frequency. By shifting such stiffness modulus versus loading time relationship for various temperatures horizontally with respect to the curve chosen as reference, a complete modulus time behavior curve is chosen and consequently reference temperature can be assembled. The proposed model is based on physical observations. It is believed to give reasonable estimates for the mix stiffness at any arbitrary loading frequency. The technique to determine of the master curve is based on the principle of time temperature correspondence or thermo rheological simplicity. The experimental data are plotted against the log frequency or log loading timing and therefore, by choosing a reference temperature, the data of the other temperatures are shifted horizontally until they fit the curve for the reference temperature. Then the data acquired from other temperatures are shifted until they fix the extended reference curve. Master curve can be constructed by fitting a sigmoid function using non linear least square regression techniques. The shifting is done using an experimental approach by solving shift factors simultaneously with the parameters of the model. This is completed without the need to assume any functional form for the shift factor equation. Based on the material, the paper tries to show that a sigmoid model can be best described as the master curve of mix stiffness of asphalt concrete. This model can also explain the physical behavior of asphalt concrete.