Predictive formulas of complex modulus for high air void content mixes

Over the last 10 years, there has been a number of trials and developments of the porous asphalt (according to definition of European standard EN 13108-7) or open-graded friction course (according to definition used in USA), which has led to the use of high air void content mixes with better acoustic performances. Mixes with air void content greater than 20% are used at present in Europe and their use is spreading in other countries (e.g. USA, New Zeeland, etc.). The dynamic modulus (|E*|) is one of the most important performance parameters for characterizing bituminous mixes, and it is used as input in the mechanistic and mechanisticempirical design methods (MEPDG). Since the measurement of stiffness in the laboratory is not straightforward, a commonly used approach is to estimate dynamic modulus by using predictive models. Several models are available in the literature for estimating |E*|, but they were developed and calibrated on hot mixes with air void content less than 15%. This paper describes a research carried out to evaluate if some predictive dynamic modulus equations work well for porous asphalt with high air void contents. Two predictive models were analyzed: the Witczak-Andrei model, and the Witczak-Bari model. The experimental values of |E*| on some high air void content mixes are compared with values obtained by previously mentioned predictive formulas. The results showed that proposed formulas “under predict” (Witczak-Andrei) or over predict (Witczak-Bari) the |E*|, but they should work well if they are recalibrated. Basing on experimental results, methodology of calibration of the predictive models was proposed in order to be used for high air void content mixes.