Practical procedure for developing dynamic modulus master curves for pavement structural design

A dynamic modulus master curve for asphalt concrete is a critical input for flexible pavement design in the mechanistic-empirical pavement design guide developed in NCHRP Project 1-37A. The recommended testing to develop the modulus master curve is presented in AASHTO Provisional Standard TP62-03, Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures. It includes testing at least two replicate specimens at five temperatures between 14 degrees F and 130 degrees F (-10 degrees C and 54.4 degrees C) and six loading rates between 0.1 and 25 Hz. The master curve and shift factors are then developed from this database of 60 measured moduli using numerical optimization. The testing requires substantial effort, and there is much overlap in the measured data, which is not needed when numerical methods are used to perform the time-temperature shifting for the master curve. This paper presents an alternative to the testing sequence specified in AASHTO TP62-03. It requires testing at only three temperatures between 40 degrees F and 115 degrees F (4.4 degrees C and 46.1 degrees C) and four rates of loading between 0.01 and 10 Hz. An analysis of data collected using the two approaches shows that comparable master curves are obtained. This alternative testing sequence can be used in conjunction with the simple performance test system developed in NCHRP Project 9-29 to develop master curves for structural design.