Air void models for the dynamic modulus, fatigue cracking, and rutting of asphalt concrete

A laboratory study has been carried out to develop mechanical models for the dynamic modulus, fatigue life, and rutting performance of asphalt concrete as a function of air void content. The experimental program includes an axial compression complex modulus test, indirect tensile (IDT) fatigue test, and triaxial repeated load permanent deformation (TRLPD) test on the two most commonly used asphalt-aggregate mixtures in North Carolina. The dynamic moduli are determined using axial compression tests with and without confining pressure, and the results are compared to evaluate the effect of confining pressure on the dynamic modulus. The relationship between the dynamic moduli that are determined from the uniaxial compression test and the air void content is developed. The growth of the tensile strain and axial permanent strain is measured from the IDT fatigue test and TRLPD test, respectively, and is used to determine the fatigue life and rutting behavior of the mixtures. The fatigue and rutting models adopted in the new NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide have been refined to represent the IDT and TRLPD test results more accurately and to incorporate the air void content as an input parameter.