Modulus Testing in Indirect Tension Mode

ABSTRACT In 2004, a new European standard (NF EN 12697-26), the object of which is the measurement of stiffness modulus, appeared. It includes five annexes corresponding to five different testing methods, in particular modulus testing in indirect tension (IDT) mode. Given that a typical asphalt layer thickness is about a few centimeters and that coring is the most effective method for obtaining specimens from actual pavements, the IDT testing of cores is bound to become very practical for routine use. Notwithstanding this fact, IDT testing is still of little use in French public and private sector laboratories and, moreover, little information is available in the technical literature concerning the comparison between stiffness modulus data obtained in uniaxial direct tension or tension-compression and in biaxial indirect tension. This paper provides rational understanding, based on principles of linear viscoelasticity in particular, of the moduli commonly used for structural evaluation of asphalt mixtures: complex, secant and resilient moduli. The assumptions and limitations of these moduli are discussed. The pros and cons of the adopted testing and analysis methods are evaluated. A simple and direct relationship was found and exemplified between stiffness moduli obtained either in uniaxial direct tension/tension-compression mode or in biaxial indirect tension mode.