Variations in Measured Resilient Modulus of Asphalt Mixes

The resilient modulus is used as a fundamental input parameter in the application of layer theory in flexible‐pavements design. The test for determining the resilient modulus is a repeated‐load indirect tension test in which specimens are loaded then unloaded diametrally and the recoverable strain is measured. The test procedure is standardized and documented by the American Society for Testing and Materials (ASTM) in ASTM D4123. The statistical variability in the test for determining the resilient modulus is important for design purposes. There exist two sources of variability in the standard test procedure set by ASTM. The first source is observed where different specimens from the same mix have a different value of the modulus. The second source is due to the testing method where the cylinders are tested diametrally, and the random choice of axis can be another source of variability within the same specimen. Also, since ASTM D4123‐90 recommends an acceptable range for the load amplitude, the choice of the load amplitude may introduce some variability. In this paper, several specimens of asphaltic concrete were cast from the same mix. Each specimen was tested on three different axes, under four different loads, and the resilient modulus was measured, thus reflecting both the specimen‐to‐specimen and the axis variability. The two sources of variability were combined statistically to obtain an estivate of the coefficient of variation (COV) in measuring the resilient modulus. The resulting estimate of the variability can be combined with other variabilities that arise in practice, to obtain an estimate of the total variability that should be considered in designs based on the measured resilient modulus.