Tensile versus compressive moduli of asphalt concrete

A laboratory investigation was performed to evaluate the modulus of asphalt concrete in compression and tension. Five modes of loading, namely, quasi-static compressive, quasi-static tensile, harmonic compressive, harmonic tensile, and alternate compressive tensile loads, were used at three temperatures of 5 °C, 25 °C, and 40 °C (41 °F, 77 °F, and 104 °F). At 5 °C, the tensile and compressive moduli were very close but at higher temperatures, the compressive modulus was always higher. These results were used in the multilayer elastic program ELSYM5 to study the effect on the stress and strain distributions of varying the modulus of asphalt concrete. A simple bimodular analysis was used in which the compressive modulus was used for the top half of the asphalt layer and the tensile modulus for the bottom half of the layer. The multilayer analysis indicates that the incorporation of the tensile modulus in the analysis gives results different from those obtained using a single compressive modulus, resulting usually in the increased predicted fatigue and rutting lives. This suggests that the use of a bimodular method of analysis that can distinguish between compressive and tensile stresses and use the appropriate modulus accordingly is more rational and provides more realistic predictions of flexible pavement responses than single-modular methods.