Issues Affecting Measurement of the Complex Modulus of Asphalt Concrete

Abstract

This paper addresses issues of machine compliance and instrumentation that affect the measurement of asphalt concrete material properties in the laboratory. Accurate determination of fundamental material properties is becoming increasingly important as the asphalt industry moves toward more mechanistic design procedures. This issue is particularly timely for the simple performance test and American Association of State Highway and Transportation Officials 2002 design guide that require the measurement of dynamic modulus, phase angle, and creep. The primary objective of this paper is to increase the awareness of the possible existence of these issues in the laboratory and the importance of attending to them appropriately. Machine compliance was found to affect the strains actually occurring in the specimen under various loading conditions, resulting in differences of several magnitudes between dynamic modulus values measured by the actuator and by surface-mounted deformation transducers. Instrumentation issues resulted in errors greater than 10% in the measurement of dynamic modulus for the mixtures studied and caused irrational trends in phase angle values as a function of frequency. Creep compliance testing was also found to be affected by instrumentation issues.