Evaluation of Testing Protocols for Dynamic Modulus of Hot-Mix Asphalt

Abstract

The dynamic modulus (| E*|) of hot-mix asphalt (HMA) is one of the fundamental inputs in the mechanistic–empirical (M-E) pavement design guide developed in NCHRP Project 1–37A. The M-E design guide provides three levels for | E*| input, which are related nominally to the reliability of pavement performance estimates generated by the guide. Level 1 | E*| inputs require laboratory-measured | E*|-values, and Level 2 and 3 | E*| inputs are estimated by using a predictive equation. To provide the laboratory-measured | E*| inputs for implementation of the M-E design guide, a comprehensive research effort was completed in Arkansas. The research included a study evaluating different | E*| testing protocols, derived by varying combinations of the number of test replicates and the number of measurement instruments affixed on each test specimen recommended in AASHTO TP 62-03. The testing protocols were evaluated in terms of the variability of the resulting | E*| test results. The total research effort included three replicate specimens from each of four aggregate types, three nominal maximum aggregate sizes, two performance grade binder grades, and two air void levels. The | E*| tests were conducted with five test temperatures and six loading frequencies. Even though all evaluated testing protocols produced standard errors of less than 15% (which is the requirement specified in AASHTO TP 62-03), a program utilizing four measurement instruments and two replicate specimens is recommended for future | E*| testing.