Evaluation of Indentation Test to Characterize Asphalt Concrete Mixtures in Pavements

Abstract

The primary material property for characterizing asphalt concrete in the USA is the dynamic complex modulus. However, the dynamic complex modulus test is expensive and time consuming, making it impractical for use as a quality control test in the field. Therefore, there is a need for a test which can characterize asphalt concrete mixtures and can be performed, relatively simply, in the field immediately after construction. In the present study, the indentation test, which measures deflection under a constant load, was investigated for this purpose. Three replicates of the following four mixtures, having a nominal aggregate size of 12.5 mm and a PG64-22 binder, were fabricated and tested at 60ºC: 3.7% asphalt content and 4% air voids; 3.7% asphalt content and 7% air voids; 4.2% asphalt content and 4% air voids; and 4.2% asphalt content and 7% air voids. Air voids and asphalt content were varied since these are the volumetric parameters which are most likely to vary in the field and at the plant, respectively, and which have the greatest influence on pavement performance. The shear compliance obtained from the indentation test was found to be repeatable and sensitive to a change in air voids. However, the results do not seem to show a significant sensitivity to asphalt content, which is believed to be due to the localized nature of the indentation test. These results suggest that the indentation test may have limited applicability as a quality control and quality acceptance test in the field.