Evaluation of Hot Mix Asphalt moisture sensitivity using the Nottingham Asphalt Test equipment

Abstract

Moisture sensitivity of Hot Mix Asphalt (HMA) mixtures, generally called stripping, is a major form of distress in asphalt concrete pavement. It is characterized by the loss of adhesive bond between the asphalt binder and the aggregate (a failure of the bonding of the binder to the aggregate) or by a softening of the cohesive bonds within the asphalt binder (a failure within the binder itself), both of which are due to the action of loading under traffic in the presence of moisture. The evaluation of HMA moisture sensitivity has been divided into two categories: visual inspection test and mechanical test. However, most of them have been developed in pre-Superpave mix design. This research was undertaken to develop a protocol for evaluating the moisture sensitivity potential of HMA mixtures using the Notthingham Asphalt Tester (NAT). The mechanisms of HMA moisture sensitivity were reviewed and the test protocol using the NAT were developed. Different types of blends as moisture-sensitive groups and non-moisture-sensitive groups were used to evaluate the potential of the proposed test. The test results were analyzed with three parameters based on performance character: the retained flow number depending on critical permanent deformation failure (RFN sub P), the retained flow number depending on cohesion failure (RFN sub C), and energy ratio (ER). Analysis based on energy ratio of elastic strain (ER sub EE) at flow number of cohesion failure (FN sub C) has higher potential to evaluate the HMA moisture sensitivity than other parameters. If the measurement error in data-acquisition process is removed, analyses based on RFN sub P and RFN sub C would also have high potential to evaluate the HMA moisture sensitivity. The vacuum pressure saturation used in American Association of State Highway and Transportation Officials (AASHTO) T 283 and proposed test has a risk to damage specimen before the load applying.