Effects of aging on the properties of asphalt at the nanoscale P.E. Yuhong Wang a,⇑ , Kecheng Zhao a , Charles Glover b , Ling Chen a , Yong Wen a , Dan Chong a , Chichun Hu c a Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong b Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX, USA c College of Civil and Transportation, South China University of Technology, Guangzhou, China highlights  Oxidative aging increases the spatial variations of asphalt properties at the nanoscale.  More severely aged asphalt takes longer to recover from micro damages.  For the same asphalt, moderate aging increases the adhesive/cohesive strength.  Both asphaltenes content and the size of microstructures play a role in determining asphalt micromechanical properties. article info Article history: Received 10 October 2014 Received in revised form 10 January 2015 Accepted 10 January 2015 Available online 14 February 2015 Keywords: Asphalt Oxidative aging Micromechanical properties Atomic force microscopy abstract Conventional rheological and chemical tests provide a global view of asphalt property and composition changes upon aging, but offer little details on the changes at the microscopic level. Using atomic force microscopy (AFM), this study analyzed the micromechanical properties of five asphalts with different aging conditions. Rheological and chemical tests were also used to characterize the global properties of the asphalts. Aging was found to significantly increase the spatial variations of the sample properties. It generally increases the ratio between the dissipated energy and total work to deform the sample during the indentation process by AFM probe. It also appears to increase the adhesive and/or cohesive strength of the sample. Certain micromechanical properties and the rheological properties are well related. The asphaltenes content and the size of microstructures both appear to affect the micromechanical properties of the binders. AFM provides a promising addition to the traditional rheological test for asphalts, but more studies are needed to connect the micromechanical properties with performance-related properties. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction As an organic material, asphalt in hot-mix asphalt (HMA) pave- ment is susceptible to oxidative aging by reacting with atmo- spheric oxygen [1]. Oxidative aging causes asphalt hardening, which leads to pavement embrittlement and the development of distresses such as cracks or fractures [1]. As a key performance fac- tor in HMA pavement, asphalt aging has received extensive atten- tion for decades [1–3]. Much progress has been made on understanding the fundamental physical–chemical process of asphalt oxidation and the oxidation kinetics [1–4]. In Superpave Ò specification, asphalt is artificially aged in a rolling-thin film oven (RTFO) to simulate aging that occurs during production and construction and in a pressure aging vessel (PAV) to simulate aging that occurs 5–7 years in the field [5]. Before and after the aging treatments, a suite of tests are conducted to characterize the asphalt binder’s rheological properties at different temperatures and loading conditions. In chemical analysis, the numerous types of molecules in asphalt are generally separated into four fractions [6]: saturates, naphthene aromatics (NAs), polar aromatics (PAs), and asphaltenes. Upon oxidation, PAs transform to asphaltenes, whereas NAs first transform to PAs and then to asphaltenes [6,7]. The increase in asphaltenes has been shown to be related to the increase in asphalt viscosity [8,9]. Chemical changes have also been examined through the changes in oxygen-containing functional groups in asphalt, in particular the carbonyl and sulfoxide func- tional groups [1,10]. Laboratory tests revealed a linear correlation between the increase of log viscosity and carbonyl formation dur- ing asphalt oxidation [8,11,12]. http://dx.doi.org/10.1016/j.conbuildmat.2015.01.059 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +852 27664489; fax: +852 23346389. E-mail address: ceyhwang@polyu.edu.hk (P.E. Yuhong Wang). Construction and Building Materials 80 (2015) 244–254 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat