Evaluation of Louisiana asphalt pavement friction

This study aims to comprehensively investigate the effect of asphalt mix designs to address skid resistance. The current Louisiana Department of Transportation and Development (LADOTD) specification for friction design considers only the friction rating of aggregate defined by the polished stone value (PSV) obtained by the British pendulum tester (BPT), which is associated with only the micro-texture of asphalt pavement surfaces. The objective of this study is to recommend an asphalt surface friction mix design guideline which is based on both micro- and macro-texture of the wearing course mix. The objective was achieved by evaluating four typical laboratory prepared Louisiana asphalt mix designs, each with three different aggregate blends. The polishing and texture properties of aggregates were characterized by the British pendulum tester, micro-deval test, and aggregate imaging system (AIMS). The micro- and macro-texture of the asphalt mix surface were evaluated with a dynamic friction tester (DFT) and circular texture meter (CTM) at different polishing cycles and test speeds. The results were combined into International Friction Index (IFI). The DFT measurements were found to be sensitive to the coarse aggregate type (micro-texture) and CTM measurements were sensitive to the mix design (aggregate gradation). Further, an inventory dataset of locked wheel skid tester (LWST) measured field skid-number (SN) was obtained from the LADOTD’s Materials Laboratory. The dataset was analyzed to determine the effects of traffic loading, aggregate, and mixture types on the measured SN values. The laboratory results indicated that the overall skid resistance of an asphalt mixture depends on both micro- and macro-texture, and it is possible to design an asphalt mix with the combination of high friction mixture and low friction aggregate or vice-versa. The study also showed that blending of low and high friction aggregates together can possibly produce an asphalt mixture with an adequate field skid resistance. An attempt was also made to estimate the friction threshold values for Louisiana pavements. Finally, a set of predictive models were developed to recommend an asphalt friction mix design procedure for Louisiana pavements