Refining a Laboratory Procedure to Characterize Change in Hot-Mix Asphalt Surface Friction

Abstract

The surface of asphalt pavements gradually lose friction resistance as a result of changes in surface texture and aggregate polishing with repeated traffic application. The loss of pavement friction is a major safety concern. The purpose of this study is to develop a laboratory testing protocol that can rapidly predict the rate and degree of Hot-Mix Asphalt (HMA) surface friction loss by conditioning the surface of HMA slabs and measuring friction and texture. The results of the laboratory conditioning are further correlated to actual change of friction in the field. HMA slabs compacted in the laboratory are conditioned using Three Wheel Polishing Device (TWPD) developed by National center for Asphalt Technology (NCAT). The surface friction loss and change in surface texture are measured using Dynamic Friction Tester (DFT) and Circular Texture Meter (CTM) respectively. The research was carried out in two phases. In Phase I, two Stone Matrix Asphalt (SMA) mixtures for six combinations of TWPD load and speed were tested. The combination with the lowest load (91 lbs.) and highest speed (60 rpm) was found to wear the HMA surface more than other combinations. In Phase II, the rate of friction change was evaluated by varying the amount of friction aggregate in a mixture. Two dense graded mixtures with three blends for each mixture were prepared and tested. The DFT results showed that the friction values decreases as the amount of friction aggregate in a mixture is decreased. A correlation was found between the DFT60 values measured in laboratory and SN64 values from NCAT test track measured using skid trailer. The results showed a high correlation between laboratory and test track friction data for three mixtures used in this study.