Using a beam wheel tracker fatigue test to evaluate fatigue performance of asphalt mixtures

Fatigue cracking is one of the key distress types, caused by traffic load repetition generating stresses and strains in asphalt layers. In response, polymer modified asphalt (PMA) has been widely used in the field of pavement engineering and the addition of polymers to asphalt has been shown to improve mechanical behaviour and pavement performance, including fatigue resistance. However, it is uncertain to what extent standard fatigue tests measure this benefit. In this study, a Beam Wheel Tracker Fatigue Test (BWTFT) was developed to investigate the fatigue behaviour of both polymer modified and unmodified asphalt mixtures. The results showed that the BWTFT worked well and appeared to simulate road pavement cracking fairly realistically. Visible cracking began to appear at 50-95% of the time to full-depth crack development, later at lower temperature. A practical calculation is presented to estimate material modulus during the test and this shows a significant reduction throughout, with differing patterns for different materials and temperatures. Early stiffness reduction is deduced to relate to the development of micro-cracking. The differences between conventional and PMA performance are highlighted.