Evaluation of Cracking Resistance and Permanent Deformation of Control and Fibre Modified Plant Produced Hot Mix Asphalt

ABSTRACT
The addition of elastomeric polymers to asphalt mixtures is a common practice for preventing premature distresses in asphalt pavements. Polymer enhances the asphalt binder to improve its rutting and cracking resistance. In cold temperatures, thermal stress in asphalt pavement builds up to the point that it can exceed the pavement’s tensile strength, causing cracks on the surface. Given the severe cold seen in Alberta’s winters, the City of Calgary is seeking to address asphalt pavement cracking issues by investigating the impact of polymer (dry) fibres on pavement cracking resistance. In the present study, a trial road section having been constructed in Calgary using aramid and wax polymer fibre-modified hot-mix asphalt adjacent to a control section, the hot-mix asphalt is modified using 0.0065% fibres by weight of asphalt mix. (Note this amount is much less than cellulose fiber, for example.) Representative samples of the fibre-modified and control mixes are collected from the asphalt plant and transferred to the University of Alberta asphalt laboratory for testing. The cracking property and rutting performance of the modified and unmodified asphalt mixes are assessed through IDEAL Cracking Test and Hamburg wheel-tracking test, respectively. The results show that the average cracking tolerance index for the control sample is found to be 123.7, whereas, for the fibre-modified sample, the value is 178.2. These findings suggest that the cracking resistance of the samples can be increased by up to 44% as a result of modification. Furthermore, the average indirect tensile strength for the control sample is found to be 789 kPa, while that of the fibre-modified sample is just 735 kPa; however, the load-displacement plots show higher post-cracking energy resulting in slower crack propagation for the reinforced mix. In addition, the Hamburg wheel-tracking test results show that, after 20,000 of wheel passes, the average rut depth of the fibre-modified sample is 4.58 mm, whereas, for the control sample, the rutting is 4.93 mm, indicating a decrease in rut depth by 7.1% as a result of the addition of fibre.

Keywords: Aramid Fibre, Asphalt Mixture Performance Tests, CT-Index, Fracture Energy, Moisture Susceptibility, Rutting, Stripping Inflection Point, Tensile Strength.