Characterisation of cracking resistance in modified hot mix asphalt under repeated loading using digital image analysis

Laboratory determination of fatigue characteristics of asphalt mixtures is a vital step in evaluating and designing asphalt pavement. This study aims to provide a comprehensive analysis of the fatigue resistance of the modified asphalt mixtures containing plastic waste and crumb rubber. These dry process-modified mixtures have been presented in the road construction on the basis of the basic understanding of the mechanical properties and lack of intensive studies on fracture mechanics. In this study, a controlled-stress, repeated load semi-circular bending test under two load levels with the effect of ageing and moisture condition was used to characterise the three stages of fatigue life of asphalt mixtures. The fatigue life was characterised on the basis of the crack mouth opening distance assessment and image analyses of the crack patterns on the sample surface. Digital image correlation was used to capture the strain field that forms the plastic zone of mixtures under consideration. Results show that rubberised asphalt mixture promotes crack propagation and failure stages by increasing the plastic zone, whilst plastic waste-modified asphalt mixtures function to increase the bonding properties. Consequently, the cracking initiation and propagation stages increase. The digital image analysis of the sample surface of modified asphalt mixtures indicates higher values of crack tortuosity, crack density and fractal dimension due to the increase in the cracking resistance of asphalt mixtures. The extracted strain field has successfully captured the effect of modifiers on the size of plastic zones under the fatigue test.