Fundamental analysis of self-healing phenomena in asphalt mixtures

When asphalt becomes cracked it will slowly begin a self-healing process, during which, the crack is either partially or fully repaired over a period of time. Upon reaching a certain temperature the bitumen in the asphalt becomes a Newtonian fluid and the rate of this self-healing is greatly increased. This research discusses ways to model this process using flow within a porous medium and using the results produced to compare current popular methods of triggering self-healing in asphalt. The first step of the research is to create a mathematical model for a gravity and surface tension driven self-healing process to model the flow of fluid within a porous medium. This was followed by the use of conformal mapping to discover a small time asymptotic solution to the movement of the bitumen into the crack. This precluded the creation of a numerical solution which used boundary integral methods combined with Green's functions to provide the equipment needed to allow the calculation of the crack healing with time. Next the numerical model was verified against the small time asymptotic solution as well as analytical solutions to ensure its reliability. In addition, experiments were conducted throughout the research to ensure the validity of the created model. The results of the numerical solution are then used to calibrate an equation which can predict the flow of bitumen into a crack in asphalt over time in a computationally cheap manner. The next stage of the research uses the equation derived in the chapter previous to it and calibrates it to the results of experiments which use three point bending to analyse different healing methods. A set of these experiments are conducted as part of this research, while many experiments carried out in the literature are also studied. Three-point bending tests conducted in this research were performed on asphalt containing large quantities of calcium alginate capsules to aid the self-healing process. These tests showed consistently better healing in asphalt containing capsules, with the peak performance occurring in asphalt containing 1% or 1.25% capsules. Comparisons were then made between the various healing methods studied in the chapter. The research concludes by creating new models to simulate the healing of different orientations of cracks in asphalt. The orientations are an inverted vertical crack, a horizontal crack and two vertical cracks in the same piece of asphalt. A numerical solution to the pressure gradient was found for each class of crack using boundary integral methods combined with Green's functions to select an appropriate domain for the calculations. These calculations were then validated through comparison to multiple series of laboratory experiments