What is the cause of asphalt failure?

If the asphalt pavement was designed and constructed properly, the most common cause of failure is water seepage into the asphalt base. Asphalt failure often begins with the oxidation of an untreated asphalt surface. Oxidation is caused by the repeated exposure of asphalt to sunlight and causes the asphalt to become dry and brittle. The fine particles on the top layer of asphalt erodes, exposing the larger aggregate and leading to small cracks on the surface. These cracks grow if left untreated, allowing water to penetrate to the base of the pavement. When water enters the base of the pavement, the base material shifts and settles leading to further cracking and a depression in the surface. As water pools in the depressed area, the asphalt further deteriorates and becomes unstable leading to a total deterioration over time.