Assuming the asphalt pavement was properly installed, the reason for most asphalt failure is the penetration of water into the asphalt base. When left unsealed, asphalt begins to oxidize, becoming dry and brittle. Once the top layers of asphalt begin to erode, small surface cracks begin to form that eventually extend down into the base layers. Once water enters the base of the pavement, it begins to shift and cause settling, further cracking and depressions. As water pools in these depressed areas, the asphalt further deteriorates and becomes unstable. Once it reaches this level of deterioration the only remedy is the removal and replacement of the old asphalt. It is key, therefore, that asphalt be maintained to maximize its life and protect if from early failure.