If stripping or raveling occurs substandard material could be the cause. If the asphalt material applied does not have the proper ratio of large aggregate and fines or if the asphalt binder itself is not adhering to the aggregate it will cause the larger aggregate to strip away or unravel. If this happens your asphalt will fail. An indicator of this type of failure is a very rough gravelly surface.
Unlike concrete, made for its rigid strength, asphalt pavement is made to flex with movement. On a hot day asphalt can actually soften enough to make a depression print of your shoe in the pavement. The sub-grade and base material, higher in its compressive strength, is actually what supports the weight of the loads above. Depending on the purpose of the pavement the asphalt layer and the base layer need to have the proper thickness and compaction to support the loads they will be bearing.
The layer of asphalt also provides a load bearing functionality. If installed at the proper thickness the asphalt layer helps by distributing the weight of the load to the base layer beneath. If the layer of asphalt is too thin it can’t distribute the weight putting too much compressive stress at the load’s point of contact. This causes fatigue cracks beneath the pavement surface. The cracks will eventually migrate to the surface and weaken the surrounding asphalt.
As mentioned above asphalt pavement does not have the compressive strength that concrete has. The Sub-grade and base layers of your pavement system is what supplements the lack of compressive strength in your asphalt. With that said it is imperative that the stability of your sub-grade and base stays intact. Water is the number one culprit in compromising sub-grade and base stability. In cold climates the freeze thaw cycle is a big problem. The ground water expands when it freezes causing the pavement to heave. The pavement splits down the middle like a pair of jeans when the pressure from within becomes too much to contain. In Southern California we do not have this problem. In fact our problem is caused by just the opposite. The excessive amount of sunshine exposure actually burns away the asphalt binder, creating deep cracks that allow rain and run off water to penetrate the sub-grade.
For those of you who think the cost of repairing your asphalt is an earth shattering tragedy; well you would be right! California is also known for its wealth of Seismic activity. Earthquakes can also cause pavement cracking.
Other factors that can cause your pavement to fail, from the ground up are; tree roots, leaky water mains, punctured plumbing pipes and faulty irrigation systems. In all these scenarios the source of the problem must also be repaired or your asphalt failures will continue to haunt your wallet. Broken pipes or water leakage must be repaired before the new asphalt is applied. Tree roots must be cut and removed at least 12” in depth. If the dead roots and other vegetation are not removed from your sub-grade they will eventually rot and deteriorate, creating empty space in the sub-grade compromising its stability.
Ultraviolet rays, Oxidation and Pollutants are all environmental elements that breakdown your pavement overtime.
Oxidation is a process that is constantly happening all around us all the time. When metal rusts, when the meat of an apple browns or when your asphalt grays and becomes brittle; that’s oxidation. When Oxygen comes into contact with the binder material in your asphalt a molecular reaction occurs that causes the molecules on the surface to become radical and break away. However, oxygen is not the only element that can cause oxidation. Ultraviolet rays from sunlight and pollution are also factors that contribute to pavement deterioration.
Due to the inherent need for oxygen and sunlight in our environment I’m afraid there is no cure for this cause. However there are things you can do to slow the oxidation process and prolong the life cycle of your pavement. Seal coat for example acts as a protective layer to your pavement like the skin of the apple provides a protective layer for the meat. Areas with high pollution, direct sunlight and low traffic volume will deteriorate at a faster rate. Skin patching will allow you to repair these areas without having to do make unnecessary repairs to the rest of your pavement. Filling cracks will prevent these environmental elements coming into contact with the inner layers of the pavement through the walls of the cracks.
Water is a powerful force! To visualize its power, picture the Grand Canyon. On a much smaller scale we can see the effects of water in our road ways and parking lots. Over spray from watering systems, leaky sprinklers, inadequate rain run-off repeatedly batter your pavement. Such assaults cause potholes, puddling, cracking, water stains and eventually sub-grade failure. Anytime water penetrates through to your sub-grade the degree of asphalt maintenance needed increases dramatically. Watering systems should be monitored regularly for overspray and leaks. Reducing the amount of overspray onto pavement will conserve water as well as perverse your pavement. The best prevention for water damage to your pavement is a properly designed water run-off system. Proper sloping and installation of flow lines allow water to run-off the pavement before it can cause damage. A good water run-off system can save you a lot of money in future maintenance.