Why Pavement deteriorates

Analyzing the Factors Involved in Pavement Damage

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Each spring, after a long winter, we find that the damage caused by "old man winter" can be quite surprising. As we look at our pavement we may notice up to nine distresses causing our asphalt to deteriorate at an accelerated rate. Asphalt pavement is designed to have a service life of between 15-20 years, depending on the construction specifications and techniques used. There may be many reasons for pavement deterioration. The four most common include:(1) weather damage; (2) load distress, (3) improper construction and (4) fluids.

Water is the number one destroyer of asphalt pavement. Weather related damage comes in many forms, moisture infiltration, moisture accumulation, freeze-thaw cycles and oxidation. It is not unusual for the Chicagoland area to have between 36 to 40 freeze-thaw cycles in an average winter season. Each freeze-thaw cycle causes our pavement to expand and contract. Reflective cracks in the pavement’s surface allow moisture, such as snow, rain and slush, to infiltrate into the stone sub base which leads to alligator cracking or complete pavement failure.

Moisture infliltration damage is a result of standing or ponding water on the asphalt surface. The ponding water is permitted to seep through the voids in the pavement surface seeping between the liquid asphalt cement and aggregate which the asphalt surface is made up of. The wearing away of the asphalt surface will lead to raveling and damage to the stone sub-base.

Oxidation is the hardening or drying out of the asphalt cement. As the pavement cures, the sun’s ultra-violet rays harden the asphalt cement to the stage it becomes brittle and small pieces of aggregate break loose from the asphalt surface. Accelerated oxidation or raveling can reduce the pavement’s thickness by 3/8" to 1/2" inch within ten years, reducing the structural integrity of the asphalt pavement.

The second cause of pavement distress is load related distresses. Asphalt pavements are flexible. They have a tendency to move and flex as traffic loads are applied. Most load-related distresses occur in traffic lanes, entrances, exits and right in front of dumpster corrals.

Load distress damage starts at the bottom of the asphalt surface where tensile stress and strain are highest under a wheel load and extended to the top of the asphalt surface. As the traffic increases, alligator cracking is formed. Alligator cracking is a series of interlocking cracks caused by fatigue failure. Alligator cracking is considered a major structural distress.

Another key issue that can affect the deterioration of pavement may occur directly at the beginning of the pavement's life cycle with the process of improper construction. Improper construction may be a result of improper site design for heavy load distress traffic (i.e. garbage trucks, semis, etc.), improper specifications such as compaction ratios, and the depth of the stone base, Binder, and Surface course asphalt that is being installed.

Lastly, fluid damage. Asphalt is made of mainly two components: liquid asphalt cement, which is a petroleum product, and aggregate, which ranges in size from sand particles to 3/4 inch stone. As vehicles drive and park on the asphalt surface they leak such petroleum products as oil, gas, transmission fluid and many others. Repeated dripping and leaking, especially in parking stalls, penetrates the asphalt surface saturating the area. This causes the asphalt cement to break down and the aggregate to become dislodged wearing away the pavement surface. A test used to determine if fluid saturation is present is to take a screwdriver and place it into the saturated area. If it penetrates easily, asphalt removal and replacement is required.