Magazine article Journal of Property Management

Potholes and Patches: The Ups and Downs of Pavement

Magazine article Journal of Property Management

Potholes and Patches: The Ups and Downs of Pavement

Article excerpt

While the average person might take the serviceability and longevity of on-grade pedestrian and vehicular pavements for granted, they are, in fact, susceptible to a host of potential problems. However, these problems may be minimized with the proper attention to the original design, construction quality, and maintenance of both parking areas and sidewalks.

The basic types of on-grade pavements are rigid, Portland cement concrete and flexible, bituminous concrete. A more recent trend is the use of loose-laid, fired-clay, or concrete pavers. Some of the problems that all of these pavement types have include settlement, frost heave, freeze-thaw durability, and poor surface drainage.

Settlement

Slabs on grade settle because the unconsolidated soil subgrade on which they are built consolidates under the weight of the pavement or loads imposed on it. If settlement occurs, rigid pavements made with Portland cement concrete may crack. If the pavement is made of relatively flexible material, such as bituminous concrete (asphalt) or masonry payers, it may simply deform the surface. Either condition will affect appearance and may result in serviceability issues and possible liability for the property owner.

The only thing that will prevent settlement is to have a stable sub-grade. During site-grading operations, if the sub-grade consists of undisturbed and well-consolidated soil, it must be protected from disturbance prior to placement of the pavement sub-base and the pavement material. If the existing soil is unsuitable to support loads, because, for example, it has high organic content or is uncontrolled backfill, that soil may have to be removed. Any backfill used to achieve the desired final grade should be clean, granular soil or crushed stone and should be compacted in maximum 12-inch thick layers to a strict standard (e.g., 90-percent modified Proctor density test of the sub-grade material as verified by the American Society for Testing and Materials test [ASTM 1557]). Sub-grades for pavements are commonly proof rolled or otherwise mechanically compacted to achieve the proper density. If the sub-grade is stable, the pavement will have much better serviceability. Any reasonable expense to achieve a good s ub-grade is money well spent.

If an existing pavement has minor cracks, routing the cracks and filling them with an elastometric, traffic-grade sealant that is formulated to be compatible with the pavement material can repair them. As bituminous pavement starts to weather and dry our, the surface can be sealed to extend its service life. However, in the case of existing, unacceptably-heaved or potholed pavements, removal of the pavement may be the best option. Removal could be followed by mechanical compaction of the existing subgrade material, followed by installation of new pavement.

Installation of new pavement over an existing settling pavement, while commonly done, and immediately less expensive, will not cure the cause of the problem and is not cost effective in the long term because the pavement is likely to keep moving and deteriorating.

A common source of degradation of existing pavements is ongoing construction of underground utility lines. When these lines are cut and trenched through pavement, care should be taken to ensure that the existing adjacent pavement sub-grade is protected from being undermined and that the new back-filled sub-grade is adequately compacted. If not, it will not be long before settlement of the sub-grade occurs followed by deformation and cracking of the pavement and the development of potholes.

Frost Heave

In the northern and Midwestern part of the U.S., repetitive freezing and thawing temperatures play havoc with on-grade pavements. Typically, water that becomes trapped under the pavement in the sub-grade and sub-base course of the pavement freezes, causing upward expansive forces that result in heaved pavements. …

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