The first part of a good pavement program starts with a survey of the current pavement condition. The first part of the survey is identifying various pavement distresses. The first distress that will develop in new pavement is cracking, which is generally identified in four forms:
- Longitudinal and transverse
- Block (thermal)
- Crescent (cracking along the edge)
- Reflective (in slurry seal and overlays)
Longitudinal, transverse and block cracking are generally the first cracking distresses to develop in pavement. Longitudinal and transverse cracking develop from paving joints separating, shrinkage of the pavement, and base or subgrade movement. Block cracking is a result of thermal or temperature changes and fluctuations. The pavement will crack from expansion and contraction and oxidation, and the cracking is in the form of squares or blocks.
Crescent cracking is a result of failure along the edge of an unconfined street, road or parking lot. This type of crack is caused from movement of the paved surface outward when exposed to a loading.
Reflective cracking develops from below a new surface (such as chip seal, slurry seal or overlay) from existing cracking. As the older pavement expands and contracts the cracking will reflect through the new surface. A fabric (stress-absorbing membrane) can be used to retard the rate of reflective cracking, but cracking will eventually reflect through.
Once cracking begins, other structural distresses will begin to develop. All cracks allow water to infiltrate (percolate) through the paved surface and saturate the base course and subgrade below the pavement. Once the base or subgrade is saturated, structural failures can begin to develop.
That is why it is very important that cracks are sealed whenever they have an opening of ¼ inch or more. This width was determined by studies that found that cracking with an opening of ¼ inch or more went all the way through to the bottom of a 2-inch to 3-inch paved surface. Also, you need a minimum of a ¼-inch opening to get proper penetration of crack sealant. For less than a ¼-inch opening you are only wasting maintenance dollars because the crackseal material is not penetrating the crack properly and is only spread on the surface.
Sealcoating will fill cracks less than ¼ inch wide and provide the protection needed. Smaller or thinner cracks in openings sometimes do not go all the way through the paved surface. As the pavement oxidizes and shrinks, smaller cracks will develop into larger cracks, and new cracks will develop.
Also, the pavement next to concrete curbs and valley gutters (concrete swales) will shrink and separate from each other. These openings, too, will need to be cracksealed when they reach a ¼ inch opening, since curbs and valley gutters are exposed to more water than the actual paved surface. Separation of the pavement from the curbs and gutters generally occurs after five-plus years from installation.
An elastomeric material, which will expand and contract with the pavement from exposure to temperature changes, should be used as the crackseal material. It should have a high softening point to eliminate tracking problems on sidewalks, pool areas and interior carpets. Different geographical areas will require material with different softening points (colder climates vs. desert climates). Several types and grades of crackseal materials are available and may be hot or cold applied.
A crack must be properly prepared before the sealer is applied. Proper preparation of the crack will allow proper adherence of the material on either side of the crack. If a crack less than ¼ inch wide is scheduled to be cracksealed it should be routed to open the crack to ¼ inch. Routing is an expensive task and, therefore, not always recommended for parking lots and home owner association streets.