We’ll help you learn the Asphalt-Base-Cracks of paving.
One of the most difficult aspects when getting pavement maintenance work done can be understanding the technical terms the work requires. To make this easier we’ve defined the various words and phrases you’re most likely to encounter as you seek bids and evaluate plans to repair your pavement. Referring to these will help make sure you and the contractor are on the same page, comparing “apples to apples” throughout the job.
Alligator Cracking
The single most-damaging pavement defect is cracks, because cracks allow water to penetrate the base beneath the surface. When water gets beneath the surface, it eventually causes greater and more widespread cracking, potholes, and eventually general pavement failure. Parking lots with minor alligator cracking can be overlaid with a new layer of asphalt. Severe cracking must be removed and replaced as surface treatments, crack sealing, and overlays are not an effective maintenance procedure for these types of failures.
Asphalt Overlay
A common and cost-effective approach to extending pavement life is an asphalt overlay (also referred to as resurfacing). As its name implies, an overlay is a new layer of hot mix asphalt, generally 1½ – 2 inches thick after compaction, that is constructed over the top of an existing asphalt or concrete pavement. Often a paving fabric interlayer is placed between the pavement and the overlay as a way to strengthen the bond and to reduce reflective cracking. (Some people refer to fabrics as “Petromat,” but Petromat is a brand name of one of a number of brands of fabric.) When constructed properly and at the appropriate time in a pavement’s life cycle, an overlay helps extend the life of your original pavement, giving you a greater return on what you have already invested in your road or parking lot.
Base
Generic term for material installed prior to asphalt paving. Base material can be crushed stone or recycled asphalt pavement. The base material is important because it provides the load-bearing strength of the finished pavement. Depending on the traffic volume and weight of vehicles expected to use the pavement, the base can range from 3–4 inches thick for a residential driveway to 18 inches thick or more for parking areas or roadways. The correct type and thickness of base material must be specified in the contract prior to paving. Lack of adequate base material is a primary cause of pavement failures.
Base Failure
Base failures occur when the crushed stone layer beneath the asphalt layers and driving surface can no longer adequately support the weight of the structure or the traffic. Base failures can occur for a number of reasons, including ground water seepage, too much weight, and inadequate design. The failure can often be corrected by excavating the failed material and replacing it with base rock, stabilization fabrics or lime/cement treatments and then repaving the surface.
Compaction
Compressing a given volume of material (such as 2 inches of hot mix asphalt) into a lesser volume (such as 1½ inches of hot mix asphalt). This process is essential both on a pavement’s subgrade and base, as well as on the hot mix asphalt paving layer. Properly compacted asphalt pavement creates a more dense pavement, which makes the pavement stronger and helps it last longer. Paving compaction is done with steel or rubber-tire rollers, often with vibration added to create greater density. Depending on the thickness of the asphalt layer, plate compactors are also effective.
Complete Reconstruction
Just what it says: complete removal and reconstruction of the asphalt pavement to the depth of the base rock section, typically used in stages 4–5 of the pavement life cycle. While every pavement eventually requires complete reconstruction, you can delay this costly job through timely use of proper pavement maintenance techniques.
Crack Sealing
Because cracks are the most lethal problem a pavement can have, all cracks ¼ inch wide or wider must be sealed to prevent water infiltration and protect the life of the pavement. Small cracks (less than ¼ inch wide) are generally not sealed because the material will not penetrate the surface, and sometimes (though rarely) very wide cracks are sealed with sand-asphalt mixtures. A number of materials are available for sealing cracks but the most well known and most cost-effective is hot-rubberized crack sealant. Cold-pour crack repair materials also are available, but these are usually considered short-term solutions.
Patch Paving
Also known as R&R (removal and replacement) or “digouts”, this process is generally used to replace the damaged pavement which has failed due to age, weather effetcs or heavy use. R&R involves cutting around the edges of the failed asphalt, removing the old pavement and base material (if necessary) down to a structurally sound foundation. Once the old material has been removed, the base is compacted and a new section of asphalt is installed. Patch paving is typically used during stages 3 and 4 of the pavement lifecycle. Not only does it improve the overall structure of the pavement surface, it also protects the surrounding pavement by removing the source of potential damage.
Patch Fabrics (Petromat)
Paving fabrics are either woven or non-woven fabrics made of polyester, polypropylene or nylon. They are applied in pavement overlays to increase tensile strength of the new surface, improve the waterproofing function of the overlay and reduce the severity and extent of reflective cracking. These fabrics are applied directly to the existing pavement prior to the application of a new layer of asphalt.
Sealcoating
Sealcoating is the process of applying a protective material to the surface of an asphalt pavement—much like applying paint to the wood siding of a house. The sealer material is a watery mixture of emulsified asphalt, water, mineral fillers, and possibly various additives such as latex and modified polymers designed to speed the drying process and strengthen the dried sealer. Sealer is applied directly to the surface of an asphalt pavement by use of a rubber squeegee, broom, or mechanical spray.
As its name implies, sealcoating seals the top of the asphalt, preventing water from penetrating the surface of the pavement and protecting the top layer of asphalt from oxidation and wear caused by exposure to sun, air, and water. While sealcoating does not improve the structure of the pavement, it does improve the look of a pavement, providing a smooth, black, even surface that is ideal for painting lines and sweeping.
Sealcoating is designed for off-highway use on pavements in parking lots, homeowner associations, and driveways, where there are low traffic speeds and the turning radius is tight. Sealcoating is different from slurry seal, a higher-tech process that requires a much coarser aggregate filler and is designed for use on high speed areas with straight rolling traffic.
