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Frost, Christenson & Associates |
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ENGINEERING COMMUNITY ASSOCIATION |
Bituminous PavementThe pavement installed at most residential multi-family projects is referred to as bituminous pavement, or flexible pavement. The pavement section consists of the supporting ground (subgrade), a stone base (subbase), the asphalt base course (base course) and the asphalt top course (wearing course). The term Flexible Pavement reflects the fact that the pavement will "move" under traffic loads. In fact, if bituminous pavement is not subjected to traffic use, the material becomes brittle, which results in numerous small, surface cracks. Heavily used bituminous pavement will have a longer service life than infrequently used bituminous pavement. The pavement derives its strength from each component of the pavement section. However, it will be no stronger than the subgrade (ground) that supports it. Practically, if the ground supporting the pavement will not support the traffic without movement, then the pavement over the unsuitable ground will fail. Of the remaining components of the pavement section, the greatest strength is obtained from the base course. This layer of material incorporates relatively large stone aggregate and bituminous binder (cement). The resulting mixture is characterized by a very rough surface, and relatively large voids. As a result, water can enter the pavement material, causing substantial damage during winter freeze/thaw cycles, if a wearing course is not installed to "protect" it. The top course, or wearing course, while providing some additional strength, provides a smoother surface for vehicles and pedestrians, and minimizes water penetration into the base course layer. Maintenance of Bituminous Pavement Pavement must be maintained regularly to attain the anticipated useful life of the material, generally fifteen (15) years. In the northeast, maintenance is generally directed at keeping water out of the pavement section (subgrade, subbase, base course and wearing course), and replacing any failed sections of pavement which would in turn allow water penetration to the subgrade in the future. Once water penetrates the pavement section, the freeze/thaw action of the winter months can cause substantial damage. Maintenance of pavement generally takes three forms; sealing cracks, full depth repair of failed pavement, and "seal coating". Cracks Crack sealing consists of cleaning cracks (with compressed air) and filling the cracks with "tar" (a petroleum-based material designed for this purpose). Crack sealing should occur annually, as the opening of surface cracks allows water to penetrate into the base course. Full Depth Repair The more obvious areas of pavement that require full depth repair are characterized by sections of pavement that have broken away, and larger areas with multiple cracks (alligatoring). Less obvious areas require judgment by a qualified engineer. Full depth repair consists of the removal of the existing pavement section (wearing course, base course and subbase), examining the subgrade (supporting ground) for soft spots (and removing unsuitable subgrade if found), replacing the subbase, base course and wearing course. The amount of full depth repair undertaken must be determined by inspection on an annual basis. The failure to remove and replace badly failed pavement typically will result in substantially larger areas of failed pavement within a short time frame. Seal Coating Seal coating places a "sealer" onto the surface of the wearing course. Acting like a "paint", it fills and seals small, hairline cracks that develop in the pavement surface. It will not seal larger cracks, and it cannot correct failed pavement. These issues must be addressed before applying a seal coat. The frequency that seal coats should be applied is the subject of some debate. The "seal coat industry" is a proponent of frequent applications. Frost, Christenson & Associates’ position is that it is cost effective to apply a seal coat about half way through the service life of the asphalt pavement, or seven (7) years. Applications at other times, in the opinion of Frost, Christenson & Associates, would be dependent on site-specific conditions, and are generally not cost effective. There are various types of seal coats. Municipalities often use an "oil and chip" coat, consisting of an asphaltic liquid covered with a layer of small "stones" or aggregate. This type of seal coat is not, in our opinion, suitable for roadways in multi-family developments. The application is messy (leaving the asphaltic liquid in areas where it can be tracked by pedestrians and vehicles) and dusty (the "stone" generates dust as vehicles drive over the coated surface). Additionally, it is typically necessary to return to pick up surplus "stone". The process and its impacts are not compatible with the residential density typical of community associations. A second type of "seal coat" is a slurry seal. This usually consists of an asphaltic emulsion with fine aggregate (sand). Generally, this type of seal coat is not used on streets. The most common type of seal coat is an asphaltic base system, similar to the material that homeowners purchase for driveways. While there are various types, Frost, Christenson & Associates usually recommends a water base material that is not susceptible to damage from the leakage for petroleum-based fluids from parked vehicles. Again, the recommended material is dependent on site specific conditions. As with any other aspect of pavement maintenance, it is necessary to properly prepare the pavement before the installation of a seal coat. In addition to cracks and failed pavement, which must be repaired, treatment of pavement damaged by leaking petroleum-based materials is critical. Failure to repair these areas usually results in a failure of the seal coat application in that area. Replacement
The term Pavement Replacement is a misnomer. Instead, the existing pavement is repaired, and a new layer of bituminous material is installed on top of (over) the original pavement. This process is referred to as an "overlay".
First, all failed sections of pavement should be repaired. Second, all cracks should be filled, and, depending on the width of the crack, the cracked area should be removed and replaced, or a crack treatment fabric should be installed over the crack before the overlay is installed. This fabric reduces the probability that the crack will reappear on the surface of the overlay shortly after installation.
Most roadway and parking pavement have some surface areas that do not drain properly. These should be examined and corrected as part of any overlay application. Equally important are drainage problems not located on the pavement surface. Usually correction of drainage problems requires installation of drainage pipes, and they usually connect to inlets located in the road or parking area. Any improvements, such as drainage, which require excavation of the pavement should obviously be installed prior to overlaying the pavement. Curbing is another major issue because the overlay will be installed adjacent to the curb. First, any damaged curb should be repaired prior to the installation of the overlay. (This is also a good time to repair/replace sidewalk.) In addition, a decision should be made as to how the reduction in curb height (reveal) will be addressed, both now and in the future. The first overlay will reduce the curb reveal by about one-third. While this may not be critical, the second application will cause a corresponding reduction. The third overlay will "bury" and require the replacement of the curb, which is a significant expense. Not only must the curbing be removed, and replaced, but the drainage will be adversely affected as the new top of curb will be six (6") inches higher than the old top of curb. To avoid the replacement of the curbing and significant costs associated with changes in grading and drainage, the paved area should be evaluated at the time of the first overlay for the possibility of milling the existing pavement. Milling is the process of removing a portion of the pavement (typically the existing surface course) by grinding the pavement surface. Because of the ability to recycle the milled bituminous material, the cost has become quite competitive. Generally, the additional cost of milling can be offset by the cost of curb replacement at a future date. SummaryPavement Maintenance, Repair and Replacement are, or should be, a major component of an Association’s Operating Budget. Once a project approaches ten (10) years of age, an annual inspection of the pavement is warranted, with annual expenditures for crack filling, and full depth repair of failed pavement sections. Failure to perform these maintenance items will result in significantly greater expenditures in the future. Pavement replacement is not just the application of a layer of bituminous material at some time in the future. The anticipated replacement should be re-evaluated annually after a site inspection. However, the overlay should be well planned, with the program developed prior to the actual need for installation. If Frost, Christenson & Associates can assist you, |
