The pavement community has strict specifications for the design and manufacturing of asphalt mixtures. But like any other process, a strict adherence to the rules costs more money. As a result most local pavements and especially parking lot pavements might not receive the highest quality asphalt mixtures. It is very common that a parking lot is constructed with materials that failed to meet the specifications of a highway project.
Whatever the circumstances that occurred during the construction process, eventually it will be the responsibility of the owner, with the help of a contractor, to keep the pavement looking good and providing its intended service. With a little education on pavement performance, most owners and contractors will be able to make smart decisions. Following are a few simple facts to keep in mind:
- As long as pavements are subjected to traffic loads and environmental factors, they will experience deterioration and eventual failure.
- Pavements must be maintained regularly. National studies have shown that every $1 spent on preventive maintenance saves $5 on major rehabilitation.
- It is wise to keep records on how the pavement is performing on a regular basis. Walk the project every 4-6 months and take pictures to document the conditions of the surface.
- Accept the fact that good pavements also need maintenance, very similar to changing the oil every three months in a brand new car. If preventive maintenance is delayed then its effectiveness is greatly reduced. In most cases, once cracking appears on the pavement surface, it is too late for preventive maintenance.
The Pavement Coating Technology Center (PCTC) is a group of manufacturers and suppliers of pavement sealers that are highly dedicated to the betterment of the entire industry. The PCTC was initiated 10 years ago with the objective of conducting research and development to improve the state of knowledge on pavement maintenance. PCTC's efforts have led to significant progress on several issues confronting the pavement sealer community, ranging from the design of sealers to the environmental concerns of the public.
Sand in the mix design
In general coal tar based sealers are made of the coal tar binder, sand, water, and additive. The overall success of the sealer depends very heavily on the proportioning of its various components. The first thing to recognize is that there is no such thing as one formula fits all. Each sealer should be designed individually to take into consideration the unique characteristics of the coal tar binder and sand that significantly influence the performance of the final product (i.e. the sealer). The PCTC developed guide specifications for the design of coal tar sealers: PCTC01 for un-modified sealers and PCTC02 for polymer-modified sealers. The guides are available at no charge through the PCTC web page "www.Pavtec.com".
The guides present recommendations on the gradation of sand and the amount of sand to be used in the design of the sealer. The amount of sand, commonly referred to as "sand loading," has been a contentious issue in the industry for quite a long time. A recent PCTC field project generated valuable data in support of the sand loading issue. Field test sections were constructed with sand loadings of 3, 5, and 18 pounds. The test sections were monitored for their resistance to wear under normal traffic loading. After four years of field monitoring, it was concluded that the sections with the 3- and 5-pound sand loadings significantly out-lasted the sections with the 18-pound sand loading. The field data showed that the 18-pound sand loading sections totally wore-off the pavement surface after nine months of traffic while the 3- and 5-pound sand loading sections performed successfully for the entire four-year period.
Based on this study, the PCTC strongly recommends that the sealer be designed to account for the unique characteristics of the coal tar binder and the sand that are being used on the job and sealer designs with high sand loadings should not be accepted.