Seal Coating Program
Seal coating is a street maintenance technique which preserves the condition of a street by sealing the surface and small cracks within the existing asphalt pavement. When this type of preventative maintenance is performed on a timely basis, a typical pavement may last 40 years before it needs to be reconstructed. Saint Paul’s residential streets are seal coated every eight years. Because of the heavier loads and higher traffic volume, arterial streets are milled and overlayed.
This street maintenance technique involves applying hot liquid asphalt to a street surface and covering the street with a graded aggregate to produce a waterproof membrane. There are several steps to seal coating:
- First, the street surface is swept clean of all loose pavement and dust.
- Next, the surface of the asphalt is completely covered with a layer of liquid asphalt using a tank truck called a distributor.
- Afterwards, a layer of gravel is placed over the liquid asphalt with a machine called a chip spreader.
- Torpedo gravel (egg shaped) or crushed granite gravel chips are then worked into the asphalt with a rubber tire roller.
- Traffic is allowed back on the street within several minutes of placing and compacting the gravel, as the weight of vehicles helps to work the gravel into the soft asphalt.
- Finally, the streets are swept to pick up any loose gravel.
- Recovered gravel is screened and re-used for the next seal coating project.