Sunnyvale

Chip sealing is the application of crushed rock (gravel) over an emulsified asphalt oil. The oil seals the pavement from water penetration while the gravel provides a wearing surface to protect the oil seal from traffic. In Sunnyvale we use a "double chip seal" technique. After the first layer of oil and gravel is applied, rollers are used to compact the gravel and seal it in the oil. Then a second application of oil and gravel is applied and compacted. The final layer is an oil seal to bind the gravel together and prevent raveling. Approximately two hours after the final oil seal, sand is applied to remove the final tackiness and the street is opened to traffic. The following day a street sweeper picks up any excess sand or gravel. Another follow up sweeping is done within two weeks to remove any gravel loosened by traffic. Each street that receives a double chip seal also has a slurry seal applied the following year. The cost of a double chip seal is about $0.16 per square foot and should last between 5 and 7 years.

Slurry Seal

Slurry seal is a mixture of fine aggregate (sand-like) with emulsified asphalt oil. This mixture is prepared in a specially equipped slurry seal truck, then the slurry mix is spread on the pavement and allowed to cure. The cost of a slurry seal is about $0.08 per square foot and lasts approximately 5 years.

Resurfacing

Resurfacing is the application of 1-1/2 to 4 inches of asphalt over an existing pavement to provide a smooth surface and add strength to the road. In some cases the top layer of old asphalt is removed and replaced if it is badly broken up. Major streets have priority for resurfacing based on traffic load and volume. The cost of resurfacing is about $2.30 per square foot and should last 15-20 years.

Pavement Reconstruction

When the condition of the street reaches the point where Preventive maintenance is no longer cost effective, then the street is put on the reconstruction list. Reconstruction involves removing the entire street and replacing it. The cost of pavement reconstruction is $6.20 a square foot depending on the depth of the asphalt replacement, and should last 20-25 years.

Petromat

Generally, several weeks prior to resurfacing or chip sealing, a layer of petromat is applied to add strength and prevent cracks in the older pavement from "reflecting" through the new surface. This polyester fabric is placed using an oil to hold it and provide some sealing of the pavement. A thin layer of sand is applied to protect the petromat and bind any extra oil.