Double Chip Seal
Chip seal resurfacing is the application of crushed rock (gravel) over emulsified asphalt oil, PMCRS-2. The oil seals the pavement from water penetration while the gravel provides a wearing surface to protect the oil seal from traffic. Sunnyvale uses a "double chip seal" technique. After the first layer of oil and gravel (3/8” gravel) is applied, rollers are used to set the gravel and seal it in the oil. Then, a second application of oil and gravel (1/4” gravel) is applied and compacted. The final layer is an oil seal, CRO, to seal and bind the gravel together which prevents raveling. Approximately two hours after the final oil seal, the street is rolled one last time, then sand is applied to remove the tackiness. The street is then opened to traffic. The following day a street sweeper picks up any excess sand or gravel. A second 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 currently $.45 per square foot and should last between five to seven years.
Slurry seal is a mixture of aggregate (sand) with emulsified asphalt oil. This mixture is prepared in a specially equipped slurry seal truck then spread on the pavement and allowed to cure. The cost of a slurry seal is currently $.11 per square foot and lasts approximately five years.
Together with chip seal, the slurry sealed streets can last 10 – 15 years and are a combined cost of $.60 per square foot.
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 $2.50 per square foot and should last 15-20 years.
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.