Approximately 50% of the washington state highway system, 3, 500 center line miles, has a bituminous surface treatment (bst) surface. The use of bst is coincident with that portion of the state system with traffic volumes of 2, 000 adt orless. Recent specification changes such as increasing emulsion yields, decreasing aggregate yields, reducing the allowable time between placement of emulsion and aggregate, and early brooming, along with central office involvement in the bst process have positively affected the quality of the washington state department of transportation's chip seals. However, some of the chip seals constructed in western washington in 1988 generated adverse publicity because of dust, traffic delays, and windshield damage. This study recaps the recent specification and construction procedure changes, looks into the details of nine recently completed chip seal projects in western washington, and also supports the following recommendations, among others: use of polymerized emulsions in western washington, strong central office support and review of the bst program, use of maintenance people with strong working bst experience as chip seal inspectors, use of finer chips in areas of heavy bicycle traffic to provide a smoother, more uniform surface, and early season completion of bst work. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Abstract