Minnesota’s Experience with Thin Bituminous Treatments for Low-Volume Roads

Abstract

Three surface treatments placed on aggregate-surfaced roads (doublechip seal, Otta seal, and oil gravel) were investigated through field trials for performance. A double-chip seal used a single-size aggregate applied to a layer of hot asphalt binder. After 6 years of service, the performance of the road has required only routine preventive maintenance. The surface has a few thermal cracks and no rutting. An Otta seal, which uses a thick layer of soft asphalt to which a dense graded aggregate is added, has proven successful. The use of a chip spreader is recommended for precise aggregate application during construction. A large top-size aggregate, 1 in. (25 mm) minus, gave a rough texture to the surface, but the performance has not been adversely affected. Because of the fines included in an Otta seal, usually a locally available aggregate can be used. In design and construction, the oil gravel surface is similar to hot-mix asphalt. All the projects had some problems with segregation, but most can be corrected during construction with proper handling techniques. One benefit of this treatment is that additional material stockpiled during construction can be used in subsequent maintenance activities on the road. All three of the surface treatments require a strong stable base to work properly. The treatments add no structural component to the road. Therefore, the condition of the road needs to be carefully evaluated before construction. The roads that performed the best had the best base stability.