Abstract
Chisago County, Minnesota, has a limited budget and many miles of gravel roads that need increasing expenditures to maintain their current condition. Paving would greatly increase the value of this infrastructure to road owner and road users. However, conventional design and construction methods are too expensive or do not give the needed performance. A team of the county engineer, consultants, a supplier, and a contractor developed a cost-effective method for upgrading Chisago's granular material roads and reducing maintenance costs. The existing gravel road is analyzed and sampled. An emulsion-stabilized base mix is designed with performance-related techniques adapted for emulsion mixes. Structural design is performed with traffic, soil, and falling weight deflectometer data. The gravel is mixed with an asphalt emulsion formulated for optimal coating and curing as well as the desired strength and resistance to thermal cracking. After construction, the newly stabilized base is overlaid with a thin, specially engineered surface mixture or sealed with a chip seal to protect the base from moisture and to improve surface texture. Stabilizing a granular base strengthens it and makes it more consistent. A project using this method was constructed in 2001, followed by nine projects in 2002. The initial project described in this study showed a 40% improvement in granular equivalency of the base. The result was a new, engineered system for a strong but flexible bituminous base and surface, ready for future staged construction when warranted. The design procedure, construction, laboratory test results, costs, and field performance measurements, including structural calculations, are discussed.
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