United States Department of Transportation
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Development of a 3/4-Inch Minus Base Course Type a Specification for Montana: Final Report
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2016-12-01
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By Cuello, Eli
[PDF-9.97 MB]
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Alternative Title:Development of a 3/4-inch minus base course type a specification for Montana.
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TRIS Online Accession Number:1624686
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Abstract:Gravel bases are a critical component of roads, providing drainage, structural support, and load distribution within the pavement structure. Montana specifications currently exist for a 2-inch minus (Grade 5A) and 1½- inch minus (Grade 6A) crushed base course; however, gravel sources in parts of Montana are becoming limited, making the option to use a ¾-inch gravel base desirable. The objective of this project was to develop a standard specification for a new gravel base course with nominal maximum aggregate size of ¾ in. This was accomplished by conducting a review of current ¾-inch minus specifications from around the U.S., using that information to generate a preliminary specification to create ¾-inch minus mixes, testing the material properties of these mixes, and modifying these mixes to determine the effect changes in the gradation primarily had on its strength, stiffness and permeability. Based on the results of multiple statistical evaluations as well as qualitative comparisons, it was concluded that a ¾-inch minus gradation specification will perform at least as well as Montana’s existing CBC-6A materials and better than CBC-5A materials. Gradation limits for a new ¾-inch minus, Grade 7A, crushed base course were suggested; however, the practicality of producing mixes that fit within the suggested gradation limits still needs to be determined.
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