Montana Department of Transportation

Malcolm “Mack” Long, Director


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Development of a 3/4-inch Minus Base Course Type A Specification for Montana

development of a 3/4 inch minus base course type a specification location

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.