Investigation of Asphalt Content Design for Open-Graded Bituminous Mixes

About the report:

Several design procedures associated with determining the proper asphalt content for open-graded bituminous mixes were investigated. Also considered was the proper amount of tack coat that should be placed on the old surface prior to paving operations. The design procedures obtained from other highway agencies were evaluated in the laboratory for their prospective usefulness to the Virginia Department of Highways. Based on the laboratory tests and evaluation of field test sections the following conclusions were obtained. 1. The maximum mixing temperature should be determined in order to avoid separation of asphalt and aggregate, which may cause flushed spots in the finished surface. 2.The EOA determination for asphalt content may be useful until experience is gained. 3. Fabrication and visual observation of Marshall type specimens may be useful: (a) in identifying mixes that over-densify under heavy traffic and (b) in indicating the proper asphalt content. 4. The "optimum fine aggregate determination" does not appear particularly useful in Virginia. It is recommended that the amount of tack be determined by the condition of the existing pavement surface.

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