Asphalt Mixture Design and Performance Properties by Using a Gyratory Compactor
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2020-02-01
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Abstract:TDOT is currently using the Marshall mix design method for designing asphalt mixtures. However, the Marshall method does not allow for designing larger stone mixes and it hinders the technical information exchange and communication among DOTs. To compare the Marshall and Superpave mix design methods and recommend an improved mix design method for TDOT, a wide range of TDOT typical asphalt mixtures were collected, designed and evaluated in this study. The plant mixtures resulted in a high variation of the results of the equivalent Ndesign. The range of equivalent Ndesign for mixtures compacted in 150-mm mold was from 38 to 77 gyrations and from 32 to 86 gyrations for mixture compacted in 100-mm mold. For BM-2 mixtures the range of Ndesign was from 39 to 75 gyrations for 150-mm mold, and from 42 to 73 gyrations for 100-mm mold. Therefore, it was necessary to repeat the process using laboratory mixtures. For laboratory mixtures, the Ndesign was defined based on the nine well-performing mixtures provided by TDOT. The results of back calculations showed that for BM2 mixes the range of equivalent Ndesign was from 71 to 75 gyrations (average 73 gyrations), while for D mixtures the range was from 64 to 72 gyrations (average 68 gyrations) by using 150-mm mold. Additionally, the concept of the locking point was investigated and a new method of determining the impact locking point was developed. This study will help TDOT keep the positive aspects of both mix design methods and take advantage of technical advancement, while a statewide campaign is necessary for the implementation of new mix design.
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