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Permeability of Granular Materials, and Blended Salvaged Granular Materials

The Department does not currently have a clear understanding of how drainable a granular base material needs to be in a roadway section to optimize long-term pavement performance. Furthermore, the Department does not fully understand how permeable the virgin granular materials used on projects are with our dense-graded material granular base sections. There is also a lack of understanding of how permeability is affected by adding salvaged granular material once it has been blended into the virgin base course, gravel cushion, or salvaged granular material. Based on the previous research project SD97-03 completed by the Department, our current practice is to blend Recycled Asphalt Pavement (RAP) into virgin granular material with a blend ratio of no more than 50% RAP. Recycled Concrete Aggregate (RCA) can be used in lieu of virgin aggregates if it meets the specified gradation for the aggregate for which it replaces. The expectation with this practice is that both materials (virgin and blended) will have similar drainage characteristics. With a better understanding of the drainage characteristics of RAP produced by various methods (process-in-place, cold-milling, micro-milling, and crushing) and RCA, the Department could better optimize the use of reclaimed materials in roadway sections and be assured that proper drainage has been achieved in the design in the most cost-effective manner possible. Currently, that clear understanding is missing from our granular base material designs and this research opportunity could provide that clarity and assure that the best use of tax-payer funds is being utilized.