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Mechanical Properties of Warm Mix Asphalt Prepared Using Foamed Asphalt Binders
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    Final report.
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    Warm mix asphalt (WMA) is a name given to a group of technologies that have the common purpose of reducing the viscosity of the asphalt binders. This reduction in viscosity offers the advantage of producing asphalt-aggregate mixtures at lower mixing and compaction temperatures, and subsequently reducing energy consumption and pollutant emissions during asphalt mix production and placement. WMA technologies reduce the asphalt binders’ viscosity through the addition of organic or chemical additives or by introducing cool water into the heated molten asphalt under controlled temperature and pressure conditions, resulting in so-called foamed asphalt binder. The latter has received increased attention in Ohio since it does not require the use of costly additives. In spite of the above-mentioned advantages of WMA mixtures, many concerns have been raised regarding the susceptibility of this material to moisture-induced damage and permanent deformation due to the reduced mixing and compaction temperatures used during WMA production. Therefore, this study was conducted to develop a laboratory procedure to produce WMA mixtures prepared using foamed asphalt binders (WMA-FA), and to evaluate their performance in comparison to conventional hot mix asphalt (HMA). Two aggregates (natural gravel and crushed limestone) and two asphalt binders (PG 64-22 and PG 70-22M) were used in this study. A laboratory scale asphalt binder foaming device called WLB10 was used to foam the asphalt binders. The aggregate gradation met ODOT Construction and Material Specifications (C&MS) requirements for Item 441 Type 1 Surface Course subjected to medium traffic. The resistance of WMA-FA and HMA mixtures to moisture-induced damage was measured using AASHTO T 283, and the resistance to permanent deformation was measured using the Asphalt Pavement Analyzer (APA) and the Simple Performance Test (SPT). Based on the experimental test results and the subsequent analyses findings, the following conclusions were made: WMA-FA mixtures are more workable and easily compacted than HMA mixtures even though they are produced at lower mixing and compaction temperatures; WMA-FA mixtures are slightly more susceptible to moisture damage than HMA mixtures. However, the difference is statistically insignificant. Therefore, if designed properly, both mixtures are expected to meet ODOT’s minimum tensile strength ratio (TSR) requirement for the proposed traffic level; and, WMA-FA mixtures, especially those prepared using natural gravel and unmodified asphalt binders, are more prone to rutting than the corresponding HMA mixtures. However, the effect of the aggregate and binder types was found to be more significant than the mix type. This result suggests that using appropriate aggregate and binder types can help in overcoming any adverse effects that WMA-FA have on the mixture performance.
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