Mechanical Properties of Warm Mix Asphalt Prepared Using Foamed Asphalt Binders

Final report.PDFTech ReportFHWA/OH-2011/6134476Hot mix paving mixturesWarm mix paving mixturesRuttingTensile strengthFoamed asphaltOhioOhio. Dept. of TransportationAbbas, Ala R.Ali, AymanUniversity of Akron. Dept. of Civil EngineeringOhio. Dept. of Transportation. Innovation, Research, and Implementation SectionUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsUS Transportation CollectionWarm mix asphalt (WMA) is a name given to a group of technologies that have the common purpose of reducing the viscosityof the asphalt binders. This reduction in viscosity offers the advantage of producing asphalt-aggregate mixtures at lower mixingand compaction temperatures, and subsequently reducing energy consumption and pollutant emissions during asphalt mix productionand placement. WMA technologies reduce the asphalt binders\ue2\u20ac\u2122 viscosity through the addition of organic or chemical additivesor by introducing cool water into the heated molten asphalt under controlled temperature and pressure conditions, resulting inso-called foamed asphalt binder. The latter has received increased attention in Ohio since it does not require the use of costlyadditives.In spite of the above-mentioned advantages of WMA mixtures, many concerns have been raised regarding the susceptibilityof this material to moisture-induced damage and permanent deformation due to the reduced mixing and compaction temperaturesused during WMA production. Therefore, this study was conducted to develop a laboratory procedure to produce WMA mixturesprepared 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 thisstudy. A laboratory scale asphalt binder foaming device called WLB10 was used to foam the asphalt binders. The aggregate gradationmet ODOT Construction and Material Specifications (C&MS) requirements for Item 441 Type 1 Surface Course subjected to mediumtraffic. The resistance of WMA-FA and HMA mixtures to moisture-induced damage was measured using AASHTO T 283, and theresistance 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 lowermixing and compaction temperatures.- WMA-FA mixtures are slightly more susceptible to moisture damage than HMA mixtures. However, the difference isstatistically insignificant. Therefore, if designed properly, both mixtures are expected to meet ODOT\ue2\u20ac\u2122s minimum tensile strengthratio (TSR) requirement for the proposed traffic level.- WMA-FA mixtures, especially those prepared using natural gravel and unmodified asphalt binders, are more prone to ruttingthan the corresponding HMA mixtures. However, the effect of the aggregate and binder types was found to be more significantthan the mix type. This result suggests that using appropriate aggregate and binder types can help in overcoming any adverseeffects that WMA-FA have on the mixture performance