Effects of various asphalt binder additives/modifiers on moisture susceptible asphaltic mixtures.

PDFTech ReportFHWA-ICT-14-004ICT-14-004UILU-ENG-2014-2004Asphalt concreteAsphalt mixturesBindersAsphalt additivesAntistrip additivesMoisture damageCalcium hydroxideStyrene butadiene styreneSurface energyTensile strengthLoad testsIllinoisIllinois Center for TransportationAl-Qadi, Imad L.Abuawad, Ibrahim M.Dhasmana, HeenaCoenen, Aaron R.Trepanier, James S.University of Illinois at Urbana-Champaign. Dept. of Civil and Environmental EngineeringIllinois. Dept. of Transportation. Bureau of Materials and Physical ResearchUnited States. Federal Highway AdministrationUS Transportation CollectionMoisture damage of asphalt concrete is defined as the loss of strength and stability caused by the active presence ofmoisture. The most common technique to mitigate moisture damage is using additives or modifiers with the asphalt binder orthe aggregate. Various additives and modifiers are used to enhance the performance of asphalt mixtures. However, some ofthese additives/modifiers may affect the moisture susceptibility of the asphaltic mixtures. The objective of this study was toinvestigate the effect, if any, of various additives and modifiers on the moisture susceptibility of asphalt concrete. Additivesand modifiers included in this study were selected as those most commonly used in Illinois: liquid anti-strip (LAS), styrenebutadiene styrene (SBS), polyphosphoric acid (PPA), and hydrated lime. Two mixtures exhibiting failed tensile strength ratio(TSR) results were selected for testing. Mixture-level lab tests were conducted including modified AASHTO T283 Lottman testwith five freezing and thawing (FT) cycles, the Hamburg wheel tracking test, and a fracture test using semi-circular bending(SCB) specimens. The modified AASHTO T283 Lottman tests showed that LAS and hydrated lime improved moisturedamage control of the asphalt mixes. In the wheel tracking tests, mixes with SBS-modified binder and mixes with hydratedlime provided the least rutting potential. The fracture tests generally showed that mixes with either hydrated lime or LAS hadthe best relative performance. Component-level tests were conducted including the direct adhesion test (DAT) and contactangle test to determine surface free energy (SFE). Results of SFE values and DAT parameters were in agreement with theresults of mixture-level tests: LAS and hydrated lime generally help to mitigate a mixture\ue2\u20ac\u2122s susceptibility to moisture. Full-scaletest sections were built and exposed to accelerated load testing. Although not all full-scale sections met the lab-mix designvolumetrics, the control mix and the mixes with LAS and SBS had similar mixture composition compared with the labpreparedmixes. This study found that LAS and hydrated lime might reduce moisture susceptibility of asphalt mixes. However,PPA may need to be used with another moisture control additive or modifier in order to avoid adverse effects on an asphaltmixture. The study also found that surface free energy values can be used to identify aggregate\ue2\u20ac\u201cbinder compatibility withrespect to moisture damage