This study was initiated to investigate some potential benefitsof polymer modification on dense-graded, heavy- duty pavementmixtures, The following polymers were used to modify asphalt bindersand mixtures: an ethyl vinyl acetate (EVA), a low-density polyethylene(LDPE), a styrene butadiene styrene (SBS), an hydrogenated SBS,and a finely ground tire rubber. Each of the polymers was blendedwith one or more of the following asphalt cements: an AC-10 andthree sources of AC-20. Both conventional and recently-developedtest methods were performed on the binders and mixtures to studythe effects of the polymer modifiers at both low temperaturesand high temperatures. Standard Marshall mixture design proceduresdid not optimize the mixtures containing tire rubber and dense-gradedcrushed limestone. The effect of polymers on low-temperature propertieswas dependent on the modifier/polymer combination. Ground tirerubber was particularly effective at these low temperatures. Thehigh-temperature performance of an AC-20 mixture, produced withcrushed gravel, was improved by modification with an SBS.