The use of additives to improve the performance of asphalt cement and asphalt concrete mixtures has increased in recent years. Polymeric additives have been proposed as a potential source of specific improvements to asphalt cements. The major use has been in surface dressings; work in asphalt concrete has only recently been conducted.Presented in this paper are the results of a comprehensive series of laboratory tests on a series of polymer additives to establish test data that can serve as performance indicators for the mixes. Five polymer blends were manufactured from a base AC-5 asphalt cement. Three standard grades of asphalt cement, the base AC-5, and AC-10, andan AC-20, were used for control. A crushed limestone was used to prepare dense-graded mixtures that met the Illinois Interstate overlaymixture criteria. Testing included the diametral resilient modulus test at three temperature levels, indirect tensile testing at temperatures ranging from 72 deg F to -20 deg F, permanent deformation testing at 72 deg F and 100 deg F, and Lottman moisture susceptibility testing. The testing indicated that the polymer additives reduced stiffness at low temperatures yet maintained adequate stiffness at elevated temperatures. Low-temperature performance was greatly improvedover that of untreated asphalt cements of all grades. The permanentdeformation characteristics were greatly improved at elevated temperatures. No moisture sensitivity was noted in any of the samples. In general, the polymeric additives improved the base asphalt characteristics to those of the next stiffer grade at normal temperatures; made them better than the base asphalt at low temperatures; and madethem better than an AC-20, two grades stiffer than the base asphalt, at elevated temperatures. Long-term fatigue characteristics will require further testing before the influence of the modifiers can be evaluated.(A).
Abstract