Moisture susceptibility of asphalt concrete (ac) mixtures is identified by performing laboratory tests on dry- and wet-accelerated conditioned specimens. Excessive moisture susceptibility is associated with low ratios of wet-to-dry mechanical properties. Highway agencies use values of cutoff wet-to-dry ratios for resilient modulus andfor indirect tensile strength as specifications. Mixtures having wet-to-dry ratios lower than the cutoff ratios have excessive moisturesusceptibility and require treatment before paving. Currently, mosthighway agencies apply either a resilient modulus cutoff ratio of 0.70 Or an indirect tensile strength cutoff ratio of 0.75. The university of idaho ac moisture damage analysis system (acmodas) programs on field performance are applied to predict cutoff ratios, compare predicted cutoff ratios to currently used ratios, classify ac mixturemoisture susceptibility, and recommend cutoff ratios to be used in practice. Two cutoff ratios are necessary to control moisture susceptibility both for fatigue cracking and for wheelpath rutting field distresses. These cutoff ratios are 0.80 For resilient modulus and 0.85 For indirect tensile strength, and both should be applied simultaneously. (Simultaneous application of the (lower) currently used cutoff ratios may only control fatigue cracking.) Applying individual cutoff ratio values to each material, about 25% of mixtures, which cannot be treated by conventional additives or other means to obtain desired fatigue cracking performance because of water-induced brittleness, have cutoff ratios greater than 1. However, the other mixturescan be treated, if need be, to obtain desired performance; their cutoff ratios are less than 1. Identification of these mixtures is discussed. This paper appears in transportation research record no. 1269, Asphalt mix materials and mixtures 1990.
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