This synthesis will be of interest to pavement designers, construction engineers, maintenance engineers, and others interested in avoiding or limiting moisture damage in asphalt concrete. Information is provided on physical and chemical explanations for moisture damage in asphalt concrete, along with a discussion of current practices and test methods for determining or reducing the susceptibility of various asphalt concrete components and mixtures to such damage. Moisture damage in asphalt concrete is a nationwide problem which often necessitates premature replacement of highway pavement surfaces. This report of the Transportation Research Board describes the underlying physical and chemical phenomena responsible for such damage. Current test methods used to determine the susceptibility of asphalt concretes, or their constituents, to moisture damage are described and evaluated. Additionally, current practices for minimizing the potential for moisture damage are examined.

The actual moisture susceptibility of 10 bituminous mixtures placed in the field was compared to the moisture susceptibility that was predicted during the laboratory evaluation of the same mix design. Laboratory mixtures were evaluated using the modified Lottman procedure and the Root-Tunnicliff procedure, in addition to routine moisture susceptibility testing which includes immersion compression testing. After two years, cores were taken from the field projects. The condition of the cores and their present susceptibility to moisture damage were determined by performing modified Lottman and Root-Tunnicliff testing. A feature of the evaluation process was the use of the ACMODAS program to predict the remaining service life of the plant mix cores.

The Virginia Department of Highways and Transportation is one of seven state and federal agencies participating in a field evaluation of a stripping test method developed under NCHRP Project 4-8(3), "Predicting Moisture-lnduced Damage to Asphaltic Concrete". In the Virginia portion of this field phase of the project, an evaluation is being made of the effectiveness of the method in predicting the degree of stripping that will occur on a 950-ft. (290-m) test section constructed with an asphaltic concrete believed to have a tendency to strip. The test method was used on specimens prepared in the laboratory and on cores taken immediately after construction of the test section in an attempt to predict the stripping susceptibility of the mix. On the basis of the results of those tests it was predicted that stripping would occur over a long period. Tests on cores being taken periodically show decreasing strength values that probably are a result of progressive stripping, that was very evident in cores taken at 22 months.