LABORATORY TEST METHODS FOR PREDICTING MOISTURE-INDUCED DAMAGE TO ASPHALT CONCRETE

A laboratory test method is described for the prediction of moisture damage in dense-graded asphalt concrete mixtures. The method consists of obtaining diametral (or indirect) tensile-strength and modulus ratios of compacted specimens subjected to vacuum saturation with water and to freeze-plus-warm-water-soak accelerated moisture conditioning. Test results for dry specimens are used to form the ratio bases. The ratios are used to predict short-term and long-term field damage. Fatigue curves for two mixtures exposed to the dry, vacuum-saturation, and accelerated moisture conditioning of the test method are presented to show effects of moisture on fatigue life. A tentative relationship shows a correlation between tensile-strength ratios obtained by the test method and pavement fatigue-life ratios. An example of the practical use of the correlation is shown. Results are presented from a five-year field evaluation study conducted by seven highway agencies on eight pavement test sections to determine whether the test method's predictive ratios and stripping tendencies correlate with field results. Short-term ratios from laboratory vacuum saturation were reached at four years of pavement age or before. Long-term ratios from laboratory accelerated moisture conditioning ranged from 0 to 0.80; they were reached at five years for some pavements and probably will be reached in a few more years for the other pavements. This ratio is considered one of maximum moisture damage to minimum moisture damage. Visual stripping in the field cores appears similar to the predicted laboratory stripping. Agency-determined layer coefficients decreased due to the loss of moisture cohesion from the associated stripping observed in the field. (Author)