Moisture is often the major factor associated with the deterioration of asphaltic concrete pavements. The most serious consequence of the adverse action of moisture is the loss of adhesion between the aggregate and asphalt cement, commonly called "stripping," resulting in substantial reduction in the tensile strength of the asphaltic concrete paving material. Because the asphalt-aggregate adhesion properties of mixtures are very complex, many tests that have been used to evaluate these properties have involved visual inspection of mixtures in the presence of water. NCHRP Reports 192 and 246 describe the development and verification of an empirical test procedure for predicting the performance of pavements built with specific asphalt-aggregate mixtures. The next needs, and the objectives of the research described in this report, are (1) the further development of procedures for predicting the effectiveness of antistripping additives used in asphaltic concrete paving mixtures and (2) the preparation of guidelines for incorporating antistripping additives in asphaltic concrete paving mixtures during construction. To accomplish the objectives, the research team of David G. Tunnicliff, Consulting Engineer, Chicago Testing Laboratory, Inc., and Richard E. Root, Vice President, first conducted a survey of state highway and other agencies to determine the extent of asphalt stripping problems, current use and experience with antistripping additives, and practices with regard to testing of asphalt-aggregate to determine the need for and effectiveness of antistripping additives. Stripping problems were found to be widespread and influenced by a large number of factors. Antistripping additives are being used extensively even though no generally accepted procedure appears to be available to evaluate or predict their effectiveness. In response to this need, the laboratory test procedure described in NCHRP Reports 192 and 246 was modified for use as an empirical procedure for evaluating the effectiveness of antistripping additives and used in an experimental program to provide limited verification. The test procedure is suitable for use on a trial basis for evaluating specific antistripping additive-aggregate asphalt combinations. A field evaluation phase of the research was begun in 1984 and is due to be completed in 1987. Test sections with and without antistripping additives will be included in regular asphaltic concrete paving projects in six states. Laboratory tests using the procedure described in this report will be conducted using the actual aggregates, asphalts, and additives from the construction projects to predict pavement performance; the pavements will be tested over a 2-year period to compare actual performance with the predictions. It is anticipated that further observations of the test sections will be made following completion of the field study phase of the project.
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