The research presented in this report was conducted to identify the important factors influencing the water sensitivity of asphalt paving mixtures, and to develop a test method to evaluate water sensitivity of asphalt concrete mixtures for mix design. The test method was to be performance related. A review of current procedures revealed that no single method was suitable for evaluation and related to field performance. Based on a hypothesis that air voids in the mixture may be the major source and cause of water damage, a test system was developed to evaluate the major factors that influence water sensitivity. The Environmental Conditioning System (ECS) was used to develop a test procedure that includes specimen preparation; measurement of permeability using air, water, or both; vacuum wetting; cycling at various temperatures; and continuous repeated loading while monitoring resilient modulus after each conditioning cycle.

This Strategic Highway Research Program study was undertaken to evaluate the hypotheses concerning the influence of binder properties on the moisture susceptibility of asphalt-aggregate mixes. Thirty-two mixes using eight asphalts and four aggregates from the Materials Reference Library were used to fabricate roller-compacted slabs from which specimens were sawed or cored. The mixes were tested by four procedures. Because the water-conditioning and testing procedures were different, it was not appropriate to make direct comparisons of results or to use the results for ranking materials. It was concluded that, for water-sensitivity, asphalts or aggregates could not be ranked alone but that combinations or pairs were more appropriate because of strong interactions.

The research performed for this report was intended to recommend alternative mix design procedures and parameters for evaluation of asphalt mixture sensitivity, with more of an emphasis on volumetric relationships. Three Minnesota Department of Transportation (Mn/DOT) projects were selected to represent the following durability issues: 1) debonding of asphalt form aggregate, 2) cohesion problems, and 3) mix design problems. Materials were obtained from these construction projects and evaluated in the laboratory. Gradations were varied from the project specifications so that mixtures with more and less asphalt were evaluated along with the project mixture. Testing included the temperature susceptibility and moisture sensitivity of the mixtures, in addition to the net adsorption test on the aggregates.

This report provides a brief summary of the processes that led to the selection of performance-related tests to define asphalt-aggregate interactions that result in fatigue, permanent deformation, thermal cracking, aging, and water sensitivity. Inherent in this test selection process was the emphasis on the ability of the tests to measure fundamental material properties that, when incorporated into prediction models, will depend less on empirical correlations than has been traditionally the case. Also included are the results of validation studies for each of the tests and frameworks for the use of the tests in mix design and analysis. Several levels of design are provided for each distress, some of which incorporate reliability concepts.

A primary objective for the Strategic Highway Research Program (SHRP) A-003A contract was to extend and verify the results obtained by other SHRP contractors on the performance-related characteristics of asphalt binders in paving mixes. This report specifically addresses validation of the following: 1) binder properties proposed by the A-002A contractor to predict asphalt-aggregate mix performance in terms of fatigue, permanent deformation, and thermal cracking; and 2) conditioning procedures that produce binder properties representative of those in a pavement immediately after construction and after several years of service. While water sensitivity requirements are not included in the binder specification, validation efforts in the water-sensitivity area are also described. Materials used in the investigation included 8 to 16 asphalt binders and 2 to 4 aggregates obtained from the SHRP Materials Reference Library.