The interaction between bitumen and aggregate is a primary determinant of asphalt mixture strength; not only is adhesion between bitumen and aggregate related to the aggregate, but it is also a bitumen property. Three different kinds of test methods are used to evaluate the bitumen aggregate bond: the water immersion test, the electro-optic colorimerty test, and the net adsorption test. Retained Marshall stability and modified Lottman test methods are used to evaluate the moisture damage to asphalt mixtures. The paper analyzes relationships between bitumen acid number and asphalt aggregate mixture performance. The results show that aggregate type has a dominant influence on the bitumen aggregate bond, but bitumen type also has an important influence on asphalt mixture performance. When the bitumen acid number is higher, the asphalt mixture is more resistant to moisture damage. The net adsorption test is a better method to evaluate the bitumen aggregate bond; the bitumen acid number can be used to evaluate moisture susceptibility with different bitumens.

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.