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.

It has been extensively documented since the late 1970's that moisture damage occurs in hot mix asphalt (HMA) pavements. A variety of test methods are available that test an HMA's ability to resist moisture sensitivity. There are also some test methods that look at an asphalt binder's moisture susceptibility. The current test method for detecting moisture sensitivity in HMA is American Association of State Highway and Transportation Officials (AASHTO) T283: Resistance of Compacted Bituminous Mixture to Moisture-Induced Damage. Inclusion of this test method in Superpave did not consider the change in specimen size from 100mm to 150mm nor difference in compaction method. The procedures in AASHTO T283 consider the loss of strength due to freeze/thaw cycling and the effects of moisture existing in specimens compared to unconditional specimens. However, mixtures do not experience such a pure phenomenon. Pavements undergo cycling of environmental conditions, but when moisture is present, there is repeated hydraulic loading with the development of pore pressure in mixtures. Thus, AASHTO T283 does not consider the effect of pore pressure, but rather considers a single load effect on environmentally conditioned specimens. This report develops moisture susceptibility procedures which would utilize repeated loading test devices (dynamic modulus or asphalt pavement analyzer) of specimens in saturated conditions and be compared to unconditioned specimens in a dry test environment. In addition to HMA mixture testing, a modified dynamic shear rheometer will be used to determine if an asphalt binder or mastic is moisture susceptible. Moisture susceptible criteria was developed using the dynamic complex modulus, asphalt pavement analyzer, and dynamic shear rheometer. Evaluation of AASHTO T283 for 150mm Superpave Gyrtaory compacted specimens is also detailed in this report along with a new criterion.

Explores whether combining the environmental conditioning system with the simple performance test would provide a superior procedure for determining the moisture susceptibility of hot-mix asphalt (HMA).

Moisture damage is one of the major causes of premature failure in asphalt pavements, and it also accelerates the severity of other distresses. To date, no moisture test has been widely accepted that is reliable and practical in predicting the field moisture performance of the asphalt mix during the design stage. One reason is because the sample conditioning methods cannot represent the field conditions, resulting in inconsistent results with the field performance of some mixtures. Taken into account this concern, this paper investigates how different testing conditions, including sample preparation, moisture saturation, and loading methods, can affect the results of laboratory moisture tests. In conclusion, it is found that the degree of vacuum pressure for achieving moisture saturation and air voids distribution has a significant impact on the moisture testing results. Multiple freeze-thaw cycles have a limited effect on the variation of mechanical performance (i.e., compressive dynamic modulus). If one or several freeze-thaw cycles are to be used in a moisture test, the effect of aging should be considered. It is recommended that a sample without coring and cutting should be used for a moisture test as the coring and cutting process is found to change the air voids distribution, i.e., the percent of connected air voids, thus making the sample not representative to the field condition. Finally, the moisture test results are more sensitive under tension mode than under compression mode.