Search

Moisture damage in asphalt mixtures is defined as the gradual loss of structural integrity caused by the presence of moisture. A simple experimental procedure was developed in this study to measure water vapor diffusion coefficients in coarse aggregates, fine aggregate mixture (blend of the fine portion of the aggregates with the asphalt binder), and hot-mix asphalt. The procedure is based on periodic weight measurements of specimen-container ensembles subjected to a controlled temperature and relative humidity environment. Fick's first law was used to estimate the diffusion coefficients of the materials. The results show that the proposed experimental method is an economic and efficient tool to quantify water vapor diffusion coefficients. Determining these material properties is fundamental to develop numerical models to study the deleterious effects of moisture vapor on the mechanical performance of asphalt mixtures. In order to exemplify the significance of the experimental measurements, a numerical simulation of transient moisture diffusion within the cross section microstructure of an asphalt mixture was conducted. The results of the simulations suggest that diffusion coefficients are fundamental for tracking the potential of a mixture to develop moisture-related degradation processes. Furthermore, it was observed that under the same environmental conditions, moisture damage in an asphalt mixture is highly influenced by the moisture diffusion coefficient of its constitutive phases. DOI: 10.1061/(ASCE)MT.1943-5533.0000059 CE Database subject headings: Water; Diffusion; Coefficients; Asphalt pavements; Aggregates; Finite element method; Simulation. Author keywords: Water; Diffusion; Coefficients; Asphalt pavements; Aggregates; Finite-element method.

This paper evaluates the relationship between the air void distribution in asphalt mixes and their moisture susceptibility. Asphalt mix specimens were prepared to have different air void distributions through using two different gradations, using two different compaction angles in the Superpave gyratory compactor, and trimming the specimens at different locations. An x-ray computed tomography system was used to capture the internal structure of the specimens, and image analysis techniques were used to quantify the air void distribution and connectivity. Specimens in unconditioned (dry) and moisture-conditioned (wet) states were subjected to dynamic loading, and damage was evaluated using a crack growth index based on fracture theory. The parameters required for the crack growth index were obtained from mechanical and surface energy tests. The analysis results clearly demonstrate the influence of air void distribution on moisture susceptibility. Consequently, the analysis method presented in this paper can be used to evaluate alternative mix designs and internal structures, even when the same materials are used, in order to optimize the resistance to moisture damage. DOI: 10.1061/(ASCE)0899-1561 (2007) 19:8(655) CE Database subject headings: Asphalt mixes; Voids; Fracture mechanics; Moisture; Damage assessment; Energy dissipation; Imaging techniques; X rays.

The presence of waIn ter in asphalt pavements deteriorates their condition and causes distresses that result in high maintenance costs to state and federal agencies. The objective of this research was to execute dynamic and relaxation tests and evaluate their effectiveness in assessing moisture susceptibility of asphalt mixture specimens with different air void structures determined using X-ray computed tomography (CT) and conditioned using the modified Lottman procedure. The dynamic test consisted of the application of a sinusoidal cyclic compressive load on the specimen while maintaining the strain within a specified range. The relaxation test, performed in both direct tension and compression, consisted of the application of a constant static strain. A statistical analysis was used to study the effectiveness of the tests in evaluating the moisture susceptibility of the asphalt mixtures. The results showed that none of the tests (dynamic or relaxation) were consistent in differentiating between the moisture conditioned and unconditioned specimens or between the responses of the different mixtures within each condition. In addition, the results of the dynamic and relaxation tests were compared after applying different methods to convert frequency-domain data to time-domain data. [ABSTRACT FROM AUTHOR]