Moisture Susceptibility Of Dense Graded Asphalt Concrete Using Cyclic Moistue Induced Stress Tester

Moisture damage in asphalt concrete causes loss in mechanical properties of asphalt material due to the presence of moisture in its microstructures in a liquid or a vapor state. Some of the common types of distress observed in asphalt pavements due to moisture damage are stripping (separation of asphalt binder and aggregate), raveling (dislodgement of aggregate particles in asphalt mixture from surface), and hydraulic scour (a process that occurs on a saturated surface by which the pavement material is eroded due to dynamic action of tires in the presence of water). This Thesis focuses on the research on the effects of such moisture in dense graded HMA samples using an accelerated moisture conditioning technique in the laboratory. The laboratory work consisted of preparation of samples from a HMA mixture type commonly used by the Texas Department of Transportation. The samples were conditioned for moisture in a Moisture Induced Stress Tester (MIST) machine which applies repeated water pressure on samples to simulate a repeated traffic load on a moisture intruded pavement layer. Dynamic Modulus Test of the samples following AASHTO - TP 62-03 and Indirect Tensile Test following Tex-226-F were carried out both before and after moisture conditioning in MIST to see the changes in stiffness parameters. Different levels of such moisture conditioning were correlated with the Dynamic Modulus and Indirect Tensile strength of asphalt samples. Results showed that moisture causes reduction in stiffness properties with high variability, which was backed up by statistical analysis. Test results were used as inputs and simulated in KENLAYER program which showed that the fatigue failure is more significant in higher frequencies and lower temperatures while the rutting basically increased after moisture conditioning