Thermal susceptibility : a new environmental deterioration mechanism for pavements

Abstract

Transverse cracking is a form of environmental deterioration that accounts for the expenditure of some twenty million dollars a year in maintenance in west Texas alone. This form of deterioration has not been predictable by previous mechanisms. A study of the environment in west Texas and installations of psychrometers beneath new construction show that freeze-thaw cycling is a major factor in west Texas, and acts primarily in the base course. The base course undergoes volumetric contraction upon freezing that is an order of magnitude larger than that of the asphaltic concrete. This contraction is related to the specific surface area of the clay mineral portion of the material with models being developed for predictive purposes. A theory of particle structure and reorientation is proposed from the data and from a theoretical interpretation of the Lennard-Jones Model for inter-particle forces. This theory is verified in scanning electron micrographs of base course samples with and without the influence of freeze-thaw cycles. A computer model is developed which uses material properties to predict crack spacing caused by this contraction. The model uses actual climatic data to calculate the rate of crack growth and the change in crack spacing with time. An example is shown for Amarillo and Abilene to illustrate the use of the model.