DAMAGE FUNCTIONS FOR RUTTING, FATIGUE CRACKING, AND LOSS OF SERVICEABILITY IN FLEXIBLE PAVEMENTS

Damage functions are required for development of load equivalence factors to be used in allocating cost responsibilities to various vehicle classes for use of highways. They are also required by pavement management systems for prediction of pavement damage or deterioration. The only damage function and set of load equivalence factors available have been those for loss of serviceability derived from the AASHO Road Test. This work is 20 years old and resulted from accelerated testing in one environment and essentially for one subgrade, so new damage functions over the range of distresses significant to deterioration of flexible pavements were needed by FHWA to respond to a Congressional mandate for new cost-allocation recommendations. Damage functions for rutting and fatigue cracking and a new damage function for loss of serviceability are provided. These damage functions resulted from multiple regressions on 216 separate sets of predicted distresses for each of four enviornmental zones. The predictions were obtained with an improved version of the VESYS flexible pavement model calibrated through comparisons with measured values from 15 test sections throughout the United States. Damage predictions from the regression equations are also compared with the damage measured on 15 test sections representing a range of environmental, support, thickness design, and traffic conditions.