PREDICTING LOW-TEMPERATURE CRACKING FREQUENCY OF ASPHALT CONCRETE PAVEMENTS

LOW-TEMPERATURE SHRINKAGE CRACKING OF ASPHALT PAVEMENTS IS A SERIOUS AND COSTLY PROBLEM THROUGHOUT MUCH OF CANADA AND THE NORTHERN UNITED STATES. THE LARGE AMOUNT OF EFFORT DEVOTED TO THE PROBLEM HAS PROVIDED SEVERAL DESIGN APPROACHES. THIS PAPER DESCRIBES THE LATEST AND MOST COMPREHENSIVE OF SUCH A DESIGN APPROACH. A MATHEMATICAL MODEL BASED ON FIELD OBSERVATIONS HAS BEEN DEVELOPED AND IS CAPABLE OF PREDICTING THE FREQUENCY OF CRACKING AT VARIOUS AGES IN THE PAVEMENT LIFE. THE VARIABLES USED INVOLVE STIFFNESS OF THE ORIGINAL ASPHALT CEMENT, WINTER DESIGN TEMPERATURE, SUBGRADE SOIL TYPE, THICKNESS OF THE ASPHALT CONCRETE, AND AGE OF THE PAVEMENT. DATA FOR THE VARIABLES ARE COMMONLY RECORDED BY HIGHWAY AGENCIES. THE MODEL PROVIDES A VERY POWERFUL DESIGN APPROACH IN THAT SERVICEABILITY LOSSES AND MAINTENANCE COSTS ARE DIRECTLY RELATED TO DEGREE OF CRACKING. IF THESE ARE INTOLERABLE, NEW DESIGNS CAN BE GENERATED AND VERY QUICKLY AND EASILY TESTED BY THE MODEL. THE PAPER PROVIDES A NUMERICAL EXAMPLE, INCLUDING A NOMOGRAPH FOR SOLVING THE MODEL. THE MODEL IS "REASONABLE" IN ITS USE OF THE VARIABLES, AND THE DEGREE OF ERROR INVOLVED IS ACCEPTABLE.