PERMEABILITY, VOID CONTENT, AND DURABILITY OF BITUMINOUS CONCRETE

THE USUAL PRACTICE IN BITUMINOUS MIXTURE DESIGN IS TO HAVE STATED VOID LIMITS IN AN EFFORT TO CONTROL DURABILITY. IT IS HYPOTHESIZED THAT SINCE PERMEABILITY MEASURES THE ABILITY OF THE MIXTURE TO TRANSMIT DETERIORATING FLUIDS IT MAY BE A BETTER CRITERIA OF DURABILITY THAN ARE VOID RELATIONSHIPS. SOME PERMEABILITY TESTS WERE RUN USING COMPRESSED AIR AND OTHERS USING WATER AS THE FLUID MEDIUM. THE DESIGN OF EQUIPMENT AND TEST METHODS ARE DESCRIBED. SAND ASPHALT AND ASPHALTIC CONCRETE MIXTURES WERE TESTED. CYLINDRICAL SPECIMENS WERE PREPARED FOR PERMEABILITY TESTS AND BEAMS FOR FREEZING AND THAWING. BEAM DETERIORATION WAS CHECKED PERIODICALLY BY DETERMINATION OF SONIC MODULUS OF ELASTICITY. SONIC TESTS WERE CONDUCTED AT 40 DEGREES F. A CONSTANT POISSON'S RATIO OF 0.4 WAS ASSUMED FOR ALL TESTS. LOSS IN SONIC MODULUS, EXPRESSED AS A PERCENT OF ORIGINAL IS CONSIDERED AN EXPRESSION OF DURABILITY. THE RELATIONSHIPS DETERMINED BETWEEN VOIDS AND PERMEABILITY IS SIMILAR TO THAT FOR SOILS. THE RELATIONSHIP IS INFLUENCED BY AGGREGATE GRADATIONS, COMPOSITION, AND AMOUNT OF ASPHALT IN THE MIXTURE. THERE IS NO GENERAL RELATIONSHIP BETWEEN PERMEABILITY AND DURABILITY AS MEASURED BY PERCENT LOSS IN SONIC MODULUS CAUSED BY LABORATORY FREEZING AND THAWING. FILM THICKNESS, AS WELL AS GRADING, INFLUENCES DURABILITY.