INFLUENCE OF LOCAL FACTORS ON THE CALCULATION OF THE THICKNESSES OF FLEXIBLE PAVEMENTS

THE AUTHORS RECALL THE TWO MAIN CHARACTERISTICS OF VISCOELASTIC BITUMINOUS MIXTURES: THEIR MODULUS OF RIGIDITY AND THEIR ULTIMATE STRENGTH. FOR A LONG TIME, RIGIDITY VALUES FOR COLD-COATED MATERIALS WERE AVAILABLE, BUT ONLY RECENTLY WERE THE SAME VALUES OBTAINED FOR HOT-COATED MATERIALS. THESE RESULTS WERE OBTAINED BY USING A CREEP TEST DEVELOPED RECENTLY (UNI-AXIAL COMPRESSION TEST WITH CONSTANT LOAD ON A FREE SPECIMEN). DETAILS ARE GIVEN OF THESE INVESTIGATIONS, RESULT INTERPRETATION AND THE PRACTICAL SIGNIFICANCE OF THESE RESULTS. AS REGARDS STRENGTH, THE BEHAVIOUR OF BITUMINOUS MIXTURES UNDER REPETITIVE LOADING IS OF PARTICULAR INTEREST AND WAS STUDIED IN DETAIL IN THE LABORATORY IN FATIGUE TESTS. AN IMPORTANT DIFFICULTY EXISTS IN THE FACT THAT THERE IS NO CORRELATION BETWEEN LABORATORY TESTS AND IN-SITU CRACKING IN EXISTING PAVEMENTS. SOME RESULTS ARE GIVEN OF MEASUREMENTS OF THE ENERGY DISSIPATED DURING REPEATED STRESS APPLICATION AND LABORATORY TESTS IN WHICH LOADED WHEELS WERE USED. THESE RESULTS SHOULD HELP TO REMEDY THE LACK OF KNOWLEDGE ON CORRELATION. THE APPLICATION OF THESE BASIC STUDIES TO THE EVALUATION OF BITUMINOUS MIXTURES IS DISCUSSED TOGETHER WITH A RATIONAL MIX-DESIGN METHOD. ANALYTICAL METHODS ARE BECOMING MORE ACCURATE; BASED ON THE ELASTIC THEORY THEY HELP TO REDUCE THE COSTS OF FLEXIBLE PAVEMENTS. IT IS NOW POSSIBLE TO DERIVE CALCULATION CHARTS WHICH TAKE INTO ACCOUNT THE PROPERTIES OF BITUMINOUS MIXTURES AS A FUNCTION OF THE TEMPERATURE, AS A FOLLOW-UP OF THE STUDIES OF RIGIDITY MENTIONED ABOVE. OTHER CHARTS CAN ALSO BE ESTABLISHED, THAT PERMIT THE COMPARISON OF THE ECONOMIC ADVANTAGES OF HIGH QUALITY CONVENTIONAL MIXTURES WITH LOWER-PRICE MIXTURES PREPARED WITH LOCAL MATERIALS. MIX DESIGN FORMULAE AND THE INFLUENCE OF THE PERFORMANCE OF VARIOUS THICKNESSES FACILITATE THE SELECTION OF PAVEMENT STRUCTURES BEST ADAPTED TO LOCAL CONDITIONS. FOR THE COVERING ABSTRACT, SEE IRRD ABSTRACT NO. 104729.