LIMITS FOR THE DETERMINATION OF MATERIAL PARAMETERS FOR THE DESIGN OF BITUMEN STABILISED PAVEMENT LAYERS

MANY TYPES OF PAVEMENT CONSTRUCTION EXHIBIT EITHER INADEQUATE RIDING COMFORT OR TOO SHORT A SERVICE LIFE. THERE STILL IS INADEQUATE KNOWLEDGE CONCERNING THE LOAD CARRYING BEHAVIOUR AND THE ENGINEERING DESIGN OF PAVEMENTS. THE AUTHOR DISCUSSES THEORETICAL MODELS AND BASES OF CALCULATION WHICH HAVE BEEN DEVELOPED IN VARIOUS COUNTRIES TO ESTABLISH THEORETICAL FUNDAMENTALS, ALTHOUGH THERE IS STILL A DIVERGENCE OF OPINION CONCERNING THE CORRECTNESS OF THE ASSUMPTIONS AND BOUNDARY CONDITIONS. SO FOR INSTANCE THE DESIGN SHOULD BE BASED ON THE BEHAVIOUR AT LOW TEMPERATURES AND FOR SHORT DURATION OF LOADING SO THAT THE ELASTIC THEORY CAN BE USED. THE TEST PROCEDURES APPLICABLE TO BITUMEN CONCRETE IN THE GDR (STANDARD TGL 20801) WITH RESPECT TO CUBE CRUSHING AND TENSILE BENDING STRENGTH, INDENTATION TEST AND MARSHALL STABILITY ARE INADEQUATE FOR DESIGN PURPOSES. THE TRIAXIAL TEST PROVIDES THE REQUIRED STRENGTH PARAMETERS, BUT HAS NOT YET BEEN STANDARDISED FOR BITUMINOUS MIXTURES, REQUIRES MUCH TIME AND THERE IS A LACK OF TEST EQUIPMENT. ANOTHER PROBLEM IS THE DETERMINATION OF THE PARAMETERS FOR STABILISED SOILS, THE REASONS FOR WHICH ARE DISCUSSED. A REVIEW IN DEPTH DEALS WITH THE CBR METHOD, IN PARTICULAR THE MATERIALS, THE DEFINITION OF THE MIX PROPORTIONS, THE MANUFACTURE, STORAGE AND CURING OF THE TEST SPECIMENS AND THE REQUIRED OBSERVATIONS. FINALLY AN EVALUATION OF THE RESULTS OF THE CBR TESTS IS CARRIED OUT WITH THE RESULT THAT IT CANNOT BE REGARDED AS SUITABLE FOR THE DETERMINATION OF MATERIAL PARAMETERS FOR DESIGN PURPOSES DESPITE APPROPRIATE ALTERATIONS TO THE TEST PROCEDURE. SUGGESTIONS ARE MADE FOR FURTHER RESEARCH INTO STILL OPEN QUESTIONS.