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OPTIMUM MIX DESIGNS
Siegfried Velske
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Abstract
FORMULATION OF OPTIMUM MIX DESIGNS MUST BE A COMPROMISE BECAUSE IT IS NOT YET POSSIBLE TO COMBINE TO THE MAXIMUM EXTENT CERTAIN OPPOSITE PROPERTIES. THIS LIMITATION TO MAXIMISATION IS ESPECIALLY APPARENT IN THE CASE OF THE RIGIDITY, WHICH IS BASED ON THE ONE HAND ON THE FRICTION IN THE GRAIN STRUCTURE AND ON THE OTHER HAND ON THE COHESION OF THE BINDER-FILLER MIXTURE. WHILE THE INTERNAL FRICTION CAN BE CONTROLLED, CERTAIN LIMITS ARE SET TO THE REGULATION OF THE BITUMINOUS MORTAR. THIS APPLIES TO THE INCREASE OF COHESION BY USING A STRONGER BITUMEN AND ALSO THE REDUCTION OF THE BINDER COATINGS BY REDUCING THE BITUMEN CONTENT OR INCREASING THE FILLER CONTENT AS WELL AS THE USE OF A STRONGER FILLER. IT SEEMS SENSIBLE TO BE SATISFIED WITH A MEAN HARDNESS OF 65 PEN IN THE PRODUCTION OF ASPHALT CONCRETE WITH BITUMEN AND TO SEEK ADEQUATE MORTAR VISCOSITY WITH A PROPORTION OF FILLER WHICH GIVES A PROPORTION OF VOIDS IN THE ASPHALT CONCRETE WHICH IS NEAR THE UPPER LIMIT.