On the SUPERPAVE Asphalt Mixture Gradations for the Mix Design of Traditional and Special Asphalts

The Author proposes a methodology for the verification of the fulfilment rate of the particle size distribution specifications of the prescriptions limit grading curves, which are commonly used for the definition of bituminous asphalts admixtures, with the SUPERPAVE conditions related to the control points and to the restricted zone boundary. The operative phases of such methodology provide for the determination of the maximum nominal size of the aggregate, referred to the average curve of the limit grading curves in the semi-logarithmic plane of the sieves opening d-% passing and in the d 0,45-% passing. Afterwards, once the referring SUPEPAVE chart where to put the prescriptions limit grading curves is found, the critical points can be characterised in this way: type “a” when the violation of control points occurs , and type “b” when violations of the restricted zone boundary are experienced. Actions modifying the limit grading curves are proposed for each of these typologies, in order to get to curves consistent with the SUPERPAVE specifications. The methodology used for the limit grading curves of the main Italian prescriptions shows that, referring to traditional asphalts, small changes can make the limit grading curves consistent with the SUPERPAVE specifications. On the contrary, the Author found a strong incompatibility with special conglomerates (porous asphalts, stone mastic asphalts, etc).