Improvement of high modulus asphalt mixtures with average quality aggregate and bitumen by application of polymeric additives

The paper deals with the development of asphalt mixtures for high performing binder and base courses, modified with both commercial and waste polymeric additives, via dry process. The focus was on the mix design of high performing mixtures making use of average quality aggregate and average penetration grade bitumen (as locally available) instead of the usually required high quality components, manly very hard bitumen, thus aiming to improve the reference mixture as made possible by suitable polymers. Mixtures were subjected not only to conventional tests for mix design purposes, but also to advanced tests for performance evaluation such as rutting resistance and fatigue resistance. The dynamic modulus was also evaluated by means of modulus tests in triaxial cell. The test results provided useful information about the use of studied additives for bituminous mixtures. In details, when selecting a High Modulus Base aggregate gradation, the addition of polymeric additives is proved to improve mechanical performances such as modulus and permanent deformation resistance even when using average quality aggregate and less hard bitumen (more easily available in Southern Italy) than those typically used for these special formulations, with beneficial environmental consequences (saving of high quality, not-renewable resources).