The Authors give an account of the performance modifications induced in the blended cements by replacing the typical pozzolanas with their zeolitic counterparts: volcanic tuffs, after suitable grinding. The advantages of such a replacement in terms of minimization of alkali aggregate expansion and of strengths increase at long ages are discussed. emphasizing also the favourable influence of expansion abatement supplied by a previous thermal treatment of the seolitic addition. The improved strength progress in interpreted in terms of a higher reactivity of the seolitic minerals in comparison with that of the pozzolanic glass and the expansion abatement in terms of ability to incorporate high alkali amounts showed by the abundant amorphous hydrated silicate.