Ideas for a volumetric mix design method for stone mastic asphalt

Stone mastic asphalt (SMA) is a flexible, stable and very durable mixture if the right materials are chosen and if the mix design, the manufacturing and construction are done well. If one of these phases is not carried out correctly, there is a big chance that the mixture will be overfilled with mortar (sand + filler + bitumen + drainage inhibitor = the binder), with the consequence that the resistance to permanent deformation will decrease soon. One of the most critical parts is the mix design. The current Dutch mix design method for SMA is explained, followed by the relevant design aspects for SMA. Recommendations are given to develop a new mix design method based on a volumetric approach. Hereby it is important that the SMA remains underfilled with mortar from mix design to design life.