Asphalt Mixtures Modified with Sulphur Pellets, Impact on Pavement Thickness

Sulphur Extended Asphalt (SEA) mixtures were used commercially in the 1970s and 1980s in North America as well other parts of the world. Performance properties of Sulphur Extended Mixtures were proven to be equal or even better than conventional asphalt mixtures. However handling and safety issues were of concern, as molten sulphur was difficult to use and occasionally generated H2S emissions. Interest in the use of SEA mixtures has been renewed by the forecast in energy demand and some recent innovations in sulphur technology with the design of modified sulphur in pellet form. The pellets allow easy handling and storage. The modified sulphur pellets are at ambient temperature when added to the Hot Mix Asphalt (HMA) during the mixing process. By keeping the mixing temperature in a range of 125 degrees C - 145 degrees C, H2S emissions are virtually eliminated. Modified sulphur pellets have been assessed in the laboratory, in performance tests used to characterize HMA. Intrinsic properties, such as complex modulus and fatigue have been measured and used in an analytical pavement analysis. The aim was to determine how the increase in stiffness affects fatigue life and how it alters a pavement design, in particular the impact on layer thickness. This paper shows that it is preferred to use an analytical method, which accounts for stiffness and fatigue rather than using a method that only utilizes stiffness, as it can propose a layer thickness reduction, which can have a detrimental effect on pavement life.