A multi faceted look into the use of Sulfur Extended Asphalt Modifier

Abstract

Sulfur Extended Asphalt Modifier (SEAM) in solid pellet form is currently being marketed as an additive for hot asphalt mixtures. Typically 40% of the bitumen phase in the asphalt mix can be replaced by SEAM using conventional mix design and production techniques. A number of full scale trials using SEAM have been reported in the literature, and except for some concerns regarding rutting and moisture resistance, it appears that overall the SEAM modified mixes have the potential for improved mechanical performance compared to conventional asphalt. The objective of this paper is to examine issues that surpass pure analysis of mechanical characterisation of asphalt mixes incorporating SEAM. The paper contains a brief overview of sulfur production, recovery processes and the global sulfur supply. It also highlights the fact that the sulfur industry is different from many other important modern mineral industries in that the disposal of surplus production of sulfur is becoming a more important issue than that of how to maintain sustainable production. To enable the reader to appreciate why in a SEAM modified asphalt excess sulfur crystallize out of the bitumen phase into the voids system, a cursory introduction to elemental sulfur allotropes and their thermodynamic stabilities in the solid and liquid states is also included. As SEAM technology is aimed at encapsulating large amounts of sulfur in asphalt mixes, a section is dedicated to examining the microbial oxidation of inorganic sulfur, its potential effects on bioleaching of polluted sediments and the relation between oxidised sulfur and the toxicity of mercury in aquatic systems. During the production stages of SEAM asphalt mixes, the sulfur component will convert from the solid into the liquid phase which requires careful thermal management to control gaseous emissions. As a consequence, this paper includes a general review of exposure limits for sulfur dioxide and hydrogen sulfide emissions and their short and long term health effects on healthy and asthmatic individuals. Finally, the potential for metal corrosion in the presence of elemental sulfur is investigated.