of hydrogen sulfide (H.2$l an< i harder, more -viscous asphalts. This type of 

 reaction is undesirable, and is one of the reasons why temperature control 

 is important in SA technology.). 



The dispersed s-ulfur is present as droplets, most of which are below 5 

 micrometers in size. These solidify as the paving material cools below the 

 melting point of sulfur (120 Celsius), and the resulting solid sulfur 

 phase imparts increased structural strength to the SA paving material. 



(2) Properties. Listed below are some of the improved properties 

 of SA paving materials: 



(a) The strength of SA, as measured by the Marshall method, 

 can be designed to be considerably higher than that of regular 

 asphalt; 



(b) the increased strength obtainable with SA may permit 

 the use of lower quality aggregates or a reduction in paving 

 thickness; 



(c) SA increases the high temperature stiffness of paving 

 materials, without a corresponding increase at low temperatures, 

 thus softer asphalts can be used to minimize winter cracking, 

 with less danger of deformation at summer temperatures; 



(d) SA has a lower viscosity than regular asphalt and can 

 be mixed at lower temperatures, resulting in reduced energy 

 consumption at the hot-mix plant; 



(e) SA improves resistance to water stripping (the breaking 

 of the bond between asphalt and aggregate by a layer of water 

 that forms on the surface of some types of aggregates) , thus 

 aggregates which would otherwise be unsuitable can be used, and 

 the use of antistripping agents can be reduced or eliminated; 



(f) resistance to gasoline, diesel fuel and other solvents 

 is improved; and 



(g) stress fatigue characteristics are improved. 



Not only are many of the properties of SA superior to other concrete 

 binder mixes, but also some of these properties may be enhanced by combina- 

 tions of SA with other materials. The combination of sulfur-asphalt and a 

 nonwoven fabric results in a high performance product that has high tensile 

 strength, is capable of withstanding considerable deformation without break- 

 ing, and remains waterproof even when placed on sharp aggregate. The lower 

 viscosity of SA improves the impregnation of the fabric and the ductility of 

 SA improves the fahric's low temperature performance. On solidification, 

 the finely dispersed sulfur particles impart additional strength to the 

 impregnated fabric. 



(3) Placement . The SA hot-mix is handled like regular asphalt hot- 

 mix paving material. Equipment and technology for transporting, placing, and 



194 



