(4) impregnating materials with sulfur, and 



(5) foamed sulfur. 



The acceptance of sulfur asphalt technology by highway departments and 

 contractors has been due not only to the desire to replace asphalt by 

 readily available sulfur, but also to the fact that the sulfur asphalt 

 materials have shown improved properties compared to asphalt, and to the 

 fact that sulfur asphalt permits the use of aggregates which would be 

 unsuitable for use with asphalt. 



It has been known for many years that mixing molten sulfur with sand or 

 aggregate produces a sulfur concrete with excellent strength. However, the 

 durability of simple sulfur concretes of this type has not been impressive, 

 particularly under conditions of high humidity and wide temperature fluctua- 

 tion. Research has centered on developing additives to sulfur to improve 

 the durability. Work carried out by the U.S. Bureau of Mines at Boulder 

 City, Nevada, and by Sulfur Innovations, Ltd., Calgary, Alberta, has 

 resulted in sulfur concretes with greatly improved properties. 



Porous materials can be impregnated with molten sulfur that, on solidify- 

 ing, imparts additional strength to the materials. Resistance to freeze- 

 thaw cycles and corrosion is also frequently improved by sulfur impregnation. 

 Recent research indicates that with suitable additives, sulfur could be 

 made into a rigid foam having excellent mechanical and insulating properties. 

 The properties of sulfur-based construction materials generally equal or 

 surpass those of conventional cementing materials. 



b. Sulfur -Asphalt (SA) Materials . Basically, all the SA technologies 

 involve combining molten sulfur and hot asphalt to produce a sulfur-asphalt 

 binder, which is then mixed with mineral aggregate to give a SA hot-mix 

 paving material. The individual technologies differ in the method and 

 equipment used to produce the SA binder. 



(1) Mixes . Depending on the technology and type of aggregate 

 used, from 1/3 to 1/2 by weight of the asphalt can be replaced by sulfur. 

 Because sulfur is about twice as heavy as asphalt, sulfur- asphalt binders 

 have higher densities than normal asphalt. Because a certain volume of 

 binder is needed to obtain an acceptable void content of the compacted 

 paving material, optimum stability of SA paving materials generally occurs 

 at a somewhat higher binder content (by weight) than when straight asphalt 

 is used. In practice, between 6.2 and 8.9 newtons (1.4 and 2 pounds) of 

 sulfur are needed to replace 4.4 newtons (1 pound) of asphalt. Because 

 SA paving materials are three-component systems (sulfur-asphalt-aggregate) 

 they permit more flexibility of design than with regular two-component 

 (asphalt-aggregate) paving materials. 



When hot asphalt and sulfur are mixed, some of the sulfur, about 20 

 percent by weight of the asphalt, will dissolve in the asphalt. The 

 remainder of the sulfur forms a dispersion of sulfur in asphalt. Both the 

 dissolved and the dispersed sulfur modify the properties of the asphalt. 



Some of the dissolved sulfur reacts chemically with the asphalt to form 

 polysulfides, which make the asphalt softer and more ductile. (At higher 



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