compacting the SA material is identical to that used for regular asphalt 

 hot-mix. 



c. Sulfur Concrete . During the past 5 years, interest in sulfur con- 

 crete (SC) has grown rapidly. Research and development on SC is currently 

 being carried out by at least 50 companies and agencies, some of which are 

 now actively marketing SC products and materials. 



Sulfur concretes are basically simple materials, made by mixing sulfur 

 plus certain additives with heated mineral aggregates. On cooling, SC sets 

 to give a high-strength material with superb corrosion resistance. Early 

 attempts to make and use SC date back more than 100 years. However, current 

 SC technology is a product of the 1960's and 1970' s following the discovery 

 and development of suitable additives or "plasticizers" for the sulfur 

 which impart durability to SC. A considerable number of compounds have 

 been screened as additives. Currently, the most popular ones are dicyclo- 

 pentadiene (DCPD), dipentene (DP), certain proprietary polymeric unsaturated 

 hydrocarbons, and combinations of these materials. Much of the current 

 research work is concentrated on finding additives or combinations of 

 additives which will further improve the durability and performance of SC. 



Sulfur concretes can be designed to have compressive and tensile 

 strengths twice or more those of comparable Portland cement concretes 

 (PCC) , and full strength is reached in hours rather than weeks. Sulfur 

 concretes are extremely corrosion resistant to many industrial chemicals, 

 including most acids and salts. Sulfur concrete is highly resistant to 

 saltwater, and marine applications may be attractive. 



(1) Additives . While satisfactory SC had been obtained by the 

 addition of 5 percent DCPD as a modifier to the sulfur, recent U.S. Bureau 

 of Mines work indicates that a superior product can be obtained by the use 

 of mixed modifiers. These consist of a mixture of DCPD fractions from DCPD 

 manufacture containing three, four, or more units of cyclopentadiene or 

 methylcyclopentadiene per molecule. Several companies market materials of 

 this type. The relative amounts of DCPD and oligomer used in the modifier 

 will vary to some extent with the type of aggregate, but a mixture of 65 

 percent DCPD and 35 percent oligomer is about optimum in most cases. Five 

 percent by weight of this mixed modifier is added with stirring to the 

 molten sulfur at 130 Celsius, and allowed to react with it for several 

 hours. To ensure complete reaction of the sulfur with the modifier, the 

 U.S. Bureau of Mines allows the mixture to react for 24 hours, but there 

 are indications that this time can be shortened considerably. 



The use of mixed modifier rather than straight DCPD results in improved 

 durability and corrosion resistance. It is also easier to prepare the 

 modified sulfur using the mixed modifier. The reaction of DCPD with sulfur 

 is exothermic, and care must be exercized when adding straight DCPD to 

 molten sulfur to prevent overheating. With mixed modifiers, the reaction 

 is easier to control. 



(2] Aggregates . A metallurgist at the U.S. Bureau of Mines (W.C. 

 McBee, Boulder City Laboratory, personal communication, 1981) stressed that 

 each aggregate system must be analyzed and evaluated as to its suitability 

 for SC. Generally, limestone aggregates tend to give SC higher strength 



195 



