Sulfur aggregate gradation

Aggregate Suitability Evaluation. As indicated earlier, most of the mixes studied were made with medium-coarse sand. However, a number of mixes were prepared to explore the range of aggregate gradations which may benefit from sulfur addition to asphalt compositions. The gradations in Table I cover materials from fine blow sands to coarse pit... 

Figure 7. Effect of sulfur content on Marshall stability for normal process mixes prepared using various aggregate gradations...

An examination of the above criteria would indicate that an optimum SAS system would have sulfur and asphalt content between 12 and 14 percent and 5 and 7 percent, respectively. The final decision will be dictated by the air void content and gradation of the aggregate, the latter of which has a bearing on the tear resistance of the mat during placement. For a fine in-depth treatment of the aggregate selection process and SAS construction procedures, the reader is referred to Volume III of Reference 22. 

Highway District 11 is located in East Texas, and the area does not have an abundant supply of conventional aggregates. Of the materials available locally, sand is the most plentiful. These local sands were first combined with asphalt in a hot-mix plant in 1962 and were evaluated on U.S. and State highways. From this experience, it was concluded that hot-hand asphalts merited consideration as base materials. Quite often two sands (usually 100% passing the 40 sieve) are combined to obtain the proper gradation. When it was subsequently learned that the Texas Transportation Institute (13) was evaluating the sulfur-asphalt binders, efforts were initiated to field test these materials. 

The U.S. Bureau of Mines participated in a field trial of sulfur-asphalt concrete pavement on U.S. Highway 93 near Boulder City, Nev. in January 1977. This test section is 2100 ft long. The aggregate-asphalt-sulfur (AAS) system was used to mix the ingredients. The sulfur and AC 40 asphalt cement were introduced into the pugmill as individual components. The sulfur comprised 27 w/o of the total binder. The aggregate used in the mixture was a crushed volcanic rock which conformed to the Asphalt Institute type IVb gradation. This test section is now in post-construction evaluation. 

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