Sulfur aggregate-asphalt

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. 

Similar considerations should be remembered when placing graded aggregate-asphalt-sulfur mixes. In this case, however, some vibration is desirable to consolidate all mixes, regardless of consistency, so that the particles are oriented in the most dense configuration. 

In conventional asphalt concrete mixes, for which stability is a foremost consideration, the design asphalt content is generally close to the optimum asphalt content for fatigue life. In aggregate-asphalt-sulfur mixes the significant mix properties should be considered independently... 

Porous Mixes. Specific aggregate-asphalt-sulfur formulations in which sulfur adds to the mix strength may be used for porous construc-... 

Pourable sand-asphalt-sulfur mix formulations may not be placed on exceedingly steep slopes as they would flow down the slope. In this case, stiffer aggregate-asphalt-sulfur mix formulations may be used. 

An Efficient Method of Mix Design. The best combination of aggregate properties, sulfur and asphalt quantities, and compaction effort may be considerably different in a sulfur-asphalt mix than in conventional asphalt concrete. Since there is little available field or laboratory experience to borrow upon, an experimental design procedure may be adopted to use laboratory experimental data most efficiently in determining the best mix. 

Readily available, inexpensive one-sized sands could replace relatively expensive dense-graded aggregates in sulfur-asphalt mixes. 

Adding enough molten sulfur to hot aggregate—asphalt mix increases its fluidity and produces a mix which can be molded or shaped. Casting these mixes requires little or no consolidation effort, and, specifically with pavements, rolling is not required. It has been demonstrated by micro-... 

Tn 1963 Shell Canada Limited initiated a laboratory program which eventually led to the development of a sand-asphalt-sulfur (S-A-S) paving material called Thermopave. This study revealed that cast S-A-S mixes with excellent engineering properties could be prepared by using locally available aggregates normally considered unacceptable for pavement construction. This concept was also investigated, to a lesser extent, by Shell Oil Co. and Shell Development Co. 

Concrete is a mixture of a coarse-grained aggregate, hydraulic binding agents (cement, gypsum, lime, asphalt, sulfur, and resin), and water (except in the case of sulfur and resin, where water is not needed). For a limited period after preparation, the mixture can be molded into different shapes until hardening occurs as a result of chemical reactions between the components. 

A variety of materials has been proposed to modify the properties of asphaltic binders to enhance the properties of the mix (112), including fillers and fibers to reinforce the asphalt—aggregate mixture (114), sulfur to strengthen or harden the binder (115,116), polymers (98,117—121), mbber (122), epoxy—resin composites (123), antistripping agents (124), metal complexes (125,126), and lime (127,128). AH of these additives serve to improve the properties of the binder and, ultimately, the properties of the asphalt—aggregate mix. 

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. 

The Shell papents broadly cover a bituminous paving composition in which the aggregate is coated with bituminous binder and the excess undissolved sulfur acts as a filler in the void spaces between the aggregate. The process is particularly adaptable for use with inexpensive, ungraded sands which are not suitable for use as an aggregate in a conventional hot mix asphalt concrete this mix class has often been called sulfur-asphalt-sand (SAS), but Shell s product is currently tradenamed THERMOPAVE. 

In the aging tests at —18 °C (0°F), however, the sulfur-asphalt-bound concrete with lightweight aggregate oertainly retains stiffness better than... 

SA Binder Concept. The principal objective of using elemental sulfur as a binder for aggregate without adversely affecting the flexibility of the in-place pavement guided the basic research approach and led to pre-mixing of sulfur and asphalt and to the SA binder concept first proposed by Bencowitz (3, 4). It is possible and tempting to produce by... 

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