Asphalt paving materials, sulfur

Highway Construction. The preparation and use of sulfur—asphalt (SA) paving materials have been reviewed (45,46). In the 1930s, asphalt (qv) was easily available and priced lower than sulfur. As of the 1990s, this is no longer the case. There are four different types of sulfur paving materials. 

McBee, W. C., and Sullivan, T. A., "Direct Substitution of Sulfur For Asphalt in Paving Materials", U. S. Bureau of Mines, Report of Investigation 8303, 1978. 

Sulfur as an Additive for Asphalt. Sulfur-extended asphalt (SEA) binders are formulated by replacing some of the asphalt cement (AC) in conventional binders with sulfur. Binders that have sulfur asphalt weight ratios as high as 50 50 have been used, but most binders contain about 30 wt % sulfur. Greater latitude in design is possible for SEA paving materials, which are three-component systems, whereas conventional asphalt paving materials are two-component systems. Introduction of sulfur can provide some substantial benefits. At temperatures above 130°C, SEA binders have lower viscosities than conventional asphalt. The lower viscosity enables the plant to produce and compact the mix at lower temperatures than with conventional... 

Construction, maintenance, and rehabilitation costs for pavements have risen sharply during the past decade, while revenue for these purposes has leveled or declined. In an effort to offset these rising costs and reduce dependence on uncertain asphalt supplies, increased research and development activity throughout the world has been devoted to the development and implementation of new and improved materials for use in pavement construction and maintenance. The use of sulfur in asphalt paving materials has proven to be one of the more promising developments to come from these activities. 

Both cellulosic wastes and lignins were found to have only limited applicability to the problem at hand. Sulfur, however, has been shown to be a very useful material for this purpose. Elemental sulfur may be used to extend asphalt, as in sulfur extended asphalt (SEA) binders, or chemically modified sulfurs may completely replace asphalt in paving mixtures. 

A major application now under very active research is the use of SC as a road paving material. This technology is considerably different from the use of sulfur as a potential substitute for asphalt which was discussed earlier. Paving with SC can be regarded as a total substitution of sulfur for asphalt, or as an... 

It has been known for many years that sulfur can modify the properties of asphalts (38). With the recent dramatic increases in oil prices and hence the price of asphalt, the use of sulfur in flexible paving materials is being examined with renewed interest (39-45), particularly in areas where sulfur is available and is less expensive than asphalt. In addition to the possible economic benefits, if asphalt can be partially or completely replaced by sulfur in flexible pavement concretes, other benefits in terms of improved material properties might also accrue. 

U ecently, interest in sulfur utilization in asphalt paving materials has been rekindled. One of the foremost reasons for this is the potential availability of surplus sulfur recovered from secondary sources in connection with meeting environmental pollution standards (I). These sources include sulfur recovered from sour gas, from refining of petroleum, and from smelter and powerplant stack gases. Another potential saving of energy and petroleum is possible by replacing part of the asphalt binder with sulfur (2). 

A test program to determine the feasibility of direct substitution of sulfur for asphalt in preparing sulfur-asphalt concretes was conducted. Properties of the resultant materials were compared with those of emulsified sulfur-asphalt binder materials and conventional materials. In addition, a test program was conducted to determine if direct-substituted binders could be used to upgrade marginal aggregates for use in paving materials. 

Sand-Sulfur-Asphalt Method. The direct substitution method was used to evaluate the substitution of sulfur for asphalt in preparing paving materials with improved properties. Sulfur and asphalt were combined and added to graded sand in the Hobart mixer and were mixed for 2 min. Test samples were prepared as described for the direct substitution method. 

Evaluation of sulfur-asphalt binders for paving materials showed no differences in materials prepared using either the emulsified or the direct substitution method in preparing the binder. Therefore, the simpler direct substitution method was used in all subsequent testing. 

Figure 2. The optimum asphalt binder concentration was 4.5 wt %, and this volume of binder was used in all tests. Properties of the paving materials prepared from the limestone with asphalt and with sulfur-asphalt binders are shown in Table VI.

Figure 18. Mixers for preparation of sulfur-asphalt paving materials...

The studies illustrate that the two sulfur-asphalt systems are complementary. The primary objective for using the sulfur-extended binder system is to use sulfur as a diluent to conserve asphalt used in conventional hot mixes. No asphalt saving is realized using Thermopave. The unique features of this process are that it permits the manufacture of high-quality paving materials using inexpensive, poorly graded sands and yields pourable mixes, similar to cement concrete. 

The Bureau of Mines has produced quality sulfur-asphalt paving materials which are blended by the shearing actions generated in the pug-... 

There are four major considerations in designing a sulfur-asphalt pavement—mix design, construction, performance, and economics. None of these are unique to sulfur-asphalt, but they must all be considered explicitly in order to show under which conditions the new sulfur-asphalt paving material may be expected to be superior to the widely used and accepted asphalt concrete pavement. 

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