Sulfur pavements

The possibility of accidental events such as fire and chemical spills revealed some possible short term undesirable effects. These were in the area of obnoxious fumes or short-time-interval pollution. Virtually all of the sulfur pavement materials were difficult to ignite and were self extinguishing. 

The effect of simulated brine and gasoline spills on sulfur pavement were studied. Whereas salt based deicers would have minimal effect, organic solvents or naphtha mixtures can solubilize free sulfur in addition to attacking the asphalt. 

Elemental sulfur has been modified In an exothermic reaction with commercially available hydrocarbon compounds to produce a pavement binder material that has been successfully utilized to construct several experimental pavement sections on public highways. The engineering properties, the formulation, and the methodology for producing and utilizing this chemically modified sulfur pavement binder, intended as a substitute for asphalt cement, are discussed. 

Cost Cutting Sulfur Pavement Making Inroads, Eng. News Rec. (Sep-... 

Full depth sand-asphalt-sulfur pavement structures should reduce the depth of frost penetration into the subgrade in low temperature regions and thus reduce frost damage to pavements. The coefficient of thermal conductivity of these mixes is approximately one third the value for asphalt concrete. 

Many existing roads fail because the asphalt becomes stiff and brittle. If the materials are too stiff, additives that lower the viscosity must be used. The feasibihty of usiag sulfur to soften or reduce the viscosity of the oxidized biader ia recycled pavements has been successfully demonstrated by the U.S. Bureau of Mines and others (55—57). 

D. Saylak and co-workers. Beneficial Uses of Sulfur in Sulfur—Asphalt Pavements, American Chemical Society, Washington, D.C., 1975. 

W. C. McBee, T. A. Sullivan, and D. Saylak, Pejcling Old Asphalt Pavements with Sulfur, ASTM STP622, American Society for Testing Materials, Philadelphia, Pa., 1978. 

The most important use of sulfur is for sulfuric acid production. Other uses range from dusting powder for roses to ruhher vulcanization to sulfur-asphalt pavements. Flower sulfur is used in match production and in certain pharmaceuticals. Sulfur is also an additive in high pressure luhricants. 

Sulfur can replace 30-50% of the asphalt in the hlends used for road construction. Road surfaces made from asphalt-sulfur hlends have nearly double the strength of conventional pavement, and it has been claimed that such roads are more resistant to climatic conditions. The impregnation of concrete with molten sulfur is another potential large sulfur use. Concretes impregnated with sulfur have better tensile strength and corrosion resistance than conventional concretes. Sulfur is also used to produce phosphorous pentasulfide, a precursor for zinc dithiophosphates used as corrosion inhibitors. 

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. 

SAS mixes with S A ratios of 1.0 to 2.5 1.0 are recommended for use in flexible pavement mixture designs, while S A ratios greater than 5 1 can be used in situations requiring rigid pavement designs. A typical SAS formulation is 82 parts sand, 6 parts asphalt and 12 parts sulfur by weight. 

Two of the more recent innovations for using sulfur modified binders are in conjunction with recycling old asphalt pavements and the construction of open graded friction courses (OGFC). 

Table 2. Properties of Recycled Asphalt Pavement Using Sulfur/ Asphalt Emulsion Binder.

Figure 21. Schematic of a central plant for sulfur recycling of old asphalt pavements.

A large number of structural materials were evaluated for possible attack by run-off from a sulfur-asphalt pavement. Of the ten materials studied, copper and steel appeared to indicate a vulnerability. The former or its alloys should never be used in equipment or structures which could bring them in contact with sulfur due to the high probability of producing the sulfates of copper. Steel reinforcing rods would be susceptible to attack by H SO produced by moisture on contact. 

McBee, W. C., Sullivan, T. C. and Saylak, D., "An Overview of Sulfur Extended Asphalt Usage", Asphalt Pavement Construction New Materials and Technique, ASTM STP 724,... 

Complementing the technical functionality of sulfur for pavement construction, U.S. sulfur production, while geographically localized, is favored with a nationwide distribution system. Sulfur is involuntarily produced from oil and natural gas, and the switch to coal promise to produce additional large U.S. surpluses of sulfur in the coming decades. Voluntary production is flexible so that the introduction of a major new sulfur use could be phased in without undue stress in the present supply and demand situation. 

The engineering properties of aggregate mixtures employing elemental sulfur as a binder are not suitable for highway pavement applications such mixtures possess adequate compressive strength, but are extremely brittle and lack satisfactory fatigue behavior to resist repetitive traffic loading. 

Sulfur-Asphalt Paying Materials (1J, ). Two different technologies are used to combine asphalt and sulfur into a binder that exhibits unique properties and often enhance the pavement performance as well as extend the supply of available asphalt. 

Foamed Sulfur (15, 1 8). By using additives and simple ma-chinery, sulfur can be turned into a foam that has very useful properties. Lighter than water, foamed sulfur can be used for building insulation, subbases for pavements, and perhaps lightweight structural members for housing and other small structures. 

Early field trials were conducted in Saudi Arabia using this technology (22, 23). Considerable interest in sulfur asphalt pavements has been generated, but not projects of significance have been completed. Considerable research and development as well as demonstrations are continuing under the guidance of the Sulphur Development Institute of Canada. 

Utilization of sulfur asphalt pavements in the Middle East appears to have an excellent chance of success. For example, in Saudi Arabia, the production of asphalt in-country has not increased much during the rapid rise of construction activities in recent years. Figure 2 shows the recent and expected production of both asphalt and sulfur in Saudi Arabia. As discussed earlier, demand for asphalt has surpassed the supply. Use of sulfur in pavements may provide the needed binder material and thereby preclude the need for added imports or increased sulfur production(7). 

In housing, for example, masonry type of construction is traditional and the sulfur concrete developments lend themselves well to meeting the local needs. The problems in asphalt pavements associated with high temperatures may be overcome by the use of SEA or SC pavements. 

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. 

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... 

Construction Procedure. Paving with a sulfur—asphalt hot mix is exactly the same as with asphalt. Conventional dump trucks are used to haul the hot mix from the asphalt plant to the road. There the mix is spread with standard pavement equipment and compacted with conventional rollers. Measurements on the completed pavements verify that sulfur asphalt mixes have good workability and are virtually indistinguishable from conventional asphalt. 

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