Sulfur mixes, sand

Figure 3. Marshall stability as a function of sulfur and asphalt contents in sand-asphalt-sulfur mixes (15,). Materials used were medium-coarse sand and 150/180 pen. asphalt. All specimens were prepared with 2 hammer blows on one face only.

Figure 5. Fatigue life as a function of sulfur content for a sand-asphalt-sulfur mix. Test temperature 50°F (10°C). Test frequency 60 Hz. Materials medium-coarse sandt and 150/180 pen. asphalt. Asphalt content 6% wt (15),...

Deme, I. J., "Basic Properties of Sand-Asphalt-Sulfur Mixes", International Road Federation World Meeting, 7th, Munich, October, 1973. 

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. 

Over 80 percent of the world s production of sulfur is mined in Louisiana and Texas by a very clever method, the Frasch process. The sulfur, mixed with limestone, occurs at depths of about one thousand feet, under strata of sand, clay, and rock. A boring is made to the deposit, and four concentric pipes are sunk (Fig. 17-3). Superheated water (155°) under pressure is pumped down the two outer pipes. This melts the sulfur, which collects in a pool around the open end. Air is forced down the innermost pipe, and a bubbly froth of air, sulfur, and water rises through the space between the innermost pipe and the next one. This mixture is allowed to flow into a very large wooden vat, where the sulfur hardens as a product 99.5% pure. 

A sharp increase in price and decrease in availability of sulfur reduced the experimental effort temporarily, but laboratory work based on the above findings continued. Pourable paving mixes were developed containing one-sized sands which could be cast in place without rolling, much as portland cement concrete is handled. Based on satisfactory laboratory findings, a test road was constructed in Richmond, British Columbia in 1970, where a sand—asphalt—sulfur mix was cast between forms (5). The success of this trial, coupled with a decrease in the price of sulfur and the forecast for a long-term world sulfur surplus, led us to initiate an extensive research and development program to exploit sand-asphalt-sulfur mixes as road base and surface materials. 

The Function of Sulfur in Sand—Aspbalt-Sulfur Mixes... 

Figure 1. Photomicrograph of a polished sand-asphalt-sulfur mix surface...

The results from full-scale experimental road projects in Canada have confirmed the above findings. When sand-asphalt-sulfur mixes were placed with vibratory screed finishers, increased vibratory energy had no significant effect on the densification of fluid mixes, whereas noticeable increases in density with corresponding increases in vibratory energy were observed with stiffer mix formulations. 

In the cement concrete industry the recommended practice is to consolidate low slump mixes by vibration and high slump mixes with hand tools. For example, ASTM Method C 192 (6) specifies consolidating test specimens by vibration if the slump is less than 1 in. Relationships between workability and ease of placing sand-asphalt-sulfur mixes are being evaluated on various field projects to assess the workability requirements for mix placement with various types of equipment. 

Sand-asphalt-sulfur mixes are not subject to particle segregation because of uniform size distribution. These mixes may be transported and handled readily. Sands are, therefore, the best materials for use in paving mixes, considering their low cost in many areas, their ample availability, and their potential for developing high strength in sand-asphalt-sulfur mixes. 

The sand-asphalt-sulfur mix stability increased to a peak value with increasing sulfur content for all asphalt levels. 

Sand-asphalt-sulfur mix stabilities were adequate even with excessively high asphalt contents, e.g., 10% asphalt. 

Considerable testing was done in the laboratory to evaluate the permeability properties of sand-asphalt-sulfur mixes. A constant head air permeameter, similar to the apparatus described in Ref. 9, was used. The coefficient of air permeability criterion below which mixes are con-... 

Figure 5. Relation between sulfur content and fatigue life for a sand-asphalt-sulfur mix...

In 1971, a three-quarter mile surface overlay was placed in Oakville, Ontario using thirteen mix formulations. Skid resistance, wear, and permeability have been measured periodically to assess the suitability of sand-asphalt-sulfur mixes as surfacing materials. 

Mix Handling Trials. The general objective in conducting field trials was to use, with minimum modification, conventional asphalt equipment for processing, transporting, and placing sand-asphalt-sulfur mixes. To date, the mixes have been processed in batch-type hot-mix asphalt plants. Details of the processing steps were published in a previous report (4). In 1975, we intend to evaluate a continuous-type hot-mix... 

Pavement Structure Bases and Surfacing. Sand—asphalt—sulfur mixes may be used in the construction of all types of pavements or for overlaying existing road structures. As the mixes are cast in place without roller compaction, they are suitable for road widening or bridging weak spots in the subgrade. 

Sand-asphalt-sulfur mixes may also be designed to be highly impervious. These mixes may be used for cement concrete bridge deck surfacing to reduce salt attack and corrosion of the bridge deck reinforcing. 

Leveling Courses. Sand-asphalt-sulfur mixes may be used as thin leveling courses over deformed or worn pavement surfaces. The mix may be placed with a bituminous finisher, and a smooth finished surface... 

The wheelpath depressions of rutted and worn surfaces may be filled with mix, with the finisher screed riding on the bumps. Sand-asphalt—sulfur mixes can be feathered out to the thickness of the maximum-sized particle. The normal city street overlaying practice requiring heater-planing of the bumps and replacing of a full width overlay need not be followed. 

Hydraulic Applications. Since sand-asphalt-sulfur mix formulations can be highly impervious, they may be used in hydraulic applications. Because the material can be cast in place without compaction, it is ideally suited for placement on slopes where conventional materials are difficult to compact such as for lining storage reservoirs, sewage lagoons, and ditches which are susceptibel to erosion. 

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. 

Castings. Pourable sand-asphalt-sulfur mixes may be cast in various shaped molds. For example, the mix may be molded in the configuration of the New Jersey rigid median barrier (11). Stiffer mixes may be extruded with an asphalt curbing machine to form a high stability curb. A small slip-form paver may be adapted for casting sidewalks in a similar fashion. 

Sand-asphalt-sulfur mixes exhibit a high degree of impermeability at higher air voids contents than conventional asphalt mixes. 

In designing sand-asphalt-sulfur mixes, a number of mix properties such as workability, stability, fatigue behavior, and mix impermeability should be considered in establishing the optimum mix formulation for its intended use. 

Sand-asphalt-sulfur mixes are prepared in the laboratory using two separate wet mix cycles. First, asphalt and sand preheated to 300°F are mixed for about 30 sec to coat the sand particles with asphalt. Sulfur, also at 300°F, is then added to the hot sand-asphalt and mixed for about 30 sec to achieve a uniform dispersion of the sulfur throughout the mix. 

Mix and material properties tests on a wide variety of S-A—S mixtures were performed using the aggregate and asphalt types discussed above. The specific mixture ratios evaluated ranged from 2 1 to 5 1 wt % sulfur to asphalt. The maximum amount of sulfur used in any mixture was 20 wt %. For comparison purposes, sand-asphalt (0% sulfur) and sand-sulfur (0% asphalt) mixes were also evaluated. 

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. 

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