Sand-asphalt-sulfur mixtures

Figure 6. Heated dump body truck developed by Shell Canada, Ltd. used for hauling sand-asphalt-sulfur paving mixtures. [Photographed at the Kenedy County Texas field trials in 1977 (28)].

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. 

A series of standard pavement evaluation tests have been performed on a large number of mixtures comprised of different percent-by-weight ratios of sand, asphalt, and sulfur. The testing program performed in this task was designed to evaluate qualitatively the influence of both material and process variables on engineering properties. The following represent some of the conclusion reached ... 

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. 

The effect of sulfur and asphalt contents in SAS mixtures on Marshall Stability is shown in Figure 3 [15]. The stability values tend to increase with sulfur content but decrease with asphalt addition. It is interesting to note that without the sulfur and asphalt, sand mixes would have little or no stability. The data also indicate a wide variety of mix designs are possible whose stabilities are consistant with Asphalt Institute suggested values for conventional asphaltic mixes. 

A characteristic of single sized sands is their comparatively high air void contents which usually exceed 30 percent. Since sulfur s role in SAS mixtures is to fill these air voids without the aid of mechanical densification, both economic and performance considerations would require analysis of the maximum permissible air void content the mixture may possess and still be relatively impermeable to water without sacrificing structural integrity. Figure 4 [15] shows the relationship between air voids content and permeability for both SAS and asphaltic concretes as determined... 

The criteria for maximum allowable air voids content in the final pavement was taken at 15% with a unit weight of about 125 lb/cu ft as established by Shell (2). Although many different mixture ratios were tested, the major comparisons were made with the Shell Thermopave mixture design, i.e., 80.5% sand-6% asphalt-13.5 % sulfur by weight. Under different situations other designs may be equally attractive both technically and economically. 

Thermal Expansion. Experimental results obtained from S—A—S mixtures and a conventional asphaltic concrete are also given in Table VII. Published data on asphalt cement, asphaltic concrete sulfur, sand, and limestone are also provided. The overall thermal expansion coefficient of the composite is derived from the combined effects of the individual ingredients in the mixture and the air voids present in the final material. Any combination which tends to decrease the air voids content... 

---