Sand-asphalt-sulfur contents

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),...

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. 

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

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

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. 

Thermopave mix (medium sand)—asphalt content, 6 wt % sulfur content, 13 wt % Plant, Cedarapids capacity, 6000 lb (2722 kg) batch batch size evaluated, 5000 lb (2268 kg) mixing time, 25 sec with sulfur. 

In the more localized context of the Athabasca deposit, inconsistencies arise presumably because of the lack of mobility of the bitumen at formation temperature (approximately 4°C, 39°F). For example, the proportion of bitumen in the tar sand increases with depth within the formation. Furthermore, the proportion of the nonvolatile asphaltenes or the nonvolatile asphaltic fraction (asphaltenes plus resins) in the bitumen also increases with depth within the formation that leads to reduced yields of distillate from the bitumen obtained from deeper parts of the formation. In keeping with the concept of higher proportions of asphaltic fraction (asphaltenes plus resins), variations (horizontal and vertical) in bitumen properties have been noted previously, as have variations in sulfur content, nitrogen content, and metals content. Obviously, the richer tar sand deposits occur toward the base of the formation, but the bitumen is generally of poorer quality. 

Tar sands from the Asphalt Ridge, Sunnyside, and Tar Sand Triangle deposits in Utah were processed in a small-scale, two-stage fluidized reactor system operating under continuous, steady-flow conditions. The oil products obtained were analyzed for viscosity, refractive index, density, sulfur content, distillation yield, and proton nmr spectra. 

The Marshall stability test results in Figure 7 indicate that all of the mixes with low sulfur contents were unacceptably unstable. The stability of all of the mixes increases with increasing sulfur content. The medium-and coarse-sand mixes benefited the most from sulfur addition. They exhibited higher Marshall stabilities at lower sulfur contents than other mixes and at higher sulfur contents exceeded 2000 lb. (8900N), the usual upper limit attainable for high quality asphalt concrete 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 use of higher amounts of sulfur, above a sulfur/asphalt weight ratio of 1.0, yields pourable mixes with a marked change in physical properties. For example, the sand mixes in Figure 8 exhibit negligible stability without sulfur addition of sulfur permits mix designs to high stability levels at a variety of asphalt contents. Other mix properties are affected in a similar fashion. 

Table II shows the results obtained by extracting several Uinta Basin, Utah outcrops with successive organic solvents. All outcrop samples are fairly low in sulfur, most are quite high in nitrogen, and all have low ratios of vanadium to nickel. Only the Raven Ridge sample, which was collected in a creek bed, has a very large fraction of organic material that is not soluble in heptane Benzene-methanol (1 1) and pyridine did not extract much material from any of these samples, so analytical data from these materials are not included in the table. The asphaltenes extracted from P. R. Spring and Southeast Asphalt Ridge tar sands are quite rich in nickel (5/jtmol/g), and nickel porphyrins are found in the heptane-soluble fractions of these tar sands as well as is the heptane-soluble fraction of Whiterocks tar sands. Crudes derived from nonmarine sources are usually much higher in nickel content than in vanadium content, and the Uinta Basin tar sands deposits are all of lacrustine origin and are of tertiary age.

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. 

The lower air void contents of the concrete sand are reflected in the higher unit weight and lower air void content of the mix, both of which increase with the amount of asphalt and sulfur present. No significant difference in the Marshall flow was revealed in using the two aggregates. 

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... 

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