Stability sulfur/asphalt

Resistance to the Solvent Action of Fuels. Sulfur—asphalt concretes were less affected by the solvent action of fuels than was normal asphaltic concrete. The solvent action of three fuels—gasoline, JP-4 jet fuel, and No. 2 diesel fuel—was tested on samples of normal asphaltic concrete and on 15-, 25-, and 35-vol % sulfur-asphalt concretes. Two test methods developed by McBee (15) were used to determine loss in weight and loss of stability on drip and total immersion testing of Marshall compaction samples. 

Marshall stability of asphalt concrete dropped 72% after immersion testing in gasoline compared with only a 21% loss with 35-vol % sulfur-asphalt concrete. Jet and diesel fuels had a lesser effect on the Marshall stabilities than did gasoline. The solvent effect on sulfur-asphalt concrete materials decreased with increasing sulfur content in the asphaltic binder in the O-35-vol % substitution range. The greater resistance of sulfur-... 

No difficulties were encountered at the plant or at the paving site. The procedures used for preparing and laying the sulfur-asphalt mixes were identical to those used for the non-sulfur-containing mixes. Hveem stabilities of the plant-mixed materials as measured in the field laboratory compared quite well with those of the design mixes as shown in Table IV. 

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. 

Short-term studies indicate that Thermopave mixes generally attain their ultimate stability after a curing time between one to five days, depending upon the sulfur/asphalt ratio and sand type. The results of a long-term aging study of Marshall briquettes stored at room temperature are presented in Table V. The data indicate a random variation in stability values but no significant change in stability over a five-year period. 

For the screening test phase, three replicate specimens of each combination of independent variables were made, and each of the indicator or control tests was run on the specimens of sulfur-asphalt concrete. These indicator tests (dependent variables) included bulk specific gravity, air voids, voids in the mineral aggregate (VMA), resilient modulus, Hveem stability, Marshall stability, and Marshall flow. Table II presents the range of dependent variables determined during the screening test for the AAS system mixtures. 

The incorporation of sulfur in asphalt emulsions also shows great potential. Although further improvements in the insulating value of asphalt might be expected by adding sulfur, such binders have other advantages over normal asphalt. In 1972 Pronk (9) produced sulfur asphalt emulsion mixes in the laboratory. More recently, Societe Nationale des Petroles d Aquitaine (SNPA) (10) reported the results of an extensive laboratory and field study using sulfur in an asphalt emulsion. Both Pronk and SNPA have shown that temperature-viscosity relationships are improved, as are Marshall stability and flow values. 

With increase of maturation and production of bitumens, asphalts and heavy oils the %S decreases and the residual stabilized sulfur becomes isotopically heavier. 

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. 

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.

The optimum or minimum allowable substitution ratio is then established by means of a series of justification tests at different binder contents. Figure 15 shows a comparison between the Marshall design properties of a conventional mixture using an asphalt binder and a 30 70 SEA binder. As indicated the optimum substitution ratio based on the maximum stability and equivalent air voids is about 1.7 1. Since minimizing the substitution ratio has a direct impact on the economic benefits to be realized by replacing the asphalt with sulfur these justification tests are to be recommended in all mix designs. 

The relative amounts of crystalline and dissolved sulfur as determined by a Perkin Elmer DSC-1B is depicted in a block diagram, Figure 2. An investigation of ageing characteristics and stability of the noncrystalline portion of the SA binder with three grades of paving asphalts at four levels of sulfur concentration indicates that the amount of dis-... 

The remaining 10.8 wt % of sulfur performs as a mix filler. These large agglomerations of sulfur do not perform in the same way as conventional mineral fillers which are dispersed in asphalt hot-mix. The latter, at the concentrations typically used, generally improve the void filling capacity of the asphalt binder (or reduce the VMA) without effecting such dramatic changes to mix stability as does sulfur. 

Increasing the proportion of sulfur in the binder, as shown by mixes No. 3, 4, 6, and 7 in Tables II and III, increases Marshall stability. This is attributed to the excess particulate sulfur, dispersed throughout the asphalt phase, which performs similar to a mineral filler. The particular sulfur may be observed using a microscope and is visible as small yellowish specks along broken mix surfaces. 

The allowable sulfur concentration in the binder depends on the properties of the asphalt. For example, asphalts A and B (Appendix, Table A-I) exhibit significantly different viscosities at the Marshall test temperature of 60°C. This difference is reflected by differences in mix stability at similar asphalt contents, shown in the Appendix and in Figure 6, i.e., 11120 N and 5960 N for asphalt A and B, respectively, at a content of 6 wt %. Asphalt B yields high-stability mixes and is not as prone to softening by low sulfur concentrations in the binder, whereas asphalt A exhibits the reverse behavior. 

The predominant role of sulfur in Thermopave is to stabilize the mix while the asphalt contributes to mix flexibility. Control of these two properties provides flexibility to mix design, permitting attainment of a variety of distinctive mix characteristics. The mix design technology for Thermopave differs significantly from conventional mix design. Mix optimization to balance the various mix properties is involved. The limited scope of this chapter restricts their consideration in detail. 

Thermopave mixes use substantially higher sulfur contents. Microscopic examination of mixes prepared in the laboratory and in a commercial Cedarapids hot-mix plant verified that some of the sulfur is finely dispersed, therefore contributing to the dilution of the asphalt, but most of the sulfur agglomerates readily to perform as a mix stabilizer. 

Sulfur New Asphalt Soften- ing Agent Resilient Modulus Bulk Air Specific Voids Marshall Stability ... 

---