Sulfur extended asphalt

Sulfur as an Additive for Asphalt. Sulfur-extended asphalt (SEA) binders are formulated by replacing some of the asphalt cement (AC) in conventional binders with sulfur. Binders that have sulfur asphalt weight ratios as high as 50 50 have been used, but most binders contain about 30 wt % sulfur. Greater latitude in design is possible for SEA paving materials, which are three-component systems, whereas conventional asphalt paving materials are two-component systems. Introduction of sulfur can provide some substantial benefits. At temperatures above 130°C, SEA binders have lower viscosities than conventional asphalt. The lower viscosity enables the plant to produce and compact the mix at lower temperatures than with conventional... 

Figure 7. Typical proportions of dissolved and crystallized sulfur in sulfur-extended asphalt blends (32). Key , dissolved sulfur and , crystalline sulfur.

Figure 15, Sulfur-extended asphalt (SEA) justification test data. Curve 1, asphalt binder and Curve 2, SEA binder (30-70) (33).

In contrast to the SAS systems, the number of sulfur extended asphalt paving projects in the United States has been consistently increasing since 1977. This is shown in Table 4 along with projects undertaken in Europe, Canada and the Middle East. 

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,... 

Sulfur-Extended-Asphalt Field Trials-MH 153, Brazos County,... 

McCullagh, F. R., "Sulfur-Extended Asphalt In Overview", Twenty-Ninth Annual Roads and Streets Conference, Arizona Transportation and Traffic Institute, Tucson, Arizona, (1980). 

Saylak, D., "Design of Open Friction Courses with Sulfur-Extended Asphalt Binders", Final Report on FHWA Contract No. DOT-FH-11-9588, May, 1981. 

Both cellulosic wastes and lignins were found to have only limited applicability to the problem at hand. Sulfur, however, has been shown to be a very useful material for this purpose. Elemental sulfur may be used to extend asphalt, as in sulfur extended asphalt (SEA) binders, or chemically modified sulfurs may completely replace asphalt in paving mixtures. 

Izatt, J. 0. "Sulfur-Extended-Asphalt Field Trials, M-153 Brazos County, Texas, A Detailed Construction Report" Report FHWA-TS-80-214, December 1979 ... 

Gallaway, . M. Saylak, D. "Sulfur Extended Asphalt (SEA) Sulphur/Asphalt Mixture Design and Construction Details - Lufkin Field Trials" Report FHWA-TS-78-203, January 1976 (reprint 1977). 

With Saudi Arabia now in its Third Plan, the demand on asphalt cement will be a very serious problem unless other measures or solutions are taken, such as utilization of sulfur extended asphalt. 

The concept of using a sulfur extender/modifier is very old, but it was not until the 1970s, during the advent of sulfur-extended asphalts, that a process was developed and started to be used on project sites (Beatty et al. 1987 Denning and Carswell 1981b Kennepohl et al. 1975). 

Beatty T.L., K. Dunn, E.T. Elarrigan, K. Stuart, and H. Weber. 1987. Field evaluation of sulfur-extended asphalt pavements. Transportation Research Record No. 1115. Washington, DC Transportation Research Board. 

Attainment of fine sulfur dispersions such as described above are crucial to utilization of sulfur as an asphalt diluent. Provided that they remain stable, the binders will exhibit the sulfur-extended binder properties described previously. 

A typical Thermopave mix using sand (Aggregate C in Table I) was prepared using the regular mixing sequence with 6 wt % asphalt and 12 wt % sulfur, a considerably higher amount than used in sulfur-extended binders. Examination of the binder phase on thin film portions of the microscope slides showed numerous finely dispersed sulfur particles. The predominant sulfur particle diameter was 4 /x, similar to the size observed for the sulfur-extended binders prepared in the blender. This also indi-... 

Sulfur Dispersion in Asphalt Plants. Sulfur-extended binder and Thermopave mixes were prepared in several batch type commercial hot-mix plants to verify the effectiveness of aggregate shear on sulfur dispersion during mixing in the pugmill. The influence of the following variables on the dispersion of sulfur was assessed. 

Sulfur-extended binder system—binder content, 6 wt % mix binder composition, 4.5 wt % asphalt, 1.5 wt % sulfur sulfur/ asphalt weight ratio 0.33. 

Microscope slides of the sulfur-asphalt binders were prepared at the plant sites. For the sulfur-extended binder mixes, the slides were photographed within 2 hr of preparation. For the Thermopave mix, the slides were photographed two days after preparation. 

This verifies that aggregate shear during mixing is effective in dispersing sulfur in commercial hot-mix plants. Addition of asphalt and sulfur to the pugmill simultaneously would permit the manufacture of sulfur-extended binder mixes at the usual mixing cycle time. 

Figure 2. Appearance of sulfur particles dispersed throughout asphalt phase of sulfur-extended binder mix after 15 sec mixing in Cedarapias pugmill. Batch size 7000 lb.

Examination of thick sulfur-extended binder films, mixed with sulfur for 30,45, and 60 sec, showed the presence of some larger sulfur particles. As the particle density on the slide is higher in thick films, this demonstrates that some coagulation of the sulfur particles takes place if the sulfur content is too great, relative to the amount of asphalt (sulfur/ asphalt weight ratio, 0.33). Similar evidence of coagulation of particles was obtained in thick films taken from the laboratory Waring blender dispersion for a similar blend. 

Aggregate and asphalt B properties appear in the Appendix. Sulfur-extended... 

A number of features distinguish sulfur-extended binder mixes from conventional hot-mix and must be considered in mix design. To illustrate this, samples have been prepared from a conventional asphalt aggregate mix and from a series of sulfur-extended binders. Information on the... 

The air-void content of asphalt concrete mixes affects mix permeability and is therefore very important from a pavement durability standpoint. The permeability of various sulfur-extended binder mixes, prepared at a variety of air-void contents, was measured with an air permeameter similar to that described in Ref. 16. The results, presented in Figure 7, indicate that the sulfur-extended binder mixes exhibit an air voids vs. 

The studies illustrate that the two sulfur-asphalt systems are complementary. The primary objective for using the sulfur-extended binder system is to use sulfur as a diluent to conserve asphalt used in conventional hot mixes. No asphalt saving is realized using Thermopave. The unique features of this process are that it permits the manufacture of high-quality paving materials using inexpensive, poorly graded sands and yields pourable mixes, similar to cement concrete. 

Based on studies performed, some guidelines have been formulated for the design of sulfur-extended binder mixes. These include recommendations for limiting sulfur content to maintain existing mix flexibility and the replacement of asphalt with sulfur on an equivalent volume basis to maintain the existing standard of mix durability. 

Sulfur-Extended Mastic Mixes. The use of sulfur in mastic or Guss-asphalt mix type formulations extends the use of this material. For example, softer asphalt grades may be used, and the mixes may be placed at lower temperatures. Using sulfur would permit variation in mix workability and control of the mechanical properties of the mixes and would extend the variety of aggregates that may be used. 

The oil embargo of 1973-74 caused the Federal Highway Administration (FHWA) to establish an R D program to investigate the production of asphalt replacements and extenders from essentially non-petroleum sources. Since its inception, this program has examined in detail the use of sulfur in elemental and chemically modified form binders derived from cellulosic materials such as wood wastes and animal manure (JL) and lignins produced as by products of the paper and pulp industries (2) ... 

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. 

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