Technology

Sulfur paving material begins road test All-sulfur paving compound

developed by Southwest

Research Institute may be

eventual replacement for

petroleum-based asphalt

The gasoline in an automobile's tank won't be the only petroleum end product to feel the effects when the petroleum runs out. So will the paving in the high­ways under the car. Looking ahead to that day, Southwest Research Institute has moved into a new phase in its develop­ment work on a total alternative to as­phalt: sulfur.

Although a number of organizations are well along in development and testing of sulfur as an extender for asphalt in paving materials, the institute's Sulphlex binders use no asphalt at all.

Late last year, work at the institute, under contract to the Department of Transportation's Federal Highway Ad­ministration, moved out of the lab and onto the ground surface at Southwest Institute's facility at San Antonio. It completed installation there of an 800-foot-long pavement using the Sulphlex plasticized sulfur binders.

"Everything we've seen to date indi­cates that this is going to be a major ad­vance in the field of highway paving," says Federal Highway Administrator Karl S.

Bowers. "At this point, we are very opti­mistic."

The test pavement will be the object of study for the next three and a half years. During that time, Southwest Research Institute will be conducting tests to de­termine such characteristics as skid re­sistance, deflection, voids, resilient mod­ulus, smoothness, and texture. Mean­while, institute workers also will be carrying out additional development work on the binder materials seeking to better their engineering properties.

According to project manager Allen Ludwig, the development program's object isn't to displace asphalt or compete with it. Rather, the Sulphlex binders are seen as an eventual alternative when as­phalt is either unavailable or too costly.

The Sulphlex binders are made by re­acting elemental sulfur with chemical modifiers at high temperature. The in­stitute is reluctant to disclose the chemi­cals other than saying that Sulphlex binders represent a family of materials involving 10 or 15 different chemicals. Ludwig says that since the idea was to produce paving materials that don't rely on petroleum, modifiers were sought from coal by-products, naval stores, and agri­culturally derived chemicals.

Sulphlex binders can be made to pro­vide pavements that are rigid like con­crete, flexible like asphalt, or intermediate between the two. Successful development of the materials, Ludwig notes, would provide highway engineers with a possible opportunity to optimize a pavement

rather than settling for a choice of the two alternatives, concrete or asphalt.

For the test paving in San Antonio, the institute made up three separate binder formulations that varied in color from brown for the rigid material to black for the flexible. To demonstrate that the materials could be used entirely with conventional asphalt equipment, each batch of 15,000 lb was transferred from the reaction vessels to an asphalt trailer, transported to a batch plant, and trans­ferred to a holding vat.

Each formulation was then mixed with a standard Texas highway specification limestone. About 50 tons of 6% binder/ 94% aggregate and 50 tons of 8% binder/ 92% aggregate were made from each for­mulation. The temperatures were com­parable to those used for asphalt: 310° F for the limestone and 200° to 250° F for the Sulphlex, with a resultant mix tem­perature of about 300° F. The mix was carried by long-bed dump trucks to the roadsite and, because of the short test sections, dumped on the ground and loaded into a Barber Greene paving ma­chine with a front-end loader.

The test paving consists of sections with each of the formulations used at 6 and 8% to study the difference in binder concentrations. Also for a control, a sec­tion of portland cement concrete was in­stalled as well as a section of Texas Highway Department specification as-phaltic pavement using 4.5% binder/ 95.5% aggregate.

The institute projects a materials cost of $70 per ton for the brown, rigid for­mulation, although actual cost, buying in 55-gal-drum quantities, was $131. It-projects a materials cost of $128 per ton for the black, flexible binder, with the actual cost having run $240 per ton. For the intermediate formulation, projected cost is $112 per ton, with actual cost hav­ing been $237 per ton. These costs are comparable to current asphalt costs of perhaps $80 to $100 per ton.

Ludwig points out that although the brown formulation provides a paving similar in rigidity to concrete, it does not require concrete construction methods such as forms. Rather it can be installed like asphalt paving, since only over time does it become hard.

Ludwig also notes that although pave­ment accounts for about half of asphalt consumption, roof materials account for most of the remainder. Sulphlex materials haven't been tested in uses other than paving yet. But, Ludwig says, researchers at the institute don't see any reason why Sulphlex materials couldn't be developed as a replacement for asphalt in any of as­phalt's uses. • Plasticized sulfur cement, Sulphlex, can be applied with conventional equipment

30 C&ENFeb. 26, 1979