Fractionating Aggregate

As highway agencies shift responsibility for aggregate specifications to contractors, contractors in turn are shifting more responsibility to aggregate producers to provide more consistent, quality processed materials. And a number of producers — including Dupo, Ill.-based Casper Stolle Quarry & Contracting Co. — are responding to the challenge by building fractionated aggregate plants, which have the ability to blend aggregates in specifically desired proportions.

The fully automated, fractionated aggregate plant at Casper Stolle's Falling Springs Quarry — featuring 14 screens, four crushers and 52 conveyors (the longest being 815 feet) — combines super-efficient crushing and screening with a unique blending tunnel to create custom mixes forits customers.

"This plant is wonderful — it gives us such flexibility," says Lanny Largent, superintendent for Falling Springs Quarry Co. and a 38-year aggregate industry veteran. "The fractionated plant allows us to supply the needs of people who are designing new mixtures for asphalt and concrete pavements. And we are able to address the needs of our customers more effectively."

The properties of coarse and fine aggregates are very important to the performance of the asphalt and concrete pavements. Particle angularity, texture and shape are among the aggregate characteristics with significant effects. With the fractionated plant, Casper Stolle can produce precise fractionated aggregate sizes — such as the specific sizes needed in Superpave mixes in asphalt construction, for example.

"There have been so many changes with the ingredients in liquid asphalt," notes John Cramer, president of Casper Stolle. "There is no margin for error and you have to be extremely specific in the gradation sizes — they have to be very tightly controlled or you get rutting along with other problems that can come out of a bad mix."

Cramer, a 33-year industry veteran who served as the 2003 National Stone, Sand & Gravel Association (NSSGA) chairman, says the new fractionated plant at Falling Springs Quarry was erected in two phases. The first phase was completed in June 1998; then, in 2003, the completion of Phase 2 included additional Deister triple-deck 8-foot by 20-foot screens and numerous Deisterhigh-speed vibrating screens.

The Falling Springs Quarry is just one of two fractionated aggregate plants currently in operation in Illinois, according to Largent. The plant is set up in four segments — a primary plant, secondary crushing station, finished plant, and the fraction plant, and is capable of producing a wide variety of products. "The list is pretty extensive," he says. "We try to consistently ship 22 to 23 products, and we actually make 52 product recipes."

Key advantages of a fractionated plant are its precision, quality and consistency. "We are able to control our quality better than with aconventional screening operation, and we can control our gradations far more effectively," says Largent. "We are able to control the percentage of the mix and make a consistent product."

Automation at Falling Springs Quarry makes it possible for the aggregate plant to run unattended — controlled from a laptop computer. Multiple sensors monitor and adjust the aggregate production process and can even shut down the process automaticallyif needed.

"I can manipulate the plant from my home," says Largent. "If bad weather comes in, I can make a few keystrokes on my laptop and shut down the plant. Then, when the storm passes through, I can start the plant back up. Also, if we have motion failure on a belt feeder, I can restart it and I can reset the time so we don't lose that production time. There is high flexibility."

According to Largent, Falling Springs' primary plant operates five days a week. "But the secondary plant runs six to seven days, depending upon what our requirements are," he says. "It is not uncommon for us to run it on a Sunday evening."

Fallings Springs Quarry Co. provides a variety of aggregate products for commercial and non-commercial customers. The plant offers a unique, computerized customer load-outstation featuring six bins and 1,200-ton capacity. "We can put anyone of our 52 recipes in anyone of those bins," Largent says.

National Stone, Sand & Gravel Association says its member companies produce more than 92 percent of the crushed stone and 75 percent of the sand and gravel consumed annually in the U.S. More than 3 billion tons of aggregates were produced in 2005 at a value of approximately $17.4 billion.

Casper Stolle, a member of NSSGA and the Illinois Association of Aggregate Producers, produces "just less than 2 million tons" of aggregates annually between its two Dupo facilities — the 350-acre Falling Springs Quarry and the 150-acre Casper Stolle Quarry.

Casper Stolle Quarry & Contracting Co.'s history dates back to the 1800s. "Casper Stolle came over to the U.S. from Germany in 1844, and in 1845 he partnered in the quarry business to do contracting in St. Louis," says Cramer. "We have been operating continuously from the Dupo location (Casper Stolle Quarry) since 1882, making us one of the oldest quarries in the country. We acquired Falling Springs Quarry about 20 years ago."