Constructing new markets for spent foundry sand.

Foundry officials are taking notice of an emerging opportunity to profitably relieve a major headache--spent sand disposal.

Time is running out. Before long, with more stringent regulations and the closing of half our nation's landfills on the way, the age-old dilemma of what to do with spent foundry sands will be coming to a head.

Much attention, however, has been focused on using spent sands in the paving industry. And this route may be exactly what foundries need to keep from getting "buried alive."

While still in its early stages, reuse in construction is a viable alternative for foundries. However, it will take some good decision making and strategic marketing to get off the ground.

At the 6th Annual AFS Environmental Affairs Conference held in Milwaukee in August, Doug Hermann, STS Consultants, Ltd., told foundries how they can make beneficial reuse a reality. Hermann's data was collected by the civil engineering consulting firm as part of an AFS-funded project.

New Use for Foundry Sand

There are some limitations to foundry sand's use in construction projects, but this could be a giant step for the foundry industry.

Foundry sands are generally too fine to be a 100% replacement of the fine aggregate used in concrete and asphalt. In almost all cases, a partial replacement is being considered, particularly for high-performance construction materials.

Even partial replacements, however, add up to strong numbers. In every ready-mix concrete or asphalt truck that's making regular replacements, there might be three tons of foundry sand.

And although it may be necessary to work with a broker unless your foundry has large volumes of sand available consistently, foundry officials should be aware of the opportunities that are out there for their spent sand.

Market Opportunities

"Except for some very exotic sands that might exist in the foundry industry, you'd probably want to work locally with somebody who would use your waste material," Hermann said. "There would be minimum transportation involved, and there'd be good communication because you'd be close to your customer. And problems could be resolved rather quickly."

He targeted five key areas for foundries to investigate as potential markets for their sands. These included concrete fine aggregate, asphalt fine aggregate, cement, geotechnical fill and brick manufacturing.

In particular, Hermann finds the concrete and asphalt fine aggregate markets appealing for foundries. The value for both concrete and asphalt fine aggregate is about $8-12/ton.

Concrete Fine Aggregate--Silica sand may replace the fine aggregate component of a concrete mix. Concrete plants are located in virtually all communities, so transportation is cheap. Foundry sand would probably be more highly valued here than for geotechnical fill and asphalt fine aggregate.

Hermann said the mix design and quality control that concrete producers must put in their system cover a broad range, meaning everything they put in the mix must be predictable. Foundries will have to supply a high-quality, consistent waste stream.

"But they will probably pay you some premium dollars for that because they are accustomed to paying premium dollars for aggregate," he said. "They'll like it because silica is very durable. The only problem is that it's a little fine. So, it will only be a partial replacement."

Because most concrete ready-mix plants are probably computerized, all batch mixing will likely be done by computer. Thus, the processor may have to purchase a bin to add foundry sand with the existing fine aggregate. That may be the investment the processor and/or foundries will need to make to get foundry sand into the plant.

Concrete producers could replace about 45% of their current fine aggregate recipe with used foundry sand--sands not containing bentonite. Above that, workability problems with the fresh concrete and with hardened concrete may exist.

Bentonite is a major concern in concrete, since it swells to 10 times its volume in the presence of water (water is required in concrete production). Although the bentonite content is normally about 5-10% in green sands, this is no small issue because of the great swelling potential.

Also included in this group are concrete pipe, bricks, parking lot blocks and other uses.

Asphalt Fine Aggregate--This tends to be a fairly local market, but not as local as ready-mix plants. Concrete and asphalt suppliers are shrinking because performance specifications are being elevated by various state highway departments to economize construction costs and prolong performance.

But there are still a lot of what Hermann calls parking lot, driveway-type applications that don't need a highway specification mix design. Plants can shift physical property requirements quickly. Again, these plants may require extra processing and storage facilities with dosing operations and automation to adapt to foundry sand.

For asphalt, replacement levels are somewhat lower, probably 10-25%, since asphalt performance is a highly specified activity with Department of Transportation (DOT) and federal highway administration work. Although the replacement is lower, more types of foundry sands can be used and bentonite is not as critical.

Foundry sand has some characteristics that are desirable in asphalt, particularly the angularity of the aggregate. In some cases, foundry sands are more angular than typical bank-run aggregates. "This could be a real opportunity," Hermann said.

Cement--One disadvantage to this market is there are relatively few cement manufacturing plants in the U.S. (fewer than 100). The problem with the cement market is that most cement plants are already close to cheap silica sources, so foundries have to compete.

Silica, which plays a chemical role in cement production, could be replaced by a substantial amount of foundry sand.

Bentonite isn't an issue because of the kiln process and temperatures involved. The value is much lower, about $2-5/ton.

It could be a major market, however. Ernest Petrey, CP Recycling, estimates that of the 80 million tons of cement manufactured each year in the U.S., 15% is silica.

Geotechnical Fill--"Foundry sands don't require a lot of compaction," Hermann said. "Typically, a uniform material like foundry sand is easy to compact in place. It doesn't take much vibratory force to position it and to densify it. It's easy to compact without a lot of extra effort."

Bentonite is potentially the greatest concern, since a stable silica mineral combined with a bentonite mineral almost contrasts each other's performance. Although silica is a stable and durable material, when mixed with bentonite, it attracts moisture, causing freeze-thaw and shrink-swell problems that could cause problems with general structural fill. For that reason, it is probably the lowest of the opportunities.

Structural fill--A higher valued material, there are a lot of applications for foundry sand in structural fill. Shrink-swell characteristics are a big concern.

Drainage material--This is a fairly high-valued material. Without bentonite and other organic additives, most foundry sands will have fairly good drainage performance and would work well for many applications. They are not dramatically well drained, but consistently well drained because of their uniform gradation.

Liner material--Used to line landfills, most foundry sands with bentonite have sufficient permeability to be classified as barrier systems that would meet liner specifications. The bentonite, however, has an electrical-chemical bond that when introduced into a contamination environment, could cause shrinkage as a result of dehydration.

Low-strength trench backfill--Some utilities like to use this kind of material. Used in urban construction such as traffic intersections, this new technique involves contractors pouring foundry sand into excavations. The customer may be a utility or utility contractor.

Slurry trench (barrier) backfill--Curtain barriers are created by excavating a notch in the earth, supporting it with a bentonite slurry and then backfilling it with the bentonite enriched soil material. Bentonite sands would be added. This is one of the few known applications where the combination of the sand and the bentonite is desirable, since the bentonite swelling can create vertical barriers.

Landfill cover--Final cover might be a good opportunity in coming years because of the Subtitle D closures of several landfills. One-half of the U.S. landfills could close in the next 5-10 years. Daily cover, which foundries have traditionally targeted, doesn't look as good, since foundries must complete with geotextiles and other materials.

However, some foundries discovered that the price to provide daily cover to local landfills dropped since the "landfill scare" began. As foundries and other manufacturers found reuse routes, landfills were forced to buy new sand in some cases for daily cover.

Issues to remember in geotechnical fill are that you have to accumulate large stockpiles and then sell them to the marketplace quickly because there's not going to be continuous use in the geotechnical area. In concrete, there is a more steady market and demand. With asphalt, it's also a seasonal cycle.

Brick Manufacturing--The chemistry and physical characteristics of foundry sands are paramount for working with a brick manufacturer. However, the vitrification (baking) temperatures for the bricks are much lower than those for silica. This market must be created. Plants must be designed and constructed to handle this type of operation, and bricks must pass construction requirements.

Properties

How the material's going to physically perform in its construction material application is a looming question.

The bentonite in green sand is probably one of the biggest issues in this project. Bentonite is almost a continuous coating of the sand grain and is needed for the molding process. Dead (spent) clay coats the outside of the active clay bond.

The clay fines content is important because it fills the interstices of fine aggregate and affects moisture or asphalt requirements for concrete, asphalt or geotechnical fill applications. The gradation or grain fineness number is important as is the loss on ignition (LOI).

Several additives are common with chemically bonded and green sand type materials. Organic materials in aggregates are generally prohibited in concrete mix designs. The concern is the organic fractions that these mixtures add to the overall mix, which might be detrimental to the performance of the material.

There are concerns about freeze-thaw performance with the use of sands in exterior applications, such as sidewalks and pavements. Unfortunately, this might be a huge market area. However, further study in field verification is necessary.

Both sands were resistant to de-icer scaling--salts that are typically placed on roads--and performed equal to the controls or better. They also had satisfactory petrographic analysis--meaning there was adequate bonding between the cement paste matrix and the aggregate under microscopic examination.

Making it Happen

The last step in the process is to make it happen, to implement it. Hermann suggests having several customers. First, he said, you'll want to develop competitive cost requirements. He noted that when considering treatment, storage and transportation, you must put them into a cost accounting system to figure out what you can afford to do and which end of the market (cheaper or expensive) you are chasing.

Foundries need to characterize and determine volumes, pick a market opportunity with a local construction vendor, size a storage and distribution plan, and pursue it with that vendor. Foundries will be required to commit to delivering a consistent, quality sand for a certain price and then support the effort in making it happen.

"It will take an entrepreneur on the construction side to make it happen," Hermann said. "Foundries seem to want someone to take it off their hands--but why would anyone want to?

"We'd love to get paid but can't expect to do so in a penetrating market. Foundries must look past their business of just making castings here and look to process their waste in other reuse areas."

As far as the project's viability, he believes foundries can make this program work: "People always think regulations stop things. We have to work with regulations, but if there's an economic opportunity in the reuse of any waste material, that opportunity will drive it and make it happen. If there's a revenue stream to support something happening, then there's a lot going for it. If not, then it fights obstacles and adequate funding, on a constant basis."

What They're Saying About Environmental Issues...

Here are some of the main concerns voiced by attendees of the AFS Environmental Affairs Conference in August:

"For years, this industry just sat back and waited to see what was going to happen to us next and then we took some 11th hour knee-jerk reaction to a new regulation. We can't afford to do that anymore and, in many ways, some of the rules and regulations we have now emerged because we sat there and didn't say anything. We deserve what we got. We have to get involved in both the regulatory and legislative process."

James White, Grede Foundries, Inc., Milwaukee, Wisconsin 

"We don't have time to do everything. There's so much reading, paperwork. The biggest challenge is finding out about everything, and in time to comply. We've all got six months of mail on our desks. This is a very scary time. Ignorance is no excuse and you could end up in jail."

Joy Cole, EBAA Iron, Inc., Eastland, Texas 

"We all want to be as close to zero discharge as practical and be totally environmentally friendly. To temper with reality, that's something we can't meet. As far as criminal sanctions for managers, that borders on ridiculous. My managers are not criminals. They should attach that 'criminal' tag to politicians."

Gary Fisher, Osco Industries, Inc., Portsmouth, Ohio 

"Air topics will be a very expensive venture. Most companies have little data to start with. We don't know where it will lead. The paperwork, chance of penalty for an innocent error--administratively, it's a nightmare. Everything's come so quickly you've got to fly by the seat of your pants and hope you've covered everything, then come back later and give a second look. Also, the government is using a hammer with foundries even when we're doing the best job possible. They're taking an adversarial approach rather than helping us."

Ken Bender, Teledyne Casting Service, LaPorte, Indiana

"My biggest fear is the environmental regulations involving air and waste that would force a restructuring that the industry isn't capable of funding. With the Clean Air Act's MACT |maximum achievable control technology~, they take the top 12%, but there's quite a difference between a foundry in Berkeley, California, and what they're allowed to do vs. a 50-man job shop foundry in the middle of nowhere in an attainment area. No one wants to recognize that. With sentencing guidelines, when the penalty is so high, people get so cautious they're no longer effective and progressive--and that's when creative solutions slow down and things stagnate."

Chuck Ruud, American Steel Foundries, Chicago, Illinois