Certain industrial waste products work in hot mix asphalt, but sometimes you may have to handle them differently than conventional additives.  Pennsylvania producer Highway Materials, Inc., discovered that when they incorporated foundry sand into the hot mix process.  Determined to make it work, they tackled the challenge with a burst of energy.

Vince Angelo, vice president of Highway Materials, Blue Bell, Pa., heard about the steel foundry residue material from a friend.  He got in touch with Process Recovery Corp. (PRC), Sinking Spring, Pa., a company which processes the material.  Company officials visited Angelo and brought samples on the material to him.

Used in other markets, the foundry sand is a new material to the asphalt industry.  And, because it is produced differently than the conventional hot mix ingredient, Angelo had a sample of the sand checked for properties.  It made a good mix, and filled the voids, so, the company began using it in 5 to 10 percent amounts.  "It actually reduced the asphalt content in some mixes," he says.  "We've had no problems in the mixes we've made with it."

The foundry sand packs another benefit, too.  Angelo says Highway Materials buys manufactured sand for their fines needs, but because of the way it's processed, they can't get intermediate sieve sizes.   So they buy natural sand to fill in gradation gaps.  "The foundry sand is actually a little more economical to use than natural sand." he says.

In the process of making castings, steel foundries line their molds with the sand.  It breaks off the molds in huge chunks, and PRC processes the chunks by removing any metal, and blends the sand.   When Highway Materials buys the sand, it's at minus 0.375 inch (9 mm) size.

As wonderful as the recycle material sounds, though, it's not without it's handling problems.  When the material was put first into the cold feed bin, the moisture in it made it difficult to feed.   Instead, it clung to the bin walls.  "We were having tons of problems feeding it," says Angelo.

Ron Fleagle, plant manager for Highway Materials in Lititz, Pa., was faced with the challenge of getting sand into a 200 ton (180 metric ton) per hour McCarter batch plant, one of eight hot mix plants the company operates in Pennsylvania.  "I had to find a system that would enable me to continue feeding the plant at a steady continuous rate," he says, "and I simply had not been able to do that feeding foundry sand."

Angelo says that in the three or four years the company has used the foundry sand at three plant locations, they've tried various types of vibrators and bin knockers without much success.  They tried air cannons for awhile, but still had problems moving the material.  The company finally met with Meeker Equipment Company Inc., in Harleysville, Pa., and discovered a modification in the way they fed the material - and a burst of energy - would solve the problem.

Fleagle put a 0.25 inch ( 6 mm) thick plastic liner in the cold feed bin so the material would slide, and then mounted six bin activators at various locations on the outside of the bin.  Hooked up to compressed air hoses, the units, manufactured by Pulsonics Inc., Belleville, N.J., introduced air bursts directly into the material.  These bursts gently keep the sand moving to the belt feeder.  The number of injectors and their positions in the bin was selected by the engineers at Pulsonics Inc.  "This system really works," says Angelo.

Fleagle and Angelo say the bin activators are designed for any type of material that is hard to feed.   "Recycled asphalt pavement (RAP) jams and bridges in the bin, depending on hot weather conditions," says Angelo.  "The units help move the RAP when this happens," he says.  Highway Materials uses the Pulsonics units for both foundry sand and RAP material.

Reprinted with permission from The Asphalt Contractor, November 1995

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