Launch Slideshow

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Help for Your Air

Help for Your Air

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    A sample of air-entrained concrete. Monitoring entrained air is a challenge for producers.

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    Above: A microscopic view of carbon from fly ash. Left: Aerated Miracon bubbles before going into the mix.

Producers who have used Miracon say their material costs have decreased because the properties of the AEA allow a reduction in other costly ingredients. They estimate their savings at 50 cents to $1.50 per yard.

Polymer AEAs involve a special machine at the plant that converts the product to precise air bubbles before it goes into the mix. A significant number of ready-mix and precast plants now have it, with others committed to adding it soon.

Fly ash benefits

To help solve the problem of too much or varying amounts of carbon from fly ash, some manufacturers have redesigned their processes. With applications integrated into coal-fired power plants where the ash is produced, the carbon content of fly ash can be reduced, leaving a low-carbon material for use in concrete.

“With our electrostatic separation process, we can produce low LOI fly ash called ProAsh,” says Dave Timmerman of Separation Technologies LLC. “It has a carbon content of 3% coming from fly ashes, with sometimes over 30% carbon content.” The high-carbon material that the patented process separates is returned to the power plant as an alternative fuel source. “Because the raw material has undergone this process, the final product is consistently low in carbon and eliminates variable air-entrainment issues,” he says.

Several power plants are currently in ventures with Separation Technologies to remove carbon from their ash. Timmerman estimates that the treated ash is now increasing the nation's supply of usable coal ash by 1-2%.

Fly ash neutralization

A different new treatment for fly ash leaves the carbon in place, but eliminates carbon fly ash's negative effects on AEAs. Its brand name is Carbon Blocker, supplied by FlyAshDirect, a fly ash marketer. It has outfitted several plants with the Carbon Blocker fly ash treatment system.

Jim Irvine, president of FlyAshDirect, explains that his system significantly reduces the absorptive tendency of carbon found in most fly ash sources, so that it cannot absorb admixture chemicals, including air entraining agents.

Carbon Blocker improves the air void matrix by minimizing bubble size and improving spacing, the company says. The improved air void system is said to be more durable, allowing it to survive mechanical mixing action and extended delivery time better.

The Carbon Blocker conditioning system is typically used at the power plant as the ash is loaded into trucks. The process costs no additional money to the producer because it is factored into the agreement the company maintains with the power plant.

It's too early to say that controlling entrained air will no longer be a problem. But it is not a stretch to think that as more ready-mix producers adopt stable new AEAs and more power plants improve fly ash quality, it will not be the major expense and headache that it is today.

Pieter VanderWerf is president of Building Works Inc., a consulting firm that researches new construction technologies. Visitwww.buildingworks.com, or telephone 617-232-2862.

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