Question

The town building department doesn't want us to use concrete mixed with flyash. Do you have any information on contamination in flyash?

Asked by Barbara Donahue
Sandy Hook, CT

Answer

Anthony Addesso

Answered by Anthony Addesso

Hawthorne, NJ

Addesso Architecture

December 9, 2010

The building inspector has no jurisdiction to keep you from using the material, because at this time it has been approved for use in concrete.

But for me, the jury is still out on the use of flyash in concrete. The immediate idea of using flyash to reduce the use of Portland cement and to gain greater strength sounds great. But like many other new materials that have come along, and later have been found to have environmental issues, flyash may also follow that path.

The information I have found may make you re-think the use of flyash.

Fly ash is widely used

The truth of the matter is that concrete manufacturers use flyash on a regular basis. The answer to my telephone calls was a resounding yes for using flyash in all of their standard mixes from 3,000-pound to 5,000-pound concrete. Most people are not aware of what is in concrete mixes and that to get concrete with no flyash, you have to submit a special order.

I have spoken to a number of people in the industry, and have received a multitude of answers.

Some facts about flyash are:

  • The use of flyash in concrete gives it more overall strength than regular concrete.
  • The use of flyash keeps the cost under control.
  • Flyash is readily available.
  • Flyash does contain elements that are toxic.
  • Stockpiles (4.5 million tons) of flyash have been known to contaminate groundwater as noted in the Washington Post.

Health effects

Contamination of groundwater at dump sites, as noted previously, with a large concentration of flyash exposed to the elements, allows water to leach through the stockpile into the ground and finally into the groundwater. This contamination occurs over long periods of time.

However, when flyash is introduced into a concrete mix it is encapsulated within the mix, and bonds with the Portland cement and the aggregates. This has a much different effect on the toxins within the flyash, and this is where the information gets less definitive.

It becomes very difficult to determine the long-term health effects of the use of flyash within concrete.

  • I have not been able to find anyone who can categorically say the offgassing of a flyash concrete basement wall causes any ill health effect.
  • Nor have I been able to find any noteworthy information about toxins leaching out of the concrete into groundwater, etc.
  • But I have also not found anything categorically showing that flyash in concrete has no health or environmental issues.
  • The EPA is considering deeming flyash a hazardous waste, and this will definitely affect the use of the material in the construction industry.

My recommendation

Considering all of this confusing information, I would recommend that you do not use flyash concrete for any structures that have an interior exposure to the occupants.

  • There is quite a debate raging, so it doesn't seem wise to install a foundation wall, for example, that in a few years may be deemed an environmental issue will be difficult to remedy.
  • Concrete with flyash can be used in exterior applications and for paving, etc., with little risk of exposure to the toxins within.

The two sides -- the concrete manufacturers and the environmentalists -- are battling it out at this time. It is partly an economic issue, as a reduction of the Portland cement usage reduces the cost and the environmental impact of producing Portland cement, but it may have environmental issues of its own.

But the truth is that flyash is already used in concrete and concrete block on a regular basis, so you most likely are getting flyash in any case.

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