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David Axt, AIA, CCS, CSI
Senior Member
Username: david_axt

Post Number: 1125
Registered: 03-2002


Posted on Friday, September 24, 2010 - 04:55 pm:   Edit PostDelete PostPrint Post

My Owner wants us to add language in the cast-in-place concrete specification restricting heavy metals, zinc, and asbestos in fly ash.

Does anyone know of any test or fly ash requirements that I can add?

BTW, I find this requirement strange because the contaminants will be encapsulated in concrete mix.
J. Peter Jordan, CSI, CCS, AIA, LEED AP (Unregistered Guest)
Unregistered guest
Posted on Friday, September 24, 2010 - 05:15 pm:   Edit PostDelete PostPrint Post

There was a relatively recent thread related to this with some useful links. My impression is that fly ash is not really a "processed" or "refined" product so that inserting this requirement in any form may mean that fly ash cannot be used/
Mark Gilligan SE,
Senior Member
Username: mark_gilligan

Post Number: 309
Registered: 10-2007
Posted on Sunday, September 26, 2010 - 02:38 am:   Edit PostDelete PostPrint Post

The fly ash in concrete and typically there is no moisture flow to leach any heavy metals out.

I agree that if you put this requirement you may not find any body who will be interested in bidding on the project.

There are other things I would rather worry about.
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick

Post Number: 1242
Registered: 03-2002
Posted on Wednesday, September 29, 2010 - 08:45 am:   Edit PostDelete PostPrint Post

Well, you can certainly specify a limit in parts per whatever, or percentage by weight. But, who figures out what those are? Zero? Tell the client that they must determine what limits to set, not you. Zero may simply be unachievable. If they're that worried, maybe they shouldn't use flyash, LEED credit be d***ed. Even then, how much of those things are in portland cement and aggregate?
Joseph Berchenko
Senior Member
Username: josephberchenko

Post Number: 28
Registered: 08-2003
Posted on Wednesday, September 29, 2010 - 11:03 am:   Edit PostDelete PostPrint Post

Environmentalists are conflicted about fly ash and there has been some previous discussion on the topic on 4specs. Flyash can replace some portland cement in concrete. Portland cement has a large carbon footprint.
In 2008, a dam collapse in Tennessee appeared to increase arsenic levels in the Emory River and raised public awareness about heavy metals in fly ash. Fly ash may contain elevated heavy metals because powerplant smokestack scrubbing operation concentrate them. However, as indicated above, some say the metals are fixed and don't leach.
Here's an editorial from the current issue of Environmental Building News: "...we call on industry or certification organizations to develop a standard for the content of mercury (and possibly other heavy metals) in fly ash. We envision the development of 'hazard concentration grades' for fly ash so that users of that material (whether cement manufacturers, ready-mix concrete companies, or manufacturers using fly ash in other products) can be aware of the level of these toxic constituents and make decisions accordingly."
I don't think you can currently control heavy metal constituents in fly ash.
Anne Whitacre, FCSI CCS
Senior Member
Username: awhitacre

Post Number: 1021
Registered: 07-2002


Posted on Wednesday, September 29, 2010 - 11:57 am:   Edit PostDelete PostPrint Post

Joe: environmentalists are conflicted about a lot of things with no end in sight.
Regarding fly ash -- there is only so much that you're going to put in the mix anyway, and in most jurisdictions you're simply adding it to the mix, not substituting it for cement (which was the original idea). As long as the AHJ has requirements for break-strengths at 3 and 7 days (and does not waive those requirements) the fly ash won't be a substitute.
I agree with John -- if the Owner wants the requirement, let them give you the number.
Mark Gilligan SE,
Senior Member
Username: mark_gilligan

Post Number: 310
Registered: 10-2007
Posted on Wednesday, September 29, 2010 - 01:16 pm:   Edit PostDelete PostPrint Post

The code does not mandate break strengths at 3 or 7 days. Concrete cylinder tests before 28 days are only required for situations such as when you want to remove floor forms and shoring early or where you have a post tensioned slab and you wnat to stress as soon as possible. This is driven by design decisions and the contractors desire to reduce the construction time.

When using high levels of fly ash you should specify the acceptance tests at 56 days instead of 28 days. The purpose of earlier cylinder tests is to get an idea if the strength gain is on track.

Fly ash can also provide other benefits such as reducing the porosity of concrete.

I recommend letting the Owner know that if you specify mercury limits that they run a real likelyhood that there will be no bidders unless the project will have a number of big pours. I would also talk with the local suppliers to understand what limits they can meet.
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 62
Registered: 12-2006
Posted on Thursday, October 07, 2010 - 10:08 am:   Edit PostDelete PostPrint Post

The other option here may be to eliminate fly ash in the mix if the concrete is being used where leaching may be a possibility such as site concrete or a dam. Perhaps this is an issue in below grade conditions in a high water table where the concrete is actually immersed, though in that instance I would expect that you're using a good waterproofing product that won't dissolve over time. Keep in mind that typically our concrete is encapsulating the fly ash and our waterproofing and vapor retarding membranes are encapsulating the concrete. Leaching from a slab-on-grade over an adequate vapor retarder/ barrier seems very unlikely to me.

What concerns are there, if any, with other replacement pozzolans?
Mark Gilligan SE,
Senior Member
Username: mark_gilligan

Post Number: 311
Registered: 10-2007
Posted on Thursday, October 07, 2010 - 03:43 pm:   Edit PostDelete PostPrint Post

Rather than spending a lot of time trying to figure out what to do when leaching may be a possibility I suggest we wait and see what the regulations will be and then adjust our practice if necessary.

The problem here is that somebody noticed that fly ash has some heavy metals without putting it into perspective. There are heavy metals in a lot of things that we regularly deal with and that we do not worry about. I will suggest that you will get more exposure to zinc from the galvanized had railing than you will ever get from fly ash whether or not you use a membrane in your structure.
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 64
Registered: 12-2006
Posted on Thursday, October 07, 2010 - 05:06 pm:   Edit PostDelete PostPrint Post

My guess is that I get more zinc from multi-vitamins and 'holistic' cold remedies than from both of those other sources combined.
J. Peter Jordan
Senior Member
Username: jpjordan

Post Number: 453
Registered: 05-2004
Posted on Friday, October 08, 2010 - 11:35 am:   Edit PostDelete PostPrint Post

There was a recent episode of House where he diagnosed zinc poisoning due to a patient overusing denture adhesive (as much as a tube a day).

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