Flooring Products on Concrete w/ Fly Ash

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Author Message Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 34 Registered: 10-2005 Posted on Tuesday, September 09, 2008 - 04:06 pm:    Seeking assistance with the following request that has been made for my research: "With the ever increasing demand for LEED points it is time to do some research on concrete containing fly-ash. Presently our 03300 specs do not permit the use of fly ash for floor-slabs that receive a flooring material, epoxy, VCT, etc. The reason isconcern that the flooring adhesives may not be compatible with the fly-ash-concrete. Please contact the flooring material representatives and inquire about the compatibility of this system (concrete w/ fly ash content) to prevent loss of adhesion/delamination. If the answer is positive, we will change the concrete specs to allow fly ash content; It is suggested that the flooring specs would then be revised to require the adhesive to be compatible with fly-ash-containing concrete." There are many flooring products out there - has anyone heard of potential concerns or problems with adhesion if fly ash is added to the concrete mix? Thank you in advance for your input. Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 120 Registered: 11-2003 Posted on Tuesday, September 09, 2008 - 04:26 pm:    Yes, as we go green, we have recently heard of similar concerns from flooring reps (vinyl, rubber, maybe even carpet). But to date have not had the opportunity to discuss any further with my Structural Eng, flooring reps, or Commissioning Agents. I have several sets of specs from LEED Certified projects and they all have fly-ash specified in the conc. I should check with project consultants that authored the specs to see if there were flooring adhesion issues or how it was resolved? Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 821 Registered: 07-2002 Posted on Tuesday, September 09, 2008 - 05:53 pm:    there are a couple of issues with fly ash used for slabs, but they are not insurmountable. 1) concrete takes longer to fully cure with high amounts of fly ash -- so you may not get a dry enough slab at the time you want it. 2) fly ash is smaller particles and the surface can be quite a bit denser than "regular" concrete. Adhesion may be affected, and this may be the flooring manufacturer's concern. 3) too much fly ash makes the mix rather unworkable. a few years ago, the City of Seattle wanted to increase fly ash requirements for concrete mixes and the consensus among concrete suppliers/workers was that 25% to 30% was the limits of workability (at least at that time; they may have relaxed since then). according to the concrete guys "too much fly ash and it just all balls up in the tremie and refuses to flow properly. This isn't an issue with the flooring material supplier, but is probably still worth paying attention to. you'll need to test products on the type of mix you propose to use.. and perhaps make some adjustments. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 447 Registered: 11-2004 Posted on Tuesday, September 09, 2008 - 06:12 pm:    Here some speculation: since the flyash is tinier and fills in the voids, might it not help the issue of vapor drive through slabs and actually improve flooring adhesion? Just an idle thought after attending a vapor-drive-through-slab seminar last month. I'd be interested in hearing what your research reveals, Dale. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 86 Registered: 10-2007 Posted on Wednesday, September 10, 2008 - 02:05 am:    IMHO I am doubtful that the flooring manufacturers really understand concrete and moisture flow in slabs. The know they have a problem and have latched on this theory to explain the problem. The fly ash should help to reduce the moisture flow through slabs. At the last firm I worked the typical concrete specification called for enhanced fly ash to do this. The typical moisture tests measure the availible moisture in the concrete near the surface and are not indicative of the moisture flow through the slab. In fact I have seen test results that imply that the amount of moisture that can "flow" through a slab is much less than the moisture tests imply. You can get different moisture readings by adjusting the grind of the salt used in the moisture test kits. This is not covered by the standard. Having said that, if you want their warrenty you may have to play by their rules. Dale Roberts CSI, CCPR, CTC Senior Member Username: dale_roberts_csi Post Number: 57 Registered: 10-2005 Posted on Thursday, September 11, 2008 - 12:05 pm:    Dale, as a manufactures rep for mortars and mastic’s for the tile and stone industry, fly ash does not affect the adhesion of our mortars or mastic’s. We have had years of test data regarding 15% to 18% fly ash. I have not seen many jobs using 25% to 35% fly ash, but this will not affect the adhesion or bond strengths of our mortars. Surface quality and moisture content on the concrete will probably play a more important role on the performance of any applied mortar, mastic or epoxy. I can tell you, using that much fly ash will delay the time you can put that slab into service. Fly ash reduces the early strength of concrete. Using more fly ash in the mix reduces the amount of water needed in the mix causing less voids left in the concrete making it less preamble, but we have manufactured mortars to bond to glass tile. Fly ashes undergo a “pozzolanic reaction” with the lime (calcium hydroxide) Created by the hydration (chemical reaction) of cement and water, to create the same binder (calcium silicate hydrate) as cement. The main benefit of fly ash in concrete is that it not only reduces the amount of non-durable calcium hydroxide (lime), but in the process converts it into calcium silicate hydrate (CSH), which is the strongest and most durable portion of the paste in concrete. Mark, our company does understand concrete and moisture flow and we have scientist that have master’s degrees in the subject. Along with reps like myself who attend lectures, read articles and books on the subject. One of the best books that I have read on concrete and moisture was written by Howard M. Kanare Concrete Floors and Moisture. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 105 Registered: 01-2008 Posted on Thursday, September 11, 2008 - 12:28 pm:    Dale, Perhaps you can rephrase your statement "...making it less preamble,.but..." Dale Roberts CSI, CCPR, CTC Senior Member Username: dale_roberts_csi Post Number: 58 Registered: 10-2005 Posted on Thursday, September 11, 2008 - 12:34 pm:    Would it help if I said I have been recently studying the American revolution and Constitution of the United States? Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 35 Registered: 10-2005 Posted on Thursday, September 11, 2008 - 01:58 pm:    Thank you for the input received so far. Based on some of the comments, I have done some additional research. I have found (as has been stated) that the fly ash does lengthen the cure time. We have already been experiencing problems with the amount of time required for the slabs to fully cure and get down to allowable moisture levels. The addition of fly ash also helps to increase the concrete strength and density - making the concrete more resistant to moisture migration and more durable in the long run which would be beneficial. Also, it appears that it helps to reduce the alkalinity of the floor slab which is a positive. I gather from some articles that I saw that there may be some problems with quality control - one article in particluar indicated that the fly ash could result in isolated areas of low surface strength. This article recommended surface strength testing if fly ash is used to identify and correct such areas. I also found a couple of articles relative to concrete staining and polishing - one advocating not to use fly ash if "staining" the concrete surface and another advocating to maintain 20% max. fly ash if polishing the floor surface - both were addressing concerns with the effect on the consistency of the final finish appearance. It appears that I am going to need to go directly to a number of various floor system manufactures to start to get feedback on any concerns that they have with the use of fly ash in the concrete. Richard Hird (Unregistered Guest) Unregistered guest Posted on Saturday, September 27, 2008 - 10:14 am:    Would agree with the above responses for concrete slabs to receive floor coverings, but it should be noted that exposed slabs for industrial and storage usage should not have flyash because of increased dusting. If it is a mechanical room in the midst of floor finishes it is not a problem. I would ask myself a lot of questions about dust issues if it is loading dock, Peggy White, CSI, CCS, CCCA, LEED AP Senior Member Username: peggy Post Number: 25 Registered: 07-2007 Posted on Saturday, September 27, 2008 - 11:19 am:    One very informative book on this topic is "Making Better Concrete - Guidelines for Using Fly Ash for Higher Quality, Eco-Friendly Structures", by Bruce King, P.E., published by Green Building Press. It gets into the chemistry, along with outlining design and construction considerations.