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Slag & fly ash geopolymer?

user-1137156 | Posted in Green Building Techniques on

The father of geo polymers, Joseph Davidovits, has proposed a standard geo-polymer cement that uses fly ash, blast furnace slag and a “user friendly” alkali activator to make a cement. It’ sets at room temperature in several hours and develops outstanding strength quickly.(7000+PSI @ 28 days). Without additional aggregates it is about 2.8/ inch. Since it uses about 90% waste materials it is quite “green”. With that kind of insulating structural concrete far less plastic foam would be needed, a typical basement floor would be r10 by itself. BTW it should cost far less than typical concrete. Why aren’t we demanding it?

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  1. GBA Editor
    Martin Holladay | | #1

    Be my guest. Demand away.

    I guess it would be useful to know more; for example, (a) copies of research papers or lab test results that document the claims you list; (b) information on the cost and availability of the raw ingredients; (c) cost comparisons of this miracle product with common concrete; (d) information on whether any Ready-Mix plants are actually interested in supplying the product.

    For starters.

  2. STEPHEN SHEEHY | | #2

    Jerry: wouldn't any concrete made with that cement still be mostly sand/stone aggregate and thus have an R value similar to concrete made with Portland cement? You wouldn't make a floor from just cement.

    Is there enough fly ash and slag to replace a significant fraction of the Portland cement we all use?

  3. user-1137156 | | #3

    Here is a webinar recording by Professor Davidovitz where he proposes the "standard".:
    I Here is one of the papers several more are available through the institute.
    I haven't, yet, gotten a price estimate for the main ingredients class F fly ash & ground blast furnace slag. Both of these are routinely added to Portland cements but only available in bulk quantities.. The most costly ingredient is the activator powder which sells for $2/ pound. !0% by weight is activator and the product density is aprox. 50#/cubic foot All the data is on pure cement, no "aggregates" ! and there is no reason to mess up a good thing by adding inferior materials,
    Pehaps even more fly ash could be added as an aggregate which would lessen strength slightl and possibly improve insulation, as well. Note fly ash is mostly hollow spheres of a mineral very much like perlite. Comparing fly ash to perlite, they are similar insulators but fly ash is very uniform and has hollow spherical particles that are very stong, when held together by the geo polymer .

  4. STEPHEN SHEEHY | | #4

    I'm highly sceptical that a foundation, for example, made entirely of cement assembled from components shipped from the nearest coal fired power plant and blast furnace, will be less costly than concrete made from local sand and stone, with only the Portland cement being shipped any distance.

    I'd be delighted to be wrong, since cement kilns are not green.

  5. iLikeDirt | | #5

    How can this stuff possibly be simultaneously R-2.8/inch and 7,000 PSI? Where is that R-value coming from?

  6. user-1137156 | | #6

    The geo -polymer contains NO Portland cement! The mix is, by weight 75% class f fly ash, 15% ground blast furnace slag 10% Agsil 16 or equivalent "user friendly" potassium silicate.. Water to mix, weighing 5% of dry mass.. Any batch plant that uses both fly ash and slag cement could mxi it .
    To compare the cost we must get equall insulation value from Foam insulated concrete for comparison to self insulating geo-polymer..

  7. iLikeDirt | | #7

    I'm reading through the technical documentation at

    So far this stuff looks like a very interesting and promising alternative to portland cement that represents a real innovation. However, so far I have found no mention of its insulation properties, let alone a claim that it reaches R-2.8/inch while remaining a structural material. Can you help me find this information, Jerry?

  8. user-1137156 | | #8

    Both the major ingredients are routinely added to Portland cement mixes, fly ash to reduce water demand and increase"workability while slag cement generates early strength Properly (NO thermal bridges) insulating foundations, with foam, is very costly in material and labor..

  9. iLikeDirt | | #9

    That's interesting. You're right; that paper shows a mix where they achieved R-2.9/inch that had a compressive strength of 1885 PSI. That's awesome. This stuff should revolutionize construction if it ever makes it out of the lab and the cost is reasonable.

  10. user-1137156 | | #10

    To access the geopolymer papers go to and fill out the form.
    Some papers are elswhere, like this one:
    Looking it up, it's where I got the insulating value which I wrote on a note, unfortunately this data is for a now obsolete way of making fly ash geo-polymers which used sodium activators. the actual r value/ inch is yet to be determined for potassium ..The Potasium based materials are generally stronger and lighter (better insulators) The paper shows one sodium mix that had the r vaalue I mentioned But only had a compressive strength of 2828PSI The paper also notes that increasing the percentage of fly ash both reduces conductivity and increases compressive strength.
    The mix in the paper also has sand (actually more sand than fly ash) as part of the mix and rice hull ash to further confuse things.. One can assume that the rice hull ash was included to improve drying and is completely unnecessary with the correct alkali metal, potassium.

  11. user-1137156 | | #11

    The 1885PSI (13MPA) is with a 7 day cure! At 28 days it's 19.05MPA or 2762PSI, real close to typical Portladgs @30000PSI. .

  12. wjrobinson | | #12

    Any bets on when one of us ever uses this?

  13. user-1137156 | | #13

    "Any bets on when one of us ever uses this?" As usual look overseas for innovation & early adoption.!

  14. user-1072251 | | #14

    above the foundation,houses today are entirely held together by glues, so what's another 8'? Precast lightweight insulated foundation walls?

  15. terryeh | | #15

    This Geopolymer technology is real. It is a better concrete in just about every way.
    But don't expect the 6000 pound gorillas of the concrete industry, like La Farge, to
    moth ball their 150 million dollar Portland cement plants any time soon.
    And any good conspiracy theory on the subject will tell you that is the big problem.
    Geopolymer concrete eliminates a big process in concrete manufacturing. (Portland cement)
    Cement plants are history ! The current supply chain delivers all the ingredients directly to the batching facility; and that is why it could be/should be cheaper.
    So if you are Lafarge, at what point do you close down half your infrastructure! Moth ball half your net worth. Well you are just going to keep being Lafarge and tell everyone you"have that coming soon."
    Also, you have been discussing "user- friendly" recipes from the "GEOASH" project which is missing a lot of information as to why they did what they did. You need to know that a lot was based on the cost and availability of materials at the time, in Europe. There are other possibilities here, when you understand the availability of materials here. (North America)
    For example: We have high availability of both fly ash F and C derived from 100% coal burning; at, in some cases, much better prices. So I question the use of slag, when you could achieve the same Ca content (12-15%) with a combination of fly ash F and C. which has several advantages, most notably plasticity, ease of mixing and the opportunity to (as mentioned) replace sand.
    I have yet to find any research on this, as to where the line is drawn in regard to flash setting due to Ca content. Also the "K-sil" solution used is not of a ratio I've been able to locate in North America.
    Though products available here will work with adjustments to that recipe. And finally when you consider that very few of us are after 90 MPa concrete. (13,000 psi) Pushing things to the limit are just not required here. I think in practise 40MPa and less should be a more relaxed recipe So if you are OK with the price of Potassium silicate and Micro-spheres (for light weight); Which is the only way you are going to get those "R" values (the lighter-the higher the R value)
    Jerry, could I see your price breakdown on material costs. $115/ yard is intriguing.
    Just having skipped through the above mentioned article on High Calcium Fly Ash concrete,
    I have noticed that the Calcium content was almost 20%. Native to that power plant where this paper was written. 30MPa was achieved. Several papers have suggested that this is too high. (accelerated curing and compressive strength loss.) In North America we could reduce that to 15% by mixing in a lower costing 2-4% class F fly ash. Again; a lot of papers have been written relative to available materials.

  16. terryeh | | #16

    Well actually, that is not my main drive. But I do see that conversation here, and in my spare time I play
    with a concept of building an entire house out of mostly LW concrete (of the 1/4 the weight variety).
    I'm not going to get in to all the spectacular things I see happening with this, but the short strokes are:
    less labour, less material costs (and substantially less material costs if you do your own pre-casting).
    More mould/water resistant structure with an unbelievable fire rating. (R value is what you make it.)
    I think there is confusion on this topic with current definitions of LW concrete. With portland cement
    most assume you mean something that is maybe 20% lighter. (which has no appreciable R value)
    And the Geopolymer conversations that talk about concrete 3 and 4 times lighter. And of course the idea of using it for the foundation, has some major engineering hurtles.

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