Eyjafjallajokull Volcanic Ash: Can it Be Used as Substitute for Portland Cement?

(Green Buildings 4-23-10)  John asks: With the Eyjafjallajokull eruption in Iceland, is there an opportunity to use the volcanic ash as a substitute in concrete? Can volcanic ash mix with calcium hydroxide the same way that fly ash does?
Answer: John, very intriguing question… something I hadn’t even considered (what the story primarily made me think about was how great it’d be to be ‘trapped’ on vacation in Europe…) So thanks for asking, because when I read your question I was really looking forward to reading up on the topic.
Fly ash is one of two solid coal ash residues derived from incineration processes of coal combustion (the other being bottom ash) and can be used as a substitute for Portland cement in concrete (and therefore a preconsumer recycled material), according to the LEED BD+C Reference Guide. Materials & Resources (MR) credit 4, Recycled Materials, cites fly ash as a supplementary cememtitious material to be used in concrete and applicable for this credit. So now the question is if this volcanic ash is the same fundamentally at the chemical level as fly ash.
Depending on the composition of the coal, components of fly ash can vary but typically fly ash includes substantial amounts of silicon dioxide and calcium oxide, making it an ideal additive to cementous processes. During combustion, fly ash is entrained in flue gases and has historically been allowed to disperse into the atmosphere unchecked (from processes like coal fired power plants). But with current environmental laws in many countries, fly ash must now be captured and disposed of or recycled.
According to the American Coal Ash Association, the materials created by coal-fueled electricity generation are recognized internationally as "products," e.g. "coal combustion products." The term "products" was coined by the U.S. Environmental Protection Agency to emphasize the commercial value of recycling industrial materials (http://www.epa.gov/osw/partnerships/c2p2/index.htm) and the chemical make-up of fly ash is nearly identical to volcanic ash (which was used historically in many famous structures in Italy, Egypt, and Greece – to name a few – as a concrete base).
To answer your second question about volcanic ash mixing with calcium hydroxide the same way that fly ash does… I had to look into this a bit since my first response was that I had to re-read the question. But since the chemical composition of volcanic ash is of a similar siliceous or alumino-siliceous material to fly ash, it shouldn’t be an issue, though addition of an activator might be required, depending. For much more interesting reading content online about coal fly ash, you can check out http://www.tfhrc.gov/hnr20/recycle/waste/cfa51.htm.
Also, I found a great paper available online called “Making Good Use of Volcanic Ash in the Philippines” by Stephanie Kirk and Alan Edwards of the Transport Research Laboratory, UK and Judy Sese, Bureau of Research and Standards, Department of Public Works and Highways, Philippines. The report is available at http://www.transport-links.org/transport_links/filearea/publications/1_4..., and while I found it intriguing, I have a hunch that with your background, you might find it even more so.
A final question, and perhaps the more pressing one, is how would one harvest volcanic fly ash… in the study I referenced above, the ash was collected from land deposits after the fact. But in an ideal world, I suppose it could be harvested in much the same way it is from coal ash at power plants (scrubbers), though I have a sneaking feeling there would be some volcanologists against that type of a retrofit. Thanks again for the interesting question!
To view the original article please go to: http://www.green-buildings.com/content/781330-eyjafjallajokull-volcanic-ash-can-it-be-used-substitute-portland-cement