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Post by Donkey on Jan 29, 2015 8:01:14 GMT -8
I really don't think that lime is going to do well in a rocket stove burn zone. Your mortar will turn back into quicklime at around 900 C. Easy temperature for rocket stoves. The clay/ash/fine sand mortar will do far better.. Use as little as possible, mortar is for filling uneven spaces only and where the bricks fit firmly, simply dipping them in clay slip should suffice.
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Post by Deleted on Jan 29, 2015 11:01:04 GMT -8
Quick lime reacts with the silica and alumino silicates in the mixture, either hydraulic with water or ceramic at high temperatures. Calcium silicates have melting points around 1400°C and calcium alumino silicates can have melting points up to 1800°C. If you use wood ash as a binder you are actualy using a mixture of quick lime, potassium oxide and other metal oxides. On average about 30% of the content of wood ash is calcium, bound as CaO aka quick lime. www.fpl.fs.fed.us/documnts/pdf1993/misra93a.pdf
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Post by ericvw on Jan 29, 2015 14:46:10 GMT -8
Dang! @karl is always on time with a piece of indispensable knowledge!
Eric VW
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Post by DCish on Jan 30, 2015 3:45:24 GMT -8
So, if I add ash, how does that change the set time? Will it then get hard if I let it sit too long, or can I mix up a bucket of it and cover it and expect it to be more or less the way I left it unless/until it dries out (the way I can with a strait clay/sand mix)?
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Post by Deleted on Jan 30, 2015 4:34:01 GMT -8
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Post by erikweaver on Jan 30, 2015 12:17:20 GMT -8
That looks like an interesting paper. I read the conclusion, and glanced through the main body. It is not however, something I'm going to read online. If anyone knows a link to a downloadable PDF, that'd be appreciated. Being that I am not an affiliated researcher I cannot download the document from this site. I am curious if it is otherwise available (without infringing copyright, of course). I didn't see the part speaking to using wood ash specifically as a binder in mortar. Perhaps, Karl, you recall which page(s) that discussion took place? My impression is that small amounts of very fine wood ash is at least not going to hurt anything. In some ways it might be beneficial. But it didn't seem to respond well to an acidic environment. Perhaps because wood ash is traditionally used to make lye in soap-making? (Lye/wood ash is a base, the opposite of an acid. I'm assuming that is the basis for wood ash concrete performing less well in an acidic environment. But that's just a guess.) But I wouldn't think this would present a difficulty for our use, in wood burning stoves and masonry heaters.
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Post by erikweaver on Jan 30, 2015 12:40:36 GMT -8
I found an online copy through another organization of which I am a member. And the scribd web site has the paper, but you have to buy a subscription to their service. My suggestion is to search for the title and add the key word "PDF" and you'll find a variety of options for obtaining the paper.
Karl, I found the section discussing mortar too (Table 4 offers the summary).
If I am reading the table correctly, adding either 5% or 10% of wood ash (replacing portland cement) first weakens the concrete in the first 90-days (with one brief exception) but then in the next measured time frame of 365-days, the strength actually increases (both in flex and compression).
Interesting.
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Post by Deleted on Jan 31, 2015 4:15:57 GMT -8
erikweaver you could have downloaded the paper by clicking the rectangle below "Full-text". The properties of wood ashes depend on the kind of wood and temperatures. If the calcium content is high enough and the temperature exceeds 860°C significantly, wood ash can become self cementing. If the content of SiO 2, Al 2O 3, and K 2O is high enough wood ash could even become a geopolymer. Special "wood ash" could be obtained by sprinkling in powdered clay and limestone prior to combustion.
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Post by erikweaver on Feb 1, 2015 10:59:36 GMT -8
erikweaver you could have downloaded the paper by clicking the rectangle below "Full-text". The properties of wood ashes depend on the kind of wood and temperatures. If the calcium content is high enough and the temperature exceeds 860°C significantly, wood ash can become self cementing. If the content of SiO 2, Al 2O 3, and K 2O is high enough wood ash could even become a geopolymer. Special "wood ash" could be obtained by sprinkling in powdered clay and limestone prior to combustion. Thank you, Karl, now I got it!
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