lawry
Junior Member
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Post by lawry on Sept 24, 2016 14:07:21 GMT -8
"@karl" this is the Fly Ash bricks I cast Tuesday. My casts normally remain grey... but these have turned brownish. Any idea why? It's the first time I used my curing box within a day of casting. Is it maybe related to the geopolymerisation process?
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Deleted
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Post by Deleted on Sept 24, 2016 16:33:46 GMT -8
The brown color is from iron minerals forming while warm curing or firing. Happens with any iron containing geopolymer, respectively ceramic.
Are you happy with the result ?
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Post by firewatcher on Sept 24, 2016 17:02:41 GMT -8
"@karl" this is the Fly Ash bricks I cast Tuesday. My casts normally remain grey... but these have turned brownish. Any idea why? It's the first time I used my curing box within a day of casting. Is it maybe related to the geopolymerisation process? That looks like it turned out really nicely!
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lawry
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Post by lawry on Sept 24, 2016 21:01:24 GMT -8
firewatcher and @karl yes I am happy with the results đ When I knock on it, it has nice ring to it. Sounds solid! This is the temperature it went up to in the box. The box The brick
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Post by firewatcher on Sept 26, 2016 17:12:46 GMT -8
While waiting for my acid activated plank to dry, I decided to give an existing geopolymer test mix another try. I've found that if I let the pucks sit for a week or two after heat curing (without doing anything further with them - including heat tests) they seem to be stronger. I'm not sure why, maybe because the larger surface area allows the pieces to dry throughout (imcomplete heat curing?)...or just because the smaller pieces are more difficult to break (or the existing cracks formed during the drying process are already separated during the strength test)...we'll see...testing again will hopefully provide some additional imformation.
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Deleted
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Post by Deleted on Sept 27, 2016 4:39:22 GMT -8
The chemical reactions can continue for quite some time.
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Post by firewatcher on Sept 27, 2016 5:32:35 GMT -8
The chemical reactions can continue for quite some time. This is the first time that I've vibrated the mix to "settle" it into the mold as well with my orbital sander. The mix was rather thick, and rather than ramming it into the mold, I decided to try that method as you had mentioned it many times before. I was very surprised at how well it worked! A lot of bubbles contained in the mix also rose to the surface. These are the non-smooth areas that you see. I'm going to try and let it ambient cure in the closed container (i put the accompanying lid on top of the container) for a week and then try heat curing. My plan, then, is to let the heat cured brick rest for another week before doing any strength or heat testing. Do you think that this is long enough, or thatbi should let it rest for a full month?
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Deleted
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Post by Deleted on Sept 27, 2016 5:55:13 GMT -8
In the scientific papers samples are often cured for a full month at ambient temperatures, before drying. Waiting a week before testing will likely improve the test results significantly. I am not patient enough for waiting a full month.
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Post by firewatcher on Sept 27, 2016 6:45:59 GMT -8
I'm hoping to end up with the kind of results that you've experienced with your mixes with regard to strength (almost all test bricks have been very hard and wear resistant). To date I've always experienced some degree of cracking on my test pucks (probably due to my camp fire cure). The temperature ramp up is no doubt WAY too fast causing the outside to harden before most of the water in the inside of the brick has a chance to evaporate. I may have to try lawry "black box" curing method to see if I can do any better of a job curing before using the camp fire to "finish dry" test pieces.
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lawry
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Post by lawry on Sept 27, 2016 7:31:58 GMT -8
The blackbox helps me a lot since it keeps the samples above the recommended 40 degrees for about 6 hours a day.
I cast a puck with aluminum oxide and silicon carbide on Friday. I notice that they are curing at a slower rate. Normal sand and gravel seem to encourage curing.... Is it bcoz aluminum oxide and silicon carbide have a low absorption rate....?
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Deleted
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Post by Deleted on Sept 27, 2016 8:23:40 GMT -8
High hardness is the result of very strong bonds in and between molecules, thus very hard substances are also chemically inert. Normal sand and gravel are prone to caustic attack.
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Post by firewatcher on Sept 29, 2016 17:50:48 GMT -8
I have 3 mixes ambient drying which I'm hoping will fare better than in the past. Weather has not been agreeable (rain and more rain), so I'm not sure when I'll get to temperature them. I'll update when I have some results, but I'm going to try to let each mix ambient dry for at least a week (unless impatience takes over), heat cure in a camp fire, let rest for a week, then strength and temperature test each of the test mixes.
I've remade two previously tested mixes with only slight alteration to the amount of lye used (increased from 5% of pozzolan to 10% of pozzolan). The reason for retrying these mixtures is because after strength testing the leftover pieces from the original pucks weeks after firing, they were unbreakable. I suppose what I'm really testing is whether these mixes just needed more time to fully "cure" and gain full strength.
The three mixes being tested were all made with slightly less liquid than previously (waterglass in my case) and were vibrated to a solid mass using an orbital sander rather than packing the material into the mold mechanically.
The last change was the use of plastic containers as molds rather than wood or cardboard.
The base mix used was the following: the 3 pozzolan's used (1 type only in each mix) were 1) powder perlite 2) powder zeolite 3) wood ash from camp fire-sifted through a window screen.
100 g (pozzolan) 35 g fire clay 400 g slag 13 g hydrated lime 10 g lye 1/2 cup waterglass (330g solids/1L water)
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Post by firewatcher on Sept 30, 2016 15:15:22 GMT -8
I got impatient (as expexted) and decided to unmould the three test mixes... From left to right the pozzolan in the mixes are perlite/zeolite/wood ash. I think the perlite (left most) was still too wet and it cracked before unmoulding due to the plastic container being too flexable and me picking it up to view the bottom while it was drying. I'll have to retry the perlite mix once again... I've been thinking about how to low temperature dry the test pieces. Due to a suggestion/nudge by @karl, I came up with the following setup until i can find something more suitable... It's a food warming fuel canister inside a larger metal can. I put some metal "screening" on top of the can and set the brick on top of that. I'll let it warm cure there until the fuel in the can runs out and then swap out rhe fuel can with the last remaining one that I have and warm cure the wood ash brick. I'm still going to have to "full heat" cure the bricks, but won't be able to do so until it stops raining or I'm able to find something suitable to use as an "outdoor oven" (I'm working on that). Thanks to Karl, once again, for all of the suggestions and great ideas to keep the testing moving forward!
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Post by firewatcher on Oct 2, 2016 8:07:12 GMT -8
Ok...so the rain let up for a few hours yesterday so I was able to both "low temp dry" and "camp fire cure" all of my test pieces yesterday. I found a bonus puck too that I had forgotten about! Here are the results: First test puck- Mix: 104 g "powder" zeolite 104 g fire clay 400 g slag 10 g hydrated lime 3/4 cup waterglass (330g solids/1L water) The surface was hard and wear resistant using the fingernail test. You can see in the picture I think where there is a piece broken off in the foreground of the picture. This area I was able to wear away scratching with my fingernail. This has been the case with all of my test mixes using the zeolite that I tried to powderize. Brick 1- Mix: 100 g "powder" zeolite 35 g fire clay 400 g slag 13 g hydrated lime 10 g lye 1/2 cup waterglass (330 g solids / 1L water) The surface was also hard and wear resistant using the fingernail test. On this brick I also scratched at a section which had a broken piece and was able to remove material. Again, this seems to be normal in all of my zeolite mixtures. Brick 2- Mix: 100 g sifted wood ash from camp fire 35 g fire clay 400 g slag 13 g hydrated lime 10 g lye 1/2 cup waterglass (330 g solids/1L water) The surface is hard and wear resistant. I scratched at all of the pucks with the following tool to see how tough the surfaces were...all test pieces were able to have the surface scratched through with enough force...this was just a "let's see what happens" test. Obviously the material would never see the kind of "focused force" as was applied by such a "sharp" scratching. As I mentioned previously, I'm going to wait a week before strength testing each of the bricks (trying to break them by hand). It would seem that more time (even after heat curing) allows for gains in strength based on revisiting past test pucks weeks after the initial cure. We'll see if that past experience holds true with these mixes as well.
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Deleted
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Post by Deleted on Oct 2, 2016 9:07:15 GMT -8
Likely your zeolite is not milled finely enough. Or did you got more milling media for a better result ?
Mine is very fine, with 50 micron for the largest particles and most are a lot smaller.
Another factor is your rather coarse aggregare. As I have suggested before you could try to add about 20% very fine sand to your aggregate to fill the space wetween the coarse particles.
Yep, ash works quite well.
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