I'm pretty new to the boards here, but I've been looking for an inexpensive "casting" material to use for my batch rocket, and after reading the referenced material several times though it seems that the perlite/waterglass mix could fit the bill? Unfortunately, I have absolutely NO knowledge of geopolymers whether in composition or usage. In your opinion, would any of the "mixes" mentioned in the paper work well for my purposes (I realize that my question probably way oversimplifies the details of the paper)?
I've been experimenting with many different "mixes" suggested on the boards here over the past 8 months or so, but to date haven't had much luck producing anything that is strong and wear resistant that I do not need to dry in a kiln. I need something which I do not have to fire in a kiln (as I don't have access to one) but that has sufficient wear properties for the fuel box. If the mix could be used for both the fuel box and the heat riser, all the better. Any comments regarding the use of the various "mixes" (based on the information in the paper) would be greatly appreciated. I was thinking that even the lower strength mix IV (100% perlite + 30 wt. % waterglass + 20% addit. water) with a compressive strength of 20.3 Mpa (2944 psi) and flexural strength of 4.2 Mpa (609 psi) might work sufficiently?
Perlite needs to be divided finely. In the paper a Blaine fineness of ~4600 cm2/g is given. Ordinary portland cement (OPC) usually ranges from 3000 – 5000 cm2/g. Expanded perlite is easy to powderize. For harder materials a ball mill could be used, look for DIY ball mills on the web.
Use as little liquid as possible. The finer the aggregate the less agregate can be added. Porous aggregates will help drying.
For high strengs curing at elevated temperatures is required or alternatively adding some lime or cement. More than 40 MPa are possible. Lime or cement with waterglass give a very short potlife, however small amounts of citric acid can be used to delay hardening.
Wear properties can be improved by hard aggregates. I have had no problem to make a very wear resistant Perlite-Geopolymer, even without hard aggregates.
Post by firewatcher on May 31, 2016 14:30:47 GMT -8
Thanks for the reply (and a speedy one at that).
If i add lime to the mix, is it possible to use hydrated lime or must i use quicklime? As best i understand, quicklime is reactive in creating the geopolymer, where as hydrated lime is a slightly different chemical composition which may or may not react properly to form a geopolymer.
I was doing some searching today for quicklime and was unable, so far, to locate any. All the construction supply sources that i contacted only carried hydrated lime. In addition, neither of the big box home improvement chains in my area carry quicklime (within 100 miles of my location) according to their web sites.
Quicklime is only needed if one wants an extremely short potlife of just a few minutes as the high heat of hydration speeds up the chemical processes. Quicklime needs to be added at the very end of the mixing. Aside from the high heat of hydration both types of lime react in the same way.
The use of lime or cement also allows to replace hydroxides of alkali metals by their less dangerous and cheaper carbonates (dehydrated (calcined) soda or potash). The lime will take the carbon from the alkali metals and leave them as their hydroxides. This has been used for millennia to get strong lye from or calcined soda, calcined potash or wood ash. But also without lime calcined soda or calcined potash can be used with waterglass as an activator.
BTW Yesterday I have mixed a small amount of Perlite-Geopolymer to which I have added some natural (uncalcined) kaolin to raise the alumina content with a very much larger amount of expanded clay 2-5 mm. Works like a charm.
Non-clumping white cat litter made from sand, which is quite cheap, works very well too. The heat treatment by production gives the cat litter some pozzolanic properties. The resulting perlite-kaolin-cat-litter geopolymer concrete is porous with relatively low density, but pretty hard and wear resistant.
Based on one of the papers that you shared a link to, I'm leaning toward trying out a mix of hydrated lime/perlite/sand. The paper specified what "recipe" they used which means that I should be able to reasonably reproduce it and see how it works.
I hope that I'm not being a pain with all of the questions, but I have another one regarding the use of the lime mortar composition I mentioned above.
I've been doing some searching online and have not been able, so far, to find information regarding temperature specifications for any type of lime mortar. The concern I have is whether, in general, lime mortar holds up to temps in the range of 1000 degrees Celsius (if memory serves, temps in the heat riser can get to around this range if the stove is operating efficiently as intended). Do you already have some ideas/experience regarding the durability of a general lime/perlite based mortar? Obviously aggregate addition (type and amount) will play some part in changing the properties of a given mix, but generally speaking, can lime mortars withstand high temperatures?
I don't want to take a mix intended for purpose x and assume that it can also be applied to purpose y knowing that the research and testing of the mix was not intended to prove its feasibility for purpose y to begin with. Most of the reading that I've done so far on the lime mortars was with mixtures to be used "in place of" ordinary Portland cement for ambient temperature use in structures.
I've experienced first hand that ordinary cement does not fare well in "high heat" conditions. My test batch rocket stove that I built to "see how they work" is cobbled together from 4 inch thick cement bricks which cost me less than $20. Almost all of the bricks that I started out with have cracked and all have become pock-marked from small bits falling out over time.
As always, any guidance that you can give is greatly appreciated and thanks for sharing your knowledge on the boards!
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deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
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deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
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deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
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