Can use Sodium carbonate (also known as washing soda or soda ash), Na2CO3
What is Geopolymer : A hardened cementitious paste made from fly ash without Portland cement. It has greater compressive and tensile strengths, high strength gain rate, lower porosity and permeability, and greatly enhanced resistance to chemical attack compared with ordinary Portland cement (OPC) concrete. It combines waste products into a useful product, conserving landfill space and promoting sustainability, and compared with Portland cement, it features a 90% or greater reduction in carbon dioxide emission. A solution of sodium hydroxide and potassium hydroxide (waste products from the chemical and petrochemical industries) must be prepared separately, then added to the liquid commercial sodium silicate; this solution may then be added to the powdered fly ash (waste product from coal and bio fuel combustion) in the same way as water is added for Portland cement.
The following discussion is from Listserv.repp.org Greenbuilding mailing list.
I was wondering if anyone here has experimented with geopolymers (coined by Joseph Davidovits) or the broader alkali-activated cements? I watched the video where Davidovits tried, and seemed to succeed, in reproducing how the Egyptians may have poured synthetic limestone using materials available to the Egyptians.
lime (hydrated) 8 parts
sodium carbonate (washing soda) 6 parts
kaolin clay 16 parts
mixed in aggregate: 450 parts loose limestone (sans clay) (???calcium
I’m here on the big island of Hawaii. I want to try to reproduce something similar. I have given myself the project of building a concrete water tank to hold rainwater. I want to do it without Portland to see if it can be done here with mostly local materials (I include neighboring islands). I am allowing myself to import hydrated lime and washing soda. I really don’t know what I’m doing. I don’t know about cements. I don’t know about soils, rocks, and minerals, but I’m trying to learn. Obviously I’m going to try very small batches to see what works. But, I would like other, more educated
guesses. Maybe I’m taking on an impossible task?
Here are what I see as local materials:
“Red Dirt” – oxisols – iron oxide, aluminum oxide, kaolin clay (comes from neighbor islands)
“Lava Rock” – basalt – I don’t mind using processed into basalt sand (this is the most local)
“Ocean Sand” – *not* silicate, I think ocean sand is a calcium carbonate, from coral, ???like limestone??? (hard to get on big island but on ocean floor)
I was thinking that the following might be a start:
lime, washing soda, red dirt, aggregate: either ocean sand, basalt sand, or both, plus larger basalt aggregates.
Does anyone have any comments and or leads? Do I need to add more red dirt because it is not pure kaolin? Will it work with the iron oxide? Does anyone know of other materials on the island that may be useful? Could basalt work without the kaolin?
I appreciate any leads,
A little follow up: I just discovered that there is a large volcanic ash deposit on the big island. I don’t know if it is pozzolonic, but this could be a significant ingredient for a low temperature cement.
I don’t have anything to add in terms of a cement alternative except that I am very interested in hearing what you find. I have known about the French organization for a while. I contacted them but didn’t get much info out of them. Rammed earth and the like is great but it lacks the chemical reaction that really makes a substance strong. I would love to get info on how to make an alternative to concrete.
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There are several pages discussing various kinds of cement in “Heat: How to Stop the Planet from Burning”, by George Monbiot. He mentions geopolymer cement, as well as pozzolan cements used by the Romans. A website reference he gives in the notes is the following: http://www.romanconcrete.com/Article1Secrets.pdf I hope it is of interest to you.
Thanks for that article. I had stumbled upon it before but did not read it. After your encouragement I read it and am glad I did. Like I said, I’m no chemist, but, one difference I see between what Davidovits (Geopolymer Institute) did, and the Roman cement in this article, is that Davidovits mixed sodium carbonate (washing soda) with the hydrated lime. I believe this produces Lye (sodium hydroxide) + calcium carbonate, which mixed with kaolin clay, or pozzolan produces water glass (sodium silicate). I wish someone could confirm this. (The list has been talking about sodium silicate as a wood preserver.) I think sodium silicate is key to geopolymers.
Davidovits also compacted (rammed earth) his concoction. However, he originally completely saturated the mix with water and let it dry over a week until it had zero slump. Then he compacted it. I don’t know if there would be difference to that method over the method of just lightly hydrating a mix.
Anyway! Let the experimentation begin! I currently have some hydrated lime and sodium carbonate. I’m going to have to get my hands on some of the volcanic ash. I also want to try some red dirt (oxisol) and crushed volcanic cinder.