Uwe,
Your interest in magesium cement as a substitute for portland cement is something I share, both in ferrocement and in papercrete. I have not yet had an opportunity to do the requisite experimenting to draw any final conclusions, but here are a few facts I have surmised:
1. There are a variety of cements made from magnesia, in these three varieties: magnesium oxychloride cement, magnesium oxysulfate cement, and magnesium phosphate cement. Each having their own pros and cons.
2. A primary benefit of magnesium cements is that they are produced at a far lower temperature than portland cement, and therefore far less CO2 is released into the atmosphere in the production. Thus, a more "green" product. If a papercrete mix could be devised using a magnesium cement, it would probably result in a broader interest in the green building field.
3. Some of the down sides of magnesium cements have been the reason for their lack of wide-spread acceptance and use. Some are more vulnerable to water and chemical deterioration, and some will leach magnesium.
4. Magnesium cements that I've read about have a very quick set time, which seriously limits batch sizes and workability. For example, I've heard that Grancrete, which is a magesium cement-based product, will set in something like 20 minutes, a time that can be perhaps doubled with retarders, but still a very fast set time. I certainly wouldn't want to be caught with a 200 gallon tank partially empty and hard as a rock...
5. Magnesium cements are more expensive, because they aren't produced in the same scale of volume that portland cement is produced.
6. Successful magnesium cement mix designs are more difficult to achieve, are often the basis of proprietary products, and are thus more closely guarded (= "secrets").
I imagine that there is a successful magesium cement-based papercrete, and I think it would have at least three positive qualities:
- quicker setting and drying, possibly less shrinkage;
- greener, less CO2 created in the production; and
- harder, greater compressive strength.
If anyone can further enlighten me on any reasons why magnesium cement would not work in a papercrete mix, or if someone has some experience with magnesium cement papercrete mix design, I would be very interested. Or, do you know of a magnesium cement expert who might help us design a magnesium cement papercrete mix?
In the meantime, I'm looking forward to when I'll have adequate time and space for the requisite experimentation...
Happy holidays,
Eric Randall
Fairfield, Iowa
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