We’ve been discussing Professor Joseph Davidovits cast stone research at the Geopolymer Institute in hopes of applying this concept to earthbag building. You have to admit the possibility of building a house with dirt cheap, natural materials that turn to actual stone and become fireproof, insect proof, bulletproof, etc. is intriguing. [Update: two people have emailed and said they are already building geopolymer earthbag homes.] Just one aspect alone – the desirability of a material that lasts for centuries – well justifies the time and effort to learn more about this subject. We know the basic science of geopolymers is sound. About two hundred labs around the world are working in this field and developing a wide range of products. My new Geopolymer House Blog has extensive information and daily updates.
Let’s think really big for a moment and try to imagine an ideal fill material for earthbags. We’ve already mentioned the desirability of using low cost, commonly available materials that turn to stone. Check. Now imagine using waste materials such as fly ash, slag from iron ore processing, and tailings from mining. Check. (Scientists are already doing this.) Imagine a material with little or no shrinkage when it dries. Check. Imagine a material that uses no Portland cement, because it’s rather expensive and a major cause of climate change. (You can eliminate one ton of greenhouse gas for every ton of material produced.) Check.
Imagine a material that…
– is carbon neutral and doesn’t need a large amount of energy to produce
– can be produced by batching processes similar to those used for Portland cement
– can be applied as shotcrete or by hand
– has rapid set binders
– is resistant to corrosive elements such as sea salt
– is not dissolved by acidic solutions
– has excellent frost resistance and withstands repeated freeze thaw cycles
Check, check, check…
Wouldn’t it be nice to create air spaces in geopolymer with air entrainment additives to increase it’s insulation value? Check. Let’s take it a step further and add scoria, pumice, perlite or possibly rice hulls to further reduce the weight and increase thermal properties. What I’m leading up to is a material similar to pumicecrete that’s made by binding these insulating materials with geopolymer cement. This hasn’t been done yet as far as I know and so the concept needs to be tested, but this general approach could lead to high performance, lightweight earthbag building. Photos show clean ½” scoria and a close-up view showing the porous structure that traps air and improves insulation value.