Geopolymers
Introduction
This may be a low-energy, strong brick technology that is also totally decentralizable in production, and may be widely accessible on many continents.
=Energy Requirements+
This graph shows that with a firing temperature of 85 degrees Celsius, geopolymers become as s strong as concrete blocks:
Caveat: there is a requirement of about 2% stabilizer (base salts) for this to happen.
What is it?
Geopolymerization is the process of polymerizing silica and alumina containing minerals with the use of alkali solvents. Discovered (or rediscovered) by Joseph Davidovits, geopolymer cements are likely similar to materials used in antiquity. Although cements are the most common application of geopolymerization, a range of refractory and structural products have been produced. The products of geopolymerization are called poly-silates.
The vast majority of minerals on the earth's surface exist as aluminosilicate crystals (for example: clays, feldspars, quartz). By disolving these and then allowing them to recondense, materials with longer range crystalline structure than its components may be formed.
The most basic inorganic polymerization process uses abundant kaolin clays and silica rich wastes to make a strong cement. A solution of simple aluminosilicates dissolved in an alkali solution acts as a binder, polycondensing upon dehydrolization into a microcrystaline structre which spans the space between silica rich particles. With little technology and at low temperatures, bricks and cements many times stronger than Portland cement are produced. With more intensive technology (artificial atmospheres, high pressures, controlled temperatures) and at hundreds to thousands of degrees celsius, much more structured polymers can be produced which will never combust at any temperature (due to a lack of carbon to react with oxygen), and which also have very low thermal expansion coefficients.
Currently, much of this research is closed source and proprietary. Room temperature setting cements, refractory mineral foams and non-combustible panels for airplanes are amongst the products being researched, and possibly already being widely produced. As the field progresses, more advanced geopolymers and geopolymerizing processes will likely emerge.
The Geopolymer Institute has many useful technical papers on the subject, and has also released several collections of papers from "geopolymere" conferences in France.
Souces of Materials
- Subsoil - methods for adequacy analysis needed
- alkali solvents - from wood ash ?
External Links
- http://www.geopolymer.org/
- Video: Geopolymer for Newcomers (Prof. J. Davidovits)
- Video: Overview: talk by Prof. J. Davidovits
- Video and technical paper [1]