Nanostructured geopolymers: Can we learn from the past for the future?

The production of conventional building materials such as cement or gypsum is dependent on deposits of primary raw materials. Alkali activated binders, on the other hand, can be made from municipal residues or industrial by-products such as ashes, slags or dusts, thus contributing actively and sustainably to the conservation of natural resources. Inorganic binders are hardened by an alkali-induced reaction of silicates containing aluminum (aluminosilicates). Since this process, which is not yet fully understood, is often compared with the polymerization of plastics, the term “geopolymers” has become established for these products.

Whether Egyptian pyramids or ancient sculptures are actually made of geopolymers has been the subject of scientific debate for many years. For instance, Prof. Joseph Davidovits, considered to be one of the pioneers of geopolymer research, cites impressive arguments and examples to prove how the Egyptians used geopolymers to build the pyramids. They are said to have produced artificial sandstones that are almost indistinguishable from naturally-formed ones. To date, however, this theory can neither be proven nor disproven.

Geopolymers or alkali activated binders have particular properties that make them highly suitable as building materials: Compared to concrete, better strength values can be achieved. Most of the products tested so far have shown to be highly resistant to acids as well as to freeze-thaw cycles (salt). This makes alkali activated building materials extremely suitable for exterior use (e.g. as facade panels), as well as for use in areas with a high exposure to chemicals (e.g. sewage pipes). In Australia, runways and ceilings of public buildings have already been made from these building materials.