Alkali-activated materials (or geopolymers) were first developed as a cement in the 1970s. With a lower carbon footprint, they also contribute to the Circular Economy, using industry by-products as raw materials.
Alkali-activated materials – also known as geopolymers – are created from a range of materials (usually industrial by-products), known as precursors. These are added to an alkaline medium to produce a cementitious material that can be used instead of Portland cement in the making of concrete.
The first alkali-activated material to be used commercially was activated blastfurnace slag in Ukraine in the 1970s, building on research from the 1940s and 1950s. The range of precursor materials has since grown to include fly and bottom ashes from coal-fired power plants, calcined clays, natural pozzolans, iron-rich clays, non-ferrous slags, clay-rich sludges from water treatment, red mud, and agricultural waste ashes.
This wide variety of possible precursor materials is one of the advantages of alkali-activated materials. However, many are also used as supplementary cementitious materials (SCMs) in blended Portland cements. This competition for precursor materials is likely to place a limit on availability, especially as their use as SCMs is much more widely understood and applied than their use in the production of alkali-activated cements.
Despite this, the production of alkali-activated materials requires less capital investment than the construction of an integrated Portland cement plant, while alkali-activated cements can be used without adaptation in existing concrete plants.
In terms of concrete performance, alkali-activated cements develop high strength at early ages, making them relevant for precast applications. They also show satisfactory performance under a range of exposure conditions with good resistance to chemically-aggressive environments and high temperatures. Workability is however more challenging that Portland cement with stricter control of water in mix required.
Potential carbon emission reductions vary between 40% and 80% compared to Portland cement, depending on conditions, while the use of industrial by-products diverts material from landfill and helps support the development of a circular economy.