Alkali activated cements (including geopolymer cements)

Alkali-activated cements (AACs) are classed as alternative binder systems for use in concrete. They can replace Portland cement-based cements (such as those described in BE EN 197-1) in may applications and considered to have lower embodied energy/carbon footprints than Portland cements (up to 80-90% but this is dependent on the constituents used).

The aluminate-containing material - the pozzolan or latent hydraulic component of the binder - can be coal derived fly ash, municipal solid waste incinerator ash (MSWIA), metakaolin, ground granulated blastfurnace slag, steel or other slags, or any other alumina-rich materials.

Alkali-activated cements gain their strength, and other properties, via chemical reaction between a source of alkali (soluble base activator) and aluminate-rich materials.

The alkali used as the activator tends to be an alkali silicate solution such as sodium silicate (waterglass) but can also be sodium hydroxide solution, or a combination of the two, or other source of alkali (such as lime).

Geopolymeric cements are particular examples of ´alkali-activated pozzolanic cements´ or ´alkali-activated latent hydraulic cements´.

Assessment of the performance of alternative binder systems such as AACs can be undertaken using BSI Flex 350 V2.0 Alternative binder systems for lower carbon concrete – Code of practice (2024) which allows direct comparison of the binder in concrete against a reference Portland cement-based concrete that has established suitability for the intended use. Previously, PAS 8820:2016 Construction materials. Alkali-activated cementitious material and concrete. Specification was the principal guidance for AACs, however this was withdrawn on publication of BSI Flex 350 V.2.0.

For more information, see: Novel cements low energy low carbon cements