Factory production of alkali-activated precast concrete products in the UK

Alkali-activated concretes (AACs) have been extensively investigated in laboratories around the world. However, there are only a limited number of demonstration projects and applications of alkali-activated materials in building and civil infrastructure. The work described in this article involved the development of geopolymer concretes in the laboratory for a range of precast concrete products to be produced in the UK and Malaysia – load-bearing wall panels, reinforced concrete slabs, precast concrete stair units, voussoirs for a pedestrian concrete arch bridge (FlexiArch) and concrete building blocks. Upscale to factory production has shown that these relatively new concretes can be used in the construction industry without any problems other than the need to ‘optimise’ the laboratory mixes to the needs of the precast concrete factories. This included careful selection of materials (precursors and activators) to be used by the factory and modifications to the laboratory mixes for longer workability retention required at the factory. The use of an in-house produced sodium silicate activator from ground glass cullet reduced the cost of the AACs and made them comparable to the cost of Portland cement mixes. The embodied carbon dioxide of these mixes was also considerably reduced.