Lagoon fly ash – a potential source of the precursor for geopolymer binders

The use of lagoon fly ash (KLFA) from the Kilroot power station in Northern Ireland was investigated as a potential source of precursor in alkali activated geopolymer concretes. Chemical composition, particle size distribution, mineralogy and morphology of the received KLFA sample were evaluated and compared to that of the silo-stored fly ashes obtained from Kilroot (KFA) and Drax (DFA) power stations. Mortar mixes were proportioned with these ashes and tested for compressive strength to assess their reactivity in the geopolymerisation process. Specifically, mixes made with KLFA samples in as received state (wet), oven-dried state and processed states (dried and milled) were compared with mixes proportioned with silo-stored fly ashes. Subsequently, samples to test the variability of the fly ash in the Kilroot lagoon were collected from different locations during a geological survey and then their chemical compositions were determined.

Samples of KLFA in the as received state and KFA had similar chemical composition, minerology and particles size distribution. However, large clumps of fly ash particles within KLFA were found. The strength of the mix made with KLFA in the processed state was comparable to that of the silo fly ash mixes, whereas KLFA used in the as received state and oven-dried state was deemed unsuitable. Most KLFA samples collected during the survey showed lower content of silicon and/or higher loss on ignition value than KFA, which could potentially adversely affect geopolymerisation. Thus, KLFA is suitable to use as a raw material for alkali activation, however preselection and processing prior to use is required.