Suitability of lagoon fly ash for use in alkali-activated binder mortar mixes

The use of lagoon fly ash (LFA) was investigated as a precursor for alkali-activated/geopolymer concretes. The chemical composition, particle size distribution, mineralogy and morphology of LFA obtained from Kilroot power station (KLFA) were evaluated and compared with those of silo-stored FA from the same site (KFA). Geopolymer mortar mixes made with KLFA and KFA were compared. To determine the variability in the chemical composition of the KLFA, samples were taken from different locations during a ‘geological’ survey of the Kilroot power station’s lagoon in Northern Ireland. The samples of KLFA and KFA had similar chemical composition, minerology and particle size distribution. However, large agglomerated particles (lumps) of FA were found in the KLFA. The strengths of the mortar mixes made with KLFA, in the processed (dried and milled) and unprocessed states, were comparable to those of the silo fly ash (KFA) mixes. Most KLFA samples collected during the survey had a lower content of silicon and/or higher loss on ignition than the KFA, which would potentially adversely affect properties of concrete, if used as a partial replacement for Portland cement. KLFA is, however, suitable to use as a precursor for alkali-activated binders with little (e.g. screening/sieving through a 2 mm sieve) or no processing prior its use.