Cementitious and pozzolanic behaviour of fly ash

Pozzolanic behaviour of fly ash was studied in mortars and pastes from lime-fly ash mixtures. Compressive strength increase of the mortar specimens that were cured in humid environment was a direct manifestation of a pozzolanic reaction of the fly ash with lime. Mineral composition of the reaction products was studied by X-ray diffraction analysis. Morphology of the samples was observed using SEM equipped with EDS detector. Analysis of a paste with the lime to fly ash ratio of 1:1 revealed that virtually all Ca(OH) 2 in the paste was consumed within 5 years. The crystalline products of the pozzolanic reaction included calcium hemicarboaluminate hydrate and monocarboaluminate hydrate and some ettringite.