This study reports the observation of efflorescence in fly ash-based geopolymers. The efflorescence rate strongly
depends on the activation conditions; at the same alkali content under ambient temperature curing, NaOHactivated
geopolymers show less and slower efflorescence than sodium silicate-activated specimens.
Geopolymers synthesised at high temperature exhibit much lower efflorescence than those synthesised at low
temperature, except for the sodium silicate-activated samples. The substitution of 20% fly ash by slag reduces
the efflorescence rate. A relationship between alkali leaching from monosized fractured particles and ‘efflorescence
potential’ is proposed. Soluble silicate and slag addition are beneficial in reducing efflorescence rate, but
have very limited influence on the overall efflorescence potential, as they appear to have a delaying rather
than mitigating effect. The partial crystallisation of geopolymers, by curing at high temperature, appears to be
the most effective method of reducing the efflorescence potential