Correlating mechanical and thermal properties of sodium silicate-fly ash geopolymers

The correlation between mechanical and dilatometric properties of aluminosilicate geopolymer binders is highlighted by analysis of a set of samples synthesised from a single ash source using different activating solution compositions and liquid/solid ratios. The geopolymers which display the best strength performance also show a small expansion in the temperature range 700–800 °C, which is identified as corresponding to the swelling of a high-silica phase present as pockets within the geopolymeric gel structure. Systems in which this phase is absent (made using hydroxide activating solutions or very low liquid/solid ratios) generally show a low extent of binder formation and do not achieve high strength, while systems in which the expansive phase dominates have a sub-optimally structured geopolymer phase and also correspondingly reduced strength.