Compressive Strength and Isothermal Calorimetry Study of Binary and Ternary Geopolymer Mortars at Early Age

The reaction process of geopolymers is closely related to their early-stage setting behaviours and mechanical properties. This paper investigates the early reaction, dissolution, and setting characteristics of composite geopolymer binders that include fly ash, calcium aluminate cement (CAC), and silica fume (SF). The reaction process of the geopolymer binders were analysed by using isothermal calorimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and scanning electron microscopy (SEM). All starting materials were activated using a combination of NaOH solution and Na2SiO3 solution at a ratio of 1:2.5. In the alkali-activated CAC/SF/fly ash system, the calorimetric curves exhibited only one peak within the first 10 minutes of reaction. In contrast, the alkali-activated CAC/fly ash system showed a second peak at around 9 hours for the mixture containing 20% CAC. A strong linear relationship was found between the cumulative heat value and the compressive strength of all investigated mixes at early ages.