Hydration process of potassium polysialate (K-PSDS) geopolymer cement

Environmental scanning electron microscope (ESEM) was used to quantitatively study in situ the hydration process of potassium polysialate (K-PSDS) geopolymer cement under an 80% relative humidity environment. An energy dispersion X-ray analysis (EDXA) was also employed to distinguish the chemical composition of the hydration products. The ESEM micrographs showed that metakaolin particles were packed loosely at 10 min after mixing, with many large voids. As hydration proceeded, gels were seen and these precipitated on the surfaces of the particles. At a later stage, the particles were wrapped by thick gel layers, and their interspaces were almost completely engulfed. The corresponding EDXA results showed that the molar ratios of K/Al and Si/Al gradually decreased with the development of hydration. As a result, the molar ratios of K/Al and Si/Al of hydration products after 9 h were 1·28 and 6·54, respectively, and these were close to the theoretical values (K/Al = 1·0, Si/Al = 6·0 for K-PSDS geopolymer cement paste). In addition, no well-developed crystals were found at any age, whereas sponge-like amorphous gels could always be observed.