In situ observing the hydration process of K-PSS geopolymeric cement with environment scanning electron microscopy

The hydration process of K-PSS geopolymeric cement was in situ quantitatively investigated by environment scanning electron microscope (ESEM) under 80% relative humidity. An energy dispersion X-ray analysis (EDXA) was also employed to determine the chemical composition of the hydration product. The ESEM micrographs showed that metakaolin particles pack loosely at 10 min after an initial mixing, resulting in an existence of many large voids. As the hydration proceeded, some gels were produced and gradually precipitated on the surfaces of these particles. At a later stage, these particles were covered by thick gel layers, and their interspaces among the metakaolin particles were also completely filled up. The corresponding EDXA results illustrated that the molar ratios of K/Al and Si/Al decreased with the development of hydration. The molar ratios of K/Al and Si/Al of the hydration products at an age of 13 h amounted to 1.06 and 2.14 respectively, which were very close to the theoretical values (K/Al = 1.0, Si/Al = 2.0) for K-PSS geopolymeric cement hardened paste. In addition, well-developed crystals could not be found at any ages, instead sponge-like amorphous gels have always been observed during the whole hydration process.