Soaking Properties of Integrated Gasification Combined Cycle Slag-Based-Geopolymers and Their Nanometer-Scale Microstructures.

In this study, non-foamed and foamed geopolymers based on IGCC (integrated gasification combined cycle) slag were prepared and their water resistance properties were examined in an immersion test in order to assess their suitability for water applications such as bridge pier, seawall, tetrapod. Particularly, the immersion characteristics were investigated according to the aging time at room temperature during the production process of the geopolymer. The pH changes of the immersion liquid were analyzed considering the immersion time, and the microstructural changes on the nanometer level of the surface of the geopolymer were observed before and after the immersion. Various shapes of crystals of the zeolite phase formed in the geopolymers prepared in this study, such as needle-like crystals with thicknesses ranging from 20 to 40 nm and lengths of 200 to 300 nm, and plate-shaped crystals overlapped with each other, which is thought to be due to the uneven composition of the slag used as a raw material or to local compositional changes of the alkali activator. By measuring the pH of immersion liquid, the following facts can be seen: foamed geopolymers synthesized from IGCC slag require a room-temperature curing period of at least 7 days, whereas non-foamed specimens require a room-temperature curing period of at least 28 days to consume alkaline activators. This is due to the increase in the specific surface area of the foamed specimen as the specimen is expanded, which thereby increases the contact area between the alkali activator and the slag. The foamed specimens, however, produced larger cracks and pores when immersed in water, while a smaller cracks and pores occurred in the non-foamed specimens.