Study on a Nano-Microstructure and Properties of Geopolymer by Recycling Integrated Gasification Combined Cycle Coal Ash Slag.

In this study, a geopolymer having a nano-scaled structure was fabricated using recycling fly ash slag discharged from IGCC (Integrated Gasification Combined Cycle), to assess the possibility of employing it to replace high strength concrete. Strength, density, crystal phase, and bonding structure, were measured and the nano-size crystal phase of the geopolymers was observed as a function of experimental parameters such as water-to-solid ratio (w/s ratio), flow of paste, and amount of sodium silicate in the alkali activator, NaOH. The geopolymer prepared with NaOH containing 50~70% sodium silicate and a w/s ratio of 0.26~0.28 showed a compressive strength of 75~80 MPa, which satisfied the design standard for high strength concrete in Korea, 40 MPa. The specimen made with NaOH containing 55% sodium silicate had plate-shaped crystals with a nanoscale size, 100 nm or less, and showed compressive strength of 77 MPa, 3.9 times higher than that made with only NaOH. From the viewpoint of microstructure, it was confirmed that nano-sized plate-like crystals and amorphous structure were both effective in improving the strength of the specimen. In conclusion, this study showed that high-strength geopolymer made from IGCC coal ash slag may replace cement used in building materials and concrete secondary products in the near future.