Study of Geopolymer Type Paste and Concrete from High Calcium Mongolian Fly Ashes

Abstract

Geopolymer type paste and concrete have been prepared by alkali activation of Mongolian fly ashes. Ash residues of Baganuur and Shivee ovoo lignite coals used by 4th thermal power plant of Ulaanbaatar city were used. Fly ashes were characterized by chemical and mineralogical compositions, granulometrical test, porosity measurement and FE-SEM as belonging to ASTM Type C. Both fly ashes contain up to 30% calcium oxide and up to 11% iron oxide by mass. Particle size distribution revealed that the average d₅₀ particle size of the Shivee ovoo fly ash is 14.5 µm while for Baganuur fly ash it is 20 µm. Initially geopolymer pastes were prepared by addition of sodium hydroxide solution to ash and curing at 70°C for different durations. After optimizing the preparation conditions of geopolymer pastes, concretes were made by mixing paste with 75% coarse aggregates. The geopolymer products were characterized by XRD, FTIR, compressive strength testing and freeze-thaw resistance method. Baganuur fly ash based geopolymer type paste and concretes showed compressive strength over 30 MPa and freeze-thaw resistance of more than 40 cycles.

Keywords:

• Geopolymer paste
• Fly ash
• XRD analysis