Amgalan Minjigmaa

Fly ash based geopolymer thin coatings on metal substrates and its thermal evaluation

Class F fly ash based Na-geopolymer formulations have been applied as fire resistant coatings on steel. The main variables for the coating formulations were Si: Al molar and water: cement weight ratios. We have determined that the adhesive strength of the coatings strongly depend on geopolymer composition. The ease with which geopolymer can be applied onto metal surfaces and the resultant thickness depend on the water content of the formulation. Adhesive strengths of greater than 3.5 MPa have been achieved on mild steel surfaces for compositions with Si:Al of 3.5. Microstructure evolution and thermal properties of the optimised coating formulations show that they have very promising fire resistant characteristics.

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

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.

Characterisation of granulometric composition of a Mongolian fly ash and its application for value added products

In Mongolia coal fired thermal power stations are producing over 90% of the countrys electricity. The 4th thermal power station uses Baganuur and Shivee-ovoo coals for firing and annually disposes over 300 thousand tonnes of coal firing by-products such as fly ash. However, in Mongolia utilisation rate of the coal firing by product is negligible and seems to be caused little knowledge of the mineralogical and physical-chemical properties. Granulometric characterization of the Baganuur and Shivee ovoo fly ashes have been performed. Specific surface area of both fly ashes varied from 1.04 to 2.75m2/g. The >74 μm fraction of Shivee ovoo fly ash comprised around 17% of the total weight while for Baganuur fly ash it was equal to 7%. The crystalline part of the >74 μm fraction of Baganuur fly ash was mostly quartz while in Shivee ovoo fly ash it was a mixture of quartz, diopside and akermanite. Raw and fine fractions of the Baganuur and Shivee ovoo fly ashes have been used for preparation of a geopolymer type binder. Raw and fine fractions of both fly ashes have been activated with 10 M NaON solution and cured at 70°C for 24h. Geopolymer type pastes based on Shivee ovoo and Baganuur fly ashes exhibited compressive strengths of over 20 and 30 MPa, respectively. Compressive strength of the geopolymer pastes based on fine fraction showed negligible change. Comprehensive characterizations of Baganuur and Shivee ovoo fly ashes and geopolymer pastes were performed using XRD, XRF, SEM, BET methods..

Preparation of geopolymer type binder from Mongolian fly ash and its characterisation

At presently there are five operating power plants in the central energy system of Mongolia which generate both heat and electricity. Together these burn about 5-6 million tonnes of coal resulting in more than 600,000 tonnes of coal combustion by-products per year. Three thermal power plants are located in Ulaanbaatar city and produce more than 80% of the total electricity in Mongolia. Within these plants, the 4th thermal power plant generates around 300,000 tonnes of fly and bottom ash and the 3rd thermal power plant around 100,000 tonnes of bottom ash. The thermal power plants in Ulaanbaatar city use coal from the Baganuur and Shivee-ovoo deposits. The chemical composition of these fly ashes indicate they belong to class C fly ashes. The physical and chemical characteristics of fly ash and boiler slags determine the how to make of use them. The physical properties of these residues will be determined by the technology, design and operational conditions of the power stations. The chemical composition of the fly ash and slags depends completely on the inorganic matter within the source coal deposits and the composition of the slags and fly ashes cannot be controlled. Comprehensive characterization of coal combustion by products were performed using XRD, XRF, SEM and gamma-spectroscopy methods. A novel geopolymer type binder was prepared using Baganuur and Shivee ovoo fly ashes from the 4th Thermal power plant. Sodium hydroxide solutions with a different molarity were used as the activating solutions. It was found that an alkali concentration increase resulted in an increase in the compressive strength of the geopolymer paste. Compressive strengths of greater than 20 MPa was achieved with Shivee ovoo fly ash based geopolymer while with Baganuur fly ash it was more than 30 MPa.