J. Temuujin

Influence of calcium compounds on the mechanical properties of fly ash geopolymer pastes

The influence of calcium compounds (CaO and Ca(OH)(2)) on the mechanical properties of fly ash based geopolymers has been studied. Calcium compounds were substituted in fly ash at 1, 2 and 3 wt%, respectively. Curing of the geopolymers was performed at ambient temperature (20 degrees C) and 70 degrees C. Addition of calcium compounds as a fly ash substitute improved mechanical properties for the ambient temperature cured samples while decreasing properties for the 70 degrees C cured samples. Seven days compressive strength of the ambient temperature cured samples increased from 11.8 (2.9) to 22.8 (3.8)MPa and 29.2 (1.1)MPa for 3% CaO and 3% Ca(OH)(2) additions, respectively.

Effect of fly ash preliminary calcination on the properties of geopolymer

The influence of preliminary calcination of fly ashes on the geopolymerisation process has been studied. Preliminary calcination at 500 and 800 degrees C causes decarbonation of the fly ash while it also leads to a decrease of the amorphous content of the fly ashes from 60 to 57%. Geopolymer prepared using raw fly ash exhibited a compressive strength 55.7(9.2)MPa, while for 500 and 800 degrees C calcined samples it reduced to 54(5.8) and 44.4(5.4)MPa, respectively. The decrease in compressive strength of the geopolymers is discussed in terms of partial surface crystallisation of the fly ash particles. Reactivity of the fly ash also has been correlated with the shrinkage rate and presence of efflorescence on the surface of geopolymers.

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.