engleski

ALKALINE ACTIVATION OF FLY ASH: DEGREE OF REACTION

The alkali activation of fly ash (AAFA) is a physical-chemical process in which this grey powder (FA)is mixed with alkaline activators (alkaline solutions) and then stored at mild temperatures (T < 100 oC) for a short period of time to produce a material with high mechanical performance known as ” alkaline cements” . This paper deals with the alkaline activation of the Croatian Class F fly ash, sourced from the Plomin 2 coal-fired Thermal Power Station, for production of novel cementitious materials. The fly ash was treated with sodium silicate (a technical grade water-glass) as alkaline activator, and than cured at 85 °C for different time intervals (8 and 24 h). The degree of reaction in the AAFA mortars was obtained by attacking samples with the 1:20 HCl solution at laboratory temperature. Fourier transforms infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD) techniques have been used to identify the new phases and to follow the progress of the alkali activation of fly ash. The results show that the glassy component of fly ash reacted with water-glass and the main reaction product formed in the AAFA system is an amorphous alkaline aluminosilicate gel that induced a shift in the T-O (T = Si or Al) asymmetric stretching band towards lower wave number compareded to one in the original fly ash used. In addition, the evolution of the mechanical properties of prepared AAFA mortars has also been studied and discussed in terms of the products formed at different time of reaction.

fly ash; alkaline activation; degree of reaction

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