A Comparative Study of Alkali Activated Fly Ashes under Heat Exposure

Seyedian Choubi, Sepehr
Meral, Çağla
Akbas, Yigit Semih
Tangüler Bayramtan, Meltem
Coal fly ash (FA) is a by-product of combustion processes in coal fired power plants. Annually over 800 million tons of fly ash is being produced all around the world. Only a small portion of this ash is reutilized; a major portion goes to landfills or dumped at the sea. The disposal of FA brings significant economic and environmental concerns. Alkali-activation (AA) of fly ashes is a possible way to put some of the FAs in a beneficial use. Alkali-activated fly ashes (AAFA) possess good mechanical properties, acid and fire resistance and thermal stability. This study aims to evaluate the alkali-activation and heat-exposure performances of FAs with varying Ca-contents from three different thermal power plants in Turkey through compressive strength tests and XRD measurements. The strength development of the AAFA samples were followed by 3-, 7- and 28-day compressive strength tests. The heat-exposure performance of the AAFA samples were determined by measuring the residual compressive strengths of the 28-day old samples after being exposed to elevated temperatures (400,700 and 1000°C). It is concluded that not only the amorphous content, but also the fineness of the FA has a critical importance on the strength development of the AAFAs. The AA samples of the FA with highest Ca-content lost considerable strength after exposure to elevated temperatures, possibly due to decomposition of the Ca-bearing phases. The AA samples with medium Cacontent did not show significant changes during heat exposure. The AA samples with low Ca-content showed enhanced performance after being exposed to 400°C. The role of Ca in performance of AAFAs under heat-exposure needs to be further studied. The X-ray Diffraction (XRD) patterns of the FAs showed that zeolite type phases has formed during activation. Zeolite phases remained stable during heat treatment until 700°C. After 700°C zeolite type phases started to dehydrate and form stable phases such as Nepheline and Haüyne.
Fourth International Conference on Sustainable Construction Materials and Technologies, (August 7-11, 2016)


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Citation Formats
S. Seyedian Choubi, Ç. Meral, Y. S. Akbas, and M. Tangüler Bayramtan, “A Comparative Study of Alkali Activated Fly Ashes under Heat Exposure,” presented at the Fourth International Conference on Sustainable Construction Materials and Technologies, (August 7-11, 2016), Las Vegas, USA, 2016, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/78312.