Abstract
Amount of fly ash which is and yet to be generated in the coming years highlights the necessity of developing new methods of the recycling where this waste can be reused in significant quantity. A new possibility for fly ash utilization is in high-temperature application (thermal insulators or/and refractory material products). As such, fly ash has to adequately answer the mechanical and thermal stability criteria. One of the ways of achieving it is by applying mechanical activation procedure on fly ash. In present study, fly ashes from two different power plants were mechanically activated in a planetary ball mill. Mechanically treated fly ashes were cemented with two different binders: standard Portland cement and high-aluminates cement. Physico-chemical analysis and investigation of mineralogical components of composites are emphasized, due to the changes occurred in fly ash during mechanical activation and sintering of composites. Macro-performance of the composites was correlated to the microstructure of fly ash studied by means of XRD and SEM analysis. Thermal stability of crystalline phases was investigated with DTA. Highlight was placed on determination of relationship between mechanically activated fly ash and obtained composites microstructure on one side and behavior of sintered composites on the other side.
Highlights
The building materials industry is not completely environmentally friendly because it is depleting natural resources
SiO2 content in all investigated fly ashes was higher than 50 %, while content of Al2O3 approximately was about 20 %
The formation of rankinite, gehlenite, anorthite and cristobalite in the composites is important because they are thermally stable (i. e. have high melting point) and they contribute to the thermal stability of the composites
Summary
The building materials industry is not completely environmentally friendly because it is depleting natural resources. The reduction-reuse-recycle principle has to be world-wide adopted [1, 2]. Reduction means minimizing waste through planning and design; Reuse means that the final products can be incorporated back into the same cycle or into another cycle without additional material processing. Recycling refers to the recovery of unavoidable waste, involving chemical or mechanical processing, into secondary materials. The annual global fly ash production was more than 600 million tons in past 10 years [3]. EU regulations are focused on the recycling of the coal combustion fly ash and reusing it as a component of added-value products [6]. About 21 million tons of fly ash is being reapplied annually in the construction industry [5]. The high recycling rates the fly ash achieved are mainly due to its pozzolanic behavior [19-24]
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