Abstract
Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical activation of the raw material considerably enhanced its reactivity with respect to the alkaline agent, as was observed using Fourier-transform infrared spectroscopy, isothermal conduction calorimetry, thermogravimetry coupled with mass spectrometry analysis of the evolved gas, and SEM/EDS. The addition of calcite to the fly ash improved the compressive strength of the geopolymers, especially during the early age of curing. For 7 d aged geopolymers based on the 90% fly ash + 10% calcite blend, the strength was 8.0-, 3.5- and 2.9-fold higher than that for the geopolymers based on the unblended fly ash for 30 s, 180 s and 400 s mechanical activation time, respectively. Using Mössbauer spectroscopy, it was revealed that iron present in the fly ash did not play a significant part in the geopolymerization process. The dominant reaction product was sodium containing aluminosilicate hydrogel (N-A-S-H gel). Calcite was found to transform, to a small extent, to vaterite and Ca(OH)2 in the course of the geopolymerization.
Highlights
Despite the intensive development of nuclear energy from the middle of the 20th century, the contribution of coal to the total generated global energy remains very large and amounts to about40% [1]
We focused on the effect of both calcium carbonate addition to fly ash and mechanical activation (MA) of this two-component mixture on the geopolymerization process
Blaine SSA of flyash ash (FA) milled for 400 s was 936 m2/kg, indicating that the SSA apparently reached a Figure 2 shows the effect of MA on the Blaine-specific surface area (SSA) of the 100% FA
Summary
Despite the intensive development of nuclear energy from the middle of the 20th century, the contribution of coal to the total generated global energy remains very large and amounts to about40% [1]. Despite the intensive development of nuclear energy from the middle of the 20th century, the contribution of coal to the total generated global energy remains very large and amounts to about. As a result of very complex processes, the mineral part of coal thermally decomposes and melts in the combustion flame to generate the solid powdered residue in the form of fly ash and bottom ash. The mineral composition of coal ash is represented mainly by the glass phase, similar. The total annual worldwide coal ash generation is 700–800 million tons, with less than 30% being reused [3,4]. The disposed coal ash has become a matter of serious environmental concern because of its heavy metal contents which may leach out causing serious pollution of natural water bodies and soil [5]
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