20 септември 2020
Kalinkin, A.M., Gurevich, B.I., Myshenkov, M.S., Chislov, M.V., Kalinkina, E.V., Zvereva, I.A., Cherkezova-Zheleva, Z., Paneva, D., Petkova, V..
(
Даниела Панева;
Зара Черкезова-Желева;
)
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 M?ssbauer 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.
Minerals, 10, 9, Multidisciplinary Digital Publishing Institute (MDPI), 2020, ISSN:2075-163X, DOI:10.3390/min10090827, art.n. 827. SJR (Scopus):0.494 Q2 (Scopus)
https://www.mdpi.com/2075-163X/10/9/827
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