TY - JOUR

T1 - Synthesis of fly ash-based geopolymers

T2 - Effect of calcite addition and mechanical activation

AU - Kalinkin, Alexander M.

AU - Gurevich, Basya I.

AU - Myshenkov, Mikhail S.

AU - Chislov, Mikhail V.

AU - Kalinkina, Elena V.

AU - Zvereva, Irina A.

AU - Cherkezova-Zheleva, Zara

AU - Paneva, Daniela

AU - Petkova, Vilma

N1 - Funding Information: Funding: The reported study was funded by RFBR, project number 20-03-00486. Funding Information: Acknowledgments: The authors acknowledge support from the Centre for Thermogravimetric and Calorimetric Research of the Research Park of St. Petersburg State University where the calorimetric measurements and thermal analysis were performed. Publisher Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/9

Y1 - 2020/9

N2 - 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.

AB - 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.

KW - Fly ash

KW - Geopolymers

KW - Mechanical activation

KW - Natural calcite

KW - mechanical activation

KW - METAKAOLIN

KW - REACTIVITY

KW - fly ash

KW - LIMESTONE

KW - natural calcite

KW - BINDERS

KW - WASTE

KW - EVOLUTION

KW - TEMPERATURE

KW - FTIR

KW - ALKALINE ACTIVATION

KW - SLAG

KW - geopolymers

UR - http://www.scopus.com/inward/record.url?scp=85091255717&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/b0a19fe0-9022-31a3-b457-1f183bced079/

U2 - 10.3390/min10090827

DO - 10.3390/min10090827

M3 - Article

AN - SCOPUS:85091255717

VL - 10

SP - 1

EP - 21

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 9

M1 - 827

ER -