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In situ x-ray diffraction at high temperatures: Formation of Ca$_{2}$SiO$_{4}$ and ternesite in recycled autoclaved aerated concrete

Ullrich, Angela 1; Garbev, Krassimir ORCID iD icon 1; Bergfeldt, Britta 1
1 Institut für Technische Chemie (ITC), Karlsruher Institut für Technologie (KIT)


This study provides an insight into possible recycling processes for autoclaved aerated concrete (AAC) at low temperatures (<1000 °C). Belite binders were synthesized from wastes of AAC by the addition of CaCO$_{3}$ and adaption of the molar CaO/SiO$_{2}$ (C/S ratio) in the range of 2 to 2.5. An in situ XRD study performed during heating up to 1000 °C and subsequent quenching to room temperature evidenced the formation of ternesite besides C$_{2}$S in sulfate-containing systems. Several factors influencing the reaction kinetics and the evolution of the phase composition were investigated thoroughly. Increased sulfate content and dwelling time during heating increase the ternesite content and promote the formation of highly crystalline α’H-C$_{2}$S. The C/S-ratio of the starting materials has to be adjusted to the sulfate content in order to prevent the formation of ternesite at the expense of C$_{2}$S. Ternesite remains stable during quenching to room temperature or even increases in amount, except in cases of very low cooling rates or high residual quartz contents (C/S-ratio ≤ 2). Temperature and range of α’H-C$_{2}$S to β-C$_{2}$S phase transition on quenching strongly depend on the cooling rate. ... mehr

Verlagsausgabe §
DOI: 10.5445/IR/1000136124
Veröffentlicht am 13.08.2021
DOI: 10.3390/min11080789
Zitationen: 5
Web of Science
Zitationen: 5
Zitationen: 8
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Technische Chemie (ITC)
Publikationstyp Zeitschriftenaufsatz
Publikationsjahr 2021
Sprache Englisch
Identifikator ISSN: 2075-163X
KITopen-ID: 1000136124
HGF-Programm 38.05.02 (POF IV, LK 01) Metals and Minerals Cycle
Erschienen in Minerals
Verlag MDPI
Band 11
Heft 8
Seiten Art.Nr. 789
Schlagwörter ternesite; dicalcium silicate; in situ; X-ray diffraction; high-temperature
Nachgewiesen in Scopus
Web of Science
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