Mineralogy of autoclaved aerated concrete and characterization of tobermorite - advanced analytical methods and effect of changes in the chemical composition

Language
en
Document Type
Doctoral Thesis
Issue Date
2020-08-31
Issue Year
2020
Authors
Schreiner, Jürgen
Editor
Abstract

This dissertation offers new concepts for the mineralogical characterization of hydrothermally synthesized tobermorite and commercial autoclaved aerated concrete (AAC). The applied key methods include X-ray powder diffraction (XRD) combined with Rietveld refinement, scanning electron microscopy (SEM) and differential thermal analysis (DTA). 11 Å tobermorite was synthesized from various compounds characterized by different dosages of metakaolin. The Al3+ incorporation into the lattice of tobermorite and the formation of katoite are verified by XRD analysis. The impact of Al3+ incorporation on the microstructural properties of tobermorite is determined by the change of lattice parameters and by use of a Rietveld-compatible approach to anisotropic peak broadening due to domain morphology. Any change of the Al2O3 dosage in the raw mix affected the lattice parameters of tobermorite, while the domain morphology was only altered within a small range of Al2O3 contents. The disadvantages of SEM analysis of tobermorite in AAC compared to XRD analysis are presented in detail. Regardless of the chemical composition, the morphology of tobermorite in AAC appeared heterogeneous and could only be observed clearly in the pores and pore surfaces. Investigation of the effect of sulfate dosage on tobermorite in AAC revealed that in most samples all of the sulfate was present in anhydrite and did consequently not affect the structure of tobermorite. Finally, improvements of the monitoring of the phase development during the entire production process of AAC are presented. Especially the tracking and characterization of portlandite and tobermorite during AAC manufacturing are refined.

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