@phdthesis{,
    author = {Scherb, Sebastian },
    title = {Methodological investigations on quantifications of in situ X-ray diffraction for a reliable characterization of the reaction kinetics of calcined clays during early hydration},
    editor = {},
    booktitle = {},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2021},
    isbn = {},
    volume = {},
    number =  {},
    pages = {},
    url = {},
    doi = {},
    keywords = {in situ X-ray diffraction, free water, metakaolin, calcined clay, reaction kinetics, early hydration},
    abstract = {In this thesis, the influence of calcined phyllosilicates (meta-phyllosilicates) during early hydration is investigated. Preliminary methodological investigations on the influence of free, not chemically bound water on a diffractogram and on the quantification of metakaolin (MK) allowed a reliable analysis of hydrating systems by in situ X-ray diffraction (XRD) using the "partial or no known crystal structures" (PONKCS) method. XRD analyses on powder samples with different water contents as well as in situ XRD analyses on a hydrating system show a clear correlation between the consistency of the sample and the scattering contribution in the diffractogram caused by the free water. A direct proportionality to the scattering contribution of the free water and thus quantifiability is given only for a pasty consistency. Even if the quantifiability of the free water is limited, its adaptation is necessary when using the PONKCS method, due to strong overlaps with other X-ray amorphous or poorly crystalline phases such as the meta-phyllosilicates. The systematic investigation of MK, as a representative of the meta-phyllosilicates, before and after treatment in different alkaline solutions shows that the alkaline solutions cause changes in the X-ray amorphous structure of MK. These structural changes do not cause any change in the position of the X-ray amorphous hump in the diffractogram since the silicon to aluminum ratio remains constant and the dissolution of the MK particles is thus congruent. Therefore, it is possible to use a single hkl-phase model for the quantification of MK and its dissolution is reflected in the decreasing X-ray amorphous hump. However, calculations of reaction degrees show significant differences between the methods used. This is due to the uptake of alkalis as well as the accuracy of the quantifications using the PONKCS method. The clarification of the methodological issues allows the investigation of the meta-phyllosilicates metakaolin (MK), metaillite (MI) and metamuscovite (MM) during early hydration. XRD quantifications in clinker-free systems with and without sulfate carrier show that all three meta-phyllosilicates can independently form both silicate and aluminate hydrate phases. Al solubility is only sufficient for MK to form the maximum ettringite content. In MI, the content of hydrate phases formed correlates very well with the solubility of Si and Al ions and is about 30 wt.% of the content of MK. However, differences between the dissolution of portlandite (CH) and the sulfate carrier to the water bound in hydrate phases indicate adsorption of calcium ions and calcium sulfate ion complexes on the negatively charged surfaces of the calcined clay particles. Here, the granulometry of the calcined clays seems to play a less important role than the BET surface area. Thus, when assessing the influence of calcined clays on early hydration, both the chemical influence due to the dissolved ions and the complex surface properties of calcined clays must be considered in addition to the physical effects. Initial qualitative investigations in cementitious systems confirm the findings obtained from clinker-free systems. Thereby, the influence of the pure meta-phyllosilicates on the early hydration is significantly stronger compared to a calcined common clay (CC). This is due to the high content of accompanying minerals in the CC.},
    note = {},
    
    school = {Universität der Bundeswehr München},
    
}