Wolf J (2021)
Publication Language: English
Publication Type: Thesis
Publication year: 2021
URI: https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/17955
CSA-OPC-C$ blends are used for applications where rapid setting and drying is desired.
The hydration process is complex due to the multitude of involved phases, metastability
issues and amorphous nature of hydrates. Overall little research concerning the early hydration kinetics in such blends has been published and this thesis aims to contribute towards
a further understanding of these systems. By means of predominantly XRD, pore solution
analysis and thermodynamic calculations, a basic hydration scheme is developed. Based on
thermodynamic modeling five different ternary blends are chosen for further investigation.
The hydration process is documented from the point of mixing up to 28 d. It was found
that the hydration process can be divided in two main periods. The early period is characterized by the rapid dissolution of ye’elimite and Ca-sulfate, resulting in the formation of
ettringite and amorphous aluminum hydroxide. During this period low pH values prevail,
with high Al and S concentrations and low Ca concentrations in the pore solution. Contrary
to predominant literature reports, alite can in fact react to significant degree under these
conditions. The early C3S dissolution kinetics were found to depend on the availability of
reactive calcium sulfate. This early C3S reaction directly contributes to the precipitation of
ettringite. An amorphous silicon bearing hydrate of unknown nature must form at this early
stage. With increasing pH values in the liquid phase and either the enrichment or depletion
of Al in the pore solution, a second state is initiated. The initially formed silicon bearing
hydrate and amorphous aluminum hydroxide are destabilized and either C-S-H precipitation
or straetlingite crystallization ensues. Upon C-S-H formation the alite reaction rate is significantly increased and the kinetics resemble the main C3S reaction in OPC systems. For the
systems poor in anhydrite high oversaturations with respect to straetlingite are observed in
this second stage. These translate to high potential crystallization pressures. It was found
that the late crystallization of straetlingite results in potential tensile stresses exceeding
the tensile strength of the material, resulting in a higher fraction of capillary pores, and
decreased mechanical performance. The addition of Li2CO3 results in accelerated dissolution of ye’elimite and alite and increased precipitation of ettringite. Significantly reduced
ye’elimite dissolution rates are observed when exceeding a critical dosage of Li2CO3. This
results in an earlier transition towards the C-S-H forming stage in the respective blend.
APA:
Wolf, J. (2021). Hydration in the ternary system calcium sulfoaluminate - ordinary Portland cement - calcium sulfate: Kinetics, mechanisms, performance and the impact of Li2CO3 addition (Dissertation).
MLA:
Wolf, Julian. Hydration in the ternary system calcium sulfoaluminate - ordinary Portland cement - calcium sulfate: Kinetics, mechanisms, performance and the impact of Li2CO3 addition. Dissertation, 2021.
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