Institute of Functional Interfaces

Correlation between Composition and Mechanical Properties of Calcium Silicate Hydrates Identified by Infrared Spectroscopy and Density Functional Theory

  • chair:

    Izadifar, M. / Königer, F. / Gerdes, A. / Wöll, C. / Thissen, P. (2019)

  • place:

    J. Phys. Chem. C, 2019, 123, 17, 10868-10873

  • Date: April 2019

Abstract

Building and construction industries are at the same time the backbone and the driving force of our modern society. Nearly all our technical infrastructure today is based on cement-based materials. Detailed spectroscopic investigations of model reactions on well-defined mineral substrates under UHV conditions are largely lacking, thus prohibiting a validation of theoretical methods. Even simple chemical processes are poorly understood. As a result, the rational design of anticorrosion strategies is virtually impossible. In this manuscript, we have worked on eight different calcium-silicate (CS) or calcium-silicate-hydrate (CSH) phases, namely, tobermorite 14 Å, tobermorite 11 Å, tobermorite 9 Å, wollastonite, jaffeite, jennite, γ-C2S, and α-C2SH. These representative model phases are calculated with the help of the density functional theory modeling method. Initially, we take care of the mechanical properties of the material. Our results revealed that jaffeite, γ-C2S, and α-C2SH have a linear bulk modulus because of the monomer structure of silicate tetrahedra. Tobermorite 14 Å and γ-C2S exhibit the lowest and highest bulk modulus, respectively. In the second part, the optimized geometries allow for the precise calculation of vibrational eigenmodes and frequencies by the force constant approach. The proportions of C/S and H/C are major criteria for the classification of the calculated wavenumber of ν(Si–O) for all phases in our model system. However, γ-C2S and α-C2SH have an equal C/S ratio. As a result of the different H/C ratios, wavenumbers were found for four characteristic vibration modes. The contribution of the C/S ratio for  α-C2SH in comparison to  jaffeite is another aspect to be considered for phases with equal H/C ratios. Because of the  lower  C/S ratio,  α-C2SH exhibits a higher wavenumber than  jaffeite.

 

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