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University of Maribor / Faculty of Civil Engineering

University of Maribor / Faculty of Civil Engineering. http:// fg .uni-mb.si. Use of low frequency dielectric spectroscopy for monitoring cement hydration kinetics L. Han ž i č , G. Mand ž uka , D. Koro š ak. Presenting: Lucija Han žič. University of Maribor / Faculty of Civil Engineering.

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University of Maribor / Faculty of Civil Engineering

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  1. University of Maribor / Faculty of Civil Engineering http://fg.uni-mb.si Use of low frequency dielectric spectroscopy for monitoring cement hydration kinetics L. Hanžič, G. Mandžuka, D. Korošak Presenting: Lucija Hanžič

  2. University of Maribor / Faculty of Civil Engineering http://fg.uni-mb.si Basic principles of dielectric spectroscopy Dipole Dielectric material • induced • permanent • electronic • molecular • orientational Capacitor Capacitance Dielectric response DC voltage ε0 permittivity of free space (8.85·10-12 F m-1) Sarea of capacitor plates (m2) d distance between capacitor plates (m) εr dielectric constant (> 1)

  3. Relaxation Orientational Molecular Electronic 10 106 Frequency (Hz) University of Maribor / Faculty of Civil Engineering Oxides CaO SiO2 Al2O3 Fe2O3 Compounds C2S C3S C3A C4AF http://fg.uni-mb.si Hydration products C-S-H Ca(OH)2 Dissolved ions Na+ K+ OH- Dielectric response AC voltage ωfrequency (Hz) σ specific conductivity (S m-1) G measured conductivity (S = Ω-1) Electrical properties of hydrating cement paste Changes of electrical properties occur due to: • Modification of chemical nature, • Change of the relative amount of individual phases, • Variation of local topology.

  4. Measuring cell w/c = 0.4 University of Maribor / Faculty of Civil Engineering w/c = 0.4 http://fg.uni-mb.si Experiment Results Equipment Quad Tech 1920 Precision Meter Quad Tech 1700-01 Test Fixture frequency: 10 – 106 Hz amplitude: 10 mV Specimens cement: CEM I 42.5 R water-cement ratio: 0.3, 0.4, 0.5 Observation time 0 h – 7.5 days

  5. University of Maribor / Faculty of Civil Engineering http://fg.uni-mb.si Conclusions Dormant period(t < 10 h) Hardening period (t> 10 h) 1. Values of parameters τ and p are constant during the dormant period, 2. Values of parameter p decrease during the hardening period, 3. Values of p decrease more rapidly in cement paste with higher water-cement ratio, 4. Time evolution of p corresponds to time evolution of parameters studied by NMR (Blinc et al., 1988).

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