PSI - Issue 13

René Čechmánek et al. / Procedia Structural Integrity 13 (2018) 1780 – 1785 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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The relationship between the orientation and the length of the fibres in the section and the flexural strengths were monitored. Advantage of using the thin sections with fluorescent dye for fibre orientation analysis is compared to other methods, described by Plagué et al (2017). In the view of the fact that the fibre orientation is one of the parameters affecting flexural strength of GFRC, it is also possible to study the distribution of aggregates and fibres in the concrete binder using thin section and fluorescence microscopy at the same time. Orientation and length of fibres in the sections by image analysis are summarized in Fig. 3.

Fig. 3. Orientation and length of fibres in section across the sample (a) maximal strength; (b) minimal strength.

For all the specimens, the distribution of fibre orientation is broader (broad range of angles) for samples having higher flexural strengths. It was previously reported that casting of the fresh mixture from the centre, by Song et al. (2018), or from the side, by Zhou and Uchida (2017), of the mould can significantly influence the flow parameters. In the section zone, the fibres are prone to form concentric circles based on their own centres. The length of fibres in this zone in 2D section can be variable, losing the bridging capability of fibres in these areas. In case of casting from the side of the mould, most fibres are oriented perpendicular to the cut. 7. Conclusions For measurement of rheological properties of fresh cement-based mixtures there were designed new experimental devices for the Discovery Hybrid Rheometer. In order to measure highly heterogeneous suspensions, such as cement paste and mortar, a helical rotor was designed and manufactured. The advantage of its use is that during measurements the material is carried by the rotor and heavier particles do not settle which avoids slippage like when coaxial cylinders or bladed rotors are used. A total of 4 formulas of different types of fibre reinforced concrete were prepared and subjected to non-destructive and destructive testing. Currently, the dependence on the values measured using ultrasound and flexural strength is being identified. It is necessary to evaluate other several sets of specimens and the results should be subjected to a correlation analysis again. After this, optimization of the process of preparation of selected fibre reinforced concrete and the related measurements will be carried out. Acknowledgements This research has been supported by institutional support for the long-term strategic development of a research organization provided by the Ministry of Industry and Trade of the Czech Republic.