PSI - Issue 13

Martina Drdlová et al. / Procedia Structural Integrity 13 (2018) 1731–1738 Drdlová and Čechmánek/ Structural Integrity Procedia 00 ( 2018) 000 – 000

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e.g. by Yan et al. (1999) or Chen et al. (2013). Ductility improvement is a vital issue in concrete science and technology. One possible solution is to incorporate fibre in concrete materials. Studies published by Wu et al. (2009), Luo et al. (2000), Masuya et al. (2000), Drdlova et al. (2015), Tabatabeai et al. (2013), Su and Xu (2013), Musselman (2007), Ginter et al. (2012) confirm the better performance of fibre reinforced concrete (FRC) under impact load compared to plain concrete without reinforcement. Adding more fibre to concrete was proven to increase the energy absorption capacity of concrete and provided a more ductile material. Special type of high performance concrete with high steel fibre reinforcement is slurry infiltrated fibre concrete (SIFCON), which is prepared by incorporating large amounts of steel fibres in cement-based composites, first published by Lankard (1984). SIFCON consists of specially designed cement paste or mortar matrices and steel fibres in amount up to 15% by volume. Compared to ordinary high-performance fibre-reinforced concrete, superior ductility, energy absorption capacity and overall integrity of SIFCON under dynamic load was reported (Lankard (1984)). Thus, SIFCON has potential for applications in protective structures. Excellent blast resistance of SIFCON in terms of overall integrity and internal damage was concluded by Drdlova et al. (2016), but some fragmentation of the matrix was admitted. This can be prevented by using small amount of micro-fibre reinforcement in the slurry, but more information in this field must be provided, as the studies comparing the high strain rate properties of fine grained fibre reinforced cementitious composites are limited (Prachar et. al (2017)), mostly focused on PVA, basalt, polypropylene and steel reinforcement and compressive load regime, as reported by Wang et al. (2008), Fan et al. (2011), Ren et al. (2014) and Zhang et al. (2013). As well known, concrete is considerably weaker in tension than in compression. The research on tensile behaviour of fibre reinforced cementitious composites at high strain rates is scarce, which is mainly because it is much harder to test and measure the dynamic response of concrete in tension than in compression. From a conceptual point of view, the most appropriate method to characterize the behavior and determining the tensile strength of concrete is by means of the direct tensile test. However, this test is not used very often due to difficulties associated with the application a pure tensile load on the plain concrete specimen, which is reflected in the fact that the regulations or recommendations for its execution are limited (Graybeal and Baby (2013)). The research on dynamic mechanical properties of cement-based materials plays an important role to improve structural safety enhancement. The main objective of the work presented herein is to provide more information about the effects of various micro-fibre reinforcement on tensile behaviour of fine-grained cementitious composites at high strain rates. Presented results of executed experimental investigation brings new knowledge needed for the design of the suitable hybrid reinforcement for ultra-high performance and SIFCON type composites.

Nomenclature SHPBT Split Hopkinson Pressure Bar Technique DIF Dynamic Increase Factor DIC Digital Image Correlation ITZ Interfacial Transition Zone SHPB Split Hopkinson Pressure Bar

2. Experimental 2.1 Materials

Specimens with various dispersed micro-fibre reinforcement were prepared. The fibres were selected to cover different properties, see Table 2. Mixture without fibres was prepared as well for comparison. Fine SiO 2 sand with grain size of 0-1 mm (Bzenec), cement CEM 52.5R (Mokrá) and water were the main components of the mixture. Superplasticizer Glenium 422 (produced by BASF) was added to achieve good workability with low water/binder ratio. Silica fume Elkem 940U (produced by Elkem) was used to create an optimized particle packing density and also for its pozzolanic properties. The mix proportion of the matrix is given in Table 1. The parameters of the used fibres and their amount in particular specimens are summarized in Table 2.

Table 1. Mix proportion of composite mixture (kg.m -3 ). Cement CEM 52.5R Fine aggregate 0-1 mm

Silica fume

Superplasticizer

Water

990

670

78

10

290