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The results of dynamic compression and tensile-splitting tests of concrete reinforced by randomly distributed short non – metallic fibres are presented. A Split Hopkinson Pressure Bar combined with a high-speed photographic system, was used to conduct dynamic Brazilian tests. Quasi static test show that the reinforcement of concrete by the non-metallic fibres leads to the improvement of mechanical properties at quasi static loading. This phenomenon was not observed at the high strain rate loading .Some explanation of this result is briefly outlined.

The utilization of waste steel fibres (coming from the recycling process of the old tires) in production of blast resistant cement based panels was assessed. Waste fibres were incorporated in slurry infiltrated fibre concrete (SIFCON), which is a special type of ultra-highperformance fibre reinforced concrete with high fibre content. The technological feasibility (i.e. suitability of the waste fibres for SIFCON technology) was assessed using homogeneity test. Test specimens were prepared with three volume fractions (5; 7.5 and 10 % by vol.) of waste unclassified fibres. SIFCON with industrial steel fibres (10% by vol.) and ultra-highperformance fibre concrete with industrial fibres were also cast and tested for comparison purposes. Quasi-static mechanical properties were determined. Real blast tests were performed on the slab specimens (500x500x40 mm) according to the modified methodology M-T0-VTU0 10/09. Damage of the slab, the change of the ultrasound wave velocity propagation in the slab specimen before and after the blast load in certain measurement points, the weight of fragments and their damage potential were evaluated and compared. Realized tests confirmed the possibility of using the waste fibres for SIFCON technology. The obtained results indicate, that the usage of waste fibres does not significantly reduce the values of SIFCON flexural and compressive strength at quasi-static load - the values were comparable to the specimens with industrially produced fibres. With increasing fibre content, the mechanical parameters are increasing as well. Using of the waste fibres reduces fragmentation of SIFCON at blast load due to the fibre size parameters. Using of low diameter fibres means more fibres in the matrix and thus better homogeneity of the whole composite with less unreinforced areas. Regarding the blast tests, the specimen with waste steel fibres showed the best resistance and outperformed also the specimen with commercial fibres. Using of waste fibres in SIFCON technology can reduce the price of this composite by 70 % by keeping the original SIFCON extraordinary properties, which makes it very competitive material in the concrete area.