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The paper is dealing with the effects of flat high-speed water jet on concretes affected by high temperature. Research should help to correct use of water jet technology in repair works on concrete structures especially after wildfires in tunnels, underground garages, etc., which are exposed to enormous thermal stress. Four concrete mixtures were prepared for tests of interaction of water jet with concrete. The samples were exposed to 200 °C and 600 °C and for comparison one third of samples were left unaffected. It was found, that both lower traversing velocity (cutting speed) and higher water pressure led to removal of higher amount of concrete. Higher temperature loading caused decrease of concrete strength and thus easier removal of surface layers by water jet. Concrete mixtures with basalt aggregate demonstrate higher resistance against water jet penetration regardless thermal loading compared to mixture with standard granodiorite aggregate. Presence of polypropylene fibres has substantial influence on concrete strength properties, however only marginal impact on resistance against water jet penetration.

Advanced technological aspects of cement based composites have been recently focused on developing new materials, which are high performance and exhibit high compressive strength. Using of carbon nanotubes improve microstructure and properties of cement matrix and make them promising fillers into many engineering materials. In this paper, experiments oriented at the study of dispersion of CNTs in water with respect to their use in cement compositions are described and a novel method of CNTs dispersion in water using pulsating water jets is proposed.