High-speed water jet technology is commonly used for removing degraded concrete surface layers selectively in the process of repair of concrete structures. This technology offers number of advantages (such as reduced noise, dust and vibrations, preservation of intact material and thus more delicate intervention into the structure), but it still requires further improvement in terms of productivity and cost effectiveness to be even more competitive to traditional methods of concrete surface layers removal. The impact of a high-velocity liquid drop or bunch of water on a rigid surface generates extremely short high-pressure transients that can cause substantially serious damage to the surface and interior of the solid material. Therefore, the use of pulsating water jets, that are able to generate repeatedly above mentioned high-pressure transients, can lead to higher performance of pulsating high-speed water jets compared to continuous ones under the same operating conditions. A special method of the generation of the high-speed pulsating water jet was developed recently and tested extensively under laboratory conditions. The method is based on the generation of acoustic waves by the action of the acoustic transducer on the pressure liquid and their transmission via pressure system to the nozzle. A series of laboratory experiments was performed to compare effects of pulsating and continuous jets (both rotating and flat fan) acting on concrete surface. A rate of concrete removal was used to evaluate the jet. Results of the study of effects of pulsating and continuous high-speed water jets on concrete surfaces using methods of optical microscopy and image analysis are also discussed in this paper.

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

The concrete samples with various erosion states simulating road or bridge damage were disintegrated by pure continuous water jets generated from pressure 380 MPa and by pulsing water jets generated from low pressure 30 MPa. The erosion states of samples were prepared applying several laboratory techniques simulating the concrete aging under the conditions corresponding to the use in practice. The influence of the erosion state on the disintegration rate was tested because water jet techniques are very effective in selective disintegration of damaged concrete without significant erosion of the unbroken concrete unlike pneumatic drills or other impacting machines usually used for such a work. The comparison of both the depth of penetration and the ratio of volume disintegration regarding the input power is performed. All results are discussed regarding their application in practice and further development of special routings.