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 analysis of phenomena related to gas transport in hard coal is important with regard to the energetic use of coal bed methane (CBM), the reduction of greenhouse gas emissions to the atmosphere (CO₂) and the prevention of natural hazards such as methane hazards and gas and rock outbursts. This article presents issues concerning the feasibility and scope of applying the unipore and bidisperse diffusion models to obtain knowledge concerning the kinetics of methane sorption and its diffusion in the carbon structure, depending on its petrography. Laboratory tests were carried out on coal samples which varied in terms of petrography. Quantitative point analyses were carried out, based on which content of groups of macerals was determined. The degree of coalification of coal samples was also determined based on measurements of vitrinite reflectivity R₀ and the volatile matter content V^daf. Sorption kinetics were also investigated, and attempts were made to adjust the unipore and bidisperse models to the real sorption kinetic courses. This allowed the identification of appropriate coefficients controlling the course of sorption in mathematical models. An attempt was also made to assess the possibility of applying a given model to properly describe the phenomenon of methane sorption on hard coal.