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The article deals with an unconventional way of simulating the erosion of concrete surfaces by means of high-speed water flows. The proposed method allows the use of short-term experiments to predict the future failure of concrete elements in specific concrete mixtures exposed in practice to the action of fast-flowing fluids, whether as regards sewers, overfalls of water reservoirs, inlet channels of retention reservoirs, etc. The article shows results of experiments on disintegration of the surface layer of model concrete test specimens of various physical-mechanical properties that were exposed to various types of high-speed water flows. It has been demonstrated that the application of high-speed water flows significantly accelerates the degradation process of the surface layers. This simulation of the real situation can considerably shorten the time needed for the development and testing of new erosion-resistant construction elements.

The study of the resistance of plain concrete to high temperatures is a current topic across the field of civil engineering diagnostics. It is a type of damage that affects all components in a complex way, and there are many ways to describe and diagnose this degradation process and the resulting condition of the concrete. With regard to resistance to high temperatures, phenomena such as explosive spalling or partial creep of the material may occur. The resulting condition of thermally degraded concrete can be assessed by a number of destructive and nondestructive methods based on either physical or chemical principles. The aim of this paper is to present a comparison of nondestructive testing of selected concrete mixtures and the subsequent classification of the condition after thermal degradation. In this sense, a classification model based on supervised machine learning principles is proposed, in which the thermal degradation of the selected test specimens are known classes. The whole test set was divided into five mixtures, each with seven temperature classes in 200 °C steps from 200 °C up to 1200 °C. The output of the paper is a comparison of the different settings of the classification model and validation algorithm in relation to the observed parameters and the resulting model accuracy. The classification is done by using parameters obtained by the acoustic NDT Impact-Echo method and image-processing tools. [ABSTRACT FROM AUTHOR]

The concrete samples with various erosion states were disintegrated inside the overpressure vessel using high-velocity water jet and depth of penetration was measured. Removing of the eroded parts of samples was also tested using low-pressure generated continuous or pulsing fan jets and rotating jets. The influence of the erosion states, water jet techniques, traverse rate and stand-off distance on the disintegration volume was studied and the surface topography was investigated. The high-pressure generated continuous water jet was applied in the overpressure vessel used for simulation of pressures equivalent to the submersion to several depths under the water level. The low-pressure generated continuous or pulsing jets were applied in air conditions. Some samples of special decorative concretes were also studied. [ABSTRACT FROM AUTHOR]

This paper describes the process of possible evaluation of costs of using high speed water jet technology for concrete removal methods. High speed water jet technology is a progressive technology of removing damaged concrete used in civil engineering since the 80's of 20th century. It has been changing and developing since that time. But there is little information in literature devoted to the economic evaluation of this technology. Detailed economic analysis is still missing. This paper aims to compare comprehensively in economic terms the costs of removing concrete using the technology of both continuous oscillating and pulsating oscillating water jets. The research was realized in cooperation with research institutions and industrial companies and was supported by state budget of the Czech Republic and from the European Union. The scheme of cooperation of the University, research institutions, industrial companies and government follows the Triple helix model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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The presented research aims to clarify the specific effect of the individual components of concrete with Portland cement CEM I 42.5 R on the volume changes of concrete. The effect of the filler component was evaluated from the point of view of the composition and type of aggregate (crushed versus mined) and from the point of view of the mineralogical composition of the aggregate. Concrete formulas with a maximum aggregate grain size of 16 and 22 mm were assessed. The effect of the binder component on the shrinkage of the concrete was monitored on the concrete mixtures produced using the same aggregate and maintaining the same strength class of concrete, C 45/55. The effect of the addition of finely ground limestone, finely ground granulated blast furnace slag and coal high-temperature fly ash was monitored. It was found that the maximum aggregate grain and the type of grading curve do not have a significant effect on the volume changes of concrete. Concretes with mined aggregates showed lower shrinkage than concretes with crushed aggregates. The most significant is the effect of the type of aggregate on the volume changes in the first 24 h. Mineral additives have a positive effect on the elimination of the volume changes of concrete, while the addition of high-temperature fly ash proved to be the most suitable. [ABSTRACT FROM AUTHOR]

Virtually every concrete structure comes into contact with abrasive effects of flowing media or solids, which have a direct impact on the durability of concrete. An abrasive effect is most pronounced in transport or water management structures, and these structures are often designed for a significantly longer service life (usually 100 years). This research evaluates the influence of the filler component in terms of the type of aggregate and its mineralogical composition on concrete abrasion resistance. As part of the impact of the binder component, several concrete mixtures were produced using the same aggregate and maintaining the same strength class with the addition of different types of active and inert mineral additives. In other parts of the research, the effect of adding fiber reinforcement on the abrasion resistance of concrete was verified. Mutual connections and correlations in different age groups (7, 28 and 90 days) were sought for all obtained results. The abrasion resistance of the composite was monitored by using standard procedures, especially using a Böhm device. It was found that for good abrasion resistance of concrete, it is not necessary to produce concretes with high strength classes using often expensive mineral additives (microsilica) and quality aggregates, but the maturation time of the composite and its microstructure plays an important role. [ABSTRACT FROM AUTHOR]