Applied Mechanics and Materials Vol. 732

Abstract: In this article the hot water test is presented on thin UHPC slabs that are reinforced by a new type of armature. It is a textile armature, which should replace the classic metal (steel) armature. Textile armature should not only reduce the cost of production, but, because it is not susceptible to corrosion as conventional steel armature, panels can be designed with significantly less cover thickness in achieving similar or longer lifetime of these elements. The combination of UHPC concrete with a minimum thickness of cover and textile armature allows design elements weighing up to 70 % lower compared to conventional concrete elements with conventional armature. This can achieve significant savings and benefits not only in economic aspects, but also in environmental aspects.

Abstract: The paper discusses the creep cement pastes with addition of fly ash. The evolution of the creep was observed in age of one year, for length one month. The size of the creep is influenced by the amount the creep physically bound water. The material properties depend on the ratio of components from which the cement paste is composed. The paper presents the results of creep measurement for the ratio of cement and fly ash 70:30, 60:40 and 50:50. The basic creep and creep of the saturated cement paste were calculated from measurements.

Abstract: The paper introduces an experimental program focused on the monitoring of water transport in surface layer of concrete aimed at monitoring the permeability of concrete, since concrete permeability is a property uniquely affecting durability of concrete. Introduced methods are complemented by experimental results and other traditional tests. These findings will serve to further optimization of the structure being created, thus ensuring its better aesthetic and functional characteristics.

Abstract: The use of recycled materials is nowadays greatly promoted and these are exploited in many industries, including construction and civil engineering. It is advantageous and efficient to exploit mainly those materials that cannot find their use in any other application. The steel wires from old automobile tires are a perfect example – they can be used as a dispersed reinforcement to stabilize subsoil in railway construction. In order to test the structural performance of the recycled wires as well as the composite behavior, gypsum was chosen a model matrix material. Such approach resulted in a relatively cheap gypsum-based composite material effectively combining gypsum as the material able to resist relatively high levels of compression and recycled wire reinforcement from old automobile tires, which is able to transfer tensile stress. The material can be removed from a formwork after less than 20 minutes of curing and immediately loaded. The study presents the results of a compression test carried out on three different materials – the reference sample was composed of a pure gypsum matrix, while the other two were reinforced by the dispersed wire reinforcement, which has been poorly and perfectly compacted. The results indicate the huge potential of the recycled material for the improvement of soils and brittle materials.

Abstract: The reinforcement of concrete with composite technical textile creates a tensile load-bearing capacity. It allows the elimination of steel reinforcement and minimisation of concrete cover. Based on this, the concrete cover is designed with respect to the cohesion of reinforcement with concrete. By using of textile reinforcement very thin structures could be created. The aim of this paper was to determine the interaction conditions of carbon and basalt composite reinforcement in a matrix of epoxy resin with high performance concrete (HPC). The tensile strength of used composite reinforcement and the other mechanical parameters of HPC were determined by experimental tests. Experiments copied the production method of technical textiles. These two combinations of materials present the influence on the design of the structures with textile reinforcements.

Abstract: This article shows the acquisition and testing of concrete from tunnel primary lining. The main objective of this article was to describe the mechanical properties of primary lining tunnel concrete at higher age. The primary lining was made from dry mixture sprayed concrete. The primary lining concrete was in contact with the surrounding rock continuously. The surrounding rock could be dry or with ground water. Some surrounding rocks could produce a highly aggressive environment for concrete. The question was, whether the sprayed concrete is still in service after 30 years in this environment.

Abstract: The use of fly ash in cement and concrete has long been a common practice. However, in the Czech Republic, one of the largest producers of fly ash in the world, there is still a great mistrust of this material. One of the main reasons is variability properties of fly ash. But standard ČSN EN 450-2 defines the possibilities of optimizing the properties of fly ash. This paper is dedicated to optimizing the properties of fly ash, namely sorting and mixing.

Abstract: Recycled construction and demolition waste, especially recycled concrete, is able to use as an aggregate for concrete. The high water absorption capacity (WA) of recycled aggregate has a negative impact of concrete mix workability and influences the water-cement ratio. This paper presents results of experimental measurement of WA of recycled aggregate and recycled concrete. Series of concrete samples with various replacement ratios of natural aggregate and recycled aggregate were prepared for this study. The main aim of this study is to analyze the influence of recycled aggregate WA, and mixture ratios on the WA of hardened concrete (HC). Regression model to estimate the WA of hardened concrete is presented.

Abstract: Education of exact and technical subjects at traditional schools of architecture faces a difficult task to bring these disciplines to students of significantly lower technical perception, now. For this reason, at the Faculty of Architecture, Czech Technical University in Prague, a series of seminars containing the design of physical and virtual models completed by measuring and static calculations to supplement existing education of statics and applied structural mechanics is currently prepared.