Proceedings from 21st Czech Concrete Day 2014

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Authors: Jiří Koukal, Ludmila Kostkova, Milada Mazurova, Jan L. Vitek
Abstract: The ELI (Extreme Light Infrastructure) Laser Centre building is a relatively complex object, which has to meet a number of unusual requirements arising from its function. A reinforced concrete structure of the laser hall is one of the most complex parts of the Centre. The structure not only fulfils its static function – withstanding the static load, but it must also minimize any incidental vibrations and shield radiation generated during operation of the laser. Structural and material solution of the structure must match these requirements.
Authors: Petr Koukolík, Jan L. Vítek, Robert Brož, Robert Coufal, Milan Kalný, Jan Komanec, Vaclav Kvasnička
Abstract: Footbridge over the Labe River in Celakovice is a cable stayed structure with the main span 156 m long. It is designed for pedestrians, cyclists and also a light utility vehicle may pass over the footbridge. Until now, the footbridge has a record span of the cable stayed structure in the Czech Republic. The ultra high performance concrete (UHPC) was first applied for the load carrying structure on the footbridge at the Czech Republic. The pylons are made of steel and the stays are made of locked coil strands. Since no obligatory codes were available for the design of structures made of UHPC, the extensive experimental verification of material parameters and structural elements was necessary.
Authors: Adam Hubáček, Tomáš Jarolím, Petra Macháňová
Abstract: The paper deals with the topic of concrete for water-tight tunnel lining. This theme is currently very topical both in the Czech Republic and abroad. The focus is on requirements and properties of fresh concrete for manufacture of these specific concrete structures. Properties of hardened concrete will be examined, too: compressive strength, resistance to pressure water, durability and other parameters.
Authors: Daniel Dobiáš, Radka Pernicová
Abstract: The article is dealing with study of chloride ions diffusion in ultra-high performance concrete UHPC, which might be potentially dangerous. Life of concrete structures, in particular in transport sector is jeopardized by risk of steel reinforcement corrosion with regards to exposure of the concrete surface to direct impact of de-icing salts. Measured data were examined in relation to the depth of penetration of chloride ions into the concrete structure. Experiment results proved that UHPC concretes are more resistant to penetration of chlorides than normal strength concretes.
Authors: David Čítek, Tomáš Mandlík, Jiří Kolísko, Jan L. Vítek, Stanislav Řeháček
Abstract: Applications of precast elements made of UHPC have been increasing in recent years. Also in the Czech Republic, UHPC can be found as a structural material in first applications in both, buildings and transport structural engineering. Structures made from this modern material required experimental programs verification of material properties and also for determination of behaviour of structural elements. In previous research of the bond of UHPC and various types of reinforcement was proven to be very good, which makes it possible to reduce radically anchorage lengths. This paper deals in more detail with determination of the bond of prestressing strands and UHPC, during the first week after casting, in particular. For prestressing of precast elements, there are very important short-time strengths and short-time bond is showing to be a decisive factor for optimum prestressing time. Second part of the paper is focused on impact of thermal stress on bond of prestressing strands and UHPC. Samples were subjected to the cycling heat/frost and effect of a number of cycles on final bond behaviour of both UHPC and ordinary concrete were investigated. The article describes differences between ordinary concrete and UHPC.
Authors: Denisa Orsakova, Rudolf Hela, Petr Novosad, Jaroslav Valek
Abstract: One of the possibilities how to activate fly ash in cement composites is to add calcium oxide as a chemical activator. This addition can improve pH of composites. Because fluidized bed combustion (FBC) fly ash contain around 15% of calcium oxide, we decided to add FBC fly ash into binder system of cement composite with classic fly ash.Three mixtures were designed. First one contain in binder system only cement and classic fly ash. In second and third mixture was part (25% resp. 50%) of classic fly ash replaced by FBC fly ash. Consistency, shrinkage, compressive strength and freeze-thaw resistance were tested. Microstructure was detected by XRD and TG analyses.
Authors: Jaroslav Kadlec, Ivailo Terzijski, František Girgle, Lukáš Zvolánek
Abstract: The main objective of this paper is connected with the search of an optimal anchorage length of reinforcement in lightweight and ultra-lightweight concretes. Experimentally obtained values of the bond stress between lightweight concrete and reinforcing bars are presented. The density classes of lightweight concrete were D1,0, D1,2 and D1,4. The results are compared with equal ones of normal density concrete. The tests with ordinary reinforcement and with non-metallic hybrid reinforcement C-GFPR (30% portion of carbon fibres) were conducted.
Authors: Karel Šeps, Iva Broukalová
Abstract: The paper refers to previous research in the field recycling and reuse of secondary raw materials. It deals with utilization of micro-grounded recycled material and fly-ash as a partial substitution of Portland cement in cementitious composites. Six sets of test specimens with varying recipe were prepared for testing of mechanical properties. Flexural strength was tested on specimens 40x40x160 mm and then compression strength was measured on fragments from flexural tests. Results of tests are presented and discussed.
Authors: Leonard Hobst, Jan Vodička, Petr Bílek, Jiří Vala
Abstract: A new test method of set fibre concrete homogeneity in finished steel fibre-concrete structure is described in this contribution. The method is based on measurements of the changes in magnetic field strength of permanent magnets which are induced by a change of wire distribution in steel fibre-concrete structure. It is evident from the method described in this contribution that the test is characterized as a local failure test using small diameter core drill. It is a semi-destructive method. Its application in practice does not affect safety and reliability of steel fibre-concrete structures.Additionally to the method described, an example of its application for the assessment of fibre concrete homogeneity of the segmental tunnel lining parts is described. The results of partial measurements give both information about fibre concrete homogeneity in a segment and a number and a selection of points for homogeneity measurements which are subject to the size and the production method of such segment.

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