24th Concrete Days 2017

Paper Title Page

Authors: Dalibor Kocáb, Petr Misák, Petr Daněk, Barbara Kucharczyková, Romana Halamová
Abstract: There is a large number of factors that have a strong influence on the elastic modulus of concrete. These are technological influences as well as issues connected with the testing methods for its determination, one of which is the choice of the upper loading stress of cyclic loading during testing the static modulus of elasticity of concrete in compression. The upper loading stress should be equal to 1/3 of the specimen’s compressive strength, however, its choice is often made incorrectly. This paper describes an experiment focused on discovering the impact that deviating from the 1/3 upper loading stress has on the measured value of the static modulus of elasticity.
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Authors: Petr Cikrle, Dalibor Kocáb, Barbara Kucharczyková, Ondřej Anton
Abstract: The paper deals with the in-situ determination of the modulus of elasticity on the bridge elements using ultrasonic pulse method. This non-destructive test method was chosen for the measurement because of its undisputed advantages that allow the measurement of relatively thick layers of material. For the purpose of the elastic modulus verification the direct measurement was used, in which a pair of transducers (transmitter and receiver) were placed directly opposite to each other. The results of performed in-situ measurements as well as the results of verification tests performed in the laboratory are presented in the paper. The article also discusses the issue of evaluation and interpretation of the results obtained by in-situ measurements using non-destructive test method.
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Authors: Dalibor Kocáb, Libor Topolář, Barbara Kucharczyková, Petr Pőssl, Michaela Hoduláková
Abstract: The paper describes an experiment focused on observing the development of the elastic modulus and compressive strength in a polymer-cement mortar during the first 28 days of aging. The specimens (aged 3 and 28 days) were tested for the static and dynamic modulus of elasticity using two methods – the ultrasonic pulse velocity test and the resonance method. During the test of the modulus of elasticity in compression the mortar’s behaviour was also examined by means of the acoustic emission method, which is based on the recording of mechanical pulses caused by dilation waves generated by microcracks that form during loading. The outcome of the experiment is an evaluation of the polymer-cement mortar’s behaviour in terms of the development of its elastic modulus and compressive strength as well as in terms of the material’s acoustic response during loading.
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Authors: Miloslav Janda, Miloš Zich
Abstract: Prefabricated panels are handled by various types of crane during the assembly (bridge crane in the production hall and construction crane on site). The panel is loaded with inertial forces during manipulation caused by crane's starting and breaking movement. These forces significantly affect the design of the transport system (anchors, ropes, etc. In literature there are different values of dynamic coefficient for different types of crane. In the experiment, the magnitude of the force in the crane hinge was measured during the handling of various panel types in the production hall and during the construction site installation. The static value of the force size was determined at the moment when the panel freely hanged on crane hinge. The measured values are further compared with the manufacturer’s recommendation for the design of the transport anchors.
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Authors: David Pytlík, Vlastimil Bílek
Abstract: Some effects of self-curing on the mechanical properties of High Performance Concrete (HPC) are discussed in this paper. The matrix of HPC is very dense and it is very difficult to deliver the curing water into the cement matrix. Two different materials in different dosages were selected to examine self-curing. Polymer curing agent (PCA) was selected as the first, and 0.2% 0.4% 0.6% and 0.8% of PCA were added by weight of cement. This additive should allow the physicochemical binding of a larger portion of the mixing water and then release it slowly for better hydration without negative effects on the products. Pre-soaked slag of 0/4 mm was tested as another source of water for internal curing. The slag was also dosed in 10%, 15%, 20% and 30% volume of sand with the fraction 0/4 mm. Referential HPC was a high-dose cement that consumes a large amount of water for hydration. The water/cement ratio was 0.2. Metakaolin was added to improve the properties of fresh and hardened HPC.
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Authors: Martin Tipka, Jitka Vašková, Jan Vodička
Abstract: The paper describes the differences in several test methods, which are used for tensile strength analysis of cementitious composites. It explains tests arrangement, their benefits and disadvantages. The conversion factors between detected strengths were quantified in experiments, depending on the particular composition of the composite.
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Authors: Michal Kropáček, Radim Čajka
Abstract: The subject of the paper is research on the development of volume changes (especially shrinkage) on cement concrete. This is a measurement of shrinkage on large samples using string strain gauges both internal and external. Parallel to this measurement, according to the real concreting conditions, the volume changes will be measured by means of shrinkage drains in the test laboratory. This will make it possible to compare a comparatively progressive method of measuring volume changes with the real behavior of the same concrete in the structure. The measurement of volume changes by the shrinkage drains is a comparatively rare test allowing continuous volume changes to be measured from the beginning of the setting of the concrete. It is possible to capture the entire process of hydration of concrete. The paper will describe the technology of measurement and comparison of both methods on ordinary concrete.
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Authors: Rudolf Hela, Martin Ťažký
Abstract: At the beginning of 2016, the legislation for regulating and reducing the emission of exhaust gases with regard to reducing nitrogen oxides came into force. The articles published to date point to the possibility of increased ammonium salt content in fly ash that has undergone a selective non-catalytic reduction process. This paper addresses other possible negative impacts of the reduction process for nitrogen oxide on the physico-mechanical properties of high-temperature fly ash, especially the morphology of its grains and its impact on the rheology of the composite and the impact on the efficiency index.
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Authors: Lukáš Lyčka, Petr Štěpánek
Abstract: This paper presents an experimental study on the shear behavior of concrete beams with fiber-reinforced (FRP) composite grating as shear reinforcement. Corrosion resistance and non-magnetic properties of FRP reinforcement allows its use in places where application of regular steel reinforcement would face difficulties. The use of FRP composites can increase the life span of constructions and reduce its maintenance costs. Shear stirrups are more susceptible to harsh conditions, due to their placement at the outer face of the reinforcement, and the use of FRP materials can lead to lower concrete cover thickness and therefore to a more effective design of an element. FRP reinforcements are highly anisotropic material with low strength in the direction perpendicular to the fibers. This causes the strength of a FRP stirrup to be limited by its strength in the bends (corners) of a stirrup. The tensile strength in the corner of the bent stirrup is around 40 to 60% of the strength of the straight bar. FRP grating doesn’t contain a bent section limiting its strength, but its behavior as a shear reinforcement is unknown. The paper contains the results of own experimental research on concrete beams with shear reinforcement made of FRP gratings done at the Faculty of Civil Engineering at the Brno University of Technology. Test specimen consisted of nine beams with different shear reinforcement ratios. Presented experimental data are then compared with the results of tests on beams with regular shear FRP stirrups found in literature.
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Authors: Radovan Hofírek, Rostislav Lang, Miloš Zich
Abstract: Concrete shrinkage is affected by the application of hydro insulation or in contrary by the removal of hydro insulation membrane from the concrete elements. Changes in shrinkage are influenced by the age of concrete, the size of the concrete element and the ratio between the different drying surface areas. This paper deals with the evaluation of the long term measurements performed in elements sized 300 x 300 x 300 mm and the application of the acquired knowledge into the modern B4 model.
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