24th Concrete Days 2017

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Authors: Tomáš Bittner, Petr Pokorný, Petr Bouška, Šárka Nenadálová
Abstract: The main point of this paper is to assess the level of corrosion damage of the composite textile fiberglass reinforcement in environments that simulate the concrete pore solution by the techniques of FT-IR (Fourier transform infrared spectroscopy), SEM (scanning electron microscopy) as well as EDS (scanning electron microscopy). Effect of corrosion on the tensile strength segmented textile glass fiber was tested and also it was investigated specific type of protective organic coating on glass fiber. The results express the evidence of local corrosion damage on the examined samples just at pH 13.5, and on the contrary high stability in the environment simulating carbonated concrete and concrete contaminated by chloride anions. The thesis also points on the unevenness of the excluded protective organic coating with localized porosity which relates to the above mentioned corrosion damage.
Authors: Adam Hubáček, Lucia Osuská
Abstract: Requirements of the quality of surface have increased recently for vibro-pressed concrete elements. As a consequence, there are new concrete products available with specially treated visual side - surface is coated with an impregnating paint and then hardened by infrared or ultraviolet light.The paper summarizes current knowledge of vibro-pressed concrete elements with surface treated in mentioned way. The focus is on description and effectiveness of individual methods, hardening principles and further possible treatments of surface of concrete aiming at higher durability of concrete. Observed parameters and properties of vibro-pressed concrete elements include resistance of surface to water and chemical de-icers, water absorbing capacity, resistance to wear, slip resistance and reduction of risk of efflorescence.
Authors: Adam Hubáček
Abstract: The paper focuses on the problems of concrete for water-tight concrete structure and with systém and regulations for design and application of these structures. The theme is currently quite topical in the Czech Republic and abroad. The accent is put particularly on the requirements and properties of fresh concrete or self-compacting concrete for manufacture of specific concrete structures. Properties of hardened concrete will be also observed; in particular compressive strength, resistance to pressure water, durability and other parameters.
Authors: Milan Rydval, David Čítek, Jiří Kolísko, Zbyšek Pavlík
Abstract: As part of the development and research of UHPC materials, the broad professional public deals mainly with the determination of the basic physical and mechanical parameters, in particular the compressive strength, that is considered as a determining parameter for these cement-based composites. The strength of the composite material is determined under normal laboratory conditions. Fine cement-based composite materials are increasingly used not only for academic purposes but also for practical applications. Therefore, it is necessary to focus on other parameters that determine these new Hi-Tech materials. The mechanical properties of materials at elevated temperatures belong to an area that is not properly defined not only in the Czech Republic but also in the world. Research into the behavior of these composite materials and their thermal loading can provide additional information and basics to expand these building materials such as France, USA, Japan and other countries around the world. In the Czech standards applicable to the design of concrete structures subjected to thermal stress, the values of the reduction coefficient Kc, θ are used only for commonly used dense concrete and also for expanded concrete. It is clear that these values cannot be used for fine-grained composite materials with cement binder reinforced hybrid reinforcements. The aim of the paper is to determine and describe the behavior of these materials in the temperature range of 20 ° C to 1000 ° C for two test modes that affect residual strength and high temperature strength.
Authors: Petr Misák, Tomáš Vymazal, Dalibor Kocáb, Barbara Kucharczyková
Abstract: In recent years, the static modulus of elasticity is one of the most discussed property of hardened concrete. The aim of this article is to show results of 6 performed experiments focused on test results precision. The measurements were made according to the standards ISO 6784 and ISO 1920-10. More than 20 participants (laboratories) from Europe took part in these experiments. Test results were compared using the statistical methods for interlaboratory comparison. Repeatability and reproducibility, which provide more detailed information about range of expected values of elastic modulus, are the most discussed characteristics in the article.
Authors: Hana Šimonová, Tomáš Trčka, Michal Bejček, Iva Rozsypalová, Petr Daněk, Zbyněk Keršner
Abstract: The aim of this paper is to describe the procedure of determining the mechanical fracture parameters of selected concrete specimens taken from panels after the fire experiments. The records (in form load vs displacement diagrams) of three-point bending fracture tests of these specimens with initial stress concentrators was first advanced corrected and subsequently evaluated using the Effective Crack Model and the work-of-fracture method. The increasing temperatures during the fire experiments ranging between 550 to 1000 °C led to a decrease of modulus of elasticity and fracture toughness values and to the increase of fracture energy value. The 2D laser profile scanner was used to estimate the degree of complexity of fracture surfaces; its statistical dependence on the mechanical fracture parameters proved to be moderate – the absolute value of the correlation coefficient was about 0.5°[–].
Authors: Ivan Hollý, Juraj Bilčík
Abstract: The reinforcing steel embedded in concrete is generally protected against corrosion by the high alkalinity (pH = 12.5 to 13.5) of the concrete pore solution. The structural degradation of concrete structures due to reinforcement’s corrosion has an impact on the safety, serviceability and durability of the structure. The corrosion of reinforcements in the construction of a transport infrastructure (especially bridges), parking areas, etc., is primarily initiated by chlorides from de-icing salts. When corrosion is initiated, active corrosion results in a volumetric expansion of the corrosion products around the reinforcing bars against the surrounding concrete. Reinforcement corrosion causes a volume increase due to the oxidation of metallic iron, which is mainly responsible for exerting the expansive radial pressure at the steel–concrete interface and development of hoop tensile stresses in the surrounding concrete. When this tensile stress exceeds the tensile strength of the concrete, cracks are generated. Higher corrosion rates can lead to the cracking and spalling of the concrete cover. Continued corrosion of reinforcement causes a reduction of total loss of bond between concrete and reinforcement.
Authors: Natalia Gažovičová, Juraj Bilčík, Ivan Hollý, Jaroslav Halvonik
Abstract: Corrosion of steel reinforcement is one of the most often deterioration reasons of RC structures. At present, the corrosion of steel reinforcement can be avoided by using non-metallic reinforcement from composite materials, especially in structures that are exposed to extreme environmental environment. These materials are durable and non-conductive. They are composited from two materials: fibres and matrix. The most commonly used FRP (Fiber Reinforced Polymers - FRP) reinforcement are glass fibre reinforced polymers (GFRP). The bar surface can be e.g. sanded, wrapped, with helically wound ribs. The bond between concrete and reinforcement is one of the basic requirements for the composite action of both materials. The transfer of forces between the steel reinforcement and the concrete is provided by the following mechanisms: adhesion, friction and mechanical interlocking. The bond between GFRP reinforcement and concrete is different and it is ensured by friction and mechanical interlocking of the rebar surface. The chemical bond does not originate between GFRP reinforcement and the surrounding concrete, so adhesion does not contribute to transfer of the bond forces. Some few test methods are used to determine the bond between GFRP reinforcement and concrete. The pull-out test were used to determine the bond behaviour between GFRP rebars and concrete. This paper describes the preparation, process, results and evaluation of the pull-out tests.
Authors: Viktar V. Tur, Stanislav S. Derechennik
Abstract: Evaluation of the concrete compressive strength in existing structures is an important problem, which is associated with structural reliability estimation as well as a quality control procedure. In accordance with a new concept of EN 13791, reported by T.A.Harrison, one of the main targets of the standard is to determine not a class, but in-situ characteristic concrete compressive strength. Hereby proposed criterion for the estimation of the in-situ characteristic concrete compressive strength is based on the non-parametric confidence interval for quantile. This criterion was verified by the both Monte Carlo simulation and test results under the real concrete structures.
Authors: Volha Semianiuk, Viktar V. Tur
Abstract: Fiber reinforced polymer (FRP) bars are widely used in building structures, especially that are exposed to the aggressive environment influence and other special conditions. Nevertheless, due to the low FRP (e.g. glass, basalt, aramid fibers reinforced polymers) bars modulus of elasticity, exceeding crack opening width, as well as deflections can be observed. FRP bars pretensioning is considered as an effective method of its structural performance increasing. Physico-chemical method of the FRP bars pretensioning based on the self-stressing concrete utilizing is an alternative to the mechanical method and in its turn doesn’t need for special devices and anchorage systems as well as qualified personnel. Assessment of the initial stress-strain state obtained during self-stressing concrete expansion stage in the reinforced self-stressed members is presented. Diagram method of the self-stressing parameters verification based on the static loading tests results is presented. Comparison of the initial stress-strain state obtained during concrete expansion stage and predicted by the proposed model, as well as assessment of its influence on the behavior at the static loading stage in cases of the self-stressed reinforced with FRP bars members and traditionally reinforced with steel bars self-stressed members was performed.

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