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    Evaluation of Selected Physicomechanical Properties of SFRC according to Different Standards
    (Hindawi, 2018-05-14) Komárková, Tereza; Láník, Jaromír; Anton, Ondřej
    Steel fiber reinforced concretes are currently very popular, especially in the construction of industrial floors of warehouses and other halls with relatively large floor areas. However, it is important to mention that despite the rapid development of steel fiber reinforced concretes, the standards and regulations for their designing and testing have not been unified yet. This paper presents findings about the physicomechanical parameters of the steel fiber reinforced concretes manufactured by adding steel fibers into the truck mixer on the building site. The experimentally obtained results from the performed tests of tensile strength in bending according to various procedures are compared, and the suitability of the methods used is assessed according to these procedures.
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    Freeze-thaw resistance of concrete with porous aggregate
    (Elsevier Ltd., 2010-06-06) Pospíchal, Ondřej; Kucharczyková, Barbara; Misák, Petr; Vymazal, Tomáš
    This paper deals with the influence of periodic freezing on lightweight concrete characteristics. Sets of lightweight concrete prismatic specimens are cyclically frozen in range from +20C to -20C and non-destructively tested after every 25 cycles. Freeze-thaw resistance is determined from measurement of the frost-attacked and non-frost-attacked (referential) specimens. The referential specimens are air/water-cured. Non-destructive methods, especially ultrasonic impulse method and resonance method are used for determination of specimen's degradation. Experiments are finished with destructive test in order to determine the static modulus of elasticity.
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    Experimental assessment of steel fibre reinforced concretes with different concentrations of fibres
    (IOP Publishing, 2018-07-16) Komárková, Tereza; Láník, Jaromír; Topolář, Libor; Štoller, Jiří; Stoniš, Patrik
    At present, steel fiber reinforced concrete can be classified as a composite material commonly used for load-bearing building structures. Adding steel fibers to fresh mixture improves its mechanical properties in comparison to plain concrete. The problem is, however, the production technology, which has not been standardized by regulations so far, and thus, proposals for the amount of steel fibers added to the mixture are still based on the long-term experience and performed tests. The paper describes an experiment focused on the determination and assessment of mechanical properties of steel fiber reinforced concretes with high concentrations of fibers. To better understand the behavior of test specimens during the three-point bending test, the acoustic emission method was used, which is able to capture active defects.
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    Properties of concrete intended for further testing measured by the Impact-Echo and the ultrasonic pulse method
    (IOP Publishing, 2018-07-16) Balkanský, Ondřej; Dvořák, Richard; Čairović, Iva; Schmid, Pavel
    The aim of the paper is non-destructive measurement of differently degraded specimens by high temperature intended for further testing of joints of stainless steel helical reinforcement glued into the groove and differently degraded concrete. Measurement intended for determination of possibilities of estimation of future properties of named joints is performed by the Impact-Echo method and by the ultrasonic pulse velocity method on specimens of dimensions 400 × 100 × 100 mm made of concrete of the C20/25 strength class degraded by different elevated temperature. Five sets of specimens were manufactured - four sets of specimens were heated in the furnace at temperatures of 400 °C, 600 °C, 800 °C and 1000 °C and one set was kept intact as reference. Specimens will be afterwards additionally strengthened at the tensile side of specimens and broken by four-point flexural strength test. The non-destructive measurement aims to evaluate the residual physical-mechanical properties of plain concrete in terms of resonance frequency of test specimen, and sound velocity in tested specimen before and after the temperature degradation. This assessment will serve as material information basis for interpretation of the expected behaviour of used helical reinforcement for a retrofitting process and the thermally damaged concrete reaction to such intervention.
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    Experimental and numerical analysis of the fracture response of alkali-activated slag-based materials
    (EDP Sciences, 2020-10-05) Lipowczan, Martin; Lehký, David; Šimonová, Hana; Kucharczyková, Barbara
    The paper deals with the experimental and numerical determination of mechanical fracture parameters of fine-grained composites based on the alkali-activated slag (AAS) at different ages of hardening. Two AAS composites, which differed only in the presence of shrinkage reducing admixture, were studied. The prismatic specimens with the nominal dimensions of 40 × 40 × 160 mm and initial central edge notch were subjected to fracture tests in a three-point bending configuration. The results of the fracture tests in the form load F versus deflection d diagrams were used as input data for the identification of parameters via the inverse analysis based on the artificial neural network whose aim is to transfer the fracture test response data to the desired material parameters. The modulus of elasticity, tensile strength, and fracture energy values were identified and subsequently compared with values obtained based on the direct fracture test evaluation using the effective crack model and work-of-fracture method.