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- ItemEarly-age behaviour of cement-based self-leveling flooring compounds(IOP Publishing, 2018-07-16) Kucharczyková, Barbara; Kocáb, DaliborThe article deals with the cement-based flooring compounds, especially with the behaviour during the early solidification process. A touch-less laser sensor and a cone-shaped mould were used for the measurement of the plastic settlement/shrinkage. The process of solidification and the strength development were determined using the ultrasonic pulse velocity measurement. Both test devices were equipped with the thermocouple to measure the real-time internal temperature evolution during solidification of the flooring compounds. The measurements presented in this paper proved to be useful for the clarification of the technological problems which arose during the manufacturing of the test specimens.
- ItemEvaluation of Shrinkage, Mass Changes and Fracture Properties of Fine-aggregate Cement-based Composites during Ageing(Elsevier, 2017-06-02) Kucharczyková, Barbara; Šimonová, Hana; Keršner, Zbyněk; Daněk, Petr; Kocáb, Dalibor; Misák, Petr; Pössl, PetrThe paper deals with the experimental determination of relative length changes development during cement based composite ageing. Special moulds with the dimensions 100 × 60 × 1000 mm were used for the measurements. These moulds were filled and placed on an advanced weighing table that enables continuous recording of mass losses caused by free drying of the specimen surface. In this way, the mass losses and changes in the length of the cement composite in the moulds were measured simultaneously. The shrinkage moulds were modified in order to measure also the long-term relative deformation of fine-aggregate concrete specimens as a result of drying. The outputs of the measurement are given in the form of the diagrams displaying the relationship between the relative length changes or the mass losses and the time of cement composites ageing. Besides the measurement of length changes, three-point bending fracture tests at the age of 3 and 28 days were also performed. The modulus elasticity, effective fracture toughness and specific fracture energy values were determined from load versus deflection diagrams recorded during fracture experiments on the specimens with dimensions 40 × 40 × 160 mm.
- ItemFreeze-thaw resistance of concrete with porous aggregate(Elsevier Ltd., 2010-06-06) Pospíchal, Ondřej; Kucharczyková, Barbara; Misák, Petr; Vymazal, TomášThis 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.
- ItemComprehensive Testing Techniques for the Measurement of Shrinkage and Structural Changes of Fine-Grained Cement-Based Composites during Ageing(Hindawi Publishing Corporation, 2017-01-15) Kucharczyková, Barbara; Topolář, Libor; Daněk, Petr; Kocáb, Dalibor; Misák, PetrThe paper deals with an experimental analysis focusing on the utilization of a specific measurement technique for determining the development of shrinkage and for monitoring structural changes in fine-grained cement-based composites during their ageing. Advanced measurement equipment and procedure allowing simultaneous measurement of length changes, mass losses, acoustic responses, and temperature development were designed and verified by the experimental investigation. The main scope of the experiments performed was focused on finding the relationships between the characteristics being investigated while maintaining a uniform test setup. For the purpose of the experimental measurement, three fine-grained cement composite mixtures were designed and manufactured. The mixtures differed in the water-to-cement ratio (w/c) and in the amount of plasticizer. The measurement outputs are presented in the form of diagrams showing the relations between the studied parameters, such as relative length changes, mass losses, temperature progress, and acoustic emission (AE) activity during solidification of the composites. The measurement results showed close relations between the examined characteristics. The progress of relative length changes together with the progress of mass losses and temperature development is reflected in the AE activity. The advanced measurement procedure and technique provided valuable information about the behaviour of cement-based composites during early setting and long-term hardening.
- ItemProperties 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, PavelThe 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.