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This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions.

Fiber reinforced polymer (FRP) rebars have increasing popularity in the construction industry all around the world although steel rebars are widely used for reinforcing of the concrete so far. FRP bars, which have higher tensile strength compared to steel rebars with the same nominal diameter under normal conditions, are composed of resin matrix and fibers. In this paper, the load-bearing capacity of FRP reinforced concrete after elevated temperature exposition are present. The results are compared with concrete sample with steel reinforcement. Commercially produced glass FRP (GFRP) and carbon FRP (CFRP) rebars with sand coatings surface treatments were implemented in concrete beam and subjected to four-point bending load. The residual flexural strength of reinforced concrete after heating to 1000°C was obtained and evaluated and compared to results of non-heated elements. The results indicate that fire resistance of FRP reinforced beams can reach at least 60 minutes according the standard ČSN EN 13501-2.

From the volumetric point of view, aggregate is the most important ingredient in any kind of concrete. It is impossible to use raw soil instead of aggregate to produce concrete. There are numerous reasons for not using soil for concrete production on Earth, and we should not use lunar soil for concrete production on the Moon for the same reasons. Nevertheless, almost all developed lunar concrete-like composites, such as sulphur or polymeric concretes, are based on raw lunar soil. In the research programme, cement composite based on lunar aggregate simulant was tested. The mechanical fracture properties of the composite were the key point of interest. It was proven that the tested lunar concrete is characterized by stable and uniform properties. The obtained results were compared with the properties of other ordinary cement composites.

Quasi-brittle materials like cement-based composites, rocks, and bricks are subjected to a number of environmental loadings throughout the life cycle of buildings. For instance, fluctuation of the ambient temperature (climatic cycles or fire) causing a variety of physical and chemical transitions resulting in structural changes and affecting the mechanical properties. In this work a special mixture containing glass spheres and Portland cement was evaluated by a combination of four-point bending and time-lapse X-ray computed tomography to verify the feasibility of this novel combined method. The effect of temperature on the behavior of investigated material in terms of sphericity of the present glass spheres and the way of crack propagation under load together with its influence to mechanical fracture parameters was studied. The described methodology was used especially to be able to monitor these changes throughout the loading process, as the characterization of the fracture surface using conventional optical methods is possible only after the complete fracture of the specimen and total damage of used material results in loosening of the matrix and filler to such an extent, that the results of these methods may be very distorted. It has been proven that the developed method can be used to characterize the internal structural changes in building materials and thus contribute to the understanding of the fracture processes during mechanical loading. Up to 600 degrees C the glass spheres stay spherical and the crack is propagating through the interfacial transition zone, while at higher temperatures the glass loses its shape and the newly formed pores cause also cracks within the inclusions. The relationship between compressive strength and the maximum loading temperature was confirmed.

The paper deals with an experimental analysis focused on the determination and evaluation of the early age shrinkage strain using Shrinkage-Cone. The measurements were performed on the cement pastes and mortars with a different w/c ratio. The authors propose a new approach to the measurement evaluation based on the determination of time-zero at the time of estimated initial setting determined as the time when the internal temperature of specimens started to rise. In this case, also the effect of the thermal expansion is taken into account in the evaluation.

This paper presents the results of an experimental study of selected characteristics of concrete following its exposure to high temperatures. The monitored parameter was the influence of high temperatures on the bond strength and tensile strength of concrete. The bond strength was tested by a pull-off test, the tensile strength was determined as the direct tensile strength. Experimental concrete panels of 2300 × 1300 × 150 mm were exposed to high temperatures (corresponding to the temperatures in a normal fire) using a fire test furnace at the AdMaS Science Centre of the Faculty of Civil Engineering, Brno University of Technology. The direct tensile strength test was performed on cylinders (diameter of 100 mm and length of 100 mm) made from core samples taken from the panel. The pull-off test was performed on the surface exposed to high temperatures. The results of the experiment show a significant influence of high temperatures on the examined characteristics, and both characteristics were found to significantly decrease with a growing thermal load.

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.

While exposed to high temperatures caused by fire, the concrete undergoes a sequence of physical and chemical structure changes causing a mechanical degradation. This paper concerns an experimental strength determination of a temperature stressed concrete. The concrete was temperature loaded according to temperature-time curve ISO 834 and left on a top temperature level for 60 minutes afterwards. This temperature heating rise is in accordance with a common fire expansion in a structure. The concrete panels sized 150 × 1300 × 2300 mm were temperature loaded up to 550, 600, 800 a 1000 °C in a horizontal position in gas furnace for fire testing of structure elements in research Centre AdMaS. The temperatures of the gas in the furnace and the panel was measured during the whole experiment by using the thermocouples. After the fire test, the specimens were drilled out using a 100 mm diameter core drill. The compressive strength and splitting tensile strength tests were made and the results were compared to the reference specimen’s test results. The objective results of a commonly used strength class concrete loaded by elevated temperature corresponding to the real fire exposure differ common linear heat exposure test results and are considered being very valuable.

Experimental concrete panels were after an appropriate aging time loaded by high temperatures (550, 600, 800 and 1000 °C) in a furnace intended for fire tests of building materials. These panels were heated according to the standard temperature-time curve according to EN 1991-1-2. One of panels was a reference without temperature load. Test specimens were obtained as cores drilled out from panels after performing fire tests. The cylindrical specimens were provided with a central chevron type notch and subsequently tested in three-point bending fracture test. The load versus displacement (deflection in the middle of span) diagrams were recorded during testing and basic fracture parameters were subsequently evaluated.

Práce se zabývá stanovením zvolených pevnostních parametrů ztvrdlého betonu v tahu a hledáním vztahů mezi nimi. Jedná se především o pevnost v prostém tahu, pevnost v tahu ohybem a pevnost v příčném tahu. Součástí práce je popis jednotlivých zkušebních postupů pro zjištění tahových pevností betonu. Dále jsou zde uvedeny výsledky zkoušení na různých typech betonů (prostý beton, lehký beton, drátkobeton, vláknobeton s polymerními vlákny a vysokopevnostní beton). Závěr práce se věnuje odvození závislostí mezi pevnostmi betonu a porovnání hodnot získaných z dostupných vztahů s výsledky provedených zkoušek., The thesis deals with a comparison of the selected strength tension properties of the hardened concrete and finding relationships between them. This is essentially a simple tensile strength, tensile flexural strength and tensile splitting strength. The text describe the testing procedures to determine the tensile strength of concrete. Furthermore, there are presented the results of testing on different types of concrete (plain concrete, lightweight concrete, steel-fiber concrete, polymer-fibre concrete and high strength concrete). The conclusion deals with the derivation of dependancy between concrete strengths and comparing the values obtained from the available relations with the results of the tests.

Bakalářská práce sumarizuje poznatky spojené s návrhem a chováním železobetonových konstrukcí a materiálů během požáru. Zabývá se prováděním nedestruktivních tvrdoměrných zkoušek za účelem zjištění tlakových pevností na zkušebních vzorcích vystavených různým teplotám požáru., The bachelor thesis summarizes the knowledge connected with the design and behavior of reinforced concrete structures and materials during a fire. It deals with the non-destructive testing of hardness tests to determine the compressive strength of test specimens exposed to different fire temperatures.

Disertační práce je zaměřena na diagnostiku betonových konstrukcí po požáru a rozšiřuje znalosti a poznatky dle definovaných cílů prezentované práce. Díky provedeným požárním zkouškám velkorozměrových betonových panelů byl pro různé hladiny teplot odpovídající skutečnému požárnímu zatížení stanoven rozsáhlý soubor materiálových charakteristik. Závěrem byly definovány stěžejní kroky postupu doporučeného pro diagnostiku betonu po vystavení požáru s využitím destruktivních i nedestruktivních metod. Zkoumáno bylo i chování FRP výztuží za zvýšených teplot. S cílem stanovení vlivu vystavení požáru na vyztužené betonové konstrukce byl navržen a realizován experimentální program, při kterém betonové nosníky vyztužené ocelovou nebo kompozitní výztuží se skleněnými či uhlíkovými vlákny byly vystaveny experimentálně simulovanému požáru. Po ochlazení se podrobily ohybovému namáhání. Experimentální program byl dále doplněn o rozsáhlou numerickou studii. Na závěr tato práce poskytuje informace o dalším nezbytném směřování výzkumu v dané oblasti., Doctoral thesis is focused on the assessment of concrete structures after fire exposure and extends the knowledge in view of the main aims of the research defined in the objectives of his work. Thanks to the performed fire tests of full-scale concrete specimens, material characteristics corresponding to actual fire load have been assessed for different temperature levels. Resulting from presented research, main steps of assessment procedure have been recommended for both destructive and non-destructive tests of concrete after exposure to fire. Furthermore, behaviour of FRP reinforcement at elevated temperatures have been investigated. Aiming to determine the effects of fire exposure on reinforced concrete structures, experimental program have been defined and performed, including concrete beams reinforced with either steel, or composite reinforcement with glass or carbon fibres and subjected to experimentally simulated fire load. After cooling, bending test have been executed. Above mentioned experimental program was further complemented by extensive numerical analysis. Finally, presented work provides guidelines regarding further investigations required in this field of research.

Disertační práce je zaměřena na diagnostiku betonových konstrukcí po požáru a rozšiřuje znalosti a poznatky dle definovaných cílů prezentované práce. Díky provedeným požárním zkouškám velkorozměrových betonových panelů byl pro různé hladiny teplot odpovídající skutečnému požárnímu zatížení stanoven rozsáhlý soubor materiálových charakteristik. Závěrem byly definovány stěžejní kroky postupu doporučeného pro diagnostiku betonu po vystavení požáru s využitím destruktivních i nedestruktivních metod. Zkoumáno bylo i chování FRP výztuží za zvýšených teplot. S cílem stanovení vlivu vystavení požáru na vyztužené betonové konstrukce byl navržen a realizován experimentální program, při kterém betonové nosníky vyztužené ocelovou nebo kompozitní výztuží se skleněnými či uhlíkovými vlákny byly vystaveny experimentálně simulovanému požáru. Po ochlazení se podrobily ohybovému namáhání. Experimentální program byl dále doplněn o rozsáhlou numerickou studii. Na závěr tato práce poskytuje informace o dalším nezbytném směřování výzkumu v dané oblasti., Doctoral thesis is focused on the assessment of concrete structures after fire exposure and extends the knowledge in view of the main aims of the research defined in the objectives of his work. Thanks to the performed fire tests of full-scale concrete specimens, material characteristics corresponding to actual fire load have been assessed for different temperature levels. Resulting from presented research, main steps of assessment procedure have been recommended for both destructive and non-destructive tests of concrete after exposure to fire. Furthermore, behaviour of FRP reinforcement at elevated temperatures have been investigated. Aiming to determine the effects of fire exposure on reinforced concrete structures, experimental program have been defined and performed, including concrete beams reinforced with either steel, or composite reinforcement with glass or carbon fibres and subjected to experimentally simulated fire load. After cooling, bending test have been executed. Above mentioned experimental program was further complemented by extensive numerical analysis. Finally, presented work provides guidelines regarding further investigations required in this field of research.

Tato diplomová práce se zabývá problematikou revitalizace historických objektů. V teoretické části jsou popsány technologie statického zajištění a sanací svislých a vodorovných nosných konstrukcí za účelem zvýšení prostorové tuhosti objektu. V praktické části je proveden návrh statického zesílení obvodového zdiva, statický návrh a posouzení spřažené dřevo-betonové desky pro celkovou revitalizaci stropní konstrukce. Návrh stropní desky je ekonomicky porovnán ve více variantách. Návrhy jsou provedeny pro existující objekt bývalého hostince ve Velichovkách., This diploma thesis deals with the problems of revitalization of historical objects. The theoretical part describes the technologies for static reinforcing and rehabilitation of vertical and horizontal bearing structures for a purpose of increasing the general stiffness of the object. As the practical part a static design project is made for reinforcing of the bearing walls and also for the general reconstruction of the slab. The slab is designed as the composite timber-concrete structure. The design project of the slab is economically compared with other variants. The designs are made for an existing object of the old restaurant in the village Velichovky.

Disertační práce je zaměřena na diagnostiku betonových konstrukcí po požáru a rozšiřuje znalosti a poznatky dle definovaných cílů prezentované práce. Díky provedeným požárním zkouškám velkorozměrových betonových panelů byl pro různé hladiny teplot odpovídající skutečnému požárnímu zatížení stanoven rozsáhlý soubor materiálových charakteristik. Závěrem byly definovány stěžejní kroky postupu doporučeného pro diagnostiku betonu po vystavení požáru s využitím destruktivních i nedestruktivních metod. Zkoumáno bylo i chování FRP výztuží za zvýšených teplot. S cílem stanovení vlivu vystavení požáru na vyztužené betonové konstrukce byl navržen a realizován experimentální program, při kterém betonové nosníky vyztužené ocelovou nebo kompozitní výztuží se skleněnými či uhlíkovými vlákny byly vystaveny experimentálně simulovanému požáru. Po ochlazení se podrobily ohybovému namáhání. Experimentální program byl dále doplněn o rozsáhlou numerickou studii. Na závěr tato práce poskytuje informace o dalším nezbytném směřování výzkumu v dané oblasti., Doctoral thesis is focused on the assessment of concrete structures after fire exposure and extends the knowledge in view of the main aims of the research defined in the objectives of his work. Thanks to the performed fire tests of full-scale concrete specimens, material characteristics corresponding to actual fire load have been assessed for different temperature levels. Resulting from presented research, main steps of assessment procedure have been recommended for both destructive and non-destructive tests of concrete after exposure to fire. Furthermore, behaviour of FRP reinforcement at elevated temperatures have been investigated. Aiming to determine the effects of fire exposure on reinforced concrete structures, experimental program have been defined and performed, including concrete beams reinforced with either steel, or composite reinforcement with glass or carbon fibres and subjected to experimentally simulated fire load. After cooling, bending test have been executed. Above mentioned experimental program was further complemented by extensive numerical analysis. Finally, presented work provides guidelines regarding further investigations required in this field of research.

Tato diplomová práce se zabývá problematikou revitalizace historických objektů. V teoretické části jsou popsány technologie statického zajištění a sanací svislých a vodorovných nosných konstrukcí za účelem zvýšení prostorové tuhosti objektu. V praktické části je proveden návrh statického zesílení obvodového zdiva, statický návrh a posouzení spřažené dřevo-betonové desky pro celkovou revitalizaci stropní konstrukce. Návrh stropní desky je ekonomicky porovnán ve více variantách. Návrhy jsou provedeny pro existující objekt bývalého hostince ve Velichovkách., This diploma thesis deals with the problems of revitalization of historical objects. The theoretical part describes the technologies for static reinforcing and rehabilitation of vertical and horizontal bearing structures for a purpose of increasing the general stiffness of the object. As the practical part a static design project is made for reinforcing of the bearing walls and also for the general reconstruction of the slab. The slab is designed as the composite timber-concrete structure. The design project of the slab is economically compared with other variants. The designs are made for an existing object of the old restaurant in the village Velichovky.