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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 intheshape ofprisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch withadepth of12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, andmarble – 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 thenanoindentation technique. Theaim of this paper is toanalyse 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 oftheinterfacial transition zone. The results of this research indicate thesignificant dependence of the effective fracture parameters onthepetrographic andrelated chemical composition of the rock inclusions.

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.

Four sets of alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors were studied in terms of their characterization by mechanical fracture parameters as a basis for considerations of durability. AAAS composites made of brick powder as a precursor and alkaline activator with various silicate moduli (Ms = 0.8, 1.0, 1.2, 1.4, and 1.6) were investigated. The sets of AAAS composites differed in terms of the used filler: quartz sand or brick rubble. Two different precursor particle size ranges of 0–1 mm and 0–0.3 mm were used for both types of filler. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were provided with a notch at midspan after 28 days of hardening. The notches were cut up to 1/3 of the height of the specimens. The specimens were subjected to three-point bending fracture tests during which force vs. deflection (F–d) and force vs. crack mouth opening displacement (F–CMOD) diagrams were recorded. Tensile strength ft,ID and specific fracture energy GF,ID values were identified using the inverse method based on a neural network ensemble. The obtained F–CMOD diagrams were subsequently evaluated using the double-K fracture model supported by the ft,ID and GF,ID values. The double-K model allows the quantification of two different levels of crack propagation: initiation, which corresponds to the beginning of stable crack growth, and unstable crack propagation.

Quasi-brittle materialslike cement-based composites, rocks,and bricksare subjected to a number ofenvironmental loadings throughout the life cycleof buildings. For instance, fluctuation ofthe ambient temperature (climaticcyclesor fire) causing a variety of physical and chemical transitionsresultinginstructural changesand affectingthe 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 tomographyto verify the feasibility of thisnovel combined method.The effectof temperature on the behavior of investigatedmaterial in terms of sphericity of the present glass spheresand the way of crack propagation under load together with its influenceto mechanical fracture parameterswas studied.The described methodology was used especially to be able to monitor these changes throughout the loading process, asthe characterization of the fracture surface using conventional optical methods is possible only after the complete fractureof the specimenandtotal 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 hasbeen 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°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 temperaturewas confirmed

This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture tests were conducted on the specimens via three-point bending and fracture parameters were evaluated. Selected specimen was investigated using micro-tomography to supplement the results with visual information about the inner structure of this newly designed material before and after the mechanical loading. Tomographic measurements and image processing were conducted for a qualitative and quantitative assessment of changes in the internal structure with an emphasis on the calculation of porosimetric parameters and visualization of the fracture surface. Fractal dimension of fracture surface was estimated.

The paper is focused on the advanced evaluation of fracture tests of selected rock specimens. Assessment of fracture response of chevron notch cylindrical specimens of Silesian granite subjected to three-point bending test was performed. The effective crack model is used and academic software chevroncylinder (author Petr Frantík) based on the finite element method is applied for the analyses. Based on the described procedures, estimation of maximum values of the effective fracture toughness are established and discussed. discussed. Článek se zabývá pokročilým vyhodnocením lomových testů vybraných horninových vzorků. Je provedeno hodnocení lomové odezvy válcových vzorků s šípovým vrubem ze Slezské žuly vystavených tříbodovému ohybu. Je použit model efektivní trhliny spolu s akademickým programem chevroncylinder (autor Petr Frantík) založeným na metodě konečných prvků. Na základě uvedených postupů je odhadnuta a diskutována maximální hodnota efektivní lomové houževnatosti.

In this paper, the attention is paid to the investigation of the influence of high temperature acting on specimens made from specially designed cement-based composite. The experimental programme was carried out on six sets of beam specimens with the dimensions of 20 × 40 × 200 mm. The specimens were loaded to a pre-set temperature of 100, 200, 400, 600, 800 and 1000 °C and then the temperature was kept for 60 minutes. When the temperature loading had been done, the specimens were left to cool down to the ambient temperature. After that, the ultrasonic pulse method was used to determine the degree of damage of temperature loaded specimens. The measured data obtained by this non-destructive method are in high correlation with values of informative compressive strength of the composite obtained after the temperature loading of specimens.

In this paper, the attention is paid to investigation of the importance of the interfacial transition zone (ITZ) in selected fine-grained cement-based composites for the global fracture behaviour. This is a region of cement paste around the aggregate particles which specific features could have significant impact on the final behaviour of cement composites with a crack tip nearby this interface under applied tension. The aim of this work is to show the basic interface microstructure by scanning electron microscopy (SEM) done by MIRA3 TESCAN and to analyse the behaviour of such composite by numerical modelling. Numerical studies assume two different ITZ thicknesses taken from SEM analysis. A simplified cracked geometry (consisting of three phases – matrix, ITZ, and aggregate) is modelled by means of the finite element method with a crack terminating at the matrix–ITZ interface. ITZ’s modulus of elasticity is taken from generalized self-consistent scheme. A few conclusions are discussed based on comparison of the average values of the opening stress ahead of the crack tip with their critical values. The analyses dealing with the effect of ITZ’s properties on the stress distribution should contribute to better description of toughening mechanisms in silicate-based composites.

The article deals with the use of computed X-ray radiography to visualize the development of the fracture process zone in the rock samples. For radiographic observations during the three-point bending loading, glauconitic sandstone from the Řeka quarry (sometimes also referred to as Godula sandstone) was used. The chevron-notched cylindrical specimens with the diameter of 29 mm and 120 mm nominal length were prepared from the sandstone blocks. These specimens were subjected to the Chevron Bend (CB) test carried out in accordance with the ISRM suggested methodology; the span was 94 mm. The evolution of the fracture process zone was continuously scanned using X-ray radiography during the realized Mode I fracture toughness tests (FTT). The scanning was conducted using an industrial X-ray micro-tomographic inspection system equipped with a flat panel X-ray detector of 4,000 × 4,000 pixels and micro-focus X-ray source with reflection target, which are very suitable for obtaining highly detailed radiographic images during the FTT tests. Three-point bending tests were carried out using an in-house designed table-top loading device, construction of which allows precise control of the loading during testing. Continuous X-ray examination and subsequent radiographic image analysis enable investigation of the crack initiation and the process zone development during FTT and represents a useful tool for a better understanding of failure behavior of the rock material during the loading process. The article deals with the use of computed X-ray radiography to visualize the development of the fracture process zone in the rock samples. For radiographic observations during the three-point bending loading, glauconitic sandstone from the Řeka quarry (sometimes also referred to as Godula sandstone) was used. The chevron-notched cylindrical specimens with the diameter of 29 mm and 120 mm nominal length were prepared from the sandstone blocks. These specimens were subjected to the Chevron Bend (CB) test carried out in accordance with the ISRM suggested methodology; the span was 94 mm. The evolution of the fracture process zone was continuously scanned using X-ray radiography during the realized Mode I fracture toughness tests (FTT). The scanning was conducted using an industrial X-ray micro-tomographic inspection system equipped with a flat panel X-ray detector of 4,000 × 4,000 pixels and micro-focus X-ray source with reflection target, which are very suitable for obtaining highly detailed radiographic images during the FTT tests. Three-point bending tests were carried out using an in-house designed table-top loading device, construction of which allows precise control of the loading during testing. Continuous X-ray examination and subsequent radiographic image analysis enable investigation of the crack initiation and the process zone development during FTT and represents a useful tool for a better understanding of failure behavior of the rock material during the loading process.

Glass is an amorphous solid substance with pozzolanic properties that can be used as a partial substitute for ordinary Portland cement (OPC) in cement based composites. In the research conducted for this paper, the PC was partially replaced by fine-ground waste laboratory borosilicate glass (in mixtures where 5, 10, 15 and 20% by mass was substituted). Beam specimens with the dimensions 40 × 40 × 160 mm were prepared from each mixture. After demoulding, the specimens were kept under standard laboratory conditions. Basic tests were conducted at the age of 7, 28, 56, and 90 days: the compressive ( f c ) and flexural ( f f ) strengths were determined according to the CSN EN 1015-11 standard. Specimens were also subjected to fracture testing at the age of 28 days. The beam specimens with an initial central edge notch were tested in three-point bending. Load vs. displacement diagrams were recorded and modulus of elasticity ( E ), fracture toughness ( K Ic e ) and fracture energy ( G F * ) were determined. It was found, that strength increased with specimen age: at the age 28 days this increase was 12–33% in case of f c , and 6–15% as regards f f . The values obtained for almost all the parameters decreased with the increasing dosage of glass as a replacement for cement: compared to a reference composite this decrease was 22–40% in the case of f c , 24–28% for f f , 3–5% for E , 9–29% for K Ic e , and 30–50% for G F * ; exceptions were recorded for glass replacement doses of 5 and 10%, where increases of 2–6% for f c and 8–10% for E were obtained.

Alkali-activated slag is a building material considered as alternative to ordinary Portland cement based materials. Addition of graphite powder increases its electric conductivity, hence, introducing new functionality to building materials such as self-sensing and self-heating properties. In this study, the effect of graphite filler on the mechanical fracture properties of alkali-activated slag composite is investigated. Graphite powder was added in the amount of 5, 10 and 15% with respect to the slag mass. Modulus of elasticity, fracture toughness and fracture energy were determined using standard three-point bending test on prismatic specimens with central edge notch. The course of fracture tests was also monitored by acoustic emission (AE) method. Compressive strength was determined on the fragments remaining after the fracture tests. Results showed that addition of graphite caused a decrease in compressive strength, fracture toughness and fracture energy but modulus of elasticity increased. Addition of graphite also caused a decrease in AE events and increase in amplitude of signals. This implies that mortars with graphite filler is more brittle than the reference mortar, and lower number of much larger cracks is formed during the fracture test.

Quasi-brittle type of fracture behaviour is viewed from a unique perspective in the paper. This view explains and extends the classification of fracture of materials, as it is commonly understood, and might provide a way to a more general understanding of this phenomenon. The proposed approach separates the ‘effective’ (brittle) fracture phenomenon from the evolution of the nonlinear zone at the crack tip. This separation is performed on the energetic level, the evaluated work of fracture, as well as on the level of geometrical description of the two separated entities which are the products of the fracture phenomenon: The crack surface and the nonlinear zone around the crack front. The approach is introduced here mainly from the philosophical and theoretical standpoint, its verification and validation is included only partially.

Fine-grained cement-based composites used in civil engineering and construction industry are usually made of cement-based matrix and natural aggregate (such as sand, gravel, crushed stone, etc.). Red ceramic waste aggregate is considered as a perspective replacement of a part of natural aggregate in modern environmentally oriented building materials. Fine-grained cement composite with natural aggregate partially replaced by ceramic waste aggregate usually show different mechanical fracture characteristics from ordinary fine-grained concrete. The specimens were tested at six different ages. This was the reason for conducting the research programme. Altogether, 6 fine-grained cement mixtures with various proportions of natural and red ceramic waste aggregate were prepared. The aim of this paper is to present and compare mechanical fracture properties obtained from static and fatigue tests. Bulk density, flexural and compressive cube strength, fracture toughness and fatigue properties (S−N − Wöhler curve) were of special interest. All of these tests are important for a practical application of concrete with ceramic aggregate for structures. All the results were statistically analysed and they showed that the fatigue and mechanical fracture properties were improved or at least kept up with the increasing levels of red ceramic waste aggregate. Environmental impact of application in construction industry of composites in question is discussed.

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.

The paper deals with the experimental determination of fracture parameters of the composites based on the alkali-activated slag (AAS) at different ages. The main aim of the experimental investigation was to verify the effect of the addition of shrinkage reducing admixture (SRA) on the overall progress of length changes and fracture properties during AAS composites ageing. Two AAS composites, which differed only in the presence of SRA, were prepared for the purpose of experiments. The mechanical fracture parameters were determined using evaluation of fracture tests carried out on 40 × 40 × 160 mm beam specimens with an initial central edge notch. The monitored parameters were modulus of elasticity, effective fracture toughness and specific fracture energy. These parameters were determined at the age of 3, 28 and 90 days. The obtained results are supplemented by the results of relative length changes measurements performed on both studied composites.

The paper reports a study of the effect of carbon fibres on the mechanical fracture parameters of alkali-activated slag mortars. The carbon fibres were added in the amount of 1, 2 and 3%, respectively with respect to the mass of the slag. The mechanical fracture parameters were determined using evaluation of fracture tests carried out on 40 × 40 × 160 mm beam specimens with an initial central edge notch. The monitored parameters were compressive strength, modulus of elasticity, effective fracture toughness and specific fracture energy. The specimen response during fracture tests was also monitored by means of acoustic emission. It was shown that as the addition of carbon fibres increased the value of compressive strength and modulus of elasticity of alkali-activated slag dropped to 50% in case of the highest amount of fibres. The effective fracture toughness is not significantly influenced by addition of carbon fibres. On the other hand, the fracture energy value gradually increases with addition of carbon fibres, up to more than twofold increase in case of the highest amount of fibres.

The aim of this paper is to quantify crack initiation and other fracture properties – effective fracture toughness and specific fracture energy – of two types of concrete with an alkali activated binder. The beam specimens with a stress concentrator were tested in a three-point bending test after 28, 90, and 365 days of maturing. Records of fracture tests in the form of load versus deflection (P–d) diagrams were evaluated using effective crack model and work-of-fracture method and load versus mouth crack opening displacement (P–CMOD) diagrams were evaluated using the Double-K fracture model. The initiation of cracks during the fracture tests for all ages was also monitored by the acoustic emission method. The higher value of monitored mechanical fracture parameters of concrete with alkali activated blast furnace slag were achieved with substitution blast furnace slag by low calcium fly ash in comparison with substitution by cement kiln dust.

The 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.

Structural concrete of the building of Vitkovice railway station from 1970s is characterized via mechanical fracture parameters. In this paper, six core-drilled cylindrical specimens with diameter of 75 mm were provided by a Chevron type notch of depth of 12 mm. Three-point bending fracture tests were conducted on these specimens supported as beams with the span of 170 mm. Load vs. deflection and load vs. crack mouth opening displacement diagrams were recorded from which modulus of elasticity ( E ), fracture toughness ( K Ic ) and fracture energy ( G F ) were determined using linear elastic fracture mechanics approach and work-of-fracture method. Mean values of these parameters (with their coefficient of variability) were obtained as follows: E = 39.4 GPa (29.1%), K Ic = 0.90 MPa·m 1/2 (18.5%), G F = 174.0 J/m 2 (26.0%). These parameters can serve as first guess or indicative values for structural assessment and life-time predictions.

Results of pilot experiments focused on monitoring of shrinkage, weight loss and mechanical fracture properties of two selected polymer-modified cement mortars (PCM) during their aging are presented in the paper. Comparison of the measurement results was carried out on the test specimens at the age of 3, 28, and 90 days. The results show that even the specimens made from PCMs, for which the manufacturer declares no shrinkage, shrank considerably. The results also show that the development of mechanical fracture parameters during ageing of these materials differs from generally expected trends and thus the monitoring of these parameters is recommended.

The paper summarizes results of a pilot study aimed at the evaluation of an experimental investigation focused on determination of the material characteristics development of selected fine-grained cement-based composites during their ageing. The composition of composites being investigated differed only in a water to cement ( w/c ) ratio and in amount of superplasticizer. Quite extensive experiments were performed with the aim to determine shrinkage, dynamic a static modulus of elasticity and fracture properties on test specimens exposed to free drying during the whole time of its ageing (including the early stage of setting and hardening). The article presents especially results (including their statistical evaluation) of shrinkage and fracture parameters development within 90 days of composites’ ageing. Experimental results show the dependence of the investigated characteristics on the value of w/c ratio. The most visible effect was observed in the case of shrinkage development. The curing conditions were reflected especially in high variability of the test results.

Fracture behaviour of a crack in a particle (silicate based) composite is studied. The crack propagation depends not only on mutual elastic mismatch of matrix and aggregate but also the influence of the interfacial transition zone (ITZ) between the matrix and the aggregate is discussed. Various combinations of materials and geometry of matrix, aggregate and ITZ can improve or degrade fracture properties of the composite. Extensive numerical simulations on a basic 3-point-bending cracked specimen via the finite element method are performed in order to analyze the stress field near the crack tip. Linear elastic fracture mechanics approach is utilized in order to assess the crack stability and summarize several conclusions. Studováno je lomové chování trhliny v částicovém (silikátovém) kompozitu. Šíření trhliny závisí nejen na vzájemných elastických vlastnostech matrice a agregátu ale současně je diskutován vliv mezifázové přechodové zóny mezi matricí a agregátem. Různé kombinace materiálů a geometrie matrice, agregátu a mezifáze mohou zlepšit nebo zhoršit lomové vlastnosti kompozitu. Pomocí metody konečných prvků jsou provedeny rozsáhlé numerické simulace na vzorku s trhlinou zatíženém tříbodovým ohybem a je zjišťováno pole napětí v blízkosti vrcholu trhliny. Pro hodnocení stability trhliny a shrnutí zjištěných závěrů je použit koncept lineárně elastické lomové mechaniky.

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.

Knowledge regarding the values of fracture-mechanical parameters is critical for the virtual failure modeling of elements and structures made of concrete. A key parameter in nonlinear fracture mechanics modeling is the specific fracture energy of concrete, and its variability. Three-point bending tests on notched-beam specimens are fundamental experiments for the determination of fracture-mechanical parameters. In the present paper, two basic approaches are applied to determine fracture-mechanical parameter values from these tests: (i) the effective crack model/work-of-fracture method, and (ii) inverse analysis using artificial neural networks and stochastic simulations. First, the paper describes suitable methods for the determination of fracture-mechanical parameters. Second, the FraMePID-3PB software tool, which has been developed in order to automate the whole time consuming process of inverse analysis, is described. Finally, the verification of methodology and software is presented using two illustrative examples.

This paper concerns an investigation into the effects of high temperatures acting on specimens made from specially designed fine-grained cement-based composite with spherical glass aggregate. The experimental programme was carried out on four sets of beam specimens with the dimensions 20 × 40 × 200 mm. The specimens were thermally loaded to pre-set temperatures of 100, 200 and 400 °C, after which these temperatures were maintained for 60 minutes (one of the sets contained three reference specimens which were placed in a laboratory at a temperature of 20 °C and were not exposed to heat). After the temperature loading had been performed, the specimens were left to cool down to ambient temperature. After that, fracture tests were used to determine the degree of damage caused to the specimens by temperature loading. Three-point bending tests were conducted on the previously loaded beam specimens, which were notched to provide them with an initial stress concentrator using a diamond blade saw before testing. The depth of the initial edge notch on the bottom side of the specimen was approximately 1/3 of the total specimen depth. The span length was 180 mm. Fracture response was evaluated via load versus deflection diagrams. The monitored parameters were modulus of elasticity, effective fracture toughness and specific fracture energy. Informative compressive strength values were also determined. Selected specimens were investigated using X-ray micro-tomography (micro-CT).

Cement and alkali activated fly ash based concrete is analyzed.Fracture properties of various compositions are investigated both experimentally and numerically.Primary attention is accorded to the influence of the amount of fly ash replacing cement on fracture energy.The influence of short synthetic fibers on mechanical properties is also studied.Artificial neural network is introduced to provide parameters of the constitutive model. Several cement and alkali activated fly ash based concrete samples are examined in this paper with emphasis on their fracture properties. These are first obtained from an extensive experimental program. The measured loading curves are then compared with those derived numerically in the framework of an inverse approach. Here, the artificial neural network and the ATENA finite element code are combined to constitute the optimization driver that allows for a reliable determination of the modulus of elasticity, fracture energy, and tensile strength of individual concretes. A brief introduction to the numerical analysis of fiber reinforced specimens again in conjunction with inverse analysis is also provided.

This paper is focused on the verification and validation of the developing technique for estimation of the extent (the size and shape) of the fracture process zone (FPZ) in quasi-brittle silicate-based specimens/structures during failure process (termed the ReFraPro -Reconstruction of Fracture Process - technique). Most experimental data published in the literature are incomplete for its sound validation; therefore, numerical simulations by means of physical discretization of continuum are used for supplementing the verification of the technique. A discrete spring network/lattice particle-type model formulated as a nonlinear dynamical system is utilized. Parallelized implementation within the CUDA environment helps to decrease the computational cost of the simulations to an admissible level. The conducted analysis demonstrates satisfactory agreement of the size and shape of the FPZ reconstructed by the ReFraPro technique with both the data of the performed simulations and selected experimental data from literature.

The basic material characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric parameters, and thermal properties of several lime–pozzolana composites with different dosage of the burnt Czech clay shale are investigated. Within the studied range of the pozzolana:lime (P:L) ratio of 0.2:2.3–1.7:0.8, the mix with P:L = 0.9:1.6 is found to be the most effective solution. Its compressive strength, bending strength, effective fracture toughness, fracture toughness, and fracture energy are up to ten times higher, as compared with the reference lime composite without pozzolana addition, the water transport parameters are several times lower, the water vapor transport parameters are only about two times higher, the freeze/thaw resistance is significantly better, and the thermal properties are comparable. In a comparison with the reference lime–metakaolin composite, the corresponding material with burnt Czech clay shale is found to achieve similar mechanical and fracture-mechanical properties, its freeze/thaw resistance is somewhat worse, the water absorption coefficient is slightly lower, the water vapor diffusion coefficient is slightly higher, and the thermal properties are comparable. Therefore, the new lime–pozzolana composites have a good potential to be used as surface layers of building structures instead of lime composites without any addition, as an alternative solution to lime–metakaolin composites.

The paper presents a fracture-mechanics study conducted on a novel test configuration based on a combination of the wedge splitting and the bending test geometry. Four variants of this configuration differing in parameters of the specimen shape and boundary conditions were considered in the study. These selected variants exhibit significantly different stress state conditions at the crack tip, or, more generally, in the whole specimen ligament. The variation of the crack-tip stress constraint is of a crucial importance for the study because the expected differences in the fracture process zone extent and the amount of energy dissipation related to this zone is of particular interest here. An extensive experimental campaign was conducted on concrete specimens made of the same mixture. Processing and evaluation of the test data using the standard work of fracture technique was accompanied with numerical simulations by means of finite elements with implemented cohesive crack model to correlate the amount of energy dissipation with the simulated damaged zone extent. Variations of the fracture energy and also the stress/inelastic strain distribution with the change of the crack-tip constraint parameter and the notch length are observed.

For application in civil engineering structures and also for strengthening existing structures cement-based composites are one of the most frequently used materials. Although many studies have been conducted on the mechanical properties of concrete from static tests, very little research has been reported on concrete fatigue properties. The purpose of this paper is to investigate the static and fatigue behavior of new cement-based composites, developed by ZPSV, a.s. a company producing bridge/train/building structures, are presented. To this end specimens were prepared and tested under static (compressive strength, bending strength, volume density and freezing and thawing resistance index) and cyclic loading (fatigue parameters — Wohler/ S − N curve). The experimentally obtained results (both static and fatigue) of cement-based composites are compared and the suitability of the composites in terms of their application for thin building elements is discussed.

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.

The goal of this paper is to show some trends and time profiles of the reliability index relevant to the Serviceability Limit State considering the design service life of RC structures. The interactive web page “RC_LifeTime” – originated by the authors – is used (see http://www.stm.fce.vutbr.cz/). The depassivation of reinforcing steel due to carbonation is considered conservatively as a limiting condition. It is based on model concrete carbonation with 12 random input variables; the Latin Hypercube Sampling simulation method is used. RC_LifeTime offers the following options: Service Life Assessment – a statistical evaluation of service life, where optionally the target value of reliability index ß may be an additional input value and then the corresponding service life is the output value; Concrete Cover Assessment – a statistical evaluation of concrete cover value for the target service life, where optionally the required concrete cover value may be input in this case and the relevant reliability index ß describes the reliability of reinforcement depassivation.

Fly ash geopolymer is amorphous aluminosilicate material which is considered as alternative to Portland cement concrete. One of the limiting factors of its utilization is an increased shrinkage and related deterioration of fracture properties. This paper reports on a study of the application of multi-walled carbon nanotubes (MWCNTs) to improve the fracture properties of fly ash geopolymer. The amount of MWCNTs added varied in the range of 0.05–0.2% of the mass of fly ash. Mechanical fracture properties were determined via evaluation of three-point bending fracture tests. Specimen response during fracture tests was also monitored by means of acoustic emission, and this method was also used for the determination of cracking tendency occurring during the hardening process. Results show that the addition of MWCNTs increases the elastic modulus and compressive strength of fly ash geopolymer. However, basic fracture parameters (fracture toughness, fracture energy) firstly decreased with very small addition of MWCNTs and were regained or slightly exceeded the reference values with higher amount of MWCNTs.