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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.

This paper concerns research into the importance of the interfacial transition zone around inclusions of selected materials in fine-grained cement-based composite. Tests were performed on eight sets of prismatic test specimens. The sets differed in the inclusion materials used, which were placed at midspan above the initial central edge notch. The first was a reference set without any inclusion, the second contained a steel inclusion, four more contained different types of rock inclusion, the seventh contained an inclusion of extruded polystyrene, and the last contained a space of the same dimensions as that occupied by the inclusions in sets 2 to 7. The test specimens were subjected to three-point bending fracture tests at the age of (usually) 28 days. The fracture response was analysed by means of fracture mechanics theory, and apparent mechanical fracture parameters (modulus of elasticity, fracture toughness and fracture energy) were evaluated. The conclusion shows that a possible relationship exists between the differences in the mechanical fracture parameters of specimens with/without an inclusion and the existence of the interfacial transition zone.

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.

The paper discusses creation of numerical models of the modified Compact Tension (CT) test configuration on specimens made of fine-grained cement composite. Numerical models of this test configuration are used for predictions of crack initiation and damage propagation and are important for the further evaluation of fracture parameters. To assemble the numerical models, ATENA FEM software was used. In this software, fracture of the structure/specimen caused by cracks, their initiation and progressive propagation throughout the loading process, can be modelled. In case of this study the material model for concrete based on cohesive law approach was used. The analysis is focused on evaluation of 2D and 3D numerical models created with real material properties obtained from experimental data.

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.

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.

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.

This paper presents selected results from a study concerning mechanical fracture parameters related to the formation of the solid structure of cement mortars. The tested mixtures were composed of an invariable quantity of cement (type CEM I 42.5 R) and an increasing amount of amorphous SiO2 (marked with a P), or a variable quantity of cement replaced by varied quantities of amorphous SiO2 (marked with an N). It was decided that the consistencies of the fresh mixtures should be identical: to ensure this, the water-cement ratio was increased as necessary. Quantification of the mechanical fracture parameters of the studied composites (fracture toughness, fracture energy, compressive strength, modulus of elasticity) was performed via the evaluation of fracture tests performed on beam specimens with an initial stress concentrator loaded in three-point bending. Subsequently, the results of the experiments in the form of load versus displacement diagrams were processed using the effective crack fracture model and the work of fracture method.

The paper is focused on the mechanical fracture properties of hardened cement mortars in which Portland cement is partially replaced by reactive admixtures. These properties are evaluated in relation to the mortars’ microstructure through the size and content of pores. The cement in the mortars was partially replaced by a diatomite that contains amorphous SiO2. The three-point bending fracture tests were performed on beams with a central edge notch. The investigated mechanical fracture properties of the aforementioned cement-based composites included flexural strength, compressive strength, elasticity modulus, effective fracture toughness and specific fracture energy.

The contribution is devoted to investigation of the fracture process zone (FPZ) in a fine-grained cement-based composite made from hydrated Portland cement. Particularly, experimental investigations and description of the stable crack propagation using fracture mechanics model are conducted. Three-point bending tests on small composite beams with a central edge notch were performed. The damage due to fracture was monitored by means of nanoindentation performed around the macroscopically observable crack. Acoustic emission events were recorded during the three-point bending test and correlated with load–displacement data. The beneficial effect on the fracture resistance of fine-grained mortar specimens compared to plain cement pastes was quantified.

The alkali-activated concrete is prepared as a new potential material for the production of concrete elements developed by ZPSV, a. s. company. Note that civil engineering structures are usually made of ordinary Portland cement (OPC) based concrete but today, the cement industry is responsible for emitting between 6% and 7% of all the CO2 emission into the atmosphere. Therefore, it is essential to seek different binders to provide environmental friendly materials. One possible alternative is the application of alkali-activated concrete. The optimal design of concrete mixture was studied in this investigation. Two types of concrete have a similar application and therefore the fatigue parameters can be compared. To this aim, specimens were prepared and tested under static (compressive cube strength) and cyclic loading (fatigue parameters − Wöhler curve). The experimentally obtained results (both mechanical and fatigue) of both types of concrete are compared and the suitability of these types of composites for its application is discussed.

A complex analysis of engineering properties of concrete containing natural zeolite as supplementary cementitious material in the blended Portland-cement based binder in an amount of up to 60% by mass is presented. The studied parameters include basic physical characteristics, mechanical and fracture–mechanics properties, durability characteristics, and hygric and thermal properties. Experimental results show that 20% zeolite content in the blended binder is the most suitable option. For this cement replacement level the compressive strength, bending strength, effective fracture toughness, effective toughness, and specific fracture energy are only slightly worse than for the reference Portland-cement concrete. The frost resistance, de-icing salt resistance, and chemical resistance to MgCl2, NH4Cl, Na2SO4, and HCl are improved. The hygrothermal performance of hardened mixes containing 20% natural zeolite, as assessed using the measured values of water absorption coefficient, water vapor diffusion coefficient, water vapor sorption isotherms, thermal conductivity, and specific heat capacity, is satisfactory.

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.

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.

This paper introduces results of fracture experiments on fine-grain concrete specimens prepared from CEM 42.5 R Portland cement of different origin (five Czech Republic localities: Mokrá, Hranice, Radotín, Prachovice, Čížkovice), with natural zeolite admixture. Although the specimens were produced using the same type of cement, this paper shows that even small differences in chemical and mineralogical composition (caused by different origin) can result in changes of mechanical fracture parameter values.

Mechanical fracture parameters obtained from three-point bending tests on concrete specimens with a central edge notch are introduced in this paper. A total of four sets of specimens were tested. The concrete used in each set differed in cement dosage, which ranged from 250 to 455 kg per m3of fresh concrete. Three specimens in each set were tested at the age of 28 days. Increasing the dosage of cement influences the mechanical fracture properties of concretes in both positive and negative ways.

This paper presents the results of three-point bending fracture tests. Specimens were made from lime mortar modified by brick powder or metakaolin. The first, reference mixture only used hydrated lime, while the other mixtures were enhanced by brick powder or metakaolin in amounts of 25, 50 and 100 % of the weight of hydrated lime.

The partial replacement of cement in concrete by an alternative admixture is a current topic in materials engineering. In order to examine the effect of replacing 20 % of the weight of Portland cement in fine-grained concrete using selected admixtures on volume changes and mechanical fracture parameter values, a set of specimens was fabricated from these quasi-brittle materials. Granulated blast-furnace slag, high-temperature fly ash, metakaolin and specially selected combinations of them were used as admixtures. Three-point bending fracture tests were conducted on these specimens and load versus crack mouth opening displacement (PCMOD) diagrams were recorded during the testing. In this paper, the outputs of the double-K fracture model were used for the prediction of beginning of stable crack propagation in fine-grained cement-based composites with admixtures.

This paper introduces the results of fracture experiments on concrete specimens of different composition modified by zeolite (7.5 to 30 % by weight of cement dosage). It presents the determination and comparison of basic mechanical/fracture parameter values such as volume density, compressive strength, elasticity modulus, effective fracture toughness and fracture energy.

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 presents experimental work regarding the basic physical characteristics, mechanical and fracture-mechanics properties, durability characteristics, hydric and thermal properties of high performance concrete (HPC) with up to 60% of Portland cement replaced by fine-ground ceramics. Experimental results show that the amount of the ceramics in the mix is limited mainly by the resistance against de-icing salts which is found satisfactory only up to the cement replacement level of 10%. The mechanical and water transport properties are not significantly impaired by ceramic additions of up to 20%, whereas the effective fracture toughness, specific fracture energy, and chemical resistance (to MgCl2 ,N H 4Cl, Na2SO4, HCl) are effectively maintained up to 40%. The frost resistance, water vapor transport and storage parameters and thermal properties are not significantly impaired even up to a 60% replacement level. 2011 Elsevier Ltd. All rights reserved.

Although the capability of metakaolin as pozzolanic material to improve mechanical and durability properties of concrete if used as partial replacement of Portland cement is well noted in concrete science, its utilization in building industry was limited to date, mainly due to its high price dictated by the low production amounts. However, with the current shortage of silica fume and high-quality slag in some countries the attitude of concrete producers to metakaolin may change in the near future. This change of mind can be facilitated by providing a more comprehensive view of the properties of composite materials with metakaolin, thus contributing to wider realization of the benefits of metakaolin in concrete. In this paper, an extensive set of parameters of high performance concrete (HPC) with metakaolin including basic physical characteristics, mechanical and fracture-mechanical properties, durability characteristics, hydric and thermal properties and chloride binding characteristics is measured. The experimental results show that the replacement of Portland cement by 10% of metakaolin as an optimal amount leads in most cases either to improvements or at least does not significantly impair substantial properties of the analyzed HPC. Basic physical properties and heat transport and storage properties are very similar to common HPC, mechanical and fracture-mechanical properties after 28 days are slightly worse but later improved, water- and water vapor transport parameters are substantially reduced, frost resistance is better, resistance against de-icing salts is slightly worse but still meets very well the required criteria. The chemical resistance of concrete with 10% of metakaolin instead of Portland cement in distilled water and HCl is found better than for Portland cement concrete, in MgCl2 it is slightly worse, and in NH4Cl, Na2SO4 and CO2 almost the same, carbonation is reduced, and chloride binding capacity is increased. (A) Reprinted with permission from Elsevier.

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.

The paper introduces the basic fracture mechanics parameters of advanced building material – cement-based composites with various types of fibres, prepared as high performance concrete/mortar developed by ZPSV, a.s. company for production of thin-walled panels/elements. To this end three-point bend specimens with starting notch were prepared and tested under static (load–deflection diagram, effective fracture toughness) and cyclic loading (fatigue parameter – Wöhler curve). The experimentally obtained results of cement-based composites are compared and the suitability of these types composites for its application are discussed.