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Insufficient determination of the effect of surface-active substances introduced in extremely low concentrations on the formation of the stability of the properties of fine-grained concrete based on composite Portland cements determined the feasibility of conducting research in this area. The studies investigated the influence of the modification of composite cement with water activated by the use of the hydrophilic hydration mechanism. It has been proven that these factors include the type and amount of applied water nano modifiers. The analysis of the study results confirmed that the introduction of water activated by the mechanism of hydrophilic hydration into concrete in extremely small doses significantly increases the rate of formation of concrete strength and reduces the coefficient of its variation. Owing to this, the strength of the resulting modified fine-grained concrete based on composite cement at the age of 3 days exceeds the strength of the similar concrete without additives by 300 %, and at the age of 27 days – by 25 %. At the same time, the coefficient of variation of strength has a minimum value at the optimal amount of nano additive – water modifier. This allows us to assert the effectiveness of the revealed mechanism of modification of composite cement. Thus, there are reasons to assert the possibility of targeted regulation of the processes of formation of a strong homogeneous structure of fine-grained concrete based on composite cement by using water activated by the mechanism of hydrophilic hydration. [ABSTRACT FROM AUTHOR]

The goal of this work is to investigate the properties of finegrained modified concrete using various aggregates and blended binders. Considering that there is a tendency to reduce the use of Portland cement worldwide, the goal was to develop fine-grained concrete compositions with low clinker binders (mixed binders), which would preserve and even improve the physico-mechanical properties of fine-grained concrete. River and lithoid pumice sands were investigated and used as fillers. Superplasticizer, microsilica, and quicklime were used in different quantities to modify fine-grained concrete. The research results show that, depending on the type of fillers used, the compressive strength of the river sand-based mortar increased by 15.33 % after 28 days, and by 6.34 % with lithoid pumice, compared to the reference sample. The use of lime resulted in an increase in the density of cement stone for heavy aggregates but a decrease in density for light aggregates, with no significant increase in strength observed. [ABSTRACT FROM AUTHOR]

Fine-grained high-strength concrete has already been tested extensively regarding its uniaxial strength. However, there is a lack of research on the multiaxial performance. In this contribution, some biaxial tests are investigated in order to compare the multiaxial load-bearing behaviour of fine-grained concretes with that of high-strength concretes with normal aggregate from the literature. The comparison pertains to the general biaxial load-bearing behaviour of concrete, the applicability of already existing fracture criteria and the extrapolation for the numerical investigation. This provides an insight into the applicability of existing data for the material characterisation of this fine-grained concrete and, in particular, to compensate for the lack of investigations on fine-grained concretes in general. It is shown, that the calibration of material models for fine-grained concretes based on literature results or normal-grained concrete with similar strength capacity is possible, as long as the uniaxial strength values and the modulus of elasticity are known. For the numerical simulation, a Microplane Drucker–Prager cap plasticity model is introduced and fitted in the first step to the biaxial compression tests. The model parameters are set into relation with the macroscopic quantities, gained from the observable behaviour of the concrete under uniaxial and biaxial compressive loading. It is shown that the model is able to capture the yielding and hardening effects of fine-grained high-strength concrete in different directions. [ABSTRACT FROM AUTHOR]

The object of research is fine-grained concrete on slag Portland cement. Owing to the significant content of metallurgical industry waste in its composition, slag Portland cement belongs to ecologically acceptable products. However, the insufficient rate of formation of its structure and, as a result, the main quality indicator, which is compressive strength, limits the field of use of slag Portland cement. Therefore, in the studies, the goal was to increase the speed of formation of the strength of fine-grained concrete made on slag Portland cement. The studies of the influence of modification of slag Portland cement with water, activated by the use of the hydrophobic hydration mechanism, established the factors affecting the speed of formation and the value of compressive strength of fine-grained concrete made on slag Portland cement. It has been proven that these factors include the type and amount of applied water nanomodifiers, as well as the type and amount of fine concrete aggregate. The analysis of the study results confirmed that the introduction of water activated by the mechanism of hydrophobic hydration into concrete in ultra-small doses significantly increases the rate of formation of concrete strength. Given this, the strength of the resulting modified fine-grained concrete based on slag Portland cement at the age of 2 days exceeds the strength of the similar concrete without additives by 60 %, and at the age of 210 days – by 25 %. This allows us to assert the effectiveness of the identified mechanism of modification of slag Portland cement. Thus, there are reasons to assert the possibility of targeted regulation of the processes of forming a strong structure of fine-grained concrete based on slag Portland cement by using water activated by the mechanism of hydrophobic hydration. [ABSTRACT FROM AUTHOR]

The construction of energy-efficient buildings is very important as it can lower the energy consumed for construction and reduce the energy required for the heating and cooling effects of buildings and reduce the global warming caused by carbon emissions in buildings. It is therefore necessary to check the thermal characteristics of any construction material. Chopped Basalt Fiber (BF) is dispersed to the fine-grained concrete matrix and after determining the optimum percentage of fiber content cement is partially replaced in the matrix with ground granulated blast furnace slag (GGBS) by different percentages. GGBS helps in providing improved structural performance and also reduces the waste material generated by the steel industry. In addition, thermogravimetric analysis (TGA) is done to ascertain the thermal stability of the material when subjected to higher temperatures. The thermal conductivity of fine-grained concrete is determined to check the conductance of heat through the sample for thermal evaluation of the structure. Furthermore, the specific heat capacity, thermal resistance and thermal diffusivity of the material are also studied. The fine-grained concrete with basalt fiber and GGBS shows better thermal properties than controlled fine-grained concrete. [ABSTRACT FROM AUTHOR]

Measuring and calculating methods of critical stress intensity factors (SIFs) have become hot topics which attracted large attention recently. In this work, anti-symmetrical four-point bending tests of cracked fine-grained concrete specimens were conducted experimentally and numerically by using a computer-controlled universal testing machine and ABAQUS code. A comparative study of the calculation method of pure mode II stress intensity factor of a fine-grained concrete was performed by utilizing the conventional finite element method (FEM) in two and three dimensions as well as the extended finite element method (XFEM) in three dimensions. The results show that in three-dimensional models, the crack mode is closest to the pure mode II at the center of specimen thickness. Pure mode II stress intensity factors obtained by SEAM2D and XFEM3D are 1.013 and 1.0617 times that by SEAM3D, respectively. Pure mode II stress intensity factors of the fine-grained concrete obtained by the conventional FEM are more stable than that by XFEM. The number of mesh circles has slight influence on the calculation results of pure mode II stress intensity factor. [ABSTRACT FROM AUTHOR]

The expediency of replacing natural quartz Sands, whose reserves are gradually exhausted, by rock screenings as part of fine-grained concretes is shown. In particular, the characteristics of granite and quartzite crushing screenings in comparison with quartz river sand are presented, as well as the results of studying the strength and abrasion of the fine-grained concrete obtained. To exclude the effect of the grain composition on the properties of concrete, aggregate samples were pre-fractionated, and the conditions for producing concrete (cement consumption, water-cement ratio, concrete mix mobility) were the same. It was found that quartz sand having rounded grains with a relatively smooth surface promotes the formation of dense particle packing and increases the strength of fine-grained concrete by 9-14%, but at the same time reduces the abrasion of similar standard samples by 20-30% compared to screenings crushing of granite and quartzite. The maximum abrasion resistance showed concrete containing quartzite screening. Quartzite - metamorphic (metasomatic) dense rock crushing which produces angular particles with a rough surface. The absence of dense packaging reduces the compressive strength of concrete samples containing quartzite aggregate compared to quartz sand. At abrasion of similar samples in a thin layer the resistance to sliding of filler particles one relative to another increases. Therefore, when choosing crushed rock fines instead of natural quartz Sands, it is important to consider the purpose of the designed fine-grained concrete. [ABSTRACT FROM AUTHOR]

This article aims to study the effects of adding steel fibers and galvanized recycled spring on mechanical properties and crack development in the fine-grained concrete exposed to the acidic environment containing magnesium sulfate. To this end, specimens containing 0.3% and 0.6% of steel fibers and springs, respectively, by concrete volume, were built in normal temperature using 10 cm × 20 cm standard steel formworks so as to conduct the compressive and tensile strength tests. All specimens were cured in 28 days exposed to the environment containing 0%, 5%, and 10% of magnesium sulfate. Based on the results, addition of steel fibers and recycled spring improves the compressive and tensile strength by 50% and 60%, respectively. Moreover, the specimens containing recycled spring better withstood against the acidic environments in comparison with the specimens including steel fibers. In general, it was found that due to the negligible difference between the strength of the specimens, the application of metal-recycled spring in the fine-grained concrete is technically and economically justifiable. [ABSTRACT FROM AUTHOR]

Under static loading, crack propagation processes are a dynamic process due to very high propagation speeds. For fine-grained concrete material under static loading, the crack propagation speed can reach 723.7 m/s, thus the crack propagation process under static loading actually can be considered as a dynamic issue, not a static issue. Crack propagations with a rapid speed are extremely unfavorable to the stability of concrete structures. Therefore, it is of significance to study the dynamic fracturing of concrete structure under static loading. Three-point bending (TPB) tests were conducted by using concrete specimens. A novel test system coupled with crack propagation gauges (CPGs) and strain gauges (SGs) was utilized to measure the crack speed and the initiation loads. The experimental results show that crack propagation velocities are not a constant and the propagation toughness of fine-grained concrete varies with the crack tip displacement. The initiation toughness is higher than the propagation toughness. [ABSTRACT FROM AUTHOR]

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In order to cost-effectively reduce the resistivity of fine-grained concrete in TRC. In this paper, the effect of two different conductive phase materials, carbon fiber and graphite, on the mechanical and conductive properties of fine-grained concrete was investigated by incorporating different conductive phase materials to modify fine-grained concrete in TRC. The research shows that compared with graphite, the fluidity of carbon fiber for fine-grained concrete decreases significantly. When two conductive phase materials were incorporated into the fine-grained concrete, the compressive strength was reduced to varying degrees. For the fine-grained concrete specimens mixed with different conductive phase materials, the resistivity of the specimens increases with the age, and the resistivity of the specimens gradually decreases with the increase of the content of the two conductive phase materials. Finally, the conductive paths in the fine-grained concrete with double-doped conductive phase materials are divided into a triple conductive path, and the resistivity calculation model of fine-grained concrete after doping with conductive phase materials is established based on the Ezquerra model. [Display omitted] • Carbon fiber reduces the fluidity of fine-grained concrete. • Resistivity of fine-grained concrete with conductive phase material increases with age. • Double-doped conductive material forms a triple conductive path in the fine-grained concrete. • Resistivity calculation model of fine-grained concrete is established based on Ezquerra model. [ABSTRACT FROM AUTHOR]

The article presents the results of experiments on the use dispersed components with reduced stiffness in concrete mixtures to assess their influence on the dynamic strength of concrete. A crushed ceramic bricks, the polystyrene foam, cellular glass and expanded clay sand were used components with reduced stiffness. Samples-cubes were subjected to various dynamic loads, and then measured their strength and were compared with the results obtained for a control sample. Furthermore by vertical dynamic koper were measured impact strength of the obtained compositions. The results of experimental studies are showing the possibility of increasing the impact strength of concrete by introducing into the concrete mix an additive with reduced stiffness. In the same time there is some reduction in other properties of the resulting concrete. Has been defined the optimum additive and its amount to use in the concrete that subjected to dynamic loads. [ABSTRACT FROM AUTHOR]

• Compaction improves splitting resistance of vertically cast specimens. • Top-cast specimens have a lower splitting resistance than bottom-cast specimens. • Higher splitting stress is generated orthogonal to the plane of the textile. • The main cause of splitting failure is the fiber strand's varying cross-section. • Bond distribution depends on the cross-section variation along the fiber strand. Textile-reinforced concrete is an innovative combination of high-performance fine-grained concrete and textile reinforcements. This combination allows the production of thin, efficient, and durable structural elements. Impregnation is commonly used to improve the textile's mechanical performance. When stiff impregnation materials are used, a fiber strand with high transverse stiffness is formed. Textile-reinforced concrete structures with such fiber strands are prone to splitting failures. This paper investigates splitting failure in textile reinforced concrete experimentally and numerically. In the experimental part, the effect of concrete compaction, casting method, and position are studied as parameters. Finite element analysis is performed to investigate failure mode, tensile and bond stress distributions, and the effect of the varying cross-section of the fiber strand. Compaction improved the splitting resistance for the vertically cast specimens. The compacted vertically cast specimens showed a higher splitting resistance than their horizontally cast equivalents. The finite element model indicated that the main cause of splitting failure is the textile reinforcement's varying cross-section coupled with its flat elliptical shape. The model also showed that the bond stress distribution depends on the fiber strand's geometric configuration. [ABSTRACT FROM AUTHOR]