Concrete Structure Formation Research Articles

Granite Crushing Screenings as a Component Factor in the Concrete Structure Formation. Part II: Experimental Studies of Structure-forming Potential

The paper considers the results of experimental studies of the individual and joint influence of macro-, meso- and micro-nanofractions of granite crushing screenings on the processes of structure formation and properties of cement concrete. It has been established that in the processes of formation of the structure of fine-grained concrete and the potential for resistance to its destruction, all fractions of stone crushing screenings perform their specific functions as a component factor. Macro-sized (crushed stone) grains of screening of the 5–10 mm fraction form a macro-scale frame of the addition system, which perceives force load with the accumulation of loading energy and braking of main cracks. Sand mesoparticles of fraction 0.16–5 mm fill the intergranular space of the system for adding macroparticles with dissipation of external loading energy in the matrix material. The microfraction of granite crushing screenings (the fraction is <0.16 mm), along with the effect of replacing the volume of cement stone, exhibits physical and chemical activity in the phase formation of hydrate compounds. It is shown that in the initial screening of granite crushing, the structure-forming role of its particles is not manifested effectively enough, the main reason for which is the “excess” of sand fractions, which push apart the grains of macrofractions and increase the water demand of the concrete mixture. Traditional methods of enriching screenings do not solve this problem. The principle of conditioning screenings by saturating them with macro- and micro-sized fractions is discussed. Based on this principle, a technology for mechanical processing of screenings has been developed to produce a “line” of products for targeted use in the building materials and products industry. The introduction of such technology will significantly increase the efficiency of construction and technological recycling of stone crushing screenings through maximum use of the structure-forming potential of their polydisperse composition.

ОТХОДЫ ОБОГАЩЕНИЯ ЖЕЛЕЗИСТЫХ КВАРЦИТОВ КАК СТРУКТУРНЫЙ КОМПОНЕНТ МЕЛКОЗЕРНИСТОГО БЕТОНА

The article describes problematic situation with waste accumulation from iron ore concentrate production (beneficiation tailings) from ferruginous quartzite at JSC Olkon (Murmansk Region). The task is to utilize beneficiation tailings as a fine-grained concrete component. The paper presents results of beneficiation tailings diagnostics and their testing as a part in the processes of fine-grained concrete structure formation in comparison with quartz sand from the Olenegorsk quarry. According to the research, the replacement of natural sand with beneficiation tailings in their original form leads to a decrease in strength due to insufficient compaction of mixture under adopted vibration compaction modes. At the same time, the use of ground beneficiation tailings in binder composition ensures increase in strength of concrete compared to concrete on "pure" cement and increase of efficiency by using clinker part of binder in formation of concrete strength by 57-58%. The study recommends the use of fine-grained concrete composition of class B40 for production of vibration-pressed urban land improvement products (paving slabs, curbstones, etc.). It reveals prospects for further research in construction and technological utilization of ferruginous quartzite enrichment tailings as a factor in the formation of biosphere-compatible living environment in the region.

Pre-treated corn straw fiber for fiber-reinforced concrete preparation with high resistance to chloride ions corrosion

Chloride ions erosion is a negative factor for concrete sustainable usage. Fiber addition is a potential solution, which promotes a tight concrete structure formation resulting in the resistance of chloride ions. Corn straw is a kind of crop waste widely sourced that can be used as sustainable concrete reinforcement material. The traditional recycling method of corn straw including burnt as straw ash is not environment friendly. This work aims to pre-treat corn straw fiber (CSF) by some convenient methods (untreated, water-treated, alkali-treated) and add treated CSFs directly into concrete to prepare fiber-reinforced concrete with excellent mechanical properties and high resistance ability to chloride ions. The component content of different treated CSFs was tested to study the fibers composition and microstructure changes. The heat of hydration, compressive strength, and flexural strength were tested to study the hydration degree and the effect of different treated CSFs on the concrete mechanical performance. The rapid chloride permeability (RCPT) and chloride migration (RCM) tests were designed to study the reinforced concretes chloride ions resistance ability change. In addition, to further explore the mechanism of mechanical performance and chloride ions resistance ability change, water absorption rate (WAR) and mercury intrusion porosity (MIP) were tested to provide more supporting information from the micro-level. It is concluded that CSF treated by Na2SiO3 has the least impurities and a rougher surface with a larger specific surface area bonding with the cement substrate. Compared to the original concrete, the compressive strength of CSF concrete, WT-CSF concrete, and NT-CSF concrete increased by 15.7 %, 17.8 %, and 33.4 % respectively. The results of RCM and RCPT show a decreasing trend with different treated CSFs addition, the NT-CSF concrete shows the greatest decrease with 20.1 %, and 17.5 %, respectively. Except for the rougher surface and less impurities of CSF, the improvement of mechanical performance and chloride ions resistance ability is mainly due to treated CSF, especially the NT-CSF contributes to a denser structure formation based on the MIP and WAR test results. The viscosity of Na2SiO3 solution acts as a binder that helps to tighten the bonding between substrate and CSF. The water adsorbed by CSF and the alkaline environment provided by Na2SiO3 facilitates hydration decreasing the chloride ions migration. At the same time, the cellulose in CSF containing many hydroxyl and carboxyl groups further contributes to the concrete chloride ion resistance improvement due to its weak conductivity and the binding force of ions exchange.

Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles

The resistance of concrete structures to the impact of cyclic freezing and thawing is one of the key long-term characteristics, which further determines the operation and its service life. To date, the resistance to alternating freeze-thawing cycles under various operating conditions of concrete structures has been little studied related to several manufacturing processes: simple vibrated, variotropic centrifuged, and improved variotropic vibrocentrifuged. The purpose of this study is to investigate the effect of heavy concrete manufacturing technology on the resistance of concrete to alternate freezing and thawing in an aggressive environment of 5% sodium chloride solution, as well as to study the trend in strength characteristics and weight loss of vibrated, centrifuged and vibrocentrifuged concretes after a series of freezing and thawing cycles. Standardized techniques for assessing the characteristics of concrete and scanning electron microscopy were used. Vibrated, centrifuged, and vibrocentrifuged concretes made from the same raw materials have differences in weight loss of 4.5%, 3%, and 2%, respectively, and in strength of 15.0%, 13.5%, and 10%, respectively, when tested for frost resistance in similar environments after 15 cycles by the accelerated method. Centrifuged and especially vibrocentrifuged variotropic concrete have greater resistance and endurance to cycles of alternate freezing and thawing compared to vibrated.

Technogenic Fiber Wastes for Optimizing Concrete.

A promising method of obtaining mineral fiber fillers for dry building mixtures is the processing of waste that comes from the production of technogenic fibrous materials (TFM). The novelty of the work lies in the fact that, for the first time, basalt production wastes were studied not only as reinforcing components, but also as binder ones involved in concrete structure formation. The purpose of the article is to study the physical and mechanical properties of waste technogenic fibrous materials as additives for optimizing the composition of raw concrete mixes. To assess the possibility of using wastes from the complex processing of TFM that were ground for 5 and 10 min as an active mineral additive to concrete, their chemical, mineralogical, and granulometric compositions, as well as the microstructure and physical and mechanical characteristics of the created concretes, were studied. It is established that the grinding of TFM for 10 min leads to the grinding of not only fibers, but also pellets, the fragments of which are noticeable in the total mass of the substance. The presence of quartz in the amorphous phase of TFM makes it possible to synthesize low-basic calcium silicate hydrates in a targeted manner. At 90 days age, at 10–20% of the content of TFM, the strength indicators increase (above 40 MPa), and at 30% of the additive content, they approach the values of the control composition without additives (above 35 MPa). For all ages, the ratio of flexural and compressive strengths is at the level of 0.2, which characterizes a high reinforcing effect. Analysis of the results suggests the possibility of using waste milled for 10 min as an active mineral additive, as well as to give better formability to the mixture and its micro-reinforcement to obtain fiber-reinforced concrete.

The Damping Effect in the Propagation of the Cracks in Fine-Grained Carbonate Concrete

The paper enlightens the connection between the specifics of the fine-grained concrete structure and the mechanics of its destruction under crack propagation with due account of damping effect of limestone fines. It is possible to obtain specific information about the ways of controlling the structure formation of concrete by finding out the relationship between the mechanism of formation, and damping mechanism of limestone additives retarding the crack propagation during consolidation and destruction of concrete.

High-early strength concretes modified with polycarboxylate admixture on different cement types

Early and grade strength of modified concrete on different cement types (CEM II/A-S 42,5 and pozzolanic cement CEM IV/A(P) 42,5 R-SR) for concrete pavements repair was explored. Application range of the polycarboxylate modifier was 0.8-1.4% by weight of cement. All concrete compositions had equal workability (slump 5…9 cm). The aim of the investigation was to determine the optimal volume of the polycarboxylate modifier to achieve high strength indicators for repair material at the early and grade age.High-strength concrete of grades C 50/60 and C 40/50 were obtained, with early strength at the 3 days age above 35 MPa, which allows them to be used as a repair concrete material for rigid road pavements.X-ray phase analysis confirmed the positive effect of the polycarboxylate admixture in the structure formation of concrete. With an increase in the dosage of the BASF MasterGlenium SKY 608 admixture to 1.2…1.4%, the intensity of the diffractogram lines, which corresponds to the metastable hydration phase in the cement-sand matrix, decreased for concretes on both cement types.

Influence of Polycarboxylate Superplasticizer and Mineral Additives of Various Compositions on the Technological and Physical-Mechanical Properties of Cement Systems

Management of the pore volume and the mineral-morphological state of the hardening system by modifying the cement stone with chemical and mineral additives introduced both separately and in complexes is considered to be one of the defining directions of concrete structure formation. The purpose of this study was to establish the regularities of the influence of mineral additives of various compositions (siliceous, aluminosilicate, sulfoaluminate, carbonate) and polycarboxylate superplasticizer on the technological and physical-mechanical properties of cement systems, with the identification of the most effective modifiers and their complexes. Based on the results of experimental studies, it was established that it is possible to obtain, on the basis of sulfoaluminate modifier, compositions with high technological parameters with a reduced content of expensive polycarboxylate plasticizer. It was found that the studied compositions with mineral additives differ in high rates of compressive strength gain of cement stone at the age of 3 and 7 days - 48÷69 and 71÷83% of the compressive strength at the age of 28 days, respectively. At the same time, in comparison with the reference composition without mineral additives, the relative compressive strength of the modified cement stone at the age of 28 days varies in the range from 0.9 to 1.2 relative units, which confirms the possibility of increasing the strength indicators of cement composites due to the use of optimal complexes of polycarboxylate superplasticizer and mineral additives of various compositions, in particular when using microcalcite, microsilica and sulfoaluminate modifier together.

Investigation of the process of hardening and structure formation of concrete using modified binders

The article presents the possibility of recycling waste from polymetallic ores and micro-silica enrichment, as well as the features of structure formation and hardening of concrete based on modified binders.

СТРУКТУРНО – МАТЕМАТИЧЕСКАЯ МОДЕЛЬ ТЕПЛОПРОВОДНОСТИ БЕТОНА

Introduction: The significance of energy saving in residential construction is associated with the reliable determination of design thermal conductivity characteristics of construction materials. The authors describe a concept of the structural and mathematical modeling of concrete thermal conductivity. The concept is based on methods of the structural approach and generalized conductivity theory. Purpose of the study: The study is aimed at developing an adequate structural and mathematical model to determine the thermal conductivity of concrete. Methods: The authors used the statistical method as a representation of the statistical homogeneity of a multi-component composite closely related to thermal homogeneity, which is understood as a medium with effective thermal resistance constant in space. Results: The authors developed a structural and mathematical model to determine the thermal conductivity of concrete. The model accounts for concrete structural factors existing at the time when the structure formation of concrete is, for the most part, complete. The model also accounts for the thermal and physical properties of concrete components as well as macro- and mesostructural features of concrete. The paper presents calculated data for potential macro- and mesostructural factors, which makes it possible to determine the thermal conductivity of concrete characterized by low thermal conductivity and use the results derived for the approximation of prediction trends related to the thermal properties of such concretes in the operation and adaptation period during the use of building envelopes.

Consideration the structure formation properties of crusher run stone screening as a solution of its construction and technological reuse environmental and economic issues

The article is dedicated to the search of ways of decreasing environmental damage from the quarry industry, generating crusher screening. Construction and technological reuse is offered as the most effective way of waste dump elimination. In this regard, screening of stone crushing are considered a valuable raw material component of high quality fine grain concretes, having mechanical, mechanical and physical as well as physical and chemical activity, which is effected in the processes of structure formation of concrete on its macro-, meso- and micronanolevels. The results of research of screening genesis, its characteristics, and its influence on the structure formation processes and the properties of fine grain concrete are presented. The suggestions for conditioning of screening with the view to increasing the efficiency of the concrete produced with their use and increasing the demand for screening in the construction market are validated.

Structure and properties of fine concretes based on composite binders

Introduction. Wide introduction of fine concretes in the practice of monolithic building construction is limited by their low crack resistance due to considerable shrinkage. To reduce the shrinkage adverse effect on structure and properties of the fine concretes, it is suggested to use for their preparation composite binders, including expanding sulphoaluminate-based cements. Using the fine concrete with enhanced physical and technical properties improves produceability of construction, reduces labor input of concrete casting and allows building installations of complicated architectural forms. Material and methods. To study processes of fine concrete structure formation and properties, concrete mixes were prepared on the base of medium silica sand, dispersed ash entrainment and expanding additive. Activity of the ash entrainment increased at the expense of mechanical and chemical activation. Dispersity of the particles was monitored by means of laser granulometry. The composite binder was prepared by means of thorough homogenization of the basic CEM 42.5 Portland cement and different sorts of mineral aggregates, including an expanding additive based on calcium sulphoaluminate. Maturing conditions at a certain moisture content were simulated for every composition with subsequent evaluation of concrete performance. Results. Results of the study include effect of different mineral additives distinguishing in mineral composition, dispersivity and degree of hydraulic activity on shrinkage amount and kinetics, fine concrete porous structure parameters and strength. It is understood that amount of expansion has an effect on porous structure characteristics of the fine concrete and its strength performance. The study assessed an influence of maturing conditions on the various-composition fine concrete. A considerable influence of maintaining optimal moisture content during hydration on fine concrete technical properties is committed. Conclusions. It is understood that introduction of up to 10 % of expanding sulphoaluminate-based component in basic Portland cement allows to obtain fine concrete with enhanced crack resistance, impenetrability and longevity.

Отсевы дробления гранита как компонентный фактор формирования структуры бетона. Часть I. Постановка проблемы. Идентификация отсевов

Отсевы дробления гранита как компонентный фактор формирования структуры бетона. Часть I. Постановка проблемы. Идентификация отсевов

Influence of steam curing on properties of fiber-reinforced concrete during hardening

To increase the efficiency of steel-fiber concrete production, the existing technological operations that could reduce the costs should be optimized. This process requires scientific research and analysis of the existing results to improve the efficiency of each production stage. One of the important stages in the steel-fiber concrete production is steam curing, which is responsible for forming the cementitious matrix structure. To increase the efficiency of this production stage, a study was conducted to develop the steam curing conditions according to the rules of steel-fiber concrete structure formation and the methods of improving durability indicators. Tests on several steel-fiber concrete compositions were conducted, and the relations between its thermal conductivity and the reinforcement coefficient of concrete were revealed. The results of the tests let us conclude that with the increase of the reinforcement coefficient its thermal capacity decreases. The temperature gradient charts along the cross-section of samples with different cement/sand ratios and reinforcement coefficients were built. According to the data obtained, the optimal industrial conditions of steam curing were discovered. The dependences determining the increase of mechanical performance of steel-fiber concrete due to the formation of prestressed fiber structure in the material were revealed.

Forecasting the strength of concrete during its hardening by the acoustic-emission method

Concrete structure formation has been studied by the acoustic-emission method. Using the results of the experimental research, a relationship has been revealed between the acoustic-emission data registered during the first 24 hours of hardening of a concrete composition and its strength at the age of 28 days. Informative parameters of acoustic-emission data have been determined that correlate with the strength of the concrete composition at the age of 28 days.

Исследование влияния наноструктурных модификаторов на процессы структурообразования базальтофибробетонов

Исследование влияния наноструктурных модификаторов на процессы структурообразования базальтофибробетонов

Effect of microfillers on the concrete structure formation

Physical and mechanical properties of concrete as a composite material are determined by structure formation processes. This paper examines the effect of dispersed mineral fillers of anthropogenic origin on concrete structure formation processes and physical and mechanical properties of fine concrete. The presence of surface charge and electrosurface potential leads to the formation of electrically heterogeneous contacts between oppositely charged surfaces which determine the strength of the material as a whole. The introduction of steel microfillers leads to the formation of strong electrically heterogeneous contacts, hardening of concrete structure and increase in its strength.

Heat-Resistant Corundum Concrete Reinforced with Aluminum Oxide Fibers Synthesized Within a Matrix During Firing. Part 5. Bases of Reinforced Corundum Concrete Technology and Study of Physicomechanical Properties

It is revealed that traditional methods for introducing discrete fibers used in a concrete composite are inadequate. A special method is developed for uniform concrete mix reinforcement. It is shown that the main processes of reinforced concrete structure formation are dehydration of cement stone minerals and synthesis of original fibers within corundum. Processes are complete at 1500 – 1600°C.

Effect of Holding Temperature on Properties of Different Types of Heat-Resistant Concrete

With a different exposure temperature within concrete based on alumina cement there is formation of different hydrated phases, i.e., amorphous or crystalline AH3, crystal hydrates CAH10, C2AH8, and C3AH6. In developing or modifying refractory concrete composition it is necessary to consider the effect of holding temperature on concrete structure formation and operating properties. Properties are studied for traditional heat-resistant concrete, modified with addition of micro-alumina, and that based on a chamotte filler with aluminate cement grade Gorkal 70 with holding temperatures of 10, 20, and 30°C. The effect of differences in concrete structure formation with maturity over 48 h is studied by an ultrasonic method. It is established that differences in structure formation during concrete maturity affect concrete properties after firing at 1100 and 1200°C.

Development of refractory concrete for extreme conditions

Comparative analysis is provided for the properties of medium-cement refractory concrete with microsilica based on mullite filler in relation to different type of deflocculant. The effect of different deflocculants on refractory concrete structure formation, hydration, rheology, strength and heat resistance is discussed. Corrosion resistance test, determined that samples with hybrid deflocculant showed better resistance for slag penetration than samples with only the sodium tripolyphosphate or polycarboxylate ether deflocculant. Moreover, a composition of hybrid deflocculant let to control the rate of the hydration process and to get features of refractory refractory concrete.