"Вестник МГСУ"

Subject of Study: the creation and analysis of mathematical models adequately describing the effect of the input variable factors - the proportions of raw components of the concrete mix - on the compressive strength of high performance fine-grained concrete at the age of 28 days of normal hardening, which are considered as output objective functions. Objectives: to determine the optimum ratios of ingredients of fine-grained concrete mixture, which allow us to achieve the maximum strength of concrete in compression. Materials: for obtaining fine-grained concrete mix, a finely distributed binder was used consisting of Portland cement of the type CEM II 42,5 N produced by the “Hoang Thach” factory, fly ash, rice husk ash (all - Vietnam) with addition of superplasticizer Ace 388 BASF (Germany) and polypropylene fine fibers Mega Mesh (Malaysia). As for the fine filler, quartz sand from the Lo river (Vietnam) was used. Methods: the compressive strength of high performance fine-grained concrete was determined in accordance with the requirements of GOST 10180-2012 “Concretes. Methods of strength determination by control samples”; the initial composition of the concrete mix was calculated using the absolute volume method. Results: the paper presents results of mathematical modeling of the effect of raw materials on the compressive strength of high performance fine-grained concrete at 28 days of normal hardening. First and second order regression equations for the dependence of the compressive strength on the ratio of raw materials x2 () and x3 () and also the image of the surface expression and the contour of the objective function for these regression equations were obtained. Conclusions: The maximum value of compressive strength of high performance fine-grained concrete at 28 days of age, evaluated by using the computer program Maple 13 in the regression equation of the second order, is R = 75.85 MPa at = 0.854 and = 0.324.

Subject: nowadays self-compacting concretes (SCC), the use of which requires no additional compaction, have become widespread for use in densely-reinforced structures and hard-to-reach places. In self-compacting concretes, finely-ground admixtures-microfillers are widely used for controlling technological properties. Their introduction into the concrete mix allows us to obtain more dense structure of concrete. The influence of micro-fillers on water consumption and plasticity of concrete mix, on kinetics of strength gain rate, heat release and corrosion resistance is also noticeable. Research objectives: the work focuses on the development of composition of self-compacting concrete with assigned properties with the use of fly ash based on coal burning waste, optimized with the help of experimental design method in order to clarify the influence of ash and cement quantity, sand size on strength properties. Materials and methods: pure Portland cement CEM I 42.5 N was used as a binder. Crushed granite of fraction 5…20 mm was used as coarse aggregate, coarse quartz sand with the fineness modulus of 2.6 and fine sand with the fineness modulus of 1.4 were used as fillers. A superplasticizer BASF-Master Glenium 115 was used as a plasticizing admixture. The fly ash from Cherepetskaya thermal power plant was used as a filler. The study of strength and technological properties of self-compacting concrete was performed by using standard methods. Results: we obtained three-factor quadratic dependence of strength properties on the content of ash, cement and fraction of fine filler in the mix of fine fillers. Conclusions: introduction of micro-filler admixture based on the fly ash allowed us to obtain a concrete mix with high mobility, fluidity and self-compaction property. The obtained concrete has high strength characteristics, delayed strength gain rate due to replacement of part of the binder with ash. Introduction of the fly ash increases degree of hydration of Portland cement due to the greater water retention capacity, and also contributes to reduction in total capillary porosity of SCC structure.

This paper presents a study of the capability to modify cement by mechanical activation of sodium silicate water solution. Admixtures or blends of binding agents were employed for modifying concrete properties. The liquid glass is applied to protect from chemically or physically unfavorable environmental impacts, such as acidic medium and high temperature. The sodium silicate is a high-capacity setting accelerator. The increasing of the liquid glass proportion in the mix leads to the degradation of the cement paste plasticity and for this reason it is necessary to reduce the amount of liquid glass in the cement paste. The activation of dilute water solution of sodium silicate into rotary pulsating apparatus directly before tempering of the cement paste is an effective way to decrease mass fraction of liquid glass in the cement paste. The results of the combined influence of liquid glass and mechanical activation on physicochemical processes taking place in cement stone are represented in this research. Thermogravimetric analysis was used in order to study cement blends. Thermogravimetric analysis of modified cement stone assays was performed by thermo analyzer SETARAM TGA 92-24. The results of the analysis of phase transition taking place under high-temperature heating of cement stone modified by the mechanical activation of the water solution of the sodium silicate were introduced. Thermograms of cement stone assays were obtained at different hardening age. The comparison of these thermograms allows us to come to a conclusion on the formation and the retention during long time of a more dense structure of the composite matrix mixed by the mechanical activation of sodium silicate water solution. The relation between the concrete composition and its strength properties was stated. Perhaps, the capability of modified concrete to keep calcium ions in sparingly soluble hydrosilicates leads to the increase in its durability and corrosion resistance.

The purpose of the research consists in development of integrated micro dispersive additives designated for effective fine-grained concretes of the new generation and based on the inferior grade quartz sand.The academic novelty of the research consists in substantiation of feasibility of generation of effective fine-grained concretes that demonstrate improved physical and mechanical properties due to the adjustment of the structure of the integrated micro additive developed by the authors.The integrated additive comprises quartz sand milled in the ball mill together with C-3 plasticizer, the content of which is equal to 1 % of the mass of the material, and the milling time is 60 min. Another objective of the research is the study of the effect of micro-additives produced onto physical-mechanical properties of samples of fine-grained concretes (dimen-sions 4×4×16 cm) made of cement M 500 D20 and quartz sand with Mhardened according to the regular procedure.= 0,9 andThus, the authors have discovered that the integrated micro-additive improves the compressive strength of the concrete to 50 MPA, flexural strength — up to 8,3 MPA, water absorption — to 1,4 % and frost resistance — to F75, while its content reaches 5—10% of the cement mass.

The subject of research is the effect of mechanic and magnetic treatment of different concentrations of the aqueous solution of fluidifier S-3 produced onto the concrete mix rheology, compressive strength and structure formation. Mechanic and magnetic treatment was performed by the pulsed rotor machine equipped with a permanent magnet. It is identified that mechanic and magnetic treatment of the water added into the fluidifier improves the flowability of the concrete mix in comparison with the flowability of the concrete mix prepared absent of treated water, although the amount of the fluidifier meets technical specifications. S-3 fluidifier content in the mix that has treated water is smaller than the same content in a standard mix by several hundreds of times. The concrete mix that has treated water demonstrates highest flowability. The water-to-cement ratio was fixed at 0.4 for all specimens under consideration. In addition, the concrete that has treated water and a minimal amount of S-3 fluidifier (5% of the cement mass) demonstrates that its compressive strength is by far higher than the one of the concrete prepared through the application of the conventional approach that contemplates a standard fluidifier consumption rate. Following a thermal analysis, a thermogravimetric analysis and an X-ray diffractometry, it was discovered that the application of treated water accompanied by the minimal consumption of S-3 fluidifier caused the structure of the concrete cement stone to be more compact, while it demonstrated higher crystallization and stronger interphase interaction. Therefore, considerable reduction in the consumption of S-3 fluidifier, coupled with mechanic and magnetic treatment of the water improves concrete strength properties while concrete flowability does not deteriorate.

The modern tendencies of construction industry development are connected with the use of new high-efficient materials with the application of resource- and energy-saving technologies of their generation. The use of industrial man-made products as the components improving the characteristics of construction products is now a promising field of research. The article presents the results of the use of waste pickling solutions of steel rolling factories, containing salts of iron as nanomodified additives for the products based on cement binder. The effectiveness of the influence of the considered additives on the structure and strength of fine-grained concrete is shown. If using this additive in the amount of 0.32 % from the mass of cement for 28 days of natural hardening, the fine concrete strength is growing by 1.8 times due to additional formation of hydrosilicates, densification of structure and reduction of the total porosity of the cement system by 2 times.

Subject: among the modern heat-insulating materials lightweight concrete on porous aggregates is widely used. Currently, porous aggregates are mainly represented by expanded clay gravel, which has some drawbacks in its physical and mechanical properties: high content of split grains and significant grain shape factor. The presence of split grains in expanded clay gravel leads to an increase in consumption of cement paste. Significant grain shape factor limits the use of expanded clay gravel in lightweight concrete of higher strength. Granulated foam glass is an alternative porous aggregate for lightweight concrete. It is characterized by high physical and mechanical properties and low values of thermal conductivity. Research objectives: in this article, the results of studies of physical and mechanical properties of expanded clay gravel and granulated foam glass are presented, the differences between these materials are revealed and the possibility of using granulated foam glass as a porous aggregate in lightweight concrete is studied. Materials and methods: properties of granulated foam glass and expanded clay gravel are determined according to the standards. Conclusions: according to the test results, it was found that granulated foam glass has higher values for a complex of physical and mechanical properties in comparison with expanded clay gravel, produced traditionally. However, the compressive strength test in the cylinder showed that the granulated foam glass has a significantly lower strength than the expanded clay gravel with the same value of their apparent density. Also during the tests, the possibility of using granulated foam glass to obtain a lightweight concrete corresponding to the grade class B5 and density class D1000 was established. In this case, there is a need to adjust the grain-size composition of the aggregate and component composition of concrete mixture.

Introduction. This study focuses on the use of silica fume partially replacing cement with 0, 5, 7.5, 10, 12.5 and 30 % constant replacement of fly ash by weight of cement in concrete. Concrete is probably the most extensively used construction material in the world. But the conventional concrete is losing its uses with time and high-performance concrete (HPC) is taking that place. HPC has superior mechanical properties and durability to normal strength concrete. Because of, the microstructure of HPC is more homogeneous than that of normal concrete (NC) due to the physical and chemical contribution of the mineral admixtures as well as it is less porous due to reduced w/c ratio with the addition of a superplasticizer. The inclusion of additives helped in improving the properties of concrete mixes due to the additional reduction in porosity of cement paste and improving the particle packing in the interfacial transition zone (between cement paste and the aggregates).In this experimental investigation the behavior of HPC with silica fume and fly ash with and without quartz powder were studied. The water-binder ratio was kept 0.3 and 20 % quartz flour as partial replacement of fine aggregate for all cases. Materials and methods. Used materials in Vietnam, as follow, Sulfate-resisting Portland cement - PCSR40 (type V) of company Luks Cement (Vietnam) Limited was used in the work. Crushed granite of fraction 9.5…20 mm - as coarse aggregate, Natural sand from Huong river of 0.15…2.5 mm fraction with the fineness modulus of about 3.0 and quartz powder with an average particle size of 5…10 μm were used as fillers; Sika® Viscocrete®-151 is a superplasticizer based on a blend of 3rd generation PCE polymers was used as a plasticizing admixture. The flg ash from Pha Lai thermal power plant and Sika silica Sikacrete® PP1 (particle size < 0.1 μm) was used as a mineral active admixture. The study of strength and technological properties of high-performance concrete was performed by using standard methods. Results. Established by icate that, the workability and strength increase at a certain level and after that, they decline with further increase in the replacement level of silica fume is 12.5 %, on the basis of 30 % FA replacement, the incorporation of 10 % SF showed equivalent or higher mechanical properties and durability compared to the reference samples. Conclusions. HPC consists of mineral admixtures such as silica fume and fly ash use combine quartz powder and superplasticizer helped in improving the strength and durability of concrete mixes due to the additional reduction in porosity of cement paste and an improved interface between it and the aggregate. With 30 % fly ash is optimum dosage used to replacement of cement, incorporation 10 % SF (by weight) and combine of partial replacement of fine aggregate by 20 % quartz powder. On the other hand, a few mathematical equations can be used to derive the durability properties of concrete based on its compressive strength.

Subject: operation of concrete and reinforced concrete hydraulic structures on river systems and in the extended coastal zone of Vietnam takes place under the influence of aggressive environments, which significantly limits their service life. Therefore, the search for ways to solve the problem of increasing the durability and terms of maintenance-free operation of such facilities is very important. Previous studies have established the possibility of increasing the operational performance of hydraulic concrete (HC) by modifying their structure with complex additives that combine the water-reducing and densification effects. The possibility of increasing the quality of hydraulic concretes by using rice husk ash (RHA) as a finely dispersed mineral additive with high pozzolanic activity was also established. Research objectives: modification of the structure of hydraulic concrete; determination of the effect of an organo-mineral modifier consisting of RHA in combination with a superplasticizer on water resistance, chloride-ion permeability and strength of hydraulic concrete. Materials and methods: portland cement of type CEM II 42.5 N was used with the addition of rice husk ashes and a superplasticizer ACE 388 “Sure Tec” BASF. Quartz sand and limestone crushed stone were used as aggregates. Composition of the concrete mixture, compressive strength of concretes, water resistance and permeability of the concrete structure for chloride ions was calculated based on methods of Russian and international standards. Results: the use of an organo-mineral modifier consisting of a water-reducing superplasticizer ACE 388 and finely dispersed rice husk ash leads to a densification of the HC structure, which increases their water resistance and decreases the permeability for chloride ions. Conclusions: it was found that the introduction of the developed organo-mineral additive into the concrete mixture leads to densification of the concrete structure, contributes not only to the growth of compression strength at the age of 28 days by 32 % for HC-10, 23 % for HC-20 and 9 % for HC-30, but also to the increase of its water resistance by one or two marks. In addition, there is a significant decrease in the permeability for chloride ions of HC samples containing 10, 20 and 30 % RHA by mass of the binder, since the average value of electric charge that have passed through the samples made of HC-10, HC-20 and HC-30 were 305, 367.5 and 382.7 K respectively against 2562 K for control samples made of non-modified concrete without RHA. (The experimental results of measuring permeability for chloride ions were obtained according to standard ASTM C1202-12). Our study has confirmed the assumption that the introduction into the concrete mix of organo-mineral modifier consisting of a polycarboxylate superplasticiser and fine ash of rice husk, up to 90 % consisting of amorphous silica, will increase the density of hydraulic concrete structure, which will increase their strength, water resistance and reduce permeability for chloride ions.