bluuebunny/crossref_metadata_2025 huggingface dataset:
Eco - concrete made with phosphogypsum-based super sulfated cement
Authors: Ngoc Lam Nguyen
Published: July 2020

Phosphogypsum is an important environmental issue for all countries with phosphate and phosphoric acid industries from phosphate rock. The problem mainly stems from the difficulty in storing phosphogypsum. Therefore, the reuse of phosphogypsum in producing construction materials plays an important role to protect human health, to decrease the environmental pollution and to reduce the building materials cost. This research aimed at developing an eco concrete using super sulfated cement (SSC) in which the phosphogypsum was recycled. The present paper deals with the experimental investigation on slump number of fresh concrete, 28-day compressive strength characteristics of concrete using only 10% cement, 30% - 60% phosphogypsum and granulated blast furnace slag in binders named super sulfated cement with 3 different water-binder ratios of 0.45, 0.50 and 0.55… It is shown that Portland cement can be replaced with super sulfated cement based on Vietnam phosphogypsum to develop a good and hardened concrete to achieve economy; The compressive strength of concrete can achieve 20-40MPa. This value is enough for the use of the eco-concrete in the construction industry. The results also indicate that the increase of replacement of phosphogypsum in concrete lead to reduction in the compressive strength but do not affect too much in the case of slump number.
Effects of some factors on compressive strength of structural polystyrene concrete
Authors: Minh Duc Hoang , Ly Le Phuong
Published: July 2020

Structural polystyrene concrete is a lightweight composite consisting of lightweight expanded polystyrene aggregates immersed in a cement matrix. Compressive strength of structural polystyrene concrete can be increased by increasing compressive strength of cement matrix. Increasing strength of lightweight expanded polystyrene aggregate or improving interfacial transition zone between them is inefficient because the strength of polystyrene beans and their bond with cement matrix are negligible. In this case, the characteristic of normal aggregate in cement matrix plays an important role. The research results in this paper show that increasing of maximum particle size of normal aggregate in cement matrix significantly decreases the compressive strength of polystyrene concrete with given density. Therefore, the coarse aggregate smaller than 10 mm is recommended for structural polystyrene concrete with density less than 1,600 kg/m3.
Internal relation between hydration kinetic and endogenous shrinkage in an ettringite-based compound
Authors: Nguyen Ngoc-Lam
Published: July 2020

Ettringite based compound is a new materials used in construction because of high early-age strength, good chemical resistance, low CO2 emission…etc. However, research on not only the microstructure characteristics but also macrostructural properties and their internal relation is very limited. The aim of this study is to evaluate the relation between the microstructure characteristics such as chemical shrinkage and ettringite development by the infrared spectroscopy method with endogenous volumetric shrinkage in case of an ettringite based compound without setting regulators. The results indicated the evolution of the ettringite measured continuously by the infrared spectroscopy method corresponds to the development curves of the endogenous and chemical shrinkage. The swelling phenomenon expressed by volumetric shrinkage measurement related to the ettringite formation is verified by infrared spectroscopy and DRX technic. The greater the amount of ettringite formation, the more swelling of the compound increases.
Influence of mortar matrix on properties of light weight concrete with foam glass granules
Authors: Hoang V L
Published: July 2020

Foam glass granule (FGG) is commonly used as an aggregate for light weight aggregate concrete (LWAC). Because bulk gravity of FGG is much less than that of mortar matrix, segregation is tended to occur in LWAC mixtures. Mortar plays an important role in properties of LWAC with FGG. Therefore, this paper presents research results of influence of mortar matrix to properties of this type of concrete. In the study, the raw materials were FGG, But Son PC40 cement, Pha Lai fly ash and Sikament plasticizer named R4. The experimental results showed that with FGG content of 40% by volume and flow of mortar at 21- 22 cm, the LWC mixture was homogeneous and its slump was at 3.5- 5.5 cm. Simultaneously, the LWAC’s density was 1400-1500 kg/m3 and its compressive strength at 28 days was over 11 MPa.
Effect of temperature on the physico-mechanical and microstructure properties of cement pastes containing fly ash and silica fume
Authors: Phuong Do Thi , Lam Nguyen , Duc Vu Minh
Published: July 2020

This study aimed to investigate the effect of heat treatment on the physico-mechanical and microstructure properties of cement pastes containing fly ash (FA) and silica fume (SF). Portland cement (OPC) has been partially replaced by 5% SF and 20, 30, 40 and 50 wt.% FA. After curing, the hardened cement pastes were dried at 100°C for 24 hours, subjected to thermal treatment at the rate of 5°C/min, and heated at temperature of 200, 400, 600, 800, 1000°C for 2 hours, then cooled to room temperature in air. Finally, their bulk density and compressive strength were determined. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods and were used for identification of the changes in the microstructure of the cement matrices. The results showed that the cement pastes containing 80% OPC + 5% SF + 15% FA is the optimum mix which gives a higher compressive strength and lower bulk density loss. Moreover, this optimum binder has the formation of inner fibers and crystalline needle like Wollastonite, Gehlenite which is responsible for the reduction in compressive strength loss from 800 up to 1000°C.
Influence of AAC grains on some properties of permeable pavement utilizing of CDW and industrial by-product
Authors: Tuan Ngo Kim , Dung Nguyen Tien , Minh Phan Quang , Tuan Nguyen Van , Kawamoto Ken
Published: July 2020

Construction and Demolition Waste (CDW) has been being accounted for a large amount of waste in urban areas around the world, especially for developing countries like Vietnam due to rapid urbanization and economic growth. The recycling and reuse of CDW are not only significant in reducing the consumption of natural materials but also can be a solution to improve the urban environment. In recent years, several studies have shown that the use of recycled materials from CDW in permeable pavement systems has a good effect on hydrological aspects and soil absorption capacity, thereby minimizing the risk of flooding and ground water depletion, increasing heat island effect. In this study, two main types of aggregates used are recycled aggregate (RA) and autoclaved aerated concrete (AAC) grains recycled from industrial by-products. The workability and forming ability are greatly affected by the moisture of the material before mixing. The results show that increasing AAC grain size leads to a slight decrease in the porosity of pervious concrete with the same AAC content. On the other hand, increasing AAC content from 5 to 10% results in significant fall in void content from 18% to 14.5%, thereby decreasing drainage speed. The compressive strength values show that without AAC, pervious concrete has the highest mechanical strength while increasing content and size of AAC leads to the compressive strength decreases. The surface temperature of pervious concrete samples is 4 – 5°C lower than that of normal concrete surface due to the increased effective surface area. The use of AAC grains helps to reduce the sample surface temperature by another 4°C.
Lightweight Geopolymer Concrete Panels for a wall in high-rise buildings: Technical- Economical- Environmental efficiency
Authors: Tong Kien T.
Published: July 2020

Brick and cement are two of the most used materials for a building wall, but the traditional brick and clinker production causes several environmental and human health impacts. Besides the demand of light-weight materials for the high-rise buildings is increasing more and more, these have encouraged the development of the new efficient materials to alternative the conventional brick. The objective of this study is to comparative technical and cost analysis as well as an environmental assessment of the wall structure used Lightweight Geopolymer Concrete Panels (LGCP). The results have revealed that the LGCP exhibits some superior engineering properties like as very low density and heat transfer coefficient, high strength,… The utilization of industrial wastes (fly ash-FA, Ground Granulated Blast furnace Slag-GGBS) as raw materials in LGCP production leads to reduce over 48% CO2 emission, and up to 17 times energy consumption, but still cheaper 42% construction cost to conventional bricks. The LGCP application is an important step to contribute better environmentally-friendly in particular and reach a sustainable development of the construction industry in general.
Contribution of calcium aluminates to the water resistance of hydrated calcium sulfates
Authors: Dung Nguyen Tien , Ambroise Jean
Published: July 2020

The water sensitivity of calcium sulphate materials has been known for a long time. In a humid atmosphere, plaster elements can become veiled under the action of their own weight because a low water uptake of 3% by mass can cause a drop in compressive strength of 50%. The low water resistance of calcium sulfates limits the applications of these materials to decorative elements or interior coatings despite their strengths compared to other construction materials: good fire resistance, low CO2 emission and low production cost. The objective of our research work is to evaluate the insensitivity of calcium sulfates to water by ettringitic binders containing calcium aluminate cement (CAC). Four types of calcium sulfates have been studied: natural gypsum, hemihydrate-α, hemihydrate-β, and synthetic anhydrite. In this research, only the majority binders of calcium sulfates will be studied: [70%, 80% of Calcium sultates with 30%, 20% of CAC]. The experiments results have shown that in high-calcium sulphate binders (≥ 70%), CAC helps reduce the water sensitivity of binders regardless of the nature of calcium sulphate by decreasing the total porosity, which leads to an increase in mechanical strengths; and reducing the connectivity of the pores, which contributes to reducing the entry of water and its movements into the material and consequently, reducing the degradation of the test pieces during immersion tests in the water.
Assessment of the compressive strength and strength activity index of cement incorporating fly ash
Authors: Trong Lam Nguyen
Published: July 2020

In recent years, the utilizations of industrial by-product as substitute for non-renewable material in cement and concrete production has received significant attention for sustainable development goals. In this study, fly ash blended cement was produced by replacing 5%, 10%, 15%, 20%, 25%, 30% and 35% by weight of Portland Cement with fly ash. In addition, the loss on ignition (LOI) content of fly ash, which used for the 20% replacement ratio, varies from 5 to 20% to assess the effect of unburnt carbon content in fly ash on the strength activity index of fly ash blended cement. The experimental results show that the addition of fly ash reduces the compressive strength of the mortar and strength activity index of fly ash blended cement at early ages. However, the presence of fly ash increases the strength of the mortar and the strength activity index of fly ash blended cement at longer ages when the fly ash replacement ratio is lower than 25%. The unburnt carbon in fly ash does not reduce the strength of the mortar and strength activity index of fly ash blended cement when its content does not exceed 20%.
Using iron alum in surface water treatment
Authors: Tuan Vo Anh , Tuan Pham Ngoc , Huy Huynh Quang , Thuy Duong Nguyen Phan , Xuan Vinh Phan Dinh , Duong Hoang Canh
Published: July 2020

Surface water contains clay, bacteria, dissolved metals, organic matter, color, other suspended solids. The purpose of coagulation and flocculation is to remove these suspended particles which ensure proper operation in treatment plant. Improper use of coagulant dosage affects water quality after treatment, cause operation problems and production costs. A study is being conducted at a surface water treatment plant at Dong Nai River with the capacity of 300,000 m3/day. The treatment process uses iron alum for coagulation and flocculation. Due to the high corrosion property of iron alum and the residue effects of the quality of treated water, it requires strict control in the treatment process as well as the chemical dosage. The main aim of this study is to determine appropriate amount of alum used for the coagulation-flocculation process. Research method is data collection including: turbidity, pH, flow rate of raw water, dosage of iron alum, lime, polymer used in current treatment process. Then, find the model using iron alum by linear regression analysis and BMA methods on R tool platform. Next, verify the appropriate linear regression model of iron alum by Jar test experiment. Results revealed that the BMA model is not suitable for the application because one Jar test results has a mean turbidity value greater than 4 NTU, which does not meet the water quality requirements after sedimentation tank according to the water treatment regulation. The linear regression analysis showed that raw water turbidity and season are two independent factors related to the alum dosage, of which these two factors explain about 78% of the differences that affect the coagulation-flocculation process. This study was successful in determining the appropriate iron alum dosage for the water treatment plant, which can be applied similarly to build appropriate chemical model for water surface water plants and raw water resources.
Modeling of water and air operation mode of sewer pipelines
Authors: Orlov Vladimir , Zotkin Sergey
Published: July 2020

An approach to complex accounting of hydraulic and aerodynamic parameters of a gravity sewage pipeline for the purpose of solution of its designing and effective operation problems has been presented herein. Consideration has been made of the variants which provide the subsurface space ventilation of a gravity pipeline in presence of aggressive and fetidly smelling gases by a mechanical air exchange system. Taking into account the complexity of manual processing of mathematical dependencies that describe the operation of a gravity pipeline and the processes that take place in it, the implementation of the problem has been achieved by developing and applying a special automated calculation program. At the corresponding values of air exchange, the dynamics of harmful gaseous substances released into the subsurface space of the gravity pipeline per unit of time, as well as the duration of their removal to the maximum permissible concentrations in the surrounding air space of populated areas, have been revealed.
Influence of ultrasound on the concentration of hydrogen ions in water
Authors: Vikulin Pavel , Vikulina Vera
Published: July 2020

The paper deals with the physical and chemical effects arising in water under the action of the energy of elastic vibrations of ultrasonic frequency in the cavitation mode. Cavitation state is characterized by the formation of the gas and air cavities - bubbles in the aquatic environment. The theory of occurrence of high temperatures at the moment of collapse of a cavitation bubble in water is given. It is noted that there is a dissimilation of the substance of free active radicals, dissociated and ionized molecules. The kinetics of chemical reactions in the ultrasonic field under the cavitation regime is described. Methods for obtaining ultrasonic cavitation in a liquid medium with a description of the generation of ultrasonic vibrations and a list of transducers and types of emitters are given. A relatively wide spectrum of radiated frequencies and instability of frequency and amplitude of oscillations are considered. The choice of ultrasonic generator is justified due to the necessary frequencies and intensities for the excitation of cavitation in water (f = 18-22 kHz, I = 2.0 W/cm2), technological considerations about the possibility of mounting the transducer in an existing production line, as well as safety and efficiency issues. The relevance, purpose and objectives of the work are formulated. The equipment and methods of experimental research are presented. Laboratory experimental studies on the effect of ultrasonic vibrations in the cavitation mode on the change of water pH were carried out. It is shown that bubbles formed in the ultrasonic field in the studied water collapse and create micro-explosions, shock waves and micro-flows. The results of studies on the change of pH in water are shown and the analysis of experimental data is performed. The experimental studies made it possible to substantiate the conclusions of this work and to formulate a conclusion about the influence of the ultrasonic field in the cavitation mode on the pH of the aqueous medium and its further application in water treatment processes.
Spread waves in a viscoelastic cylindrical body of a sector cross section with cutouts
Authors: Mirsaidov Mirziyod , Safarov Ismoil , Boltayev Zafar , Teshaev Mukhsin
Published: July 2020

In this article an analysis of well-known works related to wave propagation and dispersion dependences in a cylindrical waveguide are presented. A mathematical model, methodology and algorithm for solving the problem of wave propagation in a cylindrical waveguide, having a sector cut are developed. The obtained equations are solved by the orthogonal sweep method in combination with the Mueller and Gauss methods. The dispersion relation for a viscoelastic cylindrical waveguide, having a sector cut in cross section at an arbitrary angle is obtained. Based on the obtained results, it was found that, there are no waves in the elastic cylinder of a sector section with real parts of the phase velocity. It has been established that, in the case of a wedge-shaped viscoelastic cylindrical panel, for each mode, there are limiting wave propagation velocities and they change with a change in the radius of curvature. The spectral sets of normal waves with an increase in the angular parameter of the sector cut-out, corresponding to lower non-zero frequencies of wave locking, slowly decrease.
Centralization of gas supply systems based on butane-air mixture
Authors: Osipova Nataliya , Kultyaev Svyatoslav
Published: July 2020

The expansion of the construction of cottage villages, isolated settlements in ecologically clean areas, away from large cities, as well as the provision of gas to the settlements of the eastern part of the Russian Federation, sets the task of developing autonomous gas supply systems. A significant deterrent to the development of autonomous gas supply systems based on butane mixtures with air is their high cost and the absence of scientifically sound recommendations for choosing system parameters. To develop scientifically sound recommendations for the design of systems, considering all the factors of influence that ensure the optimal cost of gasification and subsequent maintenance by the consumer, additional studies are necessary. The article considers the choice of optimal centralization of gas supply systems based on a mixture of butane with air to determine the minimum cost of construction and operation for consumers. the systems analysis, mathematic model methods with calculation of optimal values in the presence of corresponding limits and the methods of material correlation processing are used. The data have been obtained for effective centralization of gas supply systems based on butane-air mixture. The criteria are set which influence the optimum number of houses connected to a tank installation, such as population density in a gas supplied area, climatic features of an area, a type of consumer’s gas-using equipment and a form of settlement development. As a result of the research, the optimum number of apartments has been determined for gas supply to a settlement connected to a tank installation. These recommendations will make it possible to increase efficiency of gas supply source selection and consumer connecting to a gas sup-ply network at minimum cost for consumers
Natural ventilation and aerodynamics of orthodox churches
Authors: Kochev Alexey , Sokolov Mikhail , Lushin Kirill
Published: July 2020

The paper devoted to introducing of theory and practice results of natural ventilation and properties of external aerodynamics of orthodox churches research. The features of the movement of air flows inside the temple are considered. On the example of the Transfiguration Cathedral, the analysis of the fields of aerodynamic coefficients is introduced.
Pilot studies on the river water treatment using coagulation-UF membrane filtration and direct UF membrane filtration
Authors: Nakanishi H , Yabuno Y , Nishikawa T , Yasui T , Pham A T , -A Nguyen V
Published: July 2020

The pilot tests of UF membrane filtration for river surface water were carried out with coagulation as a pre-treatment (test 1) and without coagulation (test 2). Both UF membrane filtrate water of the test 1 and the test 2 met drinking water quality standard in Vietnam. Additionally, the TMP and the filtration flow rate were kept stably during test periods without changes in operation conditions although the river water turbidity was varied due to heavy rain. It was indicated that the water treatment system can be simple by skipping coagulation and/or sedimentation as pre-treatments. The filtration flux of the test 1 and the test 2 were 138 L/m2 h and 93 L/m2 h, respectively. The flux was higher than the reported reference value indicating that the module number of modules required for the water treatment plant can be reduced by using the FG module. The test data of the test 2 was theoretically analysed by the equations based on Darcy’s low. The estimated TMP correlated highly with measured value (R2=0.71). The optimized parameters were used for the simulation of the operation. The simulation results indicated that the TMP before backwashing is increased around 35 kPa when the river water turbidity increased up to 500 NTU. It was indicated that the CIP interval should take into account the TMP increasing by turbidity variation.
Scenarios for treatment of sewage sludge from municipal wastewater treatment plants in Hanoi towards energy efficiency and resource recovery
Authors: Hoai An Vu Thi , Viet Anh Nguyen , Minh Thanh Vu Thi
Published: July 2020

Wastewater treatment plants (WWTPs) generate significant amount of sewage sludge (SS). Besides, faecal sludge (FS) generated from popularly existing septic tanks in cities need also adequate treatment. Selection of appropriate sludge treatment options is among most challenging wastewater management issues for fast growing cities. The case study has selected the central part of Hanoi city, with expected population of 2,145,437 persons by 2030, total design capacity of WWTPs 588,300 m3/day, whereas different options of SS and FS management were analysed. The calculation results shown that an energy required for operation of sludge treatment processes in scenarios 2, 3 and 4 could be fully self-sufficient. Besides, with total energy demand for operation of WWTPs was of 311,799 kWh/day, 21.3% (scenario 2), 99.3% (scenario 3) or 71.3% (scenario 4) of demand could be covered by remaining biogas produced from anaerobic co-digestion of SS and FS. A conventional SS treatment process, dewatering by centrifuge and dumping dewatered sludge to the landfill (scenario 1) did not generate any energy but required an energy of 17,371 kWh/day for SS treatment and dumping. Anaerobic co-digestion of SS, FS, other organic fractions, can be a promising sludge management solution aiming at energy efficiency and resource recovery.
Influence of weather conditions on energy consumption of controlled blowers at WWTP
Authors: Ustiuzhanin Andrei , Chizhik Konstantin , Bazhenov Victor
Published: July 2020

The object of analytical research are controlled air blower units of wastewater treatment plants (WWTPs) for wastewater utilities with pneumatic aeration systems for biological processes, based on oxygen consumption. The goal of analytical research is accounting and estimation values of temperature, relative humidity, atmospheric pressure for energy consumption by controlled air blowers. The system of equations is proposed for the joint solution: 1st equation - according to the Guide to Meteorological Instruments and Methods of Observation; 2nd equation - modification for determining the energy consumption for the blower unit P wire in kW. These form the analysed mathematical model with the following results of study. Fluctuations in the full range of operating temperatures leads to a change in power consumption in the range –14.9 to 19.9%. Fluctuation of atmospheric pressure in the full range leads to a change in power consumption in the range from –3.4 to 3.7%. Relative humidity affects power consumption only in combination with high temperature (between 20-40°C the maximum influence of relative humidity is 0.6-3.3%). The combined influence of all three parameters in the full range is from –9.2 to 11.2%. All presented data are supplied also for the range of average values.
Innovative unit for water treatment
Authors: Govorova Zhanna , Semenovykh Vasiliy , Govorov Oleg
Published: July 2020

The main pollutants of groundwater sources are compounds of iron, manganese and and dissolved gases (carbon dioxide, hydrogen sulphide). Requirements to small capacity groundwater treatment units specified by a group of consumers were reviewed in this work. Various aeration units are used at the first stage as a part of simplified aeration method in deferrization process flow chart. There is offered an innovative unit which combines several processes, such as aeration, degassing, filtering through the layer of expandable polystyrene foam. The unit allows excluding additional aeration units, washing pumps and flush water storage tanks, as well as to intensify the aeration-degassing process, increase treatment efficiency and provide specified requirements. The article contains data on modular units with capacity up to 1 m3/h, their operating principle and the laboratory equipment used, as well as the aeration and degassing processes analysis results. When the level of dissolved oxygen in groundwater reaches 1.24-1.64 mg/l and free carbon dioxide - 46.8-50 mg/l outbound of the aeration units dissolved gases are blown out (up to 36%), the concentration of oxygen increases up to 7 mg/l. which is enough for an effective water deferrization process. At the same time, this process takes less time up to 2.7) in the aeration unit rather than in the aeration column.
Investigation of groundwater recharge mechanism for sustainable urban water system planning and management in Hanoi city
Authors: Thi Viet Nga Tran
Published: July 2020

Seasonal variation of water levels and water quality of groundwaters and ponds was investigated to illustrate the recharge mechanism and seasonal effects of groundwater in Hanoi suburbs. Water level monitoring data showed that the upper aquifer had a fluctuating water level (variation: 2.0 m) corresponding to heavy rains, representing a substantial impact by infiltration of rainwater from the surface and perhaps pond water. In the area with less permeable surface, there was small response to rainy events, suggesting that the ground water levels were governed by a regional scale groundwater flow. The stable isotope ratios in pond waters had a clear seasonal change, in which isotopes were enriched throughout the dry season. In groundwater, isotope signatures indicated that the dominant sources had evaporation process. In studied areas, the isotope ratios in groundwaters and pore waters in the shallow soil (<25 m depth) were clearly heavier than that in the deep soil. Isotope results suggested that groundwaters close to the Red River are largely recharged by the river itself. In areas far from the river, surface waters having evaporation process (e.g., ponds and paddy fields) and the rainwater directly infiltrating from the surface mainly recharges the upper aquifer. The lower aquifer in inland locations would be recharged by lateral inflow, either from the Red River or surrounding mountains. The results revealed the recharge mechanism for groundwater budget which could contribute for the planning and sustainable development of urban water system in Hanoi City.
Proposal of a set of quantitative criteria for evaluating and classifying urban street flooding spots in Vietnam
Authors: Nguyen Viet-Phuong , Pham Tuan-Hung , Ung Thi-Thuy-Ha , Hoang Tung , Tong Ngoc-Tu
Published: July 2020

Street flooding in urban areas in Vietnam has always been a stress issue despite the municipal government’s investment in renovating and upgrading the drainage system. Until present, in order to evaluate and classify street flooding spots, the authorities have been applying the criteria specified in Document No. 338/BXD-KTQH issued by Ministry of Construction dated March 10, 2003. Despite their certain efficiency and value, the current criteria have not shown how the flooding spots affect traffic and not clarified how to measure or determine the parameters as a basis for flood classification, etc. Therefore, the Ministry of Construction has ordered the research team to develop a set of quantitative criteria for evaluating and classifying the street flooding spots in Vietnam. Accordingly, this paper presents the results of the study in contribution to more effective management of urban infrastructure.
Optimal use of solar collectors in small-scale districts
Authors: Zajacs Aleksandrs , Borodiņecs Anatolijs , Neviero Igors
Published: July 2020

It is vitally important to choose a sustainable, rational heating system and, in view of the trends of the European Union, as well as a system with lower harmful emissions. This work explores the efficiency of solar collector use in district heating systems. The wide application of solar panels allows to improve it overall efficiency by utilized exceed heat into district heating systems. Especially in small scale systems. Solar collectors are a type of renewable energy that is not only an ecological solution for heat generation but also increases energy independence. Within the framework of the work, a working specifics of district heating system has been studied, where different types of solar collectors are used for partial heat energy supply. By changing the area of solar collectors for constant heat consumption, the results on efficiency and effectiveness of use were obtained and analysed. The TRNSYS energy simulation tool was used for dynamic simulations. Researches, results and conclusions made in this research can be used in the work of engineers and designers to improve the existing centralized heat supply systems and to anticipate possible challenges in the newly built.
Filtration of a highly concentrated suspension in a porous medium
Authors: Kuzmina Liudmila , Osipov Yuri
Published: July 2020

The problems of filtration in porous media are in demand when strengthening foundations and building waterproof walls in rocks. Deep bed filtration of a highly concentrated monodisperse suspension in a homogeneous porous medium with size-exclusion particle retention mechanism is considered. When filtering a suspension in a porous medium, some solid particles get stuck on the porous frame and form a deposit. The concentration of suspended particles injected at the porous medium inlet decreases when moving from inlet to outlet. The mathematical model for a highly concentrated suspension in a porous medium assumes a nonlinear dependence of the deposit growth rate on the concentration of suspended particles. The exact solution to the filtration problem in implicit integral form and the Riemann invariant relating the concentrations of suspended and retained particles are obtained. The problem is solved for a linear filtration function and a general nonlinear concentration function. An asymptotic solution is constructed near the concentrations front of suspended and retained particles. It is shown that the asymptotics is close to the exact solution, the error decreases with increasing order of asymptotic expansions. The asymptotic solution explicitly defines the dependence of the solution on model parameters and can be used to solve the inverse filtration problem.
Reinforced concrete structures stress-strain state strengthen with composite materials
Authors: Telichenko Valery , Rimshin Vladimir , Ketsko Ekaterina
Published: July 2020

In recent years, innovative strengthening of reinforced concrete structures for industrial and civil use by external reinforcement based on carbon fiber has been widely used. However, there are only a few application examples of this amplification technology in the water treatment and sanitation facilities construction and rehabilitation. Based on experimental and practical data, composite amplification systems provide significant results both when working structures in normal conditions, and when they are in aggressive environments. Compared to conventional structural materials, carbon fiber-based composite materials have higher strength, significant fatigue resistance, high elastic modulus, chemical and thermal resistance.This article discusses the calculating method for strengthening reinforced concrete crossbars for coating the construction of an underground purified drinking water reservoir reinforced with composite materials. Based on the calculation methods, the reinforcing feasibility is substantiated. This work was carried out according to the results of a crossbars survey. In order to achieve these goals, a survey was made of the crossbars of the treated drinking water tank, the actual effective loads on the reinforced concrete crossbars were determined, the need to strengthen the examined structures according to the results of calibration calculations was determined, recommendations were developed to strengthen the examined structures of the reservoir construction. A survey of the structures of the structure, as well as an assessment of their technical condition, was carried out taking into account the requirements of current regulatory documents.
Analysis of numerical model parameters for dry-mixed soil-cement composite with high content of organic matter
Authors: Jendrysik Klaudia , Rybak Jarosław
Published: July 2020

Numerical modelling of geotechnical issues requires basic subgrade parameters which need to be introduced into the program. The best way of collecting such information is to commission a series of tests. Defining the parameters of the material gained when admixtures are introduced into existing soil becomes problematic. Basic strength parameters can be found from trial batches of quasi-concrete composite, however they do not ensure the full spectrum of necessary data. Numerical programs often require more parameters from the user and these data are dependent on the strength hypothesis assumed. In this situation, one of possible solution is to run a inverse analysis. The paper provides exemplary procedure of iterative determination of cohesion, internal friction angle and Poisson’s ratio for a soil-cement sample obtained in dry mixing procedure. The original soil contained relatively high content of organic parts in dry mass. The analysis was made for hypothesis of Coulomb-Mohr and Drucker-Prager. The conclusions drawn from performed studies give some recommendations, but, due to possible soil heterogeneity, emphasise the need for further studies.
Underground pipeline reliability under longitudinal impact load
Authors: Sultanov Karim , Khusanov Bakhtiyar , Rikhsieva Barno
Published: July 2020

The paper presents the results of numerical solution obtained by the modified finite difference method according to the Wilkins scheme, to a two-dimensional unsteady-state problem of the plane shock wave propagation in an underground elastic pipeline, interacting with surrounding soil. Soil is considered to be an undeformable body moving relative to the pipeline at a given velocity. The value of the friction force depends on radial stress in the pipeline, determined by numerical solution to the problem. Changes in longitudinal and radial stresses over time and pipeline length, of velocity and displacements for fixed sections of the pipeline are obtained. Two times increase in values of longitudinal and radial stresses was detected in the case of active Coulomb friction at the pipeline-soil contact. The increase in stress values occurs due to the friction force acting in the direction of wave propagation. At significant values of the friction force on the outer surface of the pipeline, the hypothesis of flat sections is fulfilled for all its sections. This result justifies the consideration of similar problems of underground pipelines earthquake resistance in a one-dimensional statement. The results also make it possible to identify the mechanisms of the stress state formation in an underground pipeline interacting with soil, which can be used in seismic resistance calculation of underground trunk pipelines.
Reliability-based design optimization of steel frames using direct design
Authors: Truong Viet-Hung , Ha Manh-Hung
Published: July 2020

This paper presents an effective method for reliability-based design optimization (RBDO) of steel frames by combining direct design using nonlinear inelastic analysis, an improved importance sampling technique for structural failure probability analysis, and an improved differential evolution (DE) algorithm for optimization. The nonlinear inelastic analysis using the beam-column approach is used to capture the second-order effects and the inelastic behavior of structures. An improved importance sampling technique based on nonlinear inelastic analysis of the structure is employed that significantly reduces the number of structural analyses required for calculating the structural failure probability. An improved DE algorithm, which can effectively eliminate the redundant structural analyses for objective function evaluation, is utilized. A six-story space frame is studied to demonstrate the computational efficiency of the proposed method.
Analysis of adhesion factors of the external reinforcement and base surface of the bent concrete element
Authors: Simakov Oleg , Simakov Aleksandr
Published: July 2020

The development of reinforcement technology for existing reinforced concrete structures requires more accurate and careful consideration of various reinforcement parameters. Refinement of the calculation theory, coefficients, and the introduction of additional criteria make possible to strength structures with greater efficiency. One of the ways to increase the effectiveness of external reinforcement accounting, in fact, increasing the calculated value of the load-bearing capacity of the reinforced section, is consideration the anchoring of the reinforcement element. Currently used methods for calculating the strength of bent elements take into account the coupling of external reinforcement with the surface of the reinforced element by limiting deformations. At the same time, if it is possible to take into account the anchoring of the external reinforcement, both the calculated and the actual bearing capacity of the reinforced element is increase. There’s an analyzes the factors that determine the anchoring of the external reinforcement, which affect the load-bearing capacity of the reinforced normal section of the reinforced concrete element. The analysis is based on previous experimental studies, as well as numerical modeling of the distribution of shear forces. The simulation was performed on a single-span reinforced concrete beam with a hinged support. The numerical simulation took into account the nonlinear nature of the deformation of reinforced concrete (reinforced element), as well as the binding external reinforcement. The work of the outermost reinforcement (carbon fibers) was considered linear, since the graph of deformation of the carbon fiber is almost a straight line before destruction.
The refinement of dynamic wind load on masts and towers
Authors: Karakozova Anastasia , Mondrus Vladimir
Published: July 2020

The article deals with the problem of calculating high flexible steel structures like masts and towers for the dynamic component of the wind load. The definition of dynamic component of the wind load in Russian and European building codes is considered and analyzed. A refined calculation procedure is proposed, which gives more favorable results.
Bearing capacity of the facade system under temperature effect
Authors: Tusnina Valentina
Published: July 2020

Hinged facade systems are the external enclosing structures of buildings. These systems are subject to a range of loads, including temperature effects. Temperature effects significantly affect the structural bearing capacity. This article presents the results of experimental and theoretical studies of the bearing capacity of a hinged facade system, taking into account the influence of temperature load on the example of a design with gear assemblies of flexible fastening of facing panels. An assessment of the stress-strain state of nodal structural elements is given. A comparative analysis of the strength and deformability of suspended facade systems with flexible and rigid joints of structural elements is given. On the basis of experimental studies, it was found that to ensure free movement during temperature influences in riveted joints, it is necessary to place the rivet “head” in the oval hole and press the rod into the round hole. Assessment of the stress-strain state of the connecting elements in flexible nodes showed that stresses from the temperature load arising in the supporting brackets are very small and amount to ∼ 1.5% of the maximum allowable stresses. This allows us to conclude that these stresses can be ignored.
Calculation of the settlement of pile foundations taking into account the influence of soil liquefaction
Authors: Ter-Martirosyan Armen , Anh Le Duc
Published: July 2020

Pile foundations are considered one of the most common foundation solutions for the construction of buildings and structures in difficult geotechnical conditions, including in seismic areas. However, during earthquakes specific processes often occur that negatively affect the interaction of piles with the surrounding soil. Soil liquefaction is one of the most difficult problems in geotechnics. Many historical cases show that buildings and structures on pile foundations are collapsed completely when the surrounding soil liquefies. One of the reasons is the increase in settlement of the foundation after soil liquefaction.

Unlike the liquefaction potential assessment, or liquefaction-induced settlement of structures on shallow foundations, which are discussed by many researchers, the settlement of pile foundations after soil liquefaction has not been studied extensively. This paper presents the calculation of the settlement of pile foundations in different cases, with and without taking into account the influence of soil liquefaction, based on the hypothesis that the additional downward loads due to self-compaction of the liquefiable soil layers have an effect on piles. The analysis method in this study refers to the finite element method via PLAXIS 3D software. Finally, a brief comparison of the calculation results in the different considered cases is presented. The comparison shows how much the foundation settlement can increase if the influence of soil liquefaction is taken into account based on the suggested hypothesis. This paper provides a useful calculation and importance of further researches of liquefaction-induced settlement of pile foundations for seismic design.
Calculation of deformations of concrete with indirect reinforcement according to limit state design
Authors: Manaenkov Ivan , Korenkov Pavel , Grezeva Anastasiya S , Zinoveva Ekaterina
Published: July 2020

Currently, the issue of increasing the efficiency of the use of traditional materials in building structures due to rational structural solutions and improving design methods and material models is relevant. The use of indirect reinforcement improves the strength and deformation characteristics of concrete. The article considers the influence of indirect reinforcement in the form of transverse welded meshes on the strength and ultimate compressibility of concrete. The main attention is paid to the determination of the strain values determining the stress-strain diagram for concrete with indirect reinforcement. It is known that with an increase in the strength of concrete, the value of its ultimate compressive strains decreases. Indirect reinforcement can significantly increase the ultimate compressibility of concrete and makes the difference in ultimate deformations even more significant for concrete of different strengths. In this context, when calculating structures in accordance with the limit state design and decreasing the strength values of concrete in order to obtain the necessary security, it is possible to overestimate the ultimate compressibility of concrete. This is unacceptable in calculations based on the deformation model, since the achievement of ultimate deformations of the material is the main criterion for structural failure. To confirm the hypothesis, the results of tests for central compression of concrete with indirect reinforcement in the form of transverse welded meshes were selected. The strain values at the peak of the diagram were calculated for the experimental samples. Calculations were also performed for the characteristic compressive strength values and the design values of strength. The results are compared with experimental data. A significant overestimation of the values of strain at the peak of the diagram was noted in the calculations based on the characteristic compressive strength values and the design values of strength.
Numerical methods in the study of seismic dynamics of underground pipelines
Authors: Bekmirzaev Diyorbek , Mirzaev Ibrakhim , Mansurova Nodirakhon , Kosimov Elbek , Juraev Donitor P
Published: July 2020

A system of equations describing the oscillations of a rectilinear pipeline that interacts with the surrounding soil in the case of seismic action functioning in an arbitrary direction is presented. A numerical implementation of problems related to the determination of the mode of deformation of a pipeline experiencing seismic movement of the soil is performed. The methods of realization of boundary problem of seismodynamics of underground pipelines at arbitrary direction of seismic load are developed, as well as the methods of realization of the problems of seismodynamics of underground pipelines of non-orthogonal configuration, based on Finite deference method.
Statistical analysis of yield strength spectrum from nanoindentation for identification of constituent phases in steel
Authors: Pham Thai-Hoan , Nguyen Ngoc-Vinh
Published: July 2020

In this study, the extension of the statistical analysis application into yield strength of constituent phases of steel was conducted. A larger number of nanoindentation tests was carried out on a type of popular structural steel SS400. The mechanical properties, such as elastic modulus, hardness, and yield strength of the indented material were extracted from nanoindentation load-depth curves. The statistical analysis was then applied to analysis the material properties spectra. The experimental and analysis results revealed that the yield strength spectrum obtained from nanoindentation tests can be used in the accurate and reliable identification of the constituent microstructural phases and their strength in structural steel by applying statistical deconvolution analysis. For the present steel, three microstructural phases are known as low characteristic ferrite, high characteristic ferrite, and pearlite with the corresponding yield strength value of
a

y
= 296.1 ± 30.8 MPa,
a

y
= 423.6 ± 34.3 MPa, and
a

y
= 573.1 ± 38.9, respectively.