Monolithic Concrete Research Articles

Bond Behavior of Cleaned Corroded Lap Spliced Beams Repaired with Carbon Fiber Reinforced Polymer Sheets and Partial Depth Repairs

The present research investigated the bond behavior of a cleaned corroded reinforcing bar repaired with a partial depth concrete repair and a partial depth concrete repair followed by the application of fiber-reinforced polymer (FRP) sheets. Twelve lap splice beams were cast and tested under static loading. The test variables considered were a partial depth repair with prepackaged self-consolidating concrete (SCC) for six lap splice beams and additional confinement with carbon fiber reinforced polymer (CFRP) sheets for another six beams. The test results for the repaired lap splice beams were compared with those for a monolithic lap splice beam. This research found that the average bond strength increased as the bar mass loss increased for all bonded lengths. The lap splice beams repaired with partial depth were able to repair concrete with similar properties to those of the monolithic concrete. However, they had higher concrete strength than the monolithic beams which showed a higher average bond strength than the monolithic lap splice beams. The beams confined with FRP sheets showed a rise in the bond strength and the equivalent slip by 34–49%, and 56–260% as compared to the unconfined beams, respectively.

Experimental study on the combined shear and bending behaviour of corbel joints in precast concrete segmental inverted-T caps

Precast construction of caps is adopted to reduce on-site construction time and facilitate installation. A corbel joint (CJ) is proposed as an innovative joint form to improve the mechanical behaviour and construction performance of precast concrete segmental inverted-T caps. To obtain a further understanding of the failure modes and resistance mechanisms of CJs subjected to combined shear and bending, eight cap specimens with different shear-span ratios (1.61, 2.37, and 3.89) and joint types (CJ, monolithic concrete, and straight joints with a single tooth or multiple teeth) were match cast and tested. The experimental results showed that the CJs achieved superior mechanical and deformation performance and higher bearing capacity compared to conventional straight joints. Owing to corbels intercepting cracks, the CJs were not fully opened similar to straight joints at the limit state. Furthermore, the reinforcement in the corbels reached the yield strength, which suggested that the CJs could transfer the shear force between two adjacent segments effectively and reliably. When the shear-span ratios changed from 1.61 to 3.89, the ultimate shear force in the joint plane reduced by 57.9%, while the ultimate bending moment increased by 5.2%. Therefore, the ultimate shear and bending moment of the CJs were correlated.

Bond behavior of cleaned corroded rebar repaired by partial depth repair

This study investigated the bond behavior of reinforced concrete members subjected to corrosion and rehabilitated by partial depth repair using self-compacting concrete. Twelve beam-end specimens (600 × 500 × 250 mm) were tested, and two bonded lengths were considered (250 mm and 350 mm) to study the bond behavior of cleaned corroded rebar repaired by partial depth repair concrete. Two levels of corrosion were studied (5% and 10%) and were compared with control specimens (non-corroded specimens). A commercial prepacked self-compacting concrete (SCC) was used as the partial depth repair concrete and was compared to monolithic normal concrete (MNC) specimens. The bond stress-slip behavior was assessed using three linear variable differential transformers (LVDTs). Two LVDTs were placed at the loaded end of the rebar, and a third was placed at the free end, to measure the free-end slip. Generally, for the same bonded length, the average bond strength of the repaired clean rebar increased as the corrosion level increased. As the bonded length increased from 250 mm to 350 mm, the average bond strength decreased, and the corresponding bar slip increased. The beam-end specimens with the 250 mm bonded length failed by splitting of the concrete. However, the failure mode of the beam-end specimens with the 350 mm bonded length was a combination of pull-out and splitting failure or bar yield and splitting failure.

Selection and classification of various additives for monolithic concrete depending on the working conditions

The article presents the results of research on the choice of chemical additives for monolithic concrete depending on their types, main properties and applications. The working conditions are analyzed under which various monolithic concrete or monolithic reinforced concrete objects are constructed. The influence of additives on the properties of concrete and its performance characteristics is considered. The recommended calculation of the strength of concrete with additives is presented. It is shown that in the case of additives, the strength calculation should be performed using refined coefficients, mainly for the water-cement ratio. The calculation of the dosage of the additive in concrete, depending on the volume of the prepared mixture, is given. The results of an experiment with the addition of calcium nitrate to the concrete structure are presented, which confirmed an increase in the strength of the product by 20% compared to normal hardening conditions. An approximate method of selecting the most rational additives for concrete, depending on the working conditions, is given. The basis for classification of recommended additives is defined in order to ensure the required properties of concrete, taking into account the conditions of production and operation of objects using elements made of monolithic concrete.

Studies on properties of Flowable Earth Mix concrete for monolithic load bearing walls

The paper presents the results of experimental studies carried out on the properties of Flowable Earth Mix (FEM) Concrete. The FEM concrete can be used for the construction of monolithic load bearing walls in buildings. Smaller structures such as sanitary units, soak pits, water storage tanks etc. can also be built with single casting. Compared to the formwork and compaction energy used in monolithic rammed earth wall constructions, casting FEM concrete requires simpler formwork (minimising the cost of formwork) and minimum compaction energy for casting. The properties of FEM Concrete such as workability, compressive strength, flexural strength, drying shrinkage and moisture movements are discussed. The variables considered included type of soil, clay content of the mix and cement content. The results indicate the feasibility of producing monolithic FEM Concrete walls for load bearing buildings. It is easy to achieve required workability and strength of FEM Concrete through the mix design.

Refined assessment of strength of concrete pavement probabilistic method

The object of research is the method of calculating the strength of cement concrete airfield pavement. According to the current regulatory documents, the calculation of the strength of the coating is carried out according to the first limit state, taking into account the internal forces arising in the slab from the impact of the wheel load and temperature. The repeated impact of loads from the wheels of the main supports of various types of air is replaced by the influence of the main support of the heaviest aircraft, causing the greatest bending moment in the design section of the plate. However, the calculations do not take into account the stochastic nature of such factors as the take-off weight of aircraft, the plate thickness, the bed ratio of the elastic foundation, the probability of the combined effect of operating loads from the main bearing wheels and temperature in the calculated section of the plate, as well as the probability distribution of loads from the aircraft spectrum across the width of the airfield elements. The article proposes a method for taking into account the probabilistic-statistical variability of operating loads, physical and mechanical properties of materials and the geometric characteristics of the plate, recommended when developing a new regulatory framework for the design of rigid airfield pavements. The method of statistical linearization of random functions of several random arguments was chosen as the research method. Using the mathematical apparatus of the theory of random functions, the statistical coefficient of the working conditions of the plate is analytically determined, and a numerical analysis of the obtained analytical solution is carried out. It has been established that with the same unfavorable combination of variability of basic arguments, the calculated absolute value of the statistical coefficient of the working conditions of the slab is more influenced by the coefficient of variation of the slab thickness than the coefficient of variation of the strength of cement concrete in bending. The condition for calculating the required thickness of the hard airfield slab of monolithic cement concrete is determined.

Reducing the Construction Time of Buildings Made of Monolithic Concrete

Reducing the Construction Time of Buildings Made of Monolithic Concrete

ANALYSIS OF THE BASIC DESIGN PRINCIPLES OF LOW-RISE RESIDENTIAL BUILDINGS

This article investigates the basic provisions of design of earthquake-resistant low-rise buildings and formulated the basic principles of design of earthquake-resistant buildings by design, erected in seismic areas: frame, volume-block, large-panel, with walls of large blocks, with walls of monolithic concrete, with walls of complex structure, with load-bearing walls of brick or stone, wooden buildings with walls of local materials. Seismically unfavorable conditions, which are designed as a large part of the terrain land (steep shores, gorge, water, etc.), impact disturbance, physiographic processes, rocks, soils, spills, mine workings and destruction of tectonic sites disasters surrounding areas. The main buildings and other structures to strengthen and strengthen the foundation, how to use any additional measures.

Flexural behavior of RC beam strengthened by stay in place SFRC sheet formwork

The paper presents results of experimental and numerical modeling of flexural behavior of RC beam strengthened be stay in place SFRC sheet formwork in a tensioned zone. Analysis of influence of the SFRC on crack propagation. As a result monolithic concrete provides the perception of tensile forces before the formation of main cracks in the steel fiber concrete.

Problems of Development and Implementation of Ultrasonic Pulse Method in the Problem of Measurement of Parameters for Determination of Physical-Mechanical Characteristics of Concrete Maintained Buildings and Constructions

The current stage of development of the construction industry of Ukraine and foreign countries contains the direction to extend the life of the operated construction projects. This direction is directly related to the research of physical and mechanical characteristics of concrete as the main building material. A significant number of such studies can be performed using the ultrasonic pulse method. But despite its potential practice shows the insufficient level of use of this method. Thus, this method, in addition to determining the strength of concrete, allows to determine its characteristics such as the level of crack formation, geometric parameters of the planes of stratification in monolithic concrete, and the like. The system analysis of technical characteristics of serial ultrasonic devices that are produced in Ukraine and foreign countries is carried out. The results of the analysis revealed that their technical characteristics allow measurements, mainly to determine the strength, uniformity of concrete. These devices also do not allow to measure vibration, noise and electrical interference, which is typical for production conditions. The conducted researches allowed to reveal the main directions of improvement of serial ultrasonic devices, Metrology. This allows us to solve the problem of expanding the application of this method in the practice of non-destructive testing of physical and mechanical characteristics of concrete operated construction projects.

Use of Solar Power at Heating Treatment of Concrete

The article considers the introduction of alternative energy as a safer and more environmentally friendly instead of the traditional, in particular when manufacturing monolithic concrete and reinforced concrete products. Monolithic concreting under the conditions of the construction site is now widespread in the construction industry. The subject of the article is the issues of heat treatment of concrete and acceleration of its hardening processes using solar energy. A brief review and classification of the most well-known and common energy sources used for acceleration of strength development in the concrete mix such as wind power, biofuels, solar energy, alternative hydropower are given. Attention is paid to solar energy - the energy obtained from solar radiation. The sun as an inexhaustible and affordable source supplies energy, exceeding several times the traditional sources. Therefore, this type of alternative energy was chosen, which is used in various spheres of the national economy, especially in the field of construction. Already existing methods of heat treatment of concrete with the help of solar technology are considered, the modern level of development of these methods is defined and further ways of their development are planned.

REDUCTION OF EMPLOYMENT OF FORMULA WORKING BY USING LOCAL FILL-ERS AND WASTE OF PRODUCTION

Objectives.The purpose of this study is to study the increase in turnover of formwork and reduce the complexity of formwork for monolithic foam concrete by regulating its properties through the optimal use of local aggregates of the Republic of Daghestan and industrial waste. In particular, the experimental work used cement grade M500, silica filler - deposits of quartz sand in Kumtorkala district of the Republic of Daghestan with a low module of size, various synthetic foaming agents, perlite sand, ground expanded clay sand (Kizilyurt, Republic of Daghestan),stone crushing roar (Kizilyurt).Method.In the production of foam concrete, a method was used in which foam was prepared in the foam generator, then a solution of cement, filler and water was prepared. Then the foam is mixed with a solution in a foam mixer until a set of appropriate multiplicity. (Multiplicity in this case was defined as the ratio of the volume of the foam concrete mixing solution after mixing to the volume of the solution before mixing). During the study, the water-cement ratio was determined using three types of aggregates (expanded clay sand, quartz sand deposits Kumtorkala district and perlite sand). The turn-over rate of the concrete mixture was determined using the Attard viscometer.Result.The results of studies have shown that with an increase in the water-cement ratio using three types of aggregates (expanded clay sand, quartz sand deposits Kumtorkala district and perlite sand ) will increase the flow rate of the foam concrete mixture.Conclusion.At the same values of the water-cement ratio, the mixture with a filler of perlite sand has the lowest fluidity, which in turn affects the further structure formation of foam concrete and allows you to choose the optimal composition with the desired properties. The possibility of increasing the turnover of artwork and reducing the complexity of artwork work for monolithic foam concrete by regulating its properties due to the optimal use of local aggregates of the Republic of Daghestan and industrial waste.

Уникальный купольный дом

The definition of the domed house is given. Its obvious advantages in comparison with the house in the form of a parallelepiped are revealed. It is shown that the domed house surpasses the usual parallelepiped house in almost all considered parameters: the internal volume of the house, strength, heat loss, construction materials consumption, construction speed, financial costs, natural lighting, air aeration inside the building, climate and seismic resistance, appearance. Comparison of the main types of domes of a dome house is made: geodesic, stratodesic and monolithic concrete, which determine the technology of erecting a domed house. The four main technologies for building domed houses that are used in construction are described: dome construction based on a geodetic sphere, erecting a house on the basis of a pneumoframe, domed house on the basis of fixed formwork and the technology of erecting a domed house, which is a prefabricated construction of the factory production of water. Comparative characteristics of the methods for erecting a domed house are given, advantages and disadvantages of each method of building a domed house are described. The negative moments in the construction and operation of the domed house are determined: the complexity of dome calculations, the lack of practice of dome construction, the large amount of building materials waste, the use of non-standard doors, windows, furniture, the unusualness and fear of owners of a domed house in a unique house. Practical recommendations for eliminating flaws in the domed house are indicated: purchase of finished projects, attraction to construction of a dome house of professional builder. Conclusions are made about the prospects of domed houses due to their capacity and stability, geometric symmetry of shapes and strength, speed of erection and uniqueness for any region of Russia.

PROPERTIES OF MODIFIED CONCRETE FOR SPECIAL PURPOSE STRUCTURES

Purpose. The paper is aimed at developing the scientific fundamentals of new-generation monolithic concrete technology for special purpose structures by controlling the processes of structure formation of a modified cement system under natural hardening conditions. Methodology. The kinetics of interaction between the cement system and aggregates was evaluated by microcalorimetry. The measurements were carried out continuously for 24 hours after preparation of the mixture. The differential and integral characteristics of the heat release of the solidifying system were recorded. Investigation of the rheological properties of concrete mixtures was carried out on the mixtures with 10...15 cm consistency. The microhardness of contact layers was investigated on concrete cubes with dimensions from 20×20×20 to 50×50×50 mm. When determining the structural characteristics, x-ray phase and differential-thermal analyzes of the concrete cement matrix were used. Infrared spectroscopy was used to determine the effect of physicochemical modification on the cement system. Tensile creep was studied over a wide load range from 0.2 R t to 0.8 R t . Findings. It is determined that the reason for changing the concrete properties of natural hardening is the change in its hygrometric and thermal state, as well as the harmonic fluctuations of these environmental factors. The hygrometry of concrete depends on the thermal moisture conditions of the environment, the type and composition of concrete, the massiveness of concrete elements. An analysis of these factors and experimental data made it possible to establish the exponential dependence of the change in the hygrometric state of monolithic natural hardening concrete. The change in the moisture state of concrete makes it possible to predict its volumetric deformations. Originality . For the first time, the features of the structure formation of a modified cement system are established, consisting in the fact that magnesium chloride hydrate crystals grow rapidly in the space between hydrated clinker minerals, and the resulting mechanical cohesion defines the development of initial strength and rigidity. Since the free growth of crystals is hampered by a lack of space, the crystals mutually intergrow, forming a dense structure, contributing to the growth of strength. The developed organo-mineral modifying complex provides disperse reinforcement of the cement matrix of concrete. Practical value . The obtained dependences of structural concrete stresses make it possible to analyze their effect on the structure of modified concrete: to determine the probability of formation around the filler particles of the plastic flow zone, the material microcrack formation zone, the crack initiation period, the microcrack onset conditions, and the change of elasticity modulus of the material caused by microcracks in its structure. Disperous modification of cement matrix allows to obtain durable concrete of special purpose with design operational properties. The developed binder disperse modification technology, the established features of the structure formation mechanism for the modified cement system, as well as the use of the principle of congruence of a complex of technological influences to the physico-chemical processes of hydration of clinker minerals allowed developing the scientific fundamentals for the special purpose concrete technology. This helps to expand the use of modified concrete in various types of construction.

OPTIMIZATION OF HEAT-SHIELDING CHARACTERISTICS OF THE EXTERIOR WALLS OF COUNTRY COTTAGES, INSULATED WITH MONOLITHIC FOAM CONCRETE

The heat-shielding properties of three-layer external walls insulated with monolithic foam concrete are considered in the article. The temperature is given in rooms operated in intermitt ent heating conditions. An optimal exterior wall design is proposed using monolithic foam concrete for the construction of country cott ages. For this design, the results of heat engineering calculations are presented using the analytical dependence of determining the heat transfer resistance, which ensures the minimum warm-up time of the wall. The results of the calculation are presented in tabular form for a given heating time and density of foam concrete. Also a relationship is described to determine the maximum allowable resistance to heat transfer of the outer wall at diff erent densities of monolithic foam concrete.

Results of experimental investigations of extra-compressible compression elements enhanced by reinforced concrete

The article considers a range of issues related to ensuring the compatibility of prefabricated and monolithic concrete in the case of reinforcement of eccentrically compressed elements with reinforced concrete cage. A calculation expression is presented to determine the required thickness of the gain from the condition of ensuring the strength of the shear joint. The main design expressions for testing the strength of the contact seam in the case of using keys and reinforcement by transverse reinforcement are considered. Based on the proposed theoretical premises, a program of experimental studies has been developed.

АНАЛИЗ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ МОНОЛИТНОЙ БЕТОННОЙ КРЕПИ ПОДЗЕМНЫХ СООРУЖЕНИЙ НЕКРУГОВОГО ОЧЕРТАНИЯ

Приведены результаты исследований напряженно-деформированного состояния (НДС) крепи и грунтового массива подземных сооружений некругового очертания глубиной заложения до 50 м в неустойчивых наносных породах с заходками от 0,3 до 0,7 м. Исследование выполнено путём моделирования НДС массива грунта и твердеющего бетона монолитной крепи, возведенной вслед за подвиганием забоя.Для реализации предлагаемых технологических решений обеспечивающих крепление подземных сооружений монолитным бетоном для исключения применения временной крепи требуется использование особобыстротвердеющих составов. На основании исследований ряда модификаторов установлены изменения механических свойств наиболее эффективных составов, которые использованы для моделирования бетонной крепи сооружений с изменяющимися во времени характеристиками.Цель: обоснование ресурсосберегающей технологии строительства подземных сооружений некругового очертания в грунтовом массиве.Метод или методология проведения работы: исследования проведены методом конечных элементов (МКЭ) с использованием оптимального планирования эксперимента.Результаты: получены распределения напряжений в твердеющей бетонной крепи сооружений, установлены зоны концентрации напряжений, установлены величины смещений в грунтовом массиве и их распространение на поверхности.Область применения результатов: результаты исследований могут применяться при проектировании вариантов строительства подземных сооружений.

Road plates with increased strength characteristics

The issues of creating road plates with increased operational properties are considered in this paper. Monolithic concrete has a number of disadvantages, such as a long period of strength accumulation, temperature and humidity regime, and the inability to produce works throughout the year. The analyzed material for the production of road slabs (fiber concrete) makes it possible to produce plates with increased strength characteristics, to prolong service life, and to improve their physical and mechanical characteristics.

Application of monolithic foam concrete in building envelopes of a cottage, used in conditions of intermittent heating

The paper focuses upon the peculiarities of application of monolithic foam concrete as a heat-insulating layer in building envelopes of houses used in conditions of intermittent heating. The researchers analyze thermal characteristics, review literature describing the application of foam concrete in construction and demonstrate this material applicability at outer walls insulating, taking buildings and constructions with variable thermal behaviour as an example. The paper outlines main criteria that building envelopes of such structures should meet. To assess the effectiveness of monolithic foam concrete in building envelopes application, the authors carried out thermo-technical calculation of the outer walls, insulated with monolithic foam concrete. The graphs of dependence of multilayer building envelope heating time upon thickness of a heat-insulating layer and upon heat transmission resistance of the construction was obtained on the basis of these calculations. The dependence of specific energy consumption upon the heating time is also given in the paper. The study reveals the optimal range of thickness and density of monolithic foam concrete for insulating outer walls of buildings, used in in conditions of intermittent heating. This calculation also proves that the application of foam concrete as an insulant on the inside of the outer wall makes it possible to reduce the load on the building foundation.

Experimental Study on Shear Behavior of Mid-rise Assembled Monolithic Concrete Shear Walls with Varying Axial Compression Ratio

Objective: Quasi-static tests of three mid-rise assembled monolithic concrete shear walls, whose aspect ratio is 2.0, were completed in this paper. The failure mode of three new-type shear walls and the effect of axial compression ratio were studied. Result and Conclusion: The result showed that the brittle failure was extinct, and the new-type shear walls had good deformability whose ductility factors were over 4.3. The axial compression ratio had significant influence on the mechanical properties of the new-type shear walls. As the increscent of the axial compression ratio, the shear capacity and initial stiffness were improved, but the energy-dissipating capacity became worst.