Papers by Keyword: Concrete Structure

Abstract: When erecting monolithic reinforced concrete structures, the structure of concrete can differ significantly from the laboratory standard due to the complexity of providing favorable conditions for hardening, and therefore the compressive strength and especially the frost resistance of concrete may not meet the design requirements, which can negatively affect the reinforced concrete structure durability and require amplification, especially in earthquake-prone areas [1, 2]. Increasing the durability of reinforced concrete structures is possible by creating a rational stress field, for example, by prestressing, incl. variable along the length of the structure [3,4], but this technique is difficult to implement for monolithic reinforced concrete structures. It is possible to use effective materials or methods of manufacturing structures [5, 6]. But this is also mainly problematic for use in the construction of monolithic reinforced concrete structures. Generally accepted methods of calculating the reinforced concrete structures durability subjected to cyclic freezing-thawing during operation, incl. in a water-saturated state, do not exist. At the design stage, ensuring the durability of such reinforced concrete structures is mainly reduced to the reasonable assignment of requirements for concrete quality indicators, depending on the operating conditions, which is the focus of BC 28.13330.2017 (EN 206) and GOST 31384-2017 from the premise of ensuring durability of at least 50 years. In the above-mentioned norms of the Russian Federation, in fact, two approaches are presented to ensure the durability of reinforced concrete structures during cyclic freezing-thawing, incl. in a water-saturated state, namely: designing a concrete structure capable of working under such conditions by standardizing the values of cement consumption, W/C ratio, class of concrete in terms of compressive strength, amount of entrained air, or rationing of concrete grades in terms of frost resistance F₁ (first base method GOST 10060-2012 provides for freezing in air, saturation and thawing in water) or F₂ (second base method GOST 10060-2012 provides for freezing in air, saturation and thawing in 5% sodium chloride solution). The purpose of this work is to compare various approaches to ensuring the durability of reinforced concrete structures operated during cyclic freezing-thawing and to analyze the provision of durability with standardized indicators when designing the structure of concrete.

Abstract: The paper deals with a comparison and interpretation of results of frost resistance tests of concrete specimens taken from a structure and test specimens produced in a laboratory using plastic moulds. A concrete block had to be produced for the experiment to simulate a real structure. The concrete used for the production of this block was also used in a laboratory to produce the test specimens. Core samples were drilled out from the concrete block and were subsequently used to make sets of core specimens. The test specimens, which differed in size, shape and the production method in particular, were subjected to frost resistance tests. The output of the paper is both a comparison of the results obtained on individual types of test specimens and a recommendation on how to approach the determination of frost resistance of concrete in a structure.

Abstract: The paper discusses means of testing the freeze-thaw resistance of concrete, which is part of an existing structure. Practically all standards and regulations dealing with freeze-thaw resistance describe tests that require cast prism-shaped specimens. This can make determining the freeze-thaw resistance of a concrete part of a structure rather difficult. The paper discusses the problem in detail, proposes solutions, and presents a real-world example of determining the freeze-thaw resistance of bridge abutments.

Abstract: The capillary-porous structure of cement stone and concrete is known to be mainly characterized by the presence of two major structural components – crystalline and gel-like products in the form of calcium sub-microcrystals of variable composition. The environmental factors cause changes in the structural-mechanical properties of the concrete structure which can be divided into “internal” and “external” ones. The number of internal properties includes those that change the relative content of the structural components of concrete – its composition, hardening conditions, and etc. The external factors include those that act directly on the already formed structure of concrete in operating conditions. These include mechanical, physical, chemical and other factors that affect the properties of the structure over time.

Abstract: Durable life of concrete structures under the chloride environment depends on the permeability of chloride ion, and the chloride ion diffusion coefficient is the main indicator that reflects the permeability of chloride ion. Based on the Fick’s second law, a multi-factor model of the chloride ion diffusion is established. In this model, the influences of temperature, humidity, age of the concrete, fly ash and carbonation are taken into consideration. And the model is verified by engineering test data from the concrete structure under the wet and dry areas of marine. The results show that the calculated and measured values of the chloride ion content agree well, the actual situation of the project could be basically reflected. The multi-factor model of the chloride ion diffusion is practical.

Abstract: In some tunnels of railway lines located in water-rich region, due to the long-term water leakage and erosion, the foundation of railway lines showed large uneven settlement deformation, so the above concrete roadbed slabs also experienced uneven settlement accordingly. The smoothness of railway tracks diminished, and the speed of passing trains had to be limited to ensure safety. To restore the smoothness of the tracks, a dedicated polymer injection technology for quick uplift rehabilitation of uneven settlement concrete roadbed slabs was studied on site just within the specified daily skylight time (about 3 hours every day) of the railway lines. A hydrophobic polymer with low-viscosity, quick-setting and high-strength properties was used for injecting, filling and uplifting the concrete slabs in water-rich foundations. The high-precision electronic levels were adopted to monitor rising height of the tracks in real time. After rehabilitation, the filling quality of polymer injection under roadbed slabs was examined using Φ50 mm core samples and the strength of hardened polymer was verified by compressive strength test. Results indicated that the polymer could uplift the concrete roadbed slabs effectively and restore the smoothness of railway tracks accurately even in the water-rich environment. The research can provide some valuable references for quick rehabilitation of uneven settlement concrete roadbed slabs in water-rich tunnels.

Abstract: Adhesion in this system is one of the most important factors that affect the reliability and durability of repair. According to the many standards and guidelines, e.g. new European Standard EN 1504-10 and ACI Concrete Repair Manual, a pull-off test is recommended for assessment of a bond quality in repair systems. The use of pull-off test, due to its semi-destructive character, is restricted by owners and managers. Therefore, the elaboration of reliable nondestructive method for an adhesion mapping could provide a quite advantageous alternative. Repair system is difficult to test with NDT methods, because of the many factors influencing the stress wave propagation. In this paper the possibility of application of various NDT methods for quality control of repair efficiency, including estimation of the bond strength, is discussed.

Abstract: The fatigue problem of concrete has long been studied through many different methods. However, the fatigue process and failure patterns of concrete structures have never been well simulated due to the lack of comprehensive understanding of the material properties under fatigue loads. In order to carry out an accurate simulation of the fatigue behavior of concrete structures, this paper proposes a new damage theory based fatigue constitutive model for concrete. The present model adopts two damage variables to describe the degradation of macro mechanical properties of concrete under tension and compression, respectively. And the tensile and compressive damage evolutions are related to the corresponding effective stress spaces. Specifically, by implementing the present model into the nonlinear finite element package, the bending fatigue process of a concrete beam is simulated. Meanwhile a set of numerical tests are presented, through which the validity and effectiveness of the proposed model for the simulation of concrete structures are illustrated.

Abstract: The presence of Robots in all engineering industries and commercial applications is tremendously growing day by day. Considering this there is a need to implement the robotic principles, which cannot be applicable to the human beings directly. One of the essential areas that lead to complications is maintenance and inspection of large vertical structures with autonomous systems; still it is an unsolved problem for the people doing research on this area. It is a challenge for mobile robots to climb a vertical wall primarily due to requirements for reliable locomotion, high maneuverability, and robust and efficient attachment and detachment. A large number of different robots exist which are able to navigate on buildings, ship hulls or other human-made structures, but most of these systems are practically limited to special situations or applications. It may be due to the design or physical factor that has been considered during the design of robotic system. While considering these issues a lot of researches state various principles and design aspects for maintenance and inspection purposes. Based on these facts, this article discusses the different methods for climbing robots and points out specifically the recent adhesion method for concrete vertical wall climbing. It also discusses about the design characteristics, practical challenges against the execution on vertical structures and suitable valid fields.

Abstract: Based on the mechanism of reinforcement corrosion in concrete structures and the experimental measurements of corrosion potential and resistance, this paper investigates the impact of concrete cover thickness and chemical alkalinity on reinforcement corrosion. Experimental results show that the rate of reinforcement corrosion decreases as the thickness of concrete cover of reinforcement increases. Moreover, given no risk of alkali-aggregate reaction, raising the chemical alkalinity of concrete cover helps maintain passivation of reinforcement. Additionally, under general atmospheric conditions, cracks that are not along bars barely affect structural durability if the width of cracks is smaller than its standard limit.