Deformation Of Concrete Research Articles

Effect of Mineral Admixtures on the Mechanical and Shrinkage Performance of MgO Concrete.

Shrinkage deformation of concrete has been one of the difficulties in the process of concrete performance research. Cracking of concrete caused by self-shrinkage and temperature-drop shrinkage has become a common problem in the concrete world, and cracking leads to a decrease in the durability of concrete and even a safety hazard. Mineral admixtures, such as fly ash and mineral powder, are widely used to improve the temperature drop shrinkage of mass concrete; fly ash can reduce the temperature rise of concrete while also reducing the self-shrinkage of concrete, there are different results on the effect of mineral powder on the self-shrinkage of concrete, but the admixture of fly ash will reduce the strength of concrete, and mineral admixtures have an inhibitory effect on the shrinkage compensation effect of MgO expander(MEA). The paper investigates the effect of mineral admixtures on the mechanical and deformation properties of C50 mass concrete with a MgO expander(MEA), aiming to determine the proportion of C50 mass concrete with good anti-cracking properties under working conditions. The experiments investigated the effect of fly ash admixture, mineral powder admixture and MgO expander admixture on the compressive strength and deformation of concrete under simulated working conditions of variable temperature and analyzed the effect of hydration of magnesite in MgO expander and pore structure of cement paste on deformation. The following main conclusions were obtained: 1. When the concrete compounded with mineral admixture was cured under variable temperature conditions, the compounded 30% fly ash and mineral powder decreased by 4.3%, 6.0% and 8.4% at 7d age, and the compounded 40% fly ash and mineral powder decreased by 3.4%, 2.8% and 2.3% at 7d age, respectively. The incorporation of MEA reduced the early compressive strength of concrete; when the total amount of compounding remained unchanged, the early compressive strength of concrete was gradually smaller as the proportion of compounding decreased. 2. The results of concrete deformation showed that when the temperature rose, the concrete expanded rapidly, and when the temperature dropped, the concrete also showed a certain shrinkage, and the deformation of concrete basically reached stability at 18d. 3. The compounding of 30% fly ash and mineral powder As the compounding ratio decreases, the deformation of concrete increases, and the 28d deformation of concrete with a compounding ratio of 2:1 is 280 × 10-6, while the final stable deformation of concrete with a compounding ratio of 2:1 in compounding 40% fly ash and mineral powder is the largest, with a maximum value of 230 × 10-6, respectively. Overall, the concrete with a total compounding of 30% and a compounding ratio of 2:1 has the best shrinkage resistance performance.

Service limit state of cast-in-place flexural member

Cast-in-place structure design distinguish them from reinforced concrete structures. Cast-in-place structures are involved in deformation and receive external load, so they possess different strength, deformation and other physical properties. In this regard, calculation methods of cast-in-place structures given in regulatory documents require clarification.Having studied the cast-in-place structure design and considering their stress-strain state, a method is proposed for the analysis of such structures according to their service limit state. This method allows taking into account different times of involvement in the external load and deformation of the cast-in-place structure as well as the difference in concrete strength and deformation properties. It is shown that the experimental data are in satisfactory agreement with theoretical calculations.

STUDY ON POLYMER CONCRETE DEFORMATIONS IN DIFFERENT ENVIRONMENTS AT HIGH TEMPERATURE

Problem statement. High stability composite materials, such as polymer concrete, play a significant role in modern practice. Due to a continuing demand for the use of building materials resistant to aggressive environments both in Ukraine and globally, as well as their prospective use in construction, metallurgy, and chemical industry, the investigation deals with deformations of polymer concrete in various types of environment at high temperature. The purpose of the research is to find mechanisms to increase the stability of polymer concrete in aggressive environment. The object of the study is polymer concrete based on modified furan resins. The subject of the study is deformation characteristics (namely creep) of polymer concrete in different environments (water, sulfuric acid) at different temperatures. Results. In the course of research of the deformation parameters of polymer concrete in various environments were identified. Conclusions. The deformation parameters of polymer concrete on modified furan resins in hot sulfuric acid solutions were determined. It has been proved that the decrease in strength and deformation properties also depends on the hygroscopicity of benzosulfonic acid. It is shown that under simultaneous influence of aggressive environment and temperature in a stressed state the phenomenon of creep is more intensive and the polymer concrete is destroyed in a short time.

Reflection of Multiple Loading in The Deformation Model for Reconstructed Reinforced Concrete

During the reconstruction, or upon expiration of the service life, as well as after external impact, reinforced concrete structures require examination and verification calculations. Existing diagrams of concrete deformation are focused on designing new structures and are not adapted to the concretes of the reconstructed structures.Using the exponential model of concrete deformation makes it possible to describe the resistance of concrete during reconstruction, including after repeated cyclic loading.A technique for creating an individual deformations model under cyclic load during the reconstruction is demonstrated on a specific example.

Evolution characteristics and mechanism of concrete performance under water pressure environment: A comprehensive review

AbstractCompared with the ground service environment, the evolution of concrete performance under a water pressure service environment is quite complex with variable conditions. Because of the coupling effect of load and pressure, water has a special impact on the strength and deformation of concrete. Meanwhile, harmful ions usually react with the cement matrix as pressure water seepages into concrete, resulting in the reduction of concrete durability. Based on this, this study provides a comprehensive review of the strength, deformation, and durability of concrete under water pressure environment. It is found that microcracks in concrete tend to propagate and connect after exposure to water pressure, leading to a decrease in strength and deformation performance. The average loss rate of strength and elastic modulus increased by 12.15% and 10.97%, respectively, when water pressure increased by 1 MPa. However, the loading process of water‐confining pressure makes concrete more compact, where the static and dynamic mechanical performance can be improved. Besides, due to the enhancement of excess pore water pressure, concrete strength under a high strain rate increases by 61.79% compared to static load. The effect of water pressure increases the ability of the liquid to penetrate concrete, and corrosive ions trapped within the liquid and freeze–thaw caused by external temperature changes would further reduce the concrete durability. This study points out that static and dynamic loading characteristics and durability of concrete under multi‐factor coupling in a water pressure environment will be the future research direction. The summarized contents can provide guidance for construction and research of concrete engineering under a water pressure environment.

Stress–strain behavior and constitutive relation of rubberized plastic concrete under uniaxial and triaxial compression

AbstractPlastic concrete is a kind of flexible concrete cutoff wall material, which is used to solve the problem of poor coordinated deformation ability between ordinary concrete cutoff wall and surrounding soil. It has the characteristics of small elastic modulus and large limit strain, which greatly improves the operation condition of cutoff wall. In order to save bentonite resources and recycle waste automobile tires, this paper crushed waste automobile tires into rubber particles and mixed them into plastic concrete, through the uniaxial compression test and triaxial compression test, obtained the corresponding stress–strain curve, rubberized plastic concrete strength and deformation properties are studied and the rubber particles and the relationship between dosage. The test results show that the compressive strength of rubberized plastic concrete decreases with the increase of rubber particles content, but the deformation capacity increases with the increase of rubber particles content. In this paper, the regression analysis of rubberized plastic concrete constitutive relation and failure criterion including the influence factor of rubber particles are helpful to promote the engineering application of rubberized plastic concrete and reduce the exploitation of natural resources and environmental pollution.

Study on Analysis Method and Control Index for Deformation of Super-High Arch Dam Suffering Alkali-Aggregate Reaction

Alkali-aggregate reaction can not only cause uneven expansion of concrete but also lead to cracking and even destruction and consequently affect the working behavior and long-term safety of hydraulic concrete structures. Present researches on alkali-aggregate reaction focus on improving the composition ratio of concrete materials through experimental study to inhibit the reaction, whereas there is a lack of quantitative calculation and analysis. In the present study, the problem of alkali-aggregate reaction in the super-high arch dam of Jinping I Hydropower Station was taken as an example. The expansion of concrete suffering the alkali-aggregate reaction was simulated by means of the overall temperature rise in the dam. Similarly, the yield zone, the expansion process, and the deformation change law with the development of concrete expansive deformation under various load combinations were analyzed by using the elastic–plastic finite element method. Finally, a control index of allowable alkali-aggregate expansion of dam concrete under various load combinations was put forward. The research results demonstrated that the control index was 400~800 με. Since the arch dam has a low safety reserve when operating at a low water level, the lowest reservoir level should be raised as much as possible in dam operation to reduce its drawdown rate, thus restraining the adverse impact of alkali-aggregate reaction in concrete on the dam.

Numerical Investigation of Axial Force–Bending Moment Interaction for FRP-Confined Reinforced Concrete Columns with Internal Steel Transverse Reinforcement

Externally bonded fiber-reinforced polymer (FRP) laminates are widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can increase the axial and bending moment capacities of these columns through a confinement mechanism. The confinement produced by FRP laminates acts in addition to that exerted by the internal transverse steel, although the latter is often neglected in current design standards and guidelines. In this study, a recently developed FRP-and-steel-confined concrete constitutive model was employed to numerically investigate the axial force–bending moment interaction for FRP-confined RC columns modeled using finite-element (FE) analysis. The proposed model was first validated against experimental data available in the literature and then used to quantify, through an extensive parametric study, the effects of transverse steel confinement, FRP strength, FRP stiffness, FRP reinforcement ratio, column diameter, concrete compressive strength, and load eccentricity ratio on the strength of FRP-confined RC columns subject to combined axial compression and bending moment. It was found that the internal steel confinement can substantially enhance the strength of these columns, especially for low concrete compressive strengths, large cross sections, and small eccentricities. When design code provisions limiting concrete and FRP deformations were considered for eccentrically loaded columns, the contribution of the steel confinement increased for increasing FRP reinforcement ratio. Based on the parametric study results, this investigation proposed an extension to eccentric axial compression of two relative confinement coefficients, which were previously developed to describe the contribution of transverse steel confinement to the peak strength of FRP-confined RC columns subject to pure compression.

Theoretical analysis on flexural strengthening of RC beams using GFRP composites in terms of strength to the weight ratio: A way forward

Aramid, Glass or Carbon Fibre Reinforced Polymer (GFRP/CFRP) are three types of composites that are commonly used in the civil, mechanical and automobile sectors worldwide. GFRP composites are often used for structural member strengthening, repairs, and rehabilitation. In comparison to CFRP and Aramid FRP composites, GFRP is easily available, inexpensive, good strength to the weight ratio, and has several additional benefits. The strength-to-weight ratio of GFRP composites and steel plates for flexural strengthening of RC beams is investigated in this work. Theoretical analysis for the RC beam strengthened with GFRP composites and steel plates were performed using the established equation based on Indian standards and the ACI code. The self-weight of the beam and the superimposed dead load owing to the block/brick work were taken into account in the design calculations. The beam's load carrying capability is inadequate due to the excessive load, thus it must be strengthened with different materials: GFRP Chopped Strand Mat (CSM) composites or steel plates. The evaluations were conducted under the assumptions that the loss of moment carrying capacity due to concrete deformation caused by bolt holes and failure due to GFRP composite delamination would be disregarded. Strength to weight ratio of GFRP composites and steel plate requirements have been computed and compared for the known dimensions, unit weight and tensile strength of the strengthening materials, and load carrying capability of the strengthened RC beam. Comparative study proves that the flexural strengthening of RC beams using GFRP composites, the strength to weight ratio is much higher than when the identical beams are strengthened with steel plate.

Dynamic Behavior of Concrete: A Review

Abstract: Concrete properties are the most essential and critical physical material property when reinforced concrete structures are designed. Considering potential catastrophic accidents, testing of dynamic mechanical properties of concrete is one of the most urgent stages of development. A large number of scientific experiments have shown that the dynamic mechanical properties of concrete are influenced by strain rate. This paper covers the existed researches on the dynamic mechanical characteristics of concrete. Review of the relationship between concrete's dynamic compressive strength, deformation properties, elastic modulus, and energy dissipation capacity with strain rate. The results may vary depending on the loading technique, test apparatus, specimen size, and other variables. The study of dynamic tensile behavior of concrete was uncommon due to the limitations of experimental tools and testing methods. The data returns so far have been inconsistent and even at conflict with one another. The most widely used test techniques to investigate the dynamic tensile behavior of concrete are the direct tensile test, splitting test, bending test and spalling test.

Calculation of the formation of normal cracks in a reinforced concrete element based on the deformation theory of plasticity of concrete by G.A. Geniev

The authors present a refined method of determining the moment of cracking in reinforced concrete bar constructions using the diagram of deformation of concrete built on the basis of the deformation theory of plasticity by G.A. Geniev in which the stress and strain invariants of concrete are linked by nonlinear dependences. In the resulting defining equations, the hypothesis of flat sections, as well as the premise of reaching the limit values of concrete deformations on the stretched fibers of the cross-section are used. Stresses in concrete are determined through deformation values in accordance with the nonlinear deformation diagram of concrete. On the basis of the assumptions accepted, analytical dependences for determining the moment of cracking in the sections of bending elements with single and double reinforcement have been acquired. The formulas obtained were used in the analysis of various factors influence on crack resistance of bendable reinforced concrete elements. It was found out that the moment of crack formation practically does not change when percentage of reinforcement of longitudinal tensile or compressed reinforcement changes. The most effective method of crack resistance improvement is the increase of concrete strength. The proposed methodology is verified by comparison with experimental results on reinforced concrete prototypes. It is concluded that the use of the diagram of nonlinear deformation of concrete on the basis of the theory of plasticity by G.A. Geniev allows to estimate more strictly the crack resistance of reinforced concrete rod elements.

Numerical Analysis of Modified PVA Fiber Rubber Concrete in Frame Beams

The feasibility of PVA fiber rubber concrete modified by modifier in the structure was investigated using the portal frame as the research object. The basic mechanical properties of modified PVA rubber concrete materials were tested mechanically first, and then ABAQUS was used to establish the ordinary concrete portal frame model, and after confirming the model’s rationality, the rubber concrete, PVA rubber concrete, and modified PVA rubber concrete models were established on this basis, and the displacement and strain comparison analysis with ordinary concrete was carried out. The simulation results show that using PVA rubber concrete material in the concrete frame structure can improve the large deformation of rubber concrete, and using PVA rubber concrete treated with a modifier can improve structural strength and deformation even more.

A global sensitivity analysis method for safety influencing factors of RCC dams based on ISSA-ELM-Sobol

Structural material parameters will directly affect the stability and deformation of roller compacted concrete (RCC) dams. To analyze the influence degree of structural material parameters of RCC dams on the safety evaluation indexes, this study proposes a global sensitivity analysis method based on extreme learningmachines optimized by an improved sparrow search algorithm with Sobol method (ISSA-ELM-Sobol). First, the safety evaluation indexes of the RCC dam and their influencing factors are determined; second, a reasonable finite element model is established; third, the sample set is generated using the Latin hypercube sampling technique; fourth, the ISSA-ELM model is established to replace the finite element calculation; finally, based on the established ISSA-ELM model, the Sobol method is used for global sensitivity analysis. A case study for a typical RCC dam in Sichuan province of China showed that the material properties of the foundation and the cohesion of potential sliding surfaces have the most obvious influence on the safety of RCC dams; the ISSA proposed in this study can overcome the problem that sparrow search algorithm is easy to mature prematurely and fall into a local optimum. The ISSA-ELM model established in this study has significant advantages in solving nonlinear regression problems.

Effect of Different Fineness of Cement on the Autogenous Shrinkage of Mass Concrete under Variable Temperature Conditions

The internal temperature of the mass concrete is not constant. In the actual project, the internal temperature of the concrete will experience a process of rapid warming to reach the peak temperature and then slow down. In this study, volume measurement method is used to simulate the internal volume deformation of mass concrete under actual engineering conditions. The embedded strain gauge was embedded in concrete with a water-cement ratio of 0.32 for 28 days, and the development of total volume deformation and autogenous volume deformation of concrete under variable temperature conditions was studied by external heating of concrete. The results show that the finer the cement, the earlier the concrete starts to shrink, and the greater the total shrinkage of the concrete. The high temperature will promote the hydration of cement with different fineness and will reduce the total porosity of their paste, but the proportion of harmful pores in the paste with finer cement particles is lower.

3D FE analysis for buckling behavior of longitudinal reinforcement embedded in LRS FRP-confined concrete under axial compression

Large rupture strain (LRS) FRPs have great potential to be used for seismic retrofit of RC columns because of its high rupture strain (i.e., > 5%) that provides better confinement effects. However, in FRP-confined RC columns, the longitudinal reinforcements may buckle before the LRS FRP rupture, especially in the case of large stirrup spacing. This study aims to present a 3D finite element (FE) model for simulating the buckling effect of longitudinal reinforcements in LRS FRP-confined RC columns. A modified concrete damaged plasticity model (CDPM) is proposed to consider the deformation and mechanical characteristics of LRS FRP-confined concrete. Removal of failed concrete elements is considered to facilitate the buckling of longitudinal reinforcements in LRS FRP-confined RC columns. The FE analysis accuracy was verified by comparisons with test results. The factors affecting the buckling of longitudinal reinforcements were discussed through an extensive parametric study. Empirical formulas for the stress and strain values at which the longitudinal reinforcement starts to soften were developed. An empirical formula for the ultimate axial strain of LRS FRP-confined RC columns determined by longitudinal reinforcement buckling was also obtained by regression analysis.

Autogenous deformation induced- stress evolution in high-volume GGBFS concrete: Macro-scale behavior and micro-scale origin

This study aims to experimentally investigate the autogenous deformation and the stress evolution in restrained high-volume ground granulated blast furnace slag (GGBFS) concrete. The Temperature Stress Testing Machine (TSTM) and Autogenous Deformation Testing Machine (ADTM) were used to study the macro-scale autogenous deformation and stress evolution of high-volume GGBFS concrete with w/b ratios of 0.35, 0.42, and 0.50. The early-age cracking (EAC) risk (quantified by stress-strength ratio) and stress relaxation were analyzed extensively based on ADTM and TSTM results. Furthermore, Environmental Scanning Electron Microscopy (ESEM), X-ray Diffraction (XRD), and Mercury Intrusion Porosimetry (MIP) were conducted to explore the micro-scale origin of the autogenous deformation of high-volume GGBFS concrete, which supports the observations on the macroscale measurement of TSTM/ ADTM tests. This study finds that the ettringite formation in the first two days results in autogenous expansion, which can delay the appearance of tensile stress. The magnitude of autogenous expansion depends on the compatibility of ettringite content and pore size. The w/b ratio of 0.42 turns out to be optimal because it produces the highest amount of ettringite and results in the highest autogenous expansion. In comparison, the w/b ratio of 0.35 introduces significant autogenous shrinkage after the expansion peak and therefore corresponds to a high early-age cracking risk.

ON THE NONLINEARITY OF DEFORMATION OF REINFORCED CONCRETE FLEXURAL ELEMENTS

It is shown that in most calculations of reinforced concrete elements, the descending branch of the concrete deformation diagram should not be taken into account. This is due to the fact that in the calculation it is impossible to exceed the value of the stress in concrete, the value of the design resistance. It is shown that the "moment-curvature" dependence has a linear character both before the formation of cracks and after the formation of cracks. At the same time, calculations using software systems are greatly simplified with almost no loss of accuracy. The use of nonlinear methods for determining the stress-strain state in design leads to significant difficulties. In addition, these methods do not add accuracy to the calculation, but lead to ill-conditioned design schemes. The ascending branch of the concrete diagram can be approximated by a 63 straight line, which greatly simplifies the calculations without a noticeabledecrease in accuracy. The use of a non-linear form of the concrete diagram complicates the calculations, especially when used in software systems. This is because the roots of any equation greater than the first degree have two or more values for the same value of moment or stress. Therefore, it is difficult to choose the desired root in the software package. The use of a linear function always has a unique solution, while the accuracy decreases quite slightly. The statement about the linear relationship "moment-curvature" is also proved by the approach that is adopted in the US standards. If we pass from the formula for determining the moment of inertia of an element with cracks to the “moment-curvature” dependence, then we can see that this dependence is linear. The article shows how to use linear dependencies in the calculations of beam elements and slabs. The proposed approach to the design of reinforced concrete slabs using the finite element method involves changing the rigidity of the finite element depending on the presence or absence of cracks. In this case, the stiffness can have only two values, which are approximated by linear dependencies

Investigation into Viscoelastic Properties of Fiber-Reinforced Asphalt Composite Concrete Based on the Burgers Model

Asphalt composite concrete pavement is one of the common pavement forms in China. However, due to the influence of design, materials, construction quality, and other aspects, asphalt composite concrete pavement develops various degrees of cracks after being put into use, which affects the service performance and life of asphalt pavement. The Burgers model is used to examine the effects of fiber-volume-fraction and length–diameter-ratio on the viscoelastic mechanical behavior model parameters and viscoelastic properties of asphalt composite concrete through the bend test for creep of polyester fiber asphalt composite concrete beam. The findings indicate that the fiber’s ability to control asphalt composite concrete bending creep deformation increases initially and subsequently diminishes as fiber-volume-fraction and length–diameter-ratio increase. Fiber-volume-fraction and length–diameter-ratio effects can be fully reflected by fiber amount characteristics. A viscoelastic mechanical behavior model of fiber-reinforced asphalt composite concrete is developed on this foundation while taking into account the influence of fiber amount characteristic factors. Theoretical study and practical research indicate that the ideal fiber volume ratio of polyester fiber asphalt composite concrete is 0.35 percent, the ideal length-to-diameter ratio is 324, and the ideal fiber amount characteristic parameter is 1.13. The test results can provide a certain reference value for the improvement of the long-term durability of fiber asphalt composite concrete pavement of road engineering.

Dynamic Behavior Analysis of I-Shaped RC Beams under Combined Blast and Impact Loads

The existing literature mainly focuses on the research of reinforced concrete (RC) beams under a single load such as blast or impact. In this paper, the slab–rib–slab RC beam, a new type of structure widely used in bridge structures, was taken as the research object. The explicit dynamic analysis software LS-DYNA was used to numerically analyze the dynamic response and failure behavior of I-shaped RC beams under combined blast and impact loads. For this reason, an effective numerical analysis model was obtained by carrying out experiments on I-shaped RC beams under contact explosion. The key factors affecting the dynamic response of the structure under combined loads were numerically analyzed. Numerical results showed that different load application sequences have important effects on the dynamic response of the structure. When the impact load was first applied to the structure, more severe concrete damage and deformation occured in the depth direction of the beam. However, when the blast load was first applied to the structure, the concrete at the lower flange was damaged in the span direction of the beam due to tension, and no large-scale concrete spallation occurred in the depth direction. This was mainly due to the different mechanisms of blast and impact loads. In addition, the vulnerability of the I-shaped RC beams varied with some structural parameters, including span, depth, and configuration of reinforcement. At the same time, the results showed that the structure is more sensitive to changes in structural parameters when it is first subjected to impact loads.

ОПРЕДЕЛЕНИЕ УСЛОВНЫХ КОЭФФИЦИЕНТОВ СНИЖЕНИЯ ЖЕСТКОСТИ МОНОЛИТНЫХ ЖЕЛЕЗОБЕТОННЫХ КОНСТРУКЦИЙ В КОНЕЧНО-ЭЛЕМЕНТНОЙ МОДЕЛИ СООРУЖЕНИЯ

The article is devoted to an urgent problem related to the reasonable consideration of changes in the stiffness characteristics of core elements in finite element models when calculating buildings and structures made of monolith reinforced concrete. The approach proposed in the article is aimed at meeting the requirements of SP 63.133330-2018 "Concrete and reinforced concrete structures" and SP 430.1325800.201 "Monolithic structural systems". The sequence and content of the stages of solving the problem of determining conditional coefficients of stiffness reduction are disclosed. The results of calculation of conditional coefficients of stiffness reduction and modulus of concrete deformation are presented on the example. The area of variation of the coefficients and modulus of deformation for a given level of loading of the structure and structure is shown. It is shown how the change in the stiffness of the finite elements affects the redistribution of bending moments in the beam structure in comparison with the calculated model with the initial stiffness of the same for all finite elements of the model.