Stress-strain Curve Of Concrete Research Articles

Research on Full Stress-strain Curve of Ecological Porous Concrete

Research on Full Stress-strain Curve of Ecological Porous Concrete

Numerical simulation of concrete strength based on microstructure and mineral composition analysis using micro-CT and XRD technology

The investigation of mechanical properties in porous materials, such as concrete, has been a significant area of interest in the fields of civil engineering and architecture. Traditional macroscopic mechanical testing methods are limited due to destructive experimental conditions, time-consuming procedures, and the inability to characterize internal structures. To overcome these limitations, researchers have utilized microscopic factors with micro-CT and simulation models. Different simulation methods demand mechanical parameters to effectively model the constituent materials; however, there exists variability in the amount and standard values of these input parameters, which leads to a decrease in the reliability of the obtained results. In order to tackle this issue, a novel approach is proposed, which integrates mineral component analysis using X-ray diffraction (XRD) and establishes coefficients to minimize the number of necessary input parameters. Simulation results demonstrate excellent agreement with experimental measurements, accurately reproducing the stages of elastic deformation, failure, and fracture in the stress-strain curve of concrete. Our findings reveal that changes in the concrete skeletal structure, microstructure, and mineral composition significantly influence compressive strength. Coarse aggregates and high-mechanical-performance minerals, in particular, have a substantial impact. Additionally, the mechanical properties show a significant linear relationship with the strength reduction coefficient of aggregates and concrete cores. In conclusion, the proposed method, combining CT scanning and XRD with FDEM, proves to be a reliable and practical approach for accurately assessing the mechanical properties of concrete. This methodology simplifies the intricate processes associated with the time-intensive parameter calibration, leading to a more efficient parameter allocation procedure. As a result, this method enhances concrete design, promotes a better understanding of parameter impacts, and enables accurate prediction of concrete behavior across diverse scenarios.

Compression stress-strain curve of lithium slag recycled fine aggregate concrete.

As one of the key materials used in the civil engineering industry, concrete has a global annual consumption of approximately 10 billion tons. Cement and fine aggregate are the main raw materials of concrete, and their production causes certain harm to the environment. As one of the countries with the largest production of industrial solid waste, China needs to handle solid waste properly. Researchers have proposed to use them as raw materials for concrete. In this paper, the effects of different lithium slag (LS) contents (0%, 10%, 20%, 40%) and different substitution rates of recycled fine aggregates (RFA) (0%, 10%, 20%, 30%) on the axial compressive strength and stress-strain curve of concrete are discussed. The results show that the axial compressive strength, elastic modulus, and peak strain of concrete can increase first and then decrease when LS is added, and the optimal is reached when the LS content is 20%. With the increase of the substitution rate of RFA, the axial compressive strength and elastic modulus of concrete decrease, but the peak strain increases. The appropriate amount of LS can make up for the mechanical defects caused by the addition of RFA to concrete. Based on the test data, the stress-strain curve relationship of lithium slag recycled fine aggregate concrete is proposed, which has a high degree of agreement compared with the test results, which can provide a reference for practical engineering applications. In this study, LS and RFA are innovatively applied to concrete, which provides a new way for the harmless utilization of solid waste and is of great significance for the control of environmental pollution and resource reuse.

Finite element analysis of stress–strain relationship and failure pattern of concrete under uniaxial compression considering freeze–thaw action

In order to study the uniaxial compression behavior of concrete before and after freeze–thaw cycles, the uniaxial compression test of 100 mm × 100 mm × 300 mm prism was carried out by comparing the experimental and numerical simulation results. A three-dimensional mesoscopic model considering the random shape and size of aggregate was established. The failure mechanism, failure pattern and stress–strain curve of concrete under uniaxial compression before and after freeze–thaw cycles were compared to verify the reliability of the three-dimensional modeling method and corresponding calculation parameters of concrete. Finally, a reliable unified constitutive model of concrete stress–strain curve relationship considering freeze–thaw damage variables is established, which can better reflect the continuous change law of concrete uniaxial compressive stress–strain relationship during freeze–thaw process. More importantly, this work provides a reference for future study of stress–strain intrinsic relationship of concrete freeze–thaw damage using numerical simulation through a small amount of experiments.

Complete Generalization of the Equations for the Stress-Strain Curves of Concrete under Uniaxial Compression.

The existence of more than thirty stress-strain equations, including those proposed by the government regulations in many countries, seems to indicate that additional, unifying, and at the same time generalizing research is necessary for this subject. Many expressions can be found to set or determine the initial modulus of elasticity of concrete, i.e., the modulus of elasticity of concrete when no load has been applied to it. This work proposes a complete generalization of the equations based on scalar damage models, applicable to all types of concrete tested under uniaxial compression with any constant rate of stress or strain, although in no case can it be considered a constitutive model. We prefer to discuss an equation that models the shape of the stress-strain curve. Thus, the shape of this curve is studied here in the same way a forensic scientist would, which is why we could see this work as an autopsy carried out on the test specimen through the trace left in the plane σ-ε by the straining process up until its inevitable outcome. That is to say, we believe in a purely phenomenological approach. The results are compared with the data obtained experimentally by analyzing test specimens made using various mixed portions of cement, water, and aggregates.

Strain regime induced by axial compression in slender reinforced concrete columns using different mathematical approaches

A mathematical investigation to determine the strain regime induced by normal compression force in concrete, including the portion due to material creep, was presented. The consideration of creep suggests the possibility of changing the constitutive law of the material since it introduces a temporal variation, hence the need to use different mathematical paths to evaluate the imposed strains. The analysis was conducted on a real reinforced concrete column, with variable geometry and high slenderness ratio, on which two different approaches were considered. In the first one, a concrete stress–strain curve, standardized by a technical norm, was used. In the second one, the integration of differential relations of displacements along the length of the structure was adopted. The analysis was performed by considering the structural system loaded by just its self-weight to the critical buckling load.

Effects of mix components on mechanical properties of marine volcanic-scoria concrete under axial compression

This study systematically investigated the mechanical properties of marine volcanic-scoria concrete (MVSC) under the coupled effects of the mix components. Six groups and 408 specimens were used, including four different experimental parameters: types of coarse and fine aggregates (volcanic-scoria aggregate and natural aggregate), types of mixing water (seawater and freshwater), and age (days 7, 14, and 28). The macro-mechanical properties, mechanism, and microstructure of MVSC were analysed using a novel test system, including an axial compression test, digital image correlation (DIC) method, and scanning-electron microscopy (SEM). Variations in the failure pattern, stress–strain curve, deformation field distribution, crack initiation, and propagation of MVSC were studied. Generally, the failure of MVSC is brittle compared to that of ordinary concrete (OC). The cubic compressive strengths of MVSC at day 7 and 14 were 82.7% and 91.7% of the cubic compressive strength at day 28, respectively. The splitting tensile strength of MVSC was 7.3% higher on average than that of OC. The mix components changed the strength of MVSC. Seawater and sea sand accelerated the development of compressive strength, volcanic-scoria fine, and coarse aggregates (VSFA and VSCA, respectively) enhanced the tensile strength. After using volcanic-scoria aggregates, the curvature of the concrete stress–strain curve decreased; however, the curve declined sharply after the peak stress (σmax). Compared with OC, the ductility of MVSC decreased by an average of 17.2%, whereas the peak strain increased by 6.9%. Furthermore, VSCA significantly changed the displacement distributions of the specimen, whereas the impacts of the mixing water and fine aggregate were small. The crack initiation and propagation of MVSC were different from those of OC; that is, microcracks first appeared in VSCA, and their characteristics propagated slowly before σmax. Finally, a theoretical model of the MVSC stress–strain curve involving the coupled impacts of the mix components was established, which can prompt the practical application of MVSC structures.

Numerical simulation of influence of coarse aggregate crushing on mechanical properties of concrete under uniaxial compression

Coarse aggregate crushing has a significant impact on concrete deformation and failure characteristics. The coarse aggregate geometries with actual shapes are imported and the mesoscopic model of concrete is established in the discrete element method. The effect of coarse aggregate crushing on the mechanical properties of normal concrete and high-strength concrete during the uniaxial compression test is investigated. The findings reveal that: (1) The coarse aggregate crushing affects the concrete stress–strain curve. Increasing the content of crushable coarse aggregates can reduce the concrete’s peak stress and peak strain. (2) The changing trend of compressive strength of normal concrete and high-strength concrete is different as the percentage of crushable coarse aggregates increases. (3) Normal concrete is more affected by coarse aggregate crushing than high-strength concrete. The compressive strength of normal concrete can be reduced significantly with less crushable coarse aggregates. (4) Coarse aggregate crushing changes the failure mode of concrete. The cracks inside the concrete can extend through the crushable coarse aggregates. In conclusion, it is beneficial to obtain a more realistic deformation failure mode of the concrete by considering the crushing of the coarse aggregate during the uniaxial compression test.

Research on Mechanical and Carbonization Properties of Hybrid Fiber Iron Tailings Concrete Based on Deep Learning.

Iron tailings sand is a kind of mineral waste, and open-air storage is a common treatment method for iron tailings, which not only has a huge impact on the ecological environment but also occupies a lot of land resources. Therefore, the preparation of high-ductility fiber reinforced iron tailings concrete and its application in practical engineering structures have good application prospects. This paper is based on the deep learning research on the mechanical and carbonization properties of hybrid fiber iron tailings concrete. Therefore, tailings sands with different substitution rates, single-mixed steel fiber, and mixed steel-PVA fiber concrete were prepared in this paper. Its compressive strength, split tensile strength, axial compressive strength, elastic modulus, strain, and carbonization depth were tested. Through the existing concrete compressive stress-strain curve equations, the nonlinear calculation of each group of concrete compressive stress-strain curve equations in this paper is carried out, some parameters are determined, and the carbonation depth equation is established. The results show that, with the increase of tailings content, the properties of concrete increase first and then decrease and the addition of fibers can effectively improve the strength, elastic modulus, peak strain, and carbonization depth of concrete. However, with the increase of PVA fiber content, its performance enhancement effect decreased.

Research on the constitutive relationship of concrete under uniaxial compression in freeze–thaw environment

• The quantitative method was used to analyze the stress–strain curve during freeze–thaw. • The quantitative relationship between freeze–thaw damage parameters and mechanical indices was determined. • The stress–strain curve model of concrete considering freeze–thaw damage variables was established. • The stress–strain curve model reflects the variation law of the curve during freeze–thaw. Through uniaxial compression tests of concrete prism specimens with strength grades ranging from C35 to C65 under without freezing–thawing (F–T) and with rapid F–T cycles, the damage form, stress–strain relationship, quasi-static mechanics performance, and deformation performance of the specimens were obtained. Further, the relationship between the F–T damage variable, and a model for the F–T damage variable stress–strain curves of the concrete were established. After F–T, the concrete prism specimen exhibited a typical split failure with the crack developed along the interface transition zone (ITZ), and severe damage. The F–T cycles reduced the mechanical properties and brittleness, and increased the ductility of concrete. The linear relationship between the peak stress, peak strain, and static elastic modulus of concrete under uniaxial compression and F–T damage was established. Finally, a unified constitutive model of the concrete stress–strain curve relationship considering the F–T damage variable was established. The resulting model can accurately reflect the stress–strain relationship of concrete under uniaxial compression during F–T, which can provide a reference for future research on the constitutive relationship of concrete F–T damage..

Research on compressive performance of high-strength concrete confined by high-strength stirrups

Axial compressive test of high-strength concrete prism specimens confined by high-strength stirrups are carried out. The yield strength of stirrups, volumetric stirrup ratio and concrete strength are investigated for the impact of pressure performance. The results show that the confined concrete specimens with high stirrup ratio, high strength, exhibits good ductility. The use of high-strength stirrups is an effective measure to prevent a sudden drop in the falling section of the high-strength concrete stress-strain curve; under the circumstances, the application of high-strength stirrups can reduce the volumetric stirrup ratio.

Study on the Full Stress-Strain Curve of High-Performance Concrete with Aar Suppression Measures Exposed to Lye Solution at 38℃ for 10 Years

Study on the Full Stress-Strain Curve of High-Performance Concrete with Aar Suppression Measures Exposed to Lye Solution at 38℃ for 10 Years

A Simplified Uniaxial Stress-strain Curve of Concrete and Its Application in Numerical Simulation

Detennining the constitutive model is a key procedure in numerical simulation of concrete structures. The uniaxial stress-strain curve is important information to determine the concrete constitutive model. This paper provided a simplified stress-strain curve of concrete that can be used in simulation. The comparison between Chinese Code and the simplified curve shows that the simplified curve of uniaxial compression is close to the code value. Numerical simulation of concrete beams show that the simplified curve proposed has high computational efficiency and good convergence.

PARÁMETROS RELEVANTES DE LA CURVA ESFUERZO-DEFORMACIÓN EN COMPRESIÓN DE CONCRETOS NO CONFINADOS PRODUCIDOS EN MÉXICO

Las Normas Técnicas Complementarias para Diseño por Sismo para la Ciudad de México especifica por primera vez, métodos de análisis sísmico no lineal de estructuras, para los cuales es necesario conocer, entre otros, los parámetros que definen la curva-esfuerzo-deformación en compresión del concreto sin confinar. En esta investigación se llevaron a cabo estudios analíticos y experimentales de concretos producidos recientemente en México. Con base en los resultados encontrados se dan recomendaciones para estimar parámetros que definen de manera importante la curva esfuerzo-deformación del concreto sin confinar. Los estudios experimentales de los especímenes de concreto se realizaron en el Instituto de Ingeniería de la UNAM, aplicando ciclos de carga en compresión de acuerdo con las normas ASTM y NMX correspondientes y tomando como resultado un promedio de las muestras ensayadas. Se proponen expresiones para obtener el módulo de elasticidad del concreto, Ec, parámetro que es relevante en el cómputo de desplazamientos laterales de estructuras en zonas sísmicas, así como en el cómputo de los periodos de vibrar de una estructura en estas zonas. También en esta investigación se dan expresiones para obtener valores de parámetros importantes de la curva esfuerzo-deformación del concreto no confinado en compresión, los cuales se emplean en el modelado de articulaciones plásticas para el análisis no lineal. Estos parámetros son la relación de Ec y el módulo secante, Esec, Ec/Esec y la deformación del concreto en f’c, e’c. Con base en los resultados de estos ensayes se dan recomendaciones para la estimación de estos parámetros para concretos producidos recientemente en México.

Parameter calculation and verification of concrete plastic damage model of ABAQUS

The purpose of this paper is to study the method for determining the parameters of ABAQUS CDP model based on the concrete stress-strain curve provided by the code for concrete structure design. A finite element model was established to calibrate the value of the stress-strain curve cutoff and the damage factor of the concrete, and a calculation method of damage factor was recommended. The results show that the relative errors between first crack load, ultimate load and deflection at ultimate load with the experimental results were less than 5%. It is accordingly concluded that the finite element analysis results adequately reflected the experimental results.

Strain-sensing characteristics of self-consolidating concrete with micro-carbon fibre

ABSTRACTBased on experimental study correlations between change in electrical resistance and properties of concrete are reported in this paper. This study is performed on concrete cubes of 100mm size containing carbon fibres in different dosages (0, 0.5, 1, 1.5 and 2%) by mass of cement. Concrete cubes were subjected to strain-sensing and damage-sensing tests. Strain-sensing test is conducted within elastic range and the correlation is obtained between change in electrical resistance and strength of concrete. From test results, it is found that concrete specimens containing carbon fibres 1.5% produces better strain and damage-sensing characteristics and can be correlated to stress strain curve of concrete. On the basis of experimental results, it is rationally explored in this study that concrete containing micro carbon fibres induce self-sensing property in it and therefore can be effectively used for health monitoring of concrete structures.

An Assessment Method for Residual Bearing Capacity of RC Bridges After Fatigue Damage

In order to realize the in-situ evaluation of reinforced concrete bridges subjected to fatigue for a long time, an evaluation method for cumulative damage of concrete structures based on unloading elastic modulus is proposed. First, according to the concrete stress-strain curve and the statistical relationship between residual strain and cumulative strain, the calculation method of static equivalent strain and residual strain concrete based on unloading elastic modulus and the method for estimating the strength of concrete after damage are proposed. The detailed steps of field test and analysis and the practical damage indicators of residual strain are given. Then, the evaluation method of existing stress and strain of Reinforced Concrete Bridge under dead load and the concept of “equivalent dead load bending moment” are put forward. On this basis, the paper analyzes the root cause of the decrease of bearing capacity of Reinforced Concrete Bridge after fatigue damage, and points out that the equivalent strain or residual strain of reinforced concrete increases under the fatigue effect, which leads to the decreasing of actual live moment and deformation performance while the ultimate load-carrying capacity remains constant or very little decrease. The evaluation method of structure residual capacity is given, which has reference value for engineering practice.

Micro carbon fiber based concrete as a strain-damage sensing material

Abstract Co-relation between change in electrical resistance and properties of concrete are reported in this paper. This study is done on concrete cubes of 150 mm containing carbon fibers in different dosages (0%, 0.5%, 1%, 1.5% and 2%) by mass of cement. Cubes were subjected to strain sensing and damage sensing test. Strain sensing test is conducted within elastic region under cyclic loading and the co-relation is obtained between change in electrical resistance and strength with respect to time. From obtained results it was found that concrete specimen containing carbon fibers 1.5% by mass of cement gives better co-relation. After strain sensing test, samples were tested for damage sensing test by applying load gradually up to failure. The co-relation between changes in electrical resistance, stress and strain is plotted. From obtained results it is found that, the same sample containing 1.5% fiber by mass of cement is best for damage sensing and can be co-related to stress strain curve of concrete. Thus from obtained it can be concluded that concrete containing carbon fibers makes concrete as self sensing concrete that can be used for health monitoring of concrete structures.

Comparison of complete stress-strain curves of concrete using test prisms and test cylinders

Without concrete stress-strain curves based on the results of experiments obtained using test prisms and test cylinders it is difficult to evaluate the compliance of the ultimate strain of concrete with the peak load and the descending arm load at the level of 0.85Rb. In this paper, an attempt was made to experimentally verify curves σ-ε. Specimens made as one batch of the same concrete mix were tested using same methods. The test results showed that the difference in ultimate rates of strain is minor, and the analytical description of the curves obtained on prisms and cylinders corresponds to the results of testing not only at the peak load points and descending arm at the level of 0.85Rb, but also at intermediate values.

Derivation of Complete Stress–Strain Curve for SSTT-Confined High-Strength Concrete in Compression

Abstract For concrete structural behavior analysis, the complete axial stress–strain curves in compression can be determined by using a closed-loop servo-controlled hydraulic testing machine. The applied loading as well as the axial deformation reading of the loaded concrete specimen is recorded from the built-in displacement transducers or externally installed transducers placed between the machine platens. However, the recorded axial strain in the ascending branch is not purely concrete deformations but includes some additional deformation because of machine flexibility and specimen’s end restraint. Strain gauges can be diametrically installed at the middle of specimen for a more precise deformation reading but additional costs are required for the gauges and data acquisition system. Moreover, the concrete stress–strain curve and ductility performance beyond its ultimate is difficult to be recorded without special strain measuring devices. Hence, a correction equation is needed to account for these effects to obtain the complete stress–strain curves for unconfined and confined concrete. In this paper, a total number of 84 unconfined and steel strapping tensioning techniques (SSTTs) confined high-strength concrete cylinders of compressive strength ranging from 62.48 MPa to 184.85 MPa were tested in compression in accordance with ASTM C39/C39M-11. The details for the testing setup, testing machine, strain measuring instruments, loading rate, loading patterns, etc. are described and at the same time a correction factor equation is proposed in this paper.