Compressive Behavior Of Concrete Research Articles

Investigation of the Effect of Nanometakaolin on the Compression Behavior of Concrete by Acoustic Emission.

To investigate the influence of nanometakaolin (NMK) on the compression behavior of concrete, acoustic emission (AE) is applied to monitor the development of cracks on ordinary concrete as a control sample and concrete with the addition of 1% or 3% NMK during the whole compressive process. The AE parameters (event, count, RA-AF, etc.) and Gaussian Mixture Model (GMM) were analyzed. The results show that the addition of NMK results in a decrease of crack number and crack width. Compared to the control concrete, the concrete with NMK inhibits the initial crack, increases the crack initiation stress and crack damage stress, and improves the energy of crack propagation. Correspondingly, we proposed a critical point where the ringing counts and amplitude fit parameters are less than a certain threshold. This index can be used as a failure precursor for crack instability. According to the criterion and the GMM, what is found from the relation between RA and AF is that the resistance to tensile and shear is improved in the case of the concrete with NMK.

A Study of the Compressive Behavior of Recycled Rubber Concrete Reinforced with Hybrid Fibers

With the development of the automotive industry, a large amount of waste rubber is produced every year. The application and development of recycled rubber concrete (RRC) can effectively reduce ‘black pollution’ caused by waste rubber. However, the addition of recycled rubber particles can lead to a decrease in the compressive behavior of concrete. Previous research has demonstrated that by preventing crack growth, fiber addition can increase the strength and ductility of concrete. In this work, a total of 28 RRC mixes are designed, and the compressive behavior of RRC reinforced by steel fibers (SFs) and glass fibers (GFs) is investigated. The workability of fresh RRC can be negatively impacted by an increase in both fiber contents, with the GF content having a more notable effect. With the addition of fibers, the maximum increase rates for the compressive strength, elastic modulus, strain at peak stress, and compressive toughness were 27%, 8%, 45%, and 152%, respectively. A constitutive model is concurrently put forward to forecast the stress–strain curves of RRC with various fiber contents. These findings indicate that the maximum improvement in compressive behavior is achieved when the GF content was 0.4% and the SF content was 1.2%. The proposed constitutive model can be used to predict the stress–strain curve of hybrid fiber-reinforced recycled rubber concrete (HFRRRC).

Effect of Sulfate Crystallization on Uniaxial Compressive Behavior of Concrete Subjected to Combined Actions of Dry–Wet and Freeze–Thaw Cycles

This study focuses on the influence of salt crystallization from sodium sulfate on uniaxial compressive properties of concrete subjected to the coupling action of dry–wet cycles and freeze–thaw cycles. Eight groups of concrete specimens with different concentrations of sodium sulfate solution (CSSS) and different numbers of drying and wetting cycles (NDWC) were designed. Three groups of specimens with different numbers of freezing and thawing cycles (NFTC) exposed to same dry–wet cycles and same sulfate concentration were prepared to study the effects of combined environmental conditions. Salt crystallization from sodium sulfate was generated under a cyclical dry–wet time ratio of 3:1. Scanning electron microscopy and X-ray diffraction analysis were used to analyze reaction products of sulfate and concrete matrix. The results show that under single sulfate dry–wet cycles, with the increase of CSSS and NDWC, the uniaxial compressive strength of concrete degrades as a parabola and corresponding strain increases as a parabola, except for the linear increase of CSSS strain. Subjected to the combined action of sulfate dry–wet cycles and freeze–thaw cycles, it shows that the uniaxial compressive strength of concrete decreases as a parabola with the increase of NFTC, but corresponding strains have no obvious variation. The sulfate salt attack in advance greatly accelerates the deterioration of specimens after freeze–thaw cycles. The common dimensionless predication model of stress–strain relationship of concrete subjected to the combined action of dry–wet cycles and freeze–thaw cycles has been established.

Combined effects of cryogenic temperature and strain rates on compressive behavior of concrete

Concrete structures in extremely cryogenic environments may be subject to dynamic loadings as a result of occasional accidents or terrorist attacks during the service life. Considering the cryogenic temperature effect and strain rate effect of each phase for concrete, a meso-scale numerical model of the concrete subjected to cryogenic temperature and dynamic loadings was presented in this study, which serves as a preliminary foundation for calculating and evaluating the performances of concrete structures at cryogenic temperature. Taking concrete cube as an example, the dynamic compressive behavior and strain rate effect of concrete specimens at cryogenic temperature from 20 °C to –160 °C were modelled and investigated. The numerical results indicate that the failure appearances and compressive strength are highly related to the cryogenic temperature and dynamic loadings. The compressive strength at cryogenic temperature is greater than that at ambient temperature, and the sensitivity of dynamic compressive strength to strain rate is enhanced at cryogenic temperature. Moreover, the absorbed energy and dynamic elastic modulus tend to increase with the decrease of temperature and increase of strain rate. According to the numerical results, an empirical formula on dynamic increase factor of compressive strength at cryogenic temperatures (CDIF T) was established.

Experimental study on shear performance of steel shell-concrete composite structure in immersed tunnel

Based on local arrangement details in the top slab of Shenzhen–Zhongshan Link immersed tunnel, steel shell-concrete (SSC) composite specimens with 1:2.5 scale were prepared and tested under shear, to investigate the effects of transverse T-shape stiffeners on shear capacities, crack development, and relative slip. Finite element models were also built and verified by the experimental results. For the specimen without transverse stiffeners, the failure at the steel plate-concrete interface occurred firstly, and then top and bottom steel plates were separated from the compression concrete core. While for the specimen with transverse T-shape stiffeners, the concrete cracks developed diagonally from the flange edge of T stiffeners near the bottom steel plate in sequence, and the corresponding tension field in the steel web enlarged gradually until full web yielding, as the shear force increased. Compared to specimens without transverse stiffeners, when transverse T stiffeners were placed in SSC composite specimens, the shear force at initial cracking was much smaller, but the yielding and ultimate shear capacities were increased by 12.2% and 14.6%, respectively. Although earlier cracking induced, the transverse T stiffeners were beneficial to improve shear capacities of SSC composite structures. The maximum relative slip at steel plate-concrete interface of specimens with and without transverse T stiffeners were 0.28 mm and 0.62 mm before the structure reaching the yielding stage, respectively, indicating that transverse T stiffeners could reduce the relative slip and separation between steel plates and concrete core, ensuring the effective composite action of steel plates and filled concrete. T stiffeners could improve the compressive behavior of concrete. With transverse T stiffeners placed in SSC composite structure, and the shear force could be resisted by both the diagonal compressive core in concrete and the arch system formed with the T stiffeners.

Finite Element Analysis on the Uniaxial Compressive Behavior of Concrete with Large-Size Recycled Coarse Aggregate

To model the concrete with complex internal structure of concrete with large sized aggregates the effect of internal structure on uniaxial compression behavior are studied. Large-sized recycled aggregates behave differently in the concrete matrix. To understand the influence on concrete matrix, a finite element model was developed to model recycled aggregate concrete composed of multiple randomly distributed irregular aggregates and cement mortar. The model was used to calculate the effect of large-size recycled coarse aggregate (LRCA) on the strength of recycled aggregate concrete and simulate the compressive strength of cubes and prisms. The factors such as the strength of new concrete, the strength of old concrete, the defective element content, the shape of LRCA, the incorporation ratio of LRCA and the size of LRCA that can affect the strength of concrete are analyzed in this paper. Results showed that the influence of various factors on concrete strength are in the following desending order: (i) strength of newly poured concrete; (ii) original strength of recycled aggregates; and (iii) defects. It can be seen that the cracking of the phase material elements starts along the bonding zones between gravel and mortar or the new and old mortar, then spreads to mortar and finally to LRCA. The cracking tendency is most significant in LRCA, which means that the fracturing is related to the fracture of the LRCA. After evaluating the variations in strength and quality of the recycled concrete, the influences on concrete strength and quality were studied. The results showed that the proposed concrete model with LRCA was successfully applied to studying the uniaxial compressive behavior of concrete with large-size recycled coarse aggregate.

Nonlinear Finite Element Analysis of Fiber Reinforced Concrete Slabs

This paper presents a study on the behavior of fiber reinforced concrete slabs using finite element analysis. A previously published finite element program is used for the nonlinear analysis by including the steel fiber concrete properties. Concrete is represented by degenerated quadratic thick shell element, which is the general shear deformable eight node serendipity element, and the thickness is divided into layers. An elastic perfectly plastic and strain hardening plasticity approach are used to model the compression behavior of concrete. The reinforcing bars were smeared within the concrete layers and assumed as either an elastic perfectly plastic material or as an elastic-plastic material with linear strain hardening. Cracks initiation is predicted using a tensile strength criterion. The tension stiffening effect of the steel fibers is simulated using a descending parabolic stress degradation function, which is based on the fracture energy concept. The effect of cracking in reducing the shear modulus and the compressive strength of concrete parallel to the crack direction is considered. The numerical results showed good agreement with published experimental results for two fibrous reinforced concrete slabs.

Anisotropic Compressive Behaviour of Concrete from Slabs Damaged by Alkali-Silica Reaction

This paper investigates the anisotropy of the compressive strength and stiffness of concrete in ASR-damaged concrete slabs through an in-depth literature review and experiments. Using Digital Image Correlation (DIC), deformations and crack propagation are closely monitored and analysed. The results show that: (i) The vertical compressive strength and stiffness are lower than the horizontal; (ii) the reduction of the vertical strength and stiffness is mainly due to closure of the horizontal ASR-induced macro-cracks and; (iii) the reduction of the horizontal strength and stiffness is mainly due to the presence of ASR-induced micro-cracks in the cement paste. It is found that the load-carrying capacity and the serviceability for ASR-damaged slabs should be assessed based on the horizontal strength and stiffness.

Nonlinear Finite Element Analysis of High Strength Fiber Reinforced Concrete Beams

This research work presents a nonlinear finite element investigation on the behavior of high strength fiber reinforced concrete beams. This investigation is carried out in order to get a better understanding of their behavior throughout the entire loading history. The three- dimensional 20-node brick elements are used to model the concrete, while the reinforcing bars are modeled as axial members embedded within the concrete brick elements. The compressive behavior of concrete is simulated by an elastic-plastic work-hardening model followed by a perfectly plastic response, which terminate at the onset of crushing. In tension, a fixed smeared crack model has been used.

Behavior analysis of concrete with recycled tire rubber as aggregate using 3D-digital image correlation

Owing to the rapid growth of world population and the usage of cars, scrap tires are causing serious environmental problems and ecological threats, which can be solved by recycling them, e.g., by using them as aggregates in concrete. In this study, an experimental investigation is established to understand the compression behavior of concrete by replacing natural aggregates with recycled tire rubber at different percentages, ranging from 10% to 50% by volume. In experimental testing, several compression tests were performed on cylindrical concrete samples, and a three-dimensional digital image correlation (3D-DIC) system was used to analyze the compression behavior of concrete structures during deformation. The experimental results indicated that the behavior of concrete changed from brittle to ductile and their ability to absorb compression energy (compression toughness) improved by increasing the crumb rubber percentage. Using 3D-DIC system which has a potential to replace the conventional tools, cracks onset locations were detected, failure mechanism and crack progress were tracked, and critical strain values which are usually at the interface of rubber particles and concrete were located. Although the cost of rubber crumbs is high compared with that of natural aggregates, incorporating recycled tire rubber in concrete structures can solve ecological problems.

High strain rate and low temperature effects on the compressive behaviour of concrete

Temperature and strain rate are important factors when considering the mechanical properties of engineering materials, as they can greatly influence the material behaviour. The research presented here is an experimental investigation to determine the effects of low temperatures and high strain rates on the compressive behaviour of concrete. The primary purpose of the research is the development of experimental stress–strain relationships under these conditions, as this is a largely unexplored research topic. Thirty-five 101.6 mm × 203.2 mm concrete cylinders were tested in uniaxial compression at the University of New Brunswick. The specimens were loaded either under static conditions or dynamically with an average strain rate of approximately 1 s−1, while being exposed to temperatures from 20°C to −70°C to simulate extreme climatic temperature and those attainable within industrial storage facilities. The compression strain of the specimens was obtained using digital image correlation. The mechanical properties studied were the compressive strength, strain associated with the peak stress and general stress–strain behaviour due to the increased strain rate and temperature variations.

Compressive Stress–Strain Response of Concrete Exposed to Low Temperatures

Temperature is an important factor when considering the mechanical properties of engineering materials because they can change drastically as temperatures change. The research presented here is an experimental investigation to determine the changes in the compressive behavior of concrete that occur because of low exposure temperatures. The primary purpose of the research is the development of detailed experimental stress–strain relationships exposed to low temperatures, which remains a largely unexplored topic. A total of twenty-seven 101.6×203.2 mm concrete cylinders were tested in uniaxial compression at the University of New Brunswick. The specimens were exposed to temperature ranges from 20°C to −70°C to simulate extreme climatic temperatures and those obtainable in industrial storage facilities. The compression strain of specimens was obtained by using three-dimensional digital image correlation. The mechanical properties studied were the relative changes in compressive strength, modulus of elasticity, and peak strain attributable to temperature variations. Predictive equations and relationships for these properties with respect to temperature are presented and compared with the existing literature.

Utilization of unprocessed steel slag as fine aggregate in normal- and high-strength concrete

With the increasing shortage of natural materials, using steel slag instead of natural sand to prepare concrete has become a promising technology. This study aims to investigate the utilization of unprocessed steel slag in normal- and high-strength concrete, focusing on the effects of steel slag as fine aggregate on the compressive behaviour of concrete. Two types of concrete (normal- and high-strength concrete) and eight replacement percentages of fine aggregate by steel slag (0%, 10%, 20%, 30%, 40%, 60%, 80%, and 100%) are used as the test parameters. A series of axial compression tests are conducted on cylinders of fine steel slag concrete (SSC). The influence of the replacement percentage of steel slag on the stress-strain relation, compressive strength, inflation ratio, elastic modulus, and toughness of normal- and high-strength concrete is analysed. Moreover, the failure mechanism of SSC under compression is discussed. The results show that the compressive strength of SSC is not monotonous with increasing steel slag content and that the use of steel slag as fine aggregate in concrete mixes has a positive effect on the energy absorption capacity. SSC with an optimal steel slag content can exhibit better compressive behaviour compared with normal concrete.

Compressive Behaviour of Concrete by Using Bagasse Ash From Sugar Mill

The materials which are useless and unwanted is called waste product and this waste product is a burden and harmful to the environment. Sugarcane bagasse ash (SCBA) is one kind of waste which can be termed as the residue left over from burning sugar cane bagasse. The utilization of this waste may be very economical and can also solve the environmental problem. Silica and alumina are the main element of SCBA which is used as a pozzolanic material. This recycling procedure of SCBA reduces environmental pollution and this is also considered the cost-effective material. In this paper, SCBA replaces the cement as a weight of 5%, 10% and 15% which is considered. After completing the compressive strength test, the result shows that the compressive strength increases when 5% cement is replaced by sugarcane bagasse ash and this is the correct replacement of cement.

Fiber-reinforced concrete containing ultra high-strength micro steel fibers under active confinement

This paper presents an experimental study on the compressive behavior of steel fiber-reinforced concrete (SFRC) under active confining pressure. Four different SFRC mixes containing ultra high-strength micro steel fibers at two volume fractions of 1% and 2% were prepared to produce concretes with two different target compressive strengths of 50 and 100 MPa. The active confining pressure was applied on SFRC using a Hoek cell at different confinement levels of 5, 10, 15, and 25 MPa. The effects of confining pressure and steel fiber volume fraction on the compressive behavior of concrete were examined through the axial compression tests on unconfined and actively confined SFRCs. The results show that the axial strength and peak axial strain of SFRCs increase with an increase in the fiber volume fraction. The fiber volume fraction also affects the post-peak branch trend of the axial stress-strain relationships of SFRCs under a given confinement level. SFRCs with a higher volume fraction exhibit more shallow post-peak branches than those of SFRCs with a lower volume fraction. The results also show that the axial strain of SFRC at a given lateral strain increases with an increase in the volume fraction, indicating a reduced rate of dilation of SFRCs at a higher volume fraction. These promising findings point to the great potential of the use of ultra high-strength micro steel fibers in the development of high performance composite structural members in applications where the concrete will be subjected to lateral confinement.

Combined usage of micro-silica and nano-silica in concrete: SP demand, cementing efficiencies and synergistic effect

It is well known that the addition of micro-silica (MS) can improve the strength and durability of concrete and the addition of nano-silica (NS) can also improve certain properties of concrete. However, systematic research is still needed to exploit the benefits of combined usage of MS and NS, and more specifically, to evaluate their cementing efficiencies and synergistic effect. In this study, an experimental program was launched to investigate the combined effects of MS and NS on the compressive behaviour of concrete. Concrete mixes with varying water/cementitious materials (W/CM) ratio, MS content and NS content but similar workability were produced for testing. It was found that NS has much higher superplasticizer (SP) demand and cementing efficiency than MS. Nevertheless, at the same strength, the SP demand of (MS + NS) is not higher than that of pure cement. More importantly, the combined usage of MS and NS offers certain synergistic effect, as evaluated by a new formula proposed in this study.

Specimen Size and Strain Rate Effects on the Compressive Behavior of Concrete

Three high-performance concrete (HPC) materials with different specimen geometries were characterized using Kolsky compression bar techniques to study the strain rate and specimen size effects on their uniaxial compressive strength. A large-diameter Kolsky bar and recently established annular pulse shaping technique were used to achieve dynamic stress equilibrium and constant strain-rate deformation in the experiments. A complimentary effort was conducted using a 19-mm-diameter Kolsky compression bar to understand the strain rate and specimen size effects on failure strength and dynamic increase factor (DIF) for concrete. It was found that, for all three concrete materials investigated, the failure strength is highly dependent on the specimen geometry, however such a relationship is not apparent for the DIF. The DIF observed in this study shows significantly lower values compared to historical data, which may indicate the importance of well-controlled dynamic testing conditions on the accuracy and validity of experimental results for concrete materials.

Simplified Constitutive Model for Fatigue Behavior of Concrete in Compression

AbstractIn the literature, three basic assumptions are used to modify monotonic constitutive models in order to simplify fatigue analysis of concrete. First, the fatigue hysteresis loop at failure ...

Behavior of rubberized concrete under active confinement

This paper presents the results of the first experimental study on the axial compressive behavior of the rubberized concrete under active confinement. Four different batches of concretes with rubber replacement ratios of 0%, 6%, 12%, and 18% were prepared. The effects of the rubber replacement ratio and confining pressure on the compressive behavior of concrete were examined through the tests of unconfined and actively confined concrete cylinders. The active confinement was applied by a Hoek cell at different pressures, including 5, 7.5, 10, 15, 20, and 25MPa. The results indicate that the rubber content significantly affects the compressive behavior of actively confined concrete. An increase in the rubber content results in a decrease in the compressive strength and an increase in the axial and lateral deformability of concrete. It is found that the axial strength and strain of rubberized concrete increase with the confining pressure following a similar trend to that in conventional concrete. On the other hand, the rubber content affects the descending branch trend of the axial stress-strain curves of concrete under active confinement, with more shallow branches seen in concretes with a higher rubber replacement ratio.

Use of Fine Rubber Particles as Fine Concrete Aggregates in Actively Confined Concrete

This study presents the results of the experimental study on the axial compressive behavior of the rubberized concrete under active confinement. Two different mixes of concretes with rubber replacement ratios of 0%, as a control mix, and 18% were prepared. The effects of the incorporation of rubber and the confining pressure on the compressive behavior of concrete were examined through tests of unconfined and actively confined concrete cylinders. The active confinement was applied by a Hoek cell at different pressures, including 5, 7.5, 10, 15, 20, and 25 MPa. The results indicate that the rubberized concrete exhibits lower compressive strength but higher axial and lateral deformation capacities than those of the conventional concrete.