Mechanical Behavior Of Concrete Research Articles

Quantification of coarse aggregate shape in concrete

The objective of this study is to choose indices for the characterization of aggregate form and angularity for large scale application. For this purpose, several parameters for aggregate form and angularity featured in previous research are presented. Then, based on these established parameters, 200 coarse quartzite aggregates are analyzed herein by using image processing technology. This paper also analyzes the statistical distributions of parameters for aggregate form and angularity as well as the correlation between form and angularity parameters. It was determined that the parameters for form or angularity of coarse aggregates could be fitted by either normal distribution or log-normal distribution at a 95% confidence level. Some of the form parameters were influenced by changes in angularity characteristics, while aspect ratio and angularity using outline slope, area ratio and radius angularity index, and aspect ratio and angularity index were independent of each other, respectively; and consequently, the independent parameters could be used to quantify the aggregate form and angularity for the purpose to study the influence of aggregate shape on the mechanical behavior of concrete. Furthermore, results from this study’s in-depth investigations showed that the aspect ratio and the angularity index can further understanding of the effects of coarse aggregates form and angularity on concrete mechanical properties, respectively. Finally, coarse aggregates with the same content, type and surfaces texture, but different aspect ratios and angularity indices were used to study the influence of coarse aggregate form and angularity on the behavior of concrete. It was revealed that the splitting tensile strength of concrete increased with increases in the aspect ratio or angularity index of coarse aggregates.

Thermodynamic gradient-based poroplastic theory for concrete under high temperatures

Concrete materials subjected to long term exposures to high temperatures suffer severe degradations in its mechanical properties (cohesion, friction, strength and stiffness) and changes in their failure mechanisms. These degradations may lead to irreversible damage or sudden collapse of the related structures. From the predictive analysis stand point, accurate constitutive theories are required to simulate the variations of concrete mechanical failure behavior under high and durable temperature fields. In the realm of the smeared crack approach, non-local model strategies are required to objectively reproduce failure behaviors under coupled thermo-mechanical loading conditions, while realistic descriptions of the involved characteristic lengths are needed to objectively reproduce the variation from ductile to brittle failure modes depending on the acting confining pressure and temperature. In this work, a thermodynamically consistent gradient poroplastic model for concrete subjected to high temperatures is proposed. A particular and simple form of gradient-based poroplasticity is considered whereby the state variables are the only ones of non-local character. The degradations of these variables due to coupled thermo-mechanical effects are described in the framework of the thermodynamic approach. After describing the material formulation, numerical analyses are presented which demonstrate the predictive capabilities of the proposed constitutive theory for different stress paths and thermal conditions.

Effect of Aggregate Type on the Concrete Matrix/Aggregates Interface and its Influence on the Overall Mechanical Behavior. A Numerical Study.

This paper investigates the effect of siliceous, limestone and plastic aggregates on the compressive behavior of concrete. Firstly, the matrix/aggregates interface is characterized using a scanning electronic microscope. Compressive test is then simulated on a 3D numerical concrete using finite element method. The influence of the matrix/aggregates interface quality is quantified. The results give a new insight and help on the understanding of the contribution of the nature of the aggregate on the overall mechanical behavior of concretes.

Digital Image Technology – Based Simulation for Internal Components and Mechanical Behavior of Asphalt Concrete

Digital image technology – based computer aided design for asphalt concrete is a new direction of asphalt pavement research. This paper focuses on description of research progress achieved by the author’s research institute in the direction, mainly including two-dimensional digital image technology – based research in the internal structure and volume of asphalt concrete, industrial CT-based identification of different substances in the asphalt concrete and acquisition of morphological characteristics for coarse aggregate and three-dimensional digital image technology – based virtual reconstruction of asphalt concrete and simple mechanical behavior simulation.

Effect of the interfacial transition zone and the nature of the matrix-aggregate interface on the overall elastic and inelastic behaviour of concrete under compression: a 3D numerical study

A 3D numerical model is developed to study the elastic and inelastic behaviour of concrete with consideration of the interfacial transition zone and the nature of the matrix – aggregate interface. Concrete is represented as a bi-phasic or tri-phasic material, consisting of spherical aggregates embedded in a matrix (mortar) surrounded or not by a transition zone. The matrix–aggregates interface is modelled taking into account a perfect contact and a sliding one. Numerical elastic modelling results are in a good agreement with those obtained by Hashin and Monteiro analytical model. Numerical results of the overall behaviour modelling show a slight influence of the transition zone on the mechanical behaviour of concrete. In contrast, a significant influence of the nature of the matrix – aggregate contact is demonstrated and explained based on local analysis of stress distribution in the material.

Recycled aggregate concrete – Mechanical behavior under uniaxial and triaxial compression

This paper presents the results of an experimental program related with the failure and mechanical behavior of Recycled Aggregate Concrete (RAC) under different load scenarios. The particular type of RAC considered herein is characterized by the partial or total replacement of natural coarse aggregates by recycled ones obtained from the crushing of waste concrete. The aim of this research is to deepen the existing knowledge related to RACs by analyzing the degradation in physical and mechanical properties when recycled coarse aggregates are used. In particular, its behavior under triaxial compression is examined.A normal strength concrete with natural coarse aggregates was designed and used to produce cylindrical samples which, after being tested, were crushed and reused as coarse aggregates in the elaboration of RAC. Samples were subjected to uniaxial compression, splitting tensile and triaxial compression tests. Experimental results related to the physical properties of recycled aggregates, fresh concrete properties, and hardened concrete mechanical behavior are presented and discussed. Moreover, the Performance Dependent Failure Criterion based on an objective definition of concrete quality, was extended and applied to predict peak stresses of RAC under triaxial compression. The comparison of experimental and numerical results demonstrated that this criterion originally developed for standard concrete is also suitable for RAC.

SHPB Test on Dynamical Mechanical Behavior of Concrete with High Temperature

An experimental system is designed by combining the split Hopkinson pressure bar (SHPB) with microwave heating device, based on numerical simulation and stress wave theory, availability of the experiment technique is analyzed. Tests of concrete whose temperature changes from room temperature to 650°C and impact velocity from 5m /s to 12m /s are completed and for the first time high-temperature dynamical damaging phenomena of concrete are obtained. Based on data analysis, the dynamical mechanical behavior of concrete with high temperature is affected by not only the strain rate effect whose influence keeps on decreasing with temperature increasing, but also the high temperature weakening effect. And the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Part 1 Mechanical Behavior of Concrete

Part 1 Mechanical Behavior of Concrete

Study on Vibrational Liquefaction Behavior of Air-Entrained Concrete

With respect to the liquefaction behavior of cement concrete material in a vibrational condition, the varying patterns of the vibrational viscosity coefficients, vibrational energy transfer and rheological mechanical behavior of air-entrained concrete and non-air-entrained concrete in a vibrational shear condition were compared by analyzing the vibrational liquefaction processes of concrete. The study has found that the vibrational viscosity coefficient of concrete with air entraining agent added increased notably so that air-entrained concrete can maintain good shuttering behavior during slip-form construction; presence of a large number of tiny bubbles in air-entrained concrete allowed more even transfer of vibrational energy in concrete; and the rheological mechanical behavior of concrete was improved after air entraining agents were added so that it became easier to liquefy by vibration and had better shaping effect upon completion of vibration. Keywords: air-entrained concrete, slip-form construction, cement concrete pavement, vibrational liquefaction

Numerical analysis of concrete under a wide range of stress and with different saturation condition

This paper is devoted to the description of elastoplastic damage behavior of concrete under a wide range of confining pressure and different saturation conditions. Based on experimental investigations, two plastic flow mechanisms are identified: plastic shearing coupled with damage at low confining pressure and plastic pore collapse at high confining pressure. The plastic shearing mechanism describes plastic distortion and failure by the formation of shear bands. On the other hand, the pore collapse mechanism is related to the destruction of pore structures. Furthermore, influences of water saturation on the mechanical behavior of concrete are also studied in this paper. The increase of water saturation induces the decrease of capillary pressure leading to an additional plastic deformation. The proposed model is implemented in a fully coupled finite element calculation code. The performance of the model is examined by comparing numerical results with laboratory data issued from triaxial compression tests under a large range of confining pressures.

Prediction of Mechanical Behavior of Concrete Filled Steel Tube Structure Using Artificial Neural Network

Artificial neural network (ANN) is applied to predict load-strain relationship of concrete filled steel tube (CFT) structural parts. An ANN prediction model, which is able to predict load-strain relationship of CFT structural parts with different dimensions and parameters, is made through training the ANN prediction model with the experimental test data. Furthermore, the prediction data and experimental test data are compared. The result shows that the combination of several characteristic parameters of CFT structural parts and ANN prediction model to predict load-strain relationship of CFT structural parts are reliable and feasible. The ANN prediction model has simple, convenience and time-saving merits.

A multiaxial constitutive model for concrete in the fire situation: Theoretical formulation

This paper aims to develop a multiaxial concrete model for implementation in finite element software dedicated to the analysis of structures in fire. The need for proper concrete model remains a challenging task in structural fire engineering because of the complexity of the concrete mechanical behavior characterization and the severe requirements for the material models raised by the development of performance-based design. A fully three-dimensional model is developed based on the combination of elastoplasticity and damage theories. The state of damage in concrete, assumed isotropic, is modeled by means of a fourth order damage tensor to capture the unilateral effect. The concrete model comprises a limited number of parameters that can be identified by three simple tests at ambient temperature. At high temperatures, a generic transient creep model is included to take into account explicitly the effect of transient creep strain. The numerical implementation of the concrete model in a finite element software is presented and a series of numerical simulations are conducted for validation. The concrete behavior is accurately captured in a large range of temperature and stress states. A limitation appears when modeling the concrete post-peak behavior in highly confined stress states, due to the coupling assumption between damage and plasticity, but the considered levels of triaxial confinement are unusual stress states in structural concrete.

A modified rigid-body-spring concrete model for prediction of initial defects and aggregates distribution effect on behavior of concrete

A modified rigid-body-spring concrete model was developed by considering the contact between elements after the failure of the springs. The discretization and definition of elements and springs were based on the three phases of concrete, including the coarse aggregates, the mortar and their interface. Based on the modified rigid-body-spring model, stress–strain curves and failure modes of concrete specimens with preset holes under uniaxial loads were simulated firstly, the simulated results were validated by those obtained from tests; and then, the effect of initial defects and distribution of coarse aggregates on mechanical behavior of concrete were investigated. It was found that with the increase of initial defects amount, the strength, elastic modulus and Poisson’s ratio of concrete decreased nonlinearly; and, the statistical analysis revealed that variability of the mechanical properties of concrete was mainly affected by the random distribution of coarse aggregates.

Tensile, compressive and flexural basic creep of concrete at different stress levels

Concrete is brittle and highly sensitive to cracking, which is detrimental to the sustainability of its applications. Although it is well known that cracks occur mainly in tension, research on the mechanical behavior of concrete is usually limited to compression and investigations of creep behavior, a major concern for concrete structures, are no exception in this respect. This paper is intended to help remedy the situation. First, the new experimental set-ups developed to achieve tensile and bending creep are presented. The precautions taken to obtain relevant experimentation are also described. Results for specimens subjected to sustained stresses of 30, 40 and 50% of the tensile or compressive strength are then presented. The final discussion compares basic creep under the different types of loading for the three stress levels.

Lattice Discrete Particle Modeling (LDPM) of Alkali Silica Reaction (ASR) deterioration of concrete structures

A large number of structures especially in high humidity environments are endangered by Alkali–Silica Reaction (ASR). ASR leads to the formation of an expansive gel that imbibes water over time. The gel expansion causes cracking and consequent deterioration of concrete mechanical behavior in the form of strength and stiffness reduction. In the recent past, many research efforts were directed towards evaluation, modeling and treatment of ASR effects on structures but a comprehensive computational model is still lacking. In this paper, the ASR effect is implemented within the framework of the Lattice Discrete Particle Model (LDPM), which simulates concrete heterogeneous character at the scale of coarse aggregate pieces. The proposed formulation, entitled ASR-LDPM, allows precise and unique modeling of volumetric expansion; expansion anisotropy under applied load; non-uniform cracking distribution; concrete strength and stiffness degradation; alkali ion concentration effect; and temperature effects of concrete subjected to ASR. In addition, a unique advantage of this formulation is its ability to distinguish between the expansion directly related to ASR gel expansion and the one associated with cracking. Simulation of experimental data gathered from the literature demonstrates the ability of ASR-LDPM to predict accurately ASR-induced concrete deterioration.

Mechanical Behavior of Concrete Subjected to Impact Loading

A 74-mm-diameter split Hopkinson pressure bar (SHPB) is used to test the dynamic mechanical behavior of concrete and cement mortar. Experimental results show that concrete and cement mortar are rate-dependent. The load-carrying capacity of concrete is higher than that of cement mortar. Whereas, the maximum strain of concrete is lower than that of cement mortar. No matter for concrete or cement mortar, with the increase of impact velocity, the fragment size of specimens after experiment decreases.

Dynamic Mechanical Behavior of Concrete under Uniaxial Stress

According to existing experimental results, a systematic analysis of stress–strain relation of concrete under uniaxial dynamic loading is carried out. Research shows that the dynamic loading rate has a direct effect on concrete strength and elastic parameters. Finally, a constitutive law is proposed in this paper.

Evaluation of partial clinker replacement by sugar cane bagasse ash: CO2 emission reductions and potential for carbon credits

This work presents a study about the viability of possible CO2 emissions reductions scenarios for the cement manufacturing through the implementation of Clean Development Mechanisms (CDM) associated with the partial replacement of cement by sugar cane bagasse ash (SCBA). Studies on the thermal, chemical and mechanical behavior of concretes containing 5 to 20% of ash indicated that there is improvement on the performance of all analyzed properties and that the ash can be used as admixture on the cement manufacturing. The CO2 emissions of two hypothetical scenarios of CDM Project implementation in the state of Sao Paulo through this technology were evaluated based on the official and applicable methodology. The results show that there are emission reductions on both scenarios, even for the most unfavorable, evidencing the possibility of obtaining negotiable carbon credits.

Mechanical Behaviors of Structural Concrete Using Recycled Aggregates from Repeatedly Recycling Waste Concrete

This paper reports an expermiental study on mechanical behaviors of structural concrete using recycled aggregates from repeatedly recycling waste concrete. Five series of natural aggregate concretes with compressive strengths of 25MPa, 30MPa, 40MPa, 50MPa and 60MPa were used as recycled coarse and fine aggregates to produce recycled concrete with an objective compressive strength of 30MPa after they were cured for 28d. These recycled concretes were used as aggregates to produce concrete with the same objective compressive strength of 30MPa. The cycles were carried on until the indices evaluating the quality of recycled coarse or fine aggregate exceeded the tolerance. The mechanical behaviors of these concrete were tested. The results indicates that that with the increase of the cyclic number, the mechanical properties of recycled concrete, including compressive strength, tensile splitting strength, modulus of elasticity, gradually stabilize after obviously decreaing in the first instance.

Mechanical Behaviors of Structural Concrete Using Recycled Aggregates from Repeatedly Recycling Waste Concrete

This paper reports an expermiental study on mechanical behaviors of structural concrete using recycled aggregates from repeatedly recycling waste concrete. Five series of natural aggregate concretes with compressive strengths of 25MPa, 30MPa, 40MPa, 50MPa and 60MPa were used as recycled coarse and fine aggregates to produce recycled concrete with an objective compressive strength of 30MPa after they were cured for 28d. These recycled concretes were used as aggregates to produce concrete with the same objective compressive strength of 30MPa. The cycles were carried on until the indices evaluating the quality of recycled coarse or fine aggregate exceeded the tolerance. The mechanical behaviors of these concrete were tested. The results indicates that that with the increase of the cyclic number, the mechanical properties of recycled concrete, including compressive strength, tensile splitting strength, modulus of elasticity, gradually stabilize after obviously decreaing in the first instance.