Material Characteristics Of Concrete Research Articles

Intelligent Analysis of Energy-Saving and Environment-Friendly Concrete Materials Based on Finite Element Simulation and Supercomputer

In this paper, based on the finite element simulation method of supercomputer, a three-dimensional intelligent modeling analysis of energy-saving and environmentally friendly concrete materials is carried out. First, the basic principles of the finite element iterative integral equation are introduced. The various characteristics of concrete materials and the interaction between steel and concrete, through calculation, people have a more comprehensive and in-depth grasp of the properties of reinforced concrete structures. In the process of nonlinear finite element analysis of reinforced concrete, physical models, numerical methods and programming techniques are involved. The final formation of the analysis program is an important part of it. By using the balanced grid division strategy of graph partition theory and sparse matrix reordering technology, the performance and scalability of the program are improved to 97.2%

Reliability assessment of concrete under external sulfate attack

The variability in characteristics of concrete material, such as pore size and chemical composition, has significant impact on the long-term performance of concrete structures under sulfate attack. This paper presents a reliability-based numerical model for assessing the long-term corrosion behaviour of concrete subject to sulfate attack. Using a reliability approach, the model can describe the reactive transport behaviour of sulfate ions and concrete degradation process. Specially, the variables in pore characteristics in interfacial transition zone (ITZ) and concrete chemical composition were quantified using a large amount of experimental data to determine the time-dependent reliability index (β) under long-term sulfate attack. The results show that the filling of ettringite and monosulfate after sulfate attack could modify the physical pore structure of ITZ at early stage. The time for concrete to reach the reliability index limit state shorten remarkably with the increase of sulfate concentration. For example, a four-fold increase of sulfate concentration (e.g. from 57 mol/m3 to 14.25 mol/m3) could shorten the time to reach the reliability index limit (i.e. β = 4.7) by 70 %. In addition, aggregate surface treatment especially with silica fume could improve the reliability of deteriorating concrete significantly by prolonging the time to reach the reliability index limit by 40 % in this study.

Impact of the self-healing agent composition on material characteristics of bio-based self-healing concrete

This paper investigates the composition of the biological self-healing agent based on its impact on material characteristics of concrete. A direct addition of the agent – a mixture of bacterial spores and nutrients – into concrete matrix has been investigated by many studies in recent decades. Under certain conditions, the applied microorganisms proved to be able to produce CaCO3, and researchers used this biocalcification process to autonomously seal microcracks in concrete. Thus, this bio-based material could potentially heal itself and lead to a more durable and economic structure. However, it has been shown that the self-healing agent, especially the indispensable nutrients, can positively or negatively influence the material characteristics. In this study, some of the most suitable and frequently proposed nutrients (calcium lactate, calcium nitrate, calcium formate, urea, and yeast extract) were directly added into cement mortar during the mixing process and their impact on material characteristics – compressive strength, flexural strength, and rheology – was evaluated and compared. Results show that calcium nitrate, calcium formate, calcium lactate, and urea have generally a potential to increase the compressive strength, especially in early ages. In contrast, the applied dose of yeast extract resulted in a drastic drop of compressive strength when compared to the control series, thus further optimization of the concentration is needed. The flexural strength was affected rather negligibly by the proposed nutritional admixtures.

Simulation Analysis of Chemically Bonded Anchors in ABAQUS

At present, the finite element analysis has been an effective method to study the mechanical properties of steel bar drawing. In this paper, finite element analysis of the influence of bond strength on anchorage performance with concrete plastic damage model based on nonlinear analysis in ABAQUS was carried out. The finite-element analysis model of the single bar was established by using the finite element software ABAQUS. The Spring2 nonlinear spring element was introduced to simulate the interface of concrete and adhesive. Chemical anchorage bond slip constitutive model was determined by Spring2 element real constants. The nonlinear characteristics of concrete materials under the single reinforcement drawing could be described with the combination of the concrete plastic damage constitutive mode and nonlinear finite element methods. The nonlinear behavior of concrete under uniaxial tension of the action, especially the crack and stress distribution, could be accurately described. In order to study the influence of adhesive bond strength of chemically-bonded rebar mechanical properties, the constitutive relation of the bonded rebar slip of test results was referenced. The nonlinear property of spring was assigned by the bond slip relationship, embodied in the F-D curve of the spring. In order to analysis the influence of bond strength on anchorage performance, the slope of linear growth stage and the peak of nonlinear growth stage in bond slip relationship curve were changed.

Mathematical Simulation of Concrete Fatigue Strength under Cyclic Loading

The problem of forecasting the durability of structures, buildings and constructions is one of the most urgent and important tasks in building sphere. In this paper, the authors propose a mathematical model of damage accumulation for the numerical simulation of the fatigue life of concrete. The results of numerical experiments with different levels of the applied load to the model are given, the fatigue characteristics of concrete material - Wohler curve - is built. On the basis of the developed method, the algorithm for research building designs using mathematical and physical modeling is formulated.

A thermodynamics-based damage constitutive model of concrete

A thermodynamics-based damage constitutive model is developed for concrete, which describes tensile and compressive damage well and follows the second thermodynamic law. Constitutive model should meet general thermodynamics, while it describes behaviour characteristic of concrete material, which are often not able to be satisfied by existing models because of various of hypotheses. Generalised stress functions and dissipative generalised stress functions are constructed from free energy function and energy dissipation function according to the physical meaning of the thermodynamic potential and the characteristic of the constitutive model of concrete. Then, a damage constitutive model of concrete is developed and the parameters of the model are identified. The numerical method of the model is also presented. The model in the paper can satisfy the second thermodynamic law automatically and simulate the tensile and compressive behaviour of concrete well. Finally, the feasibility and practicality of the model is verified by the analysis of classical experiments and Koyna dam.

Fractal Analysis on Microstructure Characteristics of Concrete Materials

The fractal characteristics of concrete materials microstructure are analyzed with fractal theory. The fractal dimension of concrete materials microstructure in the different conditions are tested and counted by code and box Dimension. The result shows that the fractal characteristics of concrete materials microstructures are highly notable, as interface of cement clinker mineral, dispersed state of unhydrated cement particles, crack of hardened cement paste, hydration product and pore structure of hydrated cement paste section. Proving it is effective to measure surface of cement clinker mineral, figures of hydration C-S-H grains and outlines, pore structure of concrete section. Using box dimension is effective to test microcracks and pore structure of section of motor samples and fiber-hydrate. In the course of fractal analysis, the dimensions of fractal are bigger than their topologic dimension, and they are smaller than their space dimension, they are keeping with the fractal theory.

A Study on the Estimation of Failure Mode in Impact Analysis Using SPH Method

This paper proposes an analysis algorithm that can appropriately distinguish shear failure from bending failure of an RC beam under impact load, by using the SPH method. As structural members, beams generally fail by one of two modes: bending failure caused by excessive bending deformation of the member, and shear failure caused by shear crack growth, leading to rapid destruction at an angle in the web. In this study, to calculate the failure behavior accurately in the local stress field in which shear stress prevails such as when a shear crack occurs, an orthotropic constitutive equation is used. This equation is derived by applying the integrity tensor proposed by Ignacio Carol, Egidio Rizzi and Kasper William, to the usual SPH method. This operation is also extended to the tensile softening characteristic of concrete material. The results confirm that the failure behavior of RC beams under a wide range of conditions can be analyzed accurately by using the proposed algorithm.

The Pore Fractal Characteristics of Concrete Materials under Salt Freezing Conditions in Cold Area

For further research on durability of concrete material under salt frozen conditions in cold area, the non air-entraining concrete with water-binder ratio of 0.4 and 0.28, air-entraining concrete with water-binder ratio 0.28 and the air content 7.0% are studied respectively. The fractal dimension of three kinds of concrete pore at different pore diameter range were determined by MIP(mereury intrusion porosimetry) before and after salt freezing and were studied in a comparative way. The research shows that the fractal dimension of pore diameter at range of 50nm ~ 550nm after salt freezing changed remarkably, namely salt frozen process has greater influence on pore within this range. Objectively the pore within this range in concrete suffered supercooled water osmotic pressure is the greatest. In addition, the total porosity reduced after salt freezing injury while fractal dimension changed more obviously. The fractal dimension of concrete pore could be a good reflection of concrete structure after salt freezing injury, showing that the diameter at 50nm ~ 550nm after salt frozen injury coarsening is obvious. Thus the fractal dimension of diameter within this range can be used as a key parameters after salt freezing injury.

Reliability Analysis of Mohr Failure Criterion

For biaxial states of stress in mass concrete structures, safety can be assessed in terms of the Mohr failure criterion. Safety is generally evaluated by a deterministic factor of safety. When loads vary and material properties are not known with certainty, reliability analysis evaluates safety probabilistically. In this paper, deterministic and probabilistic safety evaluations are compared in terms of levels of uncertainty associated with load and resistance parameters and the extent is indicated to which the probabilistic approach is more informative than the deterministic approach. The effect on this comparison of several characteristics of concrete material is investigated. Three widely recognized design criteria are likewise compared.