File Name: movement restraint and cracking in concrete structures .zip
Cracks in concrete containing chlorides easily occur due to restraint conditions and they can be the main reasons of durability and safety issues.
In this paper, analysis technique which can handle mixed chloride and its effect on restrained drying shrinkage is proposed. For the evaluation of stress development and cracking time due to restrained drying shrinkage, free and restrained drying shrinkage test are carried out for concrete specimens containing different sodium chloride NaCl content. The results show that mixed chloride content increases restraint stress but does not increase strength.
Considering the effect of chloride on shrinkage based on the test results, effective restraint stress development and cracking of concrete specimens containing different level of chloride are evaluated through utilizing previously developed models for behaviors in early-age concrete like hydration and moisture transport.
The results from this proposed technique are verified by comparison with test results. Early-age concrete undergoes heat generation and moisture transport due to hydration and drying process simultaneously, and the stresses and strains are initially induced to the concrete structures due to the restrained condition.
When changes in concrete volume due to drying shrinkage are restrained, tensile stresses may develop, and it can propagate to cracking of concrete [ 1 — 3 ]. Although, the induced micro-cracks may not degrade the structural performance immediately, these can affect durability performance by permitting the intrusions of harmful agents such as chloride ions or carbon dioxide [ 4 — 6 ].
If elasticity increases rapidly in early-age concrete, tensile stress also increases rapidly before releasing the stress due to relaxation, which may cause cracking in early-age concrete [ 9 ].
Furthermore, the evaluation for cracking with restraint stress needs a complicated technique which is capable of calculating both material behavior like hydration and moisture transport and mechanical behavior like stress and strength development with boundary conditions at the same time [ 7 ]. Recently, a great deal of sea-sand is used for concrete manufacturing due to the insufficient aggregate, which is caused by increasing demand on concrete products [ 10 , 11 ].
Much research on concrete with chloride ion is mainly performed for deterioration analysis like chloride diffusion or steel corrosion [ 12 — 14 ]. For the quantitative deterioration analysis in chloride-mixed concrete, it is important to evaluate the chloride effects on the behavior of drying shrinkage in early-age concrete.
If a reinforced concrete structure is exposed to harsh environment, cracks caused by drying shrinkage which may be accelerated by mixed chloride ions can be the main routes for intrusion of deteriorating ions.
In this paper, an analysis technique for cracking resistance is proposed for initially chloride-mixed concrete. For this study, crack-inducing tests in axially confined condition are carried out for the concrete specimens with different chloride contents. For the chloride effect on drying shrinkage, tests for water evaporation and free drying without restraint are performed.
Considering the chloride effect on experimental data on drying shrinkage, an analysis technique for the restrained drying shrinkage in concrete with chloride contents is proposed through utilizing the previously developed models [ 15 — 19 ], so called, multi-component hydration heat model MCHHM , micro-pore structure formation model MPSFM , and moisture transport model MTM.
Integrated FE analysis using the proposed models is carried out and the reduced cracking time caused by restrained drying shrinkage is evaluated in the concrete with different chloride contents. In this present paper, the experimental and numerical studies are performed for the analysis of restrained drying shrinkage in chloride-contaminated concrete. The material and mechanical behaviors of early-age concrete containing chlorides are also discussed.
In this paper, several tests for drying shrinkage under axially restrained condition are performed for concrete with different chloride contents. Test equipments are made of steel plates based on the standard method of drying shrinkage and crack resistance of concrete referring to JIS [ 20 ], as shown in Fig. Test specimens are prepared with different chloride contents of 0.
For the curing period, the surface of concrete is covered with saturated cloth. After curing period, bottom plate of the frame is detached from the concrete specimen and longitudinal restraint of shrinkage is induced by the two side surfaces of the frame. For measuring the strain of steel frame, 3 strain gauges are attached on each side surface as shown in Fig.
Additionally, the free drying shrinkage and water loss evaporated water in concrete specimens are measured in the same exposure condition. The strains of free drying shrinkage are measured through both strain gauges and one contact gauge, and the weight changes in cubic specimens are measured with a scale of 0.
The test equipment including restrained drying shrinkage, free drying shrinkage, and weight change in water loss are shown in Fig. As shown in Fig. C 3 S in NaCl solution is reported to show little effect on acceleration of hydration [ 24 ]. In this paper, NaCl is mixed in concrete so that no significant changes in mechanical properties are measured with different NaCl contents. Results showing little changes in hydration heat and strength in concrete with sodium chloride NaCl can be found also in previous research [ 1 ].
Free drying shrinkage in the specimens is measured and the results are shown in Fig. The results in Fig. Those from dial gauge on tip are not utilized since they have big deviations. The results for water loss in the cubic specimen in control condition R. From the results in Figs. However, the free drying shrinkage increases significantly with increment of NaCl content.
It can be assumed that changing density of pore water or chemically bound water due to chloride ions from NaCl is not the main reason for the increasing shrinkage in Fig. There are several parameters affecting drying shrinkage in concrete and chloride effect on drying shrinkage has been reported through experimental works.
When chloride ion is mixed in concrete, pore structure is changed to be more dense morphology [ 26 ] and this changed pore structure may cause different behavior of drying shrinkage. Increased surface tension due to higher concentration of chloride ion [ 28 ] can cause higher drying shrinkage.
In this paper, changed pore radius with different chloride ions is assumed to be main activation of increasing shrinkage since the adopted model of drying shrinkage [ 2 ] is based on the capillary pore and tension, which is explained in Sect. In order to evaluate cracking time due to restrained shrinkage, comparison with tensile strength and restraint stress which are dependent on time should be carried out.
The tensile strength is assumed based on the results of compressive strength and it will be explained in Sect. For derivation of effective restraint stress, effective restrained strain which is related to restrained shrinkage should be evaluated and converted to effective restraint stress. Effective restrained strain of the specimen which causes effective restraint stress can be defined as the difference between total restrained drying shrinkage strain and the free drying shrinkage strain.
The each strain is experimentally measured for restraint and free condition as shown in Fig. In Fig. In the Fig. Volume changes caused by hydration expansion and shrinkage actually occur before removing the bottom plate of the mold. However, it is very difficult to measure the strain in concrete before setting in the mold. The development of effective restraint stress in concrete is derived based on the effective restrained strain which is defined previously.
It can be expressed as Eq. Concrete can be in crack-free condition so long as the tensile strength keeps higher than induced effective restraint stress. The results show rapid shortening of cracking time with the larger chloride content. It is shortened from The reason for the cracking is the increased effective restraint stress due to the chloride content. These experimental results will be compared with those from proposed analysis technique. The relative humidity in the pore structure decreases with drying due to moisture gradient between exterior and interior concrete.
Considering local thermodynamic and interface equilibrium, vapor and liquid interfaces would be formed in the pore structure due to the pressure differences caused by capillarity [ 30 ]. Due to the surface tension of liquid water, the pressure of gas and liquid are not equal. The idealized pore structure and interface equilibrium is shown in Fig. Idealized structure of pores and interface equilibrium [ 15 ]. The pressure of each phase can be computed by moisture transport model [ 15 , 16 ].
From Eq. According to the previous research [ 15 ], E s can be written as Eq. The reason for this discrepancy might be the assumption of a uniform stress field due to capillary tension or perhaps some intrinsic differences in the mechanisms of deformation at micro- and macro scale due to capillary stress and that due to applied stress [ 15 , 30 ]. When experimental results of compressive strength are considered in Eq. In the constitutive relation of Eq.
If the pore radius r s decreases with chloride content, tensile stress of the pore liquid increases accordingly. In order to consider the reduced pore radius, exponential function for chloride content is assumed as Eq.
The shrinkage strain with chloride content can be written as Eq. These equations are merged in analysis framework for calculation of cracking time. Utilizing the results shown in Fig. The results with different chloride content can be normalized by control data results without chloride content and an effect on shrinkage can be obtained with respect to chloride content. Among data in Fig. The results are shown in Fig. The constants of A and B in Eq.
In this paper, previous model for creep function is used [ 23 ]. Therefore, the composition of various stresses caused by drying shrinkage due to the moisture transport and hydration, strain due to creep, and their integrated actions are considered in Eqs. They can also be rewritten as Eq. The evaluation of cracking time in stress field is determined by the time when the tensile principal stress of each node is higher than the developed tensile strength due to hydration.
The assumed tensile strength is In this section, previous models utilized for this study are briefly summarized and framework for evaluation of shrinkage behavior is introduced. In view of concept of a multi-component powder material, the effect of different type of cement can be rationally taken into account to predict overall heat generation rate. The influence of variable moisture content of free water in the hydration is also taken into consideration in the concept.
Other powder materials like slag and fly ash can also be considered in the model as pseudo clinker components. The total heat generation rate of concrete H per unit volume is idealized as Eq.
The heat rate of the entire cement H c including blending powders, is given as the sum of the heat rate of all reaction as Eq. For analytical purpose, the interlayer porosity is simply lumped with the porosity distributions of gel and capillary porosity to obtain the total porosity distribution of cement paste as Eq. If the porosity is a cylindrical shape in such a distribution, then the pore distribution parameter B i can be obtained form the following relationship of Eq.
If the porosity distribution of the microstructure is known, Eq. By integrating the pore volume that lies below pore radius r s , saturation S can be written as Eq. The expression for saturation S is changed with hysteretic behavior of isotherm. Each model is well explained and documented in following references [ 15 — 19 ].
Jared R. Wright, Farshad Rajabipour, Jeffrey A. Cracking of newly placed binary Portland cement-slag concrete adjacent to bridge deck expansion dam replacements has been observed on several newly rehabilitated sections of bridge decks. This paper investigates the causes of cracking by assessing the concrete mixtures specified for bridge deck rehabilitation projects, as well as reviewing the structural design of decks and the construction and curing methods implemented by the contractors. The work consists of 1 a comprehensive literature review of the causes of cracking on bridge decks, 2 a review of previous bridge deck rehabilitation projects that experienced early-age cracking along with construction observations of active deck rehabilitation projects, and 3 an experimental evaluation of the two most commonly used bridge deck concrete mixtures.
Crack control in base-restrained reinforced concrete walls. Following casting, concrete undergoes early-age thermal EAT and long-term LT shrinkage volumetric changes. If restrained to move, concrete invariably cracks due to its low tensile strength. Crack control is of particular concern in structures like retaining walls, liquid-retaining tanks, and cut-and-cover tunnels, where through-cracks can lead to water leakage unless their width is adequately controlled with steel reinforcement. The aim of this thesis is to increase the confidence with which engineers can predict and control crack widths in reinforced concrete RC walls with edge restraint and in walls with combined edge and end restraint. EN can require very different areas of reinforcement to BS to control crack widths — more in some situations e.
Cracks in concrete containing chlorides easily occur due to restraint conditions and they can be the main reasons of durability and safety issues. In this paper, analysis technique which can handle mixed chloride and its effect on restrained drying shrinkage is proposed. For the evaluation of stress development and cracking time due to restrained drying shrinkage, free and restrained drying shrinkage test are carried out for concrete specimens containing different sodium chloride NaCl content. The results show that mixed chloride content increases restraint stress but does not increase strength. Considering the effect of chloride on shrinkage based on the test results, effective restraint stress development and cracking of concrete specimens containing different level of chloride are evaluated through utilizing previously developed models for behaviors in early-age concrete like hydration and moisture transport.
One of the widespread issues in concrete structures is cracks occurring at early If such movements are restrained, stresses will occur. chairmen_rcthi.org
A single copy of this. Concrete Society. This is an uncontrolled copy - not for contract use Jacobs Engineering Group Inc. This is an uncontrolled copy.
Codes of practice principally focus on design to resist externally applied loads, deriving the reinforcement needed to resist axial loads, bending moments and shear forces. However, many concrete elements are lightly loaded or are affected principally by other actions, such as early-age contractions, temperature and humidity effects, creep, and long-term drying shrinkage. These all generate movements, and although they rarely determine the ultimate capacity they often affect serviceability, particularly cracking. This Report considers the various types of movement and their timescales. Any cracking or deformation is usually at least the result of shrinkage and temperature added to early-age effects, and often with contributions from other sources.
Old version of document Newer versions. Explores types, sources, restraint and strain-induced forces of movement that can affect concrete elements over time. Examines the cumulative effect, considers why cracks matter and looks at avoiding or controlling cracks.
Leg Show Jo Picture soal dan pembahasan sifat mekanik zat free download of kaspersky antivirus 7. Types 11, , 1V, and. Restrained deformations caused crack- ing in concrete.
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