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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korea Concrete Institute
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Journal DOI :
Korea Concrete Institute
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Volume & Issues
Volume 11, Issue 6 - Dec 1999
Volume 11, Issue 5 - Oct 1999
Volume 11, Issue 4 - Aug 1999
Volume 11, Issue 3 - Jun 1999
Volume 11, Issue 2 - 00 1999
Volume 11, Issue 1 - 00 1999
Selecting the target year
Tensile Creep Model of Concrete Incorporation the Effects of Humidity and Time at Loading
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 3~11
DOI : 10.22636/JKCI.19184.108.40.206
The creep characteristics of concrete under tensile stress has been usually assumed to have the same characteristics as that under compressive stress in the time-dependent analysis of concrete structures. However, it appears from the recent experimental studies that tensile creep behavior is much different from compressive one. In particular, high sustaining tensile stress may cause time-dependent cracking and thus lead to tensile failure. It is, therefore, necessary to model the tensile creep behavior accurately for realistic time-dependent analysis of concrete structures. The present paper to have been focused to suggested more realistic model for the tensile creep behavior of concrete. The models are compared with tensile creep test data available in the literature. The proposed model may allow more refined analysis of concrete structures under time-dependent loading.
An Experimental Study on the Chemical Soundness of Recycled Aggregate Concrete
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 13~20
DOI : 10.22636/JKCI.19220.127.116.11
Recently, the study for practical construction application no recycled aggregate concrete is actively being proceeded, on the purpose of technical development for recycling on the construction waste concrete occurred at the time of destruction of building construction by the rapid increase of building wastes and exhaustion of natural aggregates. But, the durability of investigation with all sorts of fluidity and engineering property for application recycled aggregate concrete to practical construction must be done at the same time. Especially, because of the real condition for chemical attack of concrete construction by the acid rain, acidification of soil, deepening of air pollution and dirty water etc. being come to the fore a serious problem, the study on the chemical soundness of concrete durability must be accompanied. This study is composed as: I series: Analysis for chemical soundness of aggregates. II series: Analysis for chemical soundness of natural and recycled aggregate concrete against
solution in drying and wet curing condition (
An Experimental Study on the Fundamental Characteristics of Antiwashout Underwater Concrete with Variation of Water-cement Ratio
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 21~29
DOI : 10.22636/JKCI.1918.104.22.168
In this study, an experiment was performed to analyze the influence of water-cement ratio on the fundamental characteristics of antiwashout underwater concrete using blended sand (sea sand:river sand = 1:1). The water-cement ratio (45%, 50%, 55%, 60%), andtiwashout underwater agent contents (0.82%, 1.00%, 1.14% of water contents per unit volume of concrete), and superplasticizer contents (1.5%, 2.0%, 2.5% of cement contents per unit volume of concrete) were chosen as the experimental parameters. The experimental results show that the underwater segregation resistance, unit weight of hardening concrete and compressive strength were increased as the water-cement ratio decreased and as the antiwashout underwater agent contents increased. On the other hand, the flowability(slump flow) was increased to the 55% of the increase of water-cement ratio, however, it was decreased at the ratio of 60%. From this study, the antiwashout underwater concrete can potentially be used as a materials underwater work of ocean if the water-cement ratio and chemical admixture contents for the suitable balance between cost and performance are properly selected.
The Resistance of Penetrability and Diffusion of Chloride Ion in Blended Low Heat Type Cement Concrete
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 31~41
DOI : 10.22636/JKCI.1922.214.171.124
Blended Low Heat type cement is ground granulated blast furnace slag and fly ash mixed ternary with ordinary portland cement. From the viewpoint of X-ray patterns of domestic LHC, the main components of cement such as
S are considerably reduced. Therefore the heat evolution of LHC paste is 42cal/g lower than of OPC paste. At early age, the compressive strength development of LHC concrete is delayed, but the slump loss ratio of fresh concrete is reduced more than 20% with elapsed time. The penetrability of LHC is lower than that of OPC by 1/7.8 with the penetrability of chloride ion into the concrete until the age of 120 days. And the PD Index value of LHC is 0.44
/s, which indicates only 39.3% of OPC. From the Mercury Intrusion Porosimetry test of cement past, we know that the pore size of LHC is more dense than that of OPC by production of C-S-H.
Evaluation on Shear Behavior of Double-tee Dap-ends with the Least Depth from Optimization Proces
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 43~54
DOI : 10.22636/JKCI.19126.96.36.199
Shear tests are performed on four full-scale 12.5 m proto-type models, "least depth double tee," which are resulted from the optimization process. Domestic superimposed live load regulation, domestic material properties which is available to product. Korean building code requirements, construction environments and economy are considered as the main factors to establish the process. All of the specimens tested fully comply with the shear strength requirements as specified by ACI 318-95. The research has shown following results. 1) The development length requirement of ACI 318-95 does not seem a good predictor for the estimation of bond failure in a beam with the strands below the supports. 2) The load required for the first initial coner cracking in the dap end and first web shear cracking does not seem to have any relation with the dimension and shear strength of the section in the test beams. 3) The strand slip has a direct relationship with the web shear cracking. However, the coner cracking in the dap end does not give any help for the slip in anchorage. 4) Use of whole area for bearing steel at the bottom of dap end is desired for safe bearing pressure design in the precast prestressed double tee beams. 5) The deflection of beam influences directly on the amount of strand slip at the anchorage after initiation of it, and relationship between them are very linear.
An Experimental Study on the Behavior of Reinforced Concrete Columns Subjected to Axial Force and Biaxial Bending
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 55~62
DOI : 10.22636/JKCI.19188.8.131.52
When stress is beyond elastic limit or cracks occur in a reinforced concrete member subjected to axial force and biaxial bending, curvature about each principal axis of uncracked section is influenced by axial force and bending moments about both major and minor principal axes. It is mainly due to the translation and rotation of principal axes of the cross section after cracking. Recently, by considering these effects, a numerical method predicting the behavior of concrete columns subjected to axial force and biaxial bending was proposed. In this study, in order to verify the proposed numerical method and investigate the effects of cracking on the behavior of reinforced concrete columns, a series of tests were carried out for 16 tied reinforced concrete columns with 100×100 mm square and 200×100 mm rectangular sections under various loading conditions. The angle between the direction of eccentricity and the major principal axis of uncracked section were 0, 30, 40° for the square section and 0, 30, 45, 60, 90° for the rectangular section, respectively. A comparison between numerical predictions and test results shows good agreements in ultimate loads, axial force-lateral deflection relations, and lateral deflection trajectories. It is also found, in this limited investigation, that the ACI's moment magnifier method is conservative in both uniaxial and biaxial loading conditions.
Effects of Specimen Length on Flexural Compressive Strength of Concrete
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 63~71
DOI : 10.22636/JKCI.19184.108.40.206
In evaluating the ultimate strength of a section for a reinforced concrete flexural member, the effect of member length is not usually considered, even though the strength tends to decrease with increase of member length. In this paper the influence of specimen length on flexural compressive strength of concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to axial compression and bending moment were tested using four different length-to-depth ratios (from 1,2,3 and 4) of specimens with compressive strength of 590 kgf/
. Results indicate that for the region of h/c <3.0 the reduction in flexural compressive strength with increase of length-to-depth ratios was apparent. A model equation was depth of an equivalent rectangular stress block was larger than that by ACI. It was also founded that the effect of specimen length on ultimate strain was negligible. Finally more general model equation is also suggested.
Overestimation of Ultimate Tendon Stress in a Prestressed Concrete Beam with Unbonded Tendons
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 73~81
DOI : 10.22636/JKCI.19220.127.116.11
The present study is to examine the ACI code equations for computing the unbonded tendon stress at flexural failure of prestressed beams. The equations examined for their validity are Eq. 18-4 and Eq. 18-5 of the ACI 318-95. Since the possibility of overestimation was expected with the equations, a numerical study, first, was carried out with influential variables included. From this study, it was found that amount of reinforcements, effective prestress, location of tendons, and loading type may affect the overestimation of the unbonded tendon stress. Then, an experimental study was carried out with those variables. A total of 8 specimens was tested to prove the theoretical findings as well as the effect of those variables. As a result. it was proven that the ACI Code equations can overestimate significantly the unbonded tendon stress for certain cases.
Tension Stiffening Effect for Reinforced Concrete Members
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 83~93
DOI : 10.22636/JKCI.1918.104.22.168
This paper presents tension stiffening effect of Reinforced concrete members obtained from experimental results on direct tension and bending. From the direct tension test program, crack patterns were investigated with tension softening behaviors of concrete. Tension stiffening effects and losses of strain energy were, also, analyzed from the load-deflection curve with the main experimental variables such as concrete strength, yielding stress and reinforcement ratio of rebar. Tension stiffening effect of RC members increase linearly until the first crack initiate, decrease inversely with number of cracks, and then decrease rapidly when splitting cracks are happened. The tension stiffening effect is shown to be more important at the member of lower reinforcement than that of higher. Therefore, it necessitates to consider the tension stiffening effects at a nonlinear analysis. From the above analysis, a tension stiffening model of concrete is proposed and verified by applying it to bending members. From the numerical analysis by finite element approach, it is shown that the proposed model evaluates a little higher in analyzing at nonlinear region of high strength concrete, but, perform satisfactorily in general.
Development and Property Analysis of Segregation-Reducing Type Flowing Concrete Using the Viscosity Agent
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 95~105
DOI : 10.22636/JKCI.1922.214.171.124
When superplasticizer is added to manufacture flowing concrete, the base concrete usually needs the adjustment to assure the sufficient fines contained to obtain flowable consistency without excessive bleeding or segregation. However, this may not only increase the cost, but also cause inconvenience in producing the base concrete. In this paper, the experiments are performed on normal base concrete to achieve a segregation-reducing flowing concrete by adding superplasticizer mixed with viscosity agents and AE admixtures. Three kinds of superplasticizer and two kinds of viscosity agent are selected. According to the results, with regard to the performance and cost of the admixtures, melamine type superplasticizer combined with the PEO viscosity agent and AE admixtures at the ratio 1:0.28:0.001 can acquire good quality and reduce the cost in producing the flowing concrete. With proper addition of combined superplasticizer, even though water to cement ratios of the base concrete are different, the segregation-reducing flowing concrete could be also achieved without reproportioning of the base concrete. However, it would be more desirable if the superplasticizer could be adjusted, before it is put into the practical use in order not to cause some other problems, such as rapid rate of slump loss and retarding of setting time.
Identification of Damage Characteristics Due to Cracking of Concrete Structures Using Acoustic Emission
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 107~116
DOI : 10.22636/JKCI.19126.96.36.199
The damage in concrete structures generally starts with microcracking and thus it is important to find and explore these microcracks in concrete in order to ensure appropriate safety and serviceability. The purpose of the present study is to identify the damage characteristics of concrete structures due to cracking by employing the acoustic emission techniques. A comprehensive experimental study has been done. The cracking damage under tensile and flexural loadings have been identified and the bond damage between steel and concrete have been also characterized. It is seen that the amplitudes and energy level of Acoustic Emission(AE) events are found to be relatively small for bond cracking damages and large for tensile cracking damages. The characteristic equations of the AE events for various cracking damages have been proposed based on the present test data. The internal microcracks are progressively developed ahead of a visible actual crack and the present study clearly exhibits these damage mechanism for various types of cracking in concrete. The present study provides useful data which can be used to identify the various types of cracking damages in concrete structures. This will allow efficient maintenance of concrete structures through monitoring of internal cracking based on acoustic emission.
Investigation on the Method of Evaluating the Resistance to Freezing and Thawing of Concrete Subjected Initial Frost Damage
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 117~127
DOI : 10.22636/JKCI.19188.8.131.52
In concrete incorporating high volume ground granulated blast-furnace slag that has frozen at early age, to evaluated the results of resistance to freezing and thawing is very difficult because the hydration of the concrete increases over the duration of rapid freezing and thawing test. Hence, the dynamic modulus of elasticity of specimens after freezing and thawing will be favorable results unless the hydration effect is taken into consideration. In this study, a method of evaluating to the resistance to freezing and thawing of concrete subjected freezing at early age, in which the effect of hydration is modified for its increase during rapid freezing and thawing test, is investigated.
An Experimental Study on the Bond Split Mechanism of High Strength Concrete
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 129~136
DOI : 10.22636/JKCI.19184.108.40.206
For the prediction of concrete-steel bond ability in reinforced concrete, many countries establish specifications for the pullout test. But these methods hardly to consider many parameters such as strength, shape, diameter and location of steel, concrete restrict condition by loading plate, strength of concrete and cover depth etc, and it is difficult to solve concentration and disturbance of stress. The purpose of this study is to propose a New Ring Test method which can be rational quantity evaluations of bond splitting mechanism. For this purpose, pullout test was carried out to assess the effect of several variables on bond splitting properties between reinforcing bar and concrete. Key variables are concrete compressive strength, concrete cover, bar diameter and rib spacing. Failure mode was examined and maximum bond stress-slip relationships were presented to show the effect of above variables. As the result, it appropriately expressed general characteristics of bond splitting mechanism, and it proved capability for standard test method.
Study on the Strength Characteristics and Flexural Toughness of Steel Fiber Reinforced Polymer Concrete
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 137~145
DOI : 10.22636/JKCI.19220.127.116.11
The use of steel fiber reinforced to improve the strength and flexural toughness of concrete is well known, but reinforcement of polymer concrete with steel fibers has been hardly reported till now. Polymer concrete has high strength, durability and freeze-thaw resistance than that of cement concrete, but it has disadvantage such as low flexural toughness. In this paper, the strength characteristics and flexural toughness of steel fiber reinforced polymer concrete are investigated experimentally with various steel fiber aspect ratios(
/d), and contents(vol.%). As the result, the flexural and splitting tensile strengths and flexural toughness were increased aspect ratio, and reach the maximums at a aspect ratio of 50. The relationship between the compressive, flexural and splitting tensile strength were high. And the relationship between flexural strength and strain energy was approximately linear.
An Application of Strength Reduction Factors to Reinforced Concrete Columns considering Ductility
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 147~156
DOI : 10.22636/JKCI.1918.104.22.168
Current design code states that the strength reduction factor shall be permitted to be increased linearly from that for axial compression to that for flexure as the design axial load strength
cPn decrease from 0.1fckAg to zero. Since this empirically adopted axial load level of
cPn=0.1fckAg considers only sectional area and concrete strength, the other variables such as steel ratio, steel yielding strength, and steel arrangement can not be considered. This research is performed to investigate the consistency and the rationality of the code requirement for determination of column design strength. A nonlinear axial force-moment-curvature analysis was conducted in order to investigate the ductility of reinforced concrete column sections. As the result of ductility analysis, it was found that the ductility at the axial force of
cPn=0.1fckAg represented a lock of consistency for the various variable contained sections. Therefore, a more reasonable application method of strength reduction factor is proposed, that is based on the strain ductility index.
Evaluation Technique of Concrete Strength Using Impact-Resonance and Combined Method
Journal of the Korea Concrete Institute, volume 11, issue 4, 1999, Pages 157~167
DOI : 10.22636/JKCI.1922.214.171.124
Among several non-destructive testing methods, ultrasonic pulse velocity method and rebound index method have been widely used for the evaluation of concrete strength. However, such methods might not provide accurate estimated results since factors influencing the relationship between strength and either ultrasonic pulse velocity or rebound index are not considered. In this paper, the evaluation method of concrete strength using rod-wave velocity measured by impact-resonance method is proposed. A basic equation is obtained by the linear regression of velocity vs, strength data at specific age and then, aging factor is employed in the equation to consider the difference of the increasing rate between wave velocity and strength. Strengths predicted by the proposed equation agree well with test results. Furthermore, the combined method of rod-wave velocity and rebound index is proposed.