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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 13, Issue 6 - Dec 2001
Volume 13, Issue 5 - Oct 2001
Volume 13, Issue 4 - Aug 2001
Volume 13, Issue 3 - Jun 2001
Volume 13, Issue 2 - Apr 2001
Volume 13, Issue 1 - Feb 2001
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Experimental Study on Thermal Conductivity of Concrete
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 305~313
DOI : 10.22636/JKCI.2001.13.4.305
Conductivity is an important thermal property which governs heat transfer in a solid medium. Generally, the determination of conductivity in concrete is very difficult, because concrete is a heterogeneous material composed of cement, water, aggregate, et cetera and time dependent material of which properties change with curing age. In this study, influencing factors on thermal conductivity of concrete are quantitatively investigated by QTM-D3, a conductivity tester developed in Japan. Then, a prediction equation of thermal conductivity of concrete is suggested from the regression analysis of test results. To consider the factors influencing thermal conductivity of concrete, mortar, and cement paste, seven testing variables (age, amount of cement, types of admixtures, amount of coarse aggregate, fine aggregate ratio, temperature, and humidity condition) of the specimens are used. According to the experimental results, the amount of coarse aggregate and humidity condition of specimen are the main factors affecting the conductivity of concrete. Meanwhile, the conductivity of mortar and cement paste is strongly affected by the amount of cement and types of admixtures. However, the curing age has minor effect on the conductivity variation. Finally, the prediction formula of concrete conductivity as a function of aggregate amount, fine aggregate ratio, specimen temperature, and humidity condition is developed.
An Experimental Study on the Quality Properties of the Expansive for Dry-Shrinkage Compensation of the On-Dol Floor Mortar
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 314~320
DOI : 10.22636/JKCI.2001.13.4.314
In this paper, the properties of an expansive agent (CaO-CaS
) for dry shrinkage compensation were investigated by a series of experimental program, which might be used at On-Dol heating system as mortar type. The expansion principle of the CaO-CaS
was mainly verified. As a result of this study, the correlation between the content of the expansive agent and the compressive strength was obtained in the form of exponential function(Y = A
), showing that as the content of expansive agent increased as the expansion performance with the compressive strength increased by only a certain amount. Also, as a results of the analysis of a correlation between the expansive performance and the chemical properties which generally accompanied a part of quality management in manufacturing the expensive cement, the expansive performance was relative to only the contents of the F-CaO among chemical properties(Blaine, +44
R, F-CaO, S
,L.O.I). And it was clarified that the results were relative to the second order function, showing that if the contents of the F-CaO increased the expansive performance Increased.d.
Tensile Behavior of Stud Bolt Connections
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 321~328
DOI : 10.22636/JKCI.2001.13.4.321
This paper presents the tensile behavior of stud connections installed between reinforced concrete and steel members. Eight specimens are tested to verify the factors influencing the tensile behavior of the connection. Major variables considered in the test are the reinforcement ratios of concrete member and connection details. Test results indicate that the reinforcing bars near stud bolts contribute to the increase of the tensile strength of the member as well as to the reduction of brittle failure. It is shown that C-type or U-type connection has relatively high ductility. From the evaluation on the tensile strength of test results including those of peformed by previous researchers, it was shown CCD (Concrete Capacity Design) method overestimated the strength. In this paper, the reduction factor of 0.75 ø instead of ø is suggested for design purpose of the stud connection.
An Experimental Study on the Properties of High Flowing Concrete according to Water/Binder Ratio(W/B)
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 329~335
DOI : 10.22636/JKCI.2001.13.4.329
Recently, in many laboratories and institutes it is being studied on the high flowing concrete widely, which has high fluidity, non-segregation ability and fillingability, and sometimes being applied to the construction field actually. And the fluidity properties of high flowing concrete are influenced according to the several factors ; binder content, water/binder ratio and water content etc. This is an experimental study to compare and analyze the effect of water/binder ratio and water content on the properties of high flowing concrete. For this purpose, the mix proportion of high flowing concrete according to water/binder ratio(W/B : 0.30, 0.35, 0.40, 0.45) and water content (W : 155, 165, 175, 185 kg/㎥) was selected. And then slump-flow, V-lot, L-passing test in fresh concrete, and compressive strength, freezing and thawing test in hardened concrete were peformed. According to test results, it was found that the viscosity of all those high flowing concrete with the water content 175 kg/㎥ was satisfied with 50 cm pass time of slump flow prescribed by Japanese Architectural Standard Specification (JASS 5) - from 3 to 8 seconds. And non-segregation ability of concrete with W/B 0.35 was better than the other mix proportions. Especially, the compressive strength after curing 24 hours(1 day) of all high flowing concrete was higher than that prescribed by JASS 5(50 kgf/㎠).
A Study for In-situ Application of High Strength Antiwashout Underwater Concrete
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 336~345
DOI : 10.22636/JKCI.2001.13.4.336
The construction of underwater structures has been increased, but underwater concrete hassome problems of quality deterioration and contamination around in-situ of civil and architecture; therefore, new materials and methods for them are demanded. In this paper in-situ application of underwater antiwashout concrete which is manufactured for trio purpose of not only decreasing suspended solids and the heat of hydration but also increasing long term strength was studied. In the case of mock-up test(Ⅰ), when underwater antiwashout concrete, whose slump flow was 58 cm, was placed in the mock-up test at a speed of 24 ㎥/hr, it took about a minute to flow to the side wall, and the surface was maintained at horizontal level. In this case, compressive strength of the core specimens in each section was higher than the standard design compressive strength of 240 kgf/㎠. In the case of mock-up test(II), pH value and suspended solids of high strength underwater antiwashout concrete were 10.0∼11.0 and 51 mg/ℓ at 30 minutes later, initial and final setting time were about 30, 37 hr, and the slump flow of that was 53
2 cm. In the placement at a speed of 27 ㎥/hr, there was no large difference in flowing velocity, with or without reinforcement and flowing slope was maintained at horizontal level. In this case, compressive strength and elastic modulus of the core specimens somewhat decreased as flowing distance was far : however, those of central area showed the highest value.
Optimum Mix Design for Waste Newsprint Paper Fiber Reinforced Cement Composites
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 346~353
DOI : 10.22636/JKCI.2001.13.4.346
This research investigates the mixture proportioning of waste newsprint paper fiber for thin-cement product. Waste newsprint paper fibers obtained through shredded mechanically by a dry process. Waste newsprint paper fiber reinforced cement composites was manufacted by slurry-dewatering method. The waste newsprint paper fiber reinforcement conditions (fiber mass fraction, level of substitution of virgin fibers, level of fiber beating) and processing variables (pressed, unpressed) are optimized through experimental studies and statistical analyses based on factorial design of experiments and analyses of variance. The optimized recycled waste newsprint paper fiber reinforced cement composites were technically evaluated. The results are shown to possess acceptable properties and strong potentials of the recycling of waste newsprint paper of the reinforcement of thin-cement products.
Effect of the Polycarboxylates on the Physical Properties of Cement Materials
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 354~361
DOI : 10.22636/JKCI.2001.13.4.354
In this paper, three kinds of poly(acrylate-co-methylacrylate) with different number average molecular weight(Mn) were synthesized and studied for the effects on the mechanical properties and the fluidities of the cement mortar admixtured with them. The physical properties of the cement mortar are more favorably enhanced by the poly(acrylate-co-methylacrylate) of Mn,, 5,000 than that of Mn, 2,000∼3,000. And the optimum dosage was decided to ca. 0.6 % of cement weight in cement mortar. However, the dispersion abilities of the polymers in cement mortar was not kept long time. This last result could not be explained by the theory that the fluidity of the cement mortar added with the slow releasing polycarboxylates is kept by the releasing of the carboxylic group of the copolymer in alkaline solution of cement paste.
Enhanced Durability Performance of High Early Strength Concrete for Early Traffic Opening
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 362~370
DOI : 10.22636/JKCI.2001.13.4.362
The internal or external restraint of thermal and dry shrinkage movements could thus generate tensile stresses in concrete pavement for early traffic opening. Restrained shrinkage and thermal stresses could produce microcracks in concrete which increase its permeability and accelerate its long-term deterioration under weathering and load effects. Fiber reinforced concrete is an effective approach to the control of microcrack and crack development under tensile stresses. This study aims at evaluation of the durability of high early strength concrete for early traffic opening and increase of service life. Three different types of regulated-set cement which recently has been used much in Korea were adopted. Fibers were added and their mixtures were compared with plain high early strength concrete mixture. The use of fibers increased durability performance of high early strength concrete using regulated-set cement than the corresponding plain mixtures.
Fracture Properties of Concrete by using the J-integral
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 371~378
DOI : 10.22636/JKCI.2001.13.4.371
Recently, the parameters, models, and experimentations, which evaluate the fracture properties of concrete, have been proposed by many researchers, and their developments allow us to analyze the non-linear and quasi-brittle fracture mechanisms. In this paper, a brief treatment of the fracture parameters was presented and the experiments of 3-point bending tests were conducted to compare J-integral(
/) with other parameters(
). The change of parameter values according to the width and notch length of concrete beam specimens was also considered. The load-displacement curves are used to experimentally measure concrete fracture toughness. From the results of experiment, it is noted that the value of
and tic decreases as the notch depth increases and
is less sensitive than
. Therefore, the former is more appropriate to use as the concrete fracture toughness parameter. The values of
increase when the width of concrete specimens increase from 75 mm to 150 mm. Therefore, the effects of specimen width need to be considered in determining the concrete fracture toughness.
Microplane Model for RC Planar Members in Tension-Compression
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 379~388
DOI : 10.22636/JKCI.2001.13.4.379
Existing microplane models for concrete use three-dimensional spherical microplanes in the analysis of two-dimensional planar members as well as three-dimensional members. Also, they do not accurately describe the post-cracking behavior of reinforced concrete in tension-compression. In this study, a new microplane model is developed to overcome the disadvantages of the existing models. Instead of the spherical microplanes, the proposed microplane model uses disk microplanes involving a less number of microplanes and two-dimensional stresses and strains. As the result, the proposed model is more effective in numerical calculations. Also, the concept of the strain boundary is introduced to describe accurately the compressive behavior of reinforced concrete with tensile cracks in tension-compression. The validity of the proposed model is verified by comparison with existing experiments. In this paper, the microplane model and the numerical techniques involved in the finite element analysis are described in detail.
Analytical Study on the fatigue Behavior of Reinforced Concrete Bridge Piers under Earthquake
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 389~396
DOI : 10.22636/JKCI.2001.13.4.389
This paper presents an analytical prediction of the fatigue behavior of reinforced concrete bridge piers under earthquake. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. In boundary plane at which each member with different thickness is connected, local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for fatigue behavior of reinforced concrete bridge piers under earthquake will be verified by comparison with reliable experimental results.
A Compound Deterioration Assessment of Concrete Subjected In Freezing-Thawing and Chloride Attack
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 397~405
DOI : 10.22636/JKCI.2001.13.4.397
In clod weather regions, a strong seasonal wind brings sea salts to the land. In addition to it, recently, the spreading amount of deicing salts has increased numerously for purpose of removing snow and ice. Thus the salts environment around concrete structures becomes so severe that various damages of concrete due to applied salts will be brought up. Much of countries such as America, Europe etc. is carried out study for effects of deicing salts on concrete. However, there are not test methods for deterioration of concrete subjected to both freezing-thawing and chloride in Korea. In this study, we carried out test for the compound deterioration subjected to both freezing-thawing and chloride attack, to investigate the effects of sodium chloride on the deterioration of concrete. The test was performed to investigate the effects of cement type, strength and air content on the scaling deterioration of concrete. As a result, the scaling deterioration was accelerated in the presence of salts. And the resistance to scaling was strongly influenced by the type of cement, the strength and air content of concrete.
Lining of Reinforced Spun Concrete Pipes using Polymer-Modified Mortars
Journal of the Korea Concrete Institute, volume 13, issue 4, 2001, Pages 406~413
DOI : 10.22636/JKCI.2001.13.4.406
Up to this day, reinforced spun concrete pipes have been widely used as drain pipes. However, many reinforced spun concrete pipes are exposed to the deteriorated environment such as freezing-thawing damage and chemical attack by the growth of a sulfur-oxidizing bacterium isolated from corroded concrete. The purpose of this study is to evaluate the effects of lining by polymer-modified mortar using polymer dispersions as cement modifier on the development in durability of reinforced spun concrete pipe. The polymer-modified mortars were prepared with various polymer types and polymer-cement ratios, and tested for compressive and flexural strengths, acid, freezing-thawing, and heat resistances. And then, the reinforced spun concrete pipe product lined by polymer-modified mortars was tested for adhesion in tension and surface conditions according to curing temperatures in the field. From the test results, it is apparent that the polymer-modified mortars have good mechanical properties and durability as a lining material. In practice, all polymers can be used as lining the materials for reinforced spun concrete pipe, and types of polymer, and polymer-cement ratio and curing conditions are controlled for a good lining product.