• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.217-224
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• 1998

This study describes examinations made for the purpose of obtaining data for strength control of mass concrete in the cold season. The examination in outline of analysis of temperatures of mass concrete(corresponding to member thickness of 1m) and comparisons with water-cured specimens of various concrete specimens cured in sealed condition. As a result, it was found that mass concrete placed in the cold season, if strength is controlled based on 28-day age, is seen to require a strength correction factor.

• Structural Engineering and Mechanics
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• v.62 no.5
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• pp.651-661
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• 2017

This paper presents an experimental study of bond-slip behavior of reinforced lightweight aggregate concrete (LC) and normal weight concrete (NC) with embedded steel bar. Tests were conducted on tension-pull specimens that had cross-sectional dimension with a reinforcing bar embedded in the center section. The experimental variables include concrete strength (20, 40, and 60 MPa) and coarse aggregate type (normal-weight aggregate and reservoir sludge lightweight aggregate). The test results show that as concrete compressive strength increased, the magnitudes of the slip of the LC specimens were greater than those of the NC specimens. Moreover, the bond strength and stiffness approaches zero at the loaded end, or close to the central anchored point of the specimen. In addition, the proposed bond stress-slip equation can effectively estimate the behavior of bond stress and steel bar slipping.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.817-820
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• 2000

Existence of void or delamination inside building foundation or tunneling lining can cause serious problems in structural safety. Therefore, 0probing of such voids in architectural and civil structures is an important process in evaluating the overall integrity of the structures. In this study, the radar method has been examined in its use in detecting voids inside concrete specimens. The dimensions of the specimens are 1,000 mm(width) $\times$ 600 mm (height) $\times$ 140 mm (thickness). A void is embedded inside concrete specimens with the dimensions of 200 mm(width) $\times$ 600 mm (height) $\times$ 50 mm (thickness). Concrete cover depth of 30 mm, 60 mm is studied for comparison. In both cases, the voids is located with 1 GHz antenna.

• Journal of the Korean Society of Safety
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• v.32 no.5
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• pp.69-75
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• 2017

Structural safety evaluation for static strength of thin plate RC member with high strength concrete is conducted in this study. Static strengths were predicted and compared with the experimental values. Predicted values were calculated by the evaluation formula based on the punching shear behavior and the yield line theory which can appear in the plate members. Static load tests were carried out for the specimens with high strength concrete and the test results were compared with the required performance in design. The comparison results show that the specimens with high strength concrete have sufficient structural safety for flexural and punching shear performance required in design. High strength concrete specimens exhibited excellent strength despite their small thickness. The range of concrete strengths applied in this study was about 60 MPa to 100 MPa.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.3
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• pp.185-190
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• 2014

The purpose of this research is to extract spectral reflectance characteristics of concretes through basic experiment on concrete specimens and site experiment on actual concrete structures using a field portable spectrometer and a VNIR hyperspectral sensor. A spectrometer (GER-3700) and a VNIR hyperspectral camera (AisaEagle VNIR Hyperspectral Camera) were utilized for extracting spectral characteristics of concrete specimens. Concretes normally show similar patterns that have correlation above 80%, while the high-strengthened concretes display very different results from the normal-strength concretes. We also made a certain conclusion in the laboratory experiment on concrete specimens that both the spectrometer and the VNIR camera vary in spectral reflectance depending on concrete strengths.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.765-768
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• 2006

This paper investigates the properties of light weight foamed concrete with variances in adding ratio of stability agent(PS). Test showed that an increase of PS adding ratio decreased fluidity due to higher viscosity and increased unit weight of specimens. A sinking depth declined as the adding ratio of PS inclines, but all specimens including control concrete was ranging in KS; 0.5 to 10mm. Compressive strength value of specimens increased as PS adding ratio inclines. As for the tensile strength, any significant feature was not observed, compared with control concrete, but the ratios of camp. to tens. increased. Appearance density of concrete increased, and thermal conductivity was satisfied in KS, except for a specimen adding 0.07 percent of PS.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.1
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• pp.113-120
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• 1999

Due to the heterogeneous nature of a concrete, periodic inspections are compulsory to maintenance of quality of concrete structures. The major object of this study is to analyze and investigate experimentally the experimental equation for the estimate of compressive strength of prestressed concrete. In this study, surface hardness method, ultrasonic method are investigated to evaluate strength of concrete specimens. Specimens are cast in laboratory and cores are cut from specimens in order to estimate the accurate strength. These values are used to compare with calculated values from test data. The result shows that the proposed equation can reproduce the results at prestressed concrete beam girders more appropriately than previous equations.

• Computers and Concrete
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• v.8 no.2
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• pp.207-227
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• 2011

In flexural strength design of unconfined reinforced concrete (RC) members, the concrete compressive stress-strain curve is scaled down from the uni-axial stress-strain curve such that the maximum concrete stress adopted in design is less than the uni-axial strength to account for the strain gradient effect. It has been found that the use of this smaller maximum concrete stress will underestimate the flexural strength of unconfined RC members although the safety factors for materials are taken as unity. Herein, in order to investigate the effect of strain gradient on the maximum concrete stress that can be developed in unconfined flexural RC members, several pairs of plain concrete (PC) and RC inverted T-shaped specimens were fabricated and tested under concentric and eccentric loads. From the test results, the maximum concrete stress developed in the eccentric specimens under strain gradient is determined by the modified concrete stress-strain curve obtained from the counterpart concentric specimens based on axial load and moment equilibriums. Based on that, a pair of equivalent rectangular concrete stress block parameters for the purpose of flexural strength design of unconfined RC members is determined.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.915-923
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• 2003

This paper presents the test results of total 35 direct tensile specimens to investigate the effect of high-strength concrete on the tension stiffening effect in axially loaded reinforced concrete tensile members. Three kinds of concrete strength 25, 60, and 80 MPa were included as a major experimental parameter together with six concrete cover thickness ratios. The results showed that as higher strength concrete was employed, not only more extensive split cracking along the reinforcement was formed, but also the transverse crack space became smaller. Thereby, the effective tensile stiffness of the high-strength concrete specimens at the stabilized cracking stage was much smaller than those of normal-strength concrete specimens. This observation is contrary to the current design provisions, and the significance in reduction of tension stiffening effect by employment of high-strength concrete is much higher than that would be expected. Based on the present results, a modification factor is proposed for accounting the effect of the cover thickness and the concrete strength.

• Structural Engineering and Mechanics
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• v.14 no.5
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• pp.543-563
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• 2002

The use of the epoxy pressure injection technique to rehabilitate reinforced concrete beam-column joints damaged by strong earthquakes is investigated experimentally and analytically. Two one-half-scale exterior beam-column joint specimens were exposed to reverse cyclic loading similar to that generated from strong earthquake ground motion, resulting in damage. Both specimens were typical of new structures and incorporated full seismic details in current building codes. Thus the first specimen was designed according to Eurocode 2 and Eurocode 8 and the second specimen was designed according to ACI-318 (1995) and ACI-ASCE Committee 352 (1985). The specimens were then repaired with an epoxy pressure injection technique. The repaired specimens were subjected to the same displacement history as that imposed on the original specimens. The results indicate that the epoxy pressure injection technique was effective in restoring the strength, stiffness and energy dissipation capacity of specimens representing a modem design.