• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.3
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• pp.47-57
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• 2023

In this study, pull-out tests were performed to investigate the effects of stirrup spacing, rebar diameter, and corrosion rate on bond strength of deformed bars in reinforced concrete. Twelve pull-out specimens with different stirrup spacing, rebar diameter, and corrosion rate were prepared following the RILEM RC6 guidelines. The test results showed that the bond strength of specimens with stirrups increased when the corrosion rate was less than 3%, whereas it decreased when the corrosion rate was more than 3%. On the other hand, the bond strength of specimens without stirrups decreased as the corrosion rate increased. The effect of rebar diameter was less significant compared to those of stirrup spacing and corrosion rate. A bond strength model for pull-out specimens was proposed considering stirrup ratio and corrosion rate, and the model showed the lowest error among the previous models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.79-86
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• 2006

This study was investigated to corrosion resistance of Cr-bearing rebars to macrocell corrosion caused by concrete with crack. Ten types of steel bars having different Cr contents were embedded in concretes with imitation crack. The corrosion resistance of the Cr-bearing rebar was examined by measuring half-cell potential, macrocell corrosion current, corrosion area and weight loss up to 105 cycles of salt spray testing. The results revealed that the Cr content required for corrosion resistance in a macrocell corrosion environment caused by chloride ion gap of $3kg/m^3$ was 9% or more. The corrosion-resisting performance of Cr-bearing rebar was particularly noticeable with a Cr content of 11% or more.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.93-102
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• 2016

The purpose of this paper is to investigate the flexural behavior of high-strength steel fiber-reinforced concrete beams with compressive strength of 130 MPa. The paper presents experimental research results of steel fiber-reinforced concrete beams with steel fiber content of 1.0% by volume and steel reinforcement ratio of less than 0.02. Both of normal-strength rebar and high-strength rebar were used in the test beams. Modeling as well as compressive and tensile strength test of high-strength steel fiber-reinforced concrete was performed to predict the bending strength of concrete beams. Tension modeling was performed by using inverse analysis in which load-crack mouth opening displacement relationship was considered. The experimental results show that high-strength steel fiber-reinforced concrete beams and the addition of high-strength rebar is in favor of cracking resistance and ductile behavior of beams. For beams reinforced with normal-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.81 to 1.42, whereas for beams reinforced with high-strength rebar, the ratio of bending strength prediction to the test result ranged from 0.92 to 1.07. The comparison of bending strength from numerical analysis with the test results showed a reasonable agreement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.281-287
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• 2011

GFRP rebars could be deteriorated by concrete alkalinity. This paper focuses on the investigation of durability of GFRP rebars with ribs exposed to alkaline environment of concrete. It has been reported that the milled E-glass fibers in the ribs of GFRP rebar can increase bond strength between GFRP rebars and the concrete. In this study, the effect of milled alkaline resistant glass fibers (milled AR glass) and milled E-glass in the ribs on the durability of GFRP rebar is investigated through ISS tests and moist absorption tests of the bare rebar. To accelerate the effect of the alkalinity, high temperature($40^{\circ}C$) was applied. According to the test results, mix ratio of milled glass fibers in the ribs by weight had significant effect on durability of GFRP rebars with ribs. It is because that the high mix ratio may leads more voids in the ribs due to lower workability and formability. On the other hand, changing fiber type in the ribs from E-glass to AR-glass had no improvements on ISS strength of the GFRP rebar. Therefore, it is found that determination of proper mix ratio of milled glass fiber in the mixture for the formation of the ribs of the GFRP rebar is important.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.120-127
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• 2016

Due to the enlargement and high-rise of reinforced concrete structure, the application of high functional material is required. However, high-strength bar is recently introduced to the country and the material is insufficient to measure the variation of quantity of rebar quantitatively when using high-strength bar. For these reasons, this study is to provide useful data in cost decision making when applying high-strength bar at a stage of architectural project planning. For residence-commerce complex buildings, we set up six types of conditions such as in case of using only rebar, in case of using only high-strength bar, in case of using rebar mixed with high-strength bar and so on. With the standard of study model 1 that applies only SD400 regardless of rebar diameter, the analyzed result of rebar variation and the cost change of construction in other study model is as follows. When the rebar amount and cost in study model I was 100%, each ratio was 88.3% and 90.5% in study model II, 80.2% and 83.4% in study model III, 91.9% and 93.5% in study model IV, 88.9% and 87.7% in study model V and 82.4% and 85.5% in study model VI. Therefore, in case of rebar amount and construction cost, study model III was evaluated as the best that was applied only SD600.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.66-71
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• 2019

In this paper, a study was conducted on the method of using GPR data to predict rebar thickness inside a facility. As shown in the cases of poor construction, such as the use of rebars below the domestic standard and the construction of reinforcement, information on rebar thickness can be found to be essential for precision safety diagnosis of structures. For this purpose, the B-scan data of GPR was obtained by gradually increasing the diameter of rebars by making specimen. Because the B-scan data of GPR is less visible, the data was converted into the heatmap image data through migration to increase the intuition of the data. In order to compare the results of application of commonly used B-scan data and heatmap data to CNN, this study extracted areas for rebars from B-scan and heatmap data respectively to build training and validation data, and applied CNN to the deployed data. As a result, better results were obtained for the heatmap data when compared with the B-scan data. This confirms that if GPR heatmap data are used, rebar thickness can be predicted with higher accuracy than when B-scan data is used, and the possibility of predicting rebar thickness inside a facility is verified.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.1-12
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• 2017

This paper concerns the structural behavior of high-strength concrete beams with compressive strength of 80 MPa subjected to flexure. Main test variables were nominal yielding strength of longitudinal rebar including normal strength rebar(SD 400) and high strength rebar(SD 600), reinforcement ratio from 0.98 to 1.58% and beam section size with $200{\times}250$, $200{\times}300mm$. The nine beams were cast and tested under flexure. The study investigated ultimate flexural strength, load-deflection relationship, crack patterns, failure patterns and ductility of the test beams. Test results indicate that when rebar ratio increased flexural strength increased and ductility decreased. In addition, the number of cracks increased and the crack width decreased as the reinforcement ratio increased. The yield strength of rebar did not affect significantly load-crack width relationship. Nonlinear analysis of test beams was performed and then test results and analytical results of ultimate load were compared. Analytical results of high-strength concrete beams overall underestimated flexural strength of test beams.

• Structural Engineering and Mechanics
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• v.30 no.6
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• pp.713-732
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• 2008

Serviceability and durability of the concrete members can be seriously affected by the corrosion of steel rebar. Carbonation front and or chloride ingress can destroy the passive film on rebar and may set the corrosion (oxidation process). Depending on the level of oxidation (expansive corrosion products/rust) damage to the cover concrete takes place in the form of expansion, cracking and spalling or delamination. This makes the concrete unable to develop forces through bond and also become unprotected against further degradation from corrosion; and thus marks the end of service life for corrosion-affected structures. This paper presents an analytical model that predicts the weight loss of steel rebar and the corresponding time from onset of corrosion for the known corrosion rate and thus can be used for the determination of time to cover cracking in corrosion affected RC member. This model uses fully the thick-walled cylinder approach. The gradual crack propagation in radial directions (from inside) is considered when the circumferential tensile stresses at the inner surface of intact concrete have reached the tensile strength of concrete. The analysis is done separately with and without considering the stiffness of reinforcing steel and rust combine along with the assumption of zero residual strength of cracked concrete. The model accounts for the time required for corrosion products to fill a porous zone before they start inducing expansive pressure on the concrete surrounding the steel rebar. The capability of the model to produce the experimental trends is demonstrated by comparing the model's predictions with the results of experimental data published in the literature. The effect of considering the corroded reinforcing steel bar stiffness is demonstrated. A sensitivity analysis has also been carried out to show the influence of the various parameters. It has been found that material properties and their inter-relations significantly influence weight loss of rebar. Time to cover cracking from onset of corrosion for the same weight loss is influenced by corrosion rate and state of oxidation of corrosion product formed. Time to cover cracking from onset of corrosion is useful in making certain decisions pertaining to inspection, repair, rehabilitation, replacement and demolition of RC member/structure in corrosive environment.

• KIEAE Journal
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• v.7 no.4
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• pp.141-146
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• 2007

It is necessary to guarantee the safety, serviceability and durability of reinforced concrete structures over their service life. However, concrete structures represent a decrease in their durability due to the effects of external environments according to the passage of time, and such degradation in durability can cause structural degradation in materials. In concrete structures, some degradations in durability increase the corrosion of embedded rebars and also decrease the structural performance of materials. Thus, the structural condition assessment of RC materials damaged by corrosion of rebars becomes an important factor that judges needs to apply restoration. In order to detect the damage of reinforced concrete structures, a visual inspection, a nondestructive evaluation method(NDE) and a specific loading test have been employed. However, obscurities for visual inspection and inaccessible members raise difficulty in evaluating structure condition. For these reasons, detection of location and quantification of the damage in structures via structural response have been one of the very important topics in system identification research. The main objective of this project is to develope a methodologies for the damage identification via static responses of the members damaged by durability. Six reinforced concrete beams with variables of corrosion position and corrosion width were fabricated and the damage detections of corroded RC beams were performed by the optimization and the conjugate beam methods using static deflection. In results it is proved that the conjugate beam method could predict the damage of RC members practically.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.2
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• pp.107-111
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• 2016

This paper presents electrochemical corrosion behaviors of cement mortar specimens in the high salinity condition. Chloride ion is known as the most detrimental parameter to cause the corrosion in reinforced concrete. Increasing the concrete cover thickness is one of the corrosion protection methods against chloride ion; so, this study mainly focuses on the effects of mortar cover thickness on corrosion protection. In specimens, rebar, which was a height of 200 mm and a diameter of 10 mm, was installed at the center of the small size form. Later on, mortar was injected into the form, and 10, 20, 30, 40, and 50 mm of the different mortar cover thicknesses were selected. Potential measurements, linear polarization resistance tests, and cyclic potentiodynamic polarization tests were performed for specimens that were exposed to seawater. These results were compared with visual inspection results of rebar. The results show that an increase in the cover thickness contributes to corrosion protection. In addition, the result of electrochemical corrosion tests generally agreed with that of an autopsy visual inspection.