• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.169-176
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• 2021

In this study, pull-out tests were conducted at room temperature, 150 ℃ and 250 ℃ to evaluate the residual bond strength of carbon fiber reinforcement polymer, CFRP after elevated temperature and deformed steel rebar of D10 and D13 were also evaluated after the high temperature heating for comparison. As a result of the experiment, the bond strength of the CFRP after 150 ℃ and 250 ℃ decreased by 9.94 % and 41 %, respectively. On the other hand, after thermal heating, both the steel rebar of D10 and D13 had a lower rate of reduction in bond strength than that of the CFRP. Also slip at the maximum bond strength also decreased after the heating for both the CFRP and the rebars. Through it, the correlation between the bond strength and the slip reduction due to thermal heating was confirmed and bond slip models were presented. Finally the experimental result was evaluated as relative bond strength to identify the residual bond performance of the CFRP and the rebar after the heating was confirmed by comparing with the existing test result of the bond strength after elevated temperature.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.155-163
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• 2009

The purpose of this paper is to investigate the bond strength between old and new concrete as well as flexural tensile strength of concrete. To achieve this purpose, a comprehensive experimental program has been set up and strength tests using a series of specimens have been carried out. The present study represents that the flexural bond strength between old and new concrete is much smaller than that of flexural tensile strength. The ratio of bond strength to flexural tensile strength ranged through 15~27%. It is seen that concrete-to-concrete bond strength has been affected by curing condition. Also, test results of tensile strength show that recommendation by ACI 363 committee is estimated to be more realistic than another recommendations for predicting tensile strength of concrete.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.615-622
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• 2003

The purpose of this study is to propose the more reasonable equation of bond strength of grout-filled splice sleeve. To accomplish this objective, total 60 full-sized specimens were tested under monotonic loading. The experimental variables are compressive strength of mortar, embedment length and size of reinforcing bars. Following conclusions are obtained; 1) If the adequacy of existing equations which estimate the bond strength of grout-filled splice sleeve are investigated, they underestimate the bond strength of grout-filled splice sleeve by 8-18%. Also the existing equations have a tendency to underestimate with decrease in the embedment length of reinforcing bars. 2) From the test result of bond failure, the equation which estimates the confining pressure of grout-filled splice sleeve was proposed by making multiple regression analyses of which independent variables are embedment length of reinforcing bars and compressive strength of mortar. This equation predicted the measured bond capacity of this test more accurately than existing equations and eliminated the deviation according to the embedment length of reinforcing bars.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.79-86
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• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.169-178
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• 1998

Bond strength of reinforcing bar to high-perfomance concrete using belite cement is explored using beam end test specimens. The key parameters for the bond test are slump of concrete, top bar effect, and strength of concrete in addition to concrete cover. The test results show that the specimens with belite cement concrete show approximately 10% higer bond strength than those with portland cement concrete. The results also show that the bond strength from the high strength concrete is function of the square root of concrete compressive strength. Bond strength of the top bar is less than bond strength of bottom bar, but the ratios of the bond strength of bottom-cast bars to those for top-cast bars are much less than the modification factor for top reinforcement found in the ACI 318-95 code. Comparisons with other reported tests identified that belite cement increased bond strength while silica fume or flyash used in high strength concrete decreased bond strength. The high-strength and high-slump concrete with belite cement performs well in terms of bond strength to reinforcing steel.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.259-266
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• 2012

A general earthquake resistant design philosophy of ductile frame buildings allows beams to form plastic hinges adjacent to beam-column connections. In order to carry out this design philosophy, the ultimate bond or shear strength of the beam should be greater than the flexural yielding force and should not degrade before reaching its required ductility. The behavior of RC members dominated by bond or shear action reveals a dramatic reduction of energy dissipation in the hysteretic response due to the severe pinching effects. In this study, a method was proposed to predict the deformability of reinforced concrete members with short-span-to-depth-ratios, which would result in bond failure after flexural yielding. Repeated or cyclic loading produces a progressive deterioration of bond that may lead to failure at lower cyclic bond stress levels. Accumulation of bond damage is caused by the propagation of micro-cracks and progressive crushing of concrete in front of the lugs. The proposed method takes into account bond deterioration due to the degradation of concrete in the post yield range. In order to verify bond deformability of the proposed method, the predicted results were compared with the experimental results of RC members reported in the technical literature. Comparisons between the observed and calculated bond deformability of the tested RC members showed reasonably good agreement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.149-160
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• 2015

This study reports the interfacial bond strength between Ultra High Performance Concrete (UHPC) and Normal Strength Concrete (NSC). While previous studies have focused on the interfacial strength between NSC substrate and UHPC overlay, this study use precast UHPC for enhanced constructability and replacement of formwork. The factors affecting the interface strength are comprehensively reviewed. It can be classified into: interface shape, degree of hardening and moisture condition of UHPC before combining with NSC, and curing condition of composite materials. Conducted experiments verify the effects of each factor on the interface strength and, accordingly show different failure modes. In particular, a new failure mode of the failure of a part of UHPC was firstly found in the case of sample with rough interface between UHPC and NSC. The other factors of the degree of hardening and the moisture and curing conditions of UHPC were discussed. This research will provide a valuable foundation to utilize the UHPC as a composite material.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.298-305
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• 2018

In this study, we investigated the tensile bond characteristics of underwater coating materials, in order to obtain useful information in support of repair work for marine and coastal concrete structures. Test variables included type of underwater coating, surface conditions of the concrete substrate, and environmental conditions. Pull-off tensile bond strength was measured at 24 h after applying underwater coatings to concrete substrates, in compliance with the procedures specified in ASTM C1583. Failure modes (coating, interface, and parent concrete) for each coating were identified through visual inspection, and comparisons were made based on measured bond strength. The tensile bond strength decreased underwater compared to that under dry conditions, while no significant effect of surface roughness on the measured bond strength was observed in underwater tests. Key aspects that need to be considered regarding selection and use of underwater coating materials for marine and coastal concrete structures were discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1153-1163
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• 2013

Bonded concrete overlay is a favorable maintenance method since the material properties are similar to existing concrete pavements. In addition, bonded concrete overlay has advantage of structural performance based on being bonded together, both for the overlay layer and the existing pavement which perform as one monolithic layer. Therefore, it is important to have a suitable bond strength criteria for long term performance of bonded concrete overlay. This study aimed to investigate the affecting of bond strength on various bond characteristics, and to compare the bond strength between direct tensile test and indirect tensile test due to various conditions such as overlay materials, compressive and flexure strength of existing pavement, and deterioration status of existing pavement. As a result of this study, bond strength occurred by both of direct and indirect tensile test due to monotonic load is highly correlated such as coefficient of determination of 0.75 and P-value of 0.002. However, bond strength by indirect tensile test was relatively higher than bond strength by direct tensile test. It was known that correlation between direct and indirect tensile test was possible to use the characteristics analysis of bond fatigue behavior based on bond strength due to cyclic load which can simulate real field behavior of bonded concrete overlay.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.109-112
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• 2008

In this study, Assessment of bond property of HSC with the rate of Blust-furnace(0, 12, and 25 percent by weight cement) and Evaluation of the relationship of the compressive strength coefficient (${\beta}$) between compressive strength with 40${\sim}$120MPa were performed. Design and Test of Bond specimens were carried out based on the ASTM C-234. Test results are follows, most specimens showed that the splitting failure in all specimens, except for B-40 series which showed that the pull-out failure. For the B-40 Series, the relation of compressive strength versus bond stress has well converged that of the proposed equation with the variation(${\beta}$=2/3) in UCB/E.E.R.C-83. The crack strength of concrete in splitting was proportioned to the compressive strength of concrete, and was the highest on the contents of blast furnace slag to 12 percent by weight of cement in each series, except for B-60 series. In the relation of admixture replacement rate versus maximum bond stress, The maximum bond stress was the highest in 12 percent by weight of cement according to less than 40MPa, and was the highest in 25 percent by weight of cement according to 80MPa.