• Journal of the Korea institute for structural maintenance and inspection
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• 제22권1호
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• pp.183-189
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• 2018

In this study, the bond strength between concrete and metal films was investigate according to changing water content ratio of substrate concrete by pull-out test in order to develop the new finishing design methods for building structures using the metal films. The following conclusions were obtained as a result of the studies. It was find that the colour of metal did not change before and after the metal spraying. Also, the water content ratio of substrate concrete must be controlled under 10% weight to confirm the standard bond strength of finishing material to concrete. 2.5 MPa. To enhance the bond strength between concrete and metal films, it is very effective to strengthen the concrete surface using the agent which strengthen the concrete surface and seal the pore of metal film by the sealing agents. Therefore, the control of concrete surface treatment and water content ratio are necessary to secure the bond strength of metal films.

• Smart Structures and Systems
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• 제17권4호
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• pp.593-610
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• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• Steel and Composite Structures
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• 제52권2호
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• pp.165-182
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• 2024

Grouted sleeve splice (GSS) is an effective type of connection applied in the precast concrete structures as it has the advantages of rapidly assembly and reliable strength. To decrease the weight and cost of vertical rebar connection in precast shear walls, a light-weight sleeve is designed according to the thick-cylinder theory. Mechanical behaviour of the light-weighted GSS is investigated through experimental analysis. Two failure modes, such as rebar fracture failure and rebar pull-out failure, are found. The load-displacement curves exhibit four different stages: elastic stage, yield stage, strengthening stage, and necking stage. The bond strength between the rebar and the grout increases gradually from outer position to inner position of the sleeve, and it reaches the maximum value at the centre of the anchorage length. A finite element model predicting the mechanical properties of the light-weighted GSS is developed based on the Concrete Damage Plasticity (CDP) model and the Brittle Cracking (BC) model. The effect of the rebar anchorage length is significant, while the increase of the thickness of sleeve and the grout strength are not very effective. A model for estimating ultimate load, including factors of inner diameter of sleeves, anchorage length, and rebar diameter, is proposed. The proposed model shows good agreement with various test data.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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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.

• Journal of the Korea Concrete Institute
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• 제15권1호
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• pp.11-16
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• 2003

The objective of this study is to clarify the seismic capacity and the characteristics in the hysteretic behavior of RC structures with non-seismic detailing. To do this, an exterior beam-column subassemblage was selected from a ten story RC building and six 1/3-scale specimens were manufactured with three variables; (1) with and without slab, (2) upward and downward direction of anchorage for the bottom bar in beams, and (3) with and without hoop bars in the joint region. The test results have shown that (1) the existence of slab increased the strength in positive and negative moment, 25% and 52%, respectively; (2) the Korean practice of anchorage (downward and 25 $d_{b}$ anchorage length) caused the 8% reduction of strength and the early strength degradation in comparison with the case of seismic details; and (3) the existence of hoop bars in the joint region shows significant role in preventing the pull-out.t.

• Journal of the Korean Ceramic Society
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• 제42권8호
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• pp.582-587
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• 2005

AlN-BN ceramic composites were fabricated and their mechanical properties were investigated. The relative density of hot-pressed composites decreased with increasing BN content, but over $99\%$ could be obtained with 30 $vol\%$ BN in AlN. YAG was formed in the composites and monolithic AlN as a second phase by the reaction between $Y_2O_3$, added as sintering aid, and $Al_2O_3$. As expected, Vickers hardness and Young's modulus decreased with increasing BN content. The three-point flexural strength also showed similar behavior decreasing from 500 MPa of monolith down to 250 MPa by the addition 30 $vol\%$ BN. However, interestingly, the standard deviation of the strength values decreased significantly as BN was added to AlN. As a result, the Weibull modulus of the AlN-30 $vol\% BN composite was 21.3, which was extremely high. Fractography and crack path studies revealed that BN platelets induced grain pull-out and crack bridging in a bigger scale during crack propagation. Consequently, fracture toughness increased as more BN was added, reaching 4.5 $MPa\sqrt{m}$ at 40 $vol\%$ BN.

• Transactions of the Korean Society of Mechanical Engineers
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• 제17권6호
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• pp.1351-1360
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• 1993

The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.

• Journal of the Korea institute for structural maintenance and inspection
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• 제15권4호
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• pp.125-135
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• 2011

The bond properties between polypropylene fiber reinforced cement composites and structural synthetic fiber have been investigated. in this paper. Three levels of polypropylene fibers volume fraction were used, 0.10%, 0.15%, and 0.20% in a series of Dog-bone pull out tests. The bond strength between structural synthetic fiber and polypropylene fiber reinforced cement composites increases with the volume fraction of polypropylene fiber, but the bond strength decreases above the amount of 0.20% by volume of polypropylene fiber reinforced cement composites. Also, the addition of polypropylene fiber a significant improved the interface toughness and the frictional resistance, The microstructure of structural synthetic fiber surface was investigated after the pullout test. The scratched of structural synthetic fiber increased with the polypropylene fiber volume fraction.

• The Journal of the Korea Contents Association
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• 제15권3호
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• pp.427-437
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• 2015

Concrete, as a construction material, needs suitable reinforcement for tensile region due to weak tensile strength. Many researches on cement reduction have been attempted for $CO_2$ emissions during cement clinker production. In this paper engineering properties of concrete enhanced with polypropylene fiber (PPF) and rice husk ash (RHA) are evaluated. Fiber volume ratios of 0.125~0.375 and RHA replacement ratio of 0~20% are considered for concrete mixture. Lots of test including compressive, split, flexural and the related crack width, impact energy, and pull out test are performed and the results are evaluated considering the fiber ratios, fiber length and RHA replacement. Fiber and RHA ratios have dominant effects on tensile and compressive characteristics respectively, and the concrete with 0.125% of PPF and 10% of RHA shows the most effective enhancement for engineering properties. Appropriate addition of RHA and PPF are very effective both for engineering property enhancement and clean technology.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1089-1092
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• 2008

The bond behavior between concrete and reinforcement is a important requirement for reinforced concrete constructions. For practical application, it is very important to study bond behavior of reinforcing bars in recycled fine aggregate concrete. Therefore, pull-out test in order to investigate the bond behavior between recycled fine aggregate concrete and deformed bars was performed. Recycled fine aggregate concrete replacement ratios (i.e., 0% and 100%) and positions of deformed bars (i.e., vertical and horizontal position) were considered as variables in this study. Test results were compared with the bond strength requirement recommended by CEB-FIP code. Based on the test results, It was found that the bond strength between the recycled fine aggregate concrete and deformed bars were influenced by both recycled fine aggregate concrete replacement ratios and positions of deformed bars. The reduction of bonded area at the soffit of horizontal reinforcement caused by concrete bleeding was observed in H type specimen. So, Only V type and HB specimen satisfied the bond strength requirement recommended by CEB-FIP code.