• 한국도로학회논문집
• /
• 제19권5호
• /
• pp.33-42
• /
• 2017

PURPOSES : The purpose of this study is to suggest the construction and quality control method for the re-repair of a deteriorated partial depth repair for sections of Portland cement concrete pavement. METHODS : An experimental construction was conducted to extend the repair width for removing an existing repair section. A removal method was used to ensure early performance for a deteriorated partial depth repair section. Bond strength and split tensile strength were measured at the near vertical interface layer between the existing pavement and repair material. The area was analyzed for various conditions such as the extended repair area and the removing method of the existing repair section. RESULTS : As a result of analysis of bond strength and split tensile strength, the bonding performance of a milling removed section was improved over a cutting and hand breaker removed section. The bond strength was analyzed to increase slightly as the extended repair width for removing the existing repair section increased. The split tensile strength did not show a clear relationship to an increased extended repair width of an existing removed repair section. CONCLUSIONS : The milling removal method should be applied in the removal of existing deteriorated partial depth repair sections. The extended repair width for a re-repair section should be wider than the existing partial depth repair with at least a 75-mm length and width for the bond strength and the split tensile strength.

• Advances in nano research
• /
• 제14권4호
• /
• pp.363-373
• /
• 2023

A novel type of steel fiber with a rounded-end shape is presented to improve the bonding behavior of fibers with Carbon Nanotubes (CNT)-reinforced Ultra-High Performance Concrete (UHPC) matrix. For this purpose, by performing a parametric study and using the nonlinear finite element method, the impact of geometric characteristics of the fiber end on its bonding behavior with UHPC has been studied. The cohesive zone model investigates the interface between the fibers and the cement matrix. The mechanical properties of the cohesive zone model are determined by calibrating the finite element results and the experimental fiber pull-out test. Also, the results are evaluated with the straight steel fibers outcomes. Using the novel presented fibers, the bond strength has significantly improved compared to the straight steel fibers. The new proposed fibers increase bond strength by 1.1 times for the same diameter of fibers. By creating fillet at the contact area between the rounded end and the fiber, bond strength is significantly improved, the maximum fiber capacity is reachable, and the pull-out occurs in the form of fracture and tearing of the fibers, which is the most desirable bonding mode for fibers. This also improves the energy absorbed by the fibers and is 4.4 times more than the corresponding straight fibers.

• 콘크리트학회논문집
• /
• 제22권6호
• /
• pp.753-760
• /
• 2010

초고성능 콘크리트(ultra high performance concrete, UHPC)는 종래의 보통 콘크리트와 다른 새로운 재료로써 높은 강도와 향상된 인성을 그 특징으로 한다. 이러한 새로운 재료의 활용을 위하여 이 연구에서 초고성능 콘크리트의 부착 성능을 평가하고자 하였다. 수정된 RILEM 방법을 사용하여 초고성능 콘크리트와 이형 철근의 인발실험(pull-out test)을 수행하였으며 보통 콘크리트와 비교하여 5~10배에 달하는 부착강도를 확인하여 기존의 설계 기준에 비하여 현저하게 감소한 정착길이와 피복 두께를 제안하였다. 700 MPa급 고장력 철근의 실험 결과의 비교로부터 초고성능 콘크리트에서 고강도 철근 활용의 유효성을 확인하였다. 강연선의 응력전달길이 측정실험을 통하여 현재 전달길이 기준이 UHPC의 경우 매우 보수적이라는 것을 확인하였다. 또한 유한요소해석을 통하여 실험 결과를 검증하였다.

• Steel and Composite Structures
• /
• 제35권4호
• /
• pp.463-474
• /
• 2020

In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young's modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16 mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16 mm was 34.3% and 45%.

• 콘크리트학회논문집
• /
• 제15권1호
• /
• pp.17-24
• /
• 2003

지진하중을 받는 철근콘크리트구조의 취성파괴의 원인은 철근과 콘크리트사이의 급속한 부착손상에 의해 발생되는 국부 부착-슬립이다. 본 연구는 반복하중하에서 부착손상에 대한 철근의 마디높이의 효과를 평가하는 것이다. 큰 상대마디면적을 가진 가공된 철근을 사용하여 부착 시험체를 제작하였다. 또 다른 변수로서 연직방향 철근에 의해 횡구속 철근량의 정도가 고려되었다. 실험결과로부터 에너지 소산력의 크기가 산정되고 여러 변수들에 대해서 비교되었다. 실험결과로서, 하중의 반복이 증가함에 따라 부착강도와 부착강성은 현저히 감소함을 알 수 있다. 횡구속량이 크고 상대마디면적이 큰 철근에서 단조하중시에 비해서 반복하중시의 부착강도의 감소가 줄어들고 국부부착저하를 지연시키는데 효과가 있음을 알 수 있다. 에너지 소산량 또한 횡구속량과 마디상대면적이 증가함에 따라 증가한다. 그러나, 마디가 매우 높은 철근의 부착실험에서 높은 강성 때문에 부착이 적은 슬립에서 손상을 입는다는 것을 알 수 있다. 본 연구는 반복하중하에서 부착저하기구를 이해하고 높은 상대마디면적을 가진 새로운 이형철근의 개발에 유용할 것이다.

• Restorative Dentistry and Endodontics
• /
• 제44권3호
• /
• pp.23.1-23.9
• /
• 2019

Objectives: The aim of this study was to investigate the microshear bond strength (${\mu}SBS$) of different universal adhesive systems applied to hybrid computer-aided design/computer-aided manufacturing (CAD-CAM) restorative materials repaired with a composite resin. Materials and Methods: Four types of CAD-CAM hybrid block materials-Lava Ultimate (LA), Vita Enamic (VE), CeraSmart (CS), and Shofu Block HC (SH)-were used in this study, in combination with the following four adhesive protocols: 1) control: porcelain primer + total etch adhesive (CO), 2) Single Bond Universal (SB), 3) All Bond Universal (AB), and 4) Clearfil Universal Bond (CU). The ${\mu}SBS$ of the composite resin (Clearfil Majesty Esthetic) was measured and the data were analyzed using two-way analysis of variance and the Tukey test, with the level of significance set at p < 0.05. Results: The CAD-CAM block type and block-adhesive combination had significant effects on the bond strength values (p < 0.05). Significant differences were found between the following pairs of groups: VE/CO and VE/AB, CS/CO and CS/AB, VE/CU and CS/CU, and VE/AB and CS/AB (p < 0.05). Conclusions: The ${\mu}SBS$ values were affected by hybrid block type. All tested universal adhesive treatments can be used as an alternative to the control treatment for repair, except the AB system on VE blocks (the VE/AB group). The ${\mu}SBS$ values showed variation across different adhesive treatments on different hybrid CAD-CAM block types.

• 한국구조물진단유지관리공학회 논문집
• /
• 제12권1호
• /
• pp.65-72
• /
• 2008

최근에 상용 FRP 판(plank)을 콘크리트 구조물의 영구 거푸집 및 보강재로 이용하기 위한 연구가 진행되고 있다. FRP 판과 타설 콘크리트가 합성효과를 발휘하기 위해서는 두 재료간의 부착이 중요한 요인 중의 하나이다. 이러한 부착을 확보하기 위하여 FRP 판에 모래를 일반적으로 건설현장에서 많이 사용하는 에폭시를 이용하여 부착하였다. FRP 판과 콘크리트 합성구조의 구조적 거동을 이해하기 위해서는 FRP판과 타설 콘크리트 사이의 정량적인 국부 부착모델이 필요하다. 본 연구에서는 이와 같은 합성구조 시스템에 간단히 적용할 수 있는 단순 부착모델을 제안한다.

• 한국건축시공학회지
• /
• 제12권5호
• /
• pp.510-517
• /
• 2012

This study evaluated the recycling potential of in-site waste soil as pile back filling material (PBFM). We performed experiments to check workability, segregation resistance, bond strength, direct shear stress test, and dynamic load test using in-site waste soil in coastal areas. We found that PBFM showed better performance than general cement paste in terms of workability, segregation resistance, and bond strength. On the other hand, the structural performance of PBFM was slightly lower than that of general cement paste due to the skin friction force of pile by Pile Driving Analyzer and direct shear stress. However, because this type of performance degradation in terms of structure can be improved through the use of piles with larger diameter or by changing the type of pile, considering the economics and environment, we considered that recycling of PBFM has sufficient value.

• 한국도로학회논문집
• /
• 제19권6호
• /
• pp.37-46
• /
• 2017

PURPOSES : A composite pavement utilizes both an asphalt surface and a concrete base. Typically, a concrete base layer provides structural capacity, while an asphalt surface layer provides smoothness and riding quality. This pavement type can be used in conjunction with rollercompacted concrete (RCC) pavement as a base layer due to its fast construction, economic efficiency, and structural performance. However, the service life and functionality of composite pavement may be reduced due to interfacial bond failure. Therefore, adequate interfacial bonding between the asphalt surface and the concrete base is essential to achieving monolithic behavior. The purpose of this study is to investigate the bond characteristics at the interface between asphalt (HMA; hot-mixed asphalt) and the RCC base. METHODS : This study was performed to determine the optimal type and application rate of tack coat material for RCC-base composite pavement. In addition, the core size effect, temperature condition, and bonding failure shape were analyzed to investigate the bonding characteristics at the interface between the RCC base and HMA surface. To evaluate the bond strength, a pull-off test was performed using different diameters of specimens such as 50 mm and 100 mm. Tack coat materials such as RSC-4 and BD-Coat were applied in amounts of 0.3, 0.5, 0.7, 0.9, and $1.1l/m^2$ to determine the optimal application rate. In order to evaluate the bond strength characteristics with temperature changes, a pull-off test was carried out at -15, 0, 20, and $40^{\circ}C$. In addition, the bond failure shapes were analyzed using an image analysis program after the pull-off tests were completed. RESULTS : The test results indicated that the optimal application rate of RSC-4 and BD-Coat were $0.8l/m^2$, $0.9l/m^2$, respectively. The core size effect was determined to be negligible because the bond strengths were similar in specimens with diameters of 50 mm and 100 mm. The bond strengths of RSC-4 and BD-Coat were found to decrease significantly when the temperature increased. As a result of the bonding failure shape in low-temperature conditions such as -15, 0, and $20^{\circ}C$, it was found that most of the debonding occurred at the interface between the tack coat and RCC surface. On the other hand, the interface between the HMA and tack coat was weaker than that between the tack coat and RCC at a high temperature of $40^{\circ}C$. CONCLUSIONS : This study suggested an optimal application rate of tack coat materials to apply to RCC-base composite pavement. The bond strengths at high temperatures were significantly lower than the required bond (tensile) strength of 0.4 MPa. It was known that the temperature was a critical factor affecting the bond strength at the interface of the RCC-base composite pavement.

• 콘크리트학회논문집
• /
• 제19권3호
• /
• pp.333-339
• /
• 2007

본 논문은 재생 PET 섬유와 시멘트 복합재료와의 부착 성능을 향상시키고자 친수성 물질인 무수말레인산이 그라프트된 폴리프로필렌을 이용하여 친수성 처리 효과를 평가하였다. 실험 변수는 무수말레인산이 그라프트된 폴리프로필렌의 농도 0%, 5%, 10%, 15% 및 20%를 고려하였다. 부착 실험은 ICI SF-8에 따라 dog bone 공시체를 이용하였으며 부착강도 및 인발 에너지를 평가하였다. 실험 결과 부착 거동, 부착강도 및 계면 인성은 무수말레인산의 농도가 증가할수록 증가하는 효과를 보여주었다. 특히 15%에서 가장 큰 효과를 발휘하였으며 농도가 20%가 되면 오히려 부착성능이 감소하였다. 이는 재생 PET 섬유의 표면은 무수말레인산이 그라프트된 폴리프로필렌의 농도가 15% 이상이 되면 전체적으로 완벽하게 코팅이 가능하나 20% 코팅시에는 코팅 부분에서 부분적으로 균열이 발생하여 이를 통하여 부착하중 작용시 균열 부분을 통한 파괴가 발생하기 때문이다. 섬유 표면의 미소 구조 관찰에서 무수말레인산의 농도에 따른 재생 PET 섬유와 시멘트 복합재료와의 부착력 향상 메커니즘을 확인할 수 있다.