• Restorative Dentistry and Endodontics
• /
• v.25 no.1
• /
• pp.109-115
• /
• 2000

This study was designed to evaluate the microhardness of restorative composite resin and dual-cured composite resin cement which were light cured through the 1.5mm thickness composite overlay. For restorative materials, Z100 and Tetric Ceram were used. For dual cured composite cements, Variolink II((VL II) of three consistency (low, high, ultra high) were used. To determine the optimal microhardness of Z100, Tetric Ceram and Variolink II, each material was packed into the 1mm thickness teflon mold without composite overlay and light cured for 60 seconds. Then the microhardnesses of each sample were measured, averaged and regarded as optimal hardness of each material. To evaluate the microhardness of restorative composite resin and dual-cured composite resin cement which were light cured through the 1.5mm thickness composite overlay, the composites were packed into 1mm thickness teflon mold, coverd with celluloid strip, and then precured composite overlay which was made of Targis(Ivoclar/Vivadent, Liechtenstein) was positioned. 2 types of visible light curing machine, the power density of one of which was 400$mW/cm^2$ and the other was 900$mW/cm^2$, and one type of argon laser were used to cure the restorative composite and dual cured cement. For each group, 10 sample were assigned. The light curing tip was positioned over the composite overlay and light cured for 1min., 2min. or 3min with visible light curing machine or 15sec, 30 sec, 45sec, and 60 sec with argon laser. The Vickers hardnesses of upper and lower surface of Z100, Tetric Ceram, and 3 types of VL II cement were measured. When the 900 $mW/cm^2$ curing light was used, 2min. was needed for optimal curing of Z100 and Tetric Ceram. Variolink II did not be cured optimally even though the curing time was extended to 3min. When 400$mW/cm^2$ curing light was used, 3min. was necessary for Z100, whereas 3min. was not enough for Tetric Ceram. Variolink II was not cured optimally even though the curing time was extended to 3min. When argon laser was used, Z100, Tetric Ceram and Variolink II were not cured optimally in 60 seconds.

• International Journal of Highway Engineering
• /
• v.9 no.2 s.32
• /
• pp.63-76
• /
• 2007

The transformed field domain analysis method was developed in this study to investigate the aspects of the stress distribution in overlaid concrete pavement systems under multi-axle vehicle loads. The overlay was assumed to be perfectly bonded or perfectly unbonded to the existing concrete pavement. The loads considered included the dual tired single-axle, tandem-axle, and tridem-axle loads, and the effects of the overlay's thickness, elastic modulus, and Poisson's ratio on the stress distribution were investigated. Details of the analysis method in the transformed field domain to analyze the overlaid pavement was described in this paper and the analysis results were verified by comparing with those obtained using the finite element method. From the analysis, it was found that the maximum tensile stress in the existing slab decreased as the overlay's thickness, elastic modulus, and Poisson's ratio increased, and the bonded overlay showed more significant effects than the unbonded one. The overlay's Poisson's ratio did not much affect the stresses, and the features of the maximum stress reduction in the existing slab due to the increase of the thickness, elastic modulus, and Poisson's ratio of the overlay were investigated. The effects of the number of axles on the stress distribution and the maximum stress were also investigated.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.475-480
• /
• 2003

Latex modification of concrete provides the material with higher flexural strength. This increase in flexural strength can attribute to the crack-arresting action of polymer in concrete, and also to the bonding they provide between the matrix and aggregates. This experimental study presents the fracture behavior of 12 flexural reinforced concrete beams repaired or strengthened by latex-modified concrete with the main experimental variables such as overlay thickness, strength thickness, and shear reinforcement. The results are as follow: All beam specimens having shear reinforcement were failed by delamination rupture at concrete interface at about 80% of ultimate loading after flexural cracking. All specimens overlayed and strengthened by latex-modified concrete (LMC) showed higher ultimate flexural strength than OPC control specimen, but lower than LMC control specimen. This increase in flexural strength could attribute to the high bonding they provide between the matrix and aggregates. All specimens except two shear unreinforced showed quite similar and consistent displacement behavior. The effect of overlay and strength thickness on the load-displacement relationship were a small at this study.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.9 no.1
• /
• pp.70-76
• /
• 2013

Several finite element models for the leak-before-break (LBB) assessment of overlay dissimilar metal weldment were constructed and analyzed to develop a simple finite element modeling method. The J-integral, crack opening displacement (COD) and J-integral distribution along the crack front in thickness direction due to the applied moment were obtained from the analysis results of the constructed finite element models, and studied compared to the previous literatures. It is concluded that the modeling with base material only is simple and produces a slightly conservative results compared to the complex modeling composed with weld metal and base metal in the calculation of J-integrals and COD values which are used for the calculation of fracture toughness and postulated leakage crack length respectively.

• Structural Engineering and Mechanics
• /
• v.65 no.5
• /
• pp.535-546
• /
• 2018

The objective of this study is to understand the behaviour of hollow core slabs strengthened with FRP and hybrid techniques through numerical and analytical studies. Different strengthening techniques considered in this study are (i) External Bonding (EB) of Carbon Fiber Reinforced Polymer (CFRP) laminates, (ii) Near Surface Mounting (NSM) of CFRP laminates, (iii) Bonded Overlay (BO) using concrete layer, and (iv) hybrid strengthening which is a combination of bonded overlay and NSM or EB. In the numerical studies, three-dimensional Finite Element (FE) models of hollow core slabs were developed considering material and geometrical nonlinearities, and a phased nonlinear analysis was carried out. The analytical calculations were carried out using Response-2000 program which is based on Modified Compression Field Theory (MCFT). Both the numerical and analytical models predicted the behaviour in agreement with experimental results. Parametric studies indicated that increase in the bonded overlay thickness increases the peak load capacity without reducing the displacement ductility. The increase in FRP strengthening ratio increased the capacity but reduced the displacement ductility. The hybrid strengthening technique was found to increase the capacity of the hollow core slabs by more than 100% without compromise in ductility when compared to their individual strengthening schemes.

• International Journal of Highway Engineering
• /
• v.16 no.2
• /
• pp.91-98
• /
• 2014

PURPOSES : The objective of this study is to investigate the effect of asphalt and geotextile interlayer on the fracture behavior of unbonded concrete overlay through a laboratory composite beam test. METHODS : In order to evaluate the effect of interlayer materials on the fracture behavior of unbonded concrete overlay, a laboratory test of composite beam was conducted with different types of interlayer. The test results of the composite beam using two types of geotextile interlayer with different thicknesses were compared to the test results of the composite beam using the tradition type of asphalt interlayer. The unbonded concrete overlay on the existing concrete pavement without interlayer was set for the control condition. RESULTS AND CONCLUSION : Overall, the laboratory composite beam test results did show the effect of asphalt and geotextile interlayer on the fracture behavior of composite concrete beams. The three-layer geotextile interlayer and HMA layer both increase the peak load when the first macrocrack occurs in the top concrete beam, while the HMA interlayer causes the smallest load drop percentage after the first macrocrack. The three-layer geotextile did show better performance than the single-layer geotextile through the greater peak load and smaller load drop percentage. It indicates that the thickness of geotextile interlayer will affect the fracture behavior of unbonded concrete overlay and the thicker geotextile interlayer is recommended.

• Magazine of the Korea Concrete Institute
• /
• v.10 no.4
• /
• pp.145-151
• /
• 1998

The vertical tensile stress, ${\sigma}_y$, in the contact zone between the overlay (mortar layer) and substratum (base concrete) can be the main cause of the failure phenomenon of overlaid concrete structures. The development of tensile stress, ${\sigma}_y$, due to external rainy condition was analytically investigated using finite element method. Rainfall intensity $(n_R\;=\;1/a,\;t_R\;=\;10min,\;60min)$, thickness of overlay (do=1,2,4,10 cm) and overlay material (CM,ECM,EM) were the main variables in the analyses. An equation was suggested with which the development of vertical tensile stress, ${\sigma}_y$, in the rainy condition could be determined. Using this equation, it is possible to select proper material properties and overlay thicknesses to prevent failure in the contact zone due to thermally transient condition caused by rainfall.

• Journal of the Korea Concrete Institute
• /
• v.14 no.5
• /
• pp.766-773
• /
• 2002

The failure phenomenon of overlaid concrete structures, such as surface crack, and peel-off failure, shear bond failure in the end contact zone, was investigated due to humidity changes. To investigate this failure phenomenon, the surface tensile stress, and the shear stress, the vertical tensile stress in the contact zone were analysed using the non-linear stress-strain relationship of material such as strain-hardening- and strain-softening diagrams. Overlay thickness and overlay material were the main variables in the analyses. It is assumed that the initial surface humidity of overlaid concrete structures was 100％ r.H. With a atmospheric humidity of 55％ r.H. and two load cases for drying(LCI), curing and drying(LC2), the stress states of overlaid concrete structures were calculated. The result shows that only fictitious cracks occurred in the overlay surface of CM2O, ECM25, and no shear bond failure occurred in the contact zone without CM2O. The peel-off failure was proved to be the main cause of the damage in the overlaid concrete structures. Only for overlay thickness of 1cm occurred no peel-off failure in the case of drying after a long-term public use(LC1). In the case of curing and drying during overlay work(LC2) occurred the peel-off failure within 1.5days for all the overlaid concrete structures.

• Korean Journal of Optics and Photonics
• /
• v.13 no.6
• /
• pp.461-466
• /
• 2002

Fiber-optic comb filters using a side-polished fiber coupler are proposed as multi-channel isolation filters on wavelength division multiplexing systems. We have demonstrated that the coupling efficiency between two waveguides is improved by the intermediate coupling layer in spite of the decrease of the optical power transfer between two waveguides due to the high-order modes of the overlay waveguide coupled with the side-polished single-mode fiber. When LiNbO$_3$with a 200-${\mu}{\textrm}{m}$-thickness was applied as a planar-overlay-waveguide, the comb filtering characteristics with a 4 nm-channel-spacing were achieved and the maximum power coupling occurred at the 1-${\mu}{\textrm}{m}$-thickness and the refractive index in range 1.52 to 1.53 of an intermediate coupling layer. If the intermediate coupling layer is optimized, an extinction ratio with more than 20 dB can be obtained. These experimental results are in good agreement with the BPM simulation.

• International Journal of Highway Engineering
• /
• v.11 no.2
• /
• pp.121-132
• /
• 2009

Thin bonded continuously reinforced concrete overlay(CRCO) was constructed on He existing jointed plain concrete pavement(HCP) surface at Seo-Hae-Ahn express highway in South Korea in order to evaluate its applicability and performance. Two sections of road were considered for this evaluation. In the first section, the concrete overlayer was placed and cut down to the existing layer to form transverse joints while CRCO was constructed on top of the existing layer in the second section. Early strength concrete(Type III) was utilized for both overlay sections. The depth of milling and the thickness of overlaid layer were 5 cm and 10 cm, respectively. Several vibrating wire gauges(VWG) were installed to evaluate the performance of CRCO with respect to curling, delamination, and crack propagation. As a result of the strength test, it was found that strength of the material reaches the design criteria within 1-3 days. Analysis with vibrating wire gauge(VWG) showed CRCO effectively restricts joint movement. High adhesive strength also was observed from the material regardless of length of aging. Meanwhile, transverse cracks were observed on the middle of the section where JPCP overlay was applied whereas arbitrarily cracks in transverse direction were observed on the section where CRCP was applied.