Goangseup Zi | Korea University (original) (raw)

Papers by Goangseup Zi

Cement & Concrete Composites, 2021

This study aims to investigate the grindability and performance of glass-blended cements dependin... more This study aims to investigate the grindability and performance of glass-blended cements depending on the grinding method and glass type. Two grinding methods, intergrinding and separate grinding, and two types of waste glass, liquid crystal display glass (LCDG) and soda-lime glass (SLG), were considered. To study grindability, the milling characteristics of the coarse waste glass and fine glass-blended mixtures were investigated. The four types of glass-blended cements produced by the two grinding methods and the two types of waste glass were evaluated on particle size distribution, chemical composition, heat flow of hydration, hydration behavior, strength development and mitigation in alkali–silica reaction (ASR) expansion. It was found that the intergrinding method was more cost-efficient in producing glass-blended cements than the separate grinding method. Intergrinding of the glass-blended mixtures resulted in finer cement and coarser glass fractions. The interground glass-blen...

$Research paper thumbnail of Stress distribution and fracture pattern analysis of spherical LNG storage tank dome caused by thermal load$

Applied Sciences

A chemo-damage model is proposed to predict the expansion caused by the alkali silica reaction (A... more A chemo-damage model is proposed to predict the expansion caused by the alkali silica reaction (ASR). The model covers the formation of the pre-expansion gel driven by alkali and the swelling of the gel driven by water. The swelling capacity of the ASR gel is quantified by the sodium to calcium ratio in the pore solution. The bound alkali in the gel recycled by calcium is also considered in this model. Both external alkali supply and internal alkali released from aggregates are included. Several sets of experimental data are compared with the simulation results for the verification of the model.

International Journal of Concrete Structures and Materials

Fracture of prestressed concrete beams is studied with a novel and robust three-dimensional meshf... more Fracture of prestressed concrete beams is studied with a novel and robust three-dimensional meshfree method. The meshfree method describes the crack as a set of cohesive crack segments and avoids the representation of the crack surface. It is ideally suited for a large number of cracks. The crack is modeled by splitting particles into two particles on opposite sides of the crack segment and the shape functions of neighboring particles are modified in a way the discontinuous displacement field is captured appropriately. A simple, robust and efficient way to determine, on which side adjacent particles of the corresponding crack segment lies, is proposed. We will show that the method does not show any "mesh" orientation bias and captures complicated failure patterns of experimental data well.

Journal of the Korean Society for Railway

This study looked into the behavior of precast concrete track due to temperature variation and in... more This study looked into the behavior of precast concrete track due to temperature variation and initial track deformation and examined the effect of initial deformation and deformation caused by temperature gradient on the stress distribution of slab under train load. In this paper, one of two papers in a series, a finite element analysis model for calculating deformation and stress of precast concrete track was proposed; the temperature distribution and displacements measured at the precast concrete track in the field were compared with the analytical results. The results show that the slab always curled up due to initial deformation; by comparing the measured displacements with the displacements calculated by taking measured temperatures at each depth as input, the effective built-in temperature (EBITD), the temperature difference between the top and bottom of the slab corresponding to the initial deformation, can be estimated. If EBITD is relevantly assumed, the calculated displacements correlate well with the measured ones.

Chemical Engineering Journal

Abstract We report on the fabrication of a fractal-designed transparent and stretchable (TS) micr... more Abstract We report on the fabrication of a fractal-designed transparent and stretchable (TS) microsupercapacitor (MSC) as a skin-attachable energy storage device for driving an integrated strain sensor (SS). The MSC is designed to have a fractal structure with long and narrow patterns to ensure high transparency and stretchability. MnO2/Carbon nanotubes (CNTs) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(methyl methacrylate) ([BMIM][TFSI]/PMMA) are used as electrodes and a stretchable electrolyte for the MSC, respectively. The fabricated MSC exhibits high transparency of 79% and an areal capacitance of 12.6 mF cm−2 at a current density of 5 mA cm−2. The TS MSC shows excellent mechanical stability in that it can maintain stable electrochemical performance even after 2000 repeated stretching cycles up to 30%. The TS SS is facilely prepared via spray coating of Ag nanowires (NWs) and subsequent curing of PDMS, where the transparency and the electrical resistance are controlled by adjusting the deposited volume of Ag NWs. Wrist bending and a wrist pulse are detected by the SS driven with the stored energy of the MSC. This work demonstrates the possible application of our TS MSC to future skin-attachable electronics as an integrated energy storage device.

Polymers and Polymer Composites

Beam tests were conducted to investigate the characteristics of a newly developed type of glass f... more Beam tests were conducted to investigate the characteristics of a newly developed type of glass fibre-reinforced polymer (GFRP) rebar as reinforcement in flexural concrete members. Nine beams over-reinforced with different types of rebar, and with varying reinforcement ratios and depths of concrete cover, were monotonically loaded up to failure. Results were characterised by failure mode, moment–curvature, flexural capacity, load–deflection, and crack width. The test results were compared with the theoretical model and the American Concrete Institute design guide, which showed that the performance of the newly- developed GFRP rebar was comparable to commercially available GFRP rebars. In addition, a theoretical model for moment–curvature and an equation for predicting the flexural capacity of the beams with multiple layers of GFRP rebar are presented, based on the experimental observations.

Magazine of Concrete Research

Sensors (Basel, Switzerland), Jan 29, 2017

This study examined the electrical and self-sensing capacities of ultra-high-performance fiber-re... more This study examined the electrical and self-sensing capacities of ultra-high-performance fiber-reinforced concrete (UHPFRC) with and without carbon nanotubes (CNTs). For this, the effects of steel fiber content, orientation, and pore water content on the electrical and piezoresistive properties of UHPFRC without CNTs were first evaluated. Then, the effect of CNT content on the self-sensing capacities of UHPFRC under compression and flexure was investigated. Test results indicated that higher steel fiber content, better fiber orientation, and higher amount of pore water led to higher electrical conductivity of UHPFRC. The effects of fiber orientation and drying condition on the electrical conductivity became minor as sufficiently high amount of steel fibers, 3% by volume, was added. Including only steel fibers did not impart UHPFRC with piezoresistive properties. Addition of CNTs substantially improved the electrical conductivity of UHPFRC. Under compression, UHPFRC with a CNT conten...

Structural Engineering and Mechanics

The loss of strength in a structure as a result of cyclic loads over a period of life time is an ... more The loss of strength in a structure as a result of cyclic loads over a period of life time is an important phenomenon for the life-cycle analysis. Service loads are accentuated at the areas of stress concentration, mainly at the connection of components. Structural components unavoidably are affected by defects such as surface scratches, surface roughness and weld defects of random sizes, which usually occur during the manufacturing and handling process. These defects are shown to have an important effect on the fatigue life of the structural components by promoting crack initiation sites. The value of equivalent initial flaw size (EIFS) is calculated by using the back extrapolation technique and the Paris law of fatigue crack growth from results of fatigue tests. We try to analyze the effect of EIFS distribution in a multiple site damage (MSD) specimen by using the extended finite element method (XFEM). For the analysis, fatigue tests were conducted on the centrally-cracked specimens and MSD specimens.

International Journal of Damage Mechanics

Fatigue life in critical parts of structure components, which is subjected to variable amplitude ... more Fatigue life in critical parts of structure components, which is subjected to variable amplitude loading, is a very complex subject. When a fatigue life is influenced by these load variations, accelerations and/or retardations in crack growth rate can occur. Thus, an accurate prediction of fatigue life requires an adequate evaluation of these stress interaction effects. There are many different indexes for calculating fatigue damage at critical locations. The crack severity index based on crack growth is one of the methodologies implemented for modern military aircrafts to define mission severity relative to a known reference usage. But, this index cannot consider stress interaction. In this study, a novel index was proposed to evaluate an effect for stress interaction by using entropy concept, and fatigue life prediction methodology was developed by using entropy index of stress interaction and crack severity index of effective stress.

Cement and Concrete Composites

ABSTRACT

ACS applied materials & interfaces, Jan 29, 2017

Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable... more Networks of silver nanowires (Ag NWs) have been considered as promising materials for stretchable and transparent conductors. Despite various improvements of their optoelectronic and electromechanical properties over the past few years, Ag NW networks with a sufficient stretchability in multiple directions that is essential for the accommodation of the multidirectional strains of human movement have seldom been reported. For this paper, biaxially stretchable, transparent conductors were developed based on 2D mass-spring networks of wavy Ag NWs. Inspired by the traditional papermaking process, the 2D wavy networks were produced by floating Ag NW networks on the surface of water and subsequently applying biaxial compression to them. It was demonstrated that this floating-compression process can reduce the friction between the Ag NW-water interfaces, providing a uniform and isotropic in-plane waviness for the networks without buckling or cracking. The resulting Ag NW networks that were...

Construction and Building Materials, 2016

ACS applied materials & interfaces, Jan 14, 2016

We report the fabrication of an encapsulated, high-performance, stretchable array of stacked plan... more We report the fabrication of an encapsulated, high-performance, stretchable array of stacked planar micro-supercapacitors (MSCs) as a wearable energy storage device for waterproof applications. A pair of planar all-solid-state MSCs with spray-coated multiwalled carbon nanotube electrodes and a drop-cast UV-patternable ion-gel electrolyte was fabricated on a polyethylene terephthalate film using serial connection to increase the operation voltage of the MSC. Additionally, multiple MSCs could be vertically stacked with parallel connections to increase both the total capacitance and the areal capacitance owing to the use of a solid-state patterned electrolyte. The overall device of five parallel-connected stacked MSCs, a microlight-emitting diode (μ-LED), and a switch was encapsulated in thin Ecoflex film so that the capacitance remained at 82% of its initial value even after 4 d in water; the μ-LED was lit without noticeable decrease in brightness under deformation including bending a...

Advanced materials (Deerfield Beach, Fla.), Jan 7, 2015

A stretchable multisensor system is successfully demonstrated with an integrated energy storage d... more A stretchable multisensor system is successfully demonstrated with an integrated energy storage device, an array of microsupercapacitors that can be repeatedly charged via a wireless radio frequency power receiver on the same stretchable polymer substrate. The integrated devices are interconnected by a liquid metal interconnection and operate stably without noticeable performance degradation under strain due to the skin attachment, and a uniaxial strain up to 50%.

Advanced materials (Deerfield Beach, Fla.), Jan 2, 2015

A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of ... more A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of single-walled carbon nanotube thin film transistors is demonstrated. The integrated temperature sensor array gives mechanical stability under biaxial stretching of 30%, and the resultant spatial temperature mapping does not show any mechanical or electrical degradation.

한국구조물진단학회 학술발표회 논문집, Oct 31, 2009