Chongku Yi - Academia.edu (original) (raw)
Papers by Chongku Yi
A Study on the Characteristics of High Strength Grout for Pile Connections Exposed to Sea Environments
Journal of the Korea Concrete Institute
미세 강섬유의 구속력이 모르타르의 알칼리-실리카 반응에 미치는 영향
한국콘크리트학회, Oct 1, 2007
Additional file 1 of Agricultural by-products and oyster shell as alternative nutrient sources for microbial sealing of early age cracks in mortar
Additional file 1: Table S1. Selected three factors and their levels for central composite design... more Additional file 1: Table S1. Selected three factors and their levels for central composite design. Table S2. Experimental design in the optimization to form an economical medium. Table S3. Equations of the linear trend lines of changes in crack width over sealing periods in four mortar specimens. Figure S1. Phenotypic and gene-expression comparison of strain AK13 in pH 7 and 10 LB media. (a) Growth curves of the strain AK13 in each of the above two conditions. Arrows indicate when total RNAs were extracted. (b) Organization by COG category of the genes whose expressions were up-regulated under neutral or alkaline conditions. Figure S2. The adaptation mechanisms of alkaliphilic Bacillus spp. to the alkaline environment including the function of riboflavin in the respiratory chain. Figure S3. Comparison of growth and spore formation when NaCl or riboflavin was added to sesame meal-medium. (a) Comparison of growth when each of two growth promoting factors were added to sesame meal-medi...
콘크리트는 낮은 단위가격에 상대적으로 높은 강도와 내구성을 지녀 건설 분야에서 가장 많이 사용되는 재료이다(Mehta and Monteiro 2006). 하지만 하중과 재료 ... more 콘크리트는 낮은 단위가격에 상대적으로 높은 강도와 내구성을 지녀 건설 분야에서 가장 많이 사용되는 재료이다(Mehta and Monteiro 2006). 하지만 하중과 재료 수축, 열화인자 유입 등으로 인해 콘크리트 내외부에 미세 균열이 지속적으로 발생하고, 미세 균열은 전체 콘크리트 구조물의 수명을 단축시킨다(Peris Mora 2007). 이에 대한 해결책으로 외부 인력의 투입 없이 스스로 미세 균열을 충진하여 열화 인자의 투입을 막아 콘크리트의 내구성을 증진시키는 자기치유 콘크리트(Self-healing concrete)가 지속적 으로 연구되었다(Van Tittelboom and De Belie 2013). 박테리아를 활용한 균열 자기치유 콘크리트는 다른 자기치유 메커니즘과 비교하여 다음과 같은 분명한 이점을 보인다. 첫째, 비활성 상태의 박테리아는 이론상 콘크리트 내부에서 반영구적으 로 생존하므로(Jonkers and Schlangen 2008) 철근 콘크리트 구 조물의 일반적인 내구연한(∼50년) 동안 자기치유 효과를 기대할 수 있다. 둘째, 박테리아는 균열로부터 유입된 수분 및 산소 등의 물질에 의해 활성화되므로 콘크리트 내부에서 치유재의 소모가 없다. 셋째, 균열이 충진된 뒤 박테리아는 스스로 비활성 상태로 전환되고, 이후 동일한 부위에 균열이 발생했을 때 재활성화되어 균열을 치유한다. 하지만 박테리아를 활용한 자기치유 콘크리트 개발 시 다음과 같은 문제점이 알려져 있다. 첫째, 다른 메커니즘에 비해 상대적으 로 균열 치유에 오랜 시간이 걸린다. 박테리아의 생장은 시간에 따른 시그모이드 곡선 형태로 나타나며, 박테리아 밀도가 적은 초 기 유도기(Lag phase)에는 박테리아 활동성이 낮다. 따라서 박테 박테리아 펠렛을 자기치유 소재로 사용한 모르타르의 강도 및 치유성능 Strength and Healing Performance of the Mortar using Bacterial Pellet as a Self-Healing Material
Materials, 2021
In this study, a new type of bacterial carrier using methylcellulose was presented, and its appli... more In this study, a new type of bacterial carrier using methylcellulose was presented, and its applicability to self-healing concrete has been explored. Methylcellulose, the main component of a 2 mm pellet-shaped carrier, can remain stable in alkaline environments and expand in neutral or acidic environments. These properties allow bacteria to survive in the high-alkaline and high-pressure environments of early age concrete, and the number of bacteria increases rapidly in the event of cracks, accelerating crack closure. The results show that the survival rate of bacterial spores inside the mortar was increased, and the pellet provides an enhanced biological anchor suitable for bacterial activity, bacterial growth, and mineral precipitation. Further, the results indicate an improved self-healing efficiency compared with mixing bacteria directly into the cement composite.
Construction and Building Materials, 2020
h i g h l i g h t s Effect of SWW on the dimensional stability of epoxy resin mortar was evaluate... more h i g h l i g h t s Effect of SWW on the dimensional stability of epoxy resin mortar was evaluated. Effect of curing methods (conventional and microwave) on the dimensional stability was assessed. Dimensional stability was assessed in terms of shrinkage and coefficient of thermal expansion.
Journal of the Korea Concrete Institute, 2008
Shrinkage Properties and Potential for Cracking of High-strength Concrete containing High-volume Blast Furnace Slag
Journal of the Architectural Institute of Korea Structure & Construction, 2015
Construction and Building Materials, 2017
h i g h l i g h t s Review on the fiber reinforcement in cement composites. Effect of embedment l... more h i g h l i g h t s Review on the fiber reinforcement in cement composites. Effect of embedment length on bond behavior is experimentally investigated. Optimum fiber geometry of the amorphous steel fiber.
Effect of fiber geometry on the electromagnetic shielding performance of mortar
Computers and Concrete, 2016
The increased awareness of electromagnetic wave hazards has prompted studies on electromagnetic s... more The increased awareness of electromagnetic wave hazards has prompted studies on electromagnetic shielding using conductive materials in the construction industry. Previous studies have explored the effects of the types of conductive materials and their mix proportions on the electromagnetic shielding performance; however, there has been insufficient research on the effect of the geometry of the conductive materials on the electromagnetic shielding performance. Therefore, in this study, the dependence of the electromagnetic shielding performance on the cross-sectional geometry, diameter and length of fibers was investigated. The results showed that the electromagnetic shielding performance improved when the fiber length increased or the diameter decreased, but the effect of the cross-sectional geometry of the fibers was smaller than the effect of the fiber spacing factor.
Mechanics of Composite Materials, 2009
re in forced poly mer bars, bond strength, con crete strength, bond fail ure sur face In this stu... more re in forced poly mer bars, bond strength, con crete strength, bond fail ure sur face In this study, the ef fects of re peated loads on the FRP-con crete bond strength were in ves ti gated ex per i men tally by di rect pull out tests ac cord ing to CSA S806-02. A con ven tional re in forc ing steel bar and two types of glass-fi ber-re in forced plas tic (GFRP) bars were em bed ded in con crete and tested un der four dif fer ent load ing pat terns. The bond strength-slip curves of the bars were ob tained and an a lyzed. The re sults showed that the max i mum bond strengths un der the re peated loads dif fered from those ob tained un der monotonic ones. In addi tion, no tice able dif fer ences in deg ra da tion of the bond strength with re spect to the mag ni tude of slip were observed be tween the dif fer ent bar types tested. On the ba sis of an im age anal y sis of fail ure sur faces, they were at trib uted to the dif fer ent bond fail ure mech a nisms as so ci ated with the steel and GFRP bars. In tro duc tion FRP (fi ber-re in forced plas tic) ma te ri als, which were first adopted by aero space in dus try to re place the costly met als and al loys, are now found in a va ri ety of civil en gi neer ing ap pli ca tions, such as bridge decks, ret ro fit of ex ist ing struc tures, and new struc tures in highly cor ro sive en vi ron ments, be cause of their high strength-to-weight ra tio and high re sis tance to static loads and chem i cals [1, 2]. In par tic u lar, the use of FRP bars/sheets has drawn much at ten tion as an al ter na tive ma te rial to the steel re in force ment in con crete. In the past de cades, many stud ies have been car ried out to in ves ti gate the use of FRP bars in con crete beams sub jected to flex ure and shear loads and to de ter mine their de for ma tion char ac ter is tics, and de sign guides for FRP bars in con crete have been proposed in the United States, Canada, and Europe [3-5]. How ever, there are top ics which need fur ther in ves ti ga tions to fully uti lize FRPs as a re li able re in force ment in concrete. The bond strength be tween a FRP and con crete, for ex am ple, is not yet as clearly un der stood as that for the con ven tional steel re in force ment. Fur ther more, the ex ist ing lit er a ture shows dis so nant re sults. Achilides et al. [6], Okelo et al. [7], and Lee et al. [8] stud ied the ef fect of con crete strength ¢ f c on the FRP-con crete bond strength t n. Achilides et al. found that t n in creased with ¢ f c up to ~50 MPa, be yond which the ef fect be came in sig nif i cant [6], while Okelo et al. stated that t n in creased in pro portion to ¢ f c , as ob served in the case of steel re in force ment [7]. Re cently, Lee et al. showed the FRP bond strength in creased pro-609 0191-5665/09/4506-0609 © 2009 Springer Sci ence+Busi ness Me dia, Inc. *De part ment of Ar chi tec tural En gi neer ing, Sungkyunkwan Uni ver sity, 300, Cheongcheong-dong, Jangan-gu, Suwon, 440-746, Re pub lic of Ko rea. **School of Civil, Ar chi tec tural, and En vi ron men tal En gi neer ing, Ko rea Uni ver sity, Anam-dong, Seongbuk-gu, Se oul, 136-701, Re pub lic of Ko rea. The cor re spond ing au thor is C.
전도성 재료 혼입 모르타르의 UHF파 차폐효과
대한건축학회논문집 구조계, 2015
Materials and Structures, 2006
Performance enhancement due to microfibers is well known. However, fracture processes that lead t... more Performance enhancement due to microfibers is well known. However, fracture processes that lead to strain hardening behavior in microfiber reinforced composites are not well understood. Crack growth resistance behavior of mortar reinforced with steel microfibers and polypropylene microfibers was investigated insitu during load application. The polypropylene fibers were inter-ground in the cement mill to enhance the fiber/matrix interfacial frictional stress. A more homogeneous fiber distribution was observed in the inter-ground polypropylene composites compared to the steel microfiber reinforced composites. In steel microfiber reinforced composites the dominant toughening mechanisms were multiple microcracking and successive debonding along the fiber/matrix interface. Fiber pullout, the dominant mechanism in conventional macrofiber reinforced composites was rarely observed. In-situ observation of crack/ fiber interaction in the inter-ground polymer fibers also revealed multiple microcracking along the length of the fibers followed by fiber pullout.
Magazine of Concrete Research, 2010
In concrete beam design, the shear capacity of the concrete beam is of great interest because she... more In concrete beam design, the shear capacity of the concrete beam is of great interest because shear failure is associated with an abrupt failure mode that undermines the flexural performance of the beam. Recently, because of the increasing cost of natural resources and environmental concerns, the use of recycled aggregate (RA) in construction is becoming the standard practice. However, the effects of recycled aggregates on the shear strength of concrete have not been fully examined. In this study the effects of RA on concrete shear strength are studied experimentally by performing flexural tests on 20 RA concrete beams with various combinations of span-to-depth ratios (a/d = 1·50, 2·50, 3·25), longitudinal reinforcement ratios (s = 0·53%, 0·83%, 1·61%) and RA replacement ratios (0%, 30%, 50%, 100%). The test results indicate that the concrete shear strength diminishes by up to 30% at 100% replacement ratio compared with the natural aggregate concrete. The shear strengths of the RA c...
International Journal of Steel Structures, 2012
Helically wrapped wire cables were first introduced to overcome the difficulties in transporting ... more Helically wrapped wire cables were first introduced to overcome the difficulties in transporting and installing straight wires. Presently, helically wrapped wire cables are used as the important load-carrying elements in many structures such as suspension bridges, cable-stayed bridges, tall guyed towers, power transmission lines, and flexible electrical conductors. In design and analysis, cables are traditionally assumed to carry axial load only; thus, studies on the bending behavior of the cables have been limited. Although the small curvature assumption of the cable may be valid for most part, the possible development of a large curvature at the bearings and anchorage cannot be ignored nor avoided. In this study, an analytical model was developed for the helically wrapped wires in a cable subjected to tension and small bending, with full consideration of the helically wrapped wire geometry. Using the developed model, an approximate upper limit of the cable curvature-for which the conventional Bernoulli-Euler-Navier kinematic beam assumption can be adapted to evaluate the stress in the wires-was obtained.
Cement and Concrete Composites, 2001
Interground ®ber cement (IFC) is a new process where ®bers are ground in with the cement clinker ... more Interground ®ber cement (IFC) is a new process where ®bers are ground in with the cement clinker during the dry cement manufacturing process. With IFC considerable strength enhancement can be achieved compared to ordinary cement even at a ®ber volume as low as 0.2% due to homogeneous ®ber distribution and ®ber surface modi®cations associated with the milling process. The cracking mechanisms associated with the strength enhancement were observed in real time during load application using a custom designed loading device. The homogeneous ®ber distribution stabilizes crack growth. Formation of multiple, stable secondary microcracks was observed during the strain hardening regime, enhancing the strain capacity at ultimate strength. Fiber pullout was the dominant toughening mechanism in the strain softening regime. For ®bers inclined to the propagating crack, ®ber pullout was preceded by secondary microcrack formations along the ®ber/matrix interface.
Applied Sciences, 2020
Rebar embedded inside reinforced concrete structures becomes corroded due to various factors. How... more Rebar embedded inside reinforced concrete structures becomes corroded due to various factors. However, few studies have focused on the corrosion of pre-rusted rebar embedded in cement composites, and the findings reported thus far are inconsistent. Therefore, in this study, an experimental program was undertaken to examine the effect of pre-rusting on the further corrosion of reinforcements in cement composites. Pre-rust was induced using two different solutions (CaCl2 and HCl). The corrosion rate in the cement composite was analyzed using the half-cell potential and polarization resistance methods. In addition, scanning electron microscopy with energy-dispersive X-ray analysis and X-ray diffraction analysis were used to examine the morphology of the rust. The results show that the corrosion rate of the rebar embedded in the cement composite can be increased by more than 3.8 times depending on the pre-rust conditions (RE: 0.0009 mm/year, HCl: 0.0035 mm/year). In addition, we found t...
Development of a novel compressed tablet-based bacterial agent for self-healing cementitious material
Cement and Concrete Composites, 2022
Preliminary Study for the Development of Alkali Activated Natural Hwangtoh Binder
Materials, 2021
Understanding the bond behavior of steel rebar in concrete is important in order to determine the... more Understanding the bond behavior of steel rebar in concrete is important in order to determine the performance of a reinforced concrete structure. Although numerous studies have been carried out by many researchers to develop a robust model for numerical analysis, no consensus has been reached as the bond behavior depends on hysteresis. In this study, the bond behavior of a steel bar in concrete with pre-existing damage is investigated under low-level cyclic loading. Based on the experimental bond stress and slip curve, a numerical model for finite element analysis to simulate the effect of low-level cyclic loading is proposed. The results from the numerical analysis show good agreement with the experimental data, including accumulated damage on stiffness and strength throughout entire load cycles.
A Study on the Characteristics of High Strength Grout for Pile Connections Exposed to Sea Environments
Journal of the Korea Concrete Institute
미세 강섬유의 구속력이 모르타르의 알칼리-실리카 반응에 미치는 영향
한국콘크리트학회, Oct 1, 2007
Additional file 1 of Agricultural by-products and oyster shell as alternative nutrient sources for microbial sealing of early age cracks in mortar
Additional file 1: Table S1. Selected three factors and their levels for central composite design... more Additional file 1: Table S1. Selected three factors and their levels for central composite design. Table S2. Experimental design in the optimization to form an economical medium. Table S3. Equations of the linear trend lines of changes in crack width over sealing periods in four mortar specimens. Figure S1. Phenotypic and gene-expression comparison of strain AK13 in pH 7 and 10 LB media. (a) Growth curves of the strain AK13 in each of the above two conditions. Arrows indicate when total RNAs were extracted. (b) Organization by COG category of the genes whose expressions were up-regulated under neutral or alkaline conditions. Figure S2. The adaptation mechanisms of alkaliphilic Bacillus spp. to the alkaline environment including the function of riboflavin in the respiratory chain. Figure S3. Comparison of growth and spore formation when NaCl or riboflavin was added to sesame meal-medium. (a) Comparison of growth when each of two growth promoting factors were added to sesame meal-medi...
콘크리트는 낮은 단위가격에 상대적으로 높은 강도와 내구성을 지녀 건설 분야에서 가장 많이 사용되는 재료이다(Mehta and Monteiro 2006). 하지만 하중과 재료 ... more 콘크리트는 낮은 단위가격에 상대적으로 높은 강도와 내구성을 지녀 건설 분야에서 가장 많이 사용되는 재료이다(Mehta and Monteiro 2006). 하지만 하중과 재료 수축, 열화인자 유입 등으로 인해 콘크리트 내외부에 미세 균열이 지속적으로 발생하고, 미세 균열은 전체 콘크리트 구조물의 수명을 단축시킨다(Peris Mora 2007). 이에 대한 해결책으로 외부 인력의 투입 없이 스스로 미세 균열을 충진하여 열화 인자의 투입을 막아 콘크리트의 내구성을 증진시키는 자기치유 콘크리트(Self-healing concrete)가 지속적 으로 연구되었다(Van Tittelboom and De Belie 2013). 박테리아를 활용한 균열 자기치유 콘크리트는 다른 자기치유 메커니즘과 비교하여 다음과 같은 분명한 이점을 보인다. 첫째, 비활성 상태의 박테리아는 이론상 콘크리트 내부에서 반영구적으 로 생존하므로(Jonkers and Schlangen 2008) 철근 콘크리트 구 조물의 일반적인 내구연한(∼50년) 동안 자기치유 효과를 기대할 수 있다. 둘째, 박테리아는 균열로부터 유입된 수분 및 산소 등의 물질에 의해 활성화되므로 콘크리트 내부에서 치유재의 소모가 없다. 셋째, 균열이 충진된 뒤 박테리아는 스스로 비활성 상태로 전환되고, 이후 동일한 부위에 균열이 발생했을 때 재활성화되어 균열을 치유한다. 하지만 박테리아를 활용한 자기치유 콘크리트 개발 시 다음과 같은 문제점이 알려져 있다. 첫째, 다른 메커니즘에 비해 상대적으 로 균열 치유에 오랜 시간이 걸린다. 박테리아의 생장은 시간에 따른 시그모이드 곡선 형태로 나타나며, 박테리아 밀도가 적은 초 기 유도기(Lag phase)에는 박테리아 활동성이 낮다. 따라서 박테 박테리아 펠렛을 자기치유 소재로 사용한 모르타르의 강도 및 치유성능 Strength and Healing Performance of the Mortar using Bacterial Pellet as a Self-Healing Material
Materials, 2021
In this study, a new type of bacterial carrier using methylcellulose was presented, and its appli... more In this study, a new type of bacterial carrier using methylcellulose was presented, and its applicability to self-healing concrete has been explored. Methylcellulose, the main component of a 2 mm pellet-shaped carrier, can remain stable in alkaline environments and expand in neutral or acidic environments. These properties allow bacteria to survive in the high-alkaline and high-pressure environments of early age concrete, and the number of bacteria increases rapidly in the event of cracks, accelerating crack closure. The results show that the survival rate of bacterial spores inside the mortar was increased, and the pellet provides an enhanced biological anchor suitable for bacterial activity, bacterial growth, and mineral precipitation. Further, the results indicate an improved self-healing efficiency compared with mixing bacteria directly into the cement composite.
Construction and Building Materials, 2020
h i g h l i g h t s Effect of SWW on the dimensional stability of epoxy resin mortar was evaluate... more h i g h l i g h t s Effect of SWW on the dimensional stability of epoxy resin mortar was evaluated. Effect of curing methods (conventional and microwave) on the dimensional stability was assessed. Dimensional stability was assessed in terms of shrinkage and coefficient of thermal expansion.
Journal of the Korea Concrete Institute, 2008
Shrinkage Properties and Potential for Cracking of High-strength Concrete containing High-volume Blast Furnace Slag
Journal of the Architectural Institute of Korea Structure & Construction, 2015
Construction and Building Materials, 2017
h i g h l i g h t s Review on the fiber reinforcement in cement composites. Effect of embedment l... more h i g h l i g h t s Review on the fiber reinforcement in cement composites. Effect of embedment length on bond behavior is experimentally investigated. Optimum fiber geometry of the amorphous steel fiber.
Effect of fiber geometry on the electromagnetic shielding performance of mortar
Computers and Concrete, 2016
The increased awareness of electromagnetic wave hazards has prompted studies on electromagnetic s... more The increased awareness of electromagnetic wave hazards has prompted studies on electromagnetic shielding using conductive materials in the construction industry. Previous studies have explored the effects of the types of conductive materials and their mix proportions on the electromagnetic shielding performance; however, there has been insufficient research on the effect of the geometry of the conductive materials on the electromagnetic shielding performance. Therefore, in this study, the dependence of the electromagnetic shielding performance on the cross-sectional geometry, diameter and length of fibers was investigated. The results showed that the electromagnetic shielding performance improved when the fiber length increased or the diameter decreased, but the effect of the cross-sectional geometry of the fibers was smaller than the effect of the fiber spacing factor.
Mechanics of Composite Materials, 2009
re in forced poly mer bars, bond strength, con crete strength, bond fail ure sur face In this stu... more re in forced poly mer bars, bond strength, con crete strength, bond fail ure sur face In this study, the ef fects of re peated loads on the FRP-con crete bond strength were in ves ti gated ex per i men tally by di rect pull out tests ac cord ing to CSA S806-02. A con ven tional re in forc ing steel bar and two types of glass-fi ber-re in forced plas tic (GFRP) bars were em bed ded in con crete and tested un der four dif fer ent load ing pat terns. The bond strength-slip curves of the bars were ob tained and an a lyzed. The re sults showed that the max i mum bond strengths un der the re peated loads dif fered from those ob tained un der monotonic ones. In addi tion, no tice able dif fer ences in deg ra da tion of the bond strength with re spect to the mag ni tude of slip were observed be tween the dif fer ent bar types tested. On the ba sis of an im age anal y sis of fail ure sur faces, they were at trib uted to the dif fer ent bond fail ure mech a nisms as so ci ated with the steel and GFRP bars. In tro duc tion FRP (fi ber-re in forced plas tic) ma te ri als, which were first adopted by aero space in dus try to re place the costly met als and al loys, are now found in a va ri ety of civil en gi neer ing ap pli ca tions, such as bridge decks, ret ro fit of ex ist ing struc tures, and new struc tures in highly cor ro sive en vi ron ments, be cause of their high strength-to-weight ra tio and high re sis tance to static loads and chem i cals [1, 2]. In par tic u lar, the use of FRP bars/sheets has drawn much at ten tion as an al ter na tive ma te rial to the steel re in force ment in con crete. In the past de cades, many stud ies have been car ried out to in ves ti gate the use of FRP bars in con crete beams sub jected to flex ure and shear loads and to de ter mine their de for ma tion char ac ter is tics, and de sign guides for FRP bars in con crete have been proposed in the United States, Canada, and Europe [3-5]. How ever, there are top ics which need fur ther in ves ti ga tions to fully uti lize FRPs as a re li able re in force ment in concrete. The bond strength be tween a FRP and con crete, for ex am ple, is not yet as clearly un der stood as that for the con ven tional steel re in force ment. Fur ther more, the ex ist ing lit er a ture shows dis so nant re sults. Achilides et al. [6], Okelo et al. [7], and Lee et al. [8] stud ied the ef fect of con crete strength ¢ f c on the FRP-con crete bond strength t n. Achilides et al. found that t n in creased with ¢ f c up to ~50 MPa, be yond which the ef fect be came in sig nif i cant [6], while Okelo et al. stated that t n in creased in pro portion to ¢ f c , as ob served in the case of steel re in force ment [7]. Re cently, Lee et al. showed the FRP bond strength in creased pro-609 0191-5665/09/4506-0609 © 2009 Springer Sci ence+Busi ness Me dia, Inc. *De part ment of Ar chi tec tural En gi neer ing, Sungkyunkwan Uni ver sity, 300, Cheongcheong-dong, Jangan-gu, Suwon, 440-746, Re pub lic of Ko rea. **School of Civil, Ar chi tec tural, and En vi ron men tal En gi neer ing, Ko rea Uni ver sity, Anam-dong, Seongbuk-gu, Se oul, 136-701, Re pub lic of Ko rea. The cor re spond ing au thor is C.
전도성 재료 혼입 모르타르의 UHF파 차폐효과
대한건축학회논문집 구조계, 2015
Materials and Structures, 2006
Performance enhancement due to microfibers is well known. However, fracture processes that lead t... more Performance enhancement due to microfibers is well known. However, fracture processes that lead to strain hardening behavior in microfiber reinforced composites are not well understood. Crack growth resistance behavior of mortar reinforced with steel microfibers and polypropylene microfibers was investigated insitu during load application. The polypropylene fibers were inter-ground in the cement mill to enhance the fiber/matrix interfacial frictional stress. A more homogeneous fiber distribution was observed in the inter-ground polypropylene composites compared to the steel microfiber reinforced composites. In steel microfiber reinforced composites the dominant toughening mechanisms were multiple microcracking and successive debonding along the fiber/matrix interface. Fiber pullout, the dominant mechanism in conventional macrofiber reinforced composites was rarely observed. In-situ observation of crack/ fiber interaction in the inter-ground polymer fibers also revealed multiple microcracking along the length of the fibers followed by fiber pullout.
Magazine of Concrete Research, 2010
In concrete beam design, the shear capacity of the concrete beam is of great interest because she... more In concrete beam design, the shear capacity of the concrete beam is of great interest because shear failure is associated with an abrupt failure mode that undermines the flexural performance of the beam. Recently, because of the increasing cost of natural resources and environmental concerns, the use of recycled aggregate (RA) in construction is becoming the standard practice. However, the effects of recycled aggregates on the shear strength of concrete have not been fully examined. In this study the effects of RA on concrete shear strength are studied experimentally by performing flexural tests on 20 RA concrete beams with various combinations of span-to-depth ratios (a/d = 1·50, 2·50, 3·25), longitudinal reinforcement ratios (s = 0·53%, 0·83%, 1·61%) and RA replacement ratios (0%, 30%, 50%, 100%). The test results indicate that the concrete shear strength diminishes by up to 30% at 100% replacement ratio compared with the natural aggregate concrete. The shear strengths of the RA c...
International Journal of Steel Structures, 2012
Helically wrapped wire cables were first introduced to overcome the difficulties in transporting ... more Helically wrapped wire cables were first introduced to overcome the difficulties in transporting and installing straight wires. Presently, helically wrapped wire cables are used as the important load-carrying elements in many structures such as suspension bridges, cable-stayed bridges, tall guyed towers, power transmission lines, and flexible electrical conductors. In design and analysis, cables are traditionally assumed to carry axial load only; thus, studies on the bending behavior of the cables have been limited. Although the small curvature assumption of the cable may be valid for most part, the possible development of a large curvature at the bearings and anchorage cannot be ignored nor avoided. In this study, an analytical model was developed for the helically wrapped wires in a cable subjected to tension and small bending, with full consideration of the helically wrapped wire geometry. Using the developed model, an approximate upper limit of the cable curvature-for which the conventional Bernoulli-Euler-Navier kinematic beam assumption can be adapted to evaluate the stress in the wires-was obtained.
Cement and Concrete Composites, 2001
Interground ®ber cement (IFC) is a new process where ®bers are ground in with the cement clinker ... more Interground ®ber cement (IFC) is a new process where ®bers are ground in with the cement clinker during the dry cement manufacturing process. With IFC considerable strength enhancement can be achieved compared to ordinary cement even at a ®ber volume as low as 0.2% due to homogeneous ®ber distribution and ®ber surface modi®cations associated with the milling process. The cracking mechanisms associated with the strength enhancement were observed in real time during load application using a custom designed loading device. The homogeneous ®ber distribution stabilizes crack growth. Formation of multiple, stable secondary microcracks was observed during the strain hardening regime, enhancing the strain capacity at ultimate strength. Fiber pullout was the dominant toughening mechanism in the strain softening regime. For ®bers inclined to the propagating crack, ®ber pullout was preceded by secondary microcrack formations along the ®ber/matrix interface.
Applied Sciences, 2020
Rebar embedded inside reinforced concrete structures becomes corroded due to various factors. How... more Rebar embedded inside reinforced concrete structures becomes corroded due to various factors. However, few studies have focused on the corrosion of pre-rusted rebar embedded in cement composites, and the findings reported thus far are inconsistent. Therefore, in this study, an experimental program was undertaken to examine the effect of pre-rusting on the further corrosion of reinforcements in cement composites. Pre-rust was induced using two different solutions (CaCl2 and HCl). The corrosion rate in the cement composite was analyzed using the half-cell potential and polarization resistance methods. In addition, scanning electron microscopy with energy-dispersive X-ray analysis and X-ray diffraction analysis were used to examine the morphology of the rust. The results show that the corrosion rate of the rebar embedded in the cement composite can be increased by more than 3.8 times depending on the pre-rust conditions (RE: 0.0009 mm/year, HCl: 0.0035 mm/year). In addition, we found t...
Development of a novel compressed tablet-based bacterial agent for self-healing cementitious material
Cement and Concrete Composites, 2022
Preliminary Study for the Development of Alkali Activated Natural Hwangtoh Binder
Materials, 2021
Understanding the bond behavior of steel rebar in concrete is important in order to determine the... more Understanding the bond behavior of steel rebar in concrete is important in order to determine the performance of a reinforced concrete structure. Although numerous studies have been carried out by many researchers to develop a robust model for numerical analysis, no consensus has been reached as the bond behavior depends on hysteresis. In this study, the bond behavior of a steel bar in concrete with pre-existing damage is investigated under low-level cyclic loading. Based on the experimental bond stress and slip curve, a numerical model for finite element analysis to simulate the effect of low-level cyclic loading is proposed. The results from the numerical analysis show good agreement with the experimental data, including accumulated damage on stiffness and strength throughout entire load cycles.