Tae Uk KIM

Hyeon Woo NOH

Min Su KYUNG

Seon Yeol LEE

Gi Joon PARK

Van Thong NYGUEN

Van Phi DANG

Van Doan TRUONG

Sun Gil KIM

Huy Viet LE

Min Kyung KIM

Jun Kil PARK

Tri Thuong NGO

Seung Hoon PARK

Ngoc Thanh TRAN

Duy Liem NGUYEN

Tuan Kiet TRAN

Han Sol JO

Ra Hwan HWANG

Hee Ae KIM

Sung Ik CHOI

Seok Hee KANG

Jung Jin KIM

Jiandong SONG

Our lab is a leading research group recognized in concrete engineering, conducting a variety of challenging studies, including ultra-high strength fiber-reinforced concrete, electrodynamic behavior of construction materials, and non-destructive inspection using electrical resistance. Recently, we are focusing on the development of meta-construction materials and structures with negative Poisson's ratios.

저희 연구실은 콘크리트 공학 분야에서 인정받는 선도적인 연구 그룹으로, 초고강도 섬유강화 콘크리트, 건설 재료의 전기역학적 거동, 전기 저항을 이용한 비파괴 검사 등 다양하고 도전적인 연구를 수행하고 있습니다. 최근에는 음의 푸아송비를 갖는 메타 건설 재료 및 구조물 개발에 주력하고 있습니다.

Auxetic meta-concrete: advances, challenges, and future directions

Abstract
                  
                    This study provides a comprehensive overview of the material and mechanical properties of lightweight fiber-reinforced cementitious composites (L-FRCCs), focusing on their classification as ultra-high-strength lightweight fiber-reinforced cementitious composites (UL-FRCCs). The L-FRCCs exhibit a density of 1440–2150 kg/m
                    3
                    , thermal coefficient of 0.22–0.33 W/mK, compressive strength of 45–145 MPa, and flexural strength of 4.3–37.5 MPa. The strength of the L-FRCCs increases linearly with matrix strength. Specifically, L-FRCCs with compressive strength &gt; 100 MPa, flexural strength &lt; 15 MPa, density &lt; 1950 kg/m
                    3
                    , and thermal conductivity &lt; 0.5 W/mK can be classified as UL-FRCCs. Pearson correlation analysis reveals that the structural efficiency (SE) of L-FRCCs increases with increasing matrix strength, fiber volume content, and reinforcing index; however, it decreases with an increase in the lightweight aggregate (LWA) ratio. For UL-FRCCs to achieve optimal SE, the LWAs should possess a crushing strength &gt; 70 MPa and specific gravity &lt; 0.5. Additionally, incorporating straight steel fibers at volumes &lt; 2.5% is recommended to achieve strengths &gt; 100 MPa. Compared to nonmetallic fibers such as polymeric fibers, steel fibers offer superior SE for flexural strength, despite their tendency to reduce workability owing to their high stiffness.

Ultra-High-Strength Lightweight Fiber-Reinforced Concrete: A Review

Crack depth estimation of concrete structures by electrical resistance measurements of crack areas

Tensile response of ultra-high performance lightweight fiber-reinforced cementitious composite containing hollow glass microspheres at high strain rates

Auxetic meta-concrete with customized materials and structures: Experiments and simulations

Mechanical resistance of reinforced concrete beams strengthened by waste fishing net hybrid fiber-reinforced cementitious composites

Experimental observation on the seismic performance of reinforced concrete columns with a well-confined plastic hinge region

Predicting dynamic increase factors for post-cracking tensile strength of fiber-reinforced cement composites using novel hybrid machine learning models

Direct tensile characteristics of textile reinforced cementitious composites: Effects of textile types and epoxy resin coating at the joints of textile grid

Effects of high-volume limestone powder substitution on hydration and mechanical-microstructural development of low-carbon cement pastes: Simulation and experiment

Damage sensing characteristics of smart ultra-high-performance concrete containing electrically conductive fiber and particle fillers under high compressive stress

Simulation-based analysis of impact of CNT dispersion on hydration of cement paste

Synergy performance of hybrid fiber-reinforced ultra-high-performance cementitious composites with low fiber contents

Loading rate effects on multifiber pullout resistance of smooth steel fibers in ultra-high-performance concrete

Effects of combined nanoparticles on dynamic strength of ultra-high-performance fiber-reinforced concrete

Electromechanical response of smart ultra-high-performance concrete beams under flexure: Effects of filler type and electrode spacing

Smart ultra-high-performance concrete under cyclic high compressive stress

A comprehensive study on predicting the elastic modulus and Poisson ratio of hardened cement pastes via micro-scale cement hydration simulations

Electromechanical response of smart ultra-high-performance concrete under uniaxial load: Experimental investigation and electric field analysis

Enhancing image resolution in single-side electrical resistance tomography (ERT) by utilizing theoretical sensitivity analysis: Experimental validation and application to cement mortar

AbstractThis study investigates the effects of matrix strength on the high‐rate tensile resistance and strain rate sensitivity of strain‐hardening fiber‐reinforced concretes (SHFRCs) under direct tensile loading. Two types of deformed steel fiber, hooked and twisted, were reinforced in two matrices, high‐performance concrete (HPC) with compressive strength of 84 MPa and ultra‐high‐performance concrete (UHPC) with compressive strength of 180 MPa. Additionally, an artificial neural network (ANN) based model was proposed to estimate the strain rate sensitivity of SHFRCs subjected to dynamic direct tensile loading. The results showed that HPC produced relatively lower post cracking strength but much higher strain capacity at a high strain rate than UHPC. Moreover, HPC was found to be more strain rate sensitivity than UHPC. Furthermore, the proposed ANN model was an efficient tool for predicting the strain rate sensitivity of SHFRCs. Based on the sensitivity analysis, the contribution of each influence factor on the final strain rate sensitivity of SHFRCs can be determined.

Strain rate sensitivity of strain-hardening fiber-reinforced concrete subjected to dynamic direct tensile loading

Pullout resistance of waste fishing net embedded in the interface between the concrete and fibrous mortar matrix: Test method and experimental investigation

Investigating dynamic compressive strength of concrete by using high-rate hydraulic universal testing machine

Self-sensing characteristics of smart high-performance cementitious composites containing multiwall carbon nanotubes, steel fibers, and steel slag aggregates under compression

Simulation of the effect of nano-CaCO3 agglomeration on the hydration process and microstructural evolution of cement paste

Improvement of the stress sensing ability of ultra-high-performance concrete using short steel fibers and steel slag aggregates under high compression

Fracture resistance of ultra-high-performance fiber-reinforced concrete containing nanoparticles at high strain rates

Feasibility of hybrid waste fishing net textile and fiber reinforced cementitious composites in strengthening concrete and retrofitting damaged concrete

Use of multiphase voxels to simulate the effects of nano-silica on cement hydration

Rate-sensitive pullout resistance of smooth-steel fibers embedded in ultra-high-performance concrete containing nanoparticles

Effects of temperature and humidity on self-stress sensing capacity of smart concrete blocks

Hydration simulation of cement pastes reinforced with carbon nanotubes

Effects of adding short fibers on impact resistance of glass textile reinforced cementitious composites under direct tension

AbstractThe mechanical behaviors and their correlations of ultra‐high‐performance fiber‐reinforced concretes (UHPFRCs) with various steel fiber types were highlighted in this investigation based on the experiment combined with sectional analysis. Under compression, five fiber types with 2.0 vol% were investigated as follows: no fibers (PL), long twisted fibers (LT), long hook fibers (LH), long smooth fibers (LS) and hybrid fibers (HB, 1% twisted blended with 1% short smooth fibers). The LT revealed the highest compressive strength and strain capacity whereas the PL exhibited the lowest ones. Compared to the PL, the HB produced significant enhancements in strength, elastic modulus and deformation capacity under compression, tension and bending. The order in effectiveness of strength enhancement owing to additional hybrid fibers was as follows: bending &gt; tensile &gt; compressive loading. Based on sectional analyses, the enhancements in moment resistance of UHPFRC beams were closely correlated with higher compressive strength and smaller compressive strain capacity. Besides, the condition for first cracking at the bottom of UHPFRC beam was explored. Finally, a simplified model, based on the tensile response of UHPFRCs, for predicting the flexural resistances of the UHPFRC beams was proposed and validated.

Mechanical behaviors and their correlations of ultra-high-performance fiber-reinforced concretes with various steel fiber types

Electromechanical response of strain-hardening fiber-reinforced cementitious composites (SH-FRCCs) under direct tension: A review

Diagnostic technologies using X-rays and/or acoustic emissions for concrete infrastructures containing internal pores, defects, and cracks have attracted considerable interest. However, computerized tomography (CT) for concrete is challenging due to its radiation shielding characteristics. Electrical impedance tomography (EIT), initially developed for medical use, has recently shown a potential for developing a macro-CT technique for concrete structures. This study derived EIT analytical solutions for rectangular cement-based samples and validated them with experimental data obtained from cubic mortar samples. The experimental validation of the three mathematical functions (Dirac delta, Heaviside step, and Gaussian) used as current injection models, the Gaussian function produced the lowest relative absolute error (4.02%). This study also explored appropriate experimental setups for cement-based materials, such as Shunt model, current flow paths, and potential distribution.

Experimentally Validated Analytical Solutions to Homogeneous Problems of Electrical Impedance Tomography (EIT) on Rectangular Cement-Based Materials

Effects of nanoparticles on the tensile behavior of ultra-high-performance fiber-reinforced concrete at high strain rates

The direct tensile resistance of strain-hardening steel-fibre-reinforced concrete (SHSFRC) was experimentally investigated and modelled. Three steel fibre types (twisted, hooked and smooth fibres) and three matrices with different compressive strengths (28 MPa (M1), 84 MPa (M2) and 180 MPa (M3)) were investigated in both single-fibre pull-out tests and direct tensile tests. A model based on machine learning was developed to predict the tensile resistance of the SHSFRCs. The experimental results showed that the twisted fibres not only exhibited the highest pull-out resistance but also the greatest tensile resistance in M1 and M2, whereas smooth fibres achieved the same results in M3. The predicted outcomes showed that the proposed model had high efficiency and accuracy in estimating the tensile resistance of SHSFRC, with a correlation coefficient of 0.951.

Experiments and prediction of direct tensile resistance of strain-hardening steel-fibre-reinforced concrete

Rate-sensitive tensile resistance of glass textile reinforced cementitious composites

Experimental evaluation on the seismic performance of reinforced concrete bridge columns with high strength reinforcement

Dynamic increase factors for fiber-reinforced cement composites: A review

Dynamic shear response of ultra-high-performance fiber-reinforced concretes under impact loading

Different electrical voltage responses of cement composites under forward and backward current directions

Improving the tensile resistance at high strain rates of high-performance fiber-reinforced cementitious composite with twisted fibers by modification of twist ratio

High-accuracy rebar position detection using deep learning–based frequency-difference electrical resistance tomography

In this study, shear resistance of ultra-high-performance fibre-reinforced concrete (UHPFRCs) containing different types (smooth, hooked and twisted fibre), fibre aspect ratios (l/d = 100, 95 and 65) and volume contents (0.0, 0.5 and 1.5 vol.%) of steel fibre was investigated using a new shear test method. Shear resistance of UHPFRCs strongly depended on the fibre type, fibre aspect ratio and fibre volume content. The twisted fibre exhibited the highest resistance in terms of shear strength, shear strain capacity and shear peak toughness, the smooth was the next and the hooked fibres produced the lowest response. The bigger the aspect ratio of fibre added to the mixture, the higher the shear resistance of UHPFRCs can be observed. Besides, the shear resistance of UHPFRCs was significantly enhanced with the increase of fibre volume content. The compressive strength and flowability of all mixtures were also checked. The compressive strength increased from 184 MPa for ultra-high-performance concrete to 210 MPa for UHPFRCs, whereas the flowability of mixtures varied from 203 mm to 250 mm. Finally, a theoretical model to predict the shear resistance of UHPFRC beams without the stirrup bar was proposed and verified.

Sensitivity of various fibre features on shear capacities of ultra-high-performance fibre-reinforced concrete

Enhancing self-stress sensing ability of smart ultra-high performance concretes under compression by using nano functional fillers

Effects of cement particle distribution on the hydration process of cement paste in three-dimensional computer simulation

Detecting embedded rebar in cement mortar by frequency-difference electrical resistance tomography

Effects of different grips and surface treatments of textile on measured direct tensile response of textile reinforced cementitious composites

Development of a smart concrete block with an eccentric load sensing capacity

This study proposes the development of a wireless sensor system integrated with smart ultra-high performance concrete (UHPC) for sensing and transmitting changes in stress and damage occurrence in real-time. The smart UHPC, which has the self-sensing ability, comprises steel fibers, fine steel slag aggregates (FSSAs), and multiwall carbon nanotubes (MWCNTs) as functional fillers. The proposed wireless sensing system used a low-cost microcontroller unit (MCU) and two-probe resistance sensing circuit to capture change in electrical resistance of self-sensing UHPC due to external stress. For wireless transmission, the developed wireless sensing system used Bluetooth low energy (BLE) beacon for low-power and multi-channel data transmission. For experimental validation of the proposed smart UHPC, two types of specimens for tensile and compression tests were fabricated. In the laboratory test, using a universal testing machine, the change in electrical resistivity was measured and compared with a reference DC resistance meter. The proposed wireless sensing system showed decreased electrical resistance under compressive and tensile load. The fractional change in resistivity (FCR) was monitored at 39.2% under the maximum compressive stress and 12.35% per crack under the maximum compressive stress tension. The electrical resistance changes in both compression and tension showed similar behavior, measured by a DC meter and validated the developed integration of wireless sensing system and smart UHPC.

Development of Low-Cost Wireless Sensing System for Smart Ultra-High Performance Concrete

An innovative smart concrete anchorage (SCA) has been developed for monitoring the stress of prestressing (PS) tendons by utilizing smart ultra-high-performance concrete (UHPC). The smart UHPC contained 2 vol% steel fibers and fine steel slag aggregates instead of silica sands. The effects of different electrode materials, arrangements, and connectors on the self-stress sensing capacity of the SCA are discussed. A prototype SCA demonstrated its feasibility and sufficient self-stress sensing capacity to be used in monitoring the prestressing loss of the PS tendon. As the tensile stress of the PS tendon increased from 0 to 1488 MPa, the fractional change in resistivity (FCR) of the prototype SCA, with horizontally paired copper wire electrodes and a plug-in type connector, decreased linearly from 0% to −1.53%, whereas the FCR increased linearly from −1.53% to −0.04% as the tensile stress of the PS tendon decreased from 1488 to 331 MPa.

An Innovative Smart Concrete Anchorage with Self-Stress Sensing Capacity of Prestressing Stress of PS Tendon

Deep Learning-Based Anomaly Detection to Classify Inaccurate Data and Damaged Condition of a Cable-Stayed Bridge

AbstractThe fracture toughness and fracture energy of ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) at both static and impact rates (43–92 s−1) were investigated using double‐edge‐notched tensile specimens. Two types of steel fiber, smooth and twisted fiber, were used in producing UHPFRC with different volume ratios of 0.5%, 1.0%, 1.5%, and 2%. The results indicated that UHPFRCs produced very high fracture resistance at impact rates, with first stress intensity factor (KIC) up to 3.995 MPa√m, critical stress intensity factor () up to 7.778 MPa√m, and fracture energy (GF) up to 86.867 KJ/m2, which were 2.5, 5.0, and 16.9 times higher than those of ultra‐high‐performance concrete, respectively. The  was clearly sensitive to the applied loading rate, whereas the KIC and GF were not. Smooth fiber specimens exhibited not only higher  and GF at impact rates but also higher dynamic increase factor than twisted fiber specimens. A minimum fiber volume content of 1% should be used in UHPFRC to provide a significant enhancement in crack resistance. The maximum value of UHPFRC crack velocity at impact rates was found to be 527 m/s by using a dynamic fracture mechanic model.

Dynamic fracture toughness of ultra-high-performance fiber-reinforced concrete under impact tensile loading

Loading rate effects on the properties of fiber-matrix zone surrounding steel fibers and cement based matrix

A review paper on direct tensile behavior and test methods of textile reinforced cementitious composites

Effects of corrosion level and inhibitor on pullout behavior of deformed steel fiber embedded in high performance concrete

Electrical properties of smart ultra-high performance concrete under various temperatures, humidities, and age of concrete

Effect of different expanded aggregates on durability-related characteristics of lightweight aggregate concrete

Structural health monitoring (SHM) is crucial for quantitative behavioral analysis of structural members such as fatigue, buckling, and crack propagation identification. However, formerly developed approaches cannot be implemented effectively for long-term infrastructure monitoring, owing to power inefficiency and data management challenges. This study presents the development of a high-fidelity and ultra-low-power strain sensing and visualization module (SSVM), along with an effective data management technique. Deployment of 24-bit resolution analog to a digital converter and precise half-bridge circuit for strain sensing are two significant factors for efficient strain measurement and power management circuit incorporating a low-power microcontroller unit (MCU), and electronic-paper display (EPD) enabled long-term operation. A prototype for SSVM was developed that performs strain sensing and encodes the strain response in a QR code for visualization on the EPD. For efficient power management, SSVM only activated when the trigger-signal was generated and stayed in power-saving mode consuming 18 mA and 337.9 μA, respectively. The trigger-signal was designed to be generated either periodically by a timer or intentionally by a push-button. A smartphone application and cloud database were developed for efficient data acquisition and management. A lab-scale experiment was carried out to validate the proposed system with a reference strain sensing system. A cantilever beam was deflected by increasing load at its free end, and the resultant strain response of SSVM was compared with the reference. The proposed system was successfully validated to use for long-term static strain measurement.

SSVM: An Ultra-Low-Power Strain Sensing and Visualization Module for Long-Term Structural Health Monitoring

AbstractA new lateral confining method is proposed for reinforced concrete columns in this study. The new scheme incorporates additional lateral confinements that are placed outside conventional lateral reinforcements within cross section of a column. Stainless steel wires or glass fiber reinforced plastic (GFRP) rings have been employed as the additional confinement. A total of seven reinforced concrete column specimens have been tested to validate the proposed new scheme. Primary parameters in the test are vertical spacing and volumetric ratio of the additional confinements amongst others. Lateral hysteretic response shows that specimens with the newly proposed scheme exhibit no strength degradation up to 6% of drift ratio, the specimen without such scheme displays somewhat sudden degradation at 5% of drift ratio. Experimental results also indicate that displacement ductility and energy dissipation of specimens confined by the additional confinements are greater than those of specimen without such confinements. Margin of safety with reference to the code‐specified ductility is 1.6, 2.2, and 2.1 for specimen with no confinements, stainless steel wires, and GFRP rings, respectively. In addition, energy dissipation ability reveals that specimens with the confinements show up to 50% higher than the specimen without confinements. In all, experimental observation confirms that the present approach is promising to provide an additional confinement and ductility. It is thus expected that the suggested scheme can be applied to reinforced concrete columns and be particularly effective for those members with relatively large vertical spacing of conventional lateral reinforcements.

A new confinement scheme for reinforced concrete columns using stainless steel or glass fiber reinforced plastic

This study investigated the electromechanical response of smart ultra-high-performance concretes (smart UHPCs), containing fine steel slag aggregates (FSSAs) and steel fibers as functional fillers, under external loads corresponding to different measurement methods. Regardless of different measurement methods of electrical resistance, the smart UHPCs under compression showed a clear reduction in their electrical resistivity. However, under tension, their electrical resistivity measured from direct current (DC) measurement decreased, whereas that from alternating current (AC) measurement increased. This was because the electrical resistivity, from DC measurement, of smart UHPCs was primarily dependent on fiber crack bridging, whereas that from AC measurement was dependent on tunneling effects.

Electromechanical Response of Smart Ultra-High Performance Concrete under External Loads Corresponding to Different Electrical Measurements

Feasibility study on use of waste fishing nets as continuous reinforcements in cement-based matrix

Enhancing impact resistance of hybrid ultra-high-performance fiber-reinforced concretes through strategic use of polyamide fibers

Mechanical behavior of waste fishing net fiber-reinforced cementitious composites subjected to direct tension

In this study, recycled waste fishing net (WFN) short fibers were proposed to be used as short fiber reinforcements. The pullout resistance of WFN short fibers embedded in cement mortar was investigated by conducting fiber pullout tests. Three types of WFN short fibers and two types of commercial polypropylene (CP) fibers were investigated. To quantitatively compare the pullout resistance of WFN short fibers and CP fibers, pullout parameters, including peak pullout load (peak bond strength), peak fiber stress, slip at peak load, and pullout energy (equivalent bond strength) of the pullout specimens, were analyzed. In addition, the analysis of fiber images, captured by using a stereoscopic digital microscope, before and after pullout tests, elucidated the different mechanisms of fiber pullout corresponding to the type of fibers. The bundled structures of the WFN fibers generated mechanical interaction between fiber and matrix during fiber pullout; consequently, they produced higher bond resistance and more damage on the surface of fibers after the pullout. Therefore, the bundled WFN fibers showed comparable pullout resistance with CP fibers.

Pullout Behavior of Recycled Waste Fishing Net Fibers Embedded in Cement Mortar

This experimental study investigates the effects of the aggregate surface conditions on the compressive strength of quick-converting track concrete (QTC). The compressive strength of QTC and interfacial fracture toughness (IFT) were investigated by changing the amount of fine abrasion dust particles (FADPs) on the aggregate surface from 0.00 to 0.15 wt% and the aggregate water saturation from 0 to 100%. The effects of aggregate water saturation on the compressive strength of the QTC and IFT were notably different, corresponding to the amount of FADPs. As the aggregate water saturation increased from 0 to 100%, in the case of 0.00 wt% FADPs, the IFT decreased from 0.91 to 0.58 MPa∙mm1/2, and thus, the compressive strength of the QTC decreased from 34.8 to 31.4 MPa because the aggregate water saturation increased the water/cement ratio at the interface and, consequently, the interfacial porosity. However, as the aggregate water saturation increased from 0 to 100%, in the case of 0.15 wt% FADPs, the compressive strength increased from 24.6 to 28.1 MPa, while the IFT increased from 0.41 to 0.88 MPa∙mm1/2 because the water/cement ratio at the interface was reduced as a result of the absorption by the FADPs on the surface of the aggregates and the cleaning effects of the aggregate surface.

Influence of the Aggregate Surface Conditions on the Strength of Quick-Converting Track Concrete

Multimetric Event-Driven System for Long-Term Wireless Sensor Operation for SHM Applications

Effects of steel slag aggregate size and content on piezoresistive responses of smart ultra-high-performance fiber-reinforced concretes

Detecting crack and damage location in self-sensing fiber reinforced cementitious composites

Characterizing the electro-mechanical response of self-sensing steel-fiber-reinforced cementitious composites

Direct tensile self-sensing and fracture energy of steel-fiber-reinforced concretes

Interfacial fracture toughness between aggregates and injected quick-hardening mortar

Concrete has high compressive strength, but low tensile strength, bending strength, toughness, low resistance to cracking, and brittle fracture characteristics. To overcome these problems, fiber-reinforced concrete, in which the strength of concrete is improved by inserting fibers, is being used. Recently, high-performance fiber-reinforced cementitious composites (HPFRCCs) have been extensively researched. The disadvantages of conventional concrete such as low tensile stress, strain capacity, and energy absorption capacity, have been overcome using HPFRCCs, but they have a weakness in that the fiber reinforcement has only 2% fiber volume fraction. In this study, slurry infiltrated fiber reinforced cementitious composites (SIFRCCs), which can maximize the fiber volume fraction (up to 8%), was developed, and an experimental study on the tensile behavior of SIFRCCs with varying fiber volume fractions (4%, 5%, and 6%) was carried out through direct tensile tests. The results showed that the specimen with high fiber volume fraction exhibited high direct tensile strength and improved brittleness. As per the results, the direct tensile strength is approximately 15.5 MPa, and the energy absorption capacity was excellent. Furthermore, the bridging effect of steel fibers induced strain hardening behavior and multiple cracks, which increased the direct tensile strength and energy absorption capacity.

Tensile Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composite with Respect to Fiber Volume Fraction

Interfacial bond characteristics of steel fibers embedded in cementitiouscomposites at high rates

Self-damage or/and stress-sensing concrete is a promising area of research for measuring the electromechanical response of structural materials using more robust sensors. However, the copper and silver paste sensors widely used in such applications can be expensive and have detrimental effects on the load carrying capacity and durability of the structural systems upon which they are installed. Accordingly, this study compared the performance of four electrode types—conventional copper tape with silver paste (CS), copper film with type 1 carbon tape (CC1), copper film with type 2 carbon tape (CC2), and copper wire and film with type 2 carbon tape (WC2)—to develop an economical and practical electrode for measuring the electromechanical response of self-damage-detecting concrete. The CC1 electrode exhibited comparable performance to the CS electrode in measuring the electromechanical response of self-damage-detecting concrete, despite requiring a longer polarization time (80 s) than the CS electrode (25 s). The CS electrode exhibited a higher damage-sensing capacity (GF2), whereas the CC1 electrode exhibited a higher strain-sensing capacity (GF1), as well as good damage-sensing capacity. Therefore, the CC1 electrode using copper film with type 1 carbon tape was determined to be the best alternative to the conventional CS electrode.

Comparative Performance of Four Electrodes for Measuring the Electromechanical Response of Self-Damage Detecting Concrete under Tensile Load

Self-stress sensing smart concrete containing fine steel slag aggregates and steel fibers under high compressive stress

The feasibility of the crack closure of cementitious composites reinforced with shape memory alloy (SMA) fibers was investigated by performing single-fiber pullout tests. To demonstrate the fast crack closing ability, in this study, a heat treatment (300 °C) was applied for a short time (10 min). A short heat treatment was applied for 10 min, after the slip reached 0.5 mm, to activate the shape memory effects of cold-drawn SMA fibers. Two types of alloys were investigated, NiTi and NiTiNb, with two geometries, either smooth or dog-bone-shaped. During the heat treatment, the pullout stress of the SMA fibers initially decreased due to thermal extension, and then increased after heating for 1–3 min, resulting from the shape memory effects. However, their pullout stress recovery during and after the heat treatment was different for the different alloys and fiber geometries. The NiTi fibers generally produced a higher and faster recovery in terms of their pullout stress than the NiTiNb fibers, while the dog-bone-shaped fibers showed a faster pullout stress recovery than the smooth fibers.

Effects of a Short Heat Treatment Period on the Pullout Resistance of Shape Memory Alloy Fibers in Mortar

The effects of adding micro-carbon fibers on the electro-mechanical response of macro-steel fiber-reinforced concretes (MSFRCs) under tension were investigated. Two MSFRCs were investigated and they had identical mortar matrix but different fiber contents: MSFRC1 and MSFRC2 contained 1.0 and 1.5 vol.% fibers, respectively. The volume contents of added micro-carbon fibers were 0 to 1.5 vol.% in MSFRC1 and 0 to 0.75 vol.% in MSFRC2, respectively. The addition of 0.5 vol.% micro-carbon fibers, in both MSFRC1 and MSFRC2, produced significantly enhanced damage-sensing capability and still retained their strain-hardening performance together with multiple micro cracks. However, when the content of carbon fibers was more than 0.5 vol.%, the MSFRCs generated tensile strain-softening behavior and reduced damage-sensing capability. Furthermore, the effects of temperature and humidity on the electrical resistivity of MSFRCs were investigated, as were the effects of adding multi-walled carbon nanotubes on the damage-sensing capability of MSFRCs.

Enhancing Damage-Sensing Capacity of Strain-Hardening Macro-Steel Fiber-Reinforced Concrete by Adding Low Amount of Discrete Carbons

Effects of abraded fine particle content on strength of quick-hardening concrete

Loading rate effect on crack velocity in ultra-high-performance fiber-reinforced concrete

Effect of matrix shrinkage on rate sensitivity of the pullout response of smooth steel fibers in ultra-high-performance concrete

The self-damage sensing capacity of high-performance fiber-reinforced cementitious composites (HPFRCCs) that blended long- (1 vol %) and medium-length (1 vol %) smooth steel fibers was considerably improved by adding milled glass fibers (MGFs) with a low electrical conductivity to a mortar matrix. The addition of MGFs (5 wt %) significantly increased the electrical resistivity of the mortar matrix from 45.9 to 110.3 kΩ·cm (140%) and consequently improved the self-damage sensing capacity (i.e., the reduction in the electrical resistivity during the tensile strain-hardening response) from 17.27 to 25.56 kΩ·cm (48%). Furthermore, the addition of MGFs improved the equivalent bond strength of the steel fibers on the basis of the higher pullout energy owing to the accumulated cementitious material particles attached to the surfaces of steel fibers.

Electromechanical Response of High-Performance Fiber-Reinforced Cementitious Composites Containing Milled Glass Fibers under Tension

Synergy in shear response of ultra-high-performance hybrid-fiber-reinforced concrete at high strain rates

Strain rate-dependent shear failure surfaces of ultra-high-performance fiber-reinforced concretes

Effects of ageing and storage conditions on the interfacial bond strength of steel fibers in mortars

Direct tensile responses of aramid fiber reinforced cementitious composites and textile reinforced cementitious composites with 3D spacer fabric at high strain rates

Electro-mechanical self-sensing response of ultra-high-performancefiber-reinforced concrete in tension

shear stress versus strain responses of ultra-high-performance fiber-reinforced concretes at high strain rates

Effect of matrix cracking on electrical resistivity of high performance fiber reinforced cementitious composites in tension

Shear resistance of ultra-high-performance fiber-reinforced concrete

Synergistic response of blending fibers in ultra-high-performance concrete under high rate tensile loads

Matrix-strength-dependent strain-rate sensitivity of strain-hardening fiber-reinforced cementitious composites under tensile impact

This research investigated the effects of direct tensile response on the flexural resistance of ultra-high-performance fiber-reinforced concretes by performing sectional analysis. The correlations between direct tensile and flexural response of ultra-high-performance fiber-reinforced concretes were investigated in detail for the development of a design code of ultra-high-performance fiber-reinforced concrete flexural members as follows: (1) the tensile resistance of ultra-high-performance fiber-reinforced concretes right after first-cracking in tension should be higher than one-third of the first-cracking strength to obtain the deflection-hardening if the ultra-high-performance fiber-reinforced concretes show tensile strain-softening response; (2) the equivalent bottom strain of flexural member at the modulus of rupture is always higher than the strain capacity of ultra-high-performance fiber-reinforced concretes in tension; (3) the softening part in the direct tensile response of ultra-high-performance fiber-reinforced concretes significantly affects their flexural resistance; and (4) the moment resistance of ultra-high-performance fiber-reinforced concrete girders is more significantly influenced by the post-cracking tensile strength rather than the tensile strain capacity. Moreover, the size and geometry effects should be carefully considered in predicting the moment capacity of ultra-high-performance fiber-reinforced concrete beams.

Direct tension-dependent flexural behavior of ultra-high-performance fiber-reinforced concretes

BOND RESISTANCE OF L-SHAPED SHAPE MEMORY ALLOY FIBERS IN MORTAR

Investigating the impact resistance of ultra-high-performance fiber-reinforced concrete using an improved strain energy impact test machine

Fresh and hardened properties of steel fiber-reinforced grouts containing ground granulated blast-furnace slag

Prestressing effect of cold-drawing short NiTi SMA fibres in steel reinforced mortar beam

Direct tensile behavior of shape-memory-alloy fiber-reinforced cement composites

Meta Construction Materials and Structures Laboratory

교수님 소개

Dong Joo Kim

연구실 소개

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Auxetic meta-concrete: advances, challenges, and future directions

Ultra-High-Strength Lightweight Fiber-Reinforced Concrete: A Review

Crack depth estimation of concrete structures by electrical resistance measurements of crack areas

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

Dong Joo Kim

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Auxetic meta-concrete: advances, challenges, and future directions

Ultra-High-Strength Lightweight Fiber-Reinforced Concrete: A Review

Crack depth estimation of concrete structures by electrical resistance measurements of crack areas

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

우리 연구실 모집