Strain rate effects on the compressive and tensile behavior of bundle-type polyamide fiber-reinforced cementitious composites

Kim, Hongseop,Kim, Gyuyong,Lee, Sangkyu,Son, Minjae,Choe, Gyeongcheol,Nam, Jeongsoo Elsevier 2019 Composites. Part B, Engineering Vol.160 No.-

<P><B>Abstract</B></P> <P>The compressive and tensile behavior of fiber-reinforced cementitious composites is significantly affected by the bonding and pull-out properties between matrix and reinforced fiber, as well as the fracture properties of the fibers. In addition, an increase in strain rate according to loading conditions influences the fracture behavior between the fiber and matrix. Steel fiber-reinforced cementitious composites with high flexural and tensile strength, toughness, and crack resistance are widely used in tunnels and plant structures. However, the high specific gravity and stiffness of steel fibers can cause rupture of concrete pump tubes, increase the rebound volume of shotcrete, and decrease durability by corrosion of fiber. Therefore, it is necessary to study the development and application of organic fiber which has similar mechanical properties to steel fiber and does not cause corrosion. In this study, polyamide fibers having the same aspect ratio as the hooked steel fibers, which are widely used as reinforcing fibers for concrete, have been developed. And strain rate effect on the compressive and tensile behaviors of bundle-type polyamide fiber-reinforced cementitious composite and hooked steel fiber-reinforced cementitious composite were evaluated. The results showed that the effect of strain rate over different fiber types influenced the tensile behavior more significantly than the compressive behavior. In polyamide fiber-reinforced cementitious composite (PAFRCC), a fracture behavior of fiber was observed regardless of a strain rate, and the tensile behavior of PAFRCC was influenced more by tensile strength of polyamide fiber itself than a bonding stress between fiber and matrix. In hooked steel fiber-reinforced cementitious composite (HSFRCC), a bonding stress between hooked steel fiber and matrix (frictional force at the interface between fiber and matrix, mechanical bond of the hooked part) influenced the tensile behavior significantly. Fracture properties that straightened pulled out the fiber from the matrix were observed at static tensile loading condition. However, non-straightened hooked steel fiber was observed along with the fracture of matrix due to an increase in mechanical bonding force of the hooked part and the bonding stress between the fiber and the matrix.</P>

Experimental Investigation on the Blast Resistance of Fiber- Reinforced Cementitious Composite Panels Subjected to Contact Explosions

남정수,김홍섭,김규용 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.1

This study investigates the blast resistance of fiber-reinforced cementitious composite (FRCC) panels, with fiber volume fractions of 2%, subjected to contact explosions using an emulsion explosive. A number of FRCC panels with five different fiber mixtures (i.e., micro polyvinyl alcohol fiber, micro polyethylene fiber, macro hooked-end steel fiber, micro polyvinyl alcohol fiber with macro hooked-end steel fiber, and micro polyethylene fiber with macro hooked-end steel fiber) were fabricated and tested. In addition, the blast resistance of plain panels (i.e., non-fiber-reinforced high strength concrete, and non-fiberreinforced cementitious composites) were examined for comparison with those of the FRCC panels. The resistance of the panels to spall failure improved with the addition of micro synthetic fibers and/or macro hooked-end steel fibers as compared to those of the plain panels. The fracture energy of the FRCC panels was significantly higher than that of the plain panels, which reduced the local damage experienced by the FRCCs. The cracks on the back side of the micro synthetic fiber-reinforced panel due to contact explosions were greatly controlled compared to the macro hooked-end steel fiber-reinforced panel. However, the blast resistance of the macro hooked-end steel fiber-reinforced panel was improved by hybrid with micro synthetic fibers.

Experimental Investigation on the Blast Resistance of Fiber-Reinforced Cementitious Composite Panels Subjected to Contact Explosions

Jeongsoo Nam,Hongseop Kim,Gyuyong Kim 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.1

This study investigates the blast resistance of fiber-reinforced cementitious composite (FRCC) panels, with fiber volume fractions of 2%, subjected to contact explosions using an emulsion explosive. A number of FRCC panels with five different fiber mixtures (i.e., micro polyvinyl alcohol fiber, micro polyethylene fiber, macro hooked-end steel fiber, micro polyvinyl alcohol fiber with macro hooked-end steel fiber, and micro polyethylene fiber with macro hooked-end steel fiber) were fabricated and tested. In addition, the blast resistance of plain panels (i.e., non-fiber-reinforced high strength concrete, and non-fiberreinforced cementitious composites) were examined for comparison with those of the FRCC panels. The resistance of the panels to spall failure improved with the addition of micro synthetic fibers and/or macro hooked-end steel fibers as compared to those of the plain panels. The fracture energy of the FRCC panels was significantly higher than that of the plain panels, which reduced the local damage experienced by the FRCCs. The cracks on the back side of the micro synthetic fiber-reinforced panel due to contact explosions were greatly controlled compared to the macro hooked-end steel fiber-reinforced panel. However, the blast resistance of the macro hooked-end steel fiber-reinforced panel was improved by hybrid with micro synthetic fibers.

Experimental Investigation on the Blast Resistance of Fiber-Reinforced Cementitious Composite Panels Subjected to Contact Explosions

Nam, Jeongsoo,Kim, Hongseop,Kim, Gyuyong Korea Concrete Institute 2017 International Journal of Concrete Structures and M Vol.11 No.1

This study investigates the blast resistance of fiber-reinforced cementitious composite (FRCC) panels, with fiber volume fractions of 2%, subjected to contact explosions using an emulsion explosive. A number of FRCC panels with five different fiber mixtures (i.e., micro polyvinyl alcohol fiber, micro polyethylene fiber, macro hooked-end steel fiber, micro polyvinyl alcohol fiber with macro hooked-end steel fiber, and micro polyethylene fiber with macro hooked-end steel fiber) were fabricated and tested. In addition, the blast resistance of plain panels (i.e., non-fiber-reinforced high strength concrete, and non-fiber-reinforced cementitious composites) were examined for comparison with those of the FRCC panels. The resistance of the panels to spall failure improved with the addition of micro synthetic fibers and/or macro hooked-end steel fibers as compared to those of the plain panels. The fracture energy of the FRCC panels was significantly higher than that of the plain panels, which reduced the local damage experienced by the FRCCs. The cracks on the back side of the micro synthetic fiber-reinforced panel due to contact explosions were greatly controlled compared to the macro hooked-end steel fiber-reinforced panel. However, the blast resistance of the macro hooked-end steel fiber-reinforced panel was improved by hybrid with micro synthetic fibers.

U-net 딥러닝 기법을 활용한 PVA 섬유 보강 시멘트 복합체의 섬유 분리

서지우,한동석 한국전산구조공학회 2023 한국전산구조공학회논문집 Vol.36 No.5

PVA 섬유 보강 시멘트 복합체는 매우 복잡한 미세구조를 가지고 있으며, 재료의 거동을 정확히 평가하기 위해서는 미세구조 특성을 반영하여 실제 실험과 시너지효과를 내며 효율적인 재료 설계를 가능하게 하는 해석 모델의 개발이 중요하다. PVA 섬유 보강 시멘트 복합체의 역학적 성능은 PVA 섬유의 방향성에 큰 영향을 받는다. 그러나 마이크로-CT 이미지로부터 얻은 PVA 섬유의 회색조 값을 인접한 상과 구분하기 어려워, 섬유 분리 과정에 많은 시간이 소요된다. 본 연구에서는 섬유의 3차원 분포를 얻기 위하여 0.65μm3의 복셀 크기를 가지는 마이크로-CT 이미지 촬영을 수행하였다. 학습에 사용될 학습 데이터를 생성하기 위해 히스토그램, 형상, 그리고 구배 기반 상 분리 방법을 적용하였다. 본 연구에서 제안된 U-net 모델을 활용하여 PVA 섬유 보강 시멘트 복합체의 마이크로- CT이미지로부터 섬유를 분리하는 학습을 수행하였다. 훈련의 정확도를 높이기 위해 데이터 증강을 적용하였으며, 총 1024개의 이미지를 훈련 데이터로 사용하였다. 모델의 성능은 정확도, 정밀도, 재현율, F1 스코어를 평가하였으며, 학습된 모델의 섬유 분리 성능이 매우 높고 효율적이며, 다른 시편에도 적용될 수 있음을 확인하였다. The development of an analysis model that reflects the microstructure characteristics of polyvinyl alcohol (PVA) fiber-reinforced cementitious composites, which have a highly complex microstructure, enables synergy between efficient material design and real experiments. PVA fiber orientations are an important factor that influences the mechanical behavior of PVA fiber-reinforced cementitious composites. Owing to the difficulty in distinguishing the gray level value obtained from micro-CT images of PVA fibers from adjacent phases, fiber segmentation is time-consuming work. In this study, a micro-CT test with a voxel size of 0.65 μm3 was performed to investigate the three-dimensional distribution of fibers. To segment the fibers and generate training data, histogram, morphology, and gradient-based phase-segmentation methods were used. A U-net model was proposed to segment fibers from micro-CT images of PVA fiber-reinforced cementitious composites. Data augmentation was applied to increase the accuracy of the training, using a total of 1024 images as training data. The performance of the model was evaluated using accuracy, precision, recall, and F1 score. The trained model achieved a high fiber segmentation performance and efficiency, and the approach can be applied to other specimens as well.

변형속도에 따른 폴라아미드 섬유 및 후크형 강섬유 보강 시멘트 복합체의 인장특성

이상규 ( Lee Sang-kyu ),김규용 ( Kim Gyu-yong ),황의철 ( Hwang Eui-chul ),손민재 ( Son Min-jae ),백재욱 ( Baek Jae-wook ),남정수 ( Nam Jeong-soo ) 한국건축시공학회 2018 한국건축시공학회 학술발표대회 논문집 Vol.18 No.2

In this study, it evaluate the tensile properties of polyamide fiber reinforced cementitious composite and hooked steel fiber reinforced cementitious Composites by strain rate. Polyamide fiber reinforced cement composites (PAFRCC) and Hooked Steel Fiber Reinforced Cement Composite(HSFRCC) were fabricated. Each specimen was reinforced with 1.0 and 2.0vol% fiber. The length of the reinforced fiber was 30 mm for both fibers, and the tensile test specimen was made in dumbbell shape. As a result, the tensile strength of fiber in polyamide fiber and the mechanical bonding between fiber and matrix in hooked steel fiber are considered to be the main factors affecting tensile behavior of fiber reinforced cement composite.

강섬유보강 시멘트 복합체의 섬유인발거동에 따른 인장성능 평가에 관한 실험적 연구

이예찬 ( Lee Yae-chan ),김규용 ( Kim Gyu-yong ),남정수 ( Nam Jeong-soo ),이상규 ( Lee Sang-kyu ),서동균 ( Shu Dong-kyun ),유하민 ( Eu Ha-min ) 한국건축시공학회 2020 한국건축시공학회 학술발표대회 논문집 Vol.20 No.2

The purpose of this study is to evaluate tensile performance of cementitious composites reinforced with steel fiber. The tensile performance of steel fiber reinforced cementitious composites is related to the tensile performance of reinforced fiber, and depends on the fracture or pull-out of fiber. Therefore, the tensile performance was compared and analyzed by conducting a direct tensile test on the tensile specimens of cementitious composites reinforced with hook-type steel fiber and amorphous steel fiber.

Shear strength of reinforced concrete beams with precast High-Performance Fiber-Reinforced Cementitious Composite permanent form

Wu, Xiangguo,Kang, Thomas H.-K.,Lin, Yang,Hwang, Hyeon-Jong Elsevier 2018 Composite structures Vol.200 No.-

<P><B>Abstract</B></P> <P>As a structural and constructional element, a thin-walled U-shaped precast permanent form consisting of High-Performance Fiber-Reinforced Cementitious Composites (HPFRCC) and steel wire mesh is considered. Prior to casting, transverse steel threaded bars are installed, as well as longitudinal reinforcing bars, connecting two sides of the U-shaped form for shear transfer between the precast and in-filled concrete sections and for fresh concrete pressure resistance. The present study investigated the effect of precast U-shaped HPFRCC section on the shear strength of the composite beams. As parameters for full-scale three-point bending tests, the type or materials of precast section, spacing of shear reinforcement, and shear span-to-depth ratio were considered. The test results showed that the precast U-shaped HPFRCC permanent form increased the shear contributions of in-filled concrete and shear reinforcement in the composite beam substantially. From the experimental and analytical assessment, the coefficients related to the composite action between precast HPFRCC and in-filled concrete sections, shear reinforcement along diagonal cracks, and shear span-to-depth ratio were proposed, which were applied to a previous shear strength model for the simplified shear design of proposed precast U-shaped HPFRCC-in filled concrete composite beams.</P>

Strengthening of reinforced concrete columns by High-Performance Fiber-Reinforced Cementitious Composite (HPFRC) sprayed mortar with strengthening bars

Cho, Chang-Geun,Han, Byung-Chan,Lim, Seung-Chan,Morii, Noharu,Kim, Jae-Whan Elsevier 2018 Composite structures Vol.202 No.-

<P><B>Abstract</B></P> <P>Under severe earthquake, lack of strength and ductility in the plastic hinge region of the reinforced concrete column raises serious concerns for overall structural safety. In the current study, experimental research was performed to improve the seismic strength and performance of reinforced concrete columns under cyclic load reversals. A new strengthening approach of reinforced concrete columns was introduced by applying High-Performance Fiber-Reinforced Cementitious Composites (HPFRC) sprayed mortar combined with additional reinforcing steel bars.</P> <P>For the practice of strengthening of old reinforced concrete columns, the surface of old concrete column section was treated and grooved in advance, later the longitudinal and/or transverse strengthening bars were placed in the groove of concrete surface, and finally the column section was increased by HPFRC sprayed mortar. As experimental variables such as the HPFRC sprayed mortar, use of additional transverse strengthening bars, and the use of additional longitudinal strengthening bars, the performance of the strengthened columns were compared with that of the conventional reinforced concrete column under reversed cyclic loads.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Seismic strengthening of concrete column was newly applied by HPFRC sprayed mortar. </LI> <LI> Damage of column plastic hinge was minimized by HPFRC and additional reinforcing bars. </LI> <LI> The crack width of concrete was controlled by multiple micro-cracks induced by HPFRC. </LI> <LI> The strengthened method could improve the hysteretic damping energy of the column. </LI> </UL> </P>

Dynamic tensile behavior of SIFRCCs at high strain rates

Seungwon Kim,Cheolwoo Park,Dong Joo Kim 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.26 No.3

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.