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>

Experiments on Tensile and Shear Characteristics of Amorphous Micro Steel (AMS) Fibre-Reinforced Cementitious Composites

Jeong-Su Kim,Chang-Geun Cho,Hyeong-Joo Moon,Hoyeon Kim,Seung-Jung Lee,Wha-Jung Kim 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.4

Amorphous micro-steel (AMS) fibre made by cooling of liquid pig iron is flexible, light and durable to corrosion, then to be compatible with high flowable and disperable states of mixing as well as high ductile post-cracked performances to apply in fibre-reinforced cementitious composites. In the current research, AMS fibre-reinforced cementitious composites based on cement and alkali-activated ground granulated blast furnace slag mortars were newly manufactured and evaluated for the strength and ductile characteristics mainly by direct tensile and shear transfer tests in the variation in the volume of AMS fibres with two different lengths of 15.0 and 30.0 mm. As a result, it was found that 1.0–1.25% fibre volume fractions were recommendable for AMS fibre-reinforced cementitious composites to maximize direct tensile strength, ductile tensile strain, and shear strength of the composites. However, a further fraction of AMS fibre lowered these mechanical characteristics. Simultaneously, it could be said that AMS fibre-reinforced cementitious composites exhibited up to about 3.7 times higher in direct tensile strength and up to 2.3 times higher in shear strength, compared to AMS fibre-free specimens.

Cementitious Porous Material Applied to Precision Aerostatics Bearings

Leandro Jos da Silva,Tulio Hallak Panzera,Luciano Machado Gomes Viera,Christopher Rhys Bowen,Jaime Gilberto Duduch,Juan Carlos Campos Rubio 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2

The use of porous materials as restrictor in aerostatic bearings provides many advantages over conventional restrictors, such as small variation of temperature, high damping, high operational speeds, limited wear and capacity to support radial, axial, and combined loads, being considered important features for precision machines and instruments. This work evaluates the load carrying capacity for different air gaps and pressures of thrust porous bearing made with cementitious composites. The cementitious composites consisted of Portland cement and monomodal silica particles (44 μm) were fabricated via uniaxial cold-pressing (10 MPa). The load capacity was determined for different air pressures, such as 3, 4, 5 and 6 bar. The air gap was measured using pneumatic transducers. A pneumatic instability was observed when the air pressure level increased from 3 to 6 bar. A similar loading capacity, for bearing gaps between 7 and 30 μm, was achieved in comparison to hot-pressed porous alumina found in the literature. In addition, the cementitious porous bearing provided a superior loading capacity for gaps higher than 10 μm when compared to graphite porous bearing found in the literature. The results revealed the cementitious composites are promising materials for porous restrictor in aerostatic thrust bearings.

Effect of length and content of steel fibers on the flexural and impact performance of self-compacting cementitious composite panels

Denise-Penelope N. Kontoni,Behnaz Jahangiri,Ahmad Dalvand,Mozafar Shokri-Rad Techno-Press 2023 Advances in concrete construction Vol.15 No.1

One of the important problems of concrete placing is the concrete compaction, which can affect the strength, durability and apparent quality of the hardened concrete. Therefore, vibrating operations might be accompanied by much noise and the need for training the involved workers, while inappropriate functioning can result in many problems. One of the most important methods to solve these problems is to utilize self-compacting cementitious composites instead of the normal concrete. Due to their benefits of these new materials, such as high tensile, compressive, and flexural strength, have drawn the researchers' attention to this type of cementitious composite more than ever. In this experimental investigation, six mixing designs were selected as a base to acquire the best mechanical properties. Moreover, forty-eight rectangular composite panels with dimensions of 300 mm × 400 mm and two thickness values of 30 mm and 50 mm were cast and tested to compare the flexural and impact energy absorption. Steel fibers with volume fractions of 0%, 0.5% and 1% and with lengths of 25 mm and 50 mm were imposed in order to prepare the required cement composites. In this research, the composite panels with two thicknesses of 30 mm and 50 mm, classified into 12 different groups, were cast and tested under three-point flexural bending and repeated drop weight impact test, respectively. Also, the examination and comparison of flexural energy absorption with impact energy absorption were one of the other aims of this research. The obtained results showed that the addition of fibers of longer length improved the mechanical properties of specimens. On the other hand, the findings of the flexural and impact test on the self-compacting composite panels indicated a stronger influence of the long-length fibers.

Influences of CNT dispersion and pore characteristics on the electrical performance of cementitious composites

Kim, G.M.,Yang, B.J.,Cho, K.J.,Kim, E.M.,Lee, H.K. ELSEVIER (APPLIED SCIENCE) 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.164 No.-

<P><B>Abstract</B></P> <P>In the present study, cementitious composite incorporating a carbon nanotube (CNT) with highly improved electrical conductivity comparable to that of a semiconductor is developed and investigated. The CNT and pore characteristics within a cementitious matrix are considered as the most influential factors which determine the overall performance of the material, and these factors are artificially controlled by incorporating silica fume and a superplasticizer. Additionally, a micromechanics-based model is proposed to predict the electrical performance and percolation threshold of the composites. A parametric study based on the developed model is conducted, and the influences of the constituent properties on the overall electrical characteristics of composites are discussed. The effectiveness of the proposed hypothesis is demonstrated by comparing it to the experimental results in the present study and from the previous work.</P>

Pseudo-strain hardening and mechanical properties of green cementitious composites containing polypropylene fibers

Hossein Karimpour,Moosa Mazloom 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.5

In order to enhance the greenness in the strain-hardening composites and to reduce the high cost of typical polyvinyl alcohol fiber reinforced engineered cementitious composite (PVA-ECC), an affordable strain-hardening composite with green binder content has been proposed. For optimizing the strain-hardening behavior of cementitious composites, this paper investigates the effects of polypropylene fibers on the first cracking strength, fracture properties, and micromechanical parameters of cementitious composites. For this purpose, digital image correlation (DIC) technique was utilized to monitor crack propagation. In addition, to have an in-depth understanding of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. To understand the effect of fibers on the strain hardening behavior of cementitious composites, ten mixes were designed with the variables of fiber length and volume. To investigate the micromechanical parameters from fracture tests on notched beam specimens, a novel technique has been suggested. In this regard, mechanical and fracture tests were carried out, and the results have been discussed utilizing both fracture and micromechanical concepts. This study shows that the fiber length and volume have optimal values; therefore, using fibers without considering the optimal values has negative effects on the strainhardening behavior of cementitious composites.

시멘트계 복합체에 대한 멀티모드 파이버 레이저 절단의 실험적 연구

서영진,표석훈,이동경 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.8

This study was performed to observe the applicability of laser cutting in cementitious composites. The multimode fiber laser cutting of cementitious composites was conducted using a laser power of 9 kW. The experimental variables were the laser cutting speed and material compositions, such as cement paste, cement mortar and ultra-high performance concrete. After laser cutting, kerf width and penetration depth were observed on the surface and crosssection, respectively. In addition to these observations, the microstructure of cut surface was observed through scanning electron microscopy to compare the microstructure of cementitious composites before and after laser irradiation. Furthermore, the changes in the chemical composition of the microstructure were evaluated through energy-dispersive x-ray spectroscopy analysis. The effects of silicate-based materials on laser cutting were confirmed on the basis of the kerf width and penetration depth. It was also observed that the glassy layer produced by the melting of a silicate-based material affected the quality of laser cutting. 본 연구는 시멘트계 복합체에 대한 레이저 절단의 적용 가능성을 관찰하기 위해 수행되었다. 시멘트계 복합체에 대한 멀티모드 파이버 레이저 절단은 9kW의 레이저 출력으로 설정되었다. 실험 변수는 레이저 절단 속도와 시멘트 페이스트, 시멘트 모르타르 및 초 고성능 콘크리트(UHPC: Ultra-high performance concrete)와 같은 재료 구성으로 지정되었다. 레이저 절단 후, 표면과 단면에서 각각 절단 폭과 침투 깊이가 관찰되었다. 이러한 관찰 외에, 레이저 조사 전과 후 시멘트계 복합체의 미세구조를 비교하기 위해 SEM을 통해 절단면의 미세구조를 관찰하였다. 또한, EDX 분석을 이용하여 미세구조의 화학적 조성의 변화를 평가하였다. 그 결과, 실리카 기반 재료가 레이저 절단에 미치는 영향을 절단 폭과 침투 깊이를 통해 확인되었다. 또한, 실리카 기반 재료의 용융으로 인해 생성된 유리질층(glassy layer)이 레이저 절단 품질에 영향을 미치는 것으로 관찰되었다.

Synergistic Effect of PVA Fiber and PTB Emulsion on Mechanical Properties of Cementitious Composites for Damage Repair in Operating Tunnels

Chunyu Zhang,Mengjun Chen,Rentai Liu,Xiuhao Li,Jia Yan,Zhijing Zhu,Fengshuai Fan 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.12

Operating tunnels are often located in complex geological conditions and are prone to various types of damage. Even after structural repair, the repaired material may be vulnerable to secondary damage. It is difficult to effectively repair operating tunnel damage. Hence, developing high-performance repair materials for tunnel structures is critical. This study aimed to develop repair materials by studying the synergistic effects of fiber and polymers. The effectof polyvinyl alcohol (PVA) fiber and PTB (COMPAKTUNA.PRO) emulsion on the compressive strength (40 × 40 × 40 mm, GB/T 17671-2020), flexural strength (40 × 40 × 160 mm, GB/T 17671-2020), uniaxial tensile properties (330 × 60 × 13 mm, JC/T 2461-2018), bond strength (40 × 40 × 160 mm, JC/T 2537-2019), rapid chloride migration coefficient (ϕ100 × 50 mm, GB/T 50082-2009), porosity (40 × 40 × 40 mm, SY/T 6490-2014), and scanning electron microscopy (less than 1 cm3, GB/T 27788-2020) was analysed. The test was completed in the laboratory of our school, and the average value of three specimens per mix ratio was taken. The results indicate that both PVA fiber and PTB emulsion addition reduce the compressive strength but significantly increase the flexural strength, tensile strength, and ultimate tensile strain of cementitious composite. The compressive-to-flexural strength ratio decreases, and the uniaxial compression toughness index increases. The cementitious composites exhibit good integrity after damage. The influence of the PVA fiber is more potent than that of the PTB emulsion. The PTB emulsion increases the impermeability and bonding strength of the cementitious composite and can improve the disadvantages caused by adding the PVA fibers. The bridging effect of the PVA fiber and the membrane-forming effect of the PTB emulsion together influence the performance and cause a synergistic effect to achieve superposition and complementation of advantages. The optimal content of the PVA fiber and PTB emulsion under the synergistic effect can be obtained. The findings can provide a theoretical basis for the optimal design and practical application of restoration materials.

Synergistic effects of carbon nanotubes and carbon fibers on heat generation and electrical characteristics of cementitious composites

Kim, G.M.,Yang, B.J.,Yoon, H.N.,Lee, H.K. Elsevier 2018 Carbon Vol.134 No.-

<P><B>Abstract</B></P> <P>The heat generation and electrical characteristics of cementitious composites incorporating carbon nanotube (CNT) and carbon fiber under various heating conditions were investigated in this study. Specifically, the synergistic effects of carbon nanotube and carbon fiber on the heat generation and electrical characteristics of cementitious composites were experimentally investigated. The test results show that the addition of carbon fiber improved the heat generation capability and the electrical stability of the cementitious composites incorporating CNT during heating. The long-term durability of construction materials is an important issue, however, there is a practical limit to measuring a property of specimen for a very long time in a laboratory level experiment. In addition, a modified micromechanical model was proposed here to estimate the long-term effect of heating on the electrical characteristics of cementitious composites. The model parameters were derived from the experimental results, and a series of numerical simulations was conducted to explore the influence of model parameters on the resistance of the composites. Comparisons between experimental data and the present predictions were made to assess the potential of the proposed model.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Delayed Strength Development of Composite Cementitious with Calcium Silicate Slag

Ru Bai,Ju Zhang,Changwang Yan,Shuguang Liu,Xiaoxiao Wang,Zhijie Yang,Hao Jing 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.6

Using pulverized calcium silicate slag (CSS) to replace part of Portland cement (PC) as composite cementitious material is the most energy-saving and clean treatment method. The main objective of this study was to investigate the delayed strength development of the CSS-PC composite cementitious. The compressive strength of the composite cementitious with 10% to 40% CSS was tested, the delayed strength was calculated, and the delayed age was analyzed. Results showed that the delayed strength and delayed age increased with the increase in the substitution rate of CSS, which was determined by the ratio of C2S and C3S. Moreover, a compressive strength prediction model of CSS–PC composite cementitious was established based on the “core-shell” hydration model. The calculated value was compared with the specification value of each country to analyze whether the compressive strength of CSS-PC composite cementitious meets the engineering requirements.