• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.186-187
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• 2014

Flexural stress and fracture energy of fiber reinforced cementitious composites is increased by bridge effect of reinforced fiber, scabbing failure is restrained. Shape, properties of fiber were SF(steel fiber), PA(polyamide), NY(nylon) have effects on flexural stress and fracture energy, impact resistance improve of fiber reinforced cementitious composites. In this study, local failure properties by impact of high velocity projectile was analyzed by mixing 3 types of fiber which have different shape and properties respectively.

• 한국농공학회논문집
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• 제50권1호
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• pp.49-57
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• 2008

This study evaluated the flexural properties and fire resistance of polyolefm based structural synthetic fiber reinforced concrete. The effects of differing fiber length, dimension and fiber volume fraction were studied. Flexural and fire resistance test were conducted in accordance with the JCI SF-4 and RABT time heating temperature curve, respectively. The Flexural test results indicated that the polyolefln based structural fiber reinforcement showed an ability to increase the flexural toughness and good fire resistance significantly(as compared to steel fiber reinforcement).

• 콘크리트학회논문집
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• 제17권4호
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• pp.543-550
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• 2005

본 연구에서는 마이크로 섬유인 탄소섬유와 매크로 섬유인 강섬유가 서로 하이브리드 형태로 결합되고 미세한 광물 혼화재인 실리카퓸이 치환된 고성능 하이브리드 섬유보강 콘크리트(HPHFRC)의 파괴계수(MOR), 휨인성 특성($I_30$과 $W_{2.0}$), 유동성(슬럼프)이 분산분석(ANOVA)을 통해 특성화된다. MOR I30(또는 $W_{2.0}$), 슬럼프 데이터들은 휨 성능과 유동성을 평가하기 위한 특성치로 사용된다. 특히, 실험회수를 줄이기 위하여 일부실시 직교배열에 따라 실험이 계획된다. 각 특성인자를 각 실험인자에 대해서 평가한 결과, 강섬유는 MOR 과 $I_{30}$의 특성인자 측면에서 상당히 유의한 실험인자로 나타난다. 또한 분산분석 결과, 실험인자의 유의도에 따라 다음과 같은 평가가 이용될 수 있다 유동성(슬럼프) 감소는 실리카 흄, 강섬유, 탄소섬유 실험인자 순서로 유의하게 나타난다. MOR 향상은 실리카퓸($\fallingdotseq$ 탄소섬유), 강섬유 실험인자 순서로 유의한 것으로 나타난다. 휨인성 증진은 실리카퓸, 탄소섬유, 강섬유 실험인자 순서로 유의하게 나타난다. 실험범위 내에서 강섬유 $1.0\%$, 탄소섬유 $0.25\%$, 실리카퓸 $5.0\%$의 조합이 각 특성치들을 가장 우수하게 향상시키고 유동성이 확보된 실험 조건으로 도출된다.

• Computers and Concrete
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• 제19권6호
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• pp.667-675
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• 2017

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

• Computers and Concrete
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• 제22권5호
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• Structural Engineering and Mechanics
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• 제80권5호
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• pp.595-608
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• 2021

To investigate the mechanical behavior of large stud shear connector embedded in hybrid fiber-reinforced concrete (HFRC), a refined 3D nonlinear finite element (FE) model incorporating the constitutive model of HFRC was developed using ANSYS. Firstly, the test results conducted by the authors (He et al. 2017) were used to validate FE model of push out tests. Secondly, a total of 27 specimens were analyzed with various parameters including fiber volume fractions of HFRC, diameter of studs and HFRC strength. Finally, an empirical equation considering the contribution of steel fiber (SF) and polypropylene fiber (PF) was recommended to estimate the ultimate capacity of large stud shear connector embedded in HFRC.

• Geomechanics and Engineering
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• 제12권3호
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• pp.441-464
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• 2017

The determination of the mixture parameters of stabilization has become a great concern in geotechnical applications. This paper presents an effort about the application of artificial intelligence (AI) techniques including radial basis neural network (RBNN), multi-layer perceptrons (MLP), generalized regression neural network (GRNN) and adaptive neuro-fuzzy inference system (ANFIS) in order to predict the unconfined compressive strength (UCS) of silty soil stabilized with bottom ash (BA), jute fiber (JF) and steel fiber (SF) under different freeze-thaw cycles (FTC). The dosages of the stabilizers and number of freeze-thaw cycles were employed as input (predictor) variables and the UCS values as output variable. For understanding the dominant parameter of the predictor variables on the UCS of stabilized soil, a sensitivity analysis has also been performed. The performance measures of root mean square error (RMSE), mean absolute error (MAE) and determination coefficient ($R^2$) were used for the evaluations of the prediction accuracy and applicability of the employed models. The results indicate that the predictions due to all AI techniques employed are significantly correlated with the measured UCS ($p{\leq}0.05$). They also perform better predictions than nonlinear regression (NLR) in terms of the performance measures. It is found from the model performances that RBNN approach within AI techniques yields the highest satisfactory results (RMSE = 55.4 kPa, MAE = 45.1 kPa, and $R^2=0.988$). The sensitivity analysis demonstrates that the JF inclusion within the input predictors is the most effective parameter on the UCS responses, followed by FTC.

• Advances in concrete construction
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• 제11권4호
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• pp.335-345
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• 2021

It is known from the literature that there are relatively few studies on the engineering properties of ultra-high performance concrete (UHPC) in early age. In fact, in order to ensure the safety of UHPC during construction and sufficient durability and long-term performance, it is necessary to explore the early behavior of UHPC. The test parameters (test control factors) investigated included the percentage of cement replaced by silica fume (SF), the percentage of cement replaced by ultra-fine silica powder (SFP), the amount of steel fiber (volume percent), and the amount of polypropylene fiber (volume percentage). The engineering properties of UHPC in the fresh mixing stage and at the age of 7 days were investigated. These properties include freshly mixed properties (slump, slump flow, and unit weight) and hardened mechanical properties (compressive strength, elastic modulus, flexural strength, and splitting tensile strength). Moreover, the effects of the experimental factors on the performance of the tested UHPC were evaluated by range analysis and variance analysis. The experiment results showed that the compressive strength of the C8 mix at the age of 7 days was highest of 111.5 MPa, and the compressive strength of the C1 mix at the age of 28 days was the highest of 128.1 MPa. In addition, the 28-day compressive strength in each experimental group increased by 13%-34% compared to the 7-day compressive strength. In terms of hardened mechanical properties, the performance of each experimental group was superior to that of the control group (without fiber and without additional binder materials), with considerable improvement, and the experimental group did not produce explosive or brittle damage after the test. Further, the flexural test process found that all test specimens exhibited deflection-hardening behavior, resulting in continued to increase carrying capacity after the first crack.