• 한국구조물진단유지관리공학회 논문집
• /
• 제25권4호
• /
• pp.37-45
• /
• 2021

논문은 조적부재에 고인성 복합체를 보강하여 내진보강 가능성을 평가하기 위한 기초연구이다. 고인성 복합체의 섬유 혼입률에 따른 성능을 검토하기 위하여 배합설계에 따라 시험체를 제조하고 유동성능, 압축강도, 휨 강도, 길이변화율 및 직접인장변형률을 측정하였다. 또한, 무보강 조적부재, 고인성 복합체로 보강한 조적부재, 고인성 복합체에 유리섬유 및 와이어 메쉬를 별도 보강한 조적부재를 제작하고 휨 강도와 최대변위를 측정하였다. 고인성 복합체를 보강한 모든 실험체들은 무보강과 비교하여 최대내력이 16배 이상의 효과가 나타났으며 균열 형상을 검토한 결과 에너지소산능력이 우수한 것으로 나타나 내진보강 가능성을 확인하였다.

• Structural Engineering and Mechanics
• /
• 제81권5호
• /
• pp.575-589
• /
• 2022

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 strain-hardening behavior of cementitious composites.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2018년도 추계 학술논문 발표대회
• /
• pp.73-74
• /
• 2018

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.

• Composites Research
• /
• 제20권2호
• /
• pp.21-26
• /
• 2007

이 논문은 합성섬유를 이용하여 포틀랜드 시멘트 모르타르를 보강한 복합재료인 ECC(Engineered Cementitious Composite)의 설계 과정과 건설현장에 이 복합재료를 적용할 수 있도록 시공성을 부여한 연구 내용을 정리하였다. 이 연구에서는 다양한 시공성, 즉 자기충전(self·consolidating)과 스프레이 시공성을 갖는 ECC를 제작하기 위하여 단계적인 재료 개발 방법론을 채택하였다. 우선 마이크로역학(micromechanics)과 안정상태균열이론(steady-state cracking theory)을 이용하여 골재와 섬유를 선정한 후, 굳기 전 재료의 레올로지를 제어하는 방법으로 시공성을 구현하였다. 여기서, 굳기 전 재료의 레올로지를 제어하기 위하여 화학첨가제(chemical admixtures)와 광물첨가재(mineral admixtures)의 양을 소량으로 조절하는 방법을 사용하였다. 이러한 방법을 활용함으로써 굳기 전에는 다양한 시공성을 나타내면서, 굳은 후에는 높은 연성(인장변형경화 거동)을 나타내는 실용적인 ECC 복합재료를 개발하였다.

• Steel and Composite Structures
• /
• 제12권2호
• /
• pp.167-181
• /
• 2012

Ultra high performance cementitious composite material is applied to the design of multifunctional permanent form for bridge pier in this paper. The basic properties and calculating constitutive model of ultra high performance cementitious composite are introduced briefly. According to momental theory of thin-walled shell, the analytical solutions of structural behavior parameters including circumferential stress, longitudinal stress and shear stress are derived for UHPCC thin-walled circular tube. Based on relevant code of construction loads (MHURD of PPC 2008), the calculating parameter expression of construction loads for UHPCC thin-walled circular tube is presented. With geometrical dimensions of typical pier, the structural behavior parameters of UHPCC tube under construction loads are calculated. The effects of geometrical parameters of UHPCC tube on structural behavior are analyzed and the design advices for UHPCC tube are proposed. This paper shall provide a scientific reference for UHPCC permanent form design and UHPCC hybrid structure application.

• Computers and Concrete
• /
• 제30권5호
• /
• pp.339-355
• /
• 2022

The high cost of ultra-high-performance engineered cementitious composite (UHP-ECC) is currently a crucial issue, especially in terms of the polyethylene (PE) fibers use. In this paper, cheap calcium carbonate whiskers (CW) were evaluated on the feasibility of hybrid with PE fibers. Diverse combinations of PE fibers and CW were employed to investigate the multi-scale enhancement on the UHP-ECC performance. A probabilistic-based UHP-ECC tensile strain reliability analysis approach was utilized, which was in general agreement with the experimental results. Furthermore, a multi-dimensional integrated representation was conducted for the comprehensive assessment of UHP-ECC. Results illustrated that CW improved the compressive strength and energy dissipation capacity of UHP-ECC owing to the microscopic strengthening mechanism. CW and PE fiber further promoted the saturated cracking of composite by multi-scale crack arresting effect. In particular, PE1.75-CW0.5 specimen possessed the best overall performance. The ultimate cracking width of PE1.75-CW0.5 group had 98 ㎛, which was 46.18% lower compared to PE2-CW0 group, the 28d compressive strength were slightly improved, the tensile strain capacity was comparable to that of PE2-CW0 group. The results above demonstrated that combinations of PE fiber and CW could significantly enhance the comprehensive performance of UHP-ECC, which was beneficial for large-scale engineering applications.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
• /
• pp.469-472
• /
• 2008

일반적으로 콘크리트는 높은 압축강도에 비해 매우 낮은 휨강도 및 인장강도를 가진 재료지만 고인성 콘크리트의 경우 다량의 섬유를 혼입함으로써 높은 인장강도를 가지는 한편, 균열 발생 후에도 변형경화 현상을 보이며 높은 인성을 가지게 된다. 따라서 이러한 고인성 콘크리트의 인장특성을 평가하기 위해서는 기존 콘크리트의 시험방법과 다른 일축인장시험이 필수적이라 할 수 있다. 그러나 콘크리트의 압축시험에 있어서도 치수, 형상, 단부조건 등의 요인이 변하면 얻어지는 결과가 상이한 상황에서, 시멘트계 재료의 인장시험에서는 재료의 특성상, 섬유의 배향 문제에서부터 섬유길이와 공시체 단면치수의 관계가 결과에 영향을 미치게 된다. 이에 본 연구에서는 시험체 치수 및 시험방법에 따른 고인성 콘크리트의 인장특성을 검토하였고, 시험체 치수가 얇아질수록 섬유배열이 곧게 되어 더 높은 성능을 발휘함을 확인 할 수 있었다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
• /
• pp.313-316
• /
• 2005

In the recent design of high ductile fiber-reinforced cementitious composite ECC, which exhibits tensile strain-hardening behavior in the hardened state, optimizing both processing mechanical properties for specific applications is critical. This study introduced a method to develop useful ECCs in field, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing, while retaining the ductile material properties. To control the rheological properties of the composite, we first determined basic ECC compositon, which is based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of suspensions were, then, mediated by optimizing dosages of chemical and mineral admixtures. The rheological properties altered by this approach were revealed to be effective in obtaining ECC hardened properties, allowing us to readily achieve the desired function of the fresh ECC.

• Structural Engineering and Mechanics
• /
• 제55권5호
• /
• pp.931-951
• /
• 2015

To improve the durability and service life of reinforced concrete column such as bridge piers, an advanced composite column made of Ultra High Performance Cementitious Composites (UHPCC) permanent form is proposed. Based on elasticity plasticity theory, axial compression behavior of the composite column was studied theoretically. The first circumferential cracking load and ultimate limit loading capacity are derived for the composite column. Short composite column compression tests and numerical simulations using FEM method were carried out to justify the theoretical formula. The effects of UHPCC tube thickness on the axial compression behavior were studied. Using the established theoretical model and numerical simulation, the large dimension composite columns are calculated and analyzed with different UHPCC tube thickness. These studies may provide a reference for advanced composite column design and application.

• Composites Research
• /
• 제23권3호
• /
• pp.50-57
• /
• 2010

섬유 보강 시멘트계 복합재료의 성능 예측 및 평가에 있어서 중요한 영향을 미치는 섬유 분포 특성을 정량적으로 평가하기 위해서는 복합재료의 단면 이미지에서 섬유를 정확히 검출하여야 한다. 이 논문은 형광원리를 이용하여 합성섬유를 매트릭스로부터 개별적으로 검출하기 위한 기초 연구로써 섬유 보강 시멘트계 복합재료 중의 하나인 ECC에 일반적으로 사용되는 PVA 섬유, PET 섬유, PE 섬유, 그리고 PP 섬유의 형광특성을 분석하였다. 또한 하이브리드 된 경우 합성섬유들 간의 상대 형광 광도값의 차이를 비교하여 종류별로 구분하기 위한 최적의 파장대를 선정하였으며, 그 파장대에서 두 분류대상을 구별할 수 있는 최적의 경계값을 통계적 방법을 이용하여 산출하였다. 또한 형광 현미경을 이용하여 각 섬유를 촬영하여 상대적인 밝기값을 비교하였다.