• 한국구조물진단유지관리공학회 논문집
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• 제23권1호
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• pp.102-112
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• 2019

본 연구는 PVA(polyvinyl alcohol) 섬유와 VAE(vinyl acetate ethylene) 분말 폴리머를 사용한 시멘트복합체의 압축 휨강도 와 온도변화에 따른 충격파괴거동을 연구하였다. 충격시험은 $-35^{\circ}C$, $0^{\circ}C$ 및 $35^{\circ}C$의 선정된 온도조건에서 실시하였다. 본 실험에서는 시멘트 복합체와 일반 모르타르에 대한 충격파괴 에너지와 변위, 시간을 얻기 위해 낙하 충격시험기(Ceast 9350)를 사용하여 충격시험을 수행하였다. 강도시험결과, PVA 섬유와 VAE 분말 폴리머의 휨강도는 모두 증가하였다. PVA 섬유보강 시멘트복합체의 경우 재령 28일에서의 압축강도는 약간 감소하였으나, 휨강도는 일반 모르타르 강도보다 24.4% 증가하였다. 낙하 충격시험 결과, PVA 섬유보강 시멘트복합체 시편은 섬유의 가교역할로 인한 균열발생의 억제와 에너지 분산에 의한 미세균열이 발생하였으며, 충격에 의한 배면파괴와 관통에 대하여 억제되었다. 반면 VAE 분말 폴리머 시멘트복합체와 일반 모르타르의 시편은 대부분 큰 균열이나 관통파괴 되었다. 충격하중을 받는 시멘트복합체와 일반 모르타르의 시편은 대부분 국부적인 취성파괴거동을 보이며, PVA 섬유보강에 의한 휨성능 증진으로 인해 충격에 대한 저항성능이 크게 향상되었다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.15-16
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• 2012

The estimation of crack damages is studied using the radio frequency system and tilt switch sensors in RC beams. If load is received on the center of the flexible specimen, sensor housing using cement mortar of the flexible specimen will be destroyed, and these are become to send signals of damages at the radio frequency system connected with tilt switch sensors. This study is fundamental research for the estimation of the damage using tilt switch sensors in RC beams.

• Structural Engineering and Mechanics
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• 제18권1호
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• pp.91-112
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• 2004

Concrete is a composite material and at meso-level, may be assumed to be composed of three phases: aggregate, mortar-matrix and aggregate-matrix interface. It is postulated herein that although non-linear material parameters are generally used to model this composite structure by finite element method, linear elastic fracture mechanics principles can be used for modelling at the meso level, if the properties of all three phases are known. For this reason, a novel meso-mechanical approach for concrete fracture which uses the composite material model with distributed-phase for elastic properties of phases and considers the size effect according to linear elastic fracture mechanics for strength properties of phases is presented in this paper. Consequently, the developed model needs two parameters such as compressive strength and maximum grain size of concrete. The model is applied to three most popular fracture mechanics approaches for concrete namely the two-parameter model, the effective crack model and the size effect model. It is concluded that the developed model well agrees with considered approaches.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2003년도 학술발표논문집
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• pp.375-378
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• 2003

Plastic shrinkage cracking occurs at the exposed surfaces of freshly placed concrete due to consolidation of the concrete mass and rapid evaporation of water from the surface. This so-called shrinkage cracking is a major concern for concrete, especially for flat structural such as pavement, slabs for industrial factories and walls. This study has been performed to obtain the plastic shrinkage properties of hydrophilic fiber reinforced mortar and concrete. The results of tests of the hydrophilic fibers were compared with plain and polypropylene fibers. Test results indicated that hydrophilic poly vinylalcohol fiber reinforcement showed an ability to reduce the total crack area and maximum crack width significantly (as compared to plain and polypropylene fiber reinforcement).

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.207-211
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• 2006

This paper presents an experimental study on the repair performance of sprayed engineered cementitious composites(ECC) serving as a repair material. Sprayable ECC, which exhibit tensile strain-hardening behavior in the hardened state and maintain sprayable properties in the fresh state, have been developed by using a parallel control of micromechanical design and rheological process design. The effectiveness of sprayable ECC in providing durable repaired structures was assessed by spraying the ECC and testing them for the assessment. The experimental results revealed that, when sprayed ECC were used as a repair material, both load carrying capacity and ductility represented by the deformation capacity at peak load of the repaired flexural beams were obviously increased compared to those of commercial prepackaged mortar(PM) repaired beams. The significant enhancement in the energy absorption capacity and tight crack width control of the ECC repair system treated with wet-mix spraying process suggests that sprayed ECC can be effective in extending the service life of rehabilitated infrastructures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.537-540
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• 2003

The effects of substituting cement with fly ash(10%, 15%, 20%) and different fiber addition(polypropylene, cellulose, poly vinyl alcohol), on the control of microcrack and enhanced durability performance of face slab concrete in CFRD was studied experimentally It was conducted experiments of plastic shrinkage of mortar and concrete, and drying shrinkage of concrete. Also, durability test were carried out the chloride permeability, abrasion resistance and freeze-thaw repetition. Through the experimental results, it was concluded that ploy vinyl alcohol fiber containing concrete was the most effective mixture in control of cracking and durability.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.551-556
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• 1996

It is the aim of this study to introduce the performence and application of new repair system for the concrete pier by durability failure caused frost damage. The elementary performance of this repair system is as follows (1) All the layer in the repair system are cement based, same with the mother con'c. (2) This repair use SBR admixture. (3) This cement and mortar powder for this repair system are premixed and ready to adding admixture at the job site.

• 콘크리트학회논문집
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• 제16권3호
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• pp.391-396
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• 2004

소성수축 균열은 경화전 콘크리트의 노출된 표면에서 과도한 수분 증발로 인하여 발생된다. 이러한 소성수축 균열은 특히 도로, 슬래브 및 옹벽 등과 같은 넓은 표면적을 가진 콘크리트 구조물에서 발생하는 가장 큰 문제 중에 하나이다. 본 연구에서는 PVA섬유보강 모르타르 및 콘크리트의 소성수축 특성과 투수성능을 파악하기 위해 실험을 실시하였다. 그 결과 PVA섬유보강 시멘트복합체는 일반 시멘트 복합체 및 폴리프로필렌섬유보강 시멘트 복합체와 비교하여 최대 균열 폭 및 총 균열 면적에 효과적으로 감소하였다. 또한 투수성 실험결과 PVA섬유보강 시멘트 복합체는 폴리프로필렌섬유보강 시멘트 복합체보다 더 낮은 투수성을 나타내었다.

• International Journal of Concrete Structures and Materials
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• 제8권1호
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• pp.83-97
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• 2014

This paper presents the results of an investigation aimed at developing reinforced concrete beams consisting of precast permanent U-shaped reinforced mortar forms filled with different types of core materials to be used as a viable alternative to the conventional reinforced concrete beam. To accomplish this objective, an experimental program was conducted and theoretical model was adopted. The experimental program comprised casting and testing of thirty beams of total dimensions $300{\times}150{\times}2,000mm$ consisting of permanent precast U-shaped reinforced mortar forms of thickness 25 mm filled with the core material. Three additional typical reinforced concrete beams of the same total dimensions were also cast to serve as control specimens. Two types of single-layer and double-layers steel meshes were used to reinforce the permanent U-shaped forms; namely welded wire mesh and X8 expanded steel mesh. Three types of core materials were investigated: conventional concrete, autoclaved aerated lightweight concrete brick, and recycled concrete. Two types of shear connections between the precast permanent reinforced mortar form and the core material were investigated namely; adhesive bonding layer between the two surfaces, and mechanical shear connectors. The test specimens were tested as simple beams under three-point loadings on a span of 1,800 mm. The behavior of the beams incorporating the permanent forms was compared to that of the control beams. The experimental results showed that better crack resistance, high serviceability and ultimate loads, and good energy absorption could be achieved by using the proposed beams which verifies the validity of using the proposed system. The theoretical results compared well with the experimental ones.

• Journal of Microbiology and Biotechnology
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• 제22권11호
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• pp.1568-1574
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• 2012

Microbiological calcium carbonate precipitation (MCCP) has been investigated for its ability to improve the durability of cement mortar. However, very few strains have been applied to crack remediation and strengthening of cementitious materials. In this study, we report the biodeposition of Bacillus subtilis 168 and its ability to enhance the durability of cement material. B. subtilis 168 was applied to the surface of cement specimens. The results showed a new layer of deposited organic-inorganic composites on the surface of the cement paste. In addition, the water permeability of the cement paste treated with B. subtilis 168 was lower than that of non-treated specimens. Furthermore, artificial cracks in the cement paste were completely remediated by the biodeposition of B. subtilis 168. The compressive strength of cement mortar treated with B. subtilis 168 increased by about 19.5% when compared with samples completed with only B4 medium. Taken together, these findings suggest that the biodeposition of B. subtilis 168 could be used as a sealing and coating agent to improve the strength and water resistance of concrete. This is the first paper to report the application of Bacillus subtilis 168 for its ability to improve the durability of cement mortar through calcium carbonate precipitation.