CFRP Rebar Research Articles

CFRP Rebar로 보강한 콘크리트 보의 휨 거동

철근의 부식을 해결하기 위해 철근의 대체 재료로 적용 가능한 FRP에 대한 연구의 적용성이 대두되었다. 그러나 취성적인 성질과 탄성계수가 낮은 단점을 가지고 있어, FRP rebar로 보강된 휨 부재의 사용성 평가 즉 처짐에 대한 연구가 필요하다. 본 연구에서는 보강비를 변수로 한, CFRP rebar로 보강된 콘크리트 보의 휨 실험을 수행하였다. 실험 결과, CFRP rebar로 보강된 실험체는 보강비가 증가함에 따라 내력 및 강성이 증가하는 양상을 보였으며, 철근 실험체와 동일한 단면성능을 발휘하기 위해서는 약 1.3배의 보강비가 요구되는 것으로 나타났다. 또한 유효단면2차모멘트에 대한 기존 제안식의 비교 결과, Bischoff & Scanlon이 제안한 식이 가장 정밀해에 가까운 처짐을 예측하였다. To address the problems caused by the corrosion of steel rebar, active research has recently been carried out on members where fiber-reinforced polymer (FRP) is used in place of rebar. As FRP bar is highly brittle and has a low modulus of elasticity, further research is needed on the evaluation of serviceability, in other words on the deflection of flexural concrete members reinforced with FRP rebars. Taking the reinforcement ratio as a variable, this paper analyzes the flexural capacity of concrete beams reinforced with CFRP rebar. The test results of specimens reinforced with CFRP rebar show an increase in stiffness and resisting force along with an increase in the reinforcement ratio. A reinforcement ratio of about 1.3 is needed for the member reinforced with CFRP rebar to show same section property of a steel member. Through a comparison for the value of an effective moment of inertia, the equation suggested by Bischoff & Scanlon predicted values closest to the actual results.

보강섬유의 표면처리에 따른 섬유보강 고강도콘크리트와 CFRP 보강근의 부착특성

본 연구에서는 CFRP 보강근과 고강도콘크리트의 부착강도에 미치는 보강섬유의 표면처리 방법의 효과를 평가하였다. 표면을 친수성 물질로 코팅된 구조용 PVA 섬유 및 기하학적 변형으로 변형된 절곡형 폴리올레핀계 구조용합성섬유를 보강섬유로 사용하였다. 섬유의 표면처리 방법에 따른 고강도콘크리트의 강도특성을 평가하기 위하여 압축강도 실험을 실시하였다. 고강도콘크리트와 CFRP 보강근 사이의 부착특성은 직접 부착강도시험을 의하여 평가하였다. 시험 결과는 섬유의 표면처리 방법은 고강도콘크리트와 CFRP 보강근 사이의 부착거동에 영향을 미쳤다. 또한 고강도 콘크리트에 섬유의 첨가는 할렬균열의 발생 및 성장을 조절함으로써 고강도콘크리트와 CFRP 보강근 사이의 부착거동, 부착강도 및 상대부착강도의 증가시켰다.

Flexural behaviour of MRBC beams (multi-reinforcing bars concrete beams), promoting the use of FRHPC

High performance concrete reinforced by short metallic fibers has been recently developed. These materials are of particular interest for civil engineering thanks to their high compression performance and to their enhanced durability. The addition of short metallic fibers provides the opportunity to obtain a more ductile material with more resistance to tension. Nevertheless, the use of reinforcement is still necessary for structural applications [1]. This paper presents results obtained on SFRHP concrete beams using mixed steel–CFRP rebar. Five beams with steel rebar or mixed CFRP–steel reinforcement were designed according to Eurocode 2. The goal is to optimize the reinforced concrete (RC) beam design by combining different reinforcement types in order to use the fiber reinforced HPC most efficiently. The first beam specimen uses a non-fibrous HPC and constitutes a reference for comparison. The tests carried out upon an FRHPC beam and reinforced by steel reinforcing bars allow the assessment of the short fiber’s effect against the bending and the shearing stresses. It is shown that the presence of short metallic fibers in the concrete does in fact contribute to the equilibrium of the beam. The sum of the internal moments in the tensile zone is increased by 10%. For the last three beams, the effect of incorporating carbon fiber reinforced polymer rebar mixed with usual steel reinforcement is studied. It is shown that beams using mixed CFRP–steel rebar are able to achieve a bending stiffness comparable to the beams reinforced by traditional steel reinforcement (in the elastic stage). A 50% increase in the failure load is observed.

Modelling of Moisture Sorption by Cfrp Rebars with Vinylester Matrix

The results of experimental investigation and modelling of moisture sorption by CFRP rebars and vinylester matrix are presented. Experimental values of the rebar diffusion coefficients essentially differ from those predicted using structural approach. Essential anisotropy of sorption process in longitudinal and transverse directions is observed. Quasi three phase model is suggested for description of the CFRP rebar sorption. The model is based on consideration of sorption process of the diffusion character in the composite consisted of two phases: resin and microplastic, which includes fibres and fibre-resin interphase. The suggested model describes the experimental sorption data quite satisfactorily and explains high anisotropy effect.

콘크리트 보강용 FRP 보강근의 내구성 설계를 위한 환경영향계수의 제안

The corrosion of steel rebars has been the major cause of reinforced concrete deterioration. FRP(Fiber-reinforced polymer) rebar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP rebar is prone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Therefore, the USA, Japan, Canada, UK. etc are using environmental reduction factor. Although difference design guidelines were drawn in many, including USA, Japan, Canada, UK etc, recommendations and coefficients that could take into account the long-term behavior of FRP reinforcement were not well defined. This study focuses on recommendation of environmental reduction factor of FRP rebar. Environment reduction factor were decided using durability test result. FRP rebars were subjected to twelve type of exposure conditions including alkaline solution, acid solution, salt solution and deionized water etc. The water absorption behavior was observed by means of simple gravimetric measurements and durability properties were investigated by performing tensile, compressive and short beam tests. Based on the experimental result, environmental reduction factor of hybrid FRP rebar(A), and (C) and CFRP rebar was decided as 0.85. Also, hybrid FRP rebar(B) and GFRP rebar were decided as 0.7 for the environmental reduction factor