Ductile Fiber Reinforced Cementitious Composite Research Articles

The utilization of active recycled powder from various construction wastes in preparing ductile fiber-reinforced cementitious composites: A case study

This work studies the feasibility of using recycled powder (RP) from construction waste to prepare fiber-reinforced cementitious composites (FRCC). The activity index of recycled powder from various construction wastes is 73.5-82.6% when RP particle size is lower relative to cement, and RP can be used as alternative binder in cementitious composites. The micro structure of RP is irregular, and the added RP decreases the hydration products and matrix strength of its prepared cementitious composites. The flexural load and displacement of RP-prepared FRCC increase with increasing dosage of PVA fiber. The utilized RP decreases the ultimate flexural load of FRCC, while increasing the ultimate flexural displacement. A good strain-hardening behavior occurs when high-volume RP incorporates, and multiple cracks form and distribute on the surface of RP-prepared FRCC; moreover, the decreased RP particle size improves the strain-hardening characteristic of its newmade FRCC. Keeping the substitution rates of fly ash and RP are the same, the ultimate flexural displacement and load of FRCC including RP are lower and higher than those of FRCC including fly ash, respectively. The utilized RP reduces the compressive strength of prepared FRCC, but the flexural strength to compressive strength ratio increases with increasing RP replacement ratios in FRCC. The addition of RP increases the toughness index of FRCC by 4.2-14.1% relative to FRCC without RP.

Control of Tensile Behavior of Ultra-High Performance Concrete Through Artificial Flaws and Fiber Hybridization

Ultra-high performance concrete (UHPC) is one of the most promising construction materials because it exhibits high performance, such as through high strength, high durability, and proper rheological properties. However, it has low tensile ductility compared with other normal strength grade high ductile fiber-reinforced cementitious composites. This paper presents an experimental study on the tensile behavior, including tensile ductility and crack patterns, of UHPC reinforced by hybrid steel and polyethylene fibers and incorporating plastic beads which have a very weak bond with a cementitious matrix. These beads behave as an artificial flaw under tensile loading. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the tensile behavior including tensile strain capacity and cracking pattern of UHPC investigated in this study can be controlled by fiber hybridization and artificial flaws.

리브를 갖는 FRP 판과 고인성섬유보강콘크리트로 이루어진 합성보의 파괴거동에 대한 실험적 연구

고인성섬유보강콘크리트는 기존의 콘크리트에 비해 인성을 크게 개선한 재료로써, 콘크리트 구조물의 여러 분야에 적용 가능한 건설 신재료로 평가되고 있다. 본 연구에서는 고인성섬유보강콘크리트와 리브를 갖는 FRP 판을 인장 보강재 및 영구거푸집으로 활용한 합성보의 파괴거동에 관한 실험을 실시하였다. 비교를 위해 일반콘크리트와 PVA계열인 RF4000과 PP계열인 PP-macro의 섬유를 사용하였으며, 각각 RF4000+RSC15, PP-macro+RSC15를 혼입하여 합성보를 제작하여 실험하였다. FRP 판에 잔골재를 미부착한 경우는 보의 중앙에 발생한 휨 균열이 크게 벌어지면서 FRP 판과 콘크리트가 미끄러짐에 의한 파괴형태를 보여주고 있음으로 잔골재 부착은 필수적 사항이라 판단되며, 파괴모드에 대한 섬유보강재의 영향은 크지 않은 것으로 판단된다. FRP 판에 잔골재를 부착한 실험 결과는 1200, 2000mm 모두 콘크리트와 FRP 사이에 충분한 부착이 형성되었다. 일반콘크리트보다 섬유보강재를 혼입한 경우 최대 하중이 높게 나타났고, 그 중 PP계열의 섬유보강재를 혼입한 경우 최대 하중이 가장 높게 나타났다. 균열이 섬유보강재에 의해 지연되면서 FRP 리브와의 합성작용에 의해 발생한 것으로 판단된다. DFRCC (ductile fiber reinforced cementitious composites), which are a significantly improved ductile material compared to conventional concrete, were evaluated as a new construction material with a high potential applications to concrete structures for a range of purposes. In this study, experiments on the failure behavior of composite beams with a DFRCC and FRP (fiber reinforced polymer) plank with a rib used as permanent formwork and tensile reinforcement were carried out. A normal concrete and a fiber reinforced concrete with PVA series of RF4000 and the PP series of PP-macro were used for comparison, and each RF4000+RSC15 and PP-macro+RSC15 was tested by producing composite beams. The experimental results of the FRP plank without a sand coating showed that sliding failure mode between the FRP plank and concrete started from a flexural crack at the beam center; therefore it is necessary for the FRP plank to be coated with sand and the effect of the fiber to failure mode did not appear to be huge. The experiment of the FRP plank with a sand coating showed that both 1200mm and 2000mm allowed sufficient bonding between the concrete and FRP plank. The maximum load of the fiber reinforced concrete was higher than that of normal concrete and the case which a series of PP fiber was mixed showed the highest value. The crack latency caused by the fibers led to composite action with a FRP rib.

고인성 섬유 시멘트 복합재료를 사용한 RC보의 전단보강효과

This paper presents the results of experimental investigations on the shear failure behaviors of reinforced concrete beams using ductile fiber reinforced cementitious composite (DFRCC). Total 10 RC beams of 150x300x1,000mm size were tested by 4-point bending under the displacement control. The main parameters of the experiment are surface treatment by grinding and preloading to the cracking point in the repair process. The load-displacement curves, diagonal tension cracking load, flexural cracking load, and shear strength were obtained. The test results showed that the DFRCC can be used effectively for restoring the shear strength approximately 99% to the original value under the condition that the appropriate thickness and surface treatment like grinding are assured. For further research, the specimens taken from real deteriorated structures will need to be tested after being repaired with DFRCC.

Comparative deflection hardening behavior of short fiber reinforced geopolymer composites

This study evaluates the behavior of a recently developed ductile fiber reinforced geopolymer composite (DFRGC) exhibiting deflection hardening and multiple cracking behavior in flexure employing four different activator combinations including two Na-based and one K-based activator solutions, and one Ca-based activator combination in the form of powder. Randomly oriented short poly vinyl alcohol (PVA) fibers (2% v/v) were used to reinforce the relatively brittle low calcium (Class F) fly ash-based geopolymer matrix. The matrix and composite properties of the developed fly ash-based DFRGCs including workability of the fresh matrix, density, compressive strength, matrix fracture properties comprising elastic modulus, fracture toughness and composite crack tip toughness, and flexural behavior were evaluated. A reference ductile fiber reinforced cementitious composite (DFRCC) with water to cement ratio corresponding to the activator solution to fly ash ratio of the DFRGCs was also made for comparison. Experimental results revealed that all DFRGCs, regardless of their type of activator combinations, exhibited deflection hardening behavior accompanied by multiple fine cracks in bending. The DFRGC-Na-1 composite exhibited superior deflection capacity, matrix fracture properties, compressive and flexural strengths with significantly enhanced composite ductility and toughness.

Freeze-thaw influence on the flexural properties of ductile fiber-reinforced cementitious composites (DFRCCs) for durable infrastructures

Abstract Ductile fiber-reinforced cementitious composites (DFRCCs) are innovative cementitious materials characterized by multiple cracking and pseudo strain-hardening behavior under static flexure . This paper investigates the effects of freeze-thaw cycles, and water-to-binder ratio (W/B) as well as reinforcing fiber combination on flexural properties and cracking procedure of DFRCC prismatic specimens. The DFRCC materials used in the present study are reinforced with hybrid polyvinyl alcohol (PVA) and ultra-high molecular weight polyethylene (PE) at the 1.5% volume fraction. These DFRCC materials were tested for modulus of rupture (MOR), relative dynamic modulus of elasticity, and change in mass. The test results for freezing and thawing actions within 300 cycles indicate that freeze-thaw cycles have little effect on the MOR of the DFRCC materials, whereas freeze-thaw cycles have a negative effect on multiple cracking behavior and deformation capacity of DFRCC prismatic specimens under flexural loadings. The results of durability tests show that the DFRCC specimens remain durable after 300 cycles of freezing and thawing actions.

Optimal Design of DFRCC Subjected to Fatigue Loading

This paper describes the optimal design of ductile fiber reinforced cementitious composite (DFRCC) under fatigue loading. First of all, fatigue tensile experiments of the DFRCC under constant strain amplitude were conducted, and the degradation of bridging stress was measured. The test results were employed to verify the micromechanics-based theoretical model developed in this research. The model accounts for the loss of fatigue ruptured fibers of which fatigue rupture is based on S-N relationships. According to the parametric study from the theoretical model, we found that the optimal choice of design variables, such as fiber length, is varied according to the maximum strain level and the number of cyclic loading. Therefore, it is required to design DFRCC optimally under given loading conditions to make the most of its excellent material properties and the developed model enables such a design.

Strengthening effects of DFRCC layers applied to RC flexural members

Abstract Ductile Fiber Reinforced Cementitious Composite (DFRCC) features a superior strain capacity of 5–6% under tensile loading. However, the strengthening effect of DFRCC on the flexural performance of RC beams is not clearly understood at present. In this study, we numerically investigate the DFRCC strengthening effect as applied to the tension region of RC beams. More specifically, numerical simulations are carried out for four-point bending RC beams strengthened with a cover thickness of DFRCC and with twice the cover thickness at the bottom tension section of the composite beam. To determine the effects of strain capacity and the strain-hardening slope of DFRCC, numerical simulations are carried out with DFRCC strain capacities ranging from 1% to 5%. From these studies, it is shown that the load carrying capacity and displacement at failure are influenced by the strain capacity and strain-hardening slope of DFRCC, but not to a significant degree. DFRCC strengthening on a tension zone can reduce both stress levels and stress concentrations in the reinforcement and can reduce crack width. It also can delay flexural failure of the structure due to the damage-tolerant behavior of DFRCC.

Mechanical Properties of Ductile Fiber Reinforced Cementitious Composites for Rehabilitation on Concrete Structures

Mechanical Properties of Ductile Fiber Reinforced Cementitious Composites for Rehabilitation on Concrete Structures

Investigation of the strengthening effect of DFRCC applied to plain concrete beams

One of the most important characteristics of Ductile Fiber Reinforced Cementitious Composite (DFRCC) is its strain hardening behavior up to 5–6% strain under tensile loading. In this study, the strengthening effect of DFRCC, applied to the tension region of plain concrete beams, is both numerically and experimentally examined. More specifically, 10%, 20%, and 30% of the beam height are replaced with DFRCC to measure the strengthening effect of the composite beam. From four-point bending tests and numerical simulations, the load–deflection behaviors are investigated and compared. To assess the effect of ultimate tensile strength, strain capacity and strain hardening slope of DFRCC, numerical simulations are carried out with DFRCC strain capacities ranging from 1% to 5%. From these studies, it is shown that DFRCC significantly contributes to the deflection capacity, load carrying capacity and failure modes of concrete beams.

Shear capacity and failure behavior of DFRCC repaired RC beams at tensile region

Many shear dominant structural members in existing concrete structures have been evaluated as below serviceable standard requiring strengthening and/or repair. In order to repair these aged reinforced concrete (RC) structures, a section replacement method of removal and replacement of old concrete and/or steel reinforcements of damaged sections with new concrete and/or steel reinforcements are commonly used. However, this repairing method is used without understanding the complicated structural behavior such as shear behavior of RC structures. Also, the materials commonly used for repairing are concrete and cement mortar. In order to implement the material superiority of newly developed cement based material and to complement the disadvantages of cement-based construction materials such as brittleness of failure, Ductile Fiber Reinforced Cementitious Composite (DFRCC), a high performance cementitious composite with superior strain capacity, is currently being used as a repair material. However, the composite behavior between old substrate and new repair material is not clearly understood at present. In order to effectively apply DFRCC as repairing material on RC structure, the interface, the weakest part in the repaired system where most failures occur, must be studied in depth. In this research, the composite behavior of a RC flexural member repaired using the superior tensile capacity of DFRCC on the tensile face of a RC specimen is studied. Two types of DFRCC repaired RC specimens are tested, one is without shear stirrups and the other is with shear stirrups. By comparing these two types of DFRCC repaired specimens, the failure mechanism and interface debonding behavior as well as repairing capacity can be effectively studied.

Tensile Characteristics Evaluation Method for Ductile Fiber-Reinforced Cementitious Composites

This paper presents a brief overview of the tensile test methods for concrete and cementitious composites. Comparisons of uniaxial tension test results for a round robin test conducted as part of a project of the Japan Concrete Institute Technical Committee (JCI-TC) for Ductile Fiber-Reinforced Cementitious Composites (DFRCC) are introduced. Four types of tensile test methods for four types of DFRCC were used in this round robin test. The results differ according to the testing method and compacting direction of DFRCC. The relationships between the tensile test results and tensile characteristics calculated from bending test results are discussed. The possibility of establishing a standard test method for the evaluation of the tensile characteristics of DFRCC has been discussed by the Japan Concrete Institute Standard Committee. This discussion was based on the report of the JCI-TC and the results of the round robin test. Items that were discussed in further detail were (a) difficulties of uniaxial tension test as a standard test method, (b) treatment of DFRCC that does not have a strain hardening branch in tension, (c) adaptability of strain-based evaluation for cracked materials, and (d) relationship between uniaxial tensile characteristics and bending characteristics. The Standard Committee proposed the standard test method using the 4-point bending test to obtain bending moment–curvature curves. An evaluation method for the tensile strength and ultimate strain of DFRCC was added as an appendix of non-mandatory information. This method is considered to be one of the evaluation methods for the tensile characteristics of DFRCC.

Experimental Response of Precast Infill Panel Connections and Panels Made with DFRCC

This paper describes the results of an experimental investigation of an infill system that utilizes precast ductile fiber reinforced cementitious composite (DFRCC) panels in lieu of traditional materials. The system is intended for use as a retrofit strategy in steel framed hospital structures. Bolted connections are utilized both between individual panels and to the frames, allowing the system to be moved or altered in the event of changes in facility use. Results from laboratory tests of panel connections and panels are presented. The connection tests studied the effect of bolt orientation with respect to applied load, the effect of the DFRCC surface condition within the connection, and time-dependent bolt tension loss. The connection tests demonstrated the viability and the capacity of the proposed connections. DFRCC panels were tested to evaluate the cyclic load-displacement response and energy dissipation in the panels with various panel geometries, panel reinforcements and DFRCC materials. The panel tests also demonstrated the viability of the connection system used. Selected panel test results are presented here, indicating the variation in stiffness and energy dissipation possible with different panel reinforcement.

Corrosion Durability and Structural Response of Functionally-Graded Concrete Beams

This paper reports the results of an experimental program on the effectiveness of a Ductile Fiber Reinforced Cementitious Composite (DFRCC) material, which exhibit strain-hardening and multiple-cracking bahavior under flexural loadings, in retarding the corrosion of steel in Reinforced Concrete (RC) beams. Based on the collective findings from theoretically-estimated steel losses, rapid chloride permeability tests, pH value tests, as well as structural tests, it was concluded that Functionally-Graded Concrete (FGC) beams, where a layer of DFRCC material was used around the main longitudinal reinforcement, had a noticeably higher resistance against reinforcement corrosion compared to a conventional RC beam. The better performance of the FGC beams was also evident from the absence of any corrosion-induced cracking and the very low tendency of the concrete cover to delaminate as measured by a concrete-embeddable fiber optic strain sensor.

On Engineered Cementitious Composites (ECC)

This article surveys the research and development of Engineered Cementitious Composites (ECC) over the last decade since its invention in the early 1990's. The importance of micromechanics in the materials design strategy is emphasized. Observations of unique characteristics of ECC based on a broad range of theoretical and experimental research are examined. The advantageous use of ECC in certain categories of structural, and repair and retrofit applications is reviewed. While reflecting on past advances, future challenges for continued development and deployment of ECC are noted. This article is based on a keynote address given at the International Workshop on Ductile Fiber Reinforced Cementitious Composites (DFRCC) - Applications and Evaluations, sponsored by the Japan Concrete Institute, and held in October 2002 at Takayama, Japan.

DFRCC Terminology and Application Concepts

This paper is a summary report based on the discussions of the JCI-DFRCC committee. The paper attempts to summarize the terminology related to DFRCCs and the structural advantages and application concepts of DFRCCs. This attempt was made for the purpose of further discussion at the JCI International Workshop on Ductile Fiber Reinforced Cementitious Composites -Application and Evaluation- held in 2002 at Takayama, Japan.