Structural Synthetic Fiber Research Articles

Influence of Macro Synthetic Fibers on the Flexural Behavior of Reinforced Concrete Slabs with Opening

In this study, the flexural behavior of one-way RC slabs after adding the macro discontinuous structural synthetic fiber (DSSF) under different opening sizes is investigated. Based on the previously conducted research, the 0.55 DSSF percentage was utilized since it was reported as the optimum value for enhancing the slab's performance. Moreover, further increases in the DSSF percentages proved to have the same improvement obtained by the 0.55%. Experimental testing was carried out on sixty-four one-way slabs under the effects of square opening existence (with or without), heat levels of 20, 200, 400, and 600 °C, and opening sizes of 100, 150, and 200 mm. The opening was created at the maximum bending moment region at the slab's center between the two loading points. For comparison purposes, the tested slabs were divided into main groups based on the DSSF existence. It was found that the resulted improvement by adding the DSSF material is affected by the size of the created opening. Furthermore, results revealed an increasing linear relationship between the applied load and the deflection and between the longitudinal concrete strain and the steel reinforcement. Besides, duplicating the opening size enhances the ductility index value by a maximum improvement percentage of 13% under an opening size ratio of less than 4.5%, while the improvement percentage becomes less under a further increase in the opening size ratio. Moreover, initial stiffness is more affected by increasing the temperature values twice those recorded for the yielding stiffness. Doi: 10.28991/CEJ-2022-08-09-016 Full Text: PDF

Mechanical and Durability Properties of Latex-Modified Hybrid Fiber-Reinforced Roller-Compacted Rapid-Set Cement Concrete for Pavement Repair.

This study evaluated the mechanical properties and durability performance of latex-modified hybrid fiber-reinforced roller-compacted rapid-set cement concrete (LMHFRCRSC) for emergency repair of concrete pavement. Experimental parameters included the blend ratio of the hybrid fiber, which comprised natural jute fiber (0–0.2 vol.%) and structural synthetic fiber (0–2 vol.%). The mechanical performance of LMHFRCRSC of various blend ratios was evaluated in terms of compressive, flexural, and splitting tensile strength. Durability assessment included chlorine ion penetration and abrasion resistance measurements. Compressive and flexural strength values of 21 and 3.5 MPa, respectively, were the set targets after 4 h of curing; a compressive strength of 35 MPa, a flexural strength of 4.5 MPa, a splitting tensile strength of 4.2 MPa, and chloride ion penetration of 2000 C or less were required after 28 days of curing. Our test results confirmed that all mix proportions satisfied the target values, regardless of the blend ratio of the hybrid fiber. Specifically, the mechanical performance of the concrete improved as the blend ratio of the structural synthetic fiber increased. With regard to durability, a greater amount of jute fiber, a hydrophilic fiber, enhanced the concrete’s durability. Additionally, incorporating jute fiber of 0.6 kg/m3 provided excellent chlorine ion penetration resistance. The optimal blend ratio for the hybrid fiber was natural jute fiber at 0.6 kg/m3 and structural synthetic fiber at 13.65 kg/m3 (mix: J0.6 + P13.65); with this mix proportion, a chloride ion penetration amount of 1000 C or less and maximum mechanical performance were achieved.

Effect of fiber type and content on the mechanical properties and shrinkage characteristics of alkali‐activated kaolin

AbstractAn experimental study was carried out to evaluate the effect of several fibers on the mechanical properties, drying shrinkage, and microstructural characteristics of alkali‐activated kaolin binders. Four different types of fibers were evaluated in this study: polypropylene (PP) fiber, discontinuous structural synthetic (DSS) fiber, brass‐coated steel (BCS) fiber, and hooked steel (HS) fiber. The fibers were added to the alkali‐activated kaolin at a volume fraction of 0%, 0.5%, 1%, and 1.5%. The experimental results revealed that the compressive strength of alkali‐activated binder increased by about 60% when 1% of PP fiber is added, whereas the addition of HS fiber substantially enhanced the flexural strength (more than 200% when 1.5% fiber volume content is added). BCS and HS fibers were found to more effective compared to PP and DSS fibers in maintaining the binder integrity prior to high temperatures exposure. All fiber‐reinforced alkali‐activated composites yielded lower drying shrinkage (≤450 microstrains), where HS fiber was found to effectively prevent the shrinkage of the binder (≤60 microstrains). The microstructural investigation revealed good interfacial bonding between the alkali‐activated binder and the fibers.

Fiber‐reinforced mortar for secondary roofing slabs

AbstractThis study investigates the feasibility of completely replacing traditional mesh reinforcement with non‐corrodible fiber‐reinforced mortar (FRM) in secondary roofing slabs. Patch‐load tests were conducted on 36 secondary roofing slabs containing mesh reinforcement, FRM with polyester or structural synthetic fibers only, or a combination of these. The ferrocement specimens carried the highest load but failed due to the sudden rupture of the steel mesh. The slabs with only polyester fibers experienced a brittle failure with low load‐carrying capacity. On the other hand, the specimens containing only structural synthetic fibers achieved the requisite residual load‐carrying capacity for secondary roofing slabs and also exhibited enhanced ductility through high flexural toughness, thereby sustaining large deflections. This study demonstrates that slabs with structural synthetic fibers alone are sufficient for practical application. The results from the test program were analyzed using yield line theory, based on the stress–strain relation for FRM recommended by the fib Model Code 2010. The first crack and residual load‐carrying capacities of the slabs were estimated with reasonable accuracy, thereby providing an analytical basis to predict the behavior of secondary roofing slabs.

Effect of macro-synthetic structural fibers on the flexural behavior of concrete beams reinforced with different ratios of GFRP bars

Fiber reinforced polymer (FRP) bars are increasingly used as internal reinforcement in concrete structures for mitigating the corrosion problems associated with steel reinforcement. However, its wide spread use in construction is limited by the parameters such as lack of awareness/usage, brittle failure mode, high initial cost, availability of comprehensive guidelines and test data on its long term effectiveness. The use of macro-synthetic structural fibers is explored in this study for improving the post-cracking, and deformability characteristics of glass FRP (GFRP) reinforced concrete beams. In total, eighteen full-scale RC beams with and without structural synthetic fibers are tested under flexure. The test specimens include: (i) control beams with steel reinforcement, (ii) GFRP bar RC beams without macro-synthetic fibers, and (iii) GFRP RC beams with 0.35%, 0.7%, and 1.0% volume of macro-synthetic fibers. The effect of fiber addition on cracking, stiffness and deformability characteristics of GFRP RC beams with different longitudinal reinforcement ratios (0.7% and 2.0%) is investigated. Experimental results reveal that the addition of fibers significantly improved the post-cracking response. Moreover, the crack widths reduced significantly at service loads with the increase in fiber dosage. Addition of 1% fibers helps in enhancing the deformability of GFRP RC beams and converts the failure from brittle flexure-shear to ductile flexure mode with higher pseudo-ductility. Analytical calculations of deflections showed a close correlation with the test results.

The influence of hand hole on the ultimate strength and crack pattern of shield tunnel segment joints by scaled model test

With the shield tunnel going deeper and deeper, the circumferential axial force becomes the governing factor rather than the bending moment. The hand hole acts as a weak point and initial damage in the segment joint especially when the circumferential axial force is extremely high. Despite the wide application of steel fiber or synthetic fiber in the tunneling, limited researches focus on the structural responses of segment joint with macro structural synthetic fiber (MSSF). In this paper, a 1:2 reduced-scale experiment was conducted to study the structural performance of the segment joint with different types of hand holes under ultra-high axial force. Special attention is paid to failure mode and structural performance (bearing capacity, deformation, cracking, and toughness). Moreover, segment joints with MSSF are also tested to evaluate the effects of MSSF on the failure mode and structural performance of the segment joints. The experiment results show that the hand hole becomes the weakest point of the segment joint under ultra-high axial force. A \ /-type crack pattern is always observed before the final failure of the segment joints. Different types and sizes of the hand hole have different degree of influences on the structural behavior of segment joints. The segment joint with MSSF shows higher ultimate bearing capacity and toughness compared to segment joint with common concrete. Besides, the MSSF improves the initial cracking load and anti-spallling resistance of the segment joint.

Bond-slip behavior between fiber reinforced concrete and CFRP composites

Abstract The influence of discontinuous structural synthetic fibers (DSSF) on the bond-slip behavior between concrete and carbon fiber reinforced polymer (CFRP) composites was investigated using a double-shear pull-off test. The tested blocks were divided into three groups depending on the DSSF content. The CFRP composites were bonded to the blocks (with and without a CFRP anchoring strip) in three lengths (Lf): 50, 75, and 100 mm. For each Lf, three widths (bf) were used: 50, 75, and 100 mm. The results showed that: addition of DSSF to concrete slightly enhances the bond strength with CFRP composites, the pull-off force and slip increase with the increase in the CFRP bond length and width, and the use of CFRP anchorage strip improves the bond characteristics. The failure mode and bonding interface showed that as the DSSF increases, more concrete was attached to the peeled CFRP composite indicating that the concrete surface gets stronger.

Acoustic Emission Characterization of Hybrid Fiber Reinforced Cellular Concrete Under Direct Shear Loads

Acoustic emission (AE) is employed in this study to understand the failure process in fiber-reinforced cellular concrete (FRCLC) subjected to direct shear load. Synthetic polyolefin fibers are used as reinforcement in FRCLC blocks, and their influence on the shear-fracture process is investigated. AE parameters are investigated to assess the effectiveness of fibers in performance improvement of shear strength and toughness of CLC. In total, 24 CLC specimens are tested under direct shear. Effect of fiber dosage and combinations of macro and microfibers are considered as study parameters. Shear crack bridging effect of fibers during the process of shear-slip is investigated. Test results indicate that AE and shear fracture energy increase with increasing fiber dosage. It is observed that discontinuous structural synthetic fibers significantly improve the ultimate shear strength, residual strength, ductility, stiffness, and toughness of CLC. Also, the structural synthetic fibers reduced the shear crack width and shear-slip of CLC. AE parameters such as counts, energy, and 3D-crack source location are presented to illustrate the role of different fiber dosages on the direct shear response. Shear crack location was found to be consistent with the observed failure planes in the specimens. AE data analysis reveals that the number of mode II type events increased with increasing fiber dosage due to increased fiber pullout. Besides, mode I type events also increased as the failure mode changed from a single split crack to distributed cracking.

Behavior of macro synthetic fiber concrete beams strengthened with different CFRP composite configurations

Thirty-two normal-strength macro discontinuous structural synthetic fiber (DSSF) concrete beams were constructed and tested. In order to determine the optimum dosage of DSSF, eight of the beams were prepared with various dosages of DSSF, while the rest beams were prepared with an optimum DSSF dosage of 0.55% and with various carbon fiber reinforced polymer (CFRP) sheet lengths and widths. The tested parameters include mode of failure, load versus mid-span deflection response, ultimate deflection, ultimate load capacity, energy absorption, stiffness, performance factor, energy absorption ductility index, displacement ductility index, and concrete and CFRP sheet strains. The addition of DSSF and CFRP sheet enhanced most of the investigated parameters by providing internal and external crack arresting mechanisms, respectively, and enhancing the post-cracking ductility after reaching the extreme load capacity.

Behavior of plain concrete beams with DSSF strengthened in flexure with anchored CFRP sheets—Effects of DSSF content on the bonding length of CFRP sheets

In this study, the behavior of the anchored carbon fiber reinforced polymer (CFRP) plain concrete beams with various dosages of macro discontinuous structural synthetic fiber (DSSF) were investigated. Seventy two plain concrete beams were casted and tested. The investigated parameters in this study are the dosages of DSSF, length of CFRP sheets, and with and without CFRP anchorage sheets. Therefore, the feasibility of using macro synthetic fibers and anchored CFRP sheets for enhancing the behavior of plain concrete beams is of enormous interest. The behavior characteristic of each tested beam was evaluated in terms of failure mode, load versus mid-span deflection curve, ultimate load capacity, ultimate deflection, stiffness, energy absorption, performance factor, displacement ductility index, energy absorption ductility index, and CFRP and concrete strain. The tested results reveal a considerable enhancement on the majority of the investigated parameters and show the efficiency of using a combination macro synthetic fibers and anchored CFRP sheets in terms of the behavior characteristic of tested beams. The enhancements were recognized primarily to the efficiency of the used anchored CFRP and macro synthetic fibers in providing external and internal, respectively, cracks arresting mechanism after cracking and even after reaching the ultimate load capacity.

Efficiency of steel and macro-synthetic structural fibers on the flexure-shear behaviour of prestressed concrete beams

The efficiency of steel and structural synthetic fibers on the performance improvement of prestressed concrete (PSC) beams under combined flexure-shear is studied. Results of eleven PSC beams tested at a shear span (a) to depth (d) ratio of five are presented. Discrete steel and macro synthetic structural polyolefin fibers of varying dosages of 0.35%, 0.7% and 1.0% by volume of concrete were used. The effect of fiber addition on overall load – displacement, load- strain, and strain energy absorption capacity of PSC beams is analysed. Other parameters such as shear span to depth ratio (a/d), compressive strength of concrete, prestressing reinforcement ratio were kept constant. The test results portray that the addition of steel fibers stiffens the post cracking response, increases the strain energy absorption capacity more efficiently when compared to macro synthetic fibers (Polyolefin). The failure mode changed from less ductile flexure-shear to more ductile flexure dominant mode at 0.35% and 0.70% volumetric dosage of steel and synthetic fibers, respectively. The strain energy absorption capacity increased by more than 100% at 1.0% fiber addition for both steel and macro-synthetic fibers.

Empirical and NLFEA prediction of bond-slip behavior between DSSF concrete and anchored CFRP composites

A precise bond-slip model between discontinuous structural synthetic fibers (DSSF) concrete and anchored carbon fiber reinforced polymer (CFRP) is of primary importance in the reaching the ultimate strength of CFRP composites as well as the modeling of Reinforced concrete (RC) structures strengthened with CFRP composites. In this paper, a new bond slip model is proposed in terms of DSSF content (0, 3, and 5 kg/m3 equivalent to fiber volume fractions (Vf) of 0%, 0.33%, and 0.55%, respectively), CFRP bonded length (Lf) (50, 75, and 100 mm), CFRP bonded width (bf) (50, 75, and 100 mm), and anchored system (with and without a CFRP anchoring strip width (bfA) of 25 mm and length (LfA) of 150 mm). This proposed model is then assessed using experimental test results on anchored CFRP-DSSF concrete bonded blocks subjected to double-shear pull-off test, existing bond-slip models in the literature, and database of pull tests published by several researchers. After that, the anchored CFRP-DSSF concrete bonded blocks were modeled and analyzed using nonlinear finite element analysis (NLFEA). After realistic validation with the experimental test results, NLFEA was expanded to proposed an expression for the influence of anchored CFRP sheet in terms of bfA (25, 50, 75, and 100 mm) and LfA (100, 125, and 150 mm) on the proposed bond-slip model. The special characteristic of the present study is that the new proposed bond-slip model is based on anchored CFRP composite and DSSF concrete; instead, the existing bond-slip models are based on CFRP composite without anchorage and ordinary concrete. Finally, the proposed bond-slip model is provided an accurate prediction of the large test database of bond strength and corresponding slippage.

Flexural behavior of lightweight concrete beams encompassing various dosages of macro synthetic fibers and steel ratios

In this study, thirty-two lightweight concrete (LWC) beams were casted and tested as simply supported beams under four points’ loading. The investigated parameters were the volume fraction (Vf) of discontinuous structural synthetic fiber (DSSF) and longitudinal steel reinforcement ratio (ρ). The modulus of rupture of structural LWC is low due to the weak lightweight aggregates used. Therefore, the feasibility of compensating for this shortcoming and providing post-cracking toughness characteristics using DSSF is of great interest. The behavior of each beam was evaluated in terms of cracking, failure mode, flexural strength, ultimate deflection, stiffness, toughness, and energy absorption. The results revealed measurable enhancements on majority of the aforementioned performance characteristics of LWC beams can be achieved when adding DSSF at Vf=0.55% and 0.77%. The enhancements were attributed mainly to the effectiveness of the used DSSF in providing internal confinement/cracks arresting mechanism and toughness characteristics after cracking and even after reaching the peak strength. The experimental results of this study compared very well with predicted values using the ACI 318-14 in terms of cracking moment, service load deflection, and moment capacity.

Influence of synthetic fibers on the shear behavior of lightweight concrete beams

Incorporating discontinuous structural synthetic fibers in general enhances the performance of concrete and increases its durability by minimizing its potential to cracking and providing crack arresting mechanism. Synthetic fibers are non-corrosive, alkali resistant, simple to apply, and added in small quantities due to their low density; thus, a substantial number of uniformly distributed fibers are added. In this research, an experimental program was undertaken to investigate the shear behavior of lightweight concrete beams containing discontinuous structural synthetic fibers. The studied parameters include fiber content and shear reinforcement. The tests were conducted under four-point loading in a simply supported span of 0.85 m. The beams were divided into three groups based on shear reinforcement. Group 1 was designed without shear reinforcement, Group 2 with closed vertical stirrups placed at d/4 spacing (where d is the effective depth), and Group 3 with closed vertical stirrups placed at d/2 spacing. Each group contains four identical specimens except in terms of the fiber content: 0, 3, 5, and 7 kg/m3 equivalent to fiber volume fractions of 0%, 0.33%, 0.55%, and 0.77%, respectively. The experimental results showed that the discontinuous structural synthetic fibers improve the ultimate shear strength, ductility, stiffness, and toughness of lightweight concrete beams significantly. Therefore, design codes are encouraged to consider their contribution to shear strength and revise the maximum stirrups spacing when discontinuous structural synthetic fibers are used. The results also showed that addition of discontinuous structural synthetic fibers reduces the crack width of lightweight reinforced concrete beams. The effectiveness of the discontinuous structural synthetic fibers decreases as the stirrups spacing decreases.

Interfacial phenomena in structural polymeric nano-clay synthetic fiber reinforced cementitious composites

This study report improved material characteristics of structural synthetic fiber polymers formed using nanomaterials. We attempted to improve the bond properties using cement-based composites via three-dimensional (3D) synthetic fibers with nano-clay. The properties of the bonds between the structural synthetic fibers with nano-clay and a cementitious matrix were evaluated according to JCI SF-8. Straight, twisted and crimped fibers were used, as well as twisted crimped fibers. Tests for straight fibers and structural synthetic fibers without nanomaterials were also carried out for comparison.We found that bonding with the cement matrix was improved as the shape of the fiber became more complex. Compared with the bond strength of the straight structural nano-clay synthetic fiber, use of twisted, crimped, and twisted crimped fiber increased the bond strength by 93%, 477%, and 393%, respectively. Interfacial toughness increased by 106%, 15% and 47%, respectively. The straight structural nano-clay synthetic fibers improved the bond properties by 150% compared with no added nanomaterials. Scanning electron microscope (SEM) observations of the bond properties revealed that the mechanism for the improved bond resistance was via surface damage of the fiber following pullout.

Manufacture and properties of a structural synthetic polymer fiber-containing nanoclay for concrete reinforcement

This study established the optimum conditions for structural synthetic polymer fiber manufacture to make a fiber having excellent tensile strength. Two polypropylene resins, differing in their melt indices, and four different draw ratio values were investigated, that is, 6, 7, 8, and 9, to establish which had the greatest influence on tensile strength. The tensile strength and the modulus of elasticity were measured for the manufactured fibers. In addition, nanoclay was added to polypropylene and polyolefin fibers to improve the mechanical properties of fiber-reinforced cementitious composites. The optimum mixing ratio and draw ratio of the synthetic polymer fibers were established prior to nanoclay addition. Fiber mixing ratios (polypropylene:polyethylene) of 100:0, 90:10, and 85:15, a draw ratio of 8, and nanoclay additions of 1, 3, and 5 wt% were studied. The modulus of elasticity improved with nanoclay addition, while the tensile strength remained almost unchanged, except in the case of 100% polypropylene with 5 wt% nanoclay. POLYM. COMPOS., 34:1698–1709, 2013. © 2013 Society of Plastics Engineers

하이브리드 섬유 보강 시멘트 복합 재료에서 구조용 합성 섬유의 인발 거동에 미치는 폴리비닐 알코올 섬유 혼입률의 효과

이 연구에서는 하이브리드 구조용 합성 섬유와 폴리비닐알코올(PVA)섬유 보강 시멘트 복합 재료에 정착된 구조용 합성 섬유의 인발 거동에 미치는 PVA 섬유 혼입률의 효과를 제시하였다. 구조용 합성 섬유와 하이브리드 섬유보강 시멘트 복합 재료와의 인발 거동은 Dog-bone 부착 시험에 의해서 결정하였다. 시험 결과 PVA 섬유의 혼입은 구조용 합성 섬유와 시멘트 복합 재료와의 인발 거동 특히, 섬유 계면인성을 강화하는 효과가 있었다. 구조용 합성 섬유의 인발 시험 결과 구조용 합성 섬유와 시멘트 복합 재료와의 계면인성은 PVA 섬유의 혼입률이 증가할수록 증가하였다. 미세 구조 분석 결과 PVA 섬유의 혼합은 구조용 합성 섬유와 PVA 섬유 보강 시멘트 복합 재료의 계면인성 메커니즘을 강화시키는데 효과적이라는 것을 확인할 수 있었다.

폴리프로필렌섬유보강 시멘트 복합재료에 정착된 구조용 합성섬유의 부착거동에 미치는 섬유 혼입률의 효과

폴리프로필렌섬유보강 시멘트 복합재료와 구조용 합성섬유의 부착특성을 평가하였다. 폴리프로필렌섬유는 0.10%, 0.15% 및 0.20%의 체적비로 적용하여 dog-bone 시험을 실시하였다. 구조용 합성섬유와 폴리프로필렌섬유보강 시멘트 복합재료 사이의 부착강도는 폴리프로필렌섬유의 혼입률이 증가할수록 증가하였으나 0.20% 이상이 되면 감소하였다. 또한 폴리프로필렌섬유의 첨가는 계면인성과 마찰저항을 증가시킨다. 인발시험 후 구조용 합성섬유 표면의 미소구조 분석은 폴리프로필렌섬유의 혼입률이 증가할수록 긁힘 현상이 증가하였다. The bond properties between polypropylene fiber reinforced cement composites and structural synthetic fiber have been investigated. in this paper. Three levels of polypropylene fibers volume fraction were used, 0.10%, 0.15%, and 0.20% in a series of Dog-bone pull out tests. The bond strength between structural synthetic fiber and polypropylene fiber reinforced cement composites increases with the volume fraction of polypropylene fiber, but the bond strength decreases above the amount of 0.20% by volume of polypropylene fiber reinforced cement composites. Also, the addition of polypropylene fiber a significant improved the interface toughness and the frictional resistance, The microstructure of structural synthetic fiber surface was investigated after the pullout test. The scratched of structural synthetic fiber increased with the polypropylene fiber volume fraction.

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.

Fracture behavior of concrete members reinforced with structural synthetic fibers

Proposed is a realistic method of analysis for the post-cracking behavior of newly-developed structural synthetic fiber reinforced concrete beams. The optimum shape of structural synthetic fiber was determined first on the basis of energy-absorption capacities from pullout tests. In order to predict the post-cracking behavior, pullout behavior of single fiber is identified by tests and employed in the model together with the realistic stress–strain behavior of concrete in compression and tension. A probabilistic approach is used to calculate the effective number of fibers across the crack faces and to calculate the probability of non-pullout failure of fibers. The proposed theory is compared with test data and shows good agreement. The proposed test results and theory can be efficiently used to predict the load–deflection behavior, moment–curvature relation and load–crack mouth opening displacement (CMOD) relation of synthetic fiber reinforced concrete beams.