Macro-synthetic Fibers Research Articles

DETERMINATION AND MODELLING OF BOND PROPERTIES OF SYNTHETIC MACRO-FIBRES IN CONCRETE

Bond behaviour of a synthetic macro-fibre in concrete is the object of this research. The bond strength and stiffness are the parameters characterising the bonding mechanism that determines the efficiency of the reinforcing material. However, there is no general methodology developed to evaluate fibre efficiency. There also exists neither a straightforward procedure to estimate the bond quality of a synthetic macro-fibre nor a reliable numerical model to simulate the bond behaviour of such fibres. In this work, the bond mechanisms of 40 mm long synthetic macro-fibres are investigated using pull-out tests: 16 concrete cubes were made for that purpose. One type of synthetic macro-fibre available at the market is considered. In each test sample, three fibres were inserted perpendicular to the top and two side surfaces; two bonding lengths (10 mm and 20 mm) were used. A gripping system was developed to protect the fibres from local damage. A physically non-linear finite element model of the pull-out sample was developed. A bond model was proposed to simulate deformation behaviour of the fibres.

The effect of polypropylene, steel, and macro synthetic fibers on mechanical behavior of cementitious composites

Incorporation of fibers in concrete has been an efficient technique to prevent crack propagation, thus improving ductility, durability, toughness and strength of concrete. In this context, a comprehensive experimental study has been conducted concerning the compressive and flexural strength of fiber reinforced concrete, through preparing nine concrete batches with polypropylene fibers, steel fibers and macro synthetic fibers; and the hybrid forms combining polypropylene (PP) and steel, polypropylene and macro synthetic fibers. Fiber inclusion in concrete caused slight variations in compressive strength. However, the flexural strength for all sample sets was significantly increased. The highest values of strength increase relative to control concrete were 60.67%, 42.45% and 27.05% incorporating steel, polypropylene and macro synthetic fibers, respectively. It was also noted that the higher aspect ratio of steel fibers resulted with better flexural performance, among the steel fiber reinforced concrete samples. Hybrid forms of polypropylene-steel and polypropylene -macro synthetic fibers achieved the highest flexural strength compared with samples including single type of fiber. In blended groups, utilization of polypropylene fibers with steel fibers and with macro synthetic fibers resulted with 69.81% and 78.99% of increase in flexural strength relative to control specimens, respectively.

Investigation and Improvement of Bond Performance of Synthetic Macro-Fibres in Concrete.

Strength and stiffness are the key parameters characterising the bond performance of fibres in concrete. However, a straightforward procedure for estimating the bond parameters of a synthetic macro-fibre does not exist. This study employs pull-out tests to investigate the bond behaviour of synthetic macro-fibres. Two types of macro-fibres available in the market were investigated. A gripping system was developed to protect the fibres from local damage. The experimental campaign consisted of two stages. At the first stage, 32 concrete specimens were manufactured for performing 96 pull-out tests (three fibre samples were embedded in each cube perpendicular to the top surface and two sides). Two types of macro-fibres with either 10 or 20 mm embedment length were tested. The obtained load–displacement diagrams from pull-out tests demonstrate that the bond performance (characterised by the strength and deformation modulus) of the “top” fibres is almost 20% weaker than fibres positioned to the side surfaces. At the second stage, one type of macro-fibre was chosen for further experimentation of the feasibility of improving the bond performance through the use of colloidal silica or steel micro-fibres. This investigation stage employed an additional 36 concrete specimens. The use of steel micro-fibres was found to be an efficient alternative. The success of this solution requires a suitable proportioning of the concrete.

Experimental investigation on flexural behaviour of composite PVC encased macro-synthetic fibre reinforced concrete walls

Composite PVC encased concrete walls provide substantial advantages in terms of structural strength and durability enhancement, ultraviolet radiation and pest infestation resistance, design flexibility, ease of construction and excellent resistance to impact. In this study, the effects of using macro-synthetic fibre reinforced concrete on flexural behaviour of composite PVC encased walls in comparison with composite PVC encased walls filled with conventional plain concrete and reinforced concrete have been experimentally investigated. Fifteen composite PVC encased concrete wall specimens were cast and tested using three-point bending test. Based on the load-deflection curves resulting from the three-point bending tests, flexural parameters including ultimate loads, ultimate flexural strengths, stiffness and flexural rigidity values for cracked and uncracked conditions were determined for three different cases including i) test specimens filled with plain concrete, ii) test specimens filled with macro-synthetic fibre reinforced concrete, and iii) test specimens filled with reinforced concrete. The determined parameters as well as the measured load-deflection curves for the three cases were compared and the final findings have been discussed. Based on this study, it has become apparent that using BarChip 48 macro-synthetic fibre reinforced concrete in composite PVC encased walls instead of plain concrete can lead to 43.5% flexural strength improvement and 25% stiffness enhancement at the age of 28 days. Based on the experimental measurements and theoretical comparison in this study, it has been concluded that composite PVC encased walls filled with BarChip 48 macro-synthetic fibre reinforced concrete, without steel reinforcement, are deemed suitable for sway-prevented structures such as retaining walls. If using steel reinforcement in composite PVC encased retaining walls is not an option due to high-risk of steel corrosion in harsh environment; it is highly recommended that the retaining walls to be filled with macro-synthetic fibre reinforced concrete instead of plain concrete to ensure the safety and structural integrity of this type of sway-prevented structures.

Effects of Hybridized Synthetic Fibers on the Shear Properties of Cement Composites.

The use of fibers in cementitious composites yields numerous benefits due to their fiber-bridging capabilities in resisting cracks. Therefore, this study aimed to improve the shear-resisting capabilities of conventional concrete through the hybridization of multiple synthetic fibers, specifically on reinforced concrete structures in seismic-prone regions. For this study, 16 hybrid fiber-reinforced concretes (HyFRC) were developed from the different combinations of Ferro macro-synthetic fibers with the Ultra-Net, Super-Net, Econo-Net, and Nylo-Mono microfibers. These hybrids were tested under direct shear, resulting in improved shear strength of controlled specimens by Ferro-Ultra (32%), Ferro-Super (24%), Ferro-Econo (44%), and Ferro-Nylo (24%). Shear energy was further assessed to comprehend the effectiveness of the fiber interactions according to the mechanical properties, dosage, bonding power, manufactured material, and form of fibers. Conclusively, all fiber combinations used in this study produced positive synergistic effects under direct shear at large crack deformations.

Experimental study of base stabilization with fibrillated fiber

Potential benefits in applying polypropylene fiber to stabilize expansive soils and cement treated bases is already been reported in previous studies. So a critical need exists to incorporate the use of fiber into the Texas Department of Transportation’s (TxDOT’s) Guidelines for Modification and Stabilization of Soils and Base for Use in Pavement Structures. The present paper discusses the results collected from the first experimental test section on FM897 in the TxDOT Paris District. Three 500-ft (152.4m) test sections were constructed with 2 percent cement on FM897 in February 2020 in the north bound lane loaded truck direction which includes a new sandstone base, full depth reclamation (FDR), and control. However, only the new sandstone base and FDR sections were built with fiber. In this project, two types of fibers were used —(a) fibrillated fiber Fibermesh300, and (b) macro-synthetic fiber Enduro 600. The surface and base layers from the new sandstone base section were removed and used for the edge widening area of the FDR and control sections. Based on the laboratory tests, the optimum fiber contents were found to be 0.6 percent and 0.4 percent for a new sandstone base and FDR, respectively. The laboratory Unconfine Compression Strength (UCS) results showed significant improvements (<112.36 percent) when fibers were added to the sandstone base. To have better control, fiber and cement were manually distributed, following the US Army Corps of Engineers’ recommendations. Becaus e of unexpected construction equipment failure that caused compaction delays of approximately 5 hours, cement was in contact with moisture for approximately 5 hours before compaction. UCS results showed an approximate 55 percent reduction when there was a 5-hour delay from the time water was introduced (resulting in the start of the hydration process) until the time of compaction. It indicated that there are detrimental effects on UCS if there is delay on compaction. There were significant reductions on the normalized W1 deflections at 5 months after construction. In particular, the FDR and new sandstone base sections (with fiber) experienced over 52 percent reduction as compared to 1 week after construction FWD data. Furthermore, the averaged W1 deflections were lower than before construction for both FDR and new sandstone base sections (with fiber). This indicates that there were rapid increases in structural capacity and significant strength developed in the fiber sections between 1 week and 5 months. Further research is needed to explain the mechanism and phenomena.

Effects of Synthetic Fibers and Different Levels of Partial Cement Replacement on Mechanical Properties of UHPFRC

AbstractThis paper presents the results of an experimental study conducted to investigate the effects of polypropylene fibers and synthetic macrofibers (barchip) with different partial cement repla...

Experimental study on hybrid precast tunnel segments reinforced by macro-synthetic fibres and glass fibre reinforced polymer bars

Increasing the popularity of using fibres in precast structures has brought questions about their usability in segmental tunnel linings as an alternative to the conventional reinforced lining. Most prior studies have already revealed that the replacement of conventional steel reinforcement is possible with steel fibres. However, the usability of macro-synthetic fibres (MSFs) as reinforcements in precast tunnel segments is still unclear and one of the controversial questions to be answered. As such, this study aims to evaluate the structural applicability of using polypropylene (PP) MSFs in precast tunnel segments by means of an experimental program on full-scale specimens. Within this framework, totally fourteen full-scale precast tunnel segments of Mecidiyekoy – Mahmutbey underground railway tunnel in Istanbul/Turkey characterized by four different reinforcement cases were analysed: i) typical conventional steel reinforcement; ii) the combination of MSFs and conventional reinforcement; iii) the combination of MSFs and glass fibre reinforced polymer (GFRP) rebars; and iv) MSFs only. Flexural tests were carried out to compare the flexural behaviour of specimens at the allowable crack opening width, while point load tests were conducted to observe the structural performance of precast tunnel segments under the effect of design thrust forces. The experimental results showed that the combination of MSFs and GFRP could be an innovative solution for precast tunnel segments in case of using a suitable quantity that satisfied the project requirements. Although PP fibres exhibited adequate spalling and splitting stress control, it is observed that they could not overcome high flexure forces without using reinforcement bars at a low volume of fractions. Thus, more comprehensive studies need to perform on GFRP + MSFs segments because of having the advantages of corrosion resistance in the presence of an aggressive surrounding environment.

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.

Effect of different fiber type on sprayed concrete support capacity

Nowadays there are several types of fiber for the reinforcement of the sprayed concrete used in tunnel support; most popular among them are steel fibers and macro synthetic fibers. However, in most cases the assessment of fiber reinforced sprayed concrete ductility is focused on the fulfillment of energy absorption capacity requirements without considering the effect of the reinforcement type on the Load-Displacement behavior. The following study aims to find out if the support capacity provided by each fiber type is the same for similar levels of energy absorption capacity or how it can be affected through the analysis of the load bearing capacity. After the analysis of energy absorption tests according to EFNARC of more than 50 specimens separately reinforced with steel and macro synthetic fibers, it was observed the specimens reinforced with steel fiber absorbed more energy since the beginning of deformation than those reinforced with macro synthetic fibers. In other words, the required work to start deforming the steel fiber reinforced sprayed concrete is greater than the required with the other fiber type. Likewise, the ultimate strength or maximum load bearing capacity provided by steel fibers was higher than the other fiber type. Therefore, the support capacity of the sprayed concrete and the related safety factor provided by each fiber type is different

Assessment of Self-Consolidation Concrete Produced with Micro Steel and Macro Synthetic Polyolefin Fibers

In the field of precast concrete, the utilize of fiber reinforced self-consolidation concrete (SCC) has big potential as it can be supplied directly into the molds without any effort for vibration or compacting. Likewise, depending on the design requirements, it has the potential to supplant conventional steel reinforcement. The using of one type of fiber in producing of SCC has been usual. Fiber reinforced self-consolidation concrete (FSCC) contains two type or more of fiber can improve the mechanical properties and may cause performance synergies. This paper investigates the combination of fibers, often referred to as hybridization, for a cementitious matrix. Control, single, two hybrid fibers were cast using different steel and macro synthetic fibers ratios. Fresh behavior, such as the ability to flow and fill and the tendency to segregate, was evaluated by a special SCC test based on its specifications. Moreover, compressive strength, splitting tensile strength, flexural strength, ductility, toughness, and the load - deflection relationship were determined to assess the hardened behavior. The results showed that the compressive strength of hybrid fiber mixes slightly improved. The increment in splitting and flexural strength for hybrid mixes was (60 and 58) % respectively. Also, these hybrid fiber mixes represent a more ductile failure further, the high toughness index, which reaches to 45% of control mix.

Comparison of the structural behavior of reinforced concrete tunnel segments with steel fiber and synthetic fiber addition

Fiber reinforced concrete, with different types of fibers, has been increasingly used in underground structures, especially for tunnel lining segments. Macro synthetic fiber reinforced concrete has a considerable structural bearing capacity. Compared to steel fiber reinforced concrete, it has the advantage of corrosion resistance and durability. However, the main application of macro synthetic fiber reinforced concrete is limited to control cracking without considering its mechanical contribution. Besides, few studies have compared the differences in mechanical properties of synthetic fibers and steel fibers. Therefore, an experimental and theoretical study of reinforced concrete segments with steel fiber and synthetic fiber addition was performed. The experiments included both traditionally reinforced concrete segments and fiber reinforced concrete segments with different ratios of steel bars and fiber dosages. By means of comparison between different segments, the advantages of fiber reinforced concrete relative to traditional reinforced concrete segments are shown as well as the differences of the mechanical behavior of reinforced concrete segments with synthetic fibers and steel fibers. In addition, the concrete section design method is extended to reinforced concrete segments with macro synthetic fibers. Using this model, the bearing capacity of experimental segments is analyzed. The results agree well with the experimental results, which indicates the design model for the reinforced concrete segments with macro synthetic fibers is reasonable and applicable.

Fatigue behaviour of macrofiber reinforced gap graded asphalt mixtures

The addition of fibres to reinforce asphalt mixtures is a prospective field for pavement engineering, where the use of glass or synthetic macrofibers could potentially help not only as reinforcement for new asphalt mixtures, but also as part of asphalt overlays applied on deteriorated pavements to diminish reflective cracking during maintenance operations. In recent studies, it has been found that the addition of macrofibres can improve the rutting and fracture resistance of asphalt mixtures. However, the response of these mixtures to fatigue has not been studied yet. In this study, a complete performance characterization of a gap graded asphalt mixture with the addition of glass and synthetic macrofibres was studied. Also, a reference asphalt mixture without macrofibres was provided for comparison. Results showed that the addition of macrofibres improves water sensibility, rutting performance and stiffness of the gap grade asphalt mixtures studied. Also, it was observed during the fatigue tests that the incorporation of both types of macrofibres greatly improved the durability of the mixtures to fatigue cracking at medium range temperatures. This improved fatigue behaviour correlates to an extended useful life for the fibre reinforced asphalt mixtures. The synthetic macrofibres showed better fatigue behaviour at lower temperatures, while glass macrofibres gave a better response at the higher temperature studied.

Mechanical characterization of structural lightweight aggregate concrete made with sintered fly ash aggregates and synthetic fibres

This study explores the development of fibre reinforced structural lightweight aggregate concrete (SLWAC) using sintered fly ash aggregate (SFA) as coarse aggregate. SFA is manufactured from fly ash, an industrial by-product, thus making SLWAC a sustainable building material. SLWAC of density 1800 kg/m3 is developed with and without the addition of synthetic polyolefin (macro and micro) fibres to achieve a target compressive strength of 40 MPa. The main objective of this study is to understand the mechanical properties of SLWAC made of SFA and the influence of fibres in improving mechanical properties of SLWAC. The effect of monofilament macro-synthetic fibre dosages of 0.2%, 0.4%, and 0.6%, as well as the fibrillated micro fibres of 0.02% on the mechanical properties of SLWAC is studied. Tests were carried out for understanding the stress-strain behaviour under compression, split tensile strength, and fracture behaviour under flexure. Digital image correlation technique is used to study the crack propagation in fracture and splitting tension tests. A significant improvement in flexural strength, splitting tensile strength and toughness of SLWAC is observed due to the addition of synthetic fibres. Fibres significantly contributed to load resistance by arresting both micro and macro cracks. Thus, with the help of synthetic fibres addition in SLWAC, the desirable mechanical properties for structural applications such as strength and ductility can be achieved at reduced density.

Punching Shear Strength of Reinforced Concrete Flat Slabs with Macro Synthetic Fibers

Discrete macro fibers such as steel and synthetic have been recognized as an attractive material to improve concrete properties such as flexural toughness, shear strength, impact characteristics, deflection capacity and concrete ductility. In this paper, the effect of macro synthetic fibers on punching shear resistance and cracking behaviour of reinforced concrete slabs was investigated. A total of six reinforced concrete slabs were designed, instrumented and tested in displacement control mode, under monotonic center-point load in simply supported configuration. Synthetic fibers were added to the concrete slabs at dosage rates of 0.5% and 1% by volume. The results have shown a significant increase of the punching shear strength, energy absorption capacity and ductility of the slabs. The addition of 0.5% and 1% of macro synthetic fiber to the slab increased punching shear strength by 30% and 70% and increased energy absorbance by 40% and 80%, respectively.

Experimental study of the steel/CFRP interaction in shear-strengthened RC beams incorporating macro-synthetic fibers

This paper presents an investigation of the performance of RC beams incorporating macro-synthetic fibers and rehabilitated using Externally Bonded Fiber Reinforced Polymer (EB-FRP) strips. A series of tests were conducted to investigate the EB-FRP contribution to the shear strength recovery of pre-damaged shear-deficient beams. The investigation included studying the effect of macro-synthetic fiber reinforcement on the contribution of EB-FRP to the shear strength of retrofitted beams, as well as the interaction between EB-FRP and steel stirrups in the presence of macro-synthetic fiber reinforcement in the concrete. The key parameters of the investigation included: (a) beam condition (damaged beams and virgin beams), (b) beam shear reinforcement (stirrups and no stirrups), and (c) macro-synthetic fiber dosage (0.5%, 0.75%, and 1.0%). The test results showed that the retrofitting of severely shear-damaged RC beams using EB-FRP significantly enhanced the original shear capacity of the beams with strength gains varying between 50% and 111% depending on the amount of macro-synthetic fibers and/or conventional shear reinforcement present in the specimens. The test results have also provided evidence for the existence of interaction between the steel stirrups, the macro-synthetic fibers and the EB-FRP strips in carrying part of the applied shear force in the retrofitted beams. Such interaction is such that with use of EB-FRP, the conventional shear reinforcement and/or macro-synthetic fibers have lesser contribution to the total shear force in the retrofitted beams. However, the presence of such additional shear reinforcement leads to enhanced crack control thereby delaying the premature debonding of EB-FRP strips and increasing the deflection capacity of the retrofitted beams.

Recent advances in structural fibre-reinforced concrete focused on polyolefin-based macro-synthetic fibres

Fibre-reinforced concrete (FRC) allows reduction in, or substitution of, steel-bars to reinforce concrete and led to the commonly named structural FRC, with steel fibres being the most widespread. Macro-polymer fibres are an alternative to steel fibres, being the main benefits: chemical stability and lower weight for analogous residual strengths of polyolefin-fibre-reinforced concrete (PFRC). Furthermore, polyolefin fibres offer additional advantages such as safe-handling, low pump-wear, light weight in transport and storage, and an absence of corrosion. Other studies have also revealed environmental benefits. After 30 years of research and practice, there remains a need to review the opportunities that such a type of fibre may provide for structural FRC. This study seeks to show the advances and future challenges of use of these polyolefin fibres and summarise the main properties obtained in both fresh and hardened states of PFRC, focussing on the residual strengths obtained from flexural tensile tests.

Enhancing the shear strength of hollow-core slabs by using polypropylene fibres

Experimental and numerical research studies demonstrated that the addition of fibres in correct proportions, enhances the shear behaviour of Reinforced Concrete (RC) elements, allowing to totally or partially replace the conventional web reinforcement. However, despite of this increase of knowledge about Fibre Reinforced Concrete (FRC), there is still a gap in the applicability of fibres as a shear reinforcement in certain prestressed structural elements where the use of conventional transverse reinforcement is difficult due to their manufacturing process, e.g. extruded elements in dry concrete. In this context, the present paper evaluates the possibility of enhancing the shear strength of Hollow-Core Slabs (HCS) by using Polypropylene Fibre Reinforced Concrete (PFRC). HCS can be critical in shear at their end zones, since these zones are disturbed regions (already stressed in tension by splitting forces) in which the beneficial effects of the prestressing actions on the shear strength are not active yet. Five full-scale HCS (42 cm high, 120 cm wide and 600 cm long) were tested under shear loading (1 in RC and 4 in PFRC). Two tests were performed on each slab varying the shear-span-to-effective depth ratio (a/d = 2.8 according to EN1168 and a/d = 3.5). Results show that macro-synthetic fibres are able to improve the shear strength of hollow-core slabs of about 25%; furthermore tests according to EN1168 are more affected by arch actions as compared to a/d = 3.5. Finally, the comparison between experimental results and predictions of four international codes (Eurocode 2, ACI 318-14, Model Code 2010 and EN1168), highlighted the need of improving the actual shear formulations.

Microstructural Study of the Interface of Polyolefin Fibers Embedded in Self-Compacting Concrete Matrices with Bond Improver Admixture

AbstractIn recent years the plastic industry has developed a new type of synthetic macrofiber based on polyolefins that complies with the requirements of existing standards in considering contribut...

Effects of pouring technique on orientation of steel and synthetic macrofibres in fibre-reinforced concrete

Fibre-reinforced concrete is a short-fibre composite material, whose properties are significantly dependent on the orientation of the mixed fibres. As a starting point, the fibres are assumed to be uniformly distributed and have a uniform orientation. However, in reality, they have a non-uniform distribution owing to various factors. Such deviations in the orientation may have a significant effect on the material parameters, both favourable and unfavourable. In this study, the orientation factors determined based on the mixing models reported in the literature are compared with the results of experimental tests performed in the laboratory, and the effects of the formwork and the pouring methods used on the orientation of both steel and synthetic macrofibres are investigated. Based on the results of the study, the orientation of the fibres (both, steel and macro synthetic) significantly depends on the pouring method, which considerably influences the material parameters of fibre-reinforced concrete.