Fibrillated Polypropylene Fibers Research Articles

Semi-circular bending setup for predicting fracture characteristics of high-strength fiber-reinforced concrete

Semi-Circular Bending (SCB) Setup is commonly used to investigate the fracture parameters of the road materials like asphalt mixtures. This paper examines the performance of the SCB setup in extracting the fracture characteristics of high-strength fiber-reinforced concrete (HSFRC). Monofilament and fibrillated polypropylene fibers with polyolefin coatings of 19, 30, and 50 mm length were added to a high-strength concrete mixture at three volume percentages of 0.5, 1, and 1.5 %. Standard cube and cylinder specimens were initially fabricated for conventional material properties tests. Subsequently, the three-point bending test specimens, i.e., intact rectangular beam, notched beam, and SCB, were made using the same concrete mix of different fibers lengths and percentages. A total of 36 beam and SCB tests with three replications was conducted to find the fracture energy and pick load of each specimen. Results showed that selecting the shortest fibers (19 mm) of 0.5 % and 1.5 % by volume increased the elastic modulus and the splitting tensile strength by 70.5 % and 43 %, respectively. Also, increasing the fiber length and volume enhanced the fracture energy of the notched beam and SCB specimens up to 90 times and 40 times, respectively. However, increasing the volume of the fibers was more effective than using longer fibers in fracture energy increase. For these three test setups, finite element models were generated and analyzed to develop a numerical framework capable of predicting the fracture characteristics of HSFRCs with acceptable accuracy (maximum error of 4 %). The concrete damaged plasticity (CDP) model in ABAQUS software package were adopted to simulate the damage initiation and progression in concrete using the material properties from the conventional tests. Comparing the results of beam setups with SCB tests, it was found that SCB can be a reliable and economical setup to find the fracture characteristics of the HSFRCs.

Impact resistance and mechanical properties of fiber‐reinforced concrete using string and fibrillated polypropylene fibers in a hybrid form

AbstractIn this study, the macro‐synthetic polypropylene fibers Forta and Barchip are used. The fibers are added at 0.5%, 1%, 1.5%, and 2% by weight of cement. Additionally, various fiber combinations with varying percentages are employed to create the concrete. Cubic specimens, bending beams, and impact specimens are all prepared on a percentage basis of fiber. The findings indicated that utilizing 1.5% fibrillated Forta fibers raised the compressive strength of the concrete by 18% and the flexural strength of the concrete by 58%. By increasing the usage of Barchip single‐strand fibers by 1.5%, the compressive strength increased by 36%, and the flexural strength increased by 89%. The highest ductility rate refers to the specimen containing 1.5% Forta fiber, with an energy capacity of 672 J. All the hybrid samples also possess a high ductility ratio. Forta fibrillated fibers are more effective in ductility, while Barchip monofilament fiber types can impressively increase the flexural strength of concrete. The hybrid usage of fibers improved compressive strength by 32% and flexural strength by 85%. Additionally, by combining fibers in hybrid form, energy absorption, ductility, impact resistance, and residual flexural strength are increased by 22, 2.3, 3.6, and 5.6 times, respectively, over the control sample.

Adobe mixtures reinforced with fibrillated polypropylene fibers: Physical/mechanical/fracture/durability performance and its limits due to fiber clustering

This study assesses the feasibility of the incorporation of fibrillated polypropylene fibers (FPFs), an engineered multidimensional and multifilament fiber mostly used to reinforce concrete mixtures, into adobe mixtures (AMs), a traditional and manually-made material used to produce adobe blocks. The incorporation of FPFs was assessed using increasing dosages (0%, 0.25%, 0.5%, and 1% in wt% of clay soil) of FPFs. These fibers were gradually added and mixed with the clayey soil prior to incorporation of water to promote uniform mixtures with adequate fiber distribution to reduce the formation of fiber clusters. The impact of FPFs was evaluated in terms of its effects on the bulk density (physical), compressive and flexural strength (mechanical), flexural toughness indices (fracture) and water erosion resistance (durability) of AMs. Results indicate that increasing dosages of FPFs monotonically reduce average values of bulk density, as well as compressive and flexural strength of AMs. On the other hand, these increasing dosages of FPFs monotonically increase average values of water erosion resistance as well as flexural toughness indices, varying the flexural failure mode from brittle (unreinforced AM) to ductile (reinforced AMs) because of the adequate bonding and FPF-bridging effect after the crack generation as confirmed by instrumentation as well as digital image correlation evaluations implemented in this study. The significant reductions of bulk densities and compressive and flexural strengths obtained for fiber-reinforced AMs were related to the increasing number of fiber clusters found for increasing dosages of FPFs within the fiber-reinforced mixtures, which was evaluated using scanning electron microscopy analyses. For example, positively the AM incorporating 1% of FPFs increased, on average, the flexural toughness by 674% and reduced the bulk density and water erosion depth by, on average, 9% and 64%, respectively, when compared to the unreinforced AM. However, this large dosage of FPFs also generated a significant reduction of the compressive strength (60% on average) and the flexural strength (43% on average) when compared to the plain mixture. On the other hand, a small dosage of FPFs (0.25%) generated less significant improvements in terms of flexural toughness, bulk density, and water erosion (on average, increment of 58% and reductions of 2% and of 38%, respectively, when compared to the unreinforced AM). Yet, the latter mixture presented reductions, on average, of compressive and flexural strengths of 24% and 16%, respectively, when compared to the plain mixture, and these reductions were significantly smaller than the reductions obtained by the largest FPF dosage, due to the significantly smaller number of fiber clusters presented by the 0.25% dosage when compared to the 1% dosage. Finally, the mechanical performance limitations exhibited by the incorporation of FPFs, especially in large dosages, are related to generated fiber clusters due to the inherent morphology of these FPFs as well as the traditional manual confection process of AMs. Therefore, this study recommends the implementation of FPFs in AMs, but in small dosages and/or suggests the implementation of a mechanical mixing/compaction process that guarantee a more uniform fiber distribution that reduces the generation of fiber clusters.

Effects of Various Mineral Admixtures and Fibrillated Polypropylene Fibers on the Properties of Engineered Cementitious Composite (ECC) Based Mortars

This study investigates the mechanical and durability properties of fly ash-based engineered cementitious composites (ECC). The effect of various mineral additions, such as wheat husk ash (WHA), rice husk ash (RHA), glass powder (GP), and fibrillated polypropylene (PP) fibers, on mechanical performance, water absorption, and porosity was investigated. Furthermore, the durability of ECC specimens was assessed in terms of sorptivity, acid/sulfate attacks, electric resistivity (ER), rapid chloride penetration (RCPT), and ultrasonic pulse velocity (UPV). The results revealed higher mechanical strength, UPV, and ER values for RHA-based ECC. After 180 days of immersion in acid and sulfate solutions, RHA-based ECC showed a lower loss in compressive strength (23.21% and 1.07% in HCl and Na2SO4, respectively) relative to the control mix (44% and 7% in HCl and Na2SO4, respectively). Moreover, analytical characterizations such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), Scanning Electron Microscopy (SEM), and Energy dispersive X-ray (EDX) analyses were also carried out to corroborate the mechanical and durability properties of ECC.

Using post-cracking strength to determine flexural capacity of ultra-thin whitetopping (UTW) pavements

Utilizing fibrillated polypropylene fibers (FPP) in Ultra-thin whitetopping (UTW) has become increasingly popular to improve the flexural capacity of concrete slabs. The calculated flexural strength (i.e., modulus of rupture (MOR)) depends on the elastic formula of ASTM C78 does not illustrate the fiber’s benefits. Therefore, the concept of effective modulus of rupture (MOReff.) that is determined from the equivalent flexural strength ratio has been used to quantify the added flexural capacity of fibers on unreinforced concrete. The purpose of this study is to investigate the benefits of testing the FRC/asphalt composite beam on the flexural capacity of UTW. Three main parameters have been taken into consideration: FPP content, pavement thickness, and failure mode. Furthermore, comparison was made to verify the effectiveness of composite beams for flexural capacity. Six different cases of concrete beams and ten cases of FRC/asphalt composite beams were performed. The results of the composite beam showed that the flexural capacity was higher than the capacity of the concrete layer. In addition, using FPP in the composite beams improved the MOReff.. The results also revealed that testing UTW under noncommon failure modes did not reflect the real flexural capacity of UTW. The required UTW thickness depends on the proposed flexural capacity of the composite beam being less than the required thickness that is calculated depends on the concrete beam.

The influence of pore pressure on fracture behaviour of Normal-Strength and High-Performance Concretes at high temperature

Explosive spalling consists in the sudden separation of concrete layers or pieces from the surface exposed to fire, due to (a) stress caused by thermal gradients and external loads and (b) pore pressure rise induced by water vaporization. As regards the material properties, the phenomenon is affected by some meso- and micro-structural aspects mainly concerning the interaction during heating among cement paste, aggregate and fibre, thus influencing porosity and permeability variation at high temperature. Focusing on the effect of pore pressure in fracture behaviour of Normal-Strength and High-Performance Concretes, an experimental campaign has been planned, aimed at investigating the role played by the mix design. Nine concrete mixes have been studied considering three grades (fc ≥ 40, 60 and 90 MPa), three aggregate types (silico-calcareous, basalt and calcareous aggregates) and different fibre types and contents (monofilament or fibrillated polypropylene fibres). The experimental study, based on indirect tension tests performed under different levels of sustained pore pressure, clearly shows that the influence of pressure on concrete fracture response during heating strongly depends on mix design.

Investigation on Improvement of Flexural Behavior of Low-Density Cellular Concrete through Fiber Reinforcement for Non-Structural Applications

During the last decades, cellular lightweight concrete (CLC), or foamed concrete, has been experiencing greater interest in geotechnical, structural, and non-structural applications. The low density and high flowability makes it a favorable construction material in relation to handling, placing, and construction costs. However, the applications of low-density cellular concrete (LDCC), the category of CLC with a unit weight less than 50 pounds per cubic foot (801 kg/m3) and generally without fine aggregates, are limited mostly to backfill applications in geotechnical engineering. The main reason lies in the brittleness of the material and low to zero resistance to flexural loads. Fiber-reinforced LDCC may be a reasonable solution to improve mechanical properties and expand the application range of the material. This study investigated the effects of adding polypropylene and hybrid fibers on physical and mechanical properties of LDCC and the feasibility of expanding LDCC utilization to non-structural applications. Results showed that although there is a slight reduction of flowability and compressive strength, the flexural behavior of LDCC can be significantly improved with the incorporation of fibers. The flexural strength and flexural toughness of LDCC was found to increase from 26.8 pounds per square inch (psi) (0.18 MPa) to 217.5 psi (1.48 MPa), and from 5.67 lb-in. (0.64 kN-mm) to 292 lb-in. (33.0 kN-mm) respectively at a 1.0% addition rate of a fibrillated polypropylene fiber selected in this study, which makes it a feasible material for non-structural applications.

Fire spalling sensitivity of high-performanceconcrete in heated slabs under biaxial compressive loading

Explosive spalling of concrete exposed to fire consists in the violentexpulsion of shards from the hot surface due to the interaction between cracking andpore pressure build-up. Fire spalling relevantly increases the overall thermaldamage of a structure exposed to fire, thus leading to much higher costs in therepair intervention, and in some cases it can even jeopardize the structuralstability due to loss of reinforcement protection and reduction of the bearingcross-sections. High-performance concrete is particularly sensitive to spallingphenomenon due to inherent material features, such as the unstable fracturebehaviour and the low permeability (favouring high values of pore pressure). In thiscontext, an experimental campaign has been carried out on high-performance concrete(fc ≈ 60 MPa withsilico-calcareous aggregate), without or with one of three different fibre types(steel fibre, monofilament or fibrillated polypropylene fibres). Tests wereperformed by means of a special test setup developed at Politecnico di Milano, basedon slabs (800 × 800 × 100 mm) subjected to Standard Fire at the bottom and tobiaxial compressive loading in the mid-plane, while monitoring pore pressure,temperature and deflection. Explosive spalling was observed in both plain concreteslabs and in one of the two slabs with steel fibre, this casting some doubts on theuse of steel fibre alone against spalling. No detachment was observed whenpolypropylene fibre was added to the mix.

Mechanical and flexural performance of synthetic fibre reinforced geopolymer concrete

A comprehensive experimental program was undertaken to analyse the structural and material characteristics of synthetic fibre reinforced geopolymer concrete. This study focused on the effect of monofilament and fibrillated polypropylene fibres and monofilament structural polyolefin fibres on mechanical and flexural performance of fly ash based geopolymer concrete. Five types of synthetic fibres at a 0.5% volume fraction were added to geopolymer concretes. The specimens’ compressive strength, indirect tensile strength, modulus of elasticity, modulus of rupture, flexural toughness and fracture energy were determined. Where possible, comparative analyses where conducted to assess the performance of fibre reinforced geopolymer concrete against conventional Portland cement based systems. The flexural toughness parameters were obtained using procedure laid down in ASTM C1018, JCI-SF4 and ASTM C1609. The results indicated that the macro polyolefin fibres exhibited the largest fracture energy which is likely due to high mechanical bonding and low fibre aspect ratio. Relationships are established to predict the compressive and tensile strengths, modulus of elasticity, compressive stress–strain curve and relation between the deflection and CMOD of synthetic fibre reinforced geopolymer concrete.

Impermeability Durability of SCC Reinforced with Fibrillated Polypropylene Fiber

The paper studied the influences of the volume content and slenderness ratio of fibrillated polypropylene fiber on the impermeability durability of self-consolidating concrete (SCC) reinforced with the fibrillated polypropylene fiber, and proposed to use the modified relative permeability coefficient method to evaluate the water-resistant properties of SCC reinforced with the fiber. Also, the influence mechanism of the fiber on the permeability of the concrete has been analyzed according to the mercury injection test, scanning electronic microscope (SEM) observation and the basic principles of fracture mechanics. Results showed that: 1) the total porosity of SCC gradually increased with the increase in the fiber content; 2) the harmful porosity of SCC decreased firstly and then increased with the increase in the fiber content, while the harmful porosity increased with the increase in the fiber length; 3) when the reference mix proportion of SCC was kept constant, the fiber volume content was not more than 0.10 %, and the appropriate fiber length ranged from 12 to 15mm; 4) when the volume content is no more than 0.15%, the hardened SCC reinforced with fibrillated polypropylene fiber possessed good water impermeability gradation (＞P12); the splitting strength and flexural tensile strength of the hardened SCC reinforced with fibrillated polypropylene fiber increased with the addition of the fiber content; the relative water penetration coefficient of the hardened SCC reinforced with fibrillated polypropylene fiber decreased with the addition of the fiber content firstly and then increased; the Coulomb value first increased smoothly (the maximum Coulomb value is less than 2000C, and low according to JTJ/T 193-2009 and ASTM C 1202), and then increased sharply.

Compaction and strength characteristics of fly ash and fiber amended clayey soil

An experimental program was undertaken to investigate the effects of discrete polypropylene fibers and Class C fly ash on the stress–strain and shear strength behavior of clayey soil. Two types of fiber (fibrillated polypropylene fiber and multifilament polypropylene fiber) in two different lengths (6.0mm and 19.0mm) and two fiber dosages (i.e. 0.5% and 1.0% by dry weight of soil) were considered. At first, compaction characteristics of the untreated soil and seven different fly ash–soil mixtures (2.5%, 5.0%, 7.5%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were evaluated at standard compaction energy. Considering compaction characteristics, unconfined compression tests of untreated soil and five different fly ash–soil mixtures (5.0%, 10.0%, 15.0%, 20.0%, and 30.0% by dry weight of soil) were carried out after 1-, 7-, 14-, 28- and 90-day curing periods. According to the obtained test results, untreated soil and two different fly ash–soil mixtures (i.e. 10.0, and 30.0% by dry weight of soil) were mixed with fibrillated polypropylene fiber and multifilament polypropylene fiber in two different lengths and in two different fiber dosages, separately. A total of 17 different fiber–fly ash–soil mixtures were composed, and their unconfined compression tests were carried out after 28-day curing period. According to unconfined compression test results, 6 different fiber–fly ash–soil mixtures were selected for UU triaxial tests at the end of 28-day curing period. The obtained test results indicated that the effect of fly ash content on the stress–strain behavior is superior to the effect of fibers. The post-peak strength behavior is strongly affected by fiber type, length and dosage. The magnitude of the effect increases as the fly ash content increases. Inclusion of fiber alone without fly ash decreases unconfined compressive strength (UCS) of the compacted fiber–clay mixtures. On the other hand, when combined with fly ash, fiber inclusion increases UCS depending on fiber type, length and dosage. Moreover, for both fiber types and fiber lengths, the higher the dosage of fiber, the higher the UCS is. The increase in UCS becomes as much as 218% for 30% fly ash content and 1.0% 19mm long fibrillated polypropylene fiber.

Enhancement of mechanical properties in polypropylene– and nylon–fibre reinforced oil palm shell concrete

In the realization of sustainable construction using structural lightweight concrete, the development of oil palm shell concrete (OPSC) faced the density bottleneck of 2000kg/m3. This study aims to compare the effect of polypropylene (PP) and nylon fibres in enhancing the mechanical properties of oil palm shell fibre-reinforced concrete (OPSFRC). The volume fractions (Vf) of 0.25%, 0.50% and 0.75% were studied for each fibre. As multi-filament PP fibres were added into OPSFRC, the marginal density reduction was reported without any change in the mechanical properties. Although mixes reinforced with nylon fibres showed an increment in density of 80–120kg/m3 and the highest enhancement in both compressive and tensile strengths, these were accompanied by a decrease in the modulus of elasticity (MOE). The optimum density reduction and MOE were obtained in OPSFRC containing fibrillated PP fibres along with a reduction in the compressive and tensile strengths. An increase in the post-failure compressive toughness of OPSFRC of up to 14% was reported in mixes reinforced with this fibre. The ultrasonic pulse velocity (UPV) was examined and the results showed that OPSC produced had attained good condition at the age of 7-days.

Strength of Normal Concrete Using Metallic and Synthetic Fibers

Based on the laboratory experiment, cube and cylindrical specimens have been designed with metallic and non-metallic groups of fibers. In metallic fibers, steel fibers of hook end with 50, 60 aspect ratio and crimped round (copper coated) of 52.85 aspect ratio containing 0% and 0.5% volume fraction were used without adding admixtures. In synthetic fibers category, fibrillated polypropylene fibers of 15 mm, 20 mm and 24 mm cut length at 0.4% by weight of cement were used without adding admixtures. Total 63 specimens were casted and tested for the work. Comparing the results of fiber reinforced concrete with plain concrete, this paper validated the positive effect of steel fibers with different aspect ratios and fibrillated polypropylene fibers with different cut length in compression and splitting strength improvement of specimen at 7 and 28 days, analyzed the sensitivity of different fibers to concrete with different strength.

Flow characteristics and acceptance criteria of fiber-reinforced self-compacted concrete (FR-SCC)

Self-compacting concrete (SCC) possesses exceptional flowability characteristics in its fresh state. While fibers are specified for their ability to limit concrete shrinkage cracks at early age and to enhance some of the concrete properties, inclusion of such fibers is expected to affect the flowability characteristics of SCC. This study investigates how the inclusion of fibrillated polypropylene fibers with different fiber content and the inclusion of steel fiber types with different aspect ratio and volume content affect the flowability of SCC. The flow characteristics were assessed by considering the slump flow test, V-funnel test and filling box test. It was found that it is quite possible to achieve self-compacting properties while using fiber reinforcement. While the mix composition and fiber type can greatly influence concrete flowability, there exists a maximum fiber content that could be used to produce fiber reinforced self-compacting concrete (FR-SCC). Moreover, our observations were used to develop a new acceptance criterion for FR-SCC.

Freeze/thaw durability in concrete with fibre additions

From recent laboratory research monofilament and fibrillated polypropylene fibres were used in structural concrete and have been tested against 150 freeze/thaw cycles. The findings show monofilament fibres to play a significant role in protecting the concrete matrix against the forces encountered. External cube integrity was shown to be a poor indicator of structural condition. A significant aspect of the work is the range of tests applied to the freeze/thaw concrete cubes against the control sample. Strong evidence of condition was obtained from ultrasonic, compressive strength and weight loss. Surface scaling was not a satisfactory indication of the structural condition of the concrete.

Use of Fibers and Welded-Wire Reinforcement in Construction of Slabs on Ground

Different types of fiber-reinforced concrete have been advocated and used as a replacement for welded-wire reinforcement (WWR) in slabs on ground, leading at times to conflicting opinion and/or unrealistic expectation about the benefits of using either WWR or different types of fiber in slabs. In order to verify some of these opinions, tests have been carried out on model slabs (2.5 m×2.5 m×150 mm thick) cast on grade in a test pit and loaded to failure. Results are compared to evaluate the load-carrying capacity for slabs having equivalent amounts of either WWR, fibrillated polypropylene fibers, or steel fibers. Test results show that steel fibers are a suitable alternative to using properly positioned WWR. However, use of polypropylene fibers at a low dosage, which is most common for slab construction (0.9 kg/m³), provides little benefit in terms of increased load-carrying capacity when compared with a plain unreinforced slab. Slab capacity is affected mainly by the postcracking strength of the concrete section, and results from flexure beam tests give a good indication of expected behavior of slabs. The test results also show that a poor subgrade support can be compensated by reinforcing a slab with a moderate amount of either WWR or steel fibers (at a dosage of 30 kg/m³).

Application of Fibrillated Polypropylene Fibers for Restraint of Plastic Shrinkage Cracking in Silica Fume Concrete

This paper presents a review of the literature and an experimental research investigation relating to restraint of plastic shrinkage cracking in silica fume concrete. The mechanism of plastic shrinkage cracking, as well as the effects of fibrillated polypropylene fibers and silica fume, are discussed. Fibers restrain cracks by promoting water retention, setting acceleration, increasing tensile strain capacity, and controlling crack growth of fresh concrete. By increasing the number of menisci capillaries and water demand, silica fume increases the plastic shrinkage cracking of fresh concrete.

Effect of Exposure to Elevated Temperature on Polypropylene Fiber-Reinforced Concrete

The effect of exposure to elevated temperature on fibrillated polypropylene fiber-reinforced concrete (FRC) is discussed. A literature review indicates that polypropylene fibers, when uniformly distributed within concrete, play an active role in improving spalling resistance of concrete induced to elevated temperature. The experimental program described herein includes specimens 100 x 100 x 350 mm with fiber volume of 0.1-0.3% and subjected to temperatures ranging from 100-200 deg C for durations of 1, 7, and 30 days. Postpeak flexural strength is used to determine the effectiveness of fibrillated polypropylene fibers in concrete reinforcement. This paper shows that ultimate bending strength, as well as postpeak flexural strength, decrease with increasing exposure temperature, duration, or both. Further, exposure to temperatures below 100 deg C does not seem to greatly affect the flexural behavior of polypropylene FRC.

Plasma treatment of polymeric fibers for improved performance in cement matrices

The surfaces of collated fibrillated polypropylene fibers and monofilament polyolefin fibers were treated by low-temperature cascade arc plasma with different gases to study the effect of interface treatment on the mechanical performance and toughening in fiber-reinforced concrete composites. Results from static flexural tests conducted in a four-point configuration on 17 concrete mixes including one unreinforced control mix, 4 mixes with untreated fibers (two volume contents for each of two fiber types—fibrillated and monofilament), and 12 mixes with plasma-treated fibers (two volume contents, above two fiber types, and three plasma treatments) are presented and discussed. It is concluded that plasma treatment of polymeric fibers is effective in improving the flexural performance and toughness of fiber reinforced concrete composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1985–1996, 2000

Dynamic properties of polypropylene fiber-reinforced concrete slabs

A series of experiments were performed on both simply supported and on-grade circular slab specimens, reinforced with different volumes of fibrillated polypropylene fibers, to gauge the fibers' influence on the slab's impact resistance and natural frequency. Numerical simulations were then used to reproduce the natural frequencies. In conjunction with these experiments, standard compression and flexural tests were run to determine the material strength of the concrete. It was found that the inclusion of fibers produced an improvement in impact resistance proportional to the fiber volume contained in the concrete and had no affect on the natural frequency. An inverse relationship between fiber volume and material strength was also found for both compression and flexure.