Types Of Polypropylene Fibers Research Articles

Shrinkage cracking and mechanical properties of cementitious composites produced with multiwall carbon nano tubes and different types of polypropylene fibres

This study was conducted to experimentally demonstrate the control the nano-, micro- and macro-scale cracking in cement-based composites by using nano-, micro- and macro-scale fibres. While micro, macro and hybrid system polypropylene (PP) fibres were used in concrete designs, micro-scale PP and multi-walled carbon nano tubes (MWCNT) were utilized in mortar mixtures. The progression of the cracks was monitored in accordance with a well-known standard and also with a modified method which enabled the investigation of plastic and restrained shrinkage. Fracture energy, flexural strength, compressive strength, modulus of elasticity and ultrasonic pulse velocity of the samples were also determined as the mechanical properties of the composites. Results showed significant improvements in the reduction of cracks, especially with hybrid fibres system.

Research on the Effect of Fire Thermal Energy on the Microstructure and Properties Mechanical of Fiber-Reinforced Cement Mortars

Cement mortar is made of a combination of cement, sand, and water, mixed in the right proportions. It is ideal for erecting walls and masonry structures, including those that must bear heavy loads. In addition, it is used in places that are exposed to higher humidity and in facilities located below ground level. The potential uses of a mortar are determined by material modification. The aim of the experimental studies was to evaluate the effect of high temperature on the microstructure and mechanical properties of cement mortars modified with polypropylene fiber. The novelty of this study is an attempt to compare the use of different types of polypropylene fibers in mortars heated at different temperatures. Cement mortars based on Portland cement CEM I 42.5 R with a constant content of three types of fibers in the amount of 0.9 kg/m3 were designed. The samples were cured and then heated in an oven at 300, 500 and 700 °C. The functional properties of cement mortars, i.e., density, flexural and compressive strength after 28 and 56 days of maturation, as well as flexural and compressive strength at elevated temperature, were determined using samples of 40 × 40 × 160 mm. By modifying cement mortars with fibers, it is possible to obtain a cement composite with good strength parameters which is, at the same time, resistant to high temperature.

Mechanical Behavior of Fiber-Reinforced Soils under Undrained Triaxial Loading Conditions

The design of fiber-reinforced soil structures, such as embankments and pavements, can be carried out using the results of unconsolidated, undrained triaxial compression tests conducted on specimens at their “as-compacted” water content and analyzed in terms of total stresses. The effects of soil and fiber type on the mechanical behavior of fiber-reinforced soils have not been methodically or adequately examined in the past under these conditions, and the effects of fiber length and content on the shear strength parameters of fiber-reinforced soils need further experimental documentation. Accordingly, five soils ranging from “excellent” to “poor” materials for use in earthwork structures were tested in the present study, in combination with five types of polypropylene fibers having lengths ranging from 9 to 50 mm. Unconsolidated undrained triaxial compression tests were conducted on specimens at their “as-compacted” water content, with fiber contents ranging from 0.5 to 2% by weight of dry soil. Fiber reinforcement reduces the stiffness and increases the deformability of the soil. The fiber-reinforced soils exhibit a more ductile behavior in comparison with the unreinforced soils. A Mohr–Coulomb type linear failure criterion satisfactorily describes the shear strength behavior of fiber-reinforced soils in total stress terms. The cohesion values of the fiber-reinforced soils range between 61 kPa and 301 kPa and increase up to seven times in comparison with the cohesion values of the unreinforced soils. The variations of the angle of internal friction of soils due to fiber reinforcement are generally limited to ±25%. The cohesion improvement due to fiber reinforcement is increased with increasing fiber content and fiber length up to 30 mm and is inversely proportional to the fine-grained fraction and the cohesion of the unreinforced soil.

Studying the Failure Behavior of Cement-fiber-treated Sand under Triaxial Direct Tension Tests

The main goal of this research is to study the failure behavior of cement-fiber-treated sand under triaxial direct tension condition tests. Thus, a new loading system and triaxial cell was designed and built for tensile loading. Samples were prepared with content cement of 3 and 5% (dry wt.) of the sand, while two types of polypropylene fibers 0.024 m in length and 23 μm and 300 μm thick were added at 0.0% and 0.5% (dry wt.) of the sand and cement mixture. After a seven-day curing period, the samples were loaded under triaxial direct tension tests under confining pressures of 100, 200, and 300 kpa in drained conditions. Stress-strain behavior, changes in volume and energy absorbed by cement-fiber reinforced sand were measured and compared with the results of other studies. Adding fibers resulted in reduced peak deviatoric stress and increased residual deviatoric stresses of the cement-fiber reinforced sand, with changes from brittle to ductile behavior. The initial stiffness and stiffness at 50% maximum tensile stress of the samples is decreased with the addition of fibers and with an increase in fiber diameter, the reduction rate of this stiffness is more evident. The absorbed energy for fibers with a thickness of 23 μm is less than fibers with a thickness of 300 μm. The effect of adding fibers to strength parameters showed that the cohesion intercept decreases, while the internal friction angle increases.

A Study of the Flexural Behavior of Fiber-Reinforced Concretes Exposed to Moderate Temperatures.

The use of synthetic fibers in fiber-reinforced concretes (FRCs) is often avoided due to the mistrust of lower performance at changing temperatures. This work examines the effect of moderate temperatures on the flexural strengths of FRCs. Two types of polypropylene fibers were tested, and one steel fiber was employed as a reference. Three-point bending tests were carried out following an adapted methodology based on the standard EN 14651. This adapted procedure included an insulation system that allowed the assessment of FRC flexural behavior after being exposed for two months at temperatures of 5, 20, 35 and 50 °C. In addition, the interaction of temperature with a pre-cracked state was also analyzed. To do this, several specimens were pre-cracked to 0.5 mm after 28 days and conditioned in their respective temperature until testing. The findings suggest that this range of moderate temperatures did not degrade the behavior of FRCs to a great extent since the analysis of variances showed that temperature is not always a significant factor; however, it did have an influence on the pre-cracked specimens at 35 and 50 °C.

Modular pavements: Developing high performance concrete

The main objective of this research is to develop high-strength concrete mixture (compressive strength ≥ 41 MPa) that is resistant to fatigue and suitable to produce slabs for modular pavements also known as precast concrete pavements. In addition to this, other characteristics (compressive strength, flexural strength and indirect tensile strength) were determined as well and the effect of fibers depending on type and amount in the presence and absence of silica fume has been revealed. Silica fume (0% and 7% by cement mass) and three types of fibers (one type of steel fibers and two types of polypropylene fibers) with three different amount of each fiber type were used to produce concrete mixtures. At all, 20 concrete mixtures were produced and tested in terms of static and cyclic bending, static compression and static tension. The research showed that the use of both fibers and silica fume in the concrete mixture leads to the best performance and steel fibers are superior to polypropylene fibers. Concrete mixture with 49.5 kg/m3 of steel fibers and 7% of silica fume by cement mass had compressive strength of 61 MPa and the highest resistance to fatigue and thus is the most potential to produce slabs for modular pavements.

Effect of multi‐scale polypropylene fiber hybridization on compressive constitutive mechanics parameters of roller compacted concrete

AbstractTo investigate the influence of hybrid effect of different sizes of polypropylene fibers (PPFs) on the compressive constitutive mechanical parameters of roller compacted concrete, nine groups of fiber reinforced concrete specimens containing different sizes of PPFs were designed and the uniaxial compressive testing was conducted. Based on the existing compressive constitutive model and the test stress–strain curves, the peak stress, peak strain, elastic modulus, and the post‐peak stage parameter with different fiber proportion were analyzed and discussed to find the optimum mixing proportion of different sizes of PPF, the calculation of compressive toughness factor were given. The results showed that the addition of PPF could improve the compressive properties of RCC. The axial compressive strength and compressive strain of RCC increased by 3%~16% and 7%~57%, respectively. Meanwhile, the coarse PPF can significantly enhance the ductility of RCC when subjected to uniaxial compressive loading, and the group of multi‐scale PPF hybridization had higher compressive toughness than groups blended with two types of PPF, showing a more obvious positive hybrid effect. Finally, multi‐scale fiber hybrid effect function was proposed, the results showed that the function can well reflect the influence of fiber hybrid effect on the compressive properties of RCC and can be used to predict the optimal fiber proportion of fiber reinforced concrete.

The Effect of the Type and Amount of Synthetic Fibers on the Effectiveness of Dispersed Reinforcement in Soil-Cements.

The paper deals with mechanical properties of soil-cement composites made with non-cohesive soil and reinforced with dispersed fibers. The research was carried out on the basis of three soil-cement matrices whose compositions varied in terms of the volumetric fraction of cement paste and the water-cement ratio. Two types of polypropylene fibers were used as dispersed reinforcement: single fibrillated-tapes polypropylene fibers (SFPF) and bundles of coiled fibrillated-tapes polypropylene fibers (BCFPF). The fibers varied in terms of their length and mass fraction. The objective of the study was to assess the effect of the addition of fibers to soil-cement composites on their flexural tensile strength and on their behavior in the post-critical state. The studies were carried out after 28 days of curing. Bending tests were carried out to determine post-critical stress values σCMODi, stress values at which the matrix is destroyed (limit of proportionality) σLOP, maximum stress values transferred by the fibers σMOR (modulus of rupture), and total fracture energy Gf,tot as well as compressive strength. The test results obtained, and their analysis, indicate the significant impact of the dispersed reinforcement used on the performance of such composites during bending.

Rheological Properties and Strength of Polypropylene Fiber-Reinforced Self-compacting Lightweight Concrete Produced with Ground Limestone

In this study, self-compacting lightweight concrete (SCLC) was prepared using crushed limestone dust, and the effects of different types of polypropylene fibers and chemical admixtures on the rheological properties of SCLC were investigated. The workability of SCLC was assessed by conducting slump flow, J-Ring, and V-funnel tests, and the compressive strength of the cubic specimens was measured at the ages of 2, 7, and 28 days. Overall, specimens containing fibers displayed lower workability than the control mix; however, a simple adjustment of the dosages of the superplasticizer and viscosity-modifying admixture remedied this problem. The results reveal that the maximum fiber content is 4 kg/m3 for microfibers and 6 kg/m3 for macrofibers. Producing SCLC containing 33% limestone powder by weight as cementitious material satisfied self-compacting concrete requirements and exhibited compressive strength greater than 55 MPa at the age of 28 days.

Drained volumetric behaviour and static liquefaction of very loose sand reinforced with synthetic fibres

Synthetic fibres may be used to reinforce soils. Fibre reinforcement may, for example, improve the mechanical behaviour of very loose sand which is usually susceptible to static liquefaction. In this study, two types of polypropylene fibres are mixed into sand to explore the effect of fibre reinforcement on drained volumetric behaviour and undrained static liquefaction. Drained and undrained stress-controlled triaxial compression tests are conducted on both unreinforced and fibre reinforced samples which are in very loose states. It is observed that, under drained compression, both unreinforced and fibre reinforced samples show volumetric contraction. In undrained compression the excess pore water pressure eventually becomes almost equal to the initial confining stress in all samples. This represents a state of liquefaction in unreinforced samples, and they become fluidised indicating the effective stress has become zero. However, in reinforced samples, the fluidised condition is absent, indicating that a conventional type of liquefaction has not occurred. It is concluded that static liquefaction in very loose sand can be prevented by fibre reinforcement, as the induced tensile stress in fibres makes the effective stress (that is the stress carried by the soil skeleton) remain above zero even when the excess pore water pressure is equal to the confining stress.

Improvement in tensile and flexural ductility with the addition of different types of polypropylene fibers in cementitious composites

The influence of addition of fibrillated and monofilament polypropylene fibers to a cementitious composite mix on the tensile strength, flexural strength and ductility characteristics of the sample are being probed in this study. The study demonstrates that addition of fibrillated variety improves the strength of the samples both in tension and flexure in comparison to that of monofilament variety, whereas the addition of monofilament variety improves the tensile and flexural ductility characteristics of the sample. A combination of both these type of fibers improves the tensile strength and ductility characteristics along with improvement in flexural ductility with no significant improvement in flexural capacity.

Effect of Polypropylene Fibers on Self-Healing and Dynamic Modulus of Elasticity Recovery of Fiber Reinforced Concrete

This study aims to evaluate self-healing properties and recovered dynamic moduli of engineered polypropylene fiber reinforced concrete using non-destructive resonant frequency testing. Two types of polypropylene fibers (0.3% micro and 0.6% macro) and two curing conditions have been investigated: Water curing (at ~25 Celsius) and air curing. The Impact Resonance Method (IRM) has been conducted in both transverse and longitudinal modes on concrete cylinders prior/post crack induction and post healing of cracks. Specimens were pre-cracked at 14 days, obtaining values of crack width in the range of 0.10–0.50 mm. Addition of polypropylene fibers improved the dynamic response of concrete post-cracking by maintaining a fraction of the original resonant frequency and elastic properties. Macro fibers showed better improvement in crack bridging while micro fiber showed a significant recovery of the elastic properties. The results also indicated that air-cured Polypropylene Fiber Reinforced Concrete (PFRC) cylinders produced ~300 Hz lower resonant frequencies when compared to water-cured cylinders. The analyses showed that those specimens with micro fibers exhibited a higher recovery of dynamic elastic moduli.

Fluidity evaluation of fiber reinforced-self compacting concrete based on buoyancy law

An experimental testing program was undertaken to evaluate the applicability of using the principles of Archimedes' law for buoyancy to assess the fluidity of self compacting concrete (SCC) as well as fiber reinforced self compacting concrete mixes (FR-SCC). A cone instrument with different apex angle values (20, 30, 40 and 45°) was implemented. One type of steel fibers (SF), three types of polypropylene fibers (PP1, PP2 and PP3) as well as one type of glass fibers (GF) with different fiber volume fractions and aspect ratios were conducted. Fourteen FR-SCC mixes in addition to a control mix were examined. A new terminology called fluidity index (FI) was proposed and evaluated based on the displaced volume rate according to the buoyancy law through performing cone penetration test. Parallel with the penetration test, traditional flow ability and segregation resistance tests were performed.The results indicated that the proposed method is effective in evaluating the fluidity of FR-SCC mixes in terms of FI. FI values between 0.8 and 1.0 indicate SCC mixes whereas, FI lower than 0.8 indicate fresh concrete with fluidity not satisfying requirements of SCC. The proposed method can be performed either at laboratory or at field with and without sampling. Moreover, it can be directly adapted to the cast concrete in structural members provided that there is no obstruction for penetration. The direct proportion between FI and the slump flow test results indicated its viability to evaluate the fluidity of both FR-SCC and SCC mixtures.

Прочностные и теплофизические свойства бетона с полипропиленовой фиброй в условиях температурного режима стандартного пожара

The paper discusses the problems of protection of reinforced concrete tunnel structures from brittle (explosive) destruction of concrete tubbing lining of the tunnel. The relevance of the research is attributed to increasing pace of construction of deep-level tunnels. Fires in such facilities could be catastrophic, often resulting in massive loss of life and great material losses, and their suppression requires involvement of considerable forces and assets. During the construction and operation of road and subway tunnels, the protecting structures - reinforced concrete lining blocks have a higher moisture content, which in the event of fire in the early stages can lead to brittle failure of concrete tubing and the premature loss of their load-bearing capacity. To reduce the effects of brittle fracture of concrete in the protective layer of concrete structures anti-spall mesh is installed, or fire retardant coating is used which reduces the intensity of heating of concrete during fire. However, recent studies have shown that the most effective way of protecting against brittle fracture of concrete from the point of view of labor and material cost is the use of additives in the concrete mixture in the form of polypropylene fibers. Earlier, experiments were carried out in VNIIPO to determine the actual limits of fire resistance of tunnel tubing and the influence of polypropylene fibers additives in concrete mix on the likelihood of brittle fracture of concrete. However it seems impossible to assess the fire resistance of similar structures using numerical methods due to the lack of baseline data on the strength and thermo-physical properties of concrete with polypropylene fibers. To achieve this goal, studies were conducted of concrete strength under axial compression with the addition of polypropylene fibers in the amount of 1 kg/m 3 and experimental data of thermal characteristics of fiber-reinforced concrete at high temperatures were obtained. The paper presents the results of experiments on the samples of fiber concrete under axial compression when exposed to temperature in the range 20-800 °C. Graphics show the process of the strength change of concrete with and without additives during heating. Analytical dependencies for determination of strength of concrete under compression were obtained with two types of polypropylene fibers at high temperatures.A comparison of the strength properties of the investigated concrete mixtures was carried out. It was established experimentally that when using the polypropylene fibers, the strength characteristics of fiber-concrete are reduced on average by 16 %, compared to the concrete without fiber additives, both at normal and high temperatures. As a result of processing of the experimental data by regression analysis the analytical dependencies were obtained for determination of strength characteristics of concrete under axial compression with the addition of domestic and imported fibers when exposed to high temperatures. Experiments to determine the thermal properties of concrete with the addition of polypropylene fibers, were conducted during one-sided heating of board samples on the temperature regime of “standard fire”. In the presence of experimental data, by solving the inverse heat conduction problem using the previously developed computer program, the thermophysical characteristics (thermal conductivity and heat capacity) of fiber-reinforced concrete at elevated temperatures were defined. With increasing temperature, the thermal conductivity decrease is more intensive in concrete with added polypropylene fibers than that of concrete without additives. At the same time, the addition of fiber does not affect the intensity of increase of the heat capacity of concrete. The obtained dependences of thermophysical properties of concrete with domestic and imported polypropylene fibers on temperature increase make it possible to carry out calculations of heating of concrete structures with selected additives on a temperature regime of “standard fire”. The conducted studies on the effect of temperature on the strength and thermal properties of concrete with addition of polypropylene fiber reinforcement can be used in calculation of the fire resistance of load-bearing and enclosing structures made of this type of fiber-reinforced concrete.

Barcelona test for the evaluation of the mechanical properties of single and hybrid FRC, exposed to elevated temperature

The mechanical behaviour of single and hybrid FRC mixtures, with one type of steel and two types of polypropylene fibres at 0.5% and 1.0% volume fractions, is investigated through the double punch Barcelona test. Indirect tensile strength and toughness characteristics are evaluated at ambient temperature and after heating of the specimens at 280°C. It is shown that the modified toughness estimated through Barcelona test may be a suitable index to classify FRC in terms of ductility, both for the unheated and for the heated specimens. It was also found that hybrid FRC, containing an appropriate amount of different fibre types, is superior in terms of ductility compared to the single FRC. Finally, equations are proposed for the calculation of the Total Circumferential Opening Displacement (TCOD) values by using the axial displacement measurements, considering basic characteristics of the fibres and of FRC mixture, such as fibre’s length, rupture strength and volume fraction, respectively.

Oil absorption and desorption by polypropylene fibers

Oil spill is a threat to the ecosystem, and there is a need for the development of highly efficient oil sorbents for environmental remediation. In this study, four different types of polypropylene fibers were evaluated for their oil absorbency and desorption characteristics. These fibers varied in their fineness and structural characteristics, i.e., hollow or solid. A modified ASTM methodology was used in the study to better represent the oil sorption capacity of a sorbent. To the best of our knowledge, this is the first study to present the effect of fiber fineness and structure on the oil desorption behavior of polypropylene fibers. Results showed that finer fibers had higher oil sorption capacity (g/g) than the coarser fibers. There was no statistical difference in the rate of desorption among the solid fibers; however, the hollow fiber had a statistically higher rate of desorption than the solid fibers.

Effect of Fibercast and Fibermesh inclusion on the direct shear and linear shrinkage response of clay

Inclusion of synthetic fibers is becoming a routine task in soil reinforcement. The ability of synthetic fibers in controlling the shrinkage cracks in concrete is the main drive to consider its benefits in clay and other soil materials. The polypropylene fibers are nonbiodegradable and can perform well even in aggressive chemical exposure conditions. The direct shear testing is a popular geotechnical approach to assess the shearing strength for a range of soils. This study is aimed at investigating the effect of fiber inclusion on the direct shear response of semi-arid clay soils. This research is conducted using two different types of polypropylene fibers, viz., Fibercast and Fibermesh, having different surface properties on the shear strength envelope and parameters (angle of internal friction and cohesion). The aspect lengths were varied as 6 and 12 mm, and the dosages were varied as 0.2, 0.4, and 0.6 % by weight of the soil. The results were viewed in relation to the fiber type, size, and dose. The soil response and shear resistance measured in consolidated undrained direct shear test is presented for the targeted doses, and the results revealed useful insight compared to unreinforced. The Fibermesh material proved to be the more appropriate fiber additive to typical semi-arid clay soils. The data provides helpful guide for the design geotechnical engineers.

Investigation on Flexural Properties of Hybrid Fibre Reinforced Self-compacting Concrete

The paper considers compressive and flexural parameters of self-compacting concrete reinforced with combination of steel and polypropylene fibers. Three volume ratios of steel fibers (0.5%, 1.0%, 1.5%) were mixed with two amounts (0.3%, 0.9%) of two types of polypropylene fibers. The influence of hybrid fibers on the compressive strength of SCC was negligible and comprised in the range of -5 to 11% of the strength of the matrix. Based on the flexural tensile tests on hybrid fibre-reinforced mixes it was noticed that steel fibers play the most important role in enhancement of the mechanical parameters. Meanwhile, in the hybrid mix of polypropylene fibers only slightly improve the toughness, irrespectively of the length of the PP fibers. The highest applied amount of the longest polypropylene fibers indeed improved the flexural parameters of the SCC matrix reinforced with steel fibers but on the other hand such concrete did not satisfy the requirements for SCC in the fresh state.

Different Performance of Foam Concrete Caused by Two Types of Fiber

400kg/m3 apparent density foam concrete consists of protein foaming agent, ordinary Portland cement and two types of polypropylene fibers is made in this study. The effects of two types of fibers (polypropylene linear fiber and polypropylene mesh fiber) on the compressive strength, flexural strength and water absorption of the foam concrete were investigated. The results showed the difference of the water absorption of the foam concrete with addition of the two types of fibers is not significant, but the difference of the compressive strength and flexural strength is clear. Moderate addition of fibers could improve the strength of the foam concrete. As compared with control, the compressive strength and flexural strength increased by as high as 60.7% and 71.2%, respectively. From the experimental results, it is clear that polypropylene linear fiber has advantage of compressive strength and flexural strength over polypropylene mesh fiber when mixed with foam concrete.

Shear strength behaviour of polypropylene fibre reinforced cohesive soils

Soil reinforcement through the inclusion of oriented or randomly distributed discrete elements such as fibres has recently attracted increasing attention in geotechnical engineering. Therefore, the purpose of this paper is to investigate the influence of certain parameters (the strength properties of the fibre, the relative size of the fibres and grains, and the rate of shear) on the shear strength of polypropylene fibre reinforced cohesive soils. A series of consolidated drained or undrained direct shear tests were conducted on unreinforced and reinforced sandy silt and silty clay specimens. Two types of polypropylene fibres with different mechanical indices were used. The fibre content was varied between 0.3% and 1.1% by weight of dry soil. The test results revealed that the inclusion of fibres in soil significantly increases the shear strength. The attainment of the high shear strength is attributed to the micromechanisms involved in the fibre/soil interactions as studied through scanning electron micrographs. The results also showed that the reinforcement effect was more pronounced under undrained shearing conditions. An important outcome from the current work is that, from the data obtained, the strength of the reinforced soil composites is not practically affected by the fibre mechanical indices.