Macro-synthetic Fibers Research Articles

Structural Health Monitoring of Fiber-Reinforced Concrete Prisms with Polyolefin Macro-Fibers Using a Piezoelectric Materials Network under Various Load-Induced Stress

This experimental study investigates the influence of synthetic macro-fibers added in fiber-reinforced concrete (FRC) prismatic specimens on their flexural response and overall cracking performance. Application of a novel structural health monitoring (SHM) system that implements the electromechanical impedance (EMI) technique and the use of piezoelectric lead zirconate titanate (PZT) transducers installed in the FRC prisms are also included. The applied PZT-enabled EMI-based monitoring system was developed to diagnose damage and the overall performance in reinforced concrete (RC) structural members subjected to cyclic repeated loading, simulating seismic excitations in existing RC buildings. The paper also aims to determine the sensitivity of the real-time, wireless, and portable monitoring technique corresponding to the location, the distance, the direction of polarization of the PZT transducers and the location and magnitude of damage due to flexural cracking. Further, the influence of the effect of stresses corresponding at various loading levels and the observed changes in the ΕΜΙ frequency response of the PZT transducers are also examined. Test results indicated that cracking detection is achieved using this SHM system by prompt damage level assessment due to the FRC’s flexural load at early seismic loading stages in existing RC buildings.

Fiber takviyeli beton döşemenin doğrusal olmayan zımbalama davranışı üzerine parametrik bir çalışma

This paper investigates the effect of fiber on the behavior of punching shear slabs; a finite element modeling approach is used to simulate the case study. The proportion mix of hybrid fiber-reinforced concrete, which contains 0.2 percent macro synthetic fibers and 0.68, 0.8, and 0.96 percent steel fibers, compressive strengths of 50 MPa, different longitudinal reinforcement used, and slab thicknesses of 150, 200, and 250 mm are all joined and investigated in this study. The ATENA software is used to perform nonlinear finite element analysis. The slab results validation was done similar to previous experimental work and the acquired results indicated that a great agreement was found. Thirty-six specimen two-way slabs with dimensions of 1900 × 1900mm were modeled in this investigation. All four sides of the slabs are simply supported. The results displayed that the ultimate shear capacity of the slabs increases with hybrid steel fiber. Nevertheless, the ultimate capacity of the slabs has decreased due to an increase in the reinforcement ratio and slab thickness.

Mechanical response of precast tunnel segments with steel and synthetic macro-fibers

Precast tunnel lining segments manufactured with synthetic macro-fibers and steel fibers as the primary reinforcement were tested under flexural and edge compression loading. Since steel fibers are usually prescribed as the primary reinforcement of tunnel sections, the dosage of synthetic fibers was determined by matching their residual flexural strength. The performance of tunnel segments was verified using the extensive data collected from instrumented deflection, crack growth, quantitative DIC, and strain gauge results and correlated with the load vs. deformation response. Results show that synthetic fibers can meet the design load requirements specified for the steel fibers reinforcement. Flexural test results indicate a 16% increase in macro-fiber content from 0.80% to 0.93% by weight resulting in a 32% increase in the residual strength of standard beam samples and a 41% increase in the residual strength of full sections. Compared to the steel fiber samples, samples with polymeric macro-fiber had a 6.5% higher average toughness. The full-scale load-deflection results were within 7% of the average values in each category of samples which is almost half the variation in the flexural ASTM C1609 results. The edge compression tests indicated that the mode of failure under concentrated jack forces is governed and dominated by the tensile lateral bursting stresses resulting from inefficient distribution of the load to the supporting edge.

Eccentric load behaviour of concrete columns retrofitted with engineered cementitious composite jackets via grooving method

The eccentric load behaviour of circular reinforced concrete columns strengthened with a novel engineered cementitious composite jackets reinforced with synthetic macro-fibres and polypropylene was investigated. Furthermore, an innovative method of interface treatment known as longitudinal grooving was used. Twelve test columns were cast, six of which were strengthened with 15 mm thick composite jackets, while three were strengthened with ultra-high-performance fibre-reinforced concrete jackets. In addition, three of the six columns strengthened with the composite jackets were confined with glass-fibre-reinforced polymer warps. The experimental results showed that both methods enhanced load-carrying capacity and energy dissipation with increasing load eccentricity. For example, the specimens strengthened with the composite jackets exhibited increases of 167% and 194% in load-carrying capacity, and enhancements of 92% and 53% at eccentricities of 30 and 60 mm, respectively. Finally, the previously reported model and different codes were used to validate the results, from which interaction diagrams were drawn. This showed a good agreement between experimental and predicted results.

Evaluation of residual flexural behavior of corroded fiber-reinforced super workable concrete beams

This study investigates the effect of macro synthetic fiber (MSF) volume and crack widths on corrosion of the reinforcing bars and residual flexural behavior of fiber-reinforced super-workable concrete (FR-SWC) beams exposed to accelerated corrosion. FR-SWC beams prepared with 0, 0.33%, and 0.66% MSF were pre-cracked at 0.2-, 0.4-, and 0.75-mm widths before corrosion testing. The controlled crack width was initiated in one set of beams that were then unloaded. The crack width was maintained for another set of beams during corrosion testing by inserting a shim. Test results showed that the use of 0.33% and 0.66% MSF reduced crack development and crack propagation, delayed corrosion initiation time, and significantly increased the residual flexural strength of beams subjected to accelerated corrosion. The beams reinforced with 0.66% MSF enhanced residual ultimate load, residual yield load, and residual flexural toughness by 10%–45%, 38%–113%, and 42%–150% compared to the corresponding non-fibrous beams. The improved flexural performance of beams made with MSF after accelerated corrosion can be attributed to the ability of MSF to reduce crack width due to corrosion damage. Crack width lower than 0.2 mm showed no significant effect on the residual flexural behavior of beams after corrosion testing. However, the pre-crack width over 0.2 mm showed a significant influence on the crack initiation and residual flexural behavior after accelerating corrosion. The pre-cracked beams with a 0.75 mm crack width retained the ultimate load of 65%–76%, yield load of 47%–80%, and toughness of 38%–83%, respectively, compared to their corresponding uncracked beams subjecting to accelerated corrosion. The un-shimmed beams allowed partial closure of cracks due to the presence of MSF after initial loading and increased the residual ultimate load, yield load, and flexural toughness by 7%–45%, 27%–82%, and 3%–56%, respectively, compared to their corresponding shimmed beams. A correlation between the residual flexural behavior and the rate of cross-sectional area loss of reinforcing bars due to corrosion was developed. Furthermore, a mechanism was proposed to explain the effect of MSF in improving the residual flexural performance in the cracked FR-SWC beams.

Influence of various fibers on the physico-mechanical properties of a sustainable geopolymer mortar-based on metakaolin and slag

Recently, studies on sustainability and ecology have become widespread in almost all sectors. One of the most important reasons for this spread is the rapid increase in industrialization and, thus, the increase in waste caused by industries. In this context, significant efforts are being made to evaluate some of these wastes. One of these efforts is the production of geopolymers. In this research, metakaolin and slag-based geopolymer mortar samples were manufactured, and polyvinyl Alcohol, basalt, and macro synthetic polypropylene fibers were used to enhance the physical, mechanical, and high-temperature resistance of the sample. Physical and mechanical tests of the produced samples were performed after 28 days. Then, elevated-temperature experiments were conducted to evaluate the behavior of the fibers under the influence of high temperature. Following the high-temperature test, physical, mechanical and microstructure tests of the samples were performed. As a result, basalt fiber enhanced the compressive strength of 800 °C-exposed samples by 7.72% compared to the fiber-free sample. Also, polyvinyl Alcohol fiber increased the energy absorption capacity of the samples by increasing Charpy impact values to 72.22% compared to fiber-free sample. Moreover, macro synthetic polypropylene fiber reduced capillary water absorption value up to 12.44% compared to fiber-free sample.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

A novel high-performance concrete based on calcium oxide-activated materials reinforced with different fibers

In this study, a high-performance concrete based on calcium oxide-activated materials (HPC-CAM) was developed and studied. Calcium chloride and calcium nitrate additives were used to improve the microstructure of such concrete. In addition, different fibers including steel, recycled PET, basalt, glass, and modified synthetic macro fibers were used to overcome the brittleness of the HPC-CAM geopolymer matrix. Compressive, flexural, water absorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests were performed to evaluate the overall characteristics of the specimens thus prepared. The results showed that adding calcium chloride and calcium nitrate increased the compressive strength of HPC-CAM by 69% and 29%, respectively. All samples containing calcium chloride had flexural strengths that were 20% higher than those with calcium nitrate. HPC-CAM samples reinforced with recycled PET fibers and modified synthetic macro-fibers recorded flexural toughness values that were 8- and 6-fold greater than those for steel fibers. The highest calcium silicate hydrate gel (C–S–H) and Si–O-T (T = Si or Al) peaks were obtained in HPC-CAM containing calcium chloride.

Macro synthetic fiber pullout behavior in short- and long-term tests

The creep phenomenon in fiber-reinforced composites is particularly important when synthetic macro fibers are used. In addition to the low modulus of elasticity, the polymers used in fibers have pronounced viscoelastic behavior even at room temperature, which can lead to changes in the cracking control over time. The long-term fiber pullout response also results from fiber and interface creep contributions. To understand the above phenomena, pullout tests with short- and long-term loads were conducted on three types of polymeric macro fibers subject to different levels of long-term loads (20, 30, 40 and 50%). The results of the pullout tests were strongly dependent on the fiber configuration, surface corrugation and modulus of elasticity. Macro fibers with crimped surfaces and higher modulus of elasticity achieved higher bond stresses and lower creep deformations. The Burgers model was applied and showed a good agreement with the experimental creep curves, therefore consisting of a promising alternative for modeling long-term behavior. Microtomography and scanning electron microscopy images showed that a large portion of the strain in tension, under sustained load, can be attributed to the creep of the fiber itself, thus making it challenging to estimate the creep of this type of composite, given the considerable variability of fiber configurations.

Effect of pore structure on shear resistance and chloride transport of macro-synthetic fiber reinforced concrete

This study proposes a method for the quantitative characterization of the complexity and uniformity of pore structure, and explores the effect of macro-synthetic fiber inclusion on the shear resistance and chloride transport of concrete from the perspective of pore structure. First, the shear capacity and chloride migration coefficient of normal concrete and macro-synthetic fiber reinforced concrete with fiber content of 3, 4.5, 6, and 9 kg/m3 were tested. Next, the porosity and pore size distribution were determined using the Rapidair 457 pore structure analyzer. The complexity of the pore structure was quantified using the fractal dimension calculated from the pore structure scans. The uniformity of spatial distribution of pores was quantified by the standard deviation of pore frequency. The results showed that increasing the fiber content increased the shear resistance and chloride transport of concrete while increasing the complexity and uniformity of pore structure. High-fidelity correlations between shear resistance and pore structure uniformity, chloride transport and pore structure complexity were established. This study will promote the fundamental understanding of concrete pore structure and properties for the development of high-performance fiber reinforced concrete.

Experimental and numerical studies on flexural behaviour of lightweight and sustainable precast fibre reinforced hollow core slabs

This study reports experimental and numerical studies on the flexural behaviour of sustainable fibre reinforced lightweight hollow core slabs (FR-LWHCS). An innovative and sustainable LWHCS is proposed for structural applications using a lightweight concrete mix of 1800 kg/m3 density, previously developed by authors. Full-scale precast LWHCS specimens are cast and tested under flexure using a four-point loading configuration. A high shear span to depth (a/d) ratio of 10 is chosen to have flexure dominant behavior. FR-LWHCS is made using sintered fly ash aggregate (SFA) as coarse aggregate and monofilament macro synthetic fibres of different volumetric fibre dosages (0.4 % and 0.6 %). A small dosage of micro synthetic fibres of 0.02 % by volume is also added to arrest shrinkage cracks. Two control slabs, one constructed with lightweight concrete and the other with conventional normal density concrete, are tested. The digital image correlation (DIC) technique is used to track the cracks and failure modes. A 3D finite element analysis is performed to supplement the test results. Test results show that FR-LWHCS satisfies all the structural requirements, leading to economy and sustainability. FR-LWHCS with 0.6 % fibre dosage performed better than hollow core slabs made of normal density concrete. Though the addition of fibres did not considerably increase peak load, a minimum dosage of fibre addition is warranted in LWHCS to improve the serviceability performance. Fibre addition significantly improved the strain energy absorption.

State-of-the-Art Review of Synthetic Fibres as Shear Reinforcement in Concrete Elements

Shear failure is considered one of the most critical modes of failure in concrete structures, especially for those elements without shear reinforcement. In the last sixty years, the research community has shown much interest to solve this problem. In fact, since the 80's years, the use of fibres dispersed in the matrix as shear reinforcement has been explored as an alternative of traditional reinforcement. Several investigations have shown that the addition of fibres in correct proportions, enhances the shear behaviour in concrete elements with and without shear reinforcement. Most of this knowledge has been built using steel fibres. However, macro-synthetic fibres have also been introduced for structural applications in concrete. Some recent publications have reported the success of macro-synthetic fibres to be used as shear reinforcement in structural elements. Within this framework, the present paper aims to review the existing literature about the use of synthetic fibres as shear reinforcement in structural concrete elements.

Experimental and numerical study on behaviour of fibre reinforced lightweight hollow core slabs under different flexure to shear ratios

The current work explores the behaviour of fibre-reinforced lightweight hollow core slabs (FR-LWHCS) intending to develop sustainable construction solutions. The FR-LWHCS investigated in this work contains sintered fly ash aggregate (SFA) as coarse aggregate. Due to the use of SFA, the behaviour of LWHCS is expected to be different from the hollow core slabs (HCS) constructed using normal density concrete. FR-LWHCS are tested at different shear span to depth (a/d) ratios of 3.5, 7 and 10 to understand the shear and flexure behaviour. Twelve full-scale hollow core slab (HCS) specimens of 3400 mm length, 600 mm width, and 150 mm thickness are tested. FR-LWHCS consists of monofilament macro synthetic fibre dosages of 0.4 %, and 0.6 %, along with fibrillated micro fibre of 0.02 % dosage. The digital image correlation (DIC) technique is adopted to understand the strain profile on the HCS at different levels of loading. The numerical analysis is performed using a commercially available finite element software and is corroborated with experimental findings and parametric studies have been performed. Both LWHCS and normal HCS specimens failed in shear, flexural-shear and flexure modes at a/d ratios of 3.5, 7 and 10, respectively. The addition of fibres increased the peak load by 65 % compared to control LWHCS specimens tested at an a/d ratio of 3.5. The use of fibres increased strain energy absorption and changed the failure to less brittle mode at all a/d ratios. The fibre reinforced specimens have nearly 3.5 times, 2.5 times and 1.3 times the strain energy absorption of the control LWHCS when tested at a/d ratio 3.5, 7 and 10 respectively.

Experimental Model for Study of Thickness Effect on Flexural Fatigue Life of Macro-Synthetic-Fiber-Reinforced Concretes

As one of the most widely used building materials, concrete has a dominantly brittle or quasi-brittle behavior. Adding fibers to concrete affects its ductility behavior as well as some mechanical properties. Finding the relationship between the addition of fibers and the change in thickness of laboratory test samples made of concrete can help in designing the optimal thickness of real concrete layers (especially concrete pavements) to withstand dynamic loads. The purpose of this research is to provide an experimental model for investigating the effect of concrete specimen size, or the thickness effect of concrete sample, on the fatigue life of concrete. Accordingly, several concrete beams with three thicknesses (80, 100 and 150 mm), constant width, and two lengths (120 mm and 450 mm) were manufactured with fiber percentages of 0 and 4% by fraction volume. The employed fiber was twisted macro synthetic fiber. After curing for 28 days, the samples were subjected to fatigue loading at three stress levels until the onset of failure and cracking stage. Here, the experimental model of the relationship between the number of loading cycles, the stress level and the thickness of the sample is presented. The results show that increasing the specimen thickness and fiber content can enhance the fatigue life of concrete up to 68%.

The impact of specimen size and alteration of fiber configuration on the flexural performance of high-performance concrete

This study examines the impact of fiber configuration and specimen size on the flexural performance and thus the energy absorption capacity of moderate and high-performance fiber reinforced concrete (FRC). A total of 180 specimens were produced using hooked-end steel fibers in lengths of 30-mm and 60-mm, and 54-mm long macro synthetic fibers. The specimens, in the form of small beams (75 × 75 × 320 mm3), large beams (150 × 150 × 750 mm3), and square panel specimens (600 × 600 × 100 mm3), were tested in accordance with EN14488-5 and ASTM C1609 standards. The results showed that as the amount of fibers increased, the flexural performance of FRC improved significantly, provided that precautions were taken to avoid mixing and placement issues when using higher amounts of fibers. 60-mm hooked-end steel fibers had the best performance among all the fibers tested with higher ultimate and post-cracking flexural strengths. 54-mm synthetic fibers seemed to be a cost-effective alternative with comparable energy absorption performance when compared to 30-mm hooked-end steel fibers. Small beams had a slightly higher ultimate (∼15% more) and post-cracking (∼35% more) flexural strengths than large beams, but the equivalent flexural strength ratio was not significantly affected by the specimen size. No clear relationship between fiber dosage and ultimate flexural strength was observed, but a relationship was observed between the fiber dosage and the equivalent flexural strength ratio, with R2 values ranging from 65% to 93% depending on the concrete matrix and the fiber type. The study also showed strong correlations (R2>91%) between the energy absorption capacity of plate specimens and beam specimens, suggesting that plate specimens can be used to reduce the time and effort required in testing during trial batches and product development. Finally, the use of high-performance concrete does not seem to be necessary, when the target is to improve the energy absorption capacity of FRC, particularly at low fiber volumes.

Punching shear behavior of RC slabs incorporating macro-synthetic fibers

The effect of macro synthetic fibers on punching shear behavior of reinforced concrete slabs was investigated. Twenty-four square reinforced concrete slabs (1500 mm × 1500 mm) were prepared, instrumented, and tested under monotonic, displacement controlled, center-point load in a simply-supported configuration. The main test parameters were the fiber volume fraction (0.5% and 1%), slab thickness (100 mm and 150 mm), and the flexural reinforcement ratio (0.9% and 1.5%). Test measurements included applied load, slab deflection, strains in the steel reinforcement and in the concrete. The development of the cracks for the duration of the test was also monitored and recorded. The test results showed that the punching shear strength, deflection capacity, and energy absorption of the FRC slabs were significantly improved by the presence of macro synthetic fibers. This improvement was associated by a more defined punching shear area, higher cracking density, higher strain in the concrete and a lower strain in the reinforcement steel. Furthermore, the level of improvement was found to be more pronounced in the FRC slabs with lower thickness, lower reinforcement ratio and higher fiber volume fraction.

Influence of short-term operating temperatures on compression and flexural behaviour of Macro Synthetic and Steel Fibre Reinforced Concretes

This study investigates the influence of operating temperatures on the mechanical properties of Fibre Reinforced Concretes (FRCs) when exposed during short-term periods (3 days). The studied parameters include types of fibres (macro synthetic and steel fibres), exposure to different environmental scenarios (with temperatures of −15, 5, 20, 40 and 60 °C as well as air exposition or submerged condition), and cracking conditions (precracked up to 0.5 mm or uncracked). A total of 126 cubes of 150 mm side and 182 prisms of 150 × 150 × 600 mm³ were tested in compression and flexion at the operating temperatures. The compression results obtained show similar effects in FRC and in plain concrete, with higher strength at low temperatures and slightly lower strength at higher temperatures. Similar effects were detected for the strength at the peak load, and to a minor extent, for the residual flexural strengths, for all the FRCs.

Influence of macro-synthetic fiber on the mechanical properties of iron ore tailing concrete

Iron ore tailing (IOT) is a hazardous by-product of iron extraction, and its disposal has resulted in serious environmental issues. This paper investigated the interfacial bond performance of macro-synthetic fiber (MSF). The effect of the IOT replacement ratio on the compressive performance of concrete and the effects of MSF on the compressive and flexural performance of IOT concrete were evaluated. Test parameters included IOT replacement ratio (0%, 50% and 100%), fiber volume fraction (0%, 0.5%, 1.0%, 1.5% and 2%) and fiber aspect ratio (43, 60 and 69). The test results indicated that the deterioration in compressive strength was observed with the increase in the IOT replacement ratio. The mechanism of the effect of IOT on the compressive performance of concrete was analyzed. However, the incorporation of MSF compensated for the reduction in compressive strength caused by iron ore tailings (IOTs). Furthermore, the post-cracking performance, which includes residual flexural tensile strength, equivalent flexural tensile strength and fracture energy, of concrete increased with the increase in fiber volume fraction. The fracture energy of IOT concrete increased by a factor of 18.06–20.19, and the post-cracking performance of IOT concrete was comparable with that of natural sand (NS) concrete at an MSF fiber volume fraction of 2%. At a given fiber volume fraction, the MSF with a higher fiber aspect ratio was more effective in improving post-cracking performance than one with a lower aspect ratio. Moreover, new empirical equations were proposed, which can accurately predict the residual flexural tensile strengths and equivalent flexural tensile strengths. These results provide important implications for determining the contribution of MSF in strengthening and toughening IOT concrete.

Comparison of hemp fibers with macro synthetic fibers in lime-metakaolin matrix incorporating pumice as coarse aggregates

Comparison of hemp fibers with macro synthetic fibers in lime-metakaolin matrix incorporating pumice as coarse aggregates