Macro-synthetic Fibers Research Articles

Pullout behavior of polypropylene macro-synthetic fibers treated with nano-silica

A study of the effects of nano-silica treatment on the bonding properties of macro synthetic polypropylene fibers embedded in a cement matrix is provided in the present paper as a step to improve interfacial properties of the fiber reinforced cementitious composites (FRCC). Polypropylene fibers were treated by sol–gel technique, allowing to obtain a nano-silica coating. Scanning electron microscopy was used to observe the morphological features of PP fibers surfaces before and after the pullout test. The effects of the treatment were investigated by comparative pullout tests on treated and untreated fibers. An increase in maximum load and energy necessary for the complete extraction of the fiber was observed, as a consequence of the improvement of the interface properties due to the nano-silica hydration activity. These two parameters control the crack-resistance and ductility properties of FRCC and are deeply influenced by bonding and friction phenomena. The hydration products act as chemical and physical anchors, thus producing a densification of the interface transition zone (ITZ). The abrasion phenomena occurring on the fiber surface during the pullout test are responsible of hardening behavior, consisting in the increase in the frictional shear stress with the fiber slip and thus in the energy required for fiber extraction.

Effects of Mineral Admixtures on Microstructure-linked Strength Properties of Macro-synthetic Fiber Reinforced Concrete

This study investigates the effects of fly ash and silica fume on the mechanical properties and microstructure characteristics of interfacial transition zone (ITZ) between macro-synthetic fiber and the bulk matrix of the fiber reinforced concrete. The experimental results show that the concrete is able to withstand significant post-cracking loads and undergo remarkable deflections under flexural loads due to the bridging effect of macro-synthetic fiber. The mechanical properties of concrete incorporating fly ash plus silica fume are much better than those prepared with no mineral admixtures or mono addition. The work of adhesion is an integrated index to evaluate the bonding behaviors between fiber and matrix, which exhibits a trend similar to that noted in the flexural toughness. The compound addition of fly ash and silica fume presents the most distinct improvement effects on microstructure of ITZ and the bonding behaviors between fiber and matrix. The amount of hydrated calcium silicate (C-S-H) gel and compaction of ITZ play key roles in the fiber - matrix interfacial bond and the mechanical properties of concrete.

Behaviour of Macro Synthetic Fiber Reinforced Concrete Columns Under Concentric Axial Compression

Previous studies have shown that fiber reinforced concretes can improve post-peak behaviour, ductility and energy-dissipation ability of concrete elements under flexure, shear and axial load. Ductile behaviour is one of the essential characteristics that have to be possessed by structures located in moderate to high seismic regions. This paper presents an experimental investigation of a series of nine macro synthetic fiber-reinforced concrete (MSNFRC) circular columns. The objective of the studies was to investigate the effects of the macro synthetic fibers on strength and ductility of the columns. The test parameters were the spacing of the spiral reinforcement and the volume fraction of the macro synthetic fibers. In two-thirds of the specimens, when macro synthetic fibers were added to the specimens, spiral reinforcement was reduced. The remaining specimens were detailed in accordance with the code minimum requirement for spiral reinforcement in order to examine the influence of the fibers on strength and ductility. A concentric axial compression load was applied monotically on the column specimens. The results show that the addition of macro synthetic fibers leads to improved ductility and strength. Furthermore, based on this study, the code required spiral reinforcement can be reduced whenever MSNFRC is used.

Contribution of fiber reinforcement in concrete affected by alkali–silica reaction

Fiber reinforced concrete (FRC) is a high performance material that is frequently used for structures in contact with aggressive environments, because the fibers can control the propagation of cracks. This paper analyzes the residual properties of FRC after the alkali–silica reaction has taken place. The potential contribution of different types of fibers for mitigating the degradation process and their effects on the mechanical and transport residual properties are discussed. The expansions, presence of cracks, compressive strength and modulus of elasticity, and the behavior under flexural loads were evaluated. Steel fibers were the most efficient for reducing the crack density, followed by synthetic macrofibers. The coefficient of air permeability followed the same tendency, showing the positive effect of macrofibers in transport properties. Concretes incorporating steel or synthetic macrofibers conserve their original post-peak loading capacity when severe alkali–silica reaction damage has taken place.

Effects of Macrosynthetic Fibers on Pervious Concrete Properties

AbstractThis paper presents the results of a testing plan designed to evaluate the effects of macrosynthetic fibers on pervious concrete material properties and durability. The effects of two lengths of fibers (38 and 56 mm) were investigated at three dosage rates (1.5, 3.0, and 4.5 kg/m3) in a single mixture. The unit weight and void content of all samples were controlled to allow determination of the effects caused directly by the fibers. Samples were tested for strength and durability properties. The results indicate that fibers in general reduced permeability and the infiltration rate, while reducing surface abrasion and improving freeze-thaw durability.

Investigation of Fiber Distribution in Concrete Batches Discharged from Ready-Mix Truck

This paper presents the findings of an investigation of the fiber content variations in concrete being discharged from a ready-mix truck at the construction site. Concrete samples were extracted from the truck drums at the beginning, middle and end of discharge. Subsequently, fibers in each sample were separated from the concrete, and weighed. Presumably, synthetic macro fibers will float towards the top, i.e. towards the drum opening, of the inclined, revolving truck-drum, while, on the other hand, steel fibers will tend to gravitate towards the lower parts of the mixer drum. Accordingly, the discharge batch, containing synthetic macro fibers, will contain a higher amount of synthetic fibers per unit volume at the start of discharge than the average unit volume fiber content of the mix, and the content will gradually decrease further down the batch. The discharge batch of steel fiber concrete will contain fewer fibers per unit volume at the start of discharge than the average unit volume fiber content of the mix, and the content should gradually increase further down the batch. The correctness of the foregoing is partly confirmed. A certain percentage of the truck loads did not comply with the proposed requirements, mainly steel fiber reinforced batches, indicating the necessity of a code or guideline amendment. A change in the Norwegian shotcrete directive was made in 2011, based upon experimental research work (2010), which, in combination with the subsequent University of Life Sciences report (2012), constitutes the foundation of this article.

Tensile creep of macro-synthetic fibre reinforced concrete (MSFRC) under uni-axial tensile loading

The increased energy absorption capacity of fibre reinforced concrete (FRC) is well known. Much, however, remains unknown about the time-dependent behaviour of FRC under sustained loading let alone the mechanism causing the phenomenon. This paper reports a study of the time-dependent behaviour of pre-cracked macro-synthetic fibre reinforced concrete (MSFRC) subjected to uni-axial tensile sustained loading. To fully understand the creep behaviour, investigation of the time-dependent fibre pull-out and fibre creep was also conducted. For the purpose of in-service simulation, the MSFRC specimens were pre-cracked before testing. Stress levels investigated were 30–70% of the residual, post crack, uni-axial tensile strength of the MSFRC. The experimental investigations revealed that cracked MSFRC shows significant creep and the fibre creep and the time-dependent fibre pull-out are the major sources of the creep behaviour.

Backcalculation of residual tensile strength of regular and high performance fiber reinforced concrete from flexural tests

The tensile stress–strain response of a fiber reinforced concrete dominates the performance under many loading conditions and applications. To represent this property as an average equivalent response, a back-calculation process from flexural testing is employed. The procedure is performed by model fitting of the three-point and four-point bending load deflection data on two types of macro synthetic polymeric fibers, one type of steel fiber and one type of Alkali Resistant (AR) glass fiber. A strain softening tensile model is used to simulate the behavior of different FRC types and obtain the experimental flexural response. The stress–strain model for each age, fiber type and dosage rate is simulated by means of the inverse analysis procedure, using closed-form moment–curvature relationship and load–deflection response of the piecewise-linear material. The method of approach is further applied to one external data set for High Performance Fiber Reinforced Concrete (HPFRC) with two different types of steel fibers and validated by tensile test results reported. Results of back-calculation of stress–strain responses by tri-linear tensile model for all mixtures are compared and correlated with the corresponding standard method parameters used for post crack behavior characterization and a regression analysis for comparative evaluation of test data is presented.

Improvement of Impact Resistance of Synthetic Macro-Fiber Reinfored Concrete

The incorporation of a small amount of steel fibers or fine polypropylene fibers in concrete can increase its impact resistance. But steel fiber has the problems of corrosion, high cost and high mess. The effect of fine polypropylene fibers in inhibiting the impact crack is not effective. The research was taken to measure the properties of fresh concrete mixture of Synthetic Macro-fiber reinforced concrete. And investigated the influence of fiber length and volume fraction on the impact resistance of Synthetic Macro-fiber reinforced concrete. The results showed that these fibers could obviously improve the impact resistance of concrete. There was a best Synthetic Macro-fiber volume fraction. The length of the Synthetic Macro-fiber had a certain influence on the impact resistance of concrete.

Interface pullout properties of macrosynthetic fibres in latex modified cement based nanosilica and silica fume composites

In this study, the bond properties between macrosynthetic fibres and latex polymer modified cement composites (LMCCs) were evaluated at different nanosilica and silica fume (microsilica) contents. The bond tests were evaluated according to Japan Concrete Institute SF-8, in which the nanosilica and silica fume contents in the cement were set to 0, 2, 4, 6 8, or 10%, based on cement weights. The addition of nanosilica and silica fume significantly influenced the bond properties between macrosynthetic fibres and LMCCs. Both bond strength and interface toughness improved with increasing silica fume content up to 10%. Both bond strength and interface toughness increased with nanosilica content up to 6% and then decreased with nanosilica content of 8% or more. This result was confirmed by observing an increase in scratching due to friction forces. This study was validated using microstructural analysis of torn macrosynthetic fibres after the bond tests.

다발형 폴리아미드섬유 보강 콘크리트의 휨거동에 관한 실험적 연구

일반적으로 건설재료 용도로 많이 사용되고 있는 유기섬유 보강 콘크리트는 섬유 자체의 인장강도 및 탄성계수는 낮지만, 휨거동, 균열에 대한 저항성 및 충격저항성 등의 특성은 우수하며, 내화학성이 뛰어나고 부식의 우려가 없는 것으로 널리 알려져 있다. 최근 해외에서는 유기섬유 보강재를 터널 숏크리트와 프리캐스트 세그먼트 라이닝, 교량 슬래브 및 PC제품 분야에서 일부 활용되고 있으며, 그 종류 또한 다양하다. 본 연구에서는 다발형 폴리아미드섬유를 혼입한 콘크리트의 휨거동 특성을 ASTM C 1609 및 KS F 2566에 준하여 하중-처짐 관계를 도출하여 유기섬유 보강 콘크리트의 적용 가능성을 검토하였다. Synthetic fiber reinforced concrete is applicable to many applications for construction material. In general, synthetic fibers have low tensile strength and elastic modulus, but they have many advantages such as high crack resistance, impact resistance, chemical resistance, flexural behavior and corrosion free in fiber reinforced concrete. Recently, fiber reinforced concrete with macro synthetic fibers has been used to improve performance of structures in tunnel shotcrete, precast segmental lining and bridge slab and precast concrete structures. This study investigated the influence of bundled type polyamide fiber reinforced concrete on the flexural behavior in accordance with ASTM C 1609 and KS F 2566 standards.

On the mechanical properties and fracture behavior of polyolefin fiber-reinforced self-compacting concrete

Fiber-reinforced self-compacting concrete uses the flowability of concrete in fresh state to improve fiber orientation, in due course enhancing toughness and energy absorption capacity. In the past few years there has been a boost in the development of concretes with macro-synthetic fibers added. In this paper the mechanical properties of a self-compacting concrete with low, medium and high-fiber contents of macro polyolefin fibers are studied. Their fracture behavior is compared with a plain self-compacting concrete and also with a steel fiber-reinforced self-compacting concrete. The results obtained showed that a polyolefin fiber-reinforced self-compacting concrete has fracture properties analogous to a steel fiber-reinforced self-compacting concrete. Furthermore, it is possible to fit this behavior within the existing standards requirements. Dispersion obtained for fracture mean values among the different amounts was analyzed by using a fracture surface analysis and the amount and distribution of fibers.

The effects of macro synthetic fiber reinforcement use on physical and mechanical properties of concrete

Attempts to find a construction material having increased strength, ductility, toughness, and durability have led to interest in high performance fiber reinforced concrete. The use of such materials increases day by day. When the fibers are distributed in a homogeneous way and used in appropriate quantity inside the concrete, they reduce cracks, contribute to tensile strength, toughness, ductility and durability, and improve other mechanical properties. In this study, four types of concrete were produced: steel fiber (SFRC), polyester fiber (PYFRC), polypropylene fiber (PPFRC) reinforced concrete and a reference sample made of plain concrete (R1); these were then compared to one another. The ratio of fibers was used 4.25% of volume of concrete. The effects of the different types of fiber on hardened concrete were determined by conducting physical and mechanical experiments. Compressive strength, surface hardness, ultrasonic pulse velocity, carbonation, abrasion, capillarity and freeze–thaw resistance experiments were conducted on hardened concretes. SFRC had higher 12.4%, PYFRC 3.4% higher and PPFRC 4.3% lower compressive strength with respect to R1. PPFRC showed 8.04% higher compressive strength than R1 when it was determined by the surface hardness method. SFRC showed 5.4% higher compressive strength than R1 when we applied the ultrasonic pulse velocity method. In the abrasion experiment, the highest abrasion was found in SFRC with ∼0.5%, while the lowest was found in PPFRC at ∼0.18%. The highest and lowest amount of capillary water absorption was seen in R1 and PYFRC, respectively. In a carbonation experiment, SFRC was determined ∼130.8% higher than R1. It was concluded that the types of fiber used for reinforcement influenced the physical and mechanical properties of the concrete.

Experimental Study on Mechanical Properties of Synthetic Macro-Fiber Reinforced Reactive Powder Concrete

Workability, strength and fracture mechanics of polypropylene macro-fiber reinforced Reactive powder concrete (RPC) were studied in this work. The results showed that the incorporation of macro-fiber could influence the workability of RPC, the slump of RPC decreased with the increasing of macro-fiber content; compressive strength decreased while splitting strength increased with the increasing of macro-fiber, meanwhile the flexural strength invariant. Macro-fiber could strongly enhance the flexural toughness of RPC and changed the failure mode from brittle to ductile; fracture energy tends to increase linearly with the increasing of macro-fiber.

Rebound and orientation of fibers in wet sprayed concrete applications

Spraying of concrete is a well-established and economical alternative to conventional casting techniques. It is widely applied in repair/reinforcement of building elements, rock consolidation and for the construction of temporary or permanent tunnel linings. Sprayed concrete (shotcrete) may be reinforced with fibers, steel rods or steel meshes to increase its mechanical performance under bending. In wet spraying, the concrete is premixed with water and then sprayed by means of compressed air. The fibers are added to the fresh concrete and then sprayed together with it. Because of their high elastic modulus and tensile strength often steel fibers are used for such applications. Recently, macro-synthetic plastic fibers have been proofed to be a suitable non-corroding alternative.The mechanical performance of fiber reinforced shotcrete is mainly influenced by the amount, the distribution and the orientation of the fibers, which are parameters that are influenced by the special application technique. Because of the relatively high impact velocity, the concrete and the fibers do not adhere completely onto the treated surface and generally a large quantity of rebound is observed.The rebound behavior of macro-synthetic polymer fibers and of steel fibers was studied in field tests as well as in laboratory experiments. Concrete was sprayed on well-defined artificial stone reliefs and the fiber as well as the material rebound was collected and analyzed. On the example of macro-synthetic fibers, the influence of different fiber parameters on the rebound behavior was studied. Single fiber shooting experiments and direct observations by means of a high speed camera revealed their impact behavior and hence the causes for fiber rebound.The fiber orientation in sprayed concrete was analyzed by means of X-ray computer tomography. Special morphological filtering allowed the analysis of the properties of plastic fibers despite their low density. A preferential orientation of these fibers along the sprayed surface was observed.

나노클레이 첨가량에 따른 나노재료 시멘트 모르타르에 정착된 보강섬유의 인발성능

Recently, it has been studied for the application of nano-materials in the concrete. Applied a small amount of nano-materials can achieve the goal of high strength, high performance and high durability. The small addition of nano clay improves strength, thermal stability, and durability of concrete because of the excellent dispersion. The present study has investigated the effectiveness, when varying with the contents of nano clay, influencing the pull-out behavior of macro synthetic fibers in nano materials cement mortar. Pullout tests conducted in accordance with the Japan Concrete Institute (JCI) SF-8 standard for fiber-reinforced concrete test methods were used to evaluate the pullout performance of the different nano clay. Nano clay was added to the 0, 1, 2, 3, 4 and 5 % of cement weight. The experimental results demonstrated that the addition of nano clay led to improve the pull-out properties as of the load-displacement curve in the precracked and debonded zone. Also, the compressive strength, flexural strength and pullout performance and of Mix No. 1 and No. 2 increased up to the point when nano clay used increased by 2 and 3 % contents, respectively, but decreased when the exceeded 3 and 4 %, respectively. It was proved by verifying increase of the scratching phenomenon in macro synthetic fiber surface through the microstructure analysis on the surface of macro synthetic fiber.

Design of macro-synthetic fibre reinforced concrete pipes

This paper presents an experimental campaign in which concrete pipes were manufactured using plastic fibres as the sole reinforcement material. In this regard, it has been demonstrated that the use of plastic fibres is compatible with pipe production systems, and that, when subjected to the crushing test (CT), plastic fibre reinforced pipes yield strength classes that are attractive in terms of the growth of this material in the concrete pipe industry. Moreover, the results obtained from both the characterisation of the material and the mechanical behaviour of the pipes have been used to verify that the Model for the Analysis of Pipes (MAPs) is an appropriate tool for the design of such pipes. Finally, this paper presents a direct design methodology which was used to establish the firsts design tables for fibre reinforced concrete pipes presented in the scientific literature. This methodology can be used to estimate the strength requirements of the fibre reinforced concrete needed to reach the strength classes set out in EN 1916:2002, without having to resort to the CT as an indirect design method.

Effect of nanosilica and silica fume content on the bond properties of macro-synthetic fibre in cement-based composites

In this study, the effects of nanosilica and silica fume content on the bond properties of macro-synthetic fibre in cement-based composites were investigated. The pullout behaviour of macro-synthetic fibre was evaluated by performing dog-bone bond tests according to JCI SF-8 at nanosilica and silica fume replacement ratios of 0, 2, 4, 6 and 8% based on cement weight. The addition of nanosilica and silica fume had a significant effect on the bond properties of macro-synthetic fibre. Specifically, the addition of 0∼2% nanosilica enhanced pullout behaviour, bond strength and interface toughness, whereas 4% or more nanosilica reduced pullout behaviour, bond strength and interface toughness. For silica fume, pullout load-to-displacement behaviour, bond strength and interface toughness increased in the range of 0 to 8%. These results demonstrate that the presence of nanosilica and silica fume strengthen the fibre–matrix interface of macro-synthetic fibre in cement-based composites by filling voids in the interface region. The relative bond strength and interface toughness were also analysed, except for compressive strength, to evaluate the bond properties of macro-synthetic fibre in cement-based composites at various nanosilica and silica fume replacement ratios. The ratios of nanosilica and silica fume had a significant effect on bond properties, regardless of the compressive strength of the cement-based composites. Microstructural analysis of macro-synthetic fibre after pullout tests showed scratches due to friction.

Influence of Aspect Ratio of Macro Synthetic Fiber on Mechanical Properties of Shotcrete

Influences of moisture content and loading rate on flexural toughness were experimentally studied for fiber reinforced shotcrete (FRSC) with steel fiber or macro synthetic polypropylene fiber. According to the four-point bending test method specified in ASTM C1609 and Chinese standard CECS 13, the flexural toughness of specimens after drying for 0h, 16h, 24h and 72h in condition of (20±2)°C and (60±5)% relative humidity was tested at a loading rate of 0.05 mm/min. For specimens after drying for 24h and 72h, flexural toughness was tested at loading rates of 0.05 mm/min, 0.10 mm/min, and 0.20 mm/min respectively. With the moisture content decreasing, the flexural toughness T100,2.0, first-peak flexural strength, and residual flexural strength at prescribed deflections of FRSC exhibited decreasing tendency. The specimens with 0.5 vol% of steel fiber showed higher T100,2.0 value than that with 0.9 vol% of macro synthetic fiber. The residual strength and flexural toughness of FRSC increased with the increase of loading rate.

Mechanical properties of a large scale synthetic fibre reinforced concrete ground slab

The existing design code for Concrete Industrial Ground Floors, TR34, by the Concrete Society states that “Macro synthetic fibres provide some post-cracking or residual moment capacity but with significantly lower performance than steel fibres. They are not known to be used in industrial floor construction”. This paper presents results of an ongoing investigation undertaken by the authors concerning the mechanical and physical properties of fibre reinforced concrete ground slabs at an industrial scale. This paper focuses and presents results concerning the punching shear failure of a 6.00m×6.00m×0.15m synthetic fibre reinforced ground supported slab. The paper demonstrates clearly the methodology adopted and the infrastructure used throughout this investigation. The presented results show clearly that the punching shear failure values obtained in this investigation are comparable to values reported for the steel fibre slabs under similar conditions. This work could potentially question the validity of the above statement in TR34. The significance of this research also is in the size of the slab investigated, as there is very limited work, if any, reported within the literature.