Polyolefin Fibre Reinforced Concrete Research Articles

Mechanical properties of polyolefin and polypropylene fibers-reinforced concrete–An experimental study

Concrete, a widely used construction material, exhibits inherent brittleness and limited tensile strength. To address these shortcomings, the incorporation of fibers has gained prominence, with polyolefin and polypropylene fibers emerging as promising reinforcements. This study experimentally conducted and examined the mechanical characteristics of polyolefin and polypropylene fibers-reinforced concrete. The study involved conducting compressive strength tests and durability tests, including sulfate resistance, acid resistance, chloride ion penetration resistance, and abrasion tests. The results demonstrated a notable enhancement in the compressive strength of both cubic and cylindrical specimens with varying dimensions, owing to the inclusion of polyolefin fibers. Polyolefin fibers exhibited a greater reinforcing effect compared to polypropylene fibers, especially in larger cubic specimens and cylindrical specimens. The quantitative results show that specimens with polypropylene fibers exhibited a 9.67 % improvement in compressive strength, while those with polyolefin fibers showed a 30.47 % enhancement compared to specimens without fibers. The acid resistance test revealed that both types of fiber-reinforced specimens exhibited higher compressive strength in acidic environments compared to plain concrete specimens. In the chloride ion penetration resistance test, the polyolefin fiber-reinforced specimen demonstrated the highest resistance to degradation, while the plain concrete specimen exhibited the lowest resistance. Polyolefin demonstrated superior reinforcement compared to polypropylene, with a 35 % increase in acid resistance and better chloride ion resistance. In contrast, specimens without fibers weakened by 35.36 % in a chloride environment. The sulfate resistance test showed that the polyolefin fiber-reinforced specimen had the highest compressive strength in a sulfate environment, while the plain concrete specimen had the lowest. In sulfate and abrasion tests, polyolefin-fiber-reinforced specimens displayed the highest resistance and the lowest abrasion rate of 34.6 %. These findings highlight the potential of polyolefin fiber-reinforced concrete for enhancing mechanical properties and durability in various applications.

Numerical Simulation of PFRC Fracture Subjected to High Temperature by Means of a Trilinear Softening Diagram.

Fibre-reinforced concrete (FRC) has been used for decades in certain applications in the construction industry, such as tunnel linings and precast elements, but has experienced important progress in recent times, boosted by the inclusion of guidelines for its use in some national and international standards. Traditional steel fibres have been studied in depth and their performance is well-known, although in recent years new materials have been proposed as possible alternatives. Polyolefin macro-fibres, for instance, have been proven to enhance the mechanical properties of concrete and the parameters that define their behaviour (fibre length, fibre proportion or casting method, for instance) have been identified. These fibres overcome certain traditional problems related to steel fibres, such as corrosion or their interaction with magnetic fields, which can limit the use of steel in some applications. The behaviour of polyolefin fibre-reinforced concrete (PFRC) has been numerically reproduced with success through an embedded cohesive crack formulation that uses a trilinear softening diagram to describe the fracture behaviour of the material. Furthermore, concrete behaves well under high temperatures or fire events, especially when it is compared with other construction materials, but the behaviour of PFRC must be analysed if the use of these fibres is to be extended. To this end, the degradation of PFRC fracture properties has been recently experimentally analysed under a temperature range between 20 °C and 200 °C. As temperature increases, polyolefin fibres modify their mechanical properties and their shape, which reduce their performance as reinforcements of concrete. In this work, those experimental results, which include results of low (3 kg/m3) and high (10 kg/m3) proportion PFRC specimens, are used as reference to study the fracture behaviour of PFRC exposed to high temperatures from a numerical point of view. The experimental load-deflection diagrams are reproduced by modifying the trilinear diagram used in the cohesive model, which helps to understand how the trilinear diagram parameters are affected by high temperature exposure. Finally, some expressions are proposed to adapt the initial trilinear diagram (obtained with specimens not exposed to high temperature) in order to numerically reproduce the fracture behaviour of PFRC affected by high temperature exposure.

Microcrack monitoring and fracture evolution of polyolefin and steel fibre concrete beams using integrated acoustic emission and digital image correlation techniques

The use of polymer and steel fibres in plain concrete appears to be an excellent solution for limiting crack propagation and improving the post-ductility performance of concrete structures. Based on this premise, this study investigated the fracture evolution of polyolefin fibre-reinforced concrete (PFRC) and steel fibre-reinforced concrete (SFRC) specimens through the integrated application of two diagnostic techniques, acoustic emission (AE) and digital image correlation (DIC), under three-point bending tests. Based on the processing of AE signals, different AE statistical parameters such as the cumulative number of hits, amplitude distribution, and some representative analysis methods including the b-value method, Ib-value method, and AE intensity analysis methods were selected to analyse the early detection of cracking and post-cracking behaviour in PFRC vs SFRC specimens during mechanical degradation. Simultaneously, the DIC technique was used to validate the fracture evolution of the AE results. Furthermore, to verify the reliability of the AE and DIC results, the damage localisation and fracture evolution of the PFRC versus SFRC specimens were confirmed by integrating the AE fracture energies and DIC outcomes. The tests and analysed results showed that the addition of steel fibres to plain concrete significantly improved the ability to restrict crack propagation and provided higher post-cracking resistance compared to PFRC specimens owing to their stronger fibre–matrix bonding, effective fibre bridging, and crack-arresting mechanism. The present study indicates that the combined AE and DIC techniques are highly effective for the early detection of damage and ductility performance in fibre-reinforced concrete structures.

Mixed mode fracture of polyolefin fibre reinforced concrete

Throughout the last 60 years, the use of fibre reinforced concrete (FRC) has evolved favourably. By this technique, it is possible to reduce or substitute the traditional steel-bar reinforcement in the structural design of concrete elements for both civil and building construction. The most used fibres for this purpose are made of steel, though there have been remarkable advances in the plastic fibres that have made them an attractive alternative. Thus, macro polyolefin fibres have shown to meet the requirements set in the standards in order to consider their contribution in the structural design. To do so, fracture behaviour under Mode I has been the main topic of research in the last years. Nevertheless, there is still a lack of knowledge about the behaviour of polyolefin fibre reinforced concrete (PFRC) under other modes of fracture or the combination of them. This study assesses the behaviour of PFRC with several fibre dosages when subjected to Mixed mode fracture with several fibre dosages as well as the influence of the size effect with various sizes. Moreover, this paper supplies relevant information about the cracking processes and the variation in the orientation factor and residual strengths that take place when Mode I and Mode II of fracture occur simultaneously.

Shear and Flexural Behavior of Flat Slabs Casted with Polyolefin Fiber-Reinforced Concrete

This paper presents the influence of polyolefin fiber on the flexural and shear attitude on the flat slabs. Three slab sets (80 cm × 80 cm) were tested, each with a thickness of 10 cm. In the first set (S1), the effect of fiber content on the flexural behavior of the flat slab was considered. Therefore, four slab specimens were cast, one of which was considered as a control specimen with no fiber content, while the other three included fibers at 0.5, 1, and 1.5 percent of the total concrete volume. The second series of experiments studied the flexural behavior of flat slabs (S2) with an opening of 15 cm × 15 cm. The first specimen contained nil polyolefin, while the second included 1% polyolefin. In the third set (S3), consideration was taken for 0 and 1% of Polyolefin to realize the shear behavior of the flat slab. The increase in polyolefin fiber content from 0 to 1.5% (for slab set 1) will decrease the deflection from 4.5 mm to 2.3 mm, with an average of 3.58 mm, which is close to the deflection of a 1% polyolefin fiber specimen. Three dimensional models for the tested slabs were simulated numerically via ABAQUS software program. The ratio of the maximum deflection between the experimental and the numerical outcomes were varied with a range of 1.01 to 1.28, with an average of 1.14.

Suitability of Constitutive Models of the Structural Concrete Codes When Applied to Polyolefin Fibre Reinforced Concrete.

The use of fibres as structural reinforcement in concrete is included in standards, providing guidelines to reproduce their behaviour, which have been proven adequate when steel fibres are used. Nevertheless, in recent years new materials, such as polyolefin fibres, have undergone significant development as concrete reinforcement. This work gives insight on how suitable the constitutive models proposed by the Model Code 2010 (MC2010) are in the case of such polymer fibres. A set of numerical models has been carried out to reproduce the material behaviour proposed by the MC2010 and the approach based on the softening function proposed by the authors. The results show remarkable differences between the experimental results and the numerical simulations when the constitutive models described in the MC2010 are employed for different polyolefin fibre reinforced concrete mixes, while the material behaviour can be reproduced with greater accuracy if the softening function proposed by the authors is employed when this type of macro-polymer fibres is used. Moreover, the relatively complex behaviour of polyolefin fibre reinforced concrete may be reproduced by using such constitutive model.

Use of digital image correlation to connect fracture curves and sectional analysis for structural design of polyolefin fibre reinforced concrete elements

The boosting of the polyolefin fibre reinforced concrete (PFRC) usage for structural design requires that a connection between the laboratory standards and the structural codes be made. This study aims to fill this gap by combining laboratory mechanical test results, digital image correlation and numerical simulations. The σ-ε and σ-w relations in PFRC elements have been connected by means of a parameter that affects the strain of concrete (lref). lref depends linearly on the crack width and exponentially on the fibre dosage. A procedure that enables an accurate multilayer sectional structural analysis for PFRC structural elements has been obtained.

Assessment of the Post-Cracking Fatigue Behavior of Steel and Polyolefin Fiber-Reinforced Concrete.

Some types of fiber-reinforced concrete (FRC) such as steel fiber-reinforced concrete (SFRC) or polyolefin fiber-reinforced concrete (PFRC) are suitable for structural uses but there is still scarce knowledge regarding their flexural fatigue behavior. This study aimed to provide some insight into the matter by carrying out flexural fatigue tests in pre-cracked notched specimens that previously reached the Service Limit State (SLS) or the Ultimate Limit State (ULS). The fatigue cycles applied between 30% and 70% of the pre-crack load at 5 Hz until the collapse of the material or until 1,000,000 cycles were reached. The results showed that the fatigue life of PFRC both at SLS or ULS was remarkably higher than the correspondent of SFRC. The fracture surface analysis carried out found a linear relation between the fibers present in the fracture surface and the number of cycles that both SFRC and PFRC could bear.

Fracture and Size Effect of PFRC Specimens Simulated by Using a Trilinear Softening Diagram: A Predictive Approach.

The size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.

Influence of High Temperature on the Fracture Properties of Polyolefin Fibre Reinforced Concrete

Concrete has become the most common construction material, showing, among other advantages, good behaviour when subjected to high temperatures. Nevertheless, concrete is usually reinforced with elements of other materials such as steel in the form of rebars or fibres. Thus, the behaviour under high temperatures of these other materials can be critical for structural elements. In addition, concrete spalling occurs when concrete is subjected to high temperature due to internal pressures. Micro polypropylene fibres (PP) have shown to be effective for reducing such spalling, although this type of fibres barely improves any of the mechanical properties of the element. Hence, a combination of PP with steel rebars or fibres can be effective for the structural design of elements exposed to high temperatures. New polyolefin fibres (PF) have become an alternative to steel fibres. PF meet the requirements of the standards to consider the contributions of the fibres in the structural design. However, there is a lack of evidence about the behaviour of PF and elements made of polyolefin fibre reinforced concrete (PFRC) subjected to high temperatures. Given that these polymer fibres would be melt above 250 °C, the behaviour in the intermediate temperatures was assessed in this study. Uni-axial tests on individual fibres and three-point bending tests of PFRC specimens were performed. The results have shown that the residual load-bearing capacity of the material is gradually lost up to 200 °C, though the PFRC showed structural performance up to 185 °C.

HORMIGÓN DE BAJAS PROPIEDADES RESISTENTES REFORZADO CON FIBRAS DE POLIOLEFINA: CONSIDERACIONES Y DISEÑO DE UN HORMIGÓN ESTRUCTURAL COMPETITIVO

Polyolefin fibre reinforced concrete (PFRC) has become an attractive alternative to steel fibre reinforced concrete for structural applications. Although PFRC has shown capacity for meeting the structural requirements set in the regulations sometimes, complying with the residual strength value at 0,5mm of crack opening (fR1) might be a challenge. That value is aimed at avoiding brittleness of the concrete element and in certain occasions require fibre dosages close to 6kg/m³. Most of the previous studies have been performed with normal or high quality concretes and consequently their strength at the end of the limit of proportionality (fLOP) is also remarkable. Given that the residual strength at fR1 is proportional to fLOP, manufacturing of a concrete with inferior mechanical properties would allow production of one that encountered fewer issues related with brittleness and offered improvement in tensile and flexural strength at a reduced cost. In this study, several concretes with reduced mechanical properties and with 6 and 7,5kg/m³ of polyolefin fibres were manufactured. Their mechanical response was analysed in order to determine if they were apt for their use in low responsibility structural concrete members. Moreover, the influence of the method used to add the fibres was studied by adding the fibres in two different ways adding them individually from sacks or using pucks (50g each one). Keywords: Polyolefin fibre reinforced concrete, regulation requirements, moderate strength concrete.

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

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

CARACTERIZACIÓN EXPERIMENTAL DE LA RESISTENCIA A TRACCIÓN Y CORTANTE DEL HORMIGÓN REFORZADO CON FIBRAS DE POLIOLEFINA

In the last decades, certain types of non-metallic fibres have been found suitable for structural concrete elements achieving analogous performance of steel fibres. Among such non-metallic fibres, polyolefin macro-fibres can meet the requirements set in the standards in order to consider their contribution in the structural design. However, EHE-08 consider the constitutive models based on steel fibre reinforced concrete as the reference for other fibres. Previous experimental campaigns carried out with polyolefin fibre reinforced concrete (PFRC) have evaluated their flexural fracture behaviour, with several amounts of fibre dosages. In addition, their constitutive models have been found. Given that the structural requirements were set based on the results obtained following UNE-EN 14651:2007+A1 that only considers the flexural behaviour, the contributions of the fibres when the structural element is subjected to more complex stress states is a matter that deserves being further studied. The main objective of this contribution was to assess the performance of PFRC subjected to tensile stresses and shear stresses. This was carried out developing uniaxial tensile tests and push-off tests. In order to do so the remaining halves of PFRC samples already tested following UNE-EN 14651 were used. Two PFRC formulations were studied, one with 6kg/m³ of fibres and another with 7.5kg/m³ of fibres. In both cases 48mm-long fibres were added. These tests were also recorded in order to analyse the damage patterns and the appearance, growing and coalescence of cracks by means of digital image correlations techniques. Non-standardised test results showed a remarkable PFRC behaviour both under tensile and shear stresses. Such results together with the flexural behaviour previouses found confirmed the suitability of PFRC as a structural material. In addition, the test results widened the knowledge of the mechanical response of PFRC under complex stress states.

Using Polyolefin Fibers with Moderate-Strength Concrete Matrix to Improve Ductility

AbstractResearch has shown that polyolefin fiber–reinforced concrete (PFRC) can meet the requirements of standards in terms of the contributions of fiber in structural design. Such results were obt...

Modelling fracture on polyolefin fibre reinforced concrete specimens subjected to mixed-mode loading

In recent years, polyolefin fibres have proved a remarkable performance as reinforcement of concrete, which has inspired a number of studies involving, among others, the simulation of fracture on polyolefin fibre reinforced concrete (PFRC) specimens. Fracture has been successfully reproduced on PFRC specimens in the past by means of an embedded crack model with a trilinear softening function, but always using for comparison the classical three-point bending test, which employs a symmetrical setup and induces fracture under pure mode I conditions. In the present study, six sets of specimens tested under an alternative setup of the three-point bending test, which induces fracture under mixed-mode conditions (I and II), are simulated using the same numerical approach. The results not only prove that the use of a trilinear softening function together with an embedded cohesive crack approach can reproduce fracture under mixed-mode conditions, but also provide interesting insights on how the trilinear softening function may be designed for suiting the usage of different fibre lengths or varying the proportions of polyolefin fibres.

Influence of Fiber Distribution and Orientation in the Fracture Behavior of Polyolefin Fiber-Reinforced Concrete.

Polyolefin fiber-reinforced concrete (PFRC) has become an attractive alternative to steel for the reinforcement of concrete elements, mainly due to its chemical stability and the residual strengths that can be reached with lower weights. The use of polyolefin fibers can meet the requirements of standards, although the main constitutive relations are based on experience with steel fibers. Therefore, the structural contributions of the fibers should be assessed by inverse analysis. In this study, the fiber dosage was fixed at 6 kg/m3, and both self-compacting concrete and conventional concrete were used to compare the influence of the positioning of the fibers. An idealized homogeneous distribution of the fibers with such fibers crossing from side to side of the specimen was added to self-compacting concrete. The experimental results of three-point bending tests on notched specimens were reproduced by using the cohesive crack approach. Hence, constitutive relations were found. The significance of this research relies on the verification of the formulations found to build constitutive relations. Moreover, with these results, it is possible to establish a higher threshold for the performance of PFRC and the difficulties of limiting the first unloading branch typical of fracture tests of PFRC.

Can Polyolefin Fibre Reinforced Concrete Improve the Sustainability of a Flyover Bridge?

The use of polyolefin fibre reinforced concrete (PFRC) as an alternative for reducing the reinforcing steel bars employed in reinforced concrete has become real in the past years. This contribution analyses the improvements in sustainability that a change in the aforementioned reinforcement configuration might provide in a flyover bridge. Economic, environmental and social parameters of both possibilities were studied by means of the integrated value model for sustainable assessment. Such model, which acronym is MIVES (Modelo Integrado de Valor para una Evaluación Sostenible, MIVES), is a multi-criteria decision-making method based on the value function concept and the seminars delivered by experts. The results of the MIVES method showed that the use of PFRC in combination with reinforced concrete (RC) has a sustainability index 22% higher. An analysis of the parameters that form this evaluation shows that there are no remarkable differences in the financial costs between the two possibilities studied. Nevertheless, social and environmental aspects provide with a better qualification the option of building a bridge by using PFRC combined with RC.

Assessment of the shear behaviour of polyolefin fibre reinforced concrete and verification by means of digital image correlation

Given that remarkable structural applications of fibre reinforced concrete have been successfully developed in the last 60 years, modern concrete codes and fib Model Code have included requirements and formulations for considering the fibre contributions in structural design. In recent times, polyolefin fibre reinforced concrete (PFRC) has been shown as an attractive alternative to steel fibres, with it being chemically stable and having a lower dosage in terms of weight to reach similar residual strengths. It is worth noting that fibre contributions are attained from flexural tensile strengths tests. However, one of the major contributions provided by fibres in rebar substitutions has involved use in replacing shear stirrups. In such a sense, while the use of steel fibres has been shown as effective there is a lack of published literature with regard to PFRC. In this study, push-off tests in specimens obtained from the remaining halves after three-point bending tests have been performed. In addition to the mechanical results obtained, digital image correlation has allowed the cracking processes of the specimens to be identified. This paper offers a significant contribution to the field, given that it relies on the assessment of the shear contributions of polyolefin fibres and comparison with the requirements of the existing codes. Moreover, it supplies notable information about residual shear strengths and the cracking processes that take place.

Constitutive relationship of polyolefin fibre–reinforced concrete: Experimental and numerical approaches to tensile and flexural behaviour

AbstractFlexural tensile tests are usually used to evaluate the suitability of fibre‐reinforced concrete (FRC) in structural applications. The constitutive relationships of FRC are derived from such tests by using several inverse analyses. Given that the structural design of FRC is based on the residual load‐bearing capacities obtained under flexural tests, the approach to analyse fracture behaviour by means of uniaxial tensile tests would mean use of more direct and reliable constitutive curves compared with those obtained by indirect means. The significance of this paper lies in the characterisation of polyolefin fibre–reinforced concrete (PFRC) not only by using fracture flexural results tests but also by comparing such results with the direct tensile behaviour of the material obtained from uniaxial tests. This comparison would both extend the knowledge of the PFRC mechanical properties and broaden the reliability of structural design by comparing the behaviour of PFRC under flexural and tensile stresses. Moreover, the suitability of an iterative method proposed by the authors for obtaining the constitutive relations of PFRC from flexural tests has been checked by performing a series of numerical simulations of the tensile tests performed. The differences in the properties obtained in the flexural tests and the tensile tests have been assessed. The experimental results gathered from the tensile tests have been accurately reproduced by using a cohesive crack approach with trilinear softening functions by the iterative inverse analysis proposed.

Fibre distribution and orientation of macro-synthetic polyolefin fibre reinforced concrete elements

Fracture behaviour of polyolefin fibre reinforced concrete (PFRC) has proved to be suitable for structural design in construction elements. As in other fibre reinforced materials, the tensile behaviour is strongly affected by the positioning of the fibres. Previous research has assessed this influence by means of fracture tests, showing reliable results. These were obtained by changing the most influencing parameters: the fibre length, the pouring and compaction methods, the concrete type and specimen sizes. However, the influence of these factors in fracture results is merely limited to the fracture surfaces, while the positioning of the fibres in the rest of the piece may be a key factor for design in structural elements. Furthermore, examination of the orientation factor within the whole piece provides relevant information about the behaviour of the fibres during the pouring processes. It may also allow preparation of future models to predict the final positioning of the fibres. This paper examines the positioning and orientation of the fibres in elements which provided fracture results previously reported in the literature. In addition to counting the fibres located in the fracture surfaces, the specimens were divided in portions. The fibre-positioning maps obtained provide sound and useful conclusions that may be considered in future design of PFRC elements. The data gathered showed how the orientation-factor varied with the flux and vibration, absence of any tendency to float and the noticeable influence of the pouring point in fibre distribution. It also showed that this type of fibre is suitable for structural-size elements, improving the orientation factor for longer distances when using self-compacting concrete.