Macro-synthetic Fibre Reinforced Concrete Research Articles

Effect of post-peak flexural toughness on the residual performance of macro synthetic fibre reinforced concrete sleepers subjected to impact loading

Dynamic impact loading is one of the predominant causes of premature failure of concrete railway sleepers, demanding a fair portion of the railway budget. Therefore, macro synthetic fibre reinforced concrete (MSFRC) is suggested as an alternative owing to its improved post-peak flexural capacity, ductility and crack arresting properties. In such adaptation, the residual behaviour after dynamic impacts caused by wheel-rail irregularities governs the reusability and the life cycle of the sleepers. Correspondingly, the residual performance of impacted MSFRC sleepers was evaluated experimentally compared to conventional prestressed concrete sleepers. The residual behaviour of the sleepers was further supported by a series of material-scale flexural experiments. The fracture toughness of MSFRC increased with the crack-opening width because of the tension stiffening associated with fibre bridging. As a result, the residual capacity, stiffness, and toughness of MSFRC sleepers were higher than conventional sleepers, thereby improving their adaptability to the rail network.

Macrosynthetic fibers as replacement of conventional steel reinforcement for concrete of partition walls

AbstractConventional reinforced concrete for building partition walls has proven numerous advantages (in terms for instance of acoustic performance and robustness) with respect to other existing alternatives. However, its use leads to high material consumption and environmental footprint together with time‐consuming processes for placing steel reinforcement. To reduce time‐consuming processes and carbon footprint, the replacement of ordinary steel reinforcement by structural macrofibers is envisioned as a suitable solution due to: (1) the acceptance of fiber reinforced concrete (FRC) for structural applications in various guidelines (as Annex L of FprEN 1992‐1‐1:2023, draft for future Eurocode 2) and (2) the fact that the amounts of fibers necessary to reach the required mechanical performance of the FRC for crack control are expected to be economically competitive. Additionally, within the spectra of types of macrofibers capable of efficiently reinforce concrete, macrosynthetic fibers (MSFs) were considered in this research due to their benefits in terms of durability performance and reduced environmental impact (potential to use cements with lower clinker content and reduced thickness of elements). Aiming at confirming both the constructability, casting procedure and structural performance of macrosynthetic fiber reinforced concrete (MSFRC) partition walls, these walls were constructed in a real building in Switzerland. In this article, the design process is presented as well as the associated MSFRC material and structural experimental programmes, conducted both in laboratory and on‐site. In addition, several FEM‐modeling considerations as well as quality control and construction aspects observed during the implementation process are raised. Finally, for reference purposes, a first approach to the economic and environmental impact (CO2eq‐based) of such MSFRC walls is presented.

Numerical investigation of prestressed concrete sleepers reinforced with high-performance macro synthetic fibres

As modern railway tracks are exposed to heavier loads and higher operational speeds, the excessive cracking and premature failure of prestressed concrete sleepers are becoming more and more critical. Towards addressing these issues, this study focuses on the numerical integration of macro synthetic (polypropylene) fibres in prestressed concrete sleepers to improve the structural behaviours (i.e. residual capacity, cracking resistance & ductility) and assess the damage evolution. Moreover, the numerical investigation performed using Abaqus attempted to validate experimental results and optimised the sleeper design by partially reducing the number of prestressing wires. The analysis reveals good agreement with the experiment at critical cross-sections (i.e. rail seat & centre) and analytically allowed a ∼ 15 % reduction in prestressing steel reinforcement for the macro synthetic fibre reinforced concrete (MSFRC) sleeper. Accordingly, the optimised MSFRC sleeper performed adequately with minimum ultimate capacity reduction that meets the permissible specifications and future demands.

Assessment of the Specimen Size Effect on the Fracture Energy of Macro-Synthetic-Fiber-Reinforced Concrete.

The most frequently used construction material in buildings is concrete exhibiting a brittle behaviour. Adding fibers to concrete can improve its ductility and mechanical properties. To this end, a laboratory study was conducted to present an experimental model for the specimens' size effect of on macro-synthetic fiber-reinforced concrete using variations in fracture energy. Composite concrete beams with different thicknesses and widths were made and tested under mode I to obtain (1) fracture toughness, (2) fracture energy, and (3) critical stress intensity factor values. Results indicated that by increasing the thickness and the width, fracture toughness and fracture energy were enhanced. Moreover, increasing the thickness and width of the beam led to critical stress intensity factors enhancement respectively by 35.01-41.43% and 7.77-8.09%.

NUMERICAL MODELLING OF MACRO SYNTHETIC FIBER REINFORCED CONCRETE SLEEPERS UNDER STATIC AND IMPACT LOADING

The structural optimization of innovative materials requires reliable numerical modelling, which can predict the structural behavior of the respective adaptation under possible scenarios. This paper presents the numerical modelling of macro synthetic fiber reinforced concrete (MSFRC) in railway sleeper applications. MSFRC is well known to improve post-peak flexural strength and toughness owing to the crack-bridging mechanism of fibers. Even though the fibers act individually along the crack interface, MSFRC depicts tension hardening as a material. Therefore, this paper highlights the integration of fiber-concrete composite action as a homogenous material towards efficient modelling of MSFRC in terms of computational resources required. The concrete damage plasticity model (CDP) being widely used to simulate the plain concrete behavior, the adaptability of CDP in the numerical analysis of MSFRC was investigated using the experimental data. Since the railway sleeper is subjected to impacts caused by wheel-rail irregularities, the accountability of the CDP parameters under both static and low-velocity impacts was also evaluated. Correspondingly, the modified CDP parameters reasonably represented the static and impact capacity, crack and damage evolution, and structural stiffness of MSFRC sleepers.

POST-PEAK FLEXURAL BEHAVIOR OF MACRO SYNTHETIC FIBER REINFORCED CONCRETE

The addition of fibers to concrete is well known for enhancing the tensile and ductility performances through an effective fiber network intersecting the propagation of cracks. However, the class, quantity and properties of the individual fibers fundamentally govern the flexural behavior, resulting in either post-cracking softening or hardening response. Moreover, previous studies have shown that while steel and synthetic fibers may provide comparable improvement of the concrete’s mechanical properties, their respective involvement occurs at different crack widths to perform best in particular applications. In this paper, more consideration is given to macro synthetic fibers that are commonly preferred over steel fibers because of their corrosion resistance and sustainable sourcing pathway (i.e., recycled waste plastics). Thus, this work investigates the post-peak flexural behavior of macro synthetic fiber reinforced concrete (MSFRC) using two fiber types at different volume dosages. Accordingly, the novelty of this paper is to identify the critical crack states of each fiber type and dosages that provide the potential engineering benefits of a pioneering design and application.

Mechanical properties of macro synthetic fiber reinforced concrete at elevated temperatures: A systematic review and meta‐analysis

AbstractThe current infrastructure boom combined with the latest outcomes from 26th UN Climate Change Conference of the Parties (COP 26) seeking a carbon neutral society by 2050 have driven the increasing need for sustainable alternatives to be considered in construction. One such alternative is macro synthetic fibers, which have been gaining acceptance on major infrastructure projects. However, only limited uptake has occurred in permanent structures, due to a lack of knowledge around the behavior of macro synthetic fiber reinforced concrete (MSFRC) when exposed to elevated temperatures. Existing Australian and international design standards do not take into account the loss of strength for MSFRC after exposure to elevated temperatures. Hence, this systematic review sets out to combine all the existing knowledge on the mechanical properties of MSFRC and lay the groundwork for determining acceptable relationships between relative strengths and elevated temperatures. This study proposes relationships between temperature and compressive strength, splitting tensile strength, elastic modulus, flexural strength and residual flexural, and tensile strengths of MSFRC. These are compared to existing relationships determined for plain concrete and steel fiber reinforced concrete to position MSFRC within the context of existing and accepted knowledge.

Structural behaviour of prestressed concrete sleepers reinforced with high-performance macro synthetic fibres

The application of macro synthetic fibre reinforced concrete (MSFRC) innovatively addresses the current cracking and corrosion issues associated with the prestressed concrete railway sleeper. In this paper, a structural assessment of traditional concrete sleepers reinforced with high-strength, prestressed steel and macro synthetic fibres is provided. Detailed review on the rail seat and centre sections of the railway sleeper is presented to critically evaluate the mechanical benefits and feasibility of a complete replacement of prestressed steel with macro synthetic (polypropylene) fibres. Three types of sleeper were individually subjected to both positive and negative moments at these critical sleeper sections for their performances to be compared at cracking, ultimate capacity and failure. Accordingly, the potential implementation of MSFRC in sleepers has been proposed to cost-efficiently improve the current design for the railway industry.

Life cycle cost analysis of macro synthetic fibre reinforced concrete for railway sleeper applications

Over the last decade, restructuring of railway systems has resulted in infrastructure management assets demanding increased performance and reliability while adopting budget limits and reduced time available for maintenance. In fact, the current routine and major programmed maintenances are such capital-intensive activities that transport operating companies always attempt to optimise the operational procedures and related assets’ performances towards minimising the costs. Characteristically, the use of macro synthetic fibre reinforcement is proposed to improve the structural performances and service life of the sleeper component. Accordingly, this study addresses the economic feasibility of implementing macro synthetic fibre reinforced concrete (MSFRC) as an alternative material for railway sleeper applications. Through a life cycle costing (LCC) approach, the study evaluates the impact of different asset phases such as acquisition, operation and maintenance, and end-of-life towards a cost comparison of MSFRC with conventional sleeper materials. Hence, the most financially viable option is identified, although key economic parameters are varied to simulate future market values.

Effects of Low Temperatures on Flexural Strength of Macro-Synthetic Fiber Reinforced Concrete: Experimental and Numerical Investigation

Fiber-reinforced concrete (FRC) is an attractive alternative to traditional steel bar-reinforced concrete structures, as evidenced by the constantly increasing market consumption of structural fibers for this purpose. In spite of significant research dedicated to FRC, less attention has been given to the effects of low temperatures on the mechanical properties of FRC, which can be critical for a variety of structural typologies and regions. With this in mind, an experimental program was carried out to assess the flexural behavior of macro-synthetic fiber-reinforced concrete (MSFRC) at different temperatures (from 20 °C to −30 °C) by means of three-point bending notched beam tests. The tested MSFRCs were produced by varying the content of polypropylene fibers (4 and 8 kg/m3). The results proved that the flexural strength capacity of all MSFRCs improved with decreasing temperature. Finite element analyses were then used to calibrate constitutive models following fib Model Code 2010 guidelines and to formulate empirical adjustments for taking into account the effects of low temperatures. The outcomes of this research are the basis for future experimental and numerical efforts meant to improve the design of MSFRCs subjected to low temperatures during service conditions.

A Proposed Evaluation Method for Three-Point Beam Tests of Fiber-Reinforced Concrete

Abstract The characteristic values of the material parameters used for structural design are usually determined from the mean and standard deviation of the material test results, and the design values are calculated from the characteristic values using the appropriate safety factor. However, if the standard deviation of the test data is high, the characteristic value is expected to be significantly lower than the mean value. In the case of fiber-reinforced concrete (FRC), the coefficient of variation is usually high, which can be attributed to the relatively small size of the specimen and the random location of the fibers. To overcome this limitation, this paper proposes a method that takes into account the number and location of the fibers when estimating the postcrack performance for a cracked cross section in a three-point notched bending beam tests. Test results of steel- and macrosynthetic FRC were evaluated using both the RILEM recommendations and the proposed method and are finally compared. Although the proposed method is more complex and the evaluation requires more effort than the existing method, it provides more repeatable material parameters, which exhibited a higher characteristic result.

Structural assessment of eccentrically loaded GFRP reinforced circular concrete columns: Experiments and finite element analysis

Although extensive research of glass fiber reinforced polymer (GFRP) reinforced concrete columns has been performed, none of the previous studies investigated the structural performance of polypropylene macro synthetic fiber reinforced concrete (MSFRC) columns having GFRP reinforcement. The present study aims to examine the structural performance of GFRP reinforced circular concrete columns consisting of polypropylene macro synthetic fibers (GMSFRC columns) under concentric and eccentric loading. Identical steel bars reinforced concrete columns (SMSFRC columns) were also fabricated and tested under the same loading conditions. The experimental program consisted of 18 columns (1200 mm high and 300 mm in diameter) to measure the axial load-carrying capacity (LCC), axial deflections, failure modes, and cracking patterns under different eccentric loadings. SMSFRC columns portrayed higher axial LCC (up to 23%) and lower deformation capacity (up to 18%) than GMSFRC columns. Both GMSFRC and SMSFRC columns depicted similar failure behavior. The eccentric loading led to similar reductions in axial LCC for both GMSFRC and SMSFRC columns. Three-dimensional finite element analysis (FEA) of GMSFRC columns was done in ABAQUS using an improved plasticity model for MSFRC. The proposed FEA model predicted the structural behavior of GMSFRC columns with only 2.35% and 7.72% deviations for axial LCC and equivalent deflections of specimens, respectively.

Improvement of Load Carrying Capacity of Concrete Pavement Slabs Using Macro Synthetic Fibers

This study presents the results of an investigation of the effect of macro synthetic fibers (MSF) reinforcement on the load carrying capacity of concrete pavement slabs. Six concrete slabs having dimensions of 800 × 800 × 50 mm3 were prepared and tested under static loads at three different positions: interior, edge and corner of the slab. Three of the slabs were Portland cement concrete (PCC) and prepared as references. The other three slabs were macro synthetic fiber reinforced concrete (MSFRC). Mechanical properties examined in this study included compressive strength, splitting tensile strength, flexural strength and modulus of elasticity and ductility of PCC and MSFRC. The findings showed that the addition of MSF to PCC improved the load carrying capacity of concrete pavement slabs. Test results obtained indicated that the ultimate load carrying capacity of MSFRC slabs was increased by 24%, 20%, and 23% for interior, edge and corner loading positions, respectively.

Flexural Strength of Composite Deck Slab with Macro Synthetic Fiber Reinforced Concrete

In this research, flexural performance was evaluated using macro-synthetic fiber-reinforced concrete (MFRC) in structural deck plates. Material tests were performed to evaluate the mechanical properties of the MFRC, and the flexural strength evaluation was conducted in two experiments, positive and negative moment tests. In the material test results, compressive strength and modulus of elasticity of the MFRC were increased compared with normal concrete. Flexural tensile tests showed that, after achieving maximum strength, the deck plates had sufficient residual strength until fracture. Structural tests showed that flexural strength and cracking load of all specimens increased according to macro synthetic fiber dosage. According to the experimental results, we proposed a flexural strength model of a steel deck plate containing macro synthetic fiber. The model showed greater accuracy than the current standard compared with the experimental results. In addition, since it was confirmed that the MFRC steel decks had greater flexural stiffness until yielding, it will be necessary to quantitatively evaluate the effect of MFRC on the effective flexural stiffness of steel decking in future studies.

An experimental study on the shear behaviour of reinforced concrete beams with macro-synthetic fibres

Shear behaviour in reinforced concrete (RC) elements can improve with an adequate amount of fibres. Research has recently determined how fibres affect shear strength, but has barely focused on macro-synthetic fibre-reinforced concrete (PFRC). This paper presents the experimental results of 16 full-scale beams (eight RC, eight PFRC), 12 without transverse reinforcement. Polypropylene fibres (10 kg/m3) were included. Mode of failure (MOF) in shear and behaviour throughout the loading process were studied. The results obtained with fibres showed significantly improved shear strength in the RC beams with/without transverse reinforcement. A synergy between transverse reinforcement and fibres was observed in some cases.

Mechanical Properties and Durability of Latex-Modified Fiber-Reinforced Concrete: A Tunnel Liner Application

This study assessed the mechanical properties and durability of latex-modified fiber-reinforced segment concrete (polyolefin-based macrosynthetic fibers and hybrid fiber-macrosynthetic fiber and polypropylene fiber) for a tunnel liner application. The tested macrosynthetic fiber-reinforced concrete has a better strength than steel fiber-reinforced concrete. The tested concrete with blast furnace slag has a higher chloride ion penetration resistance (less permeable), but its compressive and flexural strengths can be reduced with blast furnace slag content increase. Also, the hybrid fiber-reinforced concrete has higher compressive strength, flexural strength, chloride ion water permeability resistance, impact resistance, and abrasion resistance than the macrosynthetic fiber-reinforced concrete. The modified fiber improved the performance of concrete, and the hybrid fiber was found to control the formation of micro- and macrocracks more effectively. Therefore, overall performance of the hybrid fiber-reinforced concrete was found superior to the other fiber-reinforced concrete mixes tested for this study. The test results also indicated that macrosynthetic fiber could replace the steel fiber as a concrete reinforcement.

Study of temperature effect on macro-synthetic fiber reinforced concretes by means of Barcelona tests: An approach focused on tunnels assessment

This paper presents an experimental investigation on the applicability of the Barcelona (BCN) test to evaluate the mechanical properties of a macro-synthetic fiber reinforced concrete (MSFRC) submitted to high temperature environments (up to 600°C). BCN tests demonstrated that the MSFRC gradually loses tensile strength an energy consumption density with increasing temperature. Temperatures of 400°C and 570°C shown to be critical to the MSFRC mechanical performance. The residual mechanical behavior of the macro-synthetic fibers was not affected by the temperature up to 100°C. For higher temperatures, the reinforcement showed that may lose part of its crystallinity compromising the MSFRC post-cracking performance. The constitutive model used to determine the stress-strain curves of the MSFRC was capable to reproduce the composite behavior after the event of a fire.

Mechanical properties of macrosynthetic fibre-reinforced concrete exposed to sulfate attack

The performance and durability of concrete is always affected by atmospheric conditions, chemical ions and mechanical loads, which reduce its bearing capacity, leading to the occurrence of accidents. Macrosynthetic fibre-reinforced concrete, as an alternative material, is used to improve the corrosion resistance of underground structures. In this study, accelerated corrosion tests were designed to investigate the change in compressive strength, elastic modulus and fracture toughness of concrete soaked in sulfate environment. Microscopic monitoring techniques, including scanning electron microscopy and energy-dispersive X-ray spectroscopy, were adopted to find changes in the structure. Compared to macrosynthetic fibre-reinforced concrete and ordinary concrete soaked in sulfate corrosion environment, the results indicated that macrosynthetic fibre improved the structure compactness of concrete; the losses of elastic moduli and compressive strength of the specimens soaked in sulfate were reduced. The maximum crack initiation load of macrosynthetic fibre-reinforced concrete was enhanced. Through microstructure monitoring, it is found that macrosynthetic steel fibre contributes to a remarkable improvement in the fracture resistance of concrete.

Testing and modelling the creep of cracked macro-synthetic fibre reinforced concrete (MSFRC) under flexural loading

An investigation of the delayed crack opening of cracked concrete containing short discrete macro-synthetic fibres under sustained flexural loading at service conditions (30–50 % of the average residual strength of cracked specimens) over a period of 8 months is reported. The time-dependent crack opening in flexure is simulated by implementing both the material model parameters obtained from a tension softening model and a rheological model for viscoelastic behaviour in the Total Strain Crack Model using the finite element method. Prisms measuring 100 mm × 100 mm × 500 mm and 150 mm × 150 mm × 700 mm were cracked under uniaxial tensile and three point flexural tests respectively and then subjected to sustained loadings in their respectively creep frames. In all cases, specimens were produced from the same concrete mix and fibre content. All specimens were tested in a climate controlled room at a temperature of 23 ± 1 °C and relative humidity of 65 ± 5 %. Experimental results have indicated that significant lesser creep occurred in specimens subjected to flexural creep compared to the uniaxial tensile creep specimens. The result of the finite element analyses at both stress levels shows good agreement with the experimental time-dependent crack opening results in flexure.

Creep behaviour of cracked steel and macro-synthetic fibre reinforced concrete

The study of creep behaviour of fibre concrete in cracked conditions is nowadays one of the main subjects of interest; many research groups in the world are working on this matter and the development of test methods and the definition of parameters for its characterization becomes an urgent necessity. This paper explores the use of different types and levels of long term bending loads and compares the creep rates of fibre reinforced concretes (FRC) incorporating steel and two macro-synthetic fibres. Tests arrangements with three and four point loadings were used. An initial crack width of 0.5 mm was adopted. It was verified that the creep rate clearly increases in macro-synthetic FRC and that the application of loading–unloading cycles does not imply significant changes in the creep rate when compared to permanent loads of similar magnitude. After creep tests the remaining residual bending capacity of FRC is considerable. Similar creep behaviour was observed by using three or four point loading configuration.