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2021 | Book

Fibre Reinforced Concrete: Improvements and Innovations

RILEM-fib International Symposium on FRC (BEFIB) in 2020

Editors: Prof. Pedro Serna, Prof. Aitor Llano-Torre, Prof. José R. Martí-Vargas, Prof. Juan Navarro-Gregori

Publisher: Springer International Publishing

Book Series : RILEM Bookseries


About this book

This volume highlights the latest advances, innovations, and applications in the field of fibre reinforced concrete (FRC) and discusses a diverse range of topics concerning FRC: rheology and early-age properties, mechanical properties, codes and standards, long-term properties, durability, analytical and numerical models, quality control, structural and Industrial applications, smart FRC’s, nanotechnologies related to FRC, textile reinforced concrete, structural design and UHPFRC.

The contributions present improved traditional and new ideas that will open novel research directions and foster multidisciplinary collaboration between different specialists. Although the symposium was postponed, the book gathers peer-reviewed papers selected in 2020 for the RILEM-fib International Symposium on Fibre Reinforced Concrete (BEFIB).

Table of Contents


Rheology and Early-Age Properties

Influence of Different Fibre Types on the Rheology of Strain Hardening Cementitious Composites

Strain-hardening cementitious composites (SHCC) have a high tensile strength and display a remarkable strain-hardening behaviour. These unique characteristics make them an interesting choice for improving the strength and durability of new and existing structures. The tensile strain behaviour of SHCC is strongly influenced by its rheological properties as they determine the hardened state behaviour such as fibre-bridging strength and ultimately the degree of multiple cracking. The presence of fibres significantly affects the rheological performance of SHCC.This study aimed at investigating the relationship between rheological characteristics of SHCC mortar before and after the addition of different fibres. Polyvinyl alcohol (PVA), high modulus polyethylene (HDPE) and glass fibres were added at three different contents in order to assess their effect on the workability of SHCC. Flow tests along with rheological assessment were conducted to evaluate the fresh state behaviour of SHCC. The addition of fibres reduced the flowability of mix, especially at high dosages. A modified fibre influence factor was developed to characterize different types of fibres and was related to the viscosity and yield stress of the mix.

Hassan Baloch, Steffen Grünewald, Karel Lesage, Stijn Matthys
Using Fiber Reinforced Concrete to Control Early-Age Shrinkage in Replacement Concrete Pavement

Unlike ordinary concrete pavement, replacement concrete pavement needs to be open to traffic within 24 h (sooner in some cases). Thus, high early-strength concrete is used; however, it frequently cracks prematurely as a result of high heat of hydration that leads the slab to develop plastic shrinkage. FRC is known to provide good resistance to plastic shrinkage. This paper explores the potential use of fiber- reinforced concrete (FRC) in concrete pavement replacement particularly in controlling plastic shrinkage. Five different fiber types, including steel, glass, basalt, nylon, and polyethylene fibers were investigated. Additionally, the effect of fiber length was also investigated for the polyethylene fiber. The fibers were added at low dosage amounts of 0.1% and 0.3% by volume. A retrained shrinkage test was conducted to assess the cracking potential of the concrete mixtures and the ability for each fiber type to resist cracking. Results indicated that both polyethylene and nylon fibers provided the best resistance to early-age shrinkage. Short fibers (<1-in.) also had the best performance in resisting early-age shrinkage, while long fibers (>1-in.) provided additional post-cracking capacity. For replacement concrete pavement, it is recommended that a short polyethylene fiber be used to eliminate uncontrolled cracking.

Nakin Suksawang, Daniel Yohannes
Early Age Shrinkage Crack Distribution in Concrete Plates Reinforced with Different Steel Fibre Types

In structural concrete elements reinforced with steel fibres, the bearing capacity is an important criterion to be verified and designed at ultimate limit state following the existing standards or codes already in use to design and build structures in Steel Fibre Reinforced Concrete (SFRC), as for example the Model Code 2010, the Swedish standard SS813310:2014, the German guideline “Stahlfaserbeton” by DAfStb, the future Eurocode 2, etc.…This approach was obtained by defining post cracking constitutive curves validated by beam tests following EN14651 to reach residual flexural tensile strength in a given cross section, and it is basically defined today in these numerous reference documents and validated by experience with only a few points, like orientation of fibres, being topic of further research.The Serviceability Limit State is however less well defined for steel fibres only solutions, meaning without any additional rebars, and some existing equation and theories can still be today under discussion.In that context, a parametric study has been undertaken to analyse the crack distribution and the crack opening in SFRC plates made of steel fibres only in order to put in evidence the influence of the fibre type and the dosage on this crack formation under shrinkage conditions at early age, meaning during the first 7 h.The purpose of this paper is to address these results and to highlight the level of performance of a given steel fibre type compared to another, and the influence on the crack distribution and the crack opening that a given steel fibre type can play. The paper gives evidences of this statement to be able to support design methods at Serviceability Limit State.

Sébastien Wolf, Simon Cleven, Oldrich Vlasák

Technological Aspects

Influence of Synthetic Fibres on Seismic Resistance of Reinforced Concrete Sections

To provide resilient load capacity during a seismic event, longitudinal reinforcing bars within a reinforced concrete section need to be confined against buckling in compression, and concrete within the section needs to be restrained against loss from the section. The traditional approach to achieving these goals has been to include numerous stirrups at close centers along all RC members, but this approach is expensive and time-consuming to construct. An alternative to the use of closely spaced stirrups is the inclusion of fibres within the concrete. In this investigation, an experimental assessment has been undertaken into beam-columns made with steel reinforcing bars and a moderate dosage rate of various fibre types including macro- and micro-synthetic fibres, steel fibres, and amorphous metallic fibres. The beam-columns were subjected to reverse-cycle simulated seismic loading in accordance with ACI 374 [1], and results were compared in terms of residual load carrying capacity at various levels of deformation. The data indicate that stirrup spacing can safely be increased without a reduction in seismic resistance when certain types of fibre are added, but that fibres used at moderate dosage rates cannot entirely replace stirrups.

E. Stefan Bernard
Development and Mechanical Characterization of Dry Fiber-reinforced Concrete for Prefabricated Prestressed Beams

In this study, compression, bending and shear properties of the dry fibre reinforced concrete (FRC) were experimentally characterized at its early age. Considering the application of the developed FRC in prefabricated prestressed beams, three-point notched beam bending tests were executed to analyse the post-cracking flexural behaviour, and direct shear tests were performed to evaluate its behaviour shear failure. Furthermore, the consistency of the proposed material on the design has been investigated. Eurocode Standard Specifications for concrete buildings is considered for the purpose of loading and analysing of a prefabricated prestressed FRC beam, which was designed by a cross section layered model for deriving its moment-curvature response. Using the properties of developed dry FRC, the section of the prestressed beam has been suggested.

Kamyar Bagherinejad Shahrbijari, Suman Saha, Joaquim A. O. Barros, Isabel B. Valente, Salvador Dias, João Leite
Simulation of Fibre Orientation in Self-compacting Concrete: Case Studies

Recent developments in concrete technology with high potential include ultra high performance concrete and self-compacting fibre reinforced concrete, which have a flowable consistency and can transport relatively high fibre dosages. Flowability is achieved by adopted mix design and both the mix design and flow affect the distribution and orientation of the fibres, which affect the post-cracking behaviour and accordingly the structural performance. With new materials also come new manufacturing and design approaches. The prediction of fibre orientation with computational fluid dynamics (CFD) simulations can be an important instrument to predict, understand and influence fibre orientation. With better understanding the mix design and casting process can be optimized.This paper reports about a study executed to determine the applicability of the software package Autodesk Moldflow for fluid dynamics simulations of flowable fibre concrete. After a discussion of relevant literature, two reference cases address stretching and shearing flow conditions in a qualitative and quantitative way. Concrete was modelled as an incompressible Bingham material with addition of a fibre orientation model that was developed by Folgar and Tucker. A third case, a square panel, was used as a reference and structural element for flow simulations. Parameters varied were among others rotary diffusion, wall-slip and duration of casting.

Thomas Bauwens, Steffen Grünewald, Geert De Schutter
Mix Design and Properties of Self-compacting Fibrous Concrete

The development of self-compacting fiber reinforced concrete (SCFRC) marks an important milestone of the Brazilian building industry, because it combines the benefits of high fluidity in the fresh state, better performance on tensile strength and the control of the cracks. To an efficient performance, it is necessary a good granular mixture proportioning. Thus, the objective of this research is the evaluation of the influence on fiber contents in self-compacting concrete of 40 MPa and its properties in fresh and hardened state. The difference of the concretes was the volume levels of the steel fibers in each mixture proportioning: SCC0F (no addition), SCC0.5F (0,5% in volume) and SCC1F (1,0% in volume). The concrete mix design was based in the compressible particle model. The results show that the insertion of steel fibers interferes diminishing the workability and fluidity of the mixtures and improve the tensile strength.

Rafael R. Polvere, Ana R. L. Pires, Sidiclei Formagini, Andrés B. Cheung
Aligned Interlayer Fibre Reinforcement for Digital Fabrication with Concrete

This paper presents a novel concept of fibre reinforcement placement for digital fabrication with concrete, particularly suitable for 3D concrete printing, which aims at overcoming the limitations of adding the fibres to the concrete mix. In this process, the fibres are placed in-between layers, which allows aligning the fibres and grading their content according to the structural needs. The mechanical performance of this concept is investigated through a series of four-point bending tests in which the influence of different fibre contents and distributions, fibre types, sample geometries and time intervals between consecutive printing layers is studied. The crack kinematics were recorded using digital image correlation. Based on the crack kinematics, a refined inverse analysis is proposed to predict the direct tension behaviour. The results show that a deformation hardening structural behaviour might be reached at a relatively low fibre content (0.7 vol%) when the fibres are aligned. The performance is further increased when grading the fibre distribution over the height but keeping the overall fibre content constant. With an increasing number of fibres in-between the layers, however, a delamination failure caused by a concentration of anchorage stresses is observed, which limits the peak load and leads to severe softening behaviour.

Lukas Gebhard, Jaime Mata-Falcón, Tomislav Markić, Walter Kaufmann
Mixture Proportioning of Steel Fibre Reinforced Self-compacting Concrete Based on the Compressible Packaging Method: Comparison with ACI 237R-07 and RILEM TC 174-SCC Recommendations

This work evaluates the production of self-compacting concrete reinforced with steel fiber (SFRSCC). The mix designs concretes were obtained with the compressible packaging method (CPM), the concrete properties found were compared to parameters established for self-compacting concrete in ACI 237R-07 and RILEM TC 174-SCC. Using BetonLab Pro 3 software, 39 concrete mix design were produced. In this process, three classes of compressive strength were tested 20 MPa, 30 MPa and 40 MPa, each one were combined with 3 different types of steel fibers, in contents of 0.0%, 0.5%, 0.75%, 1.0% and 1.5%. Fourteen types of concrete were produced from those mixes, the concretes values of compressive strength where 20 MPa and 40 MPa, with three different types of steel fibers, in the contents of 0.5% and 1.0%. In addition, a reference concrete was produced for each compressive strength class, without fibers, a total of 14 mixtures. All the produced concrete presented the rheological characteristics of a self-compacting concrete, showing the effectiveness of CPM. When comparing all the compositions obtained and the limits cited by ACI and RILEM, the 20 MPa and 30 MPa concretes presented most of the values within the limits proposed by the standards, unlike the 40 MPa concrete compositions that in many parameters did not follow the proportions described in the concrete self-compacting standards. The results showed that, for the materials and conditions used in this research, the values proposed by the standards would serve as a reference for the experimental dosage of SFRSCC only for concretes with compressive strength range of 20 MPa and 30 MPa. In addition, a reference concrete was produced for each compressive strength class, without fibers, a total of 14 mixtures. All the produced concrete presented the rheological characteristics of a self-compacting concrete, showing the effectiveness of CPM. When comparing all the compositions obtained and the limits cited by ACI and RILEM, the 20 MPa and 30 MPa concretes presented most of the values ​​within the limits proposed by the standards, unlike the 40 MPa concrete compositions that in many parameters did not follow the proportions described in the concrete self-compacting standards. The results showed that, for the materials and conditions used in this research, the values ​​proposed by the standards would serve as a reference for the experimental dosage of SFRSCC only for concretes with compressive strength range of 20 MPa and 30 MPa.

M. G. Cardoso, R. M. Lameiras, T. T Oliveira, F. B. Santana, V. M. S. Capuzzo
Evaluation the Yield and Ultimate Strain of FRC in Compression

The design of reinforced concrete structures depends greatly on its compressive behaviours. For normal concrete, most codes assume an ultimate strain of concrete of 0.003. However, for concrete containing discrete fibres, fibre reinforced concrete (FRC), the same assumption could not be made because of its strain softening and hardening behaviours. This research used 250 point-database from the previous 24 research papers that evaluated the yield and ultimate strain in compression for different types of fibre and volume fraction for both FRC and fibre reinforced cement. In this research, a volume fraction of fibre did not affect yield strength. The significant impact on yield strength was a compressive strength. For $$ {\text{fc}}^{\prime } $$ fc ′  < 69 MPa, the yield strength is 0.85 $$ {\text{fc}}^{\prime } $$ fc ′ . For $$ {\text{fc}}^{\prime } $$ fc ′  ≥ 69 MPa, the yield strength is roughly $$ {\text{fc}}^{\prime } $$ fc ′ because the shape of the ascending branch of the stress-strain relationship becomes more linear and steeper, and the slope of the descending part also becomes steeper. The general shape of the stress-strain relationship becomes more likely to be a triangle. The ultimate strain at the extreme concrete compression fibre is taken to be 0.0035 for volume fraction less than 1%, and 0.005 for volume fraction more than or equal 1%.

Salam Wtaife, Nakin Suksawang, Ahmed Alsabbagh
Electromagnetic Shielding Characteristics of High Performance Fiber Reinforced Cementitious Composites

This study aims to investigate the effect of multi-walled carbon nanotubes (MWCNTs) and steel fibers on the electrical conductivity and electromagnetic shielding effectiveness (SE) of a high-performance, fiber-reinforced cementitious composite (HPFRCC). The electrical conductivity of the 100 MPa HPFRCC with 0.30% MWCNT was 0.093 S/cm and that of the 180 MPa HPFRCC with 0.35% MWCNT and 2.0% steel fiber was 0.0173 S/cm. At 2.0% steel fiber and 0.3% MWCNT contents, the electromagnetic SE values of the HPFRCC were 45.8 dB (horizontal) and 42.1 dB (vertical), which are slightly higher than 37.9 dB (horizontal) at 2.0% steel fiber content or 39.2 dB (horizontal) at 0.3% MWCNT content. The incorporation of steel fibers by 3.0 vol. % did not result in any electrical percolation path in the HPFRCC at the micro level; thus, a high electrical conductivity could not be achieved. At the macro level, the proper dispersion of the steel fibers into the HPFRCC helped reflect and absorb the electromagnetic waves, increasing the electromagnetic SE. The incorporation of steel fibers helped improve the electromagnetic SE regardless of the formation of percolation paths, whereas the incorporation of MWCNTs helped improve the electromagnetic SE only under the condition that percolation paths were formed in the cement matrix.

Namkon Lee, Sungwook Kim, Gijoon Park

Mechanical Properties

The Manufacture of Fiber Cement Blocks Using Chemical and Thermomechanical Pulps and Rice Husk Ash

In this work, We made fiber cement blocks by using the raw materials of Cement, Rice husk ash, Fine aggregate, Fibers of Chemical pulps (CP) and Thermomechanical pulps (TMP). The replacement amount were zero (control), 5, 10, 15, 20 and 25%. In total 36 cement blocks with dimensions of 15 * 15 * 15 cm were made. The properties of blocks which were measured include compressive strength, water absorption, density of before and after soaking. The data Statistically analysed by Spss software. Statistical analysis showed that the type of fibers had significant effect on both mechanical and physical properties at confidence level of 0.05. Based on the findings of this work, The CP fibers had better effects on the compressive strength of specimens than The TMP fibers approximately twofold. Increasing the replacement level of TMP fibers tends to reduce the compressive strength due to the low binding ability. The water absorption and density values of specimens contain fibers were lower than control. The fibers cause lighter weight, resistance to cracking and a degree of flexibility.

Javad Torkaman
Post-Fire Flexural Tensile Strength of Macro Synthetic Fibre Reinforced Concrete

Tensile cracks in plain concrete occur and propagate when the tensile stress exceeds the bond strength of the cement. These cracks are generally bridged by coarse aggregates however the inclusion of fibres in concrete provides significant additional crack bridging. The utilisation of fibres in concrete has been extensively researched however most studies have focussed on steel fibre or newer types of fibre including glass, basalt and carbon. Current Australian and international design standards do not address the loss of strength for macro synthetic fibre reinforced concrete after exposure to elevated temperatures. This paper is an experimental study of the post-fire performance of macro synthetic fibre reinforced concrete. The flexural performance of the concrete is determined by performing 4-point bending tests on prisms after being heated in a furnace. Specimens were exposed to temperatures up to 800 °C. It was observed that the addition of macro synthetic fibre in concrete has a negligible effect on the overall peak cracking load of the specimens. The significant benefits of fibres are seen after the onset of cracking as the fibres hold the crack together which allows the specimen to withstand greater deflections and achieve a high residual strength. After exposure, the specimens displayed post-cracking flexural strengths between approximately 2–3 MPa for temperatures ≤600 °C. The specimens with 0.8% fibre displayed much higher strengths than the specimens with 0.4% fibre for temperatures ≤400 °C. However, for strengths after exposure to 600 °C and 800 °C, far less variance was observed.

Olivia Mirza, Brendan Kirkland, Kurt Bogart, Todd Clarke
Experimental Investigation on the Cyclic Behaviour of Steel Fibre Reinforced Concrete Under Bending

This paper presents the results of an experimental program investigating the monotonic and cyclic flexural behaviour of steel fibre reinforced concrete (SFRC). Three-point bending tests are assessed with acoustic emission (AE) monitoring to detect concrete micro-cracking and damage propagation during the different stages of cyclic loading. LVDTs over the prism’s height investigate the evolution of the neutral axis position. Three loading patterns are applied, namely monotonic, progressive cyclic and variable cyclic. 3D and 5D hooked end steel fibres are both used in a content of 20 kg/m3 and 40 kg/m3, representing a softening and a hardening behaviour respectively. By combining traditional and advanced measurement methods, the developed test setup allows a better understanding of the cyclic behaviour of SFRC. The monotonic envelope curves agree with the cyclic stress-CMOD curves. The neutral axis position appears to be independent of the SFRC classification. Fatigue damage development occurs for multiple load cycles at high load limits. Furthermore, AE monitoring proves to be complementary to mechanical testing for evaluating damage accumulation in SFRC under bending.

Maure De Smedt, Rutger Vrijdaghs, Els Verstrynge, Kristof De Wilder, Lucie Vandewalle
Effect of Test Setups on the Shear Transfer Capacity Across Cracks in FRC

The shear transfer capacity of concrete across cracks is highly relevant in situations where the principal concrete stress directions are not aligned with the cracks. Fibres are effective in controlling the crack opening, thereby enhancing aggregate interlock and hence, the ability of transferring shear stresses across cracks. Compared to plain concrete, higher stresses can therefore be transferred across cracks in fibre reinforced concrete (FRC). However, the shear transfer across cracks in FRC has received much less attention over the past decades than the residual tensile stress transfer across orthogonally opening cracks, and no generally accepted model for this behaviour is available today. The shear transfer capacity and the calibration of most existing models are obtained from experimental tests which presume failures occurring in “pure shear”, being the most popular used test setups: (i) Z-type push-off specimen; (ii) modified JSCE-G 553; and (iii) FIP shear test method (asymmetrical four-point bending). However, significant differenced have been observed in the experimental resulting shear strength, depending on the test setup. These differences have not been evaluated systematically until now. In order to address this issue, the authors carried out an experimental campaign on specimens made from identical SFRC mixes with varying fibre dosage, testing each mix in all three mentioned setups. The paper presents the results of this experimental campaign.

Alejandro Giraldo Soto, Walter Kaufmann
Bearable Local Stress of High-Strength SFRC

In the case of partial-area loading, compressive forces are transmitted into concrete members only over a limited area. For plain concretes and conventionally reinforced concretes, numerous investigations have already been carried out analyzing the load-bearing behavior under partial-area loading. Due to the tendency towards higher concrete strengths and the increasingly widespread use of steel fibers in recent years, it becomes also necessary to investigate the performance of high-strength steel fiber reinforced concrete (SFRC) under partial-area loading. This paper describes experimental tests on high-strength steel fiber reinforced concrete under partial-area loading with spatial and plane load distribution. Different area ratios and concretes with different fiber types and contents as well as fiber cocktails were considered. On the basis of the test results, a calculation approach is proposed for the determination of the bearable ultimate local stress. It is shown that by referring to the flexural tensile strength, instead of the compressive strength, as in the case of common calculation approaches, a more precise approximation of the ultimate local stresses for high-strength steel fiber reinforced concrete is possible.

Sven Plückelmann, Rolf Breitenbücher, Mario Smarslik, Peter Mark
Impact Response of Different Classes of Fibre Reinforced Concrete

The use of fibre reinforced concrete in structural elements exposed to impacts or different types of extreme loading represents one of the main fields of application of this high-performance material. Nevertheless, there is not a general consensus about a test for impact characterization of fibre concretes and, specifically a procedure to evaluate the contribution of fibres after cracking. It is well known that fibres control the evolution of cracks, improving the durability of concrete elements. Nowadays there are many structural fibres available; one of the greatest advantages to enhance the use of different fibres is the introduction of FRC classes in the fib Model Code 2010. However, there are not references about the relationship between the residual capacity measured in static tests (i.e. EN 14651) and the impact response. A drop weight impact test method is proposed to evaluate the contribution of different fibres considering both the cracking resistance and the behaviour in cracked state. Results of FRC belonging to different classes, incorporating different contents of steel, glass and polymer macrofibres are presented and compared. The effect of the residual capacity measured on standard bending tests on the impact resistance is discussed.

Juan C. Vivas, Raúl L. Zerbino, María C. Torrijos, Graciela M. Giaccio
An Experimental Study on the Fatigue Failure Mechanisms of Pre–damaged Steel Fibre Reinforced Concrete at a Single Fibre Level

In fibre reinforced concrete (FRC), energy is dissipated in the wake of the crack tip through the actions of fibre bridging and fibre pull out. This is the main mechanism which inhibits crack growth, thus increasing the load carrying capacity of FRC by providing post–cracking ductility. Furthermore, the same mechanism is present when FRC undergoes fatigue loading. Typical applications for FRC which undergo significant fatigue loading during their service life include paving applications such as bridge decks, highways and industrial floors. The continuous exposure to cyclic loading results in a decrease in apparent stiffness of the material, which may lead to fatigue failure [1, 2]. Fatigue failures are almost always unexpected, and can have a catastrophic outcome [3, 4]. Thus, the fatigue characteristics become vital performance and design parameters [1]. In this paper, the mechanisms of fatigue failure of pre-damaged hooked-end steel fibre reinforced concrete (SFRC) are investigated at a single fibre level. An initial pre-damage was applied to the fibres before the cyclic loading commenced. The pre–pull out ranged from 0.6 mm to 2.5 mm, and the cyclic loading was applied at 70% and 85% of the maximum static pull out capacity of the fibre embedded in the concrete.

Humaira Fataar, Riaan Combrinck, William P. Boshoff
Development of an HPFRC for Use in Flat Slabs

Fibre-reinforced cementitious materials represent one of the most significant developments in the field of concrete technology of the last decades. The improved performance of this new class of materials (in terms of workability, compressive strength, flexural/tensile behaviour and/or durability) allows rethinking several of the existing structural solutions. This paper describes research on high-performance fibre reinforced concrete (HPFRC) to be used at the slab-column connection zones of flat slabs, in order to improve its punching shear resistance. Design of Experiments (DoE) approach was used to design HPFRC paste and aggregate particle phases. As such, a central composite design was carried out to mathematically model the influence of mixture parameters and their coupled effects on deformability, viscosity and compressive strength. After that, a numerical optimization technique was applied to the derived models to select the best mixture, which simultaneously, maximizes aggregates content and allows achieving a compressive strength of 90–120 MPa, while maintaining self-compactability (SF1 + VS2), incorporating 1% steel fibres content.

Julia Blazy, Sandra Nunes, Carlos Sousa, Mário Pimentel
Influence of the Steel Fibres on the Tension and Shear Resistance of Anchoring with Anchor Channels and Channel Bolts Cast in Concrete

The current design method for anchor channels with channel bolts is based on test results for fasteners installed in conventional concrete. The field of application for steel fibre concrete have been growth over the last years and recently steel fibre reinforced concrete became popular e.g. for the production of prefabricated tunnel elements. The existing design rules for fasteners including anchor channels with channel bolts do not cover steel fibre reinforced concrete. To study the load-displacement behaviour in tension and shear, exploratory tests have been carried out on anchor channel-channel bolt-systems cast in plain and steel fibre reinforced concrete. The test results demonstrate a superior performance of channel bolts installed in anchor channels which were cast-in steel fibre reinforced concrete if compared with systems cast in plain reinforced concrete. The results of the experimental investigations will be explained und discussed in this article.

Mazen Ayoubi, Christoph Mahrenholtz, Wilhelm Nell
Fiber Reinforced Concrete After Elevated Temperatures: Techniques of Characterization

The mechanical properties of fiber reinforced concrete (FRC) are negatively affected when subjected to elevated temperatures. The main concern is regarding its post-crack tensile strength, which can be severely impaired at temperatures above 300 °C. In this composite, the mechanical characterization is constantly performed by means of bending tests of prismatic specimens, as recommended by EN 14651. However, due to limiting aspects, alternative methodologies have been used for the characterization of FRC, among which are the DEWS (Double Edge Wedge Splitting) and the Double Punch tests. In this context, the present study compares the methodologies for evaluating the mechanical behavior of FRC after elevated temperatures, discussing and emphasizing its advantages and limitations. The Double Punch test does not show satisfactory response as a consequence of the degradation suffered by the sample and the puncture interaction induced by the test. On the other hand, the indirect tensile DEWS test shows that it is capable of characterizing the FRC even after exposure to elevated temperatures. Although the post-crack response of the composite varies according to the method adopted, the post-crack tensile strength in the service limit state (SLS) and ultimate limit state (ULS) are considerably reduced when compared with the ambient temperature.

Ronney Rodrigues Agra, Ramoel Serafini, Antonio Domingues de Figueiredo
Influence of the Curing Temperatures on the Mechanical Properties of Hemp Fibre-Reinforced Alkali-Activated Mortars

The aim of this research was to investigate how the curing temperature influences the mechanical properties of fibre reinforced alkali activated matrices. The mortar matrix contained fly ash as a binder, sodium water glass as an activator and sand with a particle size between 0.4 and 0.8 mm. As reinforcement hemp fibres of 10 mm in length and of volume ratio 1% of the composite were used. The prism mortars had dimension of 40 × 40 × 160 mm3 and were cured under three different temperatures: 20 °C, 60 °C and 80 °C.The results showed that after adding the fibres specimens cured at room temperature (20 °C) increased their compressive strength, flexural strength and energy absorption for 4%, 57% and 711% respectively. At the 60 °C and 80 °C curing temperatures the compressive strength of the specimens decreased for 8% and 27% respectively, whereas the flexural strength decreased for 14% in case of 60 °C curing temperature but remained the same after the curing temperature of 80 °C. The energy consumption of the specimens increased for 331% and 153% when specimens were cured at the 60 °C and 80 °C respectively.

Bojan Poletanovic, Gergely Nemeth, Ildiko Merta
Equivalence Between Flexural Toughness and Energy Absorption Capacity of FRC

The increase of toughness and residual strengths are the great benefits of incorporating fibres in concrete. However, there is still no agreement regarding the most suitable experimental procedure for its determination and the most accepted and used tests, the bending tests, are complex to execute, require of sophisticated equipment with closed loop control and are unsuitable for the systematic quality control in works. Due to the latter, some authors have proposed equivalences between the different tests with the aim of simplifying the control.This paper presents the first stage of an experimental research in which a linear correlation between the flexural toughness determined by mean of the three-point bending test given in the European standard EN 14651 and the energy absorption capacity determined by square panel test according to EFNARC recommendation, was obtained, with differences less than 13% between the experimental results and predicted values.This achievement will allow to define a flexural equivalent resistance, based on the energy absorption capacity for controlling fibre reinforced concrete properties in the construction of tunnel linings.

Sergio Carmona, Climent Molins
Alkali Resistant (AR) Glass Fibre Influence on Glass Fibre Reinforced Concrete (GRC) Flexural Properties

Glass fibre reinforced concrete (GRC) is lightweight material mostly used for façade panels and decorative elements. GRC can be made using two methods – spraying and premixing. Glass fibre in both cases has main influence on material flexural properties and ductility. Historically ordinary E type glass fibre has been used, but during concrete aging and alkaline medium fibres become fragile (weight and diameter loses). New type, alkali resistant (AR) glass fibres have been developed. In this research AR glass fibre amount and length influence on GRC flexural properties is investigated. Fibre length was changed from 6 mm till 41 mm for different samples and cut during spraying process. Fibre amount was changed from 0–7%. Samples were analysed using SEM-EDX to evaluate AR glass fibre and concrete matrix bond. GRC mechanical properties was evaluated using four-point bending tests and characterised by level of proportionality (LOP) and modulus of rupture (MOR).

S. Guzlena, G. Sakale
Fiber Reinforced Concrete Crack Opening Evaluation Using Digital Image Correlation Techniques

The analysis of mechanical properties in fiber reinforced concrete (FRC) elements is basically done through destructive tests since the results obtained by these methods are already well established in normative codes. One of them is the 3-point flexural test normalized by EN 14651 using a notched beam to measure the crack width (CMOD). Within the context of the mechanical properties evaluation that do not require the production or extraction of specimens, and can be applied in fully functioning structures, the digital image correlation (DIC) is a technique which has been proposed. This non-destructive test analyzes a group of images correlating one with each other, evaluating the changes that occurred during the load has been applied. It is a non-invasive test, capable of results with acceptable precision and a considerable low cost, proving to be a promising technique in the field of behavior analysis. Thus, this study compares the cracking results obtained through the extensometry technique (Linear Variable Differential Transformer – LVDT) and the digital image correlation. The samples were made using steel fibers. The results obtained using the DIC technique were validated by the data obtained through the LVDTs, and the absolute error was considerably low.

Kaio Cézar da Silva Oliveira, Gabriela Silva Dias, Isadora Queiroz Freire de Carvalho, Wandersson Bruno Alcides de Morais Silva, Danilo José Pereira Freitas, Christiano Augusto Ferrario Várady Filho, Aline da Silva Ramos Barboza
Effect of Distribution and Orientation of Fibers on the Post-cracking Behavior of Steel Fiber Reinforced Self-compacting Concrete in Small Thickness Elements

In this work, an experimental investigation focused on the distribution and orientation of fibers on the post-cracking behavior of Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) to cast structural small thickness elements was assessed. To achieve this purpose, two SFRSCC panels with 45 and 60 mm of thickness were cast from their center point. From each panel, cylindrical specimens were extracted and notched either parallel or perpendicular to the SFRSCC flow direction. The post-cracking behavior was determined by means of the Modified Splitting Tensile Test. The fiber distribution was evaluated by counting the number of effective fibers crossing the fractured surfaces. Moreover, the orientation of the fiber was verified using X-ray method. Notched specimens loaded in the parallel direction of the SFRSCC flux lines presented higher post-cracking strength when compared with notched specimens loaded in the perpendicular direction. Likewise, it was also determined that smaller thickness of the structural element, represents greater residual stresses and energy absorption, in consequence of the wall effect.

Néstor Fabián Acosta Medina, Rodrigo de Melo Lameiras, Ana Carolina Parapinski dos Santos, Fábio Luiz Willrich
Ductility of the Four-Year-Old Steel Fibre Reinforced Concrete

The paper deals with the results of an experimental investigation into the ductility of Steel Fibre Reinforced Concrete (SFRC) with a steel fibre content of between 0,5% and 2% by volume, and that of a comparable concrete without fibres. These investigations are part of a large-scale research project on the SFRC that lasted 4 years. At their age of 4 years high compressive strength has been achieved, with average values in the range of approximately 60 to 115 MPa. These concretes can be divided into two groups: 1st group - concrete with a maximum nominal grain size (Dmax) of 16 mm with compressive strength of 90 to 115 MPa and 2nd group - concrete with Dmax = 4 and 8 mm with a compressive strength of 60 to 80 MPa. The ductile behavior of SFRC was evaluated by the ductility factor 1/B. 1/B is a parameter for evaluating the behavior of FRC, which takes into account the entire surface under the load – CMOD curve. In this way it is possible to evaluate the behavior of the FRC with only one parameter. Wedge Spit Test (WST) method was used to obtain load – CMOD curves. In 1st group, a large influence of the fiber aspect ratio (lf/df) on the increase of 1/B and the lower impact of the aggregate type is visible. In 2nd group, the influence of polymer, Dmax in addition to fibers on ductile behavior, can be noticed.

Jakob Šušteršič, Rok Ercegovič, David Polanec, Andrej Zajc
Sensitivity of the Flexural Performance of Glass and Synthetic FRC to Fibre Dosage and Water/Cement Ratio

A comparative analysis of the flexural performance of FRC mixes with either glass or synthetic fibers is presented in this paper. The data used for such analysis were obtained from an experimental programme which comprised 42 notched prismatic specimens, produced and tested to EN 14651 at the age of 28 days. Different fibre dosages up to 15 kg/m3 were considered in two series of mixes with water/cement ratios of 0.26 and 0.39, which yielded average compressive strength values of 65 MPa and 50 MPa respectively. A direct correlation between fibre content and residual flexural strength was confirmed. However, statistically significant differences were observed between the two fibre types considered. FRC mixes with glass fibre contents up to 5 kg/m3 failed immediately after the first crack and showed no residual flexural strength. In general, specimens reinforced with synthetic fibres showed better levels of residual flexural strength and toughness than their glass fibre counterparts. The ratio between the residual flexural strength and the limit of proportionality provides a good illustration of such observations: it was 61% on average for FRC mixes with synthetic fibers at 10 kg/m3, whilst it was only 33% for FRC mixes with the same amount of glass fibers.

Razan H. Al Marahla, Emilio Garcia-Taengua
Bond Between Steel Reinforcement Bars and Fiber Reinforced Cement-Based Composites

This paper deals with the bond between steel reinforcement and strain hardening cement-based composites (SHCC). Pull-out tests were carried out according to RILEM standard on specimens made with three mixtures, characterized by different fiber content (1% and 2%) beyond the control plain mortar. Ribbed steel reinforcement bars with 8 mm and 10 mm diameter were used to observe the influence of steel bar diameter. Experimental bond-slip relationships were analysed, and results show enhanced bond resistance when fiber is used in the mixture. SHCC specimens (composite with fiber content equal to 2%) presented the best bond performance in terms of bond strength and stiffness retention capacity, as well as damage control ability.

Margareth S. Magalhães, Paulo José B. Teixeira, Maria Elizabeth N. Tavares
An Experimental Study of the Influence of Moderate Temperatures on the Behavior of Macrosynthetic Fiber Reinforced Concrete

This research shows an experimental campaign performed aiming to understand the influence of moderate temperatures (5 °C, 20 °C and 50 °C) on the mechanical behavior of macrosynthetic fiber reinforced concrete (MSFRC). To do this, a 35 MPa concrete was selected. Two types of polypropylene fibers were added in a relatively high content (10 kg/m3). Steel fiber was used in an equivalent volume as a reference fiber.Considering that there is no standardized protocol to analyze the temperature effect on MSFRCs, a testing methodology based on UNE-EN 14651:2007 + A1:2008 is proposed. This modified procedure includes a system of insulating thermal covering which allows to maintain the temperature during the tests. Additionally, this study compares the effect of temperature on the pre-cracked and uncracked sections of MSFRCs. For this purpose, MSFRC and SFRC specimens were stored in each conservation temperature. Some of these samples were pre-cracked at the age of 28 days and then, they were reassigned in their respective conservation temperature until testing at 60 days.The results show that the analyzed temperatures have some influence on the mechanical properties of MSFRCs in terms of their residual flexural strength but to a limited extent, being suitable for environments with equivalent temperatures.

Marta Caballero-Jorna, Marta Roig-Flores, Pedro Serna
Post-cracking Behaviour of Glass Fibre Reinforced Concrete with Recycled Aggregates

In the past two decades, numerous studies have demonstrated the benefit of adding fibres in structural concrete. The addition of fibres in concrete limits the crack opening after concrete cracking. For conventional concrete with natural aggregates, the post-cracking behaviour is mainly determined by the type and amount of the fibres. Due to the increased shortage of raw materials, the use of recycled aggregates (RAs) in structural concrete has gained more and more interests recently. Nevertheless, the influence of fibres on the post-cracking behaviour of concrete with RAs has not well been understood. This paper presents an extensive experimental study on the behaviour of concrete with RAs reinforced with alkali resistant (AR) glass fibres. To better understand the effect of the quality of the RAs, three types of RAs were used in the present work, which include a high grade recycled concrete aggregate (RCA+), a normal quality RCA (nRCA) as well as a mixed recycled aggregate (MA). In addition, a natural aggregate (limestone) is also used as the reference aggregate. A total of 24 fibre reinforced notched beams are tested under three-point bending load according to EN 14651. In all fibre reinforced concrete mixtures, the CEM-FIL MinibarsTM was used with a fibre content of 0.75 V%. The test results indicate that the quality of the RAs can have a significant influence on the post-cracking behaviour of the beams, especially in the Crack Mouth Opening Displacement (CMOD) range of 0.5–1.2 mm.

Brecht Vandevyvere, Lucie Vandewalle, Els Verstrynge, Jiabin Li

Long-Term Properties

A Computational Sectional Approach for the Flexural Creep Behavior of Cracked FRC

This paper presents a computational model to calculate and predict the flexural creep behavior in a cracked fiber reinforced concrete (FRC) section. The proposed model is based on uniaxial creep data and consists of three steps.In the first step, an inverse analysis algorithm is presented to model the monotonic bending behavior of a notched FRC beam in accordance with EN 14651. A simplified and numerically optimized method is compared to experimental data and a good agreement is found.In a second step, the unloading behavior of the beam is taken into account. Calibrated on experimental data, the model is able to accurately and precisely predict the unloading behavior. Further validation comes from the location of the neutral axis, and the deformation profile.In a third step, the flexural creep behavior is predicted based on the results in the second step. The creep data is supplied in uniaxial form, which allows greater applicability across various FRC mixtures. The proposed approach is able to take into account stress redistribution following fiber fracture. Furthermore, the time-dependent effects of the stress redistributions are also accounted for. As such, the model is able to predict tertiary creep and structural failure under sustained loading.

Rutger Vrijdaghs, Marco di Prisco, Lucie Vandewalle
Shrinkage of Steel-Fibre-Reinforced Lightweight Concrete

Long-term behaviour of steel fibre reinforced concrete remains rather unknown and to a large extent unquantified by equations and standards. This paper studies experimentally the free drying shrinkage of steel fibre reinforced lightweight concrete during the first 28 days using 100 × 100 × 500 mm beams. The coarse lightweight material tested (LYTAG) is recycled and offers an alternative to gravel and quarry resources which are subjected to depletion in the future. Also, this material can lead to reduction in the mass of the structure which results in economical designs. However, LYTAG aggregate can absorb up to 15% of its own weight in water. This makes it susceptible to drying shrinkage both at young age and long-term due to environmental diffusion. Shrinkage can have a detrimental effect on the concrete by inducing cracks, creating therefore weak zones in the concrete. It is thought that fibres can have a favourable effect on the reduction of shrinkage due to their ability to bridge cracks. This could be vital particularly in large concrete flat slabs, joints, beams and even columns. This project uses modern hooked-end DRAMIX 3D and 5D fibres with different dosages Vf and number of hooks and evaluates shrinkage for concrete with different characteristic strengths fck.

Hasanain K. Al-Naimi, Ali A. Abbas
Time Dependent Deflection of FRC Members Under Sustained Axial and Flexural Loading

The inclusion of steel or polypropylene fibres into a concrete matrix can considerably improve the serviceability performance of reinforced concrete members. The benefits of including fibres in structural concrete have been extensively studied, and as a result, provisions for strength, and short-term serviceability conditions are contained in national codes of practice such as the Australian Standards for Concrete Structures and Concrete Bridges. Provisions relating to the long-term serviceability behaviour of fibre reinforced concrete (FRC) are either not included or can be seen to provide limited guidance to designers. This paper describes a method of analysis that can be applied to predict the time-dependent behaviour of cracked fibre (steel or macro-synthetic) reinforced concrete. The model is versatile and can handle a wide range of geometries, material properties and loading conditions. The layered modelling approach provides a high level of flexibility which allows for the consideration of variable creep, shrinkage and fibre properties, as a function of time. Results from the model have been compared to existing experimental data available in the literature and have been shown to correlate well. In addition, a sample analysis is presented to demonstrate the effects of residual tensile stress, tensile creep and variable shrinkage gradients on a FRC flexural section.

Murray Watts, Ali Amin, R. Ian Gilbert, Walter Kaufmann
Influence of the Residual Tensile Strength on the Factor for Quasi-permanent Value of a Variable Action

Steel fibres are known to aid in deflection control, control the process of cracking and mainly improve the toughness of structural elements and the whole structure. Large experimental program was performed at the Faculty of Civil Engineering-Skopje to find out how steel fibres and the residual tensile strength affect the time-dependent deformation properties and deflections of concrete. Specific realistic loading with permanent and repeated variable loads in loading interval of 8 h per day was applied on full scale beams that were monitored up to an age of concrete of 400 days. The beams were with cross section dimensions 15/28 cm and total length of 300 cm, manufactured from concrete class C30/37. They were reinforced with same percentage of longitudinal and shear reinforcement, but with different amount of steel fibres (0, 30 kg/m3 and 60 kg/m3). Using the experimental results, detailed analysis of the time-dependent deformation properties of concrete and their effect on the time-dependent behaviour was done. A value for the factor for quasi-permanent value of variable action $$ {\varvec{\uppsi}}_{{\mathbf{2}}} $$ ψ 2 is proposed for each type of concrete. It was concluded that the factor for quasi-permanent value of a variable action $$ {\varvec{\uppsi}}_{{\mathbf{2}}} $$ ψ 2 depends linearly on the residual tensile strength.

Darko Nakov, Goran Markovski, Toni Arangjelovski, Peter Mark
Compressive and Tensile Creep and Shrinkage of Synthetic FRC: Experimental Results and Comparison to Codes

The mechanical properties of FRC mixes, namely compressive and tensile strength, are generally improved with respect to their unreinforced counterparts due to the contribution of fibres. This has implications in aspects like crack propagation or the development of time-deferred strains such as those resulting from creep and shrinkage, which in turn influence the long-term deformation of structural elements. The effect of fibres on compressive creep has been studied by various researchers, and codes and guidelines for the design of concrete structures include provisions to predict creep under compression. However, tensile creep of FRC has not attracted the same level of coverage despite its relevance to the loss of tension stiffening. This paper presents the results of an experimental study in concrete specimens reinforced with synthetic fibres were subjected to constant loading in uniaxial tension and in compression in order to evaluate the effect that increasing dosages of synthetic fibres have on the resulting time-dependent strains. The evolution of shrinkage, creep strains and the creep coefficient were analyzed in relation to the fibres dosage. The experimental strain-time curves were compared to the theoretical curves from the models adopted in the Eurocode 2, the Model Code, or by the ACI Committee 209.

Razan H. Al Marahla, Emilio Garcia-Taengua
Creep in FRC – From Material Properties to Composite Behavior

Although being the subject of numerous studies during the last 5 decades, fiber reinforced concrete (FRC) only very recently started to penetrate the construction market to a larger extent. This is mainly due to the lack of appropriate standards in the past years and the recent availability of structural codes such as fib Model Code 2010, the German DAfStb guideline “Stahlfaserbeton”, the Italian code, or codes under development, such as the Eurocode 2. However, FRC still struggles with some issues that potentially hinder, at least at a first glance, a further penetration into structural applications. Creep under tensile stress is one of these major obstacles. The creep response of a structural member in tension results from the interaction of the creep of the fiber material itself and the creep of the bond between fiber and surrounding matrix. The latter at last leads to the fact that creep is also a subject of further investigation for steel fiber reinforced concrete which shows that this is not an exclusive problem for synthetic fibers, as publicized in common literature. Unfortunately, commonly agreed test methods to investigate creep are missing. In this regard more research is required in order to specify which load levels and crack openings should be chosen to provide a realistic scenario for creep tests on FRC in general.Testing of creep in FRC is a very complex and time-consuming matter. Therefore, the subject of this paper is an investigation of a possible correlation of the creep properties of a single filament and the bond behavior of a single fiber in mortar. The most important subject of this paper is whether it is possible to derive the overall creep response of the composite material FRC from the determined component-specific characteristics. Based on a thorough test plan, two distinctly different performing polypropylene fibers (moderate to high-performing) are tested and compared. The determination of short- and long-term behavior of the filaments in this test plan is carried out in varying temperatures in a range from −10 ℃ to 60 ℃. Results indicate that the creep performances of a filament and the bond between a filament and a mortar correlate with the overall creep of the corresponding FRC. Moreover, a broad range of creep performance is revealed which strongly suggests that the performance of synthetic fibers and, in particular the creep performance, cannot be generalized.

Martin Hunger, Jürgen Bokern, Simon Cleven, Rutger Vrijdaghs


Morphology of Corrosion of Metallic Fibers in Aggressive Media

In marine and industrial environments, the steel bars embedded in concrete can corrode producing the cracking of the cover and impacting negatively in the load-bearing capacity. Metallic fibres have shown a record of good mechanical performance as reinforcing material for concrete. Those on carbon steel can corrode in the aggressive environments and although publications have reported a better impermeability in the fibre reinforced concretes, it still remains the question of how the steel fibres corrode and, in this case,, whether they can microcrack the surroundings. In present communication are presented results of long-term performance of the fibres due to chlorides and carbonation attacks during more than 20 years of exposure. The carbon fibres corrode but not cracking seems to be produced in spite of the full conversion of the fibres into oxides. The galvanized fibres corrode comparatively less, and the stainless-steel ones are in perfect condition.

Carmen Andrade, Miguel A. Sanjuán
Effects of Fibres on the Flexural Behaviour of Sound and Damaged RC Beams

The incorporation of fibres in Reinforced Concrete (RC) beams controls the width and evolution of cracks leading to positive effects on the durability of the element. The study of damage processes in concrete and their effects on the residual properties represents a key point related to the service life of RC structures. The contribution of fibres on the bending behaviour of sound and damaged RC beams was investigated. In order to use alkali silica reaction as a damaging tool, RC beams with and without fibres and reactive aggregates were subjected to service loading conditions during eight months in an environment with high humidity. The evolution of deformations and the distribution and propagation of cracks were recorded. As reference, similar RC beams without reactive aggregates were also evaluated. After the treatment, all RC beams were loaded up to failure. The free expansion, the compressive strength and the bending residual capacity of plain and fibre concrete were measured on companion specimens for material characterization. The effect of both fibres and alkali silica reaction on bearing capacity and ductility of RC beams were analysed. Results showed that alkali silica reaction damage provokes a significant reduction of RC beam ductility, while the flexural strength is preserved.

Raúl L. Zerbino, María C. Torrijos, Graciela M. Giaccio, Antonio Conforti
Fiber Reinforced Concrete Elements Exposed to Accelerated Corrosion

This study evaluates the structural performance of high performance fibre reinforced concrete elements affected by corrosion and its subsequent deteriorations.With large scale applications already set in place and enhanced mechanical and durability performance, high and ultra-high performance concrete is the construction material of the present days. However, long term performance of structural elements exposed to harsh environments is still linked to the cracking pattern. Fibre reinforcement significantly improves the tensile strength of concrete, but serviceability cracks are nevertheless inherent. These cracks are the path through which the aggressive media travels to the embedded reinforcement, leading to the corrosion of the steel, the diminution of concrete cross-section, loss of reinforcement area, increased deformations and crack widths. Therefore, the present research is focused on the corrosion of the embedded traditional reinforcement and the loss of section in high performance fibre reinforced concrete elements with and without sacrificial zinc anodes. For this purpose, several small scale beam elements are exposed to artificial accelerated corrosion and their flexural behaviour assessed in comparison to non-exposed control elements.

Camelia Negrutiu, Ioan Sosa, Bogdan Heghes, Oana Gherman, Horia Constantinescu
Effect of Corroded Steel Fibers on Mechanical Behavior of Steel Fiber Reinforced Concrete

This paper presents the exposure test results of Steel Fiber Reinforced Concrete (SFRC) beams having crack width of 0.2 mm for 3 months, 1 year and 2 years. By flexural loading test, initial stiffness of the exposed SFRC beams was decreased with increasing of exposure period. And corrosion of steel fibers themselves was observed at crack surface. The corrosion depth from the specimen surface was about 15–35 mm. There was no significant effect of fiber content on corrosion depth. Corrosion of the re-bar across the exposed crack was observed, and it may affect the reduction of stiffness of the beams due to loss of bond properties between re-bar and SFRC.

Minoru Kunieda, Masaki Tsutsui, Le V. Tri
Self-healing of Fibre Reinforced Concrete Containing an Expansive Agent in Different Exposure Conditions

While most studies about self-healing concrete investigated several healing conditions such as water immersion, humid chamber and wet/dry cycles, very few assessed the self-healing capacity of concrete in realistic outdoor condition. Furthermore, self-healing capacity is usually determined with a single testing procedure (mechanical or permeability measurements), sometimes with visual observations. Hence, this project aimed to evaluate, through mechanical and water permeability tests, as well as optical and microscopic observations on the same specimens, the self-healing capacity of high performances fibre reinforced concretes (HPFRC) containing different admixtures. This paper focuses on the water permeability evolution of two HPFRC (water to binder ratio of 0.43 and 0.75%-vol of steel macrofibres), one control and one containing calcium sulfoaluminate-based expansive agent (CSA), under different laboratory and outdoor conditions. Prisms were pre-cracked at 28 days by means of a 3-point bending test and then exposed to laboratory conditions (air, water immersion and wet/dry cycles) for 3 months and outside for one year. The results showed a better self-healing performance of the CSA HPFRC in wet/dry cycles compared to water condition. For the control HPFRC, the opposite is observed. Self-healing of outdoor prisms is slower than in laboratory (6 months outside corresponds to around 2 weeks in water immersion for CSA). Self-healing performance of the CSA HPFRC is better than the control mix in outdoor condition.

K.-S. Lauch, C. Desmettre, J.-P. Charron
Characterisation of Strain-Hardening Cementitious Composite (SHCC) Under Cyclic Loading Conditions for Self-healing Applications

The ground shaking in an earthquake often imposes cyclic loadings on infrastructures placing them in danger. Concrete is quasi-brittle in tension and easy to crack under cyclic loadings. Fibre reinforced strain-hardening cementitious composites (SHCC) featuring high ductility, high energy absorbing capacity and controlled multiple cracking have been proposed for seismic-resistant applications. The fine cracks have been proved to not only improve the durability but also enhance the autogenous self-healing ability. This study focuses on investigating the material behaviour and self-healing potential of SHCC under cyclic flexural loading conditions. Four-point flexural tests (including monotonic and cyclic tests) were performed to study its mechanical properties and cracking behaviour. The surface crack widths were measured by optical microscopy. Results showed that 28-day air cured specimens exhibited a deflection capacity of up to 9.6 mm and an average crack width of 28 μm under monotonic flexural loading. Regarding the flexural stress-deflection curves, the envelops of cyclic testing results were close to monotonic results with both elastic and hardening phases. SHCC could still maintain fine crack widths (below 60 μm) under cyclic loading conditions. SEM/EDX test was conducted to investigate the fibre-matrix interface.

Zixuan Tang, Chrysoula Litina, Abir Al-Tabbaa
Corrosion Pattern and Mechanical Behaviour of Corroded Rebars in Cracked Plain and Fibre Reinforced Concrete

This paper presents experimental results of corrosion pattern and tensile behaviour of corroded rebars extracted from 4 uncracked and 18 pre-cracked plain concrete and fibre reinforced concrete (FRC) beams. The beams were pre-cracked through three-point bending to a target maximum crack width of 0.1 and 0.4 mm, and then subjected to natural corrosion through cyclic exposure to a 16.5% NaCl solution for more than three years. 3D-scanning was used to characterise the pit morphology and evaluate the maximum local corrosion level of extracted rebars. Under the same loading condition and crack width, most rebars in FRC had smaller maximum local corrosion level than those in plain concrete. Subsequently, tensile tests were carried out on the extracted rebars, with Digital Image Correlation (DIC) technique adopted to investigate the influence of pit morphology on the local strain development. Finally, the time-dependent influence of transverse and longitudinal cracks on the pit morphology which governs the ultimate strain of corroded rebars was discussed. The time-varying nature of corrosion morphology should be considered when predicting the durability and long-term safety of conventional reinforced concrete and FRC structures with reinforcing bars under chloride environments.

E. Chen, Carlos G. Berrocal, Ingemar Löfgren, Karin Lundgren
Evaluation of the Self-healing Capability of Ultra-High-Performance Fiber-Reinforced Concrete with Nano-Particles and Crystalline Admixtures by Means of Permeability

Self-healing is the capability of a material to repair its damage autonomously. Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) has potentially higher self-healing properties than conventional concrete because of its lower water/binder content and controlled microcracking due to the high fiber content. This work uses a novel methodology based on the permeability to evaluate autogenous self-healing of UHPFRC and enhanced self-healing, incorporating several additions. To this purpose, one UHPFRC was selected and modified to include alumina nanofibers in 0.25% by the cement weight, nanocellulose (nanocrystals and nanofibers), in a dosage of 0.15% by the cement weight, and 0.8–1.6% of a crystalline admixture. The results obtained show that the methodology proposed allows the evaluation of the self-healing capability of different families of concrete mixes that suffered a similar level of damage using permeability tests adapted to the specific properties of UHPFRC.

Hesam Doostkami, Marta Roig-Flores, Alberto Negrini, Eduardo J. Mezquida-Alcaraz, Pedro Serna

Analytical and Numerical Models

Material Characterisation for Nonlinear Finite Element Analysis (NLFEA)

The design of steel fibre reinforced concrete (SFRC) structures is becoming more popular. It is beneficial to combine traditional reinforcement with SFRC, because the design becomes more robust (more ductile) and the traditional reinforcement and/or the concrete cross-section can be decreased.The modelling of the material is often based on a smeared crack approach. However good guidelines, which describe modelling strategy for SFRC are lacking. Therefore, this paper will propose a new constitutive model for SFRC and will go into detail about improving crack localization. Good crack localization is often a problem with smeared crack approach. The modelling strategy will be applied using the finite element software DIANA [1] and compared with experimental results.

P. J. van der Aa, A. A. van den Bos
Comparison Between the Cracking Process of Reinforced Concrete and Fibres Reinforced Concrete Railway Tracks by Using Non-linear Finite Elements Analysis

This study concerns the use of numerical models to analyze and compare the cracking process of two types of Railway Tracks: one in reinforced concrete and the second one in FRC. The models used are the Probabilistic Explicit Cracking models developed by IFSTTAR and fully validated in the framework of previous works.The main result obtained can be summarized as following: When in a given concrete structure, the tensile stresses are localized, the traditional rebars are more efficient to control cracks than the presence of fibres. On the contrary, when the tensile stresses are diffused, that is the case in statically indeterminate mechanical situations, the fibres are significantly more efficient than traditional rebars in regards to this cracks control. The parts of the railway track slabs which are located between the zones delimited by the joints in the foundation slab are concerned by this conclusion.

Jean-Louis Tailhan, Pierre Rossi, Thierry Sedran
Experimental/Computational-Based Determination of Material Parameters for Nonlinear Simulation of UHPFRC

The paper describes development of a soft-computing-based identification software FRCID-4PB for material parameter determination of ultra-high-performance fiber-reinforced concrete composite material. Such a determination is performed with the help of experimental data from four-point bending tests used in inverse analysis based on artificial neural networks and nonlinear computational modelling of tests. A new tensile softening model for studied composite material has been proposed and tested with the help of sensitivity analysis. The procedure also utilizes stratified statistical simulation method for the preparation of a training set for the artificial neural network. Trained network is then implemented into the software allowing routine and user-friendly identification of material parameters from the test results. The main aspects of the software implementation, its testing and application is described and discussed in the paper.

David Lehký, Martin Lipowczan, Drahomír Novák, Radomír Pukl, Milad Hafezolghorani
Mechanical Response of High Strength Fibre Reinforced Concrete Under Extreme Loads

High Strength Fibre Reinforced Concrete (HSFRC) presents great advantages when compared with conventional concrete under static loads and thus, it constitutes a promising material to withstand extreme loads. An experimental and numerical research carried out with the objective of developing design criteria for HSFRC use in protective structures construction is presented. The mechanical behaviour of HSFRC elements under extreme loads is experimentally and numerically analysed. Numerical models represent useful tools for the design of this type of HSFRC applications but they should be carefully calibrated and validated with experimental results. HSFRC prisms and slabs including different types of hooked-end steel fibres are tested under static, blast and impact loads. Material models at the meso and the macro scale are developed, they are calibrated with characterization tests and validated with experimental results. Experimental results are analysed with the aid of numerical models showing the effect of fibre type and content under extreme load. Numerical models are able to reproduce the blast and impact tests results and give additionally information about the local and structural response under impulsive loads that could be valuable for the design of protective structures.

B. Luccioni, F. Isla, F. Fiengo, R. Codina, D. Ambrosini, J.C. Vivas, Raúl L. Zerbino, Graciela M. Giaccio, María C. Torrijos
Numerical Damage Modelling of Macro-synthetic Fibre Reinforced Concrete

Macro-synthetic fibre reinforcement for concrete applications is gaining popularity in the construction industry owing to its’ advanced development towards higher mechanical properties, electrical and corrosion resistance. However, the main drawback of the effective application of macro-synthetic fibre reinforced concrete (MSFRC) is the limited analysis procedures adopted from the existing concrete behavioural models and guidelines. Indeed, the behaviour of MSFRC is mainly characterised by the post-cracking hardening/softening, which significantly differs from the brittle nature of plain concrete.Currently, material models which are available for the numerical modelling of steel fibre reinforced concrete (SFRC) characterises the hardening and softening behaviour immediately after the limit of proportionality. In regards with MSFRC modelling, the initial frictional slippage of fibres causes an instantaneous reduction in the tensile stress (i.e. post-cracking phase), wherein which the damage evolution requires a distinctive approach. Therefore, the paper herein focuses on reviewing the adoptability of current models and evaluate the sensitivity of damage parameters in macro-scale analysis. As a result, this paper provides significant insights into the different parameters and calibrations required towards the recognition of the MSFRC material model in the finite element analysis.

Dayani Kahagala Hewage, Christophe Camille, Olivia Mirza, Fidelis Mashiri, Brendan Kirkland, Todd Clarke
Finite Element Analysis of Ultra High Performance Fibre Reinforced Concrete Beams Using Microplane Modelling

Ultra high performance fibre reinforced concrete (UHPFRC) exhibits enhanced strength, ductility and durability properties in comparison to conventional and high performance concretes. This research uses results from experimental tests on small scale UHPFRC beams to validate three-dimensional finite element modelling methods developed for concrete beams using microplane theory. The effect of 0%, 1% and 2% fibre volumes were investigated on beams with varying cross-section. Beams with and without conventional steel reinforcement were tested in four point bending. The numerical models accurately replicated the behaviour of the experimental specimens. The load-deflection and failure modes in the numerical beam models provided an accurate representation of the experimental behaviour, including the observed change in failure mode from shear in the ultra high performance concrete (UHPC) beams with conventional steel reinforcement to a flexural failure in their UHPFRC counterparts.

William. Wilson, Tomas O’Flaherty
Machine Learning Prediction of Flexural Behavior of UHPFRC

To evaluate the possibility of predicting the flexural behaviour of UHPFRC, four analytical models were developed, based on artificial neural networks (ANN), to predict the first cracking tension or Limit of Proportionality (LOP), its corresponding deflection (δLOP), ultimate strength or Modulus of Rupture (MOR), and its corresponding deflection (δMOR) of UHPFRC under bending test. The models that were composed of an input level, one output level, and four hidden levels were developed through the R platform. The input level applied the most significative Principal Components (PC) of a large dimension of input dataset. To avoid overfitting K-fold validation and l2 regularization was used. After the models were created, an improvement based on assembling of models by incorporating the predicted values in the dataset of features. The results indicated that the developed assembling models have a good accuracy for the prediction of the behaviour of UHPFRC under three or four points bending test, even when containing supplementary cementitious materials and hybrid mixture of fibers.

Joaquín Abellán-García, Jaime A. Fernández-Gómez, Nancy Torres-Castellanos, Andrés M. Núñez-López
Study of Dimensioning Aspects of FRC Based on the Beam Flexion Theory

The fiber reinforced concrete (FRC) have a higher load capacity in the post-cracking stage, however, this increase only occurs if the concrete is dosed and applied properly and, for this, there are standards that establish design aspects for use of the FRC. However, in these documents, the portion of the resulting resistant strength of the fibers is not fully described in their equations and is determined for specific situations. Therefore, and with the objective of obtaining the positioning and the resultant of the fibers of a model of fluid concrete reinforced with fibers, this work presents a study related to the determination of the resultant of the fibers in the stretched part of the concrete. This determination was obtained based on the bending theory in beams, through the three-point bending test standardized by EN 14651 (2007) [8], where both beams with steel fibers and polymeric fibers were used. From this, the equation obtained analytically was compared with those determined by international codes and it was realized that, when comparing the three methods used, the intermediate value corresponded to the determined analytically, where the results showed variations due to the different forms of arrangement that each method uses.

Iva E. Pereira Lima, Aline S. Ramos Barboza
Load-Carrying Capacity of SFRC Suspended Slabs with Different Support Conditions

Traditionally, steel fibres have been used in ground- and pile-supported concrete slabs. More recently, the structural use of steel fibres in suspended concrete slabs is on the rise. In the present research study, the structural behaviour of suspended steel-fibre-reinforced concrete (SFRC) slabs was investigated by means of non-linear finite-element analysis (NLFEA). The numerical models were calibrated (at the material level) and validated (at the structural level) using existing experimental data. NLFEA-based parametric studies were carried out to extend the range of Vf beyond the one considered in the experiential investigations. The aim was to determine the correlation between the slab load-carrying capacity and the corresponding fibre dosage increase. This is useful for design purposes and can provide guidance on the amount of fibres needed to achieve a certain prescribed load resistance level. It was found that the addition of steel fibres improved the load-carrying capacity and changed the failure mode to a flexural ductile one. Other critical structural performance indicators were also examined such as deflections, ductility, energy absorption and cracking patterns. So, in essence both the ultimate and serviceability limit states were investigated. Comparisons with current design guidelines were also made and recommendations for improvements proposed.

Olugbenga B. Soyemi, Ali A. Abbas
Discrete Element Simulation of the Fresh State Steel Fiber Reinforced Self-compacting Concrete

The distribution and orientation of fibers in Steel Fiber Reinforcement Self-Compacting Concrete (SFRSCC) are paramount given its influence in the mechanical properties of the material/structural elements.A two-way coupled model based on Discrete Element Method (DEM) to simulate the flow of clumps of particles with the high aspect ratio as fibers and two-phase particles as concrete is developed and introduced briefly in this paper. The framework is capable of modelling of the movement (translation and rotation) including the separation and contact detection of the particles. The interaction of the particles is treated as a dynamic process with a developing state of equilibrium whenever the internal forces are in balance. Newton’s laws of motion provide the fundamental relationship between particle motion and the forces causing that motion.Several experiments were conducted and analyzed by means of the inductive test method (a non-destructive method to assess steel fiber content and orientation). Orientation numbers coming from the inductive test method were compared with the simulation to verify the ability of the model to properly represent the flow of the fresh state SFRSCC. Through comparison with the experimental data, it is shown that the numerical model predicts the final distribution and orientation of the fibers sufficiently accurate and in a reasonable amount of time. The results obtained represent a step forward, showing that it is possible to apply advanced numerical tools for a preliminary assessment of the performance of SFRSCC, which might have positive implications through improved reliability of the design procedures.

A. Najari, A. Blanco, A. de la Fuente, S. H. P. Cavalaro
Crack Width Simulation and Nonlinear Finite Element Analysis of Bursting and Spalling Stresses in Precast FRC Tunnel Segments Under TBM Thrust Jack Forces

Tunnel boring machine (TBM) thrust jack force is one of the governing load cases for the design of precast Fiber-Reinforced Concrete (FRC) tunnel segments. Due to the concentration of the jacking forces and partial loading of the circumferential joints, the bursting stresses are formed deep under the thrust pads while the spalling stresses are generated in the areas between the thrust pads, and between the thrust pads and the end faces of the segments. Under high thrust conditions and in conjunction with eccentricity of the thrust pads, bursting and spalling tensile stresses can exceed the tensile strength of FRC which results in segment cracking. Serviceability Limit State (SLS) design includes limiting the crack width to allowable values. This paper presents results of three-dimensional nonlinear finite element analyses (3D NFEA) of TBM thrust jack forces by modeling the actual parallelogram shape of segments, the actual size and positions of thrust pads, and maximum jacking forces for an ongoing construction project in North America. Tensile response of FRC as a multi-linear stress-strain curve is obtained following an inverse analysis procedure conducted on nominal response of standard beam tests. Presented NFEA simulation is recommended as a reliable and optimized procedure for design of FRC segments loaded by TBM thrust jack forces.

Mehdi Bakhshi, Verya Nasri
Finite Element Modelling of UHPFRC Flexural-Reinforced Elements

In our research group a simplified method to obtain the constitutive tensile parameters of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) from a four point bending test has been developed: 4P-IA. After the numerical validation of the method, a finite element modelling (FEM) of beams of different size has been carried out taking into account two different approaches: a smeared approach and a discrete approach. Moreover, important effects have been included in order to improve the model such as the shrinkage that generates internal stresses due to the influence of the reinforcement. After the FEM simulation, very reliable results can be observed for both approaches at service and ultimate load levels.

Eduardo J. Mezquida-Alcaraz, Juan Navarro-Gregori, Pedro Serna
Punching Shear Response of RC Slab-Column Connections Strengthened with UHPFRC - Finite Element Investigation

Reinforced concrete (RC) flat slabs can be retrofitted with a top thin layer of ultra-high performance fiber reinforced concrete (UHPFRC) to enhance their structural performance and service life. UHPFRC can also protect the concrete slab from impact and percolation of chemicals that could otherwise cause deterioration and corrosion of reinforcement. This study examines the punching shear performance of RC flat slabs retrofitted by fully and partially covering with a thin layer of UHPFRC. 3D non-linear Finite Element Analysis (FEA) is used to determine the response of the composite slabs. Both the concrete and the UHPFRC are modelled using the concrete damage plasticity model in ABAQUS software. The maximum shear resistance, deformation and crack patterns of the slabs with different areas of the UHPFRC layer are examined. The UHPFRC layer significantly increases the punching shear capacity and delays the crack propagation in all analyzed slabs. Incorporating a 40 mm UHPFRC layer on a 120 mm thick RC slab-column connection results in a 39% increase in ultimate punching load capacity. The partial cover of UHPFRC is a good suggestion since it results in a more economical solution and to a more ductile connection.

Demewoz W. Menna, Aikaterini S. Genikomsou
Numerical Evaluation the Effect of Specimen Thickness on Fibre Orientation in Self-consolidating Engineered Cementitious Composites

The orientation of distributed synthetic fibres in the matrix of engineered cementitious composites (ECCs) governs their capability of bearing stress and bridging micro-cracks. Understanding the orientation of synthetic fibres in ECCs matrix of different thickness specimens, therefore, is necessary. In the present work, the effect of specimen thickness on the orientation of synthetic fibres in self-consolidating (SC) ECC, a typical member of family ECC materials, is numerically investigated through the simulation of the casting of fresh SC-ECC into different thicknesses of moulds. The moulding of fresh SC-ECC, which is discretised by a limit number of separated mortar and fibre particles, is simulated using the mesh-free smoothed particle hydrodynamics (SPH) method. The synthetic fibre utilised in SC-ECC is considered as flexible fibre and virtually connected by a drag force between two adjacent fibre particles. The SPH allows tracking the movement of mortar and fibre particle during their flow, thus providing the real image of flexible synthetic fibres orientation in specimens during the casting process. A simple method is proposed to evaluate the orientation of flexible synthetic fibres at various sections of specimens after the SC-ECC stop flowing in the moulds. The results of this study reveal that thin specimens tend to have higher fibre orientation factors than thick specimens. Synthetic fibres tend to parallel with the longitudinal direction of specimens at the bottom of the formwork and rotate freely at the top surface of specimens.

Hai Tran Thanh, Jianchun Li, Y. X. Zhang
Numerical Modelling of Fiber-Reinforced Concrete Shear-Critical Beams

The numerical modelling of shear-critical reinforced concrete beam has been a traditional challenging problem due to the varying mechanisms involving the shearing problem. The inclusion of fibres improves significantly the shear strength of the beams but include in the equation a new unknown. In this study, a group of 16 beams with varying parameters including steel or macro-synthetic fibres, presence or not of transverse reinforcement, different shear-span-to-depth ratios, and different transverse reinforcement ratios are studied. The numerical modelling makes use of the nonlinear finite element analysis following the smeared crack approach and a total strain based crack material model. The numerical modelling has shown that a nonlinear finite element model can predict with great accuracy the behaviour and the strength in those beams with presence of transverse reinforcement. For the case of members without transverse reinforcement, the predictions of the shear strength are acceptable but some doubts remain unclear since these beams are characterized by a failure originated in a major critical crack. A parametric analysis based on the crack bands employed is discussed to give recommendations for a good numerical modelling of FRC shear-critical beams.

Santiago Talavera-Sánchez, Juan Navarro-Gregori, Francisco Ortiz-Navas, Pedro Serna
Experimental Analysis of Crack Development of an UHPC Wall Element Under Shear Loading

UHPC (Ultra High-Performance Concrete) is an innovative material that enables design of lightweight and structurally optimized, long-lasting structures. In this paper, an experimental analysis of precast webs of a “butterfly web” box-girder bridge on scaled-down specimens is presented. Pretensioned beam specimens were analysed in 2 variants–with continuous web and with lightened web. Based on the experimental results both variants are compared and numerical and material models suitable for UHPC modelling in software SCIA Engineer are presented. In SCIA Engineer the modified Mazarz material damage model is implemented which is applicable for material with residual strength typical for FRC and UHPFRC.

V. Příbramský, M. Kopálová, L. Dlouhý
Assessment of the Shear Behaviour of Fibre Reinforced Concrete Through Numerical Modelling of Shear-Friction Theory

Few published studies have dealt with the mechanisms of reinforcement of fibre reinforced concrete (FRC) when it is subjected to shear stresses. Possibilities for noticeable improvements and steel rebars reduction have been reported although additional research is needed in order to determine and quantify the shear resisting mechanisms of FRC.The significance of this research relies on the use of several types of FRC, previously characterized under flexural tests, to perform push-off tests. The tests were complemented with digital image correlation (DIC) techniques in order to obtain displacements and crack openings that will permit the development of the shear-friction theory adapted to FRC.The experimental campaign was performed with specimens of dimensions 270 × 150 × 150 mm3. The specimens were manufactured with six types of concrete: two moderate-strength concrete matrixes with 6 and 7.5 kg/m3 of polyolefin fibres, two medium-strength concrete (vibrated and self-compacted) reinforced with 10 kg/m3 of polyolefin fibres and two steel fibre reinforced concrete types with 50 and 70 kg/m3 of steel hooked fibres. The results showed that FRC follows an analogous behaviour compared with reinforced concrete and the shear-friction theory. The relations between the displacements and the crack openings were achieved as well as deformation maps in the push-off tests.

Álvaro Picazo, Marcos G. Alberti, Alejandro Enfedaque, Jaime C. Gálvez
Modeling the Compressive Behavior of Steel Fiber Reinforced Concrete Under High Strain Rate Loads

Concrete is a strain-rate sensitive material and shows relatively low ductility and energy dissipation capacity under high strain rate loads (HSRL) such as blast and impact, representative of terrorist attacks and accidents. Experimental research in the literature has evidenced that introducing steel fibers, into the concrete mixtures can significantly improve the concrete behavior under HSRL. Besides the experimental research, development of design models is an important aspect to provide more confidence for engineers to use SFRC in structural elements when subjected to HSRL. The existing design codes (e.g. CEB-FIP Model Code 1990 and fib Model Code 2010) propose models for the prediction of the strengths of concrete under different HSRL, but they are only function of strain rate. In this regard, the current paper deals with the improvement of design models in the fib Model Code 2010 for the prediction of the compressive behavior of SFRC by considering the effects of the important parameters such as volume fraction, aspect ratio and tensile strength of steel fibers, and concrete compressive strength, besides the strain rate effect. The developed artificial neural network mathematical model is calibrated and its predictive performance is assessed using a database collected from the existing compressive impact tests results on SFRC specimens.

Honeyeh Ramezansefat, Mohammadali Rezazadeh, Joaquim A. O. Barros, Isabel B. Valente, Mohammad Bakhshi

Structural Design

Post-cracking Strength Classification of Macro-synthetic Fibre Reinforced Concrete for Sleeper Application

Nowadays, timber and concrete are among the most extensively used materials for railway sleepers, characteristically considered as a crucial track component. However, due to recent concerns regarding the inferior quality, degradation, durability, high-cost and environmental impact of the conventional materials, this paper focuses on macro-synthetic fibre reinforced concrete (MSFRC) as a more sustainable alternative. Despite the encouraging strength characteristics of the innovative material, its practical implementation as a composite sleeper remains fairly limited due to the unknown post-cracking behaviour categorised through the fibre reinforced concrete (FRC) constitutive laws. Hence, the paper herein investigates the characteristic flexural residual strength (i.e. serviceability & ultimate) of MSFRC classified in terms of strength intervals and residual strength ratios as defined in the Fib Model Code. Experimental data will be adapted onto the design stress-strain relationship with an insightful comparison of the post-cracking propagation branch relative to different fibre volume content and fibre types. Therefore, this paper herein will present beneficial and non-beneficial behaviours of the compliant macro-synthetic fibre reinforced concrete towards railway structural applications.

Christophe Camille, Dayani Kahagala Hewage, Olivia Mirza, Fidelis Mashiri, Brendan Kirkland, Todd Clarke
Structural Behaviour of Steel-Fibre-Reinforced Lightweight Concrete

This paper evaluates the influence of adding hooked-end 3D fibres to recycled lightweight concrete beams with and without shear reinforcement. Lightweight concrete used is from recycled fly ash and can lead to reductions in the mass of the structure. However, it is typically more brittle than normal weight concrete. To enhance ductility, steel fibres were used and the complete and partial substitution of stirrups with fibres was investigated. The flexural and shear behaviour of SFRLC beams under 3-point loading with adequate, substandard and no shear reinforcement are studied. The experimental study includes Vf = 0%, 1% and 2% as well as stirrups spacing of 120 mm, 240 mm and ∞. The results in this paper are given in terms of strength, ductility, crack patterns and nature of failure. It was found out that fibre reinforcement is capable of partially replacing stirrups, however, when stirrups were completely removed the failure became brittle. Nonlinear finite element analysis (NLFEA) using ABAQUS is also used to validate a SFRLC constitutive model whose properties were derived from compressive and pullout-tests.

Hasanain K. Al-Naimi, Ali A. Abbas
Experimental Analysis of Beams Produced in Self-compacting Concrete Reinforced with Different Contents of Steel Fibres

The insertion of steel fibres into the concrete matrix can provide improvements in the control of crack propagation and increase on stiffness of structural elements. This research aims to evaluate the behavior of reinforced concrete beams in different percentages of carbon steel fibres subjected to bending. So, three reinforced beams were made with two 12.5 mm bars on the lower edge, in the dimensions of (12.5 × 25.5 × 180 cm), which were tested by four-point flexural test. One beam was used as reference, without the presence of steel fibres, and another’s were added carbon steel fibres in different volumetric fractions, 0.5% and 1.0%. During the flexural tests, measurements were made of the vertical displacements in the middle of the span, also the deformations in the longitudinal reinforcement and in the compressed region of the concrete. Results showed that the insertion of the metal fibres gave a better performance on crack control, lower deflections and deformations on the compressed region and longitudinal armour of the concrete as well as promoted slight gain in the load capacity of the beam.

Ana R. L. Pires, Rafael R. Polvere, Sidiclei Formagini, Andrés B. Cheung
Innovation in Durable Segments for CSO Tunnels

The Blacksnake Creek and storm water runoff in St. Joseph, MO, was piped along with sewage in a 100-year old pipe not large enough to carry all the storm water and sewage to the wastewater treatment plant and it overflowed to the Missouri River after most rainstorms. The Blacksnake Creek Storm Water Separation Project will convey storm water directly to the Missouri River. This will reduce water quantity in the existing sewer during storms and the quantity of combined storm water and wastewater overflowing to the river. A 2.74 m ID and 2.0 km long segmental tunnel was constructed as part of the Separation Project. This project is an America’s First, using segments solely reinforced with macro synthetic fibre (MSF). The project further features a challenging umbilical TBM launch in a small diameter secant pile shaft. This paper addresses the solutions to the technical challenges of the project, the design of the segments and the benefits associated with the use of MSF.

Ralf Winterberg, Michael R. Garbeth, Brian Glynn
Incorporation of Rate-Dependent Fracture Properties in the Design of Precast Concrete Tunnel Segment with Hybrid Reinforcement

The design of precast tunnel segment under service load condition is mostly based on the axial force and bending moment (P-M) interaction diagram. This diagram is usually derived using flexural or tensile parameters obtained from short-term testing procedure. Considering the fact that the tunnel segments are subjected to prolonged loading, the effect of the long-term loading rate on these structures needs to be incorporated. In this paper, the assumption and model used for deriving the P-M diagram is discussed and then the procedure to include the rate-dependent tensile constitutive model in the design is presented. The rate-dependence of the P-M interaction diagram of the tunnel segment with conventional reinforcement and different type and dosage of fibres is discussed.

Stefie J. Stephen, Ravindra Gettu

Codes and Standards

Developments and Standardisation of Flowable Concrete Reinforced with Fibres for Structural Design, Update of fib TG 4.3

The fib Model Codes aim at integrating in a single document the relevant knowledge for the structural design with concrete. Fibre reinforced concrete is already integrated in fib Model Code 2010 (fib MC2010) as a general category of materials. The group of flowable concrete consists of clusters of different types of concrete among others Self-Compacting Concrete, Ultra High Performance Concrete and Strain-Hardening Cementitious Composites. Being highly flowable is the distinguishing characteristic, flowable concrete might contain or not contain fibres. Although the fibre contribution on the structural level can be assessed on short-term, the structural behaviour also depends on the behaviour of the fibres and the matrix in which they are embedded. fib Task Group 4.3 worked on identifying and characterising different types of flowable concrete and discusses in a fib bulletin the most relevant aspects with regard to mix design, manufacturing, material performance and structural behaviour of flowable concrete which can allow innovative applications to be developed and realised. This paper discusses recent developments with regard to flowable concrete in a broader perspective and addresses the progress with regard to standardisation.

Steffen Grünewald, Liberato Ferrara, Frank Dehn
Assesment of Codal Provision for SFRC Beam in Minimum Shear

Natural fibres (straw, chip, horse tail, goat hair and plume, etc.), was being used from ancient time for construction purposes. Inspired from ancient time, artificial fibres (vitreous, synthetic, carbon and steel fibre, etc.) are commonly used nowadays in order to improve the mechanical properties of concrete.Literature has suggested that concrete matrix with steel fibre commonly known as Steel fibre reinforced concrete (SFRC) have enhanced flexural as well as shear behaviour as compared to conventional reinforced concrete (RC). Also it is recommended by ACI building code that steel fibre can use as minimum shear reinforcement in RC beams. In the present study, the experimental results for assessment of ACI building code provisions allowing the use of deformed steel fibres as minimum shear reinforcement in RC beams are presented. Hooked end steel fibres of length 35 mm and 60 mm have been used in concrete matrices at volume fraction of fibres ranges from 0.75 to 1.5% and 0.5 to 1% respectively. The experimental performance of the fibrous concrete beams has been compared with the Indian Standard and ACI codal provisions. It is found that in all the cases, even though at a volume fraction of 0.5%, lower than the ACI code-specified lower limit of 0.75%, the measured shear strengths were higher than the predicted values as per the ACI building code, Indian standard code, as well as from the lower bound value of 0.3√fc′MPa (3.5√fc′ psi). Also confirmed multiple diagonal cracking having crack width lower than the specified permissible values. On the basis, it is suggested that there is a need of relook into codal provisions of ACI.

Kranti Jain, Bichitra S. Negi
Laboratory Investigations on the Installation of Fasteners in Fiber Reinforced Concrete

A significant aspect regarding the use of post-installed anchors in concrete is related to constructability, and mainly the characteristics of possible geometrical configurations. Specifically for fibre reinforced concrete (FRC), as fibre strengths or dosages increase, these configurations may change. One of the critical parameters is the minimum allowable distance from the edge, which can significantly influence the flexibility of using post-installed anchors, or even the possibility to install them in the first place. This geometrical parameter strongly depends on the drilling and anchoring procedure, as various technologies are available. This paper will present and compare the various available technologies for fastenings, and it will focus on setting experiments in fibre reinforced concrete by use of challenging means for drilling and setting, i.e. hammer drilling, mortar injection and expansion anchors. The influence of fibres in the installation and tightening of post-installed anchors is particularly analysed. The results of the study reveal the possibilities for extended applications of fastenings in fibre reinforced concrete, as compared to plain concrete.

Panagiotis Spyridis, Lars Walter, Julia Dreier, Dirk Biermann

Quality Control

Applications of Statistical Process Control in the Evaluation of QC Test Data for Residual Strength of FRC Samples of Tunnel Lining Segments

Statistical process control procedures are widely applied to improve the production efficiency of industrial products. Application of quality control procedures in monitoring the production, delivery, and construction process are essential, especially when the historical data collected on various projects can be used to gain better insight to the operational procedures. Such information will promote interaction; reduce the liabilities and benefits the owners and suppliers if any of the design parameters that are below the minimum requirement can be identified as soon as possible. The longer time it takes to detect discrepancies in the data, the more the penalty, project delays, and the higher the associated costs to the owners and suppliers. A detailed analysis of the test results of flexural closed-loop control test data conducted in accordance to ASTMC1609 test is conducted for QC requirements of precast segment in tunnel lining project. More than 378 production samples are recorded. The data set contained 1 day (demolding age) and 28 days of molding. The statistical process control and the range of the data are studied in the context of material properties as well as back-calculation of the tensile parameters. The number of parameters evaluated includes flexural strength and deflection at ultimate flexural strength, the residual strength results at L/600, L/300 and L/150. A series of statistical analysis procedures to analyze the correlation of the parameters and addressed the combination of control charts for early detection of spurious shifts in the mean of the test data (out-of-control signal).

Chidchanok Pleesudjai, Devansh Patel, Mehdi Bakhshi, Verya Nasri, Barzin Mobasher
Using Decades of Data to Rethink Proportioning and Optimisation of FRC Mixes: The OptiFRC Project

Fibres enhance the mechanical properties of concrete, but residual flexural strength parameters present significant variability. The proportioning and optimisation of FRC should integrate fresh and hardened state properties as well as their variability, and this is the urgent challenge addressed by this project funded by the ACI Foundation. It follows a meta-analytical, multivariate approach, based on the creation of an exhaustive database with information on hundreds of FRC mixes compiled from papers published over two decades and adopting a data analytics perspective. First, the relationships between the relative amounts of the mix constituents, fibre geometry and dosage are modelled. Then, the strong correlations between residual flexural strength parameters, limit of proportionality, and compressive strength are exploited to develop efficient predictive tools. The final outcome will be a software package called “OptiFRC”. This will integrate capabilities to access the database compiled, to visualise and utilise the models for the optimisation of FRC mix proportionings, and to calibrate and use the derived quality control charts. This paper presents an overview of the project, reports on its progress to date and summarises the ongoing developments and anticipated impact.

Emilio Garcia-Taengua

Case Studies: Structural and Industrial Applications

Fire Resistance of Steel Fibre Reinforced Concrete Elevated Suspended Slabs: ISO Fire Tests and Conclusions for Design

Since 2004, a number of projects of multi-storey buildings have been completed in various countries where steel fibres are the only reinforcing of the cast in-situ elevated slabs. A number of full-scale tests at cold stage of these steel fibre reinforced concrete slabs have been conducted to show a very considerable safety margin between the most onerous service loading conditions and the ultimate cases at final collapse.The positive influence of steel fibre reinforcing on the material properties of the concrete under fire conditions is already well known and detailed in the literature dating back 25 years. In 2015, the ACI 544-6R 15 document, “Report on Design and Construction of Steel-Fiber Reinforced Concrete Elevated Slabs” outlines in detail the design method of such slabs but mentions also that further research is needed in the Fire Resistance area.The purpose of the paper here is precisely to address the Fire Resistance of S.F.R.C suspended elevated slabs and walls in full scale under service loadings. The paper outlines the setting-up of the tests of a number of elevated slabs and walls, subjected to the real loading conditions, the observations and then to conclude and confirm by the high positive impact on the design as well as the high safety of these slabs and walls.

Xavier Destrée, Andrejs Krasnikovs, Sébastien Wolf
Structural Behavior of a Traditional Concrete and Hollow Tiles Mixed Floor Reinforced with HPFRC

The use of high performance fiber reinforced concrete (HPFRC) in structural strengthening is widely accepted. The presence of steel fibers inside the cementitious matrix provides the hardened matrix enhanced resources in terms of strength and toughness, avoiding brittle crisis in favor of hardening/softening post-peak behavior. These performances open different scenarios in structural rehabilitation, e.g. RC column jacketing, shear strengthening of RC beam, slab reinforcement. However, the quality of the intervention is highly dependent on the technique considered for the element strengthening and on the HPFRC performance, which is strongly related to the mix design. This paper presents the results of an experimental campaign carried out on the flexural response of 4.5 × 1 m2 one-way floor elements reinforced with a commercial HPFRC material. The mechanical performances of the HPFRC adopted have been qualified following the Italian guidelines published in January 2019 for the identification and qualification of FRC products. The effect of the FRC strengthening was evaluated by comparing the performance of unreinforced and retrofitted floor elements, both using traditional r.c. and HPFRC topping. The effectiveness of the intervention is evaluated in terms of flexural strength, slab deflection and visible damage.

D. Sirtoli, P. Riva, P. Girardello
Pedestrian Bridge over Las Vegas Avenue in Medellín. First Latin American Infrastructure in UHPFRC

To introduce a new product into a new consolidated market is always a challenge, even for those products like ultra-high-performance fiber reinforced concrete (UHPFRC) which have proven their value, and it is even harder if this product does not count with local regulation that supports it, like the case of UHPFRC in Colombia. This is the reason that made local developments, both dosages and applications, of vital importance for UHPFRC wider use. That is why is important to emphasize the construction of the pedestrian bridge over Las Vegas Avenue in Medellin, the first infrastructure built in UHPC in Latin America, using a dosage with local materials developed by the company Argos SA. The new pedestrian bridge that connects the campus of the EAFIT University in Medellin with its language building is the first infrastructure work in Latin America in which UHPFRC was used. Initially the design included a metallic structure, however, Argos proposed to the University to change the steel for an UHPFRC dosage developed by Argos SA. The decision to opt for this material represented a saving of 34% in the total cost of the pedestrian bridge construction.

Joaquín Abellán-García, Andrés M. Núñez-López, Samuel E. Arango-Campo
First Experimental Full-Scale Elevated FRSCC Slab in South America

A full-scale steel fibre reinforced self-compacting concrete elevated slab was built and tested up to failure. The experimental slab (without any conventional reinforcement), consisted of four continuous panels of 3.1 × 3.1 m2 each, supported by columns two meters above ground. The nominal thickness was 130 mm. 90 kg/m3 of steel fibres were used. For the slab testing, two opposite panels were punctually loaded. Simultaneously, displacements were recorded and crack pattern registered. Results show a fan type cracking pattern, corresponding to what is reported by literature. The maximum loads obtained were Fmax,1 = 156.4 kN and Fmax,2 = 211.8 kN, (δcentral ≈ 20 mm), and the ultimate loads FU,1 = 117.3 kN and FU,2 = 187.9 kN (δcentral ≈ 60 mm), i.e. for displacements approximately three times larger than the one registered at peak load, the slab could carry more than 75% of the peak load, showing good overall ductility. A simple software, capable of modelling yield line theory, and suitable for routine applications, was used to model the slab. The software input is the slab geometry, boundary conditions, and plastic moments. The results showed that using reasonable simplifications, a good agreement between theoretical models and experimental results can be obtained if characteristic material properties are used in the model.

Luis Segura-Castillo, Diego Figueredo, Iliana Rodríguez, Nicolás García
Masonry Walls Strengthened with Fiber Reinforced Concrete Subjected to Blast Load

The aim and objective of this research project was to develop and investigate a rapid method of strengthening the Unreinforced Masonry walls (URM) for out-of-plane action. A total of 12 URM walls, built inside a precast fiber reinforced concrete boundary frame, were strengthened with a cement based concrete mix with or without steel reinforcement. The concrete mixes included Fiber Reinforced Concrete (FRC) (two dosage of fibers (4.6 & 6.0 kg/m3)), Engineered Cementitious Composite (ECC), and plain concrete shotcrete (PLS). Two out of 12 walls were strengthened with steel mesh reinforced shotcrete (MRS) such that a steel mesh was attached to the surface of the walls prior to spraying with concrete. In addition, one wall was plastered only with conventional cement mortar (RF) to serve as a reference. The strengthening materials were applied to both sides of URM walls using shotcrete technology. The walls were exposed to the air pressure of an actual blast from 10 kg of TNT explosive at a 1 m stand of distance. It was found that strengthening the walls with the proposed method significantly improved the out-of-plane behaviour of the URM walls. The results showed that the walls strengthened with ECCS exhibited the least damage followed by FRS-6, FRS-4.6, MRS, and PLS. Whereas, the reference wall (RF) did not survive the blast induced pressure and fully shattered into small pieces.

Salah Altoubat, Abdul Saboor Karzad, Moussa Leblouba, Mohamed Maalej, Pierre Estephane

Smart FRCs

Interfacial Bond Quality in Functionally Graded Concretes Incorporating Steel Fibres and Recycled Aggregates

A functionally graded material (FGM) is a material presenting gradation in composition and structure, designed to attend to specific functions. FGM produced with concrete, known as functionally graded concrete (FGC), has been studied for several applications by combining layers of distinct types of concrete showing technical benefits. Due to the material discontinuity, an interfacial zone is created between layers, named as layer transition zone (LTZ). As the weakest link between different concrete layers, the bond quality of LTZ may influence the mechanical behaviour of FGC. In this paper, the quality of LTZ in FGC was assessed considering the type of aggregate, content of steel fibres and casting delay between layers. FGC were produced with a top layer of plain cement concrete (PCC) and a bottom layer of conventional fibre reinforced concrete (FRC) or fibre reinforced recycled aggregate concrete (FRRAC). The FGC were assessed for compressive strength and bond strength between layers. The results indicate that the bond quality of LTZ is affected by casting delay and compressive strength of each layer. Moreover, it was noticed that the impact of adding steel fibres was not significant to alter the bond quality in FGC. Overall, adequate bond strengths were obtained in FGCs with casting delays of up to 24 h.

Ricardo Chan, Isaac Galobardes, Charles K. S. Moy
Towards Rebar Substitution by Fibres – Tailored Supercritical Fibre Contents

Structural application of steel fibre reinforced concrete (SFRC) progressively increases. To create load-bearing components without additional steel reinforcement, mixtures with supercritical fibre contents tailored to the structure and application must be devised. An innovative formwork concept is developed that enables for fibre contents up to 1.0 Vol.-% the steered alignment of fibres. Based on the observation that fibres orient parallel to formwork edges it applies internal formworks. The efficiency is verified by measurements of spatial fibre orientations and flexural tensile strengths. Results on single span beams indicate that favourable fibre orientations perpendicular to cracks can be achieved which is even more effectively with increasing fibre content. The impact does not go along with enhancements of flexural tensile strength. To investigate the effect of steered fibres on bearing capacities of spatial elements like slabs, the SFRC’s composition is optimized with regard to fibres’ content and orientation. The aim is to achieve two-dimensional fibre orientations in directions of principle tensile stresses by artificially limiting the specimen’s height, so that fibres align horizontally in concrete’s flow direction without additional steering. For a supercritical fibre content of 1.8 Vol.-%, it is possible to substitute conventional (mesh) reinforcements of approximate 6.7 cm2/m (fyk = 500 N/mm2).

Katharina Look, Peter Heek, Peter Mark
A Constitutive Model for Steel-Fibre-Reinforced Lightweight Concrete

A method is proposed to derive and validate material properties for lightweight fibrous concrete using experimental and numerical data. The coarse lightweight material tested (produced by LYTAG) is recycled and offers an alternative to gravel and quarry resources which are at risk of depletion in future. Also, this material can lead to reduction in the mass of the structure which results in economical designs. However, in comparison to normal weight aggregate concrete (NWAC), lightweight aggregate concrete (LWAC) tends to be more brittle as it typically shears through the aggregates leading to instantaneous drop in peak load in both compression and tension tests. Hence, to address this brittleness for LWAC, modern hooked-end DRAMIX fibres with different geometry (hooks), dosages (Vf) and bond strengths (τb) are added to mixes with different strengths (fck). This paper focuses on both tensile properties using a direct pullout and indirect notched beam tests, and compressive properties (fck, E, μ) using the conventional compression test for cylinders of plain and steel-fibre reinforced lightweight concrete (SFRLC). A tensile semi-empirical multilinear σ-ω relation was derived besides compressive σ-ε and validated against available steel fibre reinforced concrete (SFRC) constitutive models for the tested fibrous notched beams using ABAQUS.

Hasanain K. Al-Naimi, Ali A. Abbas
UV-C Treatment to Functionalize the Surfaces of Pet and PP Fibers for Use in Cementitious Composites. Adherence Evaluation

The objective of this work is to present an evaluation of the adhesion of synthetic fibers with cementitious matrices when the surface is functionalized by exposure to UV-C light.The synthetic fibers used were obtained from post-consumer containers of polyethylene terephthalate (PET). Their performances were compared with commercial macro-fibers of polypropylene (PP). Tensile strength and adhesion in two matrices—one of Portland cement and one with a partial replacement of Portland cement by ceramic waste—were evaluated at ages of between 7 days and 6 months. The obtained values ​​were compared with equal samples made with fibers whose surfaces were not exposed to this radiation.The results show that surface functionalization by this procedure does not produce the expected effects in terms of adhesion with either of the two matrices used. In commercial polypropylene fibers, functionalization is detrimental to its tensile strength by decreasing it in the environment from 70% to 80%; this loss of resistance of the polymer causes the start-up test to be interrupted by the failure of the fiber. This does not occur in PET fibers; functionalization does not substantially affect their tensile strength.

María E. Fernández, María E. Pereira, Fernando Petrone, Claudia Chocca, Gemma Rodríguez
Potential of Using Recycled Carbon Fibers as Reinforcing Material for Fiber Concrete

Carbon fibre reinforced polymers (CFRP) are taking over the aerospace, automotive, and wind energy sector. The growing demand for CFRP leads to a growing mass of CFRP waste. Landfilling and incineration are not effective and environmentally friendly routes for CFRP waste. The primary aim of this research paper is to determine the potential of using short pyrolyzed recycled carbon fibres (rCF) from CFRP waste to enhance the mechanical properties of fibre reinforced concrete (FRC). The secondary objective is to enhance the mechanical properties of FRC by optimizing fibre-matrix bonding in the interphase region. Recycled carbon fibre reinforced concrete (rCFRC) 60 specimens were prepared. These specimens consist of different rCF volume content of 0.00, 0.25, 0.5, 0.75 and 1 vol.-%. 4-point bending test procedure, along with visual analysis was performed for the characterization of the specimens. Oxygen (O2) plasma treatment has been used to improve the rCF (reinforcement) and concrete (matrix) adhesion. A maximum gain of 31% was achieved in flexural strength at fibre volume content of 0.5 vol.-% as compared to plain concrete. O2 plasma-treated rCFRC has a much higher value for elongation at break as compared to untreated rCFRC series.

Magdalena Kimm, Amna Sabir, Thomas Gries, Piyada Suwanpinij

Textile Reinforced Concrete (TRC)

Development of Textile Reinforced UHPC with Reduced Steel Fiber Contents

Textile reinforced ultra high performance concrete (TR-UHPC) is developed to further improve the tensile strength and ductility with reduced steel fiber contents. Alkali resistant glass textiles are used to partially replace steel fibers in a hybrid manner. The effects of different steel fiber content on the tensile and bending properties is investigated for four short fiber content levels. It is found that the synergistic effects of the hybrid reinforcements can be used to enhance of strengthening and toughening mechanisms with reduced cost. Pronounced strain hardening and deflection hardening are observed under tension and bending tests. The highest ductility of the TR-UHPC specimens are obtained when the steel fiber content is 1.0% vol with enhanced strength.

Mengchao Zhai, Yiming Yao, Jingquan Wang, Barzin Mobasher
Reinforcement of Concrete with Glass Multifilament Yarns: Effect of the Impregnation on the Yarn Pull-Out Behaviour

The impregnation of the yarn by the cementitious matrix is a key parameter to predict the mechanical behaviour of textile reinforced concrete. The mechanism of this impregnation is specific because of the heterogeneous nature of both materials. Since there is no method to observe and quantify this impregnation, all the models defined to describe the mechanical failure of this type of composite are based on statistics and incomplete observations. To adjust those models to the experimental results and to understand the influence of the matrix on the impregnation, several pull-out tests were performed on samples composed of a glass multifilament yarn and several matrices. After pull-out test, some samples were impregnated with resin in a three steps process that includes cementitious matrix dissolution and enable to visualize the remaining filaments and to assess their impregnation degree by the cementitious matrix.

A. -C. Slama, J. -L. Gallias, B. Fiorio
Influence of Fibres Impregnation on the Tensile Response of Flax Textile Reinforced Mortar Composite Systems

Textile Reinforced Mortar (TRM) composite systems as a technique to retrofit and reinforce existing structures represents, nowadays, an efficient application. The use of plant fibres textile as reinforcement, instead of the most employed industrial ones, resulted a promising solution as response to the sustainability criteria more and more required in the construction sector. However, some issues have been manifested as well related to the use of such natural reinforcements in cement- and lime-based matrices mainly lying in the fibre-to-matrix interaction and in the durability of both the overall composite and the reinforcement embedded within the mortar.In this context, the present study proposes an experimental activity aimed at investigating the efficiency of an impregnation treatment (by using styrene butadiene rubber latex) of flax fabrics on the mechanical behaviour of TRMs.The study confirms that the use of impregnated textile leads to an improvement of the overall behaviour of the composite system and paves the way for further investigations aimed at verifying the efficiency also in terms of durability.

Giuseppe Ferrara, Marco Pepe, Enzo Martinelli, Romildo D. Tolêdo Filho
Experimental Investigation of Mechanical Properties of Smart Textile Reinforced Concrete Pipes

Leakages in pipes results in a 35% loss of the total water supplied worldwide, which is a critical issue given the impact of climate change and global warming. Therefore, early leakage warning systems have to be developed in order to reduce the water losses occurring due to cracks and leakages in pipes. However, conventional pipes available today do not contain any integrated leakage detection mechanism. Hence, the proposed solution, of using conductive carbon fibres in the reinforcement as leakage sensors allowing for the fault and leakage determination, is being developed. This principle has paved the way for research into sustainable hybrid textile reinforced concrete (TRC) pipe systems. With the aim of realizing an industrial production method for TRC pipes, different grid-shaped textile reinforcement structures, with integrated sensory rovings, are developed for concrete pipes at the Institut fuer Textiltechnik (ITA) of RWTH Aachen University. This work forms the future basis of an automated pipe production.The aim of this study is to characterise the mechanical properties of these new age TRC pipes. For this purpose, lab scale TRC pipes with a length of l = 500 mm, an outer diameter of do = 300 mm and a wall thickness of d = 25 mm are casted using these smart hybrid textile reinforcement structures made by using alkali-resistant (AR) glass and carbon rovings. Thereafter, mechanical tests for compressive strength of the TRC pipes are carried out according to the DIN EN 1916 standards. The results are evaluated and compared with each other.

Gozdem Dittel, Michelle Wangler, Bastian Maiworm, Thomas Gries


Full-Scale Construction Test for Improvement of RC Void Slab Bridges Using UHPFRC – Part 1: Experimental Test Plan

Kajima Corporation and NEXCO Central started a joint research and development (R&D) project to develop a method for improving existing RC void slab bridges using cast-in-situ UHPFRC in 2016 and as the final investigation of the R&D project a full-scale construction test was conducted. This paper is the first one of the two papers dealing with the construction test. UHPFRC mix used in the construction test is called AFt-UHPFRC because it is characterised by its matrix densified by controlled ettringite (AFt) formation. UHPFRC was produced in a batching plant built in a testing field of that production capacity is 3.0 m3 per hour. A slab-on-ground (SOG) structure modelling top part of RC void slab bridge decks was built in the testing field and UHPFRC was cast on top of the SOG structures where UHPFRC was transported and placed by a wheel loader and spread/compacted/finished by newly developed construction equipment.

Tohru Makita, Yuji Watanabe, Shuji Yanai, Hirokazu Kitagawa
Full-Scale Construction Test for Improvement of RC Void Slab Bridges Using UHPFRC – Part 2: Test Results

In Japan, a growing number of damaged and deteriorated bridges on expressways have been seen in recent years, and the number of bridges in such conditions is set to increase in the coming decades. In order to address this issue, an extensive expressway renewal project was launched in 2015. Research and development have begun upgrading bridge decks by utilizing UHPFRC where either overlaying UHPFRC or replacing top surface concrete with UHPFRC is conducted, which leads to an increase in bridge deck stiffness. A full-scale UHPFRC casting test was carried out at the final stage of the research and development project. This paper is the second of the two papers regarding the UHPFRC casting test. Several evaluations of the construction test are presented regarding the compaction of thixotropic UHPFRC, the bonding properties of UHPFRC with existing slabs, and the transport properties of UHPFRC.

Yuji Watanabe, Shuji Yanai, Tohru Makita, Hirokazu Kitagawa
Influence of Fiber Type on the Tensile Behavior of High-Strength Strain-Hardening Cement-Based Composites (HS-SHCC) During and After Exposure to Elevated Temperatures

The paper summarizes selected results of an extensive experimental investigation, in which high-strength strain-hardening cement-based composites (HS-SHCC) made with different high-performance polymer fibers were investigated in terms of mechanical behavior under and after exposure to elevated temperatures of 105 °C, 150 °C and 200 °C. Besides the ultra-high molecular-weight polyethylene (UHMWPE) fibers, which are commonly used in HS-SHCC, high-modulus poly(p-phenylene-2,6-benzobisoxazole) (PBO-HM) fibers have been analyzed, since they exhibit a considerably higher temperature resistance in comparison to UHMWPE fibers. In contrast to the expectations, the in-situ and residual tension experiments at temperatures of up to 150 °C showed that the high-strength SHCC reinforced with UHMWPE fibers yielded considerably superior performance and less pronounced decrease of the mechanical properties compared to the composites made with PBO-HM fibers. Furthermore, the SHCC made with UHMWPE fibers showed a significant recovery after being cooled down, while the SHCC made with PBO-HM fibers exhibited a limited recovery; the degradation was proportional to the temperature increase. The 200 °C treatment led to brittle failure of both composites with dramatically reduced tensile strength and with low recovery after specimen cooling in the residual experiments.

Iurie Curosu, Sarah Burk, Marco Liebscher, Viktor Mechtcherine
Tensile and Compressive Performance of High-Strength Engineered Cementitious Composites (ECC) with Seawater and Sea-Sand

Marine infrastructures play an important role in the social-economic development of coastal cities. However, the shortage of river/manufactured sand and fresh water is a major challenge for producing concrete on site, as the transportation of these materials is not only costly but also environmentally unfriendly, while desalination of sea-sand and seawater is also pricey. Seawater sea-sand Engineered Cementitious Composites (SS-ECC) have a great potential for marine/coastal applications; but the present knowledge on SS-ECC is extremely limited. This study aims to explore the feasibility of producing high-strength SS-ECC. The effects of key composition parameters including the length of polyethylene (PE) fibers (6 mm, 12 mm, and 18 mm) and the maximum size of sea-sand (1.18 mm, 2.36 mm, and 4.75 mm) on the mechanical performance of SS-ECC were investigated. SS-ECC with compressive strength over 130 MPa, tensile strength over 8 MPa and ultimate tensile strain about 5% were achieved. Test results also showed that the tensile strain capacity increased with increasing fiber length, while sea-sand size had limited effects on the tensile performance of SS-ECC. The findings provide insights into the future design and applications of ECC in marine infrastructures for improving safety, sustainability, and reliability.

Jing Yu, Bo-Tao Huang, Jia-Qi Wu, Jian-Guo Dai, Christopher K. Y. Leung
Effect of Fiber Content Variation in Plastic Hinge Region of Reinforced UHPC Flexural Members

Ultra-high performance concrete (UHPC) is used for the construction of resilient structures that can sustain dynamic loadings such as blast, impact, and earthquake loadings, among others. In structural components subjected to such loading, it is essential to ensure the formation of a ductile plastic hinge mechanism for suitable load transfer mechanisms and global stability of the structure. Experimental research is needed to understand the formation of plastic hinges in UHPC materials and the impact of plastic hinges on the rotation capacity of reinforced UHPC structural components. The study presented herein aims to understand the spread of plasticity and formation of plastic hinge regions in reinforced UHPC flexural members. Two reinforced UHPC beams with variation in fiber volume fraction (i.e., $$ V_{f} $$ V f  = 1% and 2%) were subjected to monotonic loading. The test results demonstrated that the reinforcement plasticity length increased by 26% with a decrease in fiber volume fraction from 2% to 1%. The plastic hinge region of specimens with 2% fiber content had crack localization within the maximum moment region, whereas the specimen with 1% fiber content had a more uniformly distributed localized crack pattern. Further, analytical models and a recently proposed equivalent plastic hinge length equation were used to predict and compare the flexural strength and rotation values at various damage states.

Mandeep Pokhrel, Yi Shao, Sarah Billington, Matthew J. Bandelt
An Eco-Friendly UHPC for Structural Application: Tensile Mechanical Response

This paper presents and discusses experimental results on the tensile mechanical performance of a newly developed ultra-high performance cementitious material, UHPC, incorporating spent equilibrium catalyst (ECat), a waste generated by the oil refinery industry, as a supplementary cementitious material. The results are compared to a previously developed conventional UHPC. The influence of ECat on the heat of hydration in UHPC is evaluated by isothermal calorimeter under a constant temperature of 20 ℃. To determine the evolution of the tensile behaviour with time, a series of uniaxial tensile tests are performed on the specimens at different ages, i.e. 1, 3, 7, 28 and 91 days after casting. Afterwards, the fibre to matrix interfacial bond properties were characterized by executing a series of single fibre pullout tests at the age of 28 days on the steel fibres embedded in UHPCs with 0°, 30° and 60° orientation angles. The results confirmed the adequate performance of the new developed UHPC for the structural application.

Amin Abrishambaf, Mário Pimentel, Sandra Nunes
Characterization of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) Tensile Behaviour

Ultra-high performance fiber reinforced concrete (UHPFRC) is considered a promising material for many applications where high compressive and tensile strength, small thickness and high energy absorption capacity are required. However, although these materials were introduced in the mid-1990s, a comprehensive investigation regarding its tensile characterization is still particularly challenging. Different tensile test setups have been used by many researchers, in order to obtain reliable results, but today there are currently no testing standards available that define test conditions, specimen geometry and analytical procedures to fully characterize the tensile properties of UHPFRC.In this study, the tensile behaviour of UHPFRC has been investigated with direct tensile tests on dog-bone specimens, using a gripping system with rotating boundary conditions. Tests have been performed in displacement control. Digital Image Correlation (DIC) has been used to measure displacements, deformations, number and width of cracks in experimental testing.The effect of hooked steel fibers with diameter of 0.38 mm and length of 30 mm on the tensile behaviour of UHPFRC has been investigated, varying the amount of fibers from 0% up to 2.6% by volume. The fiber volume fraction greatly influences the tensile strength of the material, strain at peak strength, energy absorption capacity and post-cracking behaviour.

Nicola Generosi, Jacopo Donnini, Valeria Corinaldesi
Slip-Hardening Bond: A Key to the Success of Ultra High Performance FRC Composites

Bond is recognized as a fundamental causal parameter in the mechanics of fiber reinforced composites. Its paramount function is to transmit forces between fibers and matrix and vice-versa. This paper focuses on “slip-hardening bond” which can be achieved in cement composites with some fibers, as compared to commonly observed slip-softening bond or constant bond. In particular: 1) it describes how bond is characterized from a pull-out test or a pull-through test on a single fiber; 2) it gives examples of fibers with bond stress versus slip exhibiting slip-hardening behavior; and 3) it clarifies how slip-hardening response can be likely achieved. Slip-hardening bond is an extremely important characteristic which should be evaluated at the onset of design; it implies that, at the composite level, once a crack is formed in the matrix, the fibers bridging the crack provide increasing resistance to crack opening. This is likely to encourage multiple cracking in the composite and helps lead to composites with strain-hardening behavior in tension, as well as large composite strains at failure. Slip-hardening bond is considered critical for the further development and success of high performance and ultra-high performance fiber reinforced cement composites [1, 6].

Antoine E. Naaman
Testing of Thin UHPFRC Cantilever Stairs with Bolted Connections

The purpose of this research is to analyze the suitability of UHPFRC for applications to precast cantilever stairs that can be easily connected to the main structure. Several cantilever stair elements were tested under a concentrated static load applied at the free end. The anchored end was connected to the testing frame with four bolts that provided a partial fixed end. Each stair had a tread, a riser and an end plate casted with four holes to accommodate the bolts. The riser and the tread had a thickness of 20 mm whereas the end plates were 20 mm and 30 mm thick. The length of the stairs was 600 mm. Only short steel fibers were provided as reinforcement (2.35 vol.%) resulting a 180 MPa compression strength and 25 MPa flexural strength. The failure of the elements occurred at concentrated load values of 4 to 7 kN depending on the thickness of the end plate. The equivalent static force was above the one resulting from standardized static loads for staircases.

Ioan Sosa, Camelia Negrutiu, Bogdan Heghes, Adel Todor
Studying of Processing-Structure-Properties Relation of Strain Hardening Cementitious Composites (SHCC)

Strain hardening cementitious composites (SHCC) are a class of fiber reinforced materials exhibiting tensile strain hardening behavior up to strain of several percent, accompanied by the formation of fine multiple cracks with openings below 50 μm. To model the full stress-strain relation of SHCC (which governs ductility and energy absorption) and the crack width versus strain relation (which governs durability), the sequential formation of cracks needs to be analysed. The cracking process is related to the internal structure of SHCC, such as the fiber and flaw size distributions, which varies with material rheology and mixing sequence. As a first study of the processing-structure-property relation of SHCC, tensile specimens are prepared with mixes exhibiting different viscosities. To account for sequential cracking, the variation in SHCC ‘structure’ is represented by the size variation of equivalent spherical flaws inside the member according to the normal distribution, while fibres are assumed to be uniformly distributed. By fitting the measured tensile stress-strain curves for various mixes with a micromechanical model developed at HKUST, the effect of matrix viscosity on the flaw size distribution is determined. The results will provide insight on the micromechanics-based design of SHCC for various requirements on ductility and crack control.

Zhenghao Li, Jiajia Zhou, Cong Lu, Christopher K. Y. Leung
The Effect of Fiber Content on the Post-cracking Tensile Stiffness Capacity of R-UHPFRC

Concrete cracking can be controlled by adding fibers to concrete, with the expected desirable behavior under serviceability conditions due to narrower close space cracks compared to similar concrete without fibers. Using fibers to produce Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) has enhanced the post-cracking tensile capacity of composite material and increased the related energy absorption capacity for the cracked member. Accordingly, the amount and type of fiber in the matrix affect post-cracking behavior. In this experimental study, specimens reinforced by conventional steel rebars with a constant cross-sectional dimension and reinforced steel ratio were tested. The tested variables were: 1) type and length of fibers; 2) fiber content. The Direct Tensile Test was conducted, and the tensile behaviour of specimens was obtained. The results showed that the increment in fiber content (80 kg/m3 to 160 kg/m3 in this research) or the combination of micro and macro steel fibers with the same content (80 kg/m3 for each fiber type) had no significant effect on the post-cracking stiffness capacity. Moreover, all the R-UHPFRC specimens provided the full tension stiffening with the quasi same post-cracking stiffness capacity close to the bare bar axial stiffness.

M. Khorami, Juan Navarro-Gregori, Pedro Serna
Controlling Strength and Ductility of Strain-Hardening Cementitious Composites by Nano-Engineering

Considering the hierarchical nature of cracking in cement composites, multi-scale reinforcement bears the potential to enhance the fracture performance of fibre-reinforced cementitious composites. This study shows how nanoscale cellulose filaments (CF) can be used as a novel tool for tailoring the properties of strain-hardening cementitious composites (SHCC) towards improved strength and ductility. SHCC with fly ash-to-cement ratio of 1.2 and incorporating CF at rates 0.03, 0.05 and 0.10% of cement mass were developed following the micromechanical principles for pseudo-ductile cement composites. Results indicate that the incorporation of CF in SHCC allows nanoengineering matrix and interface properties by increasing matrix elastic modulus and imparting a significant slip-hardening effect. Consequently, higher complementary energy and lower crack tip toughness were obtained, thereby leading to enhanced ductility as also validated by tensile and flexural tests. As such, the incorporation of CF enhanced composite tensile strength by up to 23% and increased the ultimate strain capacity in tension by up to 26% and the deflection capacity in flexure by up to 36%. Therefore, nano-engineering SHCC with CF yields multi-scale composites with higher ductility without necessarily increasing the volume fraction of PVA fibres while exhibiting higher strength without necessarily increasing the binder content.

Ousmane A. Hisseine, Arezki T. Hamou
Comprehensive Characterization of UHPFRC Mixes for Seismic and Durability Rehabilitation of Bridge Piers

Towards design of UHPFRC jacketing for rehabilitation of bridge piers, one UHPFRC mix has been extensively characterized in order to provide the necessary material characteristics for such a design verification process. This mix is an innovative environmental-friendly UHPFRC mix, comprising recycled glass powder as cement and quartz powder replacement. The mechanical characterization of the mix comprises compressive strength and its evolution, Young’s modulus at early age and mature state, development of autogenous and total shrinkage, and tensile behaviour identified by flexural testing both on standard prismatic specimens as well as on thin plates representative of the UHPFRC jacketing layer cast around the existing concrete pier. Development of this effort has been undertaken in a joint project within ECOMAT international laboratory with Université de Sherbrooke (Canada) and the Materials and Structures Department of Université Gustave Eiffel (France).

C. Sevigny-Vallières, P. Marchand, B. Terrade, N. Roy, F. Toutlemonde, A. Tagnit-Hamou
Evaluation of the Splitting Tensile Strength of Ultra-High Performance Concrete

The splitting tensile strength of ultra-high performance concrete (UHPC) is much larger than that of normal concrete. It was found that the studies on UHPC has mainly focused on the direct tensile strength or flexural strength, while there has been insufficient work to evaluate the splitting strength characteristics of UHPC. Therefore, this study is aimed at presenting experimental and statistical evaluation of the splitting tensile strength of UHPC. The splitting tests were conducted on cylindrical specimens of 100 × 200 mm size. UHPC was designed to achieve a nominal compressive strength of 200 MPa at the age of 28 days. Macro steel fibers were used to reinforce the UHPC by volumetric percentages of 0, 1, and 2%. The effect of fiber volume on the splitting tensile strength was investigated by the test results. The values of the splitting tensile strength of UHPC with and without fibers in some previous studies were collected together with this study and subsequently verified with the predictions of the splitting tensile strength obtained from the existing models. The appropriateness of these existing models was clarified. Finally, based on the regression analysis on the collected test results, a simplified equation was proposed to estimate the splitting tensile strength of UHPC having compressive strength varying between 120 and 200 MPa.

An Hoang Le
Fibre Reinforced Concrete: Improvements and Innovations
Prof. Pedro Serna
Prof. Aitor Llano-Torre
Prof. José R. Martí-Vargas
Prof. Juan Navarro-Gregori
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