Guidance for the design of steel-fibre-reinforced concrete

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SFRC has been widely used in segmental tunnel linings all over the world. Although fibres have been used by the construction industry for several decades, their use in structural applications is still very modest if one considers the gigantic potential of concrete structures around the world and the benefits expected of their mechanical behaviour and durability.

However, recent technological developments and large scale applications have demonstrated that FRC has reached a level of maturity such that these innovative materials can be used by engineers with confidence. From that perspective, the aim of the FRC workshop was to provide the state-of-the-art on the recent progress attained in terms of specifications and actual applications. Presentations covered several design guidelines adopted worldwide illustrating the progress made in the last ten years, and also a wide spectrum of FRC applications such as beams, elevated floors, tunnel linings, slabs, pavements, precast elements, bridge elements, and many others.

More than fifty papers were presented at the workshop, from which 44 were selected for this joint ACI-fib publication. The papers are organised into six themes:. The papers cover a wide range of applications and illustrate the maturity of FRC as the choice material for improving the serviceability, sustainability, and performance of concrete structures. The workshop chairs would like to express their sincere recognition to all authors and reviewers who contributed to the quality of the document.

Special thanks to both ACI and fib officers and staff who supported the organisation of the workshop, editorial support, and dissemination of the workshop proceeding as an ACI Symposium Publication and an fib Bulletin.

Steel fiber concrete reinforcement – the process of steel fiber into the concrete

While significant progress has been made in the introduction of FRC in codes and structures, the current accomplishment should be viewed as the beginning, and significant follow up work is still needed. Indeed, introducing new technologies and new materials in structural applications brings technical and scientific challenges and responsibilities. The necessity to achieve the objectives set worldwide for sustainable development requires that 21st century concrete structures meet higher performances than those of the previous one, a role that FRC can definitely help achieve.

It is the responsibility of all actors to move forward in that direction.

Guidance for the Design of Steel Fibre Reinforced Concrete

The recently published codes and design guidelines, available worldwide, constitute a first step into the implementation of FRC in the construction industry. However, before the structural use of FRC becomes a common practice, several benchmarks need to be accomplished. The numerous factors that still inhibit the use of FRC in structural applications should be viewed as challenges that could only be solved through a joint effort of all key players.

Professor Sidney Mindess, a pioneer of FRC research, indicated in his opening speech at the Montreal Workshop four challenges to increase the structural use of FRC: education and training, performance specifications, more appropriate testing methods, and comprehensive research programs focused on the combined use of FRC and continuous reinforcement.

Without claiming to provide an exhaustive list of actions, the following presents some challenges that need to be addressed by the scientific community, fibre producers, structural design community, construction industry, and stakeholders to achieve the objective of building more durable concrete structures. The scientific community should contribute to the elimination of artificial divisions between different types of FRC based on the compressive strength and type of fibres.

They should put the emphasis on the benefits brought by fibres on the performance of concrete structures and present FRC as a continuum of materials with different characteristics and performances. Approaching research on FRC more holistically with the emphasis on applications is essential for the sound development of the scientific knowledge.

Internal industrial floors and external industrial pavements | EUPAVE

Among the exceptions to this rule, however, are certain pre-cast applications. Steel fibre reinforcement may be used in conjunction with structural steel. What properties of the concrete are improved by using Steel Fibres? Steel fibre reinforced concrete acts as a uniform composite material. Compared to plain or conventionally reinforced concrete, the most immediate differences are improved ductility and post-crack performance. However, the specific effects on matrix mechanical properties greatly depend on the type and quantity of fibre used.

Generally speaking, smaller fibres with a high fibre count offer superior first-crack strength and better fatigue endurance. Should a crack open widely, longer fibres with mechanical anchorage mechanisms offer better post-crack performance. Impact— steel fibres greatly increase 1. Shrinkage— although the steel fibres themselves do not affect shrinkage rate, they can minimise and help eliminate shrinkage cracks, particularly in a restrained situation. Abrasion— steel fibres do not affect the abrasion rate of concrete mortar itself.

But they do offer a high degree 1. Spalling is dramatically reduced. But by effectively controlling micro-cracking — and the resulting susceptibility to moisture and chemical penetration — SFR can help reduce the overall porosity of the matrix. If SFRC is so good, will it entirely eliminate cracking?

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Nothing protects against bad materials and methods and nothing can entirely eliminate cracking. SFRC offers an extremely effective means of controlling cracks — and can substantially reduce opportunities for cracking. Design and installation practices can yield unpredictable results. Can Steel Fibre slabs be substantially thinner? Steel fibre reinforced slabs can be designed in a couple of different ways.

Using the more conventional elastic state theory Westergaard , if the critical load on the slab is static the slab thickness will be much the same as with traditional materials. What about the use of plastic state design method? The exceptional post-crack performance of SFRC does permit use of a plastic state design method, such as Myerhof, which will, in turn, allow substantial reductions in slab thickness.

TG8.7 - Durability design of steel fibre reinforced concrete

However employing this type of design approach will result in radial cracking under the load, as well as increased slab deflection. What is the typical dosage rate? SFRC dosage rates depend on the application and the concrete properties required. Lower dosages tend to be used when replacing conventional steel mesh.

SFRC Consortium - First demonstration project was a success

At higher concentrations vastly improved mechanical strength properties allow SFRC to be used in the most demanding applications. How does SFRC lower costs over the installation's life?

Guidance for the design of steel-fibre-reinforced concrete

Depending on the type, quantity and complexity of reinforcement in traditional design, SFRC can offer substantial cost savings. On occasions, initial costs of steel fibre alone might be slightly higher, but when labour, time, material and activities savings are considered, SFRC costs per m2 actually diminish.

How should Steel Fibre specifications read? The fibre shall be made from deformed steel wire with a tensile strength in the range of Mpa and have sufficient ductility to permit degree bends without rupture. Fibres shall have an aspect ratio in the range of 40 to 50 and a length of 38 mm.

Polypropylene fibres mainly help control plastic shrinkage cracking, which can occur in the very early stages of concrete life.

Steel fibres reinforce the concrete in its hardened state, thereby improving its strength and durability. Steel fibres have a sufficiently high modulus of elasticity and tensile strength to assume excess strain across a crack — and hold it tightly. In ground-bearing industrial floor slabs, common design practice occasionally dictates using two mesh layers. However, this steel is not acting in a structural capacity and can therefore be readily be replaced with Fibercon steel fibre reinforcement.

How are the fibres added to the concrete? Fibres can be added at the batching plant by depositing onto an aggregate conveyor. Product can also be added by gantry or lightweight conveyor directly into the back of a transit mixer on site. Don't Steel Fibres "ball up" when mixing? If this number exceeds 55, the risk of fibres bunching together increases. But if the aspect ratio falls below this critical range, fibres can be added directly into the mix at virtually any stage — without fear of balling.

The fibres are made from mild steel - what about rusting? The relative density of Steel is 7. Subsequent operations such as floating and trowelling further embed the fibres, so the number of fibres exposed at the surface of a finished installation is minimal. If subjected to conditions that promote corrosion, however, these fibres will rust, but will almost certainly not create a cosmetic problem.

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