Steel fibre reinforced concrete is becoming the preferred alternative to replace traditional mesh reinforced concrete. The reason is that fibres offer remarkable qualities that improve the floor’s mechanical behaviour.
Concrete is a very hard and durable material. However, it is also a brittle material, being especially weak under tensile or flexural forces, which is why it cracks and chips easily.
To overcome this problem, during the construction process, liquid concrete can be poured over steel bars to create a stronger structure which is more durable.
On the other hand, steel bars expand and contract with temperature changes, for this reason, the concrete should be placed ideally on slabs with expansion joints between them.
But what if you want a concrete floor without expansion joints? How do you get the same strength without using steel bars? The answer is steel fibre reinforced concrete (SFRC).
What is steel fibre concrete?
Steel fibre concrete is a type of reinforced concrete. It’s basically made up of cement, water, sand, gravel and steel fibres. In some cases additives are added.
Steel fibres are discontinuous and isotropic, short metal reinforcements similar to metal filaments or threads. These can be corrugated, wavy or smooth, with flat or shaped ends.
Are generally recycled from other industrial activities. A popular source of steel fibre is automobile and truck scrap tires.
The SFRC short strands (usually about 4 or 5 cm in length) are added to the concrete mix in a ratio of between 25 and 100 kg per cubic meter of concrete, depending on the degree of reinforcement required. The mixture is then poured directly on site.
The metal fibre reinforcements are distributed throughout the concretes volume, modifying its properties in all directions.
A concrete reinforced with steel fibres is mainly characterized by having a high resistance to compression, traction and flexion. At the same time, it has better ductility and therefore, less tendency to crack.
A disadvantage of SFRC is the probability that some fibers will protrude through the concrete surface. A solution to this is the addition of a “dry shake” treatment during the curing process.
Dry shake is a granular mixture of cement, ground aggregate, pigment, and surface hardener that is spread across the surface of the new concrete whilst curing. The concrete is then leveled to create a smooth surface.
Advantages and disadvantages of using concrete with steel fibres
Steel fibre reinforced concrete has replaced wire mesh concrete because it allows optimizing construction processes, reducing execution time and construction costs.
Steel fiber reinforced concrete | BECOSAN®However, using concrete with steel fibres has advantages and disadvantages. To gain a better understanding of steel fibre reinforced concrete, we present the advantages and disadvantages of its use.
Advantages of steel fiber reinforced concrete
It allows to lay concrete floors up to 2500 m2 without joints and is, therefore, easier to maintain and clean.
Disadvantages of steel fiber reinforced concrete
When is it worth using concrete with steel fibres?
The evaluation of advantages and disadvantages of reinforced concrete with steel fibres clearly shows that it’s a beneficial material that is in consistency with its wide spectrum of application.
What is steel fibre reinforced concrete | BECOSAN®Among the uses of steel fibre concrete are:
, military and commercial.
The industrial sector is one of the environments that has benefited the most from the steel fibre concrete performance. The construction of warehouses and storage areas with flooring (and walls) of reduced thickness offering large areas without joints.
In addition, industrial flooring with steel fibre are capable of withstanding the stresses and abrasion caused by the static and dynamic loads of industrial activity, minimizing the appearance of fissures, cracks and dust.
Steel fibre concrete flooring is recommended for industries with high traffic and heavy machinery.
How to make steel fibre reinforced concrete excellent?
We also recommend the use of the BECOSAN® System for this type of floor.
This system polishes the floor and removes any micro-roughness from the surface, increasing its resistance to wear by adding the BECOSAN® Densifier. Lastly, the floor is polished and treated with BECOSAN® Sealer to make it resistant to liquids.
The BECOSAN® treatment is one of the most outstanding treatments on the market. It uses a special formula that allows to densify and compact concrete floors, increasing its strength and improving its resistance and durability.
We offer concrete polishing services in the UK and Europe.
10 years dust proof guarantee. Unique BECOSAN® patent
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As a rule of thumb, small fibres tend to be used where control of crack propagation is the most important design consideration. High fibre count (number of fibres per kg) permits finer distribution of steel fibre reinforcement throughout the matrix – and consequently, greater crack control during drying process. On the other hand, because they exhibit better matrix anchorage at high deformations and large crack widths, longer, heavily deformed fibres afford better post-crack "strength". However, unlike shorter fibres, the dramatically reduced fibre count of longer product yields correspondingly less control of initial crack propagation.
When steel fibres are added to mortar, Portland cement concrete or refractory concrete, the flexural strength of the composite is increased from 25% to 100% - depending on the proportion of fibres added and the mix design. Steel fibre technology actually transforms a brittle material into a more ductile one. Catastrophic failure of concrete is virtually eliminated because the fibres continue supporting the load after cracking occurs. And while measured rates of improvement vary, Steel fibre reinforced concrete exhibits higher post-crack flexural strength, better crack resistance, improved fatigue strength, higher resistance to spalling, and higher first crack strength, Figure 2 shows concrete flexural strengths when reinforced at various fibre proportions. Additionally, deformed fibres provide a positive mechanical bond within the concrete matrix to resist pull-out. Steel fibres are available in lengths from 38 mm to 50 mm and aspect ratios between 40 and 60. The fibres are manufactured either deformed or hook end, and conform to ASTM A-820.
Conventional practice usually concentrates welded wire fabric reinforcement within a single plane of a floor slab. Fabric does very little to reinforced the outer zones, which is why spalling is common at the joints and edges. The primary function of welded wire fabric is to hold the floor slab together after the first small hairline cracks have propagate to larger fractures. This serves to maintain some degree of "structural integrity". Conventional wisdom’s approach to floor slabs is to maintain "material integrity" through SFRC mix designs. This integrity is accomplished by:
Industrial Ground Floor Slabs – Warehouses, Factories, Aircraft Hangers, Roads, Bridge Decks, Parking Areas, Runways, Aprons and Taxiways, Commercial and Residential Slabs, Piling, Shotcrete, Tunnels, Dams and stabilisation.
Steel fibre reinforced concrete is a castable or sprayable composite material of hydraulic cements, fine, or fine and coarse aggregates with discrete steel fibres of rectangular cross-section randomly dispersed throughout the matrix. Steel fibres strengthen concrete by resisting tensile cracking. Fibre reinforced concrete has a higher flexural strength than that of unreinforced concrete and concrete reinforced with welded wire fabric. But unlike conventional reinforcement – which strengthens in one or possibly two directions – Steel fibres reinforce iso tropically, greatly improving the concrete’s resistance to cracking, fragmentation, spalling and fatigue. When an unreinforced concrete beam is stressed by bending, its deflection increases in proportion with the load to a point at which failure occurs and the beam breaks apart. This is shown in Figure 1. Note that the unreinforced beam fails at point A and a deflection of B. A Steel fibre reinforced beam will sustain a greater load before the fist crack occurs (point C). It will also undergo considerably more deflection before the beam breaks apart (point D). The increased deflection from point B to point D represents the toughness imparted by fibre reinforcement. The load at which the first crack occurs is called the "first crack strength". The first crack strength is generally proportional to the amount of fibre in the mix and the concrete mix design.
Two theories have been proposed to explain the strengthening mechanism. The first proposes that as the spacing between individual fibres become closer, the fibres are better able to arrest the propagation of micro cracks in the matrix. The second theory holds that the strengthening mechanism of fibre reinforcement relates to the bond between the fibres and the cement. It has been shown that micro cracking of the cement matrix occurs at very small loads. Steel fibres, then service as small reinforcing bars extending across the cracks. So as long as the bond between the fibres and cement matrix remains intact the Steel fibres can carry the tensile load. The surface area of the fibre is also a factor in bond strength. Bond strength can also be enhanced with the use of deformed fibres, which are available in a variety of sizes.
The proportions of Steel fibres in mix designs usually range from 0.2% to 2.0% (15 to 150 kg/m3 ) of the composite’s volume. Key factors to consider largely depend on the application under consideration and/or the physical properties desired in the finished project. Mix designs with fibre proportions above 60kg/m3 are usually adjusted to accommodate the presence of millions of steel fibre reinforcing elements. The adjustments are an increase in the cement factor, a reduction in the top size of the coarse aggregate and the addition of a super plasticiser. Prototype testing is recommended to determine the optimum design for each application.