General introduction of steel fibre reinforced concrete

Steel fibre reinforced concrete is a composite material in which steel fibres are added to the concrete mixture to maintain or increase the tensile strength of concrete after a crack has formed. Steel fibres are used to replace or reduce the use of traditional reinforcement in concrete structures.

The use of fibre reinforced concrete has increased a bit today. In addition to the floors built on soil, steel fibre reinforced concrete can also used for the following applications:

• slabs supported by piles,
• slab and strip foundations,
• inserted ceilings,
• in walls.

Using fibre-reinforced concrete significantly speeds up the construction process, as there is no need for the operations which are related to the installation of the reinforcement. It is also guaranteed that the reinforcement is always located in the right place and there is a minimum risk for reinforcement errors.

The properties of steel fibre reinforced concrete largely depend on the steel fibre used. Laboratory tests show that the most optimum fibre has the following properties:

• made of drawn wire,
• tensile strength: 1100–1500 MPa,
• diameter: 0.75 mm and
• length: 50 mm.

The operating principle of steel fibres

There are special hooks at the ends of the fibres to improve the anchoring (Hooked End). The product name of the steel fibre in the product selection of Betotrade OÜ is BT-HE75/50.

There are several different standards and guidelines on steel fibre reinforced concrete. The behaviour of steel fibres in concrete has been determined by testing which involves identifying the behaviour of the steel fibre reinforced concrete after cracking in the case of using different steel fibres. In the course of the test, a fibre-reinforced concrete beam supported at both ends is loaded in the middle.

The task of the steel fibres is to reinforce the concrete and prevent the development of cracks at the level of micro-cracks. This feature enables, for example, to increase the widths of the shrink joints on floors compared to the regular reinforcement. The accurate dose of steel fibres can be calculated by using special programmes. The contracting entity must provide the following information for the calculations:

• loads,
• details of the base,
• other requirements.

Betotrade OÜ has the capability of making these calculations to find the dose of steel fibres and the thickness of the slab.

The steel fibres sold must be certified and compliant with the standard. Fibres of the same shape may not behave similarly in concrete which may result in serious consequences. The steel fibres specified in the building design documentation should be used.

The steel fibres provided by Betotrade OÜ are classified under system 1 based on EN 14889-1:2006, which means that they can be used on concrete or grout as calculated reinforcements. The contracting entity can make sure that the amount of steel fibres is compliant with the building design documentation on the basis of EN 14721:2005, based on which the amount of steel fibres specified in the standard is washed out and weighed and the compliance with the dose prescribed is checked.

It is common practice that concrete with the required amount of steel fibres dosed is delivered by the manufacturer of the concrete. Betotrade OÜ cooperates with all concrete factories in Estonia. The customer should simply provide to the manufacturer of the steel fibre reinforced concrete the make of the concrete, the dose of fibres, the volume, and the delivery terms should be agreed on. We are always happy to give technical advice, if requested.