The construction industry uses fibre reinforced concrete (FRC) for various applications like pavements, airfield aprons and precast pipes. Different materials imbue the concrete with their properties, so the fibre choice is determined by the application.
Steel fibers in concrete improve flexural strength, transforming brittle concrete into a more malleable material. Polypropylene fibers reduce the shrinkage and permeability of concrete, allowing for a more extensive temperature range. The aspect ratio or ratio between the fibres' length and diameter also needs to be controlled to achieve a good FRC mix. Below, we look at the types of fibres used in concrete reinforcement and the benefits of using these fibres.
Steel fiber reinforced concrete (SFRC) uses cold drawn wire, cut sheet, melt extracted, and modified cold-drawn wire as reinforcing fibres in the concrete. The steel fibers increase:
- Resistance to cracking
- Flexural strength
- Tensile strength
SFRC uses typically include tunnelling, mining, paving, and bridges.
Glass fibre reinforced concrete (GFRC) uses fine glass fibers to bond with the concrete in much the same way as a composite material like glass-reinforced plastic (GRP). Reinforced concrete GFRC is lightweight and usually used for building facades and decoration. If you polish GFRC, the fibres tend to show through, but sometimes, like in countertops, this adds to the aesthetics.
Polypropylene is one of the synthetic fibers used as concrete reinforcement. It's mainly used to reduce cracking from drying shrinkage. Longer fibres provide increased concrete strength but require a coarser aggregate to separate the bundles and ensure that the material is uniformly dispersed.
Carbon fibre has a high strength for its weight but is brittle. Typically carbon fibers form part of a composite material allowing builders to take advantage of its high-temperature resistance, chemical tolerance and high strength.
Natural fibers have been used to improve the strength of concrete since 3000BC when the Egyptians used straw and horsehair to bind dried bricks. Although we use synthetic fibres today, natural fibers are still a viable alternative for concrete fibre reinforcement. Although we use cellulose fibres from pine trees today, other natural fibers have found use in concrete globally. The low cost and abundance of natural fibers suitable for concrete reinforcement make this option especially attractive in developing countries.
We have summarised the most common fibres used to enhance concrete today, but fibre reinforcement options are limitless. The idea of concrete and concrete reinforcement has been around for a long time, but the modern forms of fibre reinforcement can be traced back to 1970. All forms of reinforcement reduce cracking from shrinkage, and most provide added strength.
To decide on the best fibre reinforcement, you need to examine the properties of the materials available and use the one that best matches the structure's requirements. It would help if you also consider the additional cost and the other changes in the concrete properties before making a final decision.
Bisley has been part of the concrete admixture industry since the early 1980's.