CEMENT & CONCRETE
Fibres
in the mix
Concrete properties can be altered and improved with the addition of fibres. Bryan Perrie discusses the role of synthetic fibres and their effects on concrete.
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here are two basic types of synthetic fibres: stiff macrofibres such as carbon, and micro-fibres such as polypropylene. Generally, synthetic macro-fibres are used to impart improved properties to the hardened concrete, such as flexural strength (much as steel and glass fibres do), while the micro-fibres are generally used to improve crack resistance in plastic concrete. Synthetic fibres are man-made and developed by the petrochemical and textile industries. There are two different physical fibre forms: mono-filament fibres and fibres produced from fibrillated tape. Two different synthetic fibre volumes are generally used in application: low-volume percentage (0.1% to 0.3% by volume) and high-volume percentage (0.4% to 0.8% by volume). Most synthetic fibre applications are at the 0.1% by volume level, which generally do not affect the strength of the concrete.
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IMIESA September 2020
Micro-fibres are used to improve crack resistance in plastic concrete (Credit: Chryso SA)
Key types Here are the main types of synthetic fibres used in concrete mixes: Acrylic fibres Acrylic fibres, used to replace asbestos fibre in many fibre-reinforced concrete products, are initially dispersed in a mixture of diluted water and cement. A composite thickness is then built up in layers, through pressure forming and vacuum dewatering. Acrylic
Bryan Perrie, managing director, TCI
fibres are usually added to conventional concrete at low volumes to reduce the effects of plastic-shrinkage cracking. Aramid fibres Aramid fibres are 2.5 times stronger than glass fibres and five times stronger than
When it comes to fabric and composite fibres, South African manufacturers have been extremely innovative in developing new versions of fibre for use with concrete.�
