Fibre reinforcement in precast concrete elements

Prefabrication of concrete elements — from internal walls to façade panels and stairs — is a production process in which time, weight and precision all count. Fibre reinforcement fits particularly well here, with concrete examples of gains in production speed and environmental impact. This article discusses the applications.

Why precast calls for a different approach than in-situ cast concrete

With prefabrication, concrete is cast in a controlled factory environment instead of on the building site. This already offers advantages over traditional, in-situ cast concrete: execution is less dependent on weather conditions, no scaffolding is needed on site, and construction time is shorter thanks to series production. Traditional reinforcement (mesh, bars), however, remains a labour-intensive step within that production process: transporting, reading reinforcement drawings, tying and inspecting all take time — precisely the time that prefabrication aims to save.

Why fibre reinforcement fits precast so well

• Optimisation of the production process. Using structural synthetic fibres optimises the production process of, for example, precast internal walls: traditional reinforcement can largely be replaced, with at most steel edge reinforcement and lifting provisions still needed for safely moving the element.

• Higher production speed. Because no time is lost tying and positioning reinforcement mesh, the production capacity of a precast factory can increase — relevant for large-scale, series production.

• Slimmer, lighter elements. With precast façade elements, transport and lifting are a significant cost item. Fibre reinforcement, like prestressing, enables slimmer concrete structures, which can reduce the weight of an element.

Concrete figures: environmental gains in precast applications

Practical examples of structural synthetic fibre in precast elements show a considerable environmental cost saving compared with traditional reinforcement:

• Precast internal wall — MKI with traditional reinforcement €17.51, MKI with synthetic fibre €1.13; a saving of 93%.

• Concrete stairs — MKI with traditional reinforcement €52.54, MKI with synthetic fibre €10.82; a saving of 79%.

These figures are based on recognised structural synthetic fibres (such as Concrix, Fibrofor Diamond and Fibrofor High Grade), which come with a Life Cycle Assessment (LCA) and an MRPI/EPD certificate, and whose dosage (for Concrix, for example, 3 kg per m³ of concrete) is substantiated through a Life Cycle Assessment.

Specialised fibre products for precast

Besides the better-known brands, there are manufacturers that focus specifically on fibres for ready-mix concrete, sprayed concrete and precast elements. Adfil (Zele, Belgium), for example, develops the macro and micro synthetic fibres Durus EasyFinish (ATG-certified since 2018) and Crackstop, which are increasingly used as a durable, rust-free alternative to, or supplement for, steel reinforcement — with demonstrable cost and time savings during construction, substantiated with an EPD certificate. This type of fibre is used both in precast elements and in infrastructural applications, for example in a fibre-reinforced concrete layer on a bridge.

Glass fibre reinforced concrete for façade elements

For architectural façade panels, glass fibre reinforced concrete is also used. Because glass fibre gives concrete a considerably higher splitting tensile strength, the material can be cast into very thin, lightweight panels — down to a few millimetres thick — in almost any desired shape, colour and surface texture, including complex 3D forms. This makes glass fibre concrete particularly suited to façade cladding where low weight and a specific aesthetic are important.

Where is fibre-reinforced precast concrete used?

• Internal walls and fire walls: where largely replacing traditional reinforcement delivers production gains.

• Stairs: with demonstrated environmental cost savings compared with traditional reinforcement.

• Façade panels and sandwich panels: where weight, aesthetics and fast assembly are central.

• Box walls, retaining walls and plinths: where fibre reinforcement can supplement or replace traditional reinforcement.

• Infrastructural precast elements: such as fibre-reinforced overlay layers on bridges.

Points of attention

For elements that are lifted during transport and assembly, steel edge reinforcement and/or lifting provisions are usually still needed, even when the rest of the element is fibre-reinforced. For heavily loaded, load-bearing precast elements, a structural calculation (in accordance with the applicable Eurocodes) is also needed to determine to what extent fibres can replace traditional reinforcement.

In conclusion

Fibre reinforcement fits exceptionally well with the controlled, series-based nature of prefabrication: it speeds up production, demonstrably lowers environmental impact (with savings of up to 93% on the MKI score in the examples cited), and enables slimmer, lighter elements — from internal walls to façade panels and stairs.