What is fibre-reinforced concrete and should I use it in NB?

Fibre-reinforced concrete has small fibres — typically synthetic polypropylene or steel — mixed directly into the concrete batch to improve certain performance characteristics. In New Brunswick, fibre reinforcement is a useful upgrade for flatwork, but it is a supplement to — not a replacement for — conventional steel reinforcement.

The most common type used in residential NB concrete is synthetic fibre (polypropylene). The ready-mix plant adds small fibre bundles (typically 12–19 mm long) to the batch at a rate of about 0.9 kg per cubic metre. The fibres distribute randomly throughout the mix and do two important things: they reduce plastic shrinkage cracking (the surface cracks that form in the first few hours after placement while the concrete is still plastic), and they improve impact resistance and toughness in the hardened concrete. Synthetic fibre typically adds $15–$30 per cubic yard to the mix cost.

Steel fibre is less common in residential work but used in commercial floors, industrial slabs, and applications requiring high toughness and crack control. Steel fibres are heavier, harder on finishing equipment, and cost $30–$50 more per cubic yard. They are more effective than synthetic fibres at controlling cracks after hardening, but the finishing difficulty makes them less practical for typical NB residential patios and driveways.

Should you use fibre in NB? For driveways, patios, garage floors, and sidewalks, synthetic fibre is a worthwhile low-cost upgrade. It helps manage the surface cracking that is especially common during hot, dry summers when moisture evaporates quickly from fresh concrete — a real issue on August pours in Moncton or Fredericton. The fibres reduce the surface cobwebbing that homeowners sometimes see on new concrete.

However — and this is critical — fibre does not replace rebar or wire mesh. The fibres are too short and too randomly oriented to provide the structural tensile reinforcement that holds cracked slab sections together. You still need properly placed rebar or mesh at mid-slab height. Think of fibre as improving the concrete matrix itself, while rebar and mesh work as the structural skeleton.

For foundation walls, retaining walls, and structural slabs, conventional rebar is always required regardless of whether fibre is also added.

The bottom line: specify fibre as an add-on for flatwork if your budget allows. It improves surface quality and reduces early cracking. But never let a contractor talk you into fibre as a reason to skip the rebar or mesh.