CO₂ savings with fibre reinforcement: a worked example

The CO₂ emissions per m³ of concrete amount to an indicative 150 to 300 kg of CO₂ equivalent, depending on the cement type. Traditional steel reinforcement adds another 45 to 90 kg CO₂-eq per m³ on top. Synthetic macro fibre reinforcement brings that reinforcement share back to around 4 to 12 kg per m³ — a reduction of up to 98% on the reinforcement, traceable with EPD figures from the Dutch National Environmental Database.

Where do the CO₂ emissions per m³ of concrete come from?

The CO₂ footprint of concrete is dominated by the cement. Producing Portland cement clinker releases CO₂ from both the firing process and the chemical conversion of limestone; the cement thus accounts for the vast majority of a concrete mix's emissions. Indicatively: a mix based on CEM I quickly reaches 250–300 kg CO₂-eq per m³, while a blast furnace cement mix (CEM III) comes out at around 150–220 kg CO₂-eq per m³. The exact value per mix is stated in the environmental declaration (EPD) of the concrete plant.

What is often forgotten in discussions about the CO₂ emissions of concrete: the reinforcement counts too. A traditionally reinforced floor or foundation easily contains 30 to 60 kg of reinforcing steel per m³ of concrete; in heavily reinforced (precast) structures that can rise to well over 100 kg/m³. That steel represents 10 to 25% of the total CO₂ footprint of the reinforced element — and it is precisely on that share that fibre reinforcement delivers the greatest gain.

CO₂ emissions of reinforcing steel: the figure per kilo

For the CO₂ emissions of reinforcing steel, varying figures circulate in EPDs and the National Environmental Database (NMD), depending on the production route:

• Primary steel (blast furnace route) — indicatively 1.9 to 2.5 kg CO₂-eq per kg of steel.

• Scrap-based steel (electric arc furnace route) — indicatively 0.4 to 0.8 kg CO₂-eq per kg.

• Reinforcing steel as supplied in the Netherlands (mix of routes) — in practice often 0.6 to 1.9 kg CO₂-eq per kg, depending on the specific EPD.

For the worked examples in this article we use 1.5 kg CO₂-eq per kg of steel as a conservative mid-range figure, and 2.0 kg CO₂-eq per kg for polypropylene macro fibre (polymer plus fibre production). Important: these are indicative calculation assumptions. For a tender or Ladder report you always use the project-specific EPD values — category 1 data from the NMD where available.

Why do a few kilos of fibre replace tens of kilos of steel?

The heart of the CO₂ saving lies in the mass ratio. Structural macro fibres are dosed in kilograms per cubic metre: for TwistR that is 2.0 to 6.0 kg/m³, depending on the required performance. A traditional reinforcement mesh or bar package in the same cubic metre weighs 30 to 100+ kg. The ratio between fibre and steel mass thus lies between roughly 1:10 and 1:50.

That is possible because fibres work differently from bars. Millions of fibres distribute themselves three-dimensionally throughout the concrete matrix and bridge cracks the moment they arise; the post-cracking tensile strength is tested according to EN 14651 and the fibres themselves are certified according to EN 14889-2. A mesh of Ø8-150 only does its work in one plane, has to be fixed and set on spacers — and therefore weighs many times more. How that works out structurally for foundations is covered in our article on fibre reinforced concrete for foundations.

One caveat belongs here: fibres do not fully replace traditional reinforcement in every situation. For structural work, the structural engineer determines on the basis of a calculation whether, and at what dosage, fibre reinforcement can take over from the steel.

The worked example: foundations for tree and planter boxes

In a public realm project, the foundations for tree and planter boxes were redesigned from traditional steel reinforcement to fibre reinforcement. The facts from that project:

• A net 1,500 kg of reinforcing steel saved by switching to fibre reinforcement.

• 98% CO₂ reduction compared with the original steel solution.

• Design conversion time: two days, including approval from the municipality.

How that 98% is traceable

That 98% is not a marketing figure, but follows directly from the mass ratio and the figures per kilo. The reconstruction, using indicative EPD figures:

• Avoided steel — 1,500 kg × 1.9 kg CO₂-eq/kg (primary route, as in the original design) ≈ 2,850 kg CO₂-eq.

• Added fibre — in the order of 30 kg of macro fibre (ratio of ±1:50 for this heavily reinforced precast design) × 2.0 kg CO₂-eq/kg ≈ 60 kg CO₂-eq.

• Reduction — 1 − (60 / 2,850) ≈ 98% less CO₂ on the reinforcement.

If you calculate with scrap-rich reinforcing steel at 0.7 kg CO₂-eq per kg, the same design comes out at around 94% reduction — still substantial. The range in practice: the heavier the original steel design and the lower the fibre dosage, the closer you get to 98%. With lighter reinforcement designs, the gain tends to sit around 85 to 95%.

CO₂ of reinforcement per m³ of concrete: four variants compared

The same figures (1.5 kg CO₂-eq per kg of steel, 2.0 per kg of synthetic fibre) applied to one cubic metre of concrete give this picture — the concrete itself (indicatively 150–300 kg CO₂-eq/m³) comes on top in all cases:

• Unreinforced concrete — 0 kg CO₂-eq of reinforcement per m³.

• Traditional reinforcement (mesh/bars, 30–60 kg/m³) — 45 to 90 kg CO₂-eq per m³.

• Steel fibre concrete (20–35 kg/m³) — 30 to 55 kg CO₂-eq per m³.

• Synthetic macro fibre concrete (2–6 kg/m³) — 4 to 12 kg CO₂-eq per m³.

The CO₂ saving on concrete from moving from traditional reinforcement to synthetic macro fibre amounts in this comparison to 41 to 86 kg CO₂-eq per m³ — on the reinforcement share a reduction of roughly 85 to 95%, rising to 98% for steel-intensive designs. Steel fibre concrete also saves compared with mesh and bars, but considerably less, because the dosage remains in the same order of magnitude as the steel weight it replaces.

Scaling up: what does it save on a 1,000 m² industrial floor?

The planter box case is small-scale; the gain scales with the steel weight you replace. Take an industrial floor of 1,000 m² at 180 mm thickness — 180 m³ of concrete:

• Traditional — 35 kg of steel per m³ → 6,300 kg of reinforcing steel → ± 9.5 tonnes CO₂-eq (at 1.5 kg/kg).

• Macro fibre — 4 kg of fibre per m³ → 720 kg of fibre → ± 1.4 tonnes CO₂-eq (at 2.0 kg/kg).

• Saving — ± 8 tonnes CO₂-eq per 1,000 m² of floor, around 85% less on the reinforcement.

For reference: 8 tonnes of CO₂-eq corresponds to roughly 40,000 car kilometres (at ±0.2 kg CO₂ per km). And that does not yet count the indirect gains: no transport and crane movements for mesh, no steel fixing, a shorter construction period. With our calculator you can work out the dosage and the replaced steel weight for your own floor or paving.

And the CO₂ emissions of asphalt?

With asphalt, the centre of gravity of the CO₂ emissions lies elsewhere: not in reinforcement, but in producing the hot mix (heating aggregate and bitumen) and in transport. Here fibres mainly save indirectly: aramid fibres increase resistance to rutting and cracking, so a surface course lasts longer and fewer maintenance and replacement cycles — and thus fewer production emissions — are needed over the life of the road. How life extension and material savings add up together is covered in circular construction with fibre reinforced concrete and asphalt.

Using these figures in the CO₂ Performance Ladder, MKI and EMVI

A fully calculated case is only worth something once it lands in the instruments contracting authorities steer by. Three routes:

• CO₂ Performance Ladder — the official conversion factors of the Ladder (co2emissiefactoren.nl) mainly cover fuels, energy and transport. Material-related gains such as fibre reinforcement are entered under scope 3, substantiated with a chain analysis based on EPD data. How to go about that is set out in fibre reinforcement and the CO₂ Performance Ladder.

• MKI and DuboCalc — for infrastructure projects you convert the environmental gain into a lower environmental cost indicator; the CO₂ module is the heaviest item in it. See MKI and DuboCalc with fibre reinforcement for the calculation methodology.

• EMVI — a project-specific, traceable worked example like the one above scores considerably better in a quality plan than a generic sustainability claim. What assessors expect is covered in EMVI tenders: meaning and criteria.

Important for the evidence: use fibres with a verified environmental declaration. TwistR is EPD-documented fibre reinforcement (EN 15804+A2, ISO 14025/21930) with a low MKI, so your calculation ties in directly with the NMD and DuboCalc systematics. More background on standards and sustainability instruments can be found in our overview of sustainability, standards and innovation.

Calculating it yourself for your project

The calculation method in this article can be applied to any design in four steps:

• Step 1 — determine the steel weight (kg) in the traditional design, from the reinforcement drawing or the specification.

• Step 2 — multiply by the EPD figure for the reinforcing steel (indicatively 0.6–1.9 kg CO₂-eq per kg).

• Step 3 — calculate the fibre variant: dosage (kg/m³) × concrete volume × the fibre's EPD figure.

• Step 4 — the difference is your saving; have the structural equivalence checked in parallel by the structural engineer.

Would you like this calculated for a specific project, including EPD substantiation for your Ladder or EMVI dossier? Start with the calculator or request a project-specific calculation — we will run the CO₂ comparison for you free of charge.