White topping: fibre concrete over existing asphalt

White topping is a renovation technique in which a thin concrete overlay of fibre concrete is poured directly over existing asphalt. The old asphalt stays in place and functions as the foundation. On the cycle paths along the N344, that delivered a 12 cm thick concrete layer, around 25% lower project costs and an expected service life of more than 20 years.

What is white topping?

In white topping, a layer of concrete — often relatively thin compared with a classic concrete road — is applied directly over an existing, aged asphalt pavement. Instead of milling off the asphalt completely, hauling it away and replacing it, the old construction is reused as a load-bearing base layer. That saves raw materials, transport movements and CO₂ emissions, and it delivers a low-maintenance pavement that behaves like a fully fledged concrete road.

Internationally, the technique is broadly classified by layer thickness:

• Conventional white topping — a concrete layer of around 18 cm or thicker, which largely carries the load by itself.

• Thin white topping — around 10 to 18 cm, where composite action with the underlying asphalt already plays a larger role.

• Ultra-thin white topping — less than around 10 cm, fully dependent on a good bond to the asphalt.

For Dutch applications — cycle paths, car parks, industrial yards and lighter-trafficked road sections — the layer thickness usually falls in the thin segment. That is exactly where fibre reinforcement comes in: a thin layer offers no room for traditional reinforcement mesh, while crack control is essential.

When white topping instead of milling and resurfacing?

The classic reflex with a worn asphalt surface course is to mill and resurface. That is a fine solution if the problem sits in the surface course and the road authority wants to keep an asphalt pavement. White topping becomes interesting as soon as the surface keeps returning as a structural cost item, while the underlying construction is still sound.

Typical triggers to consider white topping:

• Rutting — asphalt deforms under heavy or slow-moving loads; concrete is virtually insensitive to it. Read also what causes rutting and how to solve it.

• Ravelling and repeated surface-course maintenance — if a new surface course is needed every 10 to 15 years, a concrete pavement with a 20+ year service life quickly wins the whole-life cost comparison.

• Heavy or turning loads — loading and unloading zones, bus lanes, roundabouts and access roads where asphalt keeps deforming.

• Sustainability requirements in the tender — reusing the existing construction scores directly in ECI calculations: less removal, less new material.

White topping is not a solution for every situation. With subsidence, a poor foundation or insufficient residual bearing capacity of the asphalt, the problem simply shifts through to the new concrete layer. An assessment of the residual bearing capacity — for example with falling weight deflection measurements — is therefore always the first step. Where the pavement level cannot rise (connections, thresholds, cables and pipes), the thin build-up also demands bespoke design work.

Why fibre reinforcement for a thin concrete layer?

Because white topping layers are thinner than a regular concrete pavement, the construction is more susceptible to cracking from shrinkage and temperature changes. At the same time, a layer of 10 to 12 cm offers hardly any room to position reinforcement mesh with sufficient concrete cover. Fibre reinforcement solves both problems in one go:

• Crack control throughout the volume — macro fibres are homogeneously distributed through the concrete and deliver residual strength after cracking (tested to EN 14651), exactly what a thin layer demands.

• No separate reinforcement stage — laying, aligning and fixing mesh is eliminated entirely. That saves labour hours and shortens the execution time of the renovation.

• Slimmer construction — fibres increase the crack resistance of the concrete, allowing the required concrete thickness to come down. Less concrete means less transport and lower CO₂ emissions.

In practice, white topping with TwistR fibre concrete is the usual choice: a hybrid synthetic macro fibre that fully replaces the steel mesh in this kind of pavement. For projects where a mineral fibre is preferred, for aesthetic or environmental reasons for instance, the corrugated basalt fibre Basalt Wave is an alternative. Fibre type and dosage are matched to layer thickness and traffic loading; structural applications require a calculation by the structural engineer.

Step by step: how a white topping renovation proceeds

A white topping project broadly runs through seven steps:

• 1. Residual bearing capacity survey — deflection measurements and cores determine whether the asphalt can continue to function as the foundation.

• 2. Local repairs — potholes, subsidence and severely cracked sections are repaired first, so the substrate bears evenly.

• 3. Surface preparation — rutting is milled flat and the asphalt is cleaned. A rough, clean milled surface is decisive for the bond between concrete and asphalt — with thin layers, the critical point of the construction.

• 4. Pouring the fibre concrete — the fibres are dosed at the concrete plant or on site; the mix is placed in a single pass, with no waiting for steel fixers.

• 5. Finishing — levelling and applying the desired surface texture (a broom finish for skid resistance, for example).

• 6. Curing — a curing compound or covering prevents overly rapid drying, extra important for a thin layer with a relatively large surface area.

• 7. Sawing joints — contraction joints are sawn shortly after pouring. The thinner the layer, the smaller the bays: with ultra-thin layers these are small bays in the order of one to two metres; at 12 cm the bays are more generous.

After a few days of strength development, the pavement can be opened. Because removing the old asphalt and the reinforcement stage are eliminated, the total lead time is shorter than with full reconstruction.

Costs: white topping versus full reconstruction

The cost gain of white topping lies in what does not happen: no removal and disposal of the old asphalt, no new foundation, less new material and a shorter closure. On the cycle paths along the N344, around 2,500 tonnes of asphalt remained in the construction and 1,900 tonnes of new concrete sufficed — good for roughly a 25% saving on project costs compared with traditional replacement.

Then there is the service-life effect. A fibre-reinforced concrete pavement lasts well over 20 years with minimal maintenance, where asphalt in the same period usually needs at least one surface-course replacement. In a whole-life cost calculation (LCC) and in the ECI score for tenders, that counts double. Specific prices per square metre are highly project-dependent — layer thickness, accessibility, area and the condition of the asphalt determine the outcome. Therefore request a project-specific quotation; indicatively, at 2026 price levels, the saving grows the more of the existing construction can be reused.

Field examples: cycle paths along the N344 and N355

The method has been proven on the public road in the Netherlands, with cycle paths leading the way. In 2019, Schagen Infra renovated the cycle paths along the N344 between Voorthuizen and Garderen for the municipality of Barneveld. On the reused asphalt construction came a 12 cm thick concrete pavement with a total of 7,000 kg of TwistR HYBRID fibres. The result: 2,500 tonnes of asphalt that did not need to be hauled away, around 25% lower project costs, lower CO₂ emissions, improved cycling comfort and an expected service life of more than 20 years.

Along the N355 in Friesland it went a step further: there, white topping was applied to a cycle path as a European first — a thin concrete layer with TwistR macro fibres, directly over the existing asphalt, executed by Schagen Infra for the province of Friesland. The concrete is moreover 100% reusable at the end of its life.

For road authorities struggling with an ageing asphalt network, these projects are a usable reference for a cycle path of fibre concrete — the approach scales from a single cycle path to a complete renovation programme.

Concrete pavements in asset management: beyond the cycle path

White topping is one of the ways fibre concrete makes the assets of municipalities and provinces more sustainable. The same consideration — making use of the existing construction, crack control without mesh, less maintenance — applies to car parks, industrial yards and the replacement of timber bridge decks with fibre concrete. How fibre reinforcement fits into road management more broadly is covered in our article on fibre reinforcement for municipalities and on the pillar page applications and target groups.

If it concerns existing concrete with damage, overlaying is not always necessary: targeted repair often suffices. See repairing concrete and fixing cracks for that.

Applying white topping in your project

Considering a concrete overlay on existing asphalt? Three pieces of information determine feasibility: the residual bearing capacity of the asphalt construction, the traffic loading and the available pavement height. With that information, we draw up a fibre recommendation together with your structural engineer — type, dosage and layer thickness — and calculate the saving compared with full reconstruction. We will send the reference sheets of the N344 and N355 projects on request.