The benefits of ultra-high-performance fibre-reinforced concrete as a repair material are widely recognised; it is ideal for lightweight, thin, watertight and durable reinforcement applications. Its high compressive and tensile strength; ductility; resistance to impact, abrasion, freeze-thaw cycles and chloride penetration make it the perfect choice for repairs with a design lifetime of 50 to 100 years.

  • Name of the owner & client
    VINCI Autoroutes, ASF (Autoroutes du Sud de la France)
  • Delivery date of the project
    September 2020
  • Partners of the project
    UHPFRC supplier: LafargeHolcim
UHPFRC dry-sprayed application

Opening up a world of possibilities for UHPFRC reinforcement

The self-levelling rheology of UHPFRC meant that, until recently, its use was limited to cast-in-place or prefabricated solutions. It was not technically possible to spray it onto inclined surfaces, vertical walls or slab soffits.

The innovation of a sprayable version of UHPFRC for civil engineering projects represents a breakthrough in the existing technologies for repair and retrofitting of structures. It came about through collaboration between concrete premix designer LafargeHolcim, and Freyssinet, which developed the application method.

Such cooperation between a specialist contractor in the field of structural repair and strengthening, a supplier of UHPFRC premix and the research department of the French Ministry of Transport, has proven that the new technology is suitable for retrofitting corrugated steel culverts.

First implementation of
UHPFRC reinforcement on steel culverts

The first implementation of the system, to repair corroded steel culverts under a highway, was funded through an innovation programme backed by the French Ministry of Environmental Transition. Development and verification of the new system involved three key stages:

1- Adapt the concrete mix design and the application equipment.

Since UHPFRC is usually a self-compacting material, a suitable formulation was necessary to enable it to be pumped and sprayed onto vertical surfaces, or overhead. This was designed by LafargeHolcim Ductal, whilst Freyssinet developed the on-site manufacturing, pumping and spraying equipment.

2-Validate the calculations

The second stage involved validation of the calculations required for the design of a repair project, as well as developing methods by which the Ultra High Performance Reinforced Sprayed Concrete could be applied to a corrugated metal pipe culvert.

A test area set up by Freyssinet enabled load tests to be carried out on a corrugated metal pipe to which the UHPFRC had been applied, measuring the deformations versus the applied loads. In addition, bending tests on corrugated flat sprayed samples were also performed to obtain more accurate data.

3- Assess the technique under site conditions

This meant choosing a test site to demonstrate that a corroded corrugated steel culvert could be repaired and reinforced by applying a thin UHPFRC layer. This solution provides structural reinforcement using a layer of the spray-applied material with a mean thickness of just 6 cm. It preserves the semi-rigid mechanical behaviour of the structure while minimising the clearance reduction.

The high mechanical performance of UHPFRC means that the quantity of material required can be cut by two thirds, in comparison with a traditional reinforced concrete solution. This reduces the intervention time and logistics, and hence also the disruption and environmental impact. It enables buried culverts to retain the same headroom and does not reduce the flow capacity in case of hydraulic culverts.

UHPFRC mobile unit

Freyssinet has recently developed a compact, mobile batching and pumping unit specially for UHPFRC application. It can be rapidly installed on site, and provides high quality and productivity standards in the fabrication of the material, with controlled pumping over distances of up to 100 m. Around 90 t of UHPFRC was spray-applied to the Barbazan farm access culvert on the A64 highway near Tarbes in south-west France using this new mobile unit in September 2020. The 59 m-long corrugated steel culvert has a diameter of 4.4 m and application of the new lining was carried out over a four-week period.

The next stage is the development of other applications for the new material; for example thin layers to reinforce, protect or waterproof structures such as dams, canals, vaults, tunnels, marine structures, and so on.

Its mechanical characteristics and durability make UHPFRC suitable for wide number of applications in other sectors. Although the material itself is quite expensive, savings can be achieved in terms of overall construction and maintenance costs, since it requires less material, can be applied in a shorter time, and the repair will outlast traditional solutions.

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