APRR: innovative use of UHPFRC to repair engineering structures

APRR has just trialled ultra-high-performance fibre-reinforced concrete to renew the sealing of the deck of an A36 motorway bridge in Côte-d'Or. A first in France and an experiment set to be repeated by APRR on other structures of its network.

APRR recently used ultra-high-performance fibre-reinforced concrete (UHPFRC) to repair the deck of a motorway bridge on the A36 (Beaune-Mulhouse), which crosses the Saône diversion channel in the Côte-d'Or department.
All the traditional sealing techniques proved to be unsatisfactory in dealing with the complex problems presented by this 100-metre long structure, built 40 years ago and consisting of a large metal framework (so-called Warren beams made up of metal bars). There were several problems: heat dissipation in this imposing metal substructure in high temperatures, adherence problems of the existing seal due to the low asphalt thickness and asphalt creep (appearance of a 6 to 7 cm bulge under the traffic lanes and holes in the road surface). Numerous emergency repairs were undertaken to ensure the safety and comfort of motorway users. However, precautionary measures could not guarantee the structure's longevity.

This was where UHPFRC came in, a material with a cement matrix reinforced by fibres (metal or organic) and offering, in particular, notably greater compressive strength than current or high-performance concretes. More expensive than traditional concretes as it has to be prepared and poured on site, UHPFRC offers incomparable physical and mechanical qualities and exceptional durability (meaning it can be used in extremely aggressive environments).
It also provides extremely low creep, which was the main objective sought by the teams of APRR, Freyssinet and Vicat the two companies tasked with preparing, pouring and spreading the precious concrete.

An experimental protocol
Although UHPFRC has been used in construction for many years, it hasn't yet been used to repair engineering structures in France. The work was completed in record time (2 and a half months) thanks to the support of a committee of UHPFRC technical experts from France and Switzerland. While this technique is highly novel in France, it has been in use for more than 15 years in Switzerland and is technically recognised by SIA Standard 2052:2016.

"In France, everything still had to be demonstrated as no technical evaluations of the system had been conducted and French standards did not cover all the requirements needed to guarantee performance," says Romain Pittet, manager of engineering structures and superstructures at APRR.
And so APRR developed an experimental protocol with the help of the expert committee, resulting in the creation of an application test slab, adaptations in the works phase on the bridge and monitoring the ageing of a control slab over 10 years.

Thanks to the success of this audacious trial, APRR intends to use UHPFRC again for repairs and renovations on another aging engineering structure, the Pont-d'Ouche bridge on the A6 motorway north of the town of Beaune, also in Côte d'Or.