Fire safety is one of the major concerns with regard to repair work in the Mont Blanc Tunnel. The spalling of concrete is a phenomenon which can affect special concrete or concrete that has been heated quickly and/or to a high temperature. The regulations applicable to tunnels require the performance of the concrete to be tested, using the HCM curve, in relation to this phenomenon.

Slab MontBlancTunnel   Slab of the Mont Blanc tunnel

The spalling phenomenon depends on several factors, such as the water content of the concrete, the compactness of the concrete, the type of aggregate used, the heating speed, the stress state of the element, and the geometry of the element.

In 2017 Efectis France carried out a characterization test in the laboratory at Les Avenières of the concrete spalling of the slabs used in the Mont Blanc tunnel.

There are many constraints on the type of test, such as:

Concrete slab1   Set-up of the test                                             

Several methods exist to determine the spalling depth:

Concrete slab   Example of the spalling of a concrete slab

The test confirmed the spalling depth used by the designer for the structural fire design.


Contact: Pierre Lonchampt – [pierre.lonchampt@efectis.com]