As part of the refurbishment of the Mont Blanc tunnel vault and at the request of our customer SPIE BATIGNOLLES, Efectis carried out laboratory fire tests to determine the spalling depth of the used concrete. Fire spalling in concrete is necessary for ensuring fire resistance of structures in the event of a fire. The tests were carried out in 2023, under the HCM curve (1300°C), on different concrete formulations depending on the parts of the vault being treated. The project was carried out in two main stages:

• Stage 1: Efectis’ fire engineering team carried out a preliminary study for designing the testing element, which must be representative of the actual structure. This stage consists of making advanced calculations using the finite element method to ensure that the stress level in the tested element during the tests is representative of the service conditions of the actual structure. This stage is also important for ensuring the safety of the tests.
• Stage 2: the concrete elements designed in stage 1 are heated in the large-scale furnace while being mechanically loaded on the testing bench at the Efectis fire laboratory in the Netherlands. The element is simultaneously loaded horizontally and vertically to achieve the required stress level throughout the test. This testing bench (used regularly, like recently for a new tunnel in Hong Kong) has a loading capacity of up to 1,000 tonnes horizontally and 300 tonnes vertically.

As part of this project, the Efectis France and Netherlands teams provided their expertise on fire resistance testing of construction products, and in particular in the spalling behaviour of concrete used in underground engineering structures. The Efectis teams would like to thank SPIE BATIGNOLLES again for entrusting us with this mission. For further information, please contact Dorjan Dauti