SFR CONCRETE | LINING


● The notch will provide a controlled cracking process, thereby reducing the risk of a sudden fall; and,


● The test provides the required residual flexural strength values needed in structural designs according to Model Code and existing standards.


Different recent research and publication have confirmed that the Test standard EN14488-3 Method B is particularly useful for characterising fibre reinforced sprayed concrete and the Performance Class 3c could be achieved with Dramix steel fibre. The paper published by Universitat Politecnica de


Catalunya (UPC) during WTC 2025 presented results from an experimental programme aimed at developing a sprayed steel fibre reinforced concrete (S-SFRC) mix that consistently achieved the 3c strength class (Annex L, EC-2) by analysing the strength class obtained via Method B of EN 14488-3. Sprayed panels were produced to evaluate the mechanical performance of S-SFRC with 40kg/m3


Dramix steel fibre:


● Sprayed panels show lower variability (CoV 10%-15%) than cast beams (20%-29%) due to differences in cracked area, resulting in higher strength classes for the same S-SFRC with Method B;


● S-SFRC panels (Method B) reached strength class 3c according to Model Code with 40 kg/m³ of Dramix 4D 65/35BG steel fibres and the tested concrete mix, demonstrating sufficient potential to meet mechanical performance requirements for the target class; and,


In other paper presented by Catherine Larive, of CETU, during the WTC conference, underlined the: ● Achievability of mechanical performances of strength class 4c with very high performance Dramix fibre; and,


● Test standard EN14488-3 method B is particularly useful for characterising fibre-reinforced sprayed concrete, for several reasons: the larger specimens, used without sawing, are more representative of in-situ sprayed concrete; and, dispersions are greatly reduced, which makes it possible to obtain more interesting characteristic strengths that can be considered relevant for dimensioning.


Numerous improvements were made to the concrete mix design: increasing the cement dosage; reducing the water/cement ration (W/C); optimising the granular


skeleton; adding silica fume; selecting a high- performance fibre (reducing diameter and increasing tensile strength). Steel still is the most recycled material, and the


Bekaert R&D team, together with universities, continues to investigate recyclability. Remelted or reused steel could be directly reused as steel fibres to reinforce tunnels and mines. From the increasing number of tunnel projects — where environmental authorities approved tunnel muck disposal in the sea or river — steel fibre spray concrete delivers a microplastic and pollution free solution, as is increasingly required by governments, and as seen with Norway where plastic fibres are banned.3 To provide additional peace of mind for dosage in-


situ on sprayed concrete linings, a new inductive test to determine the content and orientation of steel fibres in reinforced concrete has been developed in collaboration with UPC. The equipment allows to determine the content and orientation of the fibres present in the concrete from the variation produced by them in a magnetic field generated by the equipment. A clear view of how fibres are distributed helps to verify that design requirements are being met before commitment to large-scale pours of steel fibre reinforced concrete. The eyeD®


Inspector helps to reduce risks, optimise


performance, and save time. The assessment of concrete linings requires


the definition of both the Sustainability Index and Mechanical Index. Designers, constructors and suppliers must work together to achieve reductions of CO2 equivalent (CO2e) emissions in design and construction, and this


collaboration must be incentivised by the client. The tunnelling supply chain’s objective needs to be to


reduce the carbon footprint of tunnel construction and contribute to the prevention of climate change. Every available lever needs to be used to reduce CO2


e


emissions, but first there needs to be focus on the areas the supply chain can make the biggest difference: ● Design Optimisation ● Reducing Portland Cement & Steel ● No microplastics pollution


We believe tunnels should use smart and sustainable construction materials. The future of tunnelling is choosing these materials today.


REFERENCES 1 Carlesso, D. M., Leporace-Guimil, B., Aguado, A., De la Fuente, A. & De Rivaz, B. (2025) ‘Sprayed steel fibre reinforced concrete: strength classes obtained through EN 14488-3 Method B’. WTC 2025, Stockholm.


2 Larive, C., Chalencon, F., Leclere, N., De Rivaz, B., Tolka, N., Bonjour, T., Mestari, A., Zghondi, J. & Bouteille, S. (2025) ‘New experiments to improve sprayed concrete performances for final support and lining’. WTC 2025, Stockholm.


3 Myren, S. A., Hagelia, P. & Bjøntegaard, Ø. (2018) ‘The ban of polymer fibre in FRSC in Norwegian road tunnels’. 8th International Symposium on Sprayed Concrete - Modern Use of Wet Mix Sprayed Concrete for Underground Support. Trondheim, Norway, 11-14 June 2018.


September 2025


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