TECHNICAL | CONCRETE
that the notched panel test had several advantages, including using a test specimen that better represents the material in the real structure with reduced variability. In 2022, EN 14487 was amended to include reference
to the alternate methodologies for residual flexural strength determination. In 2020, Chris Peaston included the prEN notched panel test in the SCL specification for the HS2 high-speed rail project’s Si/S2 contract, provided by Arup for SCS. There is provision in the SCL specification for the notched panel test to be used as an alternative to the notched beam.
KEY PERFORMANCE CRITERIA FOR PSCL By adopting pr EN 14488-3 Method B for the post-peak characterisation of the sprayed FRC, it is so possible to derive the parameters fct,L
, fR1 , fR3 that are necessary
for the design according to Model Code 2010. A performance class type C35/45 3c could be considered. It is recommended for permanent SCL the minimum
performance level to be: Fr1k/frlk > 0.8 and fr3k/fr1k >0.9
CONCLUSION Steel still is the most recycled material, and the Bekaert R&D team, together with universities, continue to investigate recyclability. Remelted or reused steel could be directly reused as steel fibres to reinforce tunnels and mines. SFRC delivers a microplastic and pollution free solution, as is increasingly required by government in shotcrete applications for subsea tunnels. For a sustainable use of structural concrete,
Above:
spraying lining work below London
PHOTO CREDIT: CROSSRAIL design methodologies; and, an EN 14488-3 flexural
strength test in which residual strengths are determined using notched beam specimens in accordance with EN 14651, consistent with limit state design to fib Model Code 2010. In 2011, EFNARC introduced a notched panel test,
based on the EN 14488-5 energy absorption test specimen, as a geometrically analogous alternative to the notched beam methodology thereby providing equivalent residual flexural strengths. It was suggested
environmental and mechanical performances of concrete structures must have the same importance. By means of sufficiently high mechanical performances, the structural safety of a construction is ensured. This the reason why a great challenge for the coming
years will be develop solution for low carbon tunnel lining based mainly on the following approach: ● Lower thickness ● New generation of binder ● Use of FRC, which would eliminate traditional rebar in all types of lining
● Production process improvement
REFERENCES 1 Jarast, P, Bakhshi, M. & Nasri, V. (2023) Carbon footprint emissions of different tunneling construction methods. ITA’s World Tunnel Congress (WTC) 2023, Athens, Greece
2 ITA Report ‘Permanent Sprayed Concrete Lining’, 2020 3 Schwartzentruber, L. D’Aloia. What might be our vision of the ecological transition in tunnels and underground spaces for the years to come? Centre d’Etudes des Tunnels (CETU), France. WTC 2023
4 Moe, E.S., Holter, K. G. & Strømsvik, H. (2023) Waterproof sprayed concrete with improved sustainability performance. WTC 2023
5 Nasri, V. & Vovou, T. (2023) Design and construction of the deepest underground station in Canada. WTC 2023
14 | July 2023
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