SAFETY/FIRE | TECHNICAL
Left:
Fire test of narrower Ignis PP fibre in concrete block, at IBS facility in Austria, in early 2023
PHOTO CREDIT: ADFIL
R&D: FIRE TESTS To enhance performance of the range further, with even narrower diameter fibres, Adfil conducted fire tests with the 17µm diameter PP fibres in concrete blocks. The tests were undertaken in April, at the Institut für
Brandschutztechnic und Sicherheitsforschung (IBS), in Linz, Austria, in accordance with the OBV norm of the Austrian fire classification system. The objective was to evaluate the newly developed product in extreme fire conditions and seek to obtain the BBG fire classification at the lowest dosage possible of PP fibres in the concrete mix. During the testing, two concrete samples of 1.8m x 1.4m x 0.5m were subjected to conditions of a RWS fire curve for 120 minutes. After only 10 minutes the temperature increased to 1200°C and subsequently reached a maximum of 1350°C after 60 minutes from the beginning of the test. Before the start of the test, the concrete samples
were put under tension loading of 0.5MPa longitudinally and 1.2MPa across the block. These loads created the standard tension in concrete that would cause it to undergo spalling quicker. The results of these fire tests showed that by adding of the new size of Ignis PP fibres to the
only 1.34 kg/m3
BBG fibre concrete mix design (April 2015 guideline) of the OBV norm, a significant outcome was then achieved: no explosive cracking and spalling was observed. There was a shallow area at the transition zone to the formwork where minor, slight, shallow spalling (a few hand-widths, only to 5mm maximum) took place. The report of the fire tests said the mean value of the
spalling depths on the entire fire-exposed surface was significantly less than 1cm. EUROCODE 22
in Section 6 – High Strength Concrete
(HSC), Chapter 6.2, recommends the use of more than 2 kg/m3
of monofilament fibres. However, this does not August 2023 | 21
take into the account the diameter of the fibre nor its performance during fire tests. This breakthrough in using narrower diameter PP
fibres in structural concrete is significant for passive fire resistance in tunnel safety, mitigate the risk of spalling, and also with benefits to optimise dosages and workability, and cost-effectiveness.
CONCLUSION Adfil has provided fire protection fibres to support tunnel safety for decades. The recent fire tests conducted according to the
Austrian fire classification system have further validated the effective performance of the Ignis range of PP fibres for passive fire resistance of concrete in tunnels. Achieving the result of no explosive spalling with a
mere 1.34kg/m³ of new, narrower diameter Ignis PP fibres incorporated into the concrete mix underscores its effectiveness for various structures in tunnels that could be subject to extreme fire conditions. By significantly reducing the risk of the occurrence of explosive spalling, the new PP fibres thereby further enhance the safety of both tunnel users and emergency responders. The long-term economic integrity of the concrete structures are also supported.
REFERENCES 1 Khoury, G.A. (2010) Explosive spalling of concrete in fire role of fibre diameter. BRE Global Interim Report (29 June 2010), Fire Testing of Fibre Reinforced Concrete
2 EN 1992-1-2. (2004) Eurocode 2: Design of Concrete Structures—Part 1–2: General Rules—Structural Fire Design. The European Union Per Regulation 305/2011, Directive 98/34/EC, Directive 2004/18/EC.
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