Concrete special: Putting precast to the fire test

31 January 2020 | By Professor Ali Nadjai and Dr Naveed Alam

With fire safety coming under closer scrutiny, precast firm FP McCann ran tests on its insulated sandwich panels at Ulster University’s specialist facility. Professor Ali Nadjai and Dr Naveed Alam explain the results.

Fire safety has become one of construction’s hottest topics in recent years, chiefly due to the tragic events at the Grenfell Tower in June 2017, but also because of other subsequent blazes, including at the University of Bolton before Christmas and at an apartment block in Worcester Park, London, in September.

The masonry sector has always had strong fire safety credentials. Concrete has an undefined melting point, since it disintegrates into its base constituents at around 1,000°C and possesses a low thermal conductivity (approximately 2W/m-K, upper limit at 20°C, EN 1992-1-2).

However, precast concrete firm FP McCann wanted up-to-date evidence that would give more confidence to clients and end users. With this in mind, the Northern Ireland firm approached Ulster University’s Fire Safety Engineering Research & Testing centre (FireSERT) to organise tests on its insulated precast sandwich panels. The UKAS-accredited FireSERT is one of the largest fire safety centres in Europe and one of only two in the UK which runs the BS 8414 facade test.

From top: Installation of the insulated sandwich panels at the test facility; The fire test; Dr Naveed Alam from Ulster University surveys the impact on the precast panels

The tests were backed by the European Union’s Research Fund for Coal and Steel (RFCS), with FP McCann as a local sponsor. They were conducted inside a fire test compartment comprising a steel-framed structure and hollowcore precast slabs.

The insulated sandwich panels comprised an outer layer of precast concrete, a central layer of polyisocyanurate (PIR) insulation and a structural internal layer of concrete with a power-floated plain grey concrete finish. The external concrete layer is connected and supported by the internal concrete layer using proprietary ties which have low thermal conductivity.

Two insulated sandwich panels were installed along the full length of one side of the test compartment. Detailed instrumentation – thermocouples – monitored the temperatures in the wall panels’ inner and outer concrete layers, plus the insulation layer, and inside the test compartment.

“The insulated precast sandwich panels were exposed to three fire tests. Timber was used as the fuel. During the fire tests, temperatures in excess of 1,000°C were recorded in the compartment.”

The insulated precast sandwich panels were exposed to three fire tests. Timber was used as the fuel.

During the fire tests, temperatures in excess of 1,000°C were recorded in the compartment. Despite being exposed to multiple fire scenarios, the insulated precast sandwich panels contained the fire while maintaining their structural integrity. There was spalling on the exposed surface of concrete, but this was relatively small and required limited remedial work to restore the precast panels back to full functionality.

The PIR insulation core of the sandwich panels remained encased within the layers of the precast concrete. The outer concrete layers, due to their low thermal conductivity, protected the PIR insulation core from direct exposure to heat and flames. As a result, the PIR insulation core remained unharmed.

The tests by FP McCann and FireSERT at Ulster University have demonstrated that the insulated sandwich panels provide a scientifically fire-rated precast construction solution.

Professor Ali Nadjai is director of the Fire Safety Engineering Research Technology Centre (FireSERT) at Ulster University and Dr Naveed Alam is a research associate in Structural Fire Engineering at Ulster University

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