Passive fire proteccion panels PANACOR PANEL ROCK

The physical and chemical transformations that take place in the concrete, including its melting at 1200º C, inevitably lead to its collapse and destruction, making it unrecoverable at the end of the incident, so it must be replaced. In any case, it is considered that when it reaches 300 ºC, the concrete loses a significant part of its resistant capacity and must be replaced after suffering the effects of a fire.

Another very important consequence is the spalling effect. The extraordinary rapidity with which the concrete is heated generates the passage of the water contained in the mass into steam with explosive speed. As the concrete used generally has a small pore, this vapor cannot be properly released, which produces a pressure capable of destroying the outermost layers of concrete, exposing the reinforcement and increasing the risk of the tunnel collapsing. The moments in which spalling occurs are in the initial 20-30 minutes of the fire, the most important causes of this effect being the heating rate (especially when it exceeds 2-3º C/minute), the permeability of the material and the pore saturation level (especially above 2-3% by weight of concrete moisture content); This has the result that high-performance, low-permeability concretes are the most vulnerable to this effect.

Spalling has been studied in some laboratories, such as the test carried out by the Norwegian SINTEF in December 1988, in which this effect is verified with thermal actions of hydrocarbon fire, observing an almost total decrease when the concrete receives adequate protection.

Several systems have been proposed to minimize the effects of the action of fire on concrete, but the one that has proven to be the most effective is the thermal barrier. The function of this barrier, as is obvious, is to protect the substrate from the direct action of fire, limiting the flow of heat through it and, therefore, reducing the speed of heating and the time in which the maximum temperature allowed is reached.

The most used barriers are those formed by cement mortars with mesh or by special plates mechanically fixed to the substrate. These systems with mechanical anchors eliminate adherence problems, have no spalling effect and are not sensitive to humidity. This type of product has been extensively tested in the most important laboratories in Europe –TNO (Holland), MPA Braunschweig (Germany), CSTB (France), etc., with results that confirm that the required degrees of protection have been obtained.

The planned protections (and their fastening systems) must have proven characteristics of behavior in case of fire, as well as others that allow them to resist the actions of their situation and normal use of the tunnel, such as pressure variations due to the passage of vehicles, at high speed, which can reach ±800 Pa in road tunnels, ±1,100 Pa in transport railway tunnels and up to ±5,000 Pa in high-speed railway tunnels.

These demonstrated characteristics must be proven by corresponding test reports. In the case of fire resistance, this type of test consists of preparing a concrete sample and its protection as close as possible to how it will actually be installed, with sizes of 4×3 m. Sample is submitted to a suitable installation (oven), to the action of a normalized thermal program such as those previously exposed, measuring during the whole process the deformations of the concrete, the appearance of the spalling phenomenon and the temperature gradients on the underside of the material and in the reinforcement. The information is collected by a certain number of control thermocouples suitably located in the concrete mass.

The requirements that the protection system must meet depend on the type of tunnel, the use and the legislation in this regard in each country. Here are some of the most common encountered recently in our involvement on various projects:

German ZTV requirements:

• Maximum temperature on the underside of the concrete < 300º C when subjected to the RABT curve.
• Permanence of protection during the test period.
• Minimal and shallow spalling effect.
• Temperature in the sealing of the expansion joint between 60º C and 150º C depending on the material.

Dutch RWS requirements:

• Resist the effects of the RWS Curve for at least two hours in two different tests.
• Maximum allowable temperature on the underside of the concrete < 380º C, complemented by a maximum temperature of 250º C on the reinforcing bars, with a 25 mm concrete cover.
• Temperature in the expansion joints below 60º C.

The issuance of a test report by the laboratory classifies and endorses the tested solution for its use in tunnel protection and can be complemented by other types of tests, such as freeze-thaw cycles, resistance to gases from exhaust pipes and abrasion tests (Taber Test). In addition, we have to consider high speed passages of vehicles that create some dynamic stress. In road tunnels is considered up to ±800, while in the case of railways it can have variations from ±1100 Pa for rail traffic for local transport and up to ±5,000 Pa for high-speed trains, in cycles that can vary depending on the type of tunnel considered and its volume of traffic.

Other critical elements in which the action of passive protection can be decisive is ventilation and smoke control. The main problem with each fire is that of smoke extraction, given the problems they cause. All firefighters know that to successfully attack an underground fire it is of paramount importance to obtain good heat and smoke extraction, which are the direct causes of most personal misfortunes in this type of accident. For this reason, the proper design and installation of extraction ducts that resist the effects of fire and maintain their function for a certain period of time is essential. The foregoing is also valid when we talk about ventilation systems, especially in security areas, with which the execution of fire-resistant ducts must also be considered.

In the cases in which the pipes are integrated into the tunnel structure, the separation elements are made of concrete and everything previously mentioned in the previous section applies to them. Thermal barrier protections (with plates, for example) are used to prevent damage to these separations, which would compromise their conduction function. Smoke extraction can also be carried out through independent ducts made of fire-resistant materials, which allow it to maintain its correct operation and stability for a certain period. Of course, these construction systems must also pass the corresponding tests in accordance with the specific standard for ducts.

The conclusion that we can draw from the above is that passive protection should undoubtedly be taken into account when designing tunnels to make them safer.

And with this objective in mind, PANACOR has developed, through a long R&D&i process, a protection system based on a coating using metal acoustic panels that not only manages to provide a minimum of 2 hours of fire resistance following the hydrocarbon curve, but also which also manages to attenuate the noise generated by road traffic, avoiding the inconvenience of traffic to residents. In the following video you can see the 2 hours that the fast-motion rehearsal lasted:

Fit in an urban environment

As you can see in the images below, the highway crosses a fully urbanized area. Argentina is beginning to have a high demand for noise barriers, as it is often difficult to build new roads in areas where the environment provides natural noise reduction.

In this case, the road was initially buried to allow goods to leave the port without crossing the city of Buenos Aires, increasing traffic, but also to break the direct propagation of highway traffic noise towards residents without the need for use large acoustic screens that can obstruct views.

However, unlike light, sound energy can diffract around objects, so by reducing noise reverberation, our panels make design much more efficient.