The main objective any passive system to protect concrete against fire must achieve is that, if a fire breaks out, the mechanical characteristics of the structural elements of the concrete remain stable during the process of evacuation and action by the fire brigade (in a tunnel for example), avoiding the loss of human life. Thus, the protection system must act during the first moments of the fire.
When concrete is exposed to fire, the surface temperature begins to increase and the water vapour generated inside gravitates toward the core of the matrix where the temperatures are lower. This phenomenon causes an increase in the internal temperature that eventually exceeds the actual resistance of the concrete, causing a series of violent explosions during the first 20 minutes of the fire (depending on the nature of the material that is burning). The result is flaking of the surface face of the concrete, more commonly known as the SPALLING effect.
Recent research and testing concludes that addition of polypropylene microfibres of diametres under 32 µm significantly reduces the SPALLING phenomenon in concrete during a fire and there is a relation between the number of fibres included in the matrix and the improved behaviour of the concrete in the event of fire.
FibroMac® polypropylene fibres are manufactured from extremely fine filaments, produced by an extrusion process. They are designed to protect the integrity of the concrete when it is subjected to high temperatures and direct fire. They also reduce the fissure formation phenomenon caused by retraction or plastic settling and increase control over exudation and segregation phenomena.
FibroMac® fibres improve the features of hardened concrete, increasing its resistance to multiple phenomena:
• Wear: through exudation control, one avoids increase in the water / cement relation, which is responsible for decreased resistance on the surface of the concrete.
• Impact: on controlling the fissure depth index, it helps to preserve the integrity of the structure.
• Fire: when the fibres melt at high temperatures, micro-channels are created, that relieve the pressure generated by steam that causes the spalling phenomenon, increasing the time the structures take to degrade in the event of fire.
In these test images one may observe the improved resistance and characteristics of the samples of concrete reinforced with Fibromac® compared with the samples of non-reforced concrete.