BETONG OCH BRANDSPJÄLKNING : Aktuella lösningar för brandspjälkning

Dense, damp concrete structures can be damaged by fire. Concrete spalling in the event of a fire causes serious damage to concrete structures, which entails significant economic conse-quences as well as the risk of putting human life at risk. The problem of spalling in some concrete structures has been known for decades but it has been highlighted more recently due to more intense tunnel fires around the world. Many tunnels and buildings have been exposed to fire, which in turn allows the concrete to spall seriously when exposed to it. The fire re-sistance of newly developed concrete types has been called into question due to serious dam-age to tunnels that have not yet been put into operation. The relative humidity in a tunnel is higher than in residential buildings. Moisture and com-pressive stress are the most important factors for fire resistance. This is a clear indication that moisture plays a major role in fire fractures in concrete. To increase the durability of these types of structures, the requirements for maximum water cement ratio (w/c) have been tight-ened.Some different methods have been investigated to find a relevant solution and research has been conducted in both Sweden and other countries. Testing a concrete element on fire can be the preliminary method for finding solutions. Carrying out different tests provides the opportunity to test different concrete mixtures to prevent or minimize spalling. As early as 2011, the Swedish Concrete Association published a review of factors and recommendations. Some recurring factors are moisture content, tightness, and strength as well as compressive load.Adding a small amount of polypropylene fibers to the concrete mixture, usually between 0.5 and 2.0 kg/m3 is so far strongly recommended against fire spalling. Normally, 1.5 kg/m3 PP -fibers give a good effect, but analytical methods for fire dimensioning are needed for each individual tunnel construction. High amounts of PP-fibers can give low strength. The more fibers added, the lower the strength. Because these fibers can introduce problems such as increased air in the concrete and thus reduced machinability. There are also other fiber materials that can limit fire spalling. Optimization of the fiber content is often necessary and therefore new test methods on small specimens are needed because tests on large specimens are very time consuming and expensive to perform. Another method is thermal insulation, which is useful against fire spalling