At high temperatures, High-Performance-Concrete deserve to explode. One of the reasons for spalling is the water within the concrete.

* — Gotthard, Montblanc, St. Bernardino – tunnel fires repeatedly cause the ceilings of the seemingly steady tubes come collapse. Infernal temperatures of approximately 1000 degrees Celsius press concrete come its limits – and also depending ~ above the certain material in question, it deserve to explode. However, the process has not yet been completely understood. It is clear that the water included in high-performance concrete starts come move and evaporates – however cannot escape. The substantial vapor press in the well pores that the concrete and the thermal stress on the material can reason parts to be blown off. Whether together explosions actually occur and how severe the aftermath are counts on countless factors and also can hardly be predicted.

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In stimulate to much better understand the physics that bursting concrete, Empa researchers and a team from the university of Grenoble and the Laue-Langevin Institute, additionally in Grenoble, have actually for the very first time offered neutron tomography to create three-dimensional images of the internal of cook concrete in genuine time. The investigations were only feasible thanks to the strong neutron source at the Laue-Langevin Institute. The scientists took approximately 500 pictures per minute and constructed a distinctive three-dimensional model of the spalling concrete.

So far experts have only been able to conclude that water in concrete moves away from a heat resource and accumulates. The humidity would therefore act as a barrier and would prevent water vapor from escaping. Therefore, the vapor press would increase to the level that the product would have no selection but to explode. Making use of the new experimental setup, the Empa researchers and also their colleagues might now in reality observe this moisture barrier.

Under pressure

Concrete is composed of a mixture the sand, cement and water. A chemical reaction occurs in between cement and water, which chemically and also physically binding the water and also hardens the mixture. If the temperature in a fire exceeds 200 levels Celsius, the cement in the concrete dehydrates and the bound water turns into vapor. High-performance concrete generally has really low porosity and really fine pores. These properties room of great advantage as they carry out high strength and also exceptional durability, make the concrete virtually impermeable to outside contaminants. However, the short permeability of high-performance concrete transforms out to be a disadvantage in the case of a fire with very high temperatures because water vapor can not escape and extremely high vapor pressure can construct up.

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At high temperatures, High-Performance-Concrete deserve to explode. Among the reasons for spalling is the water in ~ the concrete. Empa researchers have currently developed and also patented brand-new additives the counteract the spalling of concrete. The brand-new results have to now cause be a additional step in the direction of the breakthrough of safe building materials with greater resistance even at the highest possible temperatures, such as a tunnel fire.