usually , the polypropylene fiber insertion in the concrete to improve the fire resistance of the concrete. what the role of the this type of fiber? and, which the optimum volume fraction ?
PP fibres act 'sacrificially' in high-strength concrete subjected to fire. The pore structure in high-strength concrete is segmented and the permeability is low. During a fire, high pressures build up within the surface layers of the concrete, as water produced by decomposition of CSH gel at high temperatures turns to water vapour which cannot escape. This tends to produce explosive spalling; the surface layers of the concrete are violently delaminated and ejected by the rising pressure, exposing further concrete to the fire and initiating rapid and catastrophic damage.
If PP fibres are added, then as the temperature rises above ~130°C, the fibres melt and the channels left behind provide pathways for superheated water vapour to escape, reducing or eliminating spalling and prolonging the structural integrity of the concrete. Normal dosage rates are around 1 - 3 kg per cubic meter of concrete.
- Badges
- Science topic