Dynamic stiffness - property for porous materials - Printable Version

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Dynamic stiffness - property for porous materials - sunil zende - 08-22-2014

Dynamic stiffness

Dynamic stiffness is a very important property for porous materials, especially when the material is mounted directly between two solid layers (sandwich-element, floating floor). For mineral wools, it is presented per unit MN/m3 because mineral wool is usually continuous.

Stone wool is composed of solid material and air. When it is used as a resilient layer, we have to determine dynamic stiffness for both mineral fibres and air separately; so dynamic stiffness = sd + sa (sd is the material stiffness and sa is the stiffness for enclosed air).

In accordance with testing standards, the dynamic stiffness of stone wool must be stated for a loading of 200kg/m2 when it is used under a floating concrete floor. The lower the dynamic stiffness values, the better the impact sound insulation.

The stone wool products used as step sound insulation are specially designed for floor application. The fibre orientation is mainly horizontal compared to, for example, roof slabs or ground slabs. The horizontal fibres block better the sound from passing through. The difference when used in a floor may be 5 dB or even more. This means a one class difference.

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