The strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive or shear.
Compressive strength and modulus
Compressive strength answers the question of how much load can be added before the insulation material breaks. Compressive stress answers the question of how much load can be added before the insulation material reaches certain relative deformation (e.g. 10 %). The higher the CS-value, the heavier the load the material can carry. This load is usually from snow, wind, soil, other materials and traffic during installation (10 kPa = 1000 kg/m2).
Compressive strength (σm
) is determined if the test specimen breaks and compressive stress of 10 % relative deformation is reached. It is necessary to define load-displacement curves during the test. The curve shows the dependence of the test piece deformation on load. Such curves provide additional information on the product behaviour.
- Compressive stress for stone wool slab is up to 100 kP
- Compressive strength for stone wool lamellas is up to 400 kPa
The compressive modulus shows the stiffness of the wool and is determined as the ratio between the stress increase and the relative displacement increase and is determined from the linear part of the load-displacement curve.
Tensile strength and modulus
Measures the force required to pull something to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure and it is measured according to EN 1607. It is necessary to define load-displacement curves during the test. The curve shows the dependence of the test piece deformation on load. Such curves provide additional information on the product behaviour.
The tensile modulus shows the stiffness of the wool and is determined as the ratio between the stress increase and the relative displacement increase and is determined from the linear part of the load-displacement curve.
Shear strength and modulus
The strength of the material to resist deformation under "sliding" forces is called shear strength. It answers the question of how much power is needed to split the material to faces. The test is done in according to EN 12090 and the results are declared in kilopascals (e.g. 35, 50, or 75 kPa). Good shear strength properties of constructive insulation material are needed to carry a load from, for example, rendering or in sandwich panels.
For sandwich panels, the shear strength and modulus is determined according to product standard EN 14509.
- Shear strength for stone wool lamellas is up to 300 kPa
Point load tells how much concentrated load can be added before insulation is compressed to 5 mm in an area of Ø 79.8 mm. This test is conducted according to EN 12430. (10 N = 1 kg)
The higher the PL –value, the heavier the concentrated load insulation can carry. The load can come from walking, studs or other material during the installation.
- Stone wool in roofs can carry a point load of 200–700N.
Material has to be “soft” but also “hard” to achieve good dynamic stiffness values. The unit MN/m³ tells how much force has to be used to compress the material down by one metre. The lower the SD-value, the better the step sound insulation.
This property is needed for damping vibration, for example, in floating floors.
- Mineral wool has dynamic stiffness values of 5–50 MN/m3.
Flexural tensile strength
Flexural tensile strength is a safety test and ensures that the products have the ability to support their own mass. For stone wool products, this is only measured for acoustic slabs which are installed horizontally from their edges only. The slab has to be rigid enough that it will not bend and drop out from the suspension system.
Flexural tensile strength can also be measured with load. This means it can be determined if some lightweight installations, such as spotlights, sprinklers or smoke detectors, can be installed directly on the slab or if they need separate support to the load bearing structure.
Pull through strength
In some applications where mechanical fasteners are going through the insulation layer, it is relevant to perform a pull through test to see how great a force is needed to pull the insulation slab out through the fastener. Most commonly, this test is conducted for rendered facade products.