In normal layers in a road pavement, the material in each layer is usually subjected to an increase in the vertical stress during traffic loading. This stress increase may cause the material to expand slightly in a horizontal direction. However, the surrounding layer material resists this expansion, resulting in an increase in the horizontal stress σ3.

The K-mould-test system is designed to simulate this condition in the laboratory, and may be described as a mechanical device in which the lateral restraint is automatically increased as the soil or asphalt specimen is vertically loaded.

The K-mould is used to determine the elastic (i.e. Esec, v) and shear properties (c and φ) of road- building materials at similar conditions as expected in the pavement (i.e. dry density, moisture or binder content, and vertical stress level), in order to design the pavement structure optimally.

It is also used to determine the materials resistance to permanent deformation.
It uses samples with a height: diameter ratio of less than one and has been used to evaluate granular materials with a maximum particle size of up 53 mm (2.1in) although the maximum particle size is usually 37.5 mm. (1.5 in).

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