Bumper Plate BP "Anthracite"

Apparent density is the ratio of mass to total volume, including all pores and voids. It differs from true density, which refers only to the solid substance itself and excludes voids. For comparison, water at 4 °C has a density of 1,000 kg/m³. Recycled tyre rubber granules (ELT), consisting mainly of SBR and natural rubber, have a true density of around 1,200 kg/m³. EPDM rubber granules have a true density of around 1,600 kg/m³.

For a moulded component made from rubber granules bonded with polyurethane, apparent density is calculated from its mass and external dimensions: length, width and overall height. This volume includes two types of void. The first consists of pores between the granules that remain after pressing during manufacture. Their proportion depends on moulding pressure, granule size, granule shape and the proportion of binder. As a simplified example, a uniformly compacted tile with a flat underside and an apparent density of 800 kg/m³ has a pore volume of around one third, assuming a granule true density of 1,200 kg/m³ and disregarding the binder proportion.

The second type consists of moulded voids created by a structured underside. Drainage channels, studs, drainage feet or pedestal feet leave open spaces beneath the wearing layer. These spaces form part of the overall height but contain no rubber granules. A moulded component with a pronounced underside profile can therefore have a low apparent density even where its wearing layer is densely pressed. Apparent density describes the complete moulded component, not the constituent substance alone. At WARCO, apparent density ranges from around 600 to 1,250 kg/m³.

The compaction of the wearing layer shapes the properties of the floor covering.

• Surface: the higher the density, the less open and more resistant the surface becomes.

• Water permeability: lower density means more open pores and, in most cases, greater water permeability.

• Elasticity: lower density makes the floor covering more yielding and elastic, while higher density makes it harder and stiffer.

• Weight: together with overall height, apparent density determines dry weight per square metre. When wet, water held in the pores adds to this weight. This matters for transport, installation and the load-bearing capacity of balconies, terraces and roof areas.

The scale runs from Rating 1 to Rating 5. Each rating represents a density range, for example Rating 2 for 780 to 840 kg/m³. For moulded components with a structured underside, the rating says less about the wearing layer than it does for a tile with a flat underside.

Rubber is an elastomer. Under load, it deforms and, once the load is removed, its cross-linked molecular chains draw it back largely to its original shape. In floor coverings made from rubber granules bonded with polyurethane, the porous structure adds a further mechanism. Pores remain between the rubber granules, while the elastic binder holds them together. Under load, it is mainly these pores that close, while the granules and binder deform at the same time. As deformation increases, the floor covering generally becomes stiffer and its resistance to further deformation increases. Elasticity and internal friction determine how it absorbs impacts, vibrations and footstep sound.

Shock absorption: when a body strikes the floor covering, its kinetic energy is absorbed over the deformation distance. One part is stored elastically and returned as rebound, while another is converted into heat through internal friction. The longer the deceleration distance, the lower the forces acting on the body and substrate. Under light loads, the floor covering yields only slightly. Only severe impacts make substantial use of the available deflection. A greater thickness of floor covering extends this distance. For safety tiles, the effect is assessed as critical fall height in accordance with BS EN 1177.

Vibration damping: rubber is viscoelastic, combining spring-like and viscous behaviour. Under cyclic loading from weights being set down, equipment in operation or machinery, deformation follows the applied force with a delay. The work done in this process is dissipated as heat through internal friction. The floor covering therefore acts as both a spring and a damper. Above the natural frequency of the system formed by the mass and floor covering, it decouples the vibration source from the substrate and reduces transmitted vibrations and shocks. The amount transmitted depends on the excitation frequency, the moving mass and the dynamic stiffness of the floor covering.

Footstep sound reduction: footstep sound is structure-borne sound. Walking, jumping or setting down objects introduces an impact into the substrate. It travels through the floor or ceiling structure and walls and may be heard as noise in other rooms. An elastic floor covering introduces a compliant layer into this transmission path. The peak force is spread over a longer period and is therefore lower, while part of the energy is converted into heat within the floor covering. The amount of structure-borne sound entering the building depends on the dynamic stiffness and thickness of the floor covering, as well as on the substrate.

The damping provided by a rubber granule tile depends on its density and pore content, the granule size and shape, the proportion of polyurethane binder and its thickness. As a rule, a dense, fine-grained tile deforms less and provides lower damping, whereas a porous, coarser or thicker tile provides greater damping. The scale ranges from Rating 1, noticeable damping, to Rating 5, very high damping, and is based on comparative measurements of WARCO products. Whether a product is suitable for a particular application is best assessed on site using a sample tile.

Abrasion resistance describes how effectively a floor covering resists mass loss caused by rubbing and abrasive action. Typical sources include shoe soles, wheels, and sand or dirt moving across the surface under load. Rubber wears differently from a rigid solid. As the surface yields elastically beneath a sliding body, it is locally stretched and sheared before being relieved again. These repeatedly changing stresses fatigue the rubber over time. Fine cracks may develop and small particles can detach from the surface. In floor coverings made from rubber granules bonded with polyurethane, the bond between the granules is also relevant. The binder must retain each granule so that frictional loading does not pull whole granules from the surface. Abrasion resistance is therefore a property of the complete system, including the rubber, granule size and shape, binder content and curing, adhesion between granules and binder, and compaction, rather than of the rubber alone.

Testing to BS 7188 uses a Taber Abraser. Two standardised abrasive wheels pass over the test specimen at a defined contact force and rotational speed for a specified number of revolutions. The specimen is weighed before and after each test interval, and the resulting mass loss provides the measure of abrasion. The abrasion index and abrasion ratio are calculated from the test intervals specified in the standard. This indicates not only how much mass is lost during the first interval, but also whether abrasion decreases, remains constant or increases as loading continues.

The scale runs from Rating 1 to Rating 5. Rating 1 means that the requirements of BS 7188 are met. Ratings 2 to 4 denote good, high and very high abrasion resistance. Rating 5 is the highest rating on the scale. Classification is based on tests of representative products, with results interpolated between the tested values. In use, a high rating is reflected in a surface that retains its granule texture and visual appearance for a long period under foot traffic, rolling loads and the ingress of sand.