Noise reduction in concrete surfaces can be achieved by using a porous (top) layer of concrete. The open structure of the concrete allows the air to escape between the tyre and the road surface, which reduces the rolling noise of a vehicle.
Rolling noise is reduced by about 2 dB (A) in exposed aggregate concrete surfaces, compared with an ‘AC 16 surf’, at a driving speed of 80 kilometres per hour.
- Top layer of fine-grained concrete, with grain sizes of 4-8 mm, 7 cm thick
- Bottom layer of coarse-grained concrete, with grain sizes of 4-32 mm, 18 cm thick
- The bottom layer has dowelled connection joints
- The mixture of the top layer has been determined in a laboratory to achieve the best results
The surface is laid with a machine (‘wet on wet’). The bottom layer is made with a slipform paver without a finishing beam, the top layer is made with a slipform paver with a finishing beam.
After the second paver, another machine sprays a chemical surface retarder onto the top layer. This retarder prevents the setting of the upper millimetres of the concrete, which still needs to be washed to expose the aggregate. The concrete below this thin layer is allowed to set as it normally would.
After around 20 hours (depending on the outside temperature) the surface is scrubbed and washed with water until the surface has its intended texture.
The shape and quality of the aggregate in the top layer is the foundation of this innovation. The layer is washed with great skill, which results in the desired noise reduction.