Porous paving materials
Application: In well-drained ground
Advantage: Low-tech, low maintenance
Disadvantage: No buffering capacity
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Porous and permeable paving materials have several advantages: rainwater can be absorbed into the ground, supplementing the ground water and relieving the sewage system. Porous pavements consist of porous material through which water can pass; permeable pavements contain or create open parts through which water can infiltrate. All porous and partially-open materials are very suitable for these pavements. For example, open cell concrete blocks, grass concrete pavers, woodchips, shells or gravel can be used as paving materials. Precipitation can infiltrate into the ground without any appreciable difficulty; the percentage of openings varies from around 15% to 40%. This type of paving material can be used for such purposes as footpaths, playgrounds, fire service roads and central reservations, for aeration around trees, as edging for paving materials, in verges and in private gardens. For roads and car parks that are used extensively, paving materials such as porous clinkers, open-joint clinkers, open paving patterns, gravel or shells can be used.
Porous paving materials cannot be used for intensively used roads or car parks owing to the risk of pollution, and because those materials cannot bear large loads. [Geiger et al., 2009]
Porous clinkers have a grain structure with a high percentage of pores that let through water and air. Combined with a porous joint filler, or if the clinkers are laid on a porous foundation and not joined, surfaces with porous clinkers can achieve infiltration percentages of up to 100%. Porous clinkers can be used for footpaths and cycle paths. One drawback, however, is that the clinkers become clogged with sediment after a while and the infiltration effect is lost.
These clinkers have nubs on their sides, ensuring that a gap always remains between separate clinkers and the joints remain open.
Open paving patterns
Ordinary clinkers can also be laid in open or semi-open patterns. The open parts can be filled with grass, gravel or shells. With only a small amount of creativity, all manner of patterns can be conceived, and stones also come in a range of different types. Even the percentage of openings in the paving can be determined by varying the pattern. Important factors for preventing subsidence are the quality of the foundation and the stability of the pattern. This type of paving cannot support heavy loads.
Grass concrete pavers
Grass concrete pavers are concrete tiles that create large open space between the tiles. Car parks, roads and garage drives that are less intensive use can be paved with them. The grass does not develop sufficiently in intensively used parking spaces. Depending on the type of foundation under the tiles, the infiltration percentage can be as high as 100%.
Gravel, stone chippings and shells
Gravel or stone chippings with a consistent average grain diameter can be used on porous foundations. On less solid foundations, subsidence will mean that holes will have to be filled periodically. Gravel and stone chippings can be used for footpaths and for cycle paths and car parks that are used less intensively.
Shells and stone chippings can be used as loose covering layers or strewn to become embedded in sand or clay. With less solid foundations, these types of paving, like gravel and stone chippings, can require a great deal of maintenance. Stabilisation mats can be used for added stability and to help the material retain its shape, and for use on less solid foundations.
Mixtures of road metal and grass
These surfaces consist of a mixture of humus and road metal or gravel in a stabilising mat. Grass is sown on the top layer, after which it is compacted.
Woodchips and pine bark
These are natural products that both let through water and air. They are suitable for playgrounds and garden paths. Since woodchips and pine bark prevent vegetation from growing, they are an alternative to weed killers. As paving materials, woodchips and pine bark need to be topped up with new material after a few years.