Water-permeable pavements are mainly surface pavements in road and path construction, where rainwater can seep away directly to a large extent. The aim of this construction method is to reduce surface sealing. The reduced or delayed discharge of rainwater leads to a reduced load on the sewer system and the sewage treatment plants. The area of application of these coverings is versatile, but soil mechanical, hydrological and other conditions must be observed. The leachate must be uncontaminated and must not pose a risk to soil, vegetation and groundwater.
This bauwion knowledge page deals with common water-permeable coverings for outdoor use. When planning, it is important to take into account the local conditions and to pay attention to a suitable substructure. For use in public traffic areas, the leaflet "Infiltration Traffic Areas" of the Research Society for Roads and Transport applies in Germany. It describes surface pavements with water-permeable paving systems, paving stones with seepage joints, drain asphalt layers and drain concrete layers . These pavements are listed in the "Guidelines for Planning, Construction and Maintenance of Greenable Pavements" of the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL). In 2007, a technical report by the FLL was published on the subject of "Planning, construction and maintenance of water-bound paths".
planning materials: In addition to the design properties (colour, format and laying pattern), the material quality and the installation construction method must also be suitable for the respective situation. For outdoor use, weather and frost resistance is generally required in our latitudes. The base course must be designed for the expected load. In addition, there is abrasion resistance, sliding and slip resistance, water absorption and porosity. The use of de-icing salt is not possible on all water-permeable surfaces.
Possibilities for revision or repair and the maintenance costs of the respective surface should be agreed with the client in advance. The manufacturer should be involved in the consultation, as the different systems can vary greatly.
Construction methods: The type of stress, the use, but also the installation situation of the pavement must be taken into account when deciding on the material to be used. The client should be informed by the planner or the contractor with regard to the respective possibilities, advantages and disadvantages.
Water-bound surface
1 Surface layer
2 Dynamic layer (levelling layer)
3 Base course (frost protection layer)
4 Planum (substrate or substructure)
Water-bound ceilings are considered multi-layer covering systems without binders and are purely mineral. A proper construction of the substructure up to the base course in accordance with DIN 18035 Part 5 or FLL is required. The layer structure is precisely prescribed to avoid problems such as possible rinsing or sagging.
With this design, a stable edge edging can be helpful to prevent lateral slipping or washing away. This can be done with the help of special edging stones, metal rails, kerbstones or paving stones, which are laid in the concrete bed.
The gradient required later must already be taken into account in the compacted subsoil. This is usually 2.5 – 3 %, as a side slope or roof profile. In the longitudinal direction, the inclination should not exceed 6%, also with regard to accessibility. Steeper paths may be possible with natural stone binder.
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Water-bound road surfaces:
Base course: It consists of gravel or gravel 0/32 or 0/45 mm (0 = fines in the mixture up to gravel pieces of 32 mm) and, depending on the subsequent stress, is usually paved 20 to 40 cm thick.
Levelling layer: The levelling layer, also known as the dynamic layer, is placed on top of the base course. It is usually made of crushed stone (according to FLL) 0/16 mm and is 6 to 8 cm thick.
Surface course: The surface course, the actual path surface, is placed on top of the levelling layer. It usually has a grain size of 0/5 – 0/11 mm, is best applied with a moist surface and then compacted to about 3-5 cm with a roller. In the case of surface courses with 0/11, the dynamic layer can be dispensed with if necessary.
Compacting is usually static by rolling. In between, the path can be moistened. A vibratory plate should not be used for compaction, otherwise the different grain sizes can separate. After completion, the water-bound path surface usually needs 2-3 weather changes until it reaches final strength.
Drain asphalt:
Underground: The subsoil should meet the requirements of ZTV E-StB 09. The kf value should > be 5.4 * 10-5 [m/s] and the thickness of the permeable subsoil/substructure should not be less than 1 m. In addition, a distance from the groundwater of at least 2 m must be taken into account.
Construction and dimensioning: Since the structure and dimensioning of the individual layers depend on the use, they are divided into load classes. These can be found in the guidelines for the standardisation of the superstructure of traffic areas (RStO).
Stone carpet:
Base course: It usually consists of gravel 0/32 or 0/45 mm (0 = fines in the mixture up to pieces of gravel of 32 mm) and is paved approx. 30 cm thick, depending on the later stress.
Leveling layer: The dynamic layer is placed on top of the base course. This is usually made of gravel (according to FLL) 0/16 mm, is at least 6 cm thick and is installed earth-moist.
Top course: The top layer usually has a grain size of 2/5 - 2/8 mm and is best applied with soil moisture and then compacted and smoothed to about 3-5 cm. After completion, the material must harden. The curing time depends on the temperature. At an outside temperature of about 10 °C, the curing time is about 72 hours. During this time, the pavement should be kept free of use.
Gravel turf:
Base course: A two-layer structure is usually carried out if a high load, such as driving with trucks or buses, is to be expected, or if the condition of the subsoil has too low a load-bearing capacity. In the two-layer construction method, two different grain sizes are installed. A drainage layer with a grain size of 0/45 to 0/63, as is usually used in road construction, is suitable as a substructure material.
Vegetation base layer: This is the upper layer, has a thickness of 15 - 30 cm and consists of finer-grained material, e.g. 0/32 or 0/45, which also contains the compost or soil content. It should be installed "earth-moist", with a layer thickness of more than 20 cm in 2 layers. Interlocking the individual layers with each other is of great importance. This is done, for example, by slightly roughening the surface again with the teeth of the excavator bucket after the first layer has been compacted. In the single-layer structure, a 15 - 30 cm thick vegetation base layer is built up directly on the substrate. The complete construction is carried out by excavator. After levelling, a seed mixture is applied and compacted and fastened with the help of a roller, without the need for shaking. The area is then lightly irrigated and kept moist for the next few weeks. Driving on or using should take place after three months at the earliest.
Lawn grid stones:
Subsoil: The depth of the excavation depends on the later use. Guideline values can be found in the RSTO and the ZTV SOB. An excavation of 25 cm is usually sufficient for footpaths, 35 – 40 cm for driveways and parking lots, and at least 50 cm for truck entrances and parking spaces. Once the soil has been excavated, the subsoil is compacted with a vibrator. For stability reasons, the subsoil needs a layer of gravel.
Edge edging: This is necessary to prevent the stones from shifting or slipping. For this purpose, there are kerbstones, which are available in different heights and widths.
Base course: If a lawn grid is to be drivable later, a base course and a laying bed are required. The lower part of the base course consists of a layer of gravel with a grain size of 16/32. This is applied to the surface at a height of about 20 cm. Compaction is then carried out by rolling or shaking to create a load-bearing substructure. For this purpose, the gravel (or mineral concrete) is filled in layers and compacted. This achieves a significantly higher compaction than when shaking off a thick layer of gravel. A gravel layer of approx. 20 - 25 cm is recommended for driveways, approx. 10 cm for paths. An approx. 3 – 4 cm thick layer of fine chippings is then applied over this gravel layer, as bedding for the lawn grids.
Laying: After the fine layer of fine chippings has been cleanly removed, the lawn grid stones can be laid in a compound on the area. Expansion joints of approx. 3 – 5 mm should be left free between the stones. The stones are then compacted with a vibratory plate. A vibratory plate weighing 130 kg and 20 kN is sufficient. In order not to damage the stones, a hard rubber plate is mounted on the vibrator, for example. The shaking is always carried out evenly from the edge area to the middle of the laying surface.
Plastic honeycomb grid:
Substrate: A gravel layer of 25 cm is required for cars, at least 40 cm for truck entrances and parking spaces. Once the soil has been excavated, the subsoil is compacted with a vibrator. A layer of gravel serves to stabilize the subsoil.
Base course: Installation of a layer consisting of gravel/gravel 2/32 - 2/45, and subsequent shaking. The built-in layer thickness should be approx. 15 – 45 cm. A mixture of sand/crushed sand is added over this layer as a levelling layer. This layer thickness is about 4 cm.
Installation: In the case of a plastic honeycomb grid , a vibratory plate should not be used for compaction, as the material could break. Ground anchors can be inserted into the base course to attach the grids to them and prevent them from slipping. The plastic honeycomb grids are hooked into each other to prevent them from slipping apart. After laying, the honeycombs and gaps are filled with a suitable substrate or with grit or fine gravel. For planned greening with substrate filling, there are seed mixtures that are especially suitable for lawn grid stone greening or for plastic honeycombs, these are more robust than conventional lawn seeds.
Water-permeable paving stones:
Subsoil: The non-load-bearing soil layers (e.g. clay, topsoil) are excavated until stable soil is reached. This should be at least 30 – 35 cm below the later upper edge of the pavement and is compacted with a suitable vibrator. Then a base or frost protection layer at least 25 cm thick is filled. Frost-proof, graded material such as gravel or gravel (grain size: 0/32 or 0/45) is best suited for this purpose. The base course is also compacted with the vibrator.
Edge edging: This is necessary to prevent the stones from shifting or slipping. For this purpose, there are lawn edging stones in different heights and widths. The edging can be achieved by means of kerbstones, special paving stones, special edging stones, but also with boundary wall or wall surfaces. The stones are placed at an exactly determined height with the help of a so-called concrete back support to the garden area on a concrete foundation (thickness according to DIN 18318 at least 20 cm).
Bedding: It consists of sand or a crushed sand-chippings mixture with a grain size of 0/5. In the case of seepage pavement, the grain size of the chippings is 1/3 or 2/5. The thickness of the paving bed should be between 3 and 4 cm when loose. This layer remains uncompacted and is only shaken off together with the stones laid. The final height of the paving surface is only reached after shaking. Therefore, depending on the material, the paving bed should be placed about 1 cm higher. It is important that the sand/chippings are pulled off evenly, for example with a straightening bar that is guided over two squared timbers as rails. After stripping, the paving bed must no longer be walked on when laying the stones.
Laying: In the case of concrete paving with joint infiltration , the joints are filled as desired before shaking. It can be filled with a mixture of topsoil and sand (mixing ratio 1:1) in order to then be able to sow a suitable turf mixture. However, the joints can also simply be filled with chippings, for example. When vibrating, the vibrator should have a plate sliding device. After shaking, the backfill material should reach up to about 1 cm below the top edge of the stone. Paving stones with debris pores should be laid with the joint of 3–5 mm prescribed for paving. When selecting the joint material, it is important to ensure sufficient water permeability and grain size. Mineral mixtures without ultrafine or zero components, such as chippings 0.5/1 mm or 1/3 mm, are suitable. The seepage openings are also filled with a mineral mixture without ultrafine or zero components, such as chippings 0.5/1 mm or 1/3 mm.
DIN 18130-1 Subsoil - Examination of soil samples; Determination of the water permeability coefficient - Part 1: Laboratory tests
DIN 18130-2 Subsoil - Examination of soil samples; Determination of the water permeability coefficient - Part 2: Field tests
DIN 18318 VOB Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Traffic route construction work - Paving surfaces and slab coverings in unbound design, edging
DIN 18507 Paving stones made of porous concrete - Definitions, requirements, tests, monitoring
Guidelines for the planning, construction and maintenance of greenable pavements published by the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL)
Technical report on the planning, construction and maintenance of water-bound paths published by the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V. (FLL)
FGSV leaflet "Infiltration traffic areas"
MFP Leaflet for Surface Reinforcements with Pavements and Slab Coverings in Unbound
M FP – (2015) – 618/1 Leaflet for Surface Reinforcements with Paving Surfaces and Slab Coverings in Unbound Design as well as for Edging
RStO Guidelines for the Standardization of the Superstructure of Traffic Areas
ZTV-StB Layers without Binder
FLL – Case report (2007) Water-bound path surfaces
Source: bauwion
