Until the early 90s of the last century the "green" car parks were built using concrete blocks with openings that allowed the passage of vehicular traffic and at the same time the formation of a sparse grassy lawn on the surface between a concrete partition and the other.
At that time a small revolution had already been made as we had passed from asphalt car parks to those with a more “green” aspect. However, concrete gratings had advantages and disadvantages:
The advantages include:
- High resistance to vehicular traffic
- Durability of the artifact
- Resistance to atmospheric agents
- Different surface shapes
- High dimensional stability under the effect of the sun
Among the disadvantages we can include:
- High weight of the single piece
- High installation costs
- High transport costs
- Reduced grass area
- High probability of grass annoyance in summer
- Reduced draining surface
At the turn of the century, grassy driveways made of recycled plastic became popular on the market, taking up a large space in the construction of green car parks, both for some technical advantages they enjoy compared to the concrete product, both for the new regulations that impose a relationship between the surfaces built with respect to the green and on the need to make the horizontal areas as draining as possible.
The materials that are normally used are of three types:
- LDPE for non-driveway surfaces
Speaking of car parks, HDPE is a material that allows for good product elasticity but at the same time good resistance to compression, bending and torsion. This last element must be carefully considered as the grating must withstand the force that a stationary machine impresses on the product by turning the wheels.
It also has excellent resistance to low temperatures but, at the same time, less stability under the effect of solar radiation if not duly counterbalanced with mineral charges.
The PP/PE compound has good compressive strength and high solar temperatures, but has poor torsional and flexural strength.
Also the flexural strength, in addition to the torsional strength that we have seen before, is an element to consider when the substrate does not properly perform its duty of static capacity and coplanarity with the plastic surface. It also has a poor resistance to low temperatures with the possibility of crumbling of the plastic parts above ground.
The choice of the two materials that have advantages and disadvantages is to be made considering the seasonality, the latitude of the construction site, the expertise in the installation and the type of vehicular traffic.
However, there are corrective recipes to be used, once you have all the design elements, which also take into account the cost of the different raw material between the two families, the type of mold, the machine for printing the product, the colors and protective additives required.
Of course, the correct choice of regenerated raw materials does not exhaust the decisions that must be made to design and build a good “green” car park. We can list below some details to keep in mind:
- The shape of the alveolus is recommended to be honeycomb or circular so that the tensions are distributed evenly
- The connection between one tile and another must take into account the thermal expansion that the product undergoes under the sun. In the absence of space between the elements, it is necessary to consider leaving expansion joints in both directions.
- The feet in the intrados of the grating should be no less than 3.5 cm long. to allow a suitable grip to the underlying ground
- The layering on which the grassy grating rests must include two inert materials with different granulometry divided by a draining non-woven fabric, preferably in continuous thread polypropylene and a finishing one suitable for sowing grass.
- Mechanical leveling through pressing is very important to prevent subsidence of the flooring
- Providing the area with automatic irrigation and providing fertilization and restoration of the missing crop soil after opening the area would be recommended.
Automatic translation. We apologize for any inaccuracies. Original article in Italian.