DE20007305U1 - Gravel or base layer formed from it with a high proportion of pores for use in traffic areas - Google Patents

Description

GERMAN PATENT OFFICE
80331 Munich

Jörg Theelen

At the Source 36

41334 Nettetal-Kaldenkirchen

February 23, 2000

Gravel or base layer formed from it with a high porosity for use in traffic areas

The invention relates to gravel made from crushed material or base layers formed therefrom, in particular for traffic areas.

From the above-mentioned main patent application, a water pipe is known which consists of a drainage pipe above a barrier layer with a substructure and floor covering arranged thereon, in which liquid can be absorbed and drained away in a controlled manner.

Among the embodiments covered in the main patent, a storage casing made of liquid-storing gravel is already mentioned, although this is not specified in more detail in the main patent.

This inventive aspect of storage volume optimization of gravel suitable for road construction is taken into account more intensively than in the main patent.

Various types of gravel are known from the relevant regulations for road construction and their physical properties such as load-bearing behaviour, grain grading (grading curve), etc. are described.

The invention is based on the object of creating types of gravel, in particular for traffic areas such as roads, but also squares and all types of property paving, which, at given surface loads, depending on the strength of the gravel-forming material, have an increased to as high as possible pore proportion in order to be able to absorb, store and drain liquids in this pore proportion.

Contrary to the dogmatic view that has prevailed in road construction for many years that rainwater should be drained away from the roads as quickly as possible in order to prevent frost damage caused by water penetrating the base layer, or to prevent grain redistribution in the base layer and similar negative experiences, the inventive task is to create types of gravel that can be used in road construction and for comparable applications and that, due to their pore or cavity content between the gravel grains, form a liquid reservoir that can be used under all weather conditions to absorb rainwater and/or other liquids.
With these types of gravel according to the invention, liquid reservoirs can be formed within traffic areas that absorb and retain pollutants or rainwater, for example, in order to avoid the need for complex storage spaces such as storage channels or rainwater retention basins.

Depending on the base materials used for the gravel, such as various slags, sandstone, limestone, greywacke, basalt, granite, demolition recycling, etc., the gravel according to the invention has different properties due to the different rock properties (in particular the strength values are decisive).

Grain compositions (grading curves) which result from the different grain diameters (gravel rock of a diameter range) and their respective proportion in the total grain mixture (gravel ready for installation) and, depending on this, different pore proportions (voids between the individual rock grains forming the gravel) result.

In addition to the physical properties, the shape of the gravel plays an important role.

Rounded rocks such as gravel cannot bond with each other because the smooth rock surfaces do not interlock and can therefore slip against each other when subjected to stress.
To a lesser extent, this can also be observed in broken rock of the same grain diameter, since the lack of a supporting grain of smaller diameter means that only a few contact points or anchoring points (gussets) are available between the grains, which can break away under corresponding load and thus do not result in a secure bond.

In view of this experience, crushed gravel rocks have been used for many decades, the grading curves of which range from very small grains of a few thousandths of a millimetre to the grains of around forty-five millimetres, which are common today, or occasionally even larger.

These graded, low-porosity gravel types, which are basically made from broken rock or slag, ensure intensive interlocking at the contact points (gussets).

When creating gravel that is as load-bearing and porous as possible, it is important to have grain gradations that allow as many contact points as possible between the individual gravel stones of different sizes that are mixed together.

A grain structure is created by mutually supporting gravel grains. Basically, it can be said that with each additional contact point (gusset), the load-bearing capacity of the gravel material increases.

With graded gravel materials, considerably more interstices are possible than with a grain size of the same grain diameter.

In order to produce an optimally balanced, porous gravel, the following procedure is required:

- Determination of the underlying load-bearing capacity of the ballast.

- Determination of the rock parameters from which the gravel is formed
should.

- Determine a design that takes into account the installation conditions
Grain size range.

- Determination of the sieve curve with the best pore optimization possible.

If one of the above parameters is changed, at least one other parameter must be changed to ensure optimally porous gravel.

It makes sense to adjust the gravel as a rule via the grain size range and the grading curve arranged between the grain size ranges, since the load-bearing capacity is usually an unchangeable external specification and the rock values are determined by the gravel base material of the nearest quarry or other gravel source.

The disadvantage of conventional, low-porosity gravel materials is that with graded material, the cavities are partially or even completely filled with loose rock or rock dust, depending on the gravel material (soft sandstone or shell limestone can break when compacted) and/or gravel mixture (it contains unacceptably large amounts of small grain), and thus no precisely traceable and thus usable cavity remains in the base layer in the sense of the gravel according to the invention.

This can subsequently lead to damage, since with the gravel commonly used today, due to excessive compaction or too large a proportion of small grains, it cannot be ruled out that, if the subgrade is damp, water will penetrate into the base layer via capillary forces and can cause serious damage to it in the event of frost.

In order to counteract the aforementioned disadvantage, it is important to minimize the small grain content as much as possible, which is fulfilled in one go by the porous gravel according to the invention due to the task at hand.

This leads to a very safe frost behavior of the ballast according to the invention, since after the controlled water inlet and outlet no frost-damaging capillary water remains in the ballast.
Any residual moisture that freezes can displace its frost-related increase in volume unhindered into the free pore space between the gravel grains, so that the increase in volume cannot lead to frost heave of the base layer, as would be expected with conventional gravel materials.

If the gravel according to the invention is used as a retention space for rainwater, the residence time of the water in the gravel base layer must be included in the frost-related considerations, since a retention space without at least a throttled drainage can also cause frost heave if the retained water freezes from above and volume equalization is therefore not possible.

To further increase the load-bearing capacity, the grain structure can be reinforced with binding agents such as cement, bitumen, adhesive or similar.

This can be done by mixing the binding agent into the porous gravel before installation or by applying it evenly to the gravel in liquid form after installation, depending on the thickness of the gravel, so that it then automatically distributes itself around the gravel grains.

This achieves additional stabilization of the contact points (gussets), which, due to their mutual contact or small distance between the individual gravel grains, will represent the primary concentration points for a liquid binding agent.
After the binding agent has hardened, the gusset is artificially widened in this way and can withstand higher compressive loads in accordance with the strength values of the binding agent, and the gravel grains are additionally connected to one another in a way that prevents displacement.

The open porosity of the ballast according to the invention also leads to an improvement in the equally important ability of the liquid to flow into and out of the ballast.

In order to ensure the fastest possible liquid inflow and outflow, the gravel can be equipped with a drainage system.

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Depending on the task, the system can consist of drainage pipes and/or drainage sheets.

In many applications, it is advisable to seal the gravel to the subsoil to control liquids or to protect the subsoil. This can be done using existing or installed liquid-tight soil layers or using artificial base seals made of bentonite, metal, plastic or similar.

The gravel according to the invention is also ideally suited for infiltration systems such as trenches, pipe trenches and the like, since in combination it can directly fulfil the function of the base layer and thus contribute to considerable savings in the production of infiltration systems.

Thus, the gravel according to the invention can be installed downstream of a trough in areas with soil conditions that are very difficult to infiltrate, and can absorb the rainwater that accumulates below a traffic area over a large area, e.g. by means of a drainage system, distribute it and allow it to infiltrate into the subsoil.

Installed in a tray made of waterproofing, the porous gravel can be used not only for the temporary retention of rainwater but also preventively to absorb water-polluting liquids beneath road surfaces. The drainage system already described can be used for the inflow and outflow, plus standard road construction components such as depressions and shafts.

In a further application, the drainage and pipe system can be used to clean the porous gravel by introducing flushing water under pressure through the drainage and pipe system and then sucking it out again, for example to clean introduced sediments.

Another cleaning option is in-situ cleaning of the gravel by flushing in chemicals, minerals and/or microorganisms.

In particular, physical processes with appropriately conditioned minerals or systems (e.g. Plocher, Grander systems, etc.) and/or biological systems based on microorganisms have proven to be very environmentally friendly in these cases and have a very positive effect on the quality of the outflowing water.

For ballast cleaning using microorganisms adhering to the ballast, the supply of oxygen is an important functional criterion, since if the oxygen supply is too low, the cleaning process can turn into an anaerobic process, which can result in significantly lower cleaning performance and unpleasant odors.
This situation is successfully counteracted by the large supply of oxygen in the porous gravel and, if necessary, the integrated drainage and pipe system supports this by blowing in recirculated air or extracting the used air in the gravel.

Depending on the thickness of the gravel layer, the temperature gradient in the gravel layer itself also ensures a low convection flow of air between the gravel grains, which can support a well-functioning microorganic cleaning.

In order not to unnecessarily pollute the rainwater discharged into the gravel, it is advisable to wash the gravel before installation for applications in rainwater management, as otherwise the large amounts of dust adhering to the gravel grain can cause considerable pollution in the discharged water for a limited period of time.

In order to ensure frost-proof operation of a drainage system, which is made from porous gravel, it can be useful to integrate a heating system into the gravel during installation. In this case, the drainage and piping system, if integrated, can also be used to thaw the gravel by introducing heated air or water into the system.
But it can also be useful to run heating wires or cables through the ballast.

The drawings show several embodiments of the invention
They show

Fig. 1 a grain structure of a gravel with high void content with a
graded grading curve

Fig. 2 the ballast from Fig. 1 with a load-bearing capacity increasing
Provide binding agent

The base layer shown in Figure 1 consists of compacted gravel grains (10) of different diameters, in whose grading curve small grains were completely omitted.

The resulting grain structure of the grains supporting each other at the contact points (10) or interstices with the large pore portions formed thereby (11) can be clearly seen.

Despite the compaction, individual gravel grains (13) that are not integrated into the composite or grain structure can be identified.

The enormous surfaces of the grain boundaries (12) provide an ideal base for a microorganic cleaning film.

The gravel (10,11) is evenly filled with accumulated rainwater (14) up to the liquid level (15).

Figure 2 shows the same grain structure as Figure 1, with the one difference that in order to increase the load-bearing capacity, the ballast (10) was covered with a watery cement, which was concentrated at the interstices (17) according to the surface tension of the liquid binding agent. The entire ballast grain (10) was only thinly coated with the binding agent (16) outside the interstices (17).
A further consolidation of the base layer is achieved by additionally incorporating the free gravel grains (13) into the composite.

List of reference symbols

10 Gravel grains 11 Pore space 12 Grain boundaries 13 free gravel grains 14 liquid 15 Fluid level 16 Binder layer 17 Binder concentrations

Claims (10)

1. Gravel made from broken material or base layers formed therefrom, in particular for traffic areas, characterized in that the compacted gravel ( 10 ) has an increased or the maximum possible pore proportion ( 11 ) depending on the predetermined load-bearing capacity. 2. Ballast according to claim 1, characterized in that the increased or maximum possible pore proportion ( 11 ) depending on the predetermined load-bearing capacity is to be determined from the strength values of the ballast rock ( 10 ) and a grading curve adapted to the predetermined load-bearing capacity and strength values. 3. Ballast according to claim 1 or 2, characterized in that the maximum possible pore proportion ( 11 ) of the ballast ( 10 ) is to be used as a liquid reservoir ( 10 , 11 ). 4. Ballast according to one of the preceding claims, characterized in that the ballast ( 10 ) is installed within a liquid-tight excavation. 5. Ballast according to one of the preceding claims, characterized in that in order to increase the load-bearing capacity, the contact points ( 17 ) of the ballast grains ( 10 ) are to be mutually connected by the addition of liquid cements or binding agents. 6. Ballast according to one of the preceding claims, characterized in that the ballast ( 10 ) is equipped with a system for liquid inlet and/or outlet for better inlet and outlet of liquid ( 14 ). 7. Gravel according to one of the preceding claims, characterized in that the system for the introduction and discharge of liquids ( 14 ) is formed from drainage pipes. 8. Ballast according to one of the preceding claims, characterized in that the ballast ( 10 ) is equipped with physical and/or chemical and/or biological processes for the degradation of pollutants. 9. Gravel according to one of the preceding claims, characterized in that due to the high pore content ( 11 ) an aerobic pollutant degradation can be arranged. 10. Ballast according to one of the preceding claims, characterized in that it is equipped with a heating system when installed.