FR2964097A1 - System for filtering water e.g. rainwater, comprises permeable concrete block comprising water receiving face and filtered water supplying face, substrate layer covering water receiving face, plant, and edge surrounding the substrate layer - Google Patents

Abstract

The water filtration system comprises a permeable concrete block (10) comprising a water receiving face (12) and a filtered water supplying face (13), a substrate layer (18) partially covering the water receiving face, a plant (20) consisting of lolium, sorghum, hordeumand trifolium, where roots of the plant extend partly in the substrate layer, and an edge surrounding the substrate layer. The water receiving face comprises a recess (14). The substrate layer is disposed partially in the recess. The water filtration system comprises a permeable concrete block (10) comprising a water receiving face (12) and a filtered water supplying face (13), a substrate layer (18) partially covering the water receiving face, a plant (20) consisting of lolium, sorghum, hordeumand trifolium, where roots of the plant extend partly in the substrate layer, and an edge surrounding the substrate layer. The water receiving face comprises a recess (14). The substrate layer is disposed partially in the recess. The permeable concrete block comprises fresh concrete in cubic meter consisting of: 100-400 kg of a hydraulic binder; 60-400 kg of Portland cement; 0-180 kg of a particulate material or a mixture of materials with average particle size of less than 100 mu m; 0.3-3 kg of a plasticizer; 1300-1800 kg of a gravel or a mixture of gravel with an average size of 3-20 mm; and 40-200 kg of water, and has a hardened density of 1500-2200 kg/m 3>, a porosity of 10-40 vol.% and a compression strength of >= 6 MPa after 28 days.

Description

WATER FILTRATION SYSTEM

The invention relates to a water filtration system, in particular rainwater and a method of manufacturing such a filtration system.

It may be desirable for rainwater to be at least partly free of the polluting agents it contains before infiltrating the soil. In residential areas, a large part of the soil is usually covered by impermeable elements, such as impervious bitumen or concrete pavements. Floors covered by impermeable surfaces do not receive or little water. In fact, rainwater tends to run off these impervious surfaces until it reaches a soil not covered by an impermeable surface. No filtration operation of water that reaches the ground is then carried out. Rainwater can also be recovered by the sewage system and be conducted to a purification system adapted to the treatment of polluted water and whose use for rainwater, generally low pollution, is a significant cost. It would be desirable to have a water filtration system, including rainwater, which has lower manufacturing, installation and operating costs and is suitable for covering a permeable soil.

For this purpose, the present invention provides a water filtration system, comprising: - a block of a permeable concrete comprising a water receiving face and a filtered water supply face; a layer of a substrate covering at least part of the reception face; and at least one plant, the roots of which extend at least in part in the layer of the substrate, chosen from the group comprising the genus sedum, lolium, sorghum, hordeum and trifolium. The invention offers at least one of the following advantages: the system is adapted to cover a permeable soil and then allows infiltration into the permeable soil of water, in particular rainwater, at least partially removed from the agents pollutants it contains; and - the maintenance of the filtration system is almost non-existent. In addition, the selected plants are advantageously adapted to grow suitably in alkaline medium and therefore tend to grow appropriately in contact with the concrete block.

Finally, the invention has the advantage of being implemented in at least the building industry, construction markets (building, civil engineering or prefabrication plant), the construction industry or the cement industry. Other advantages and characteristics of the invention will become clear from reading the description and examples given by way of purely illustrative and nonlimiting that will follow. By the term "hydraulic binder" is meant according to the present invention a powdery material which, mixed with water, forms a paste which sets and hardens as a result of reactions and hydration processes, and which after curing , retains its strength and stability even under water. According to the invention the term "mineral additions" refers to one or more particulate materials having an average particle size of less than 100 μm. This is, for example, fly ash (as defined in the standard "Cement" NF EN 197-1 paragraph 5.2.4 or as defined in the standard "Concrete" EN 450), pozzolanic materials (such as defined in the "Cement" standard NF EN 197-1 paragraph 5.2.3), silica fumes (as defined in the "Cement" standard NF EN 197-1 paragraph 5.2.7 or as defined in the "Concrete" standard PrEN 13263: 1998 or NF P 18-502), slags (as defined in the "cement" standard NF EN 197-1 paragraph 5.2.2 or as defined in the "Concrete" standard NF P 18-506) , calcined schists (as defined in the "Cement" NF EN 197-1 paragraph 5.2.5), calcareous additions (as defined in the "Cement" NF EN 197-1 paragraph 5.2.6 or as defined in the "Concrete" standard NF P 18-508) and siliceous additions (as defined in the "Concrete" standard NF P 18-509) or their mixtures. The term "sand" according to the present invention means a granulate having a particle size strictly less than 4 mm. The term "chippings" according to the present invention means aggregates having a particle size of 4 to 20 mm.

By the term "plasticizer / water reducer" is meant an adjuvant which, without modifying the consistency, makes it possible to reduce the water content of a given concrete, or which, without modifying the water content, increases the water content of the concrete. slumping / spreading, or that produces both effects at once. EN 934-2 provides that the water reduction must be greater than 5%. The water reducers may, for example, be based on lignosulfonic acids, hydroxycarboxylic acids or treated carbohydrates.

The D90, also noted as Dv90, is the 90th percentile of the grain size volume distribution, that is 90% of the grains are smaller than D90 and 10% are larger than D90. Similarly, D10, also denoted Dv10, corresponds to the 10th percentile of the grain size volume distribution, ie 10% of the grains are smaller than D10 and 90% are larger than D10. D10. Among the plants of the genus Sedum (family Crassulaceae), the plant is preferably the sedum acre (or acrid orpin) or the sedum Kamtschaticum (sedum Kamchatka). Among the plants of the genus lolium (family Poaceae), the plant is preferably lolium perenne (or ryegrass or English ryegrass). Among the plants of the genus sorghum (family Poaceae), the plant is preferably the sorghum bicolor (or blue stool or common sorghum). Among the plants of the genus hordeum (family Poaceae), the plant is preferably hordeum vulgare (or common barley). Among the plants of the genus trifolium (fabaceae family), the plant is preferably trifolium repens (or white clover). According to one embodiment, the plant is chosen from the group comprising the genus lolium, sorghum, hordeum and trifolium. According to one embodiment, the plant is chosen from the sedum group. According to one embodiment, the plant is chosen from the lolium group.

According to one embodiment, the plant is chosen from the sorghum group. According to one embodiment, the plant is chosen from the hordeum group. According to one embodiment, the plant is chosen from the trifolium group. The substrate layer is favorable to the growth of the plant. This is for example potting soil, possibly including fertilizers.

Several plants of the same kind or of different genera can be arranged in the substrate layer. In particular, turf may be placed in the substrate layer, the turf corresponding to a mixture of several varieties of plants of the family Poaceae. The turf comprises, for example, a mixture of perennial lolium, bluegrass (Poa pratensis) of the tracer, semi-tracer and turf varieties. The plants may be disposed in the substrate layer in the form of seeds sown in the substrate layer or separately planted plants. By way of example, the plants are arranged in the substrate layer in the form of plants for plants of the genus Sedum. For example, the plants are arranged in the substrate layer in the form of seeds for plants of the genus lolium. By way of example, the plants are arranged in the substrate layer in the form of seeds or plants for plants of the genus sorghum, hordeum or trifolium. According to one embodiment, the number of plants per square meter is less than 10 plants per square meter.

According to an exemplary embodiment of the invention, the water-receiving face comprises a depression, the substrate layer being disposed at least in part in the recess. The depression may have an average depth greater than 1 cm, preferably greater than 3 cm with respect to the remainder of the receiving face of the permeable concrete block, which is for example flat. The depression may have a cylindrical, parallelepipedic shape, etc. The depression corresponds, for example, to one or more openings or cavities formed in the permeable concrete block for receiving the plants. According to an exemplary embodiment of the invention, the filtration system comprises a border surrounding the substrate layer. The border can be placed on or attached to the concrete block. The border is, for example, a metal frame or frame made of wood, plastic, stone, concrete, etc. The average height of the edge may be greater than 1 cm, preferably greater than 3 cm, for example about 5 cm, with respect to the receiving face of the concrete block permeable, which is for example flat. The substrate layer is then disposed on the receiving face within the border. The border facilitates the maintenance of the substrate layer and the protection of plants. The substrate layer may also be disposed within at least a portion of the pores of the concrete block over a portion of the thickness of the block, preferably less than a few centimeters, for example 2 cm, from the face of the block. receiving the block. The substrate layer can be depressed by a deliberate action in the pores of the concrete block or spread in the pores by entrainment, especially by rainwater. A film of flexible and permeable material may be disposed at least between the bottom of the recess and the substrate layer. The flexible and permeable material may be a woven or non-woven geotextile. Preferably, the permeable concrete comprises, for a cubic meter of fresh concrete: from 100 kg to 400 kg (preferably from 140 kg to 300 kg, even more preferably from 200 kg to 300 kg) of a hydraulic binder; and from 1300 kg to 1800 kg (preferably from 1300 kg to 1600 kg, even more preferably from 1300 kg to 1500 kg) of a gravel or a mixture of gravel having an average size of from 3 to 20 mm (preferably from 3 to 10 mm, even more preferably 6 to 10 mm). Preferably, the permeable concrete according to the invention does not comprise sand.

The hydraulic binder forms a paste connecting the chippings while preserving an interconnection between the voids of the concrete. According to one embodiment, the permeable concrete has a density in the cured state of 1500 to 2200 kg / m3, preferably 1600 to 1900 kg / m3. According to one embodiment, the permeable concrete has a porosity, that is to say a percentage of voids, in the cured state of 10 to 40% by volume, preferably 18 to 30% by volume. The permeability of the permeable concrete, measured according to standard NF EN 12697-19, may range from 0.01 mm / s to 1000 mm / s, preferably from 0.1 mm / s to 100 mm / s, even more preferably from 1 to 20 mm / s.

According to one embodiment, the permeable concrete has a compressive strength after 28 days greater than or equal to 6 MPa, preferably from 7 to 20 MPa. The hydraulic binder may comprise cement, especially Portland cement, and at least one particulate material (or mineral addition) having an average particle size of less than 100 μm, or a mixture of particulate materials. Mineral additions may include pozzolanic or non-pozzolanic materials or a mixture thereof. Suitable cements are the Portland cements described in "Lea's Chemistry of Cement and Concrete". Portland cements include slag, pozzolana, fly ash, shale, limestone and composite cements. It is for example a CEM I, CEM II, CEM III, CEM IV or CEM V cement according to the "Cement" NF EN 197-1 standard. A preferred cement for the invention is CEM I (usually PM ES) or CEM II / A. Preferably, the permeable concrete comprises, for a cubic meter of fresh concrete: 300 kg, still more than 60 kg to 400 kg (preferably 80 kg, preferably from 150 kg to 300 kg) of Portland cement; 120 kg, still more than 0 kg to 180 kg (preferably 0 kg, preferably 0 kg to 90 kg) of said minus one particulate material or said at least one mixture of particulate materials; from 0.3 kg to 3 kg (preferably from 0.3 kg to 2 kg, even more preferably from 0.3 kg to 1 kg) of solids content of a plasticizer; from 1300 kg to 1800 kg (preferably from 1300 kg to 1600 kg, even more preferably from 1300 kg to 1500 kg) of the chippings or mixture of chippings; and from 40 to 200 kg (preferably from 40 to 100 kg) of water. The pea gravel is usually a gravel of silica or limestone. An example of particulate material is slag, especially granulated blast furnace slag.

Suitable pozzolanic materials include fumed silica, also known as micro-silica, which is a by-product of the production of silicon or ferrosilicon alloys. It is known as a pozzolanic reactive material. Its main constituent is amorphous silicon dioxide. The individual particles generally have a diameter of about 5 to 10 nm. The individual particles agglomerate to form agglomerates of 0.1 to 1 μm, and then can aggregate together into aggregates of 20 to 30 μm. The silica fumes generally have a BET specific surface area of 10 - 30 m 2 / g. Other pozzolanic materials include fly ash which generally has a D10 of greater than 10 μm and a D90 of less than 120 μm and has, for example, a D50 of about 30 to 50 μm. Other pozzolanic materials include materials rich in aluminosilicate such as metakaolin and natural pozzolans with volcanic, sedimentary, or diagenic origins. Suitable non-pozzolanic materials include materials containing calcium carbonate (eg ground or precipitated calcium carbonate), preferably crushed calcium carbonate. The ground calcium carbonate may, for example, be Durcal® 1 (OMYA, France). The non-polyazolanic materials preferably have an average particle size of less than 5 μm, for example 1 to 4 μm. Non-pozzolanic materials may be ground quartz, for example C800 which is a substantially non-pozzolanic silica filler supplied by Sifraco, France. The preferred BET surface area (determined by known methods) of calcium carbonate or ground quartz is 2-10 m 2 / g, generally less than 8 m 2 / g, for example 4 to 7 m 2 / g, preferably less of 6 m2 / g. Precipitated calcium carbonate is also suitable as a non-pozzolanic material. Individual particles generally have a size (primary) of the order of 20 nm. The individual particles agglomerate into aggregates having a (secondary) size of about 0.1 to 1 μm. The aggregates themselves form clusters having a (ternary) size greater than 1 μm. A single non-pozzolanic material or a mixture of non-pozzolanic materials may be used, for example ground calcium carbonate, ground quartz or precipitated calcium carbonate or a mixture thereof. A mixture of pozzolanic materials or a mixture of pozzolanic and non-pozzolanic materials can also be used. The concrete according to the invention can be used in combination with reinforcing elements, for example metal fibers and / or organic fibers and / or glass fibers and / or other reinforcing elements described hereinafter. By the term "plasticizer / water reducer" is meant an adjuvant which, without modifying the consistency, makes it possible to reduce the water content of a given concrete, or which, without modifying the water content, increases the water content of the concrete. slumping / spreading, or that produces both effects at once. EN 934-2 provides that the water reduction must be greater than 5%. The water reducers may, for example, be based on lignosulfonic acids, hydroxycarboxylic acids or treated carbohydrates and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino methyl-siliconate, sulfanilic acid and casein. The plasticizer may, in addition, be a superplasticizer. By the expression "superplasticizer" or "superfluidifier" or "super water reducer" is meant a water reducer which makes it possible to reduce by more than 12% the quantity of water necessary for producing a concrete ( standard EN 934-2). A superplasticizer has a fluidizing action insofar as, for the same quantity of water, the workability of the concrete is increased in the presence of the superplasticizer. Superplasticizers have been broadly classified into four groups: sulphonated naphthalene formaldehyde condensate (or SNF), (generally a sodium salt); or sulphonated formaldehyde melamine condensate (or SMF, acronym for Sulphonated Melamine Formaldehyde Condensate); modified lignosulphonates (or MLS, acronym for Modified Lignosulfonates); and others. Next generation superplasticizers include polycarboxylic compounds such as polyacrylates. The superplasticizer is preferably a new generation of superplasticizer, for example a copolymer containing polyethylene glycol as a graft and carboxylic functions in the main chain such as a polycarboxylic ether. Sodium polysulphonate polycarboxylate and sodium polyacrylates may also be used. In order to reduce the total amount of alkaline, the superplasticizer can be used as a calcium salt rather than a sodium salt.

Other adjuvants may be added to the concrete according to the invention, for example an antifoaming agent (for example, polydimethylsiloxane). It may also be silicones in the form of a solution, a solid or preferably in the form of a resin, an oil or an emulsion, preferably in water. The amount of such an agent in the concrete is generally at most 5 parts by weight relative to the cement. The concrete according to the invention may also comprise hydrophobic agents for increasing the repulsion of water and reducing the absorption of water and penetration into solid structures comprising the concrete according to the invention. Such agents include silanes, siloxanes, silicones and siliconates; commercially available products include liquid and solid products which can be diluted in a solvent, for example into granules. The concrete according to the invention may comprise a viscosity agent and / or a flow limit modifier (generally to increase viscosity and / or flow limit). Such agents include: cellulose derivatives, for example, water-soluble cellulose ethers, such as carboxymethyl, methyl, ethyl, hydroxyethyl and sodium hydroxypropyl ethers; alginates; and xanthan, carrageenan or guar gum. A mixture of these agents can be used. The concrete may include a curing agent to prevent the concrete from drying too quickly during its setting and the first days of hardening. The curing agent is then present in the mass of the concrete block. Examples of curing agents are polyethylene glycol or the product marketed under the name RHEOMAC 885 F by the company BASF. The concrete according to the invention may comprise an activating agent which makes it possible to promote the hydration reactions of vitreous materials. Such agents include sodium and / or calcium salts. The concrete according to the invention may comprise an accelerator and / or an air-entraining agent and / or a retarder. The concrete according to the invention preferably has a Vicat setting time of 2 to 18 hours, for example from 4 to 14 hours.

The water / cement mass ratio of the concrete according to the invention may vary if substitutes for the cement are used, more particularly pozzolanic materials. The water / binder ratio is defined as the mass ratio between the quantity of water E and the sum of the quantities of cement and of all pozzolanic materials: it is generally from 0.27 to 0.4, preferably from 0.3 to 0.4. The volume of dough (which includes cement, water, plasticizer and the pozzolanic or non-pozzolanic particulate material or materials) is 100-200 L per cubic meter of fresh concrete, preferably 120-160 L per meter fresh concrete cube.

The method of manufacturing the filtration system comprises a step of manufacturing a permeable concrete block as described above and a step of placing the plant and the substrate layer, the roots of the plant extending to less partially in the substrate layer. More specifically, the method may comprise a step of placing the substrate layer at least partially covering the receiving face of the concrete block. In the case of seeds, the seeds can then be planted in the substrate layer. In the case of plants, only a portion of the substrate layer can be first set up. The plants are then placed on the portion of the substrate layer and the remainder of the substrate layer is then distributed around the plants.

The manufacturing method includes, for example, a planting step of the plant in the substrate layer. Before the deposition of the substrate layer in the depression, the method comprises for example the deposition of a film of a flexible and permeable material, for example a geotextile, between the substrate layer and the concrete block. However, it may be preferable not to have a flexible and permeable material between the substrate layer and the concrete block. In this way, during the growth of the plant, the roots of the plant according to the invention may possibly grow at least partly in the pores of the permeable concrete block. A better grip of the plant to the concrete block is thus obtained. Permeable concrete can be prepared by known methods, including the mixing of solid components and water, shaping and hardening. In order to prepare the permeable concrete according to the invention, the constituents are mixed with water. The following order of mixing may, for example, be adopted: mixing of the powder constituents of the matrix; introduction of water and a fraction, for example half, of adjuvants; mixed ; introduction of the remaining fraction of adjuvants; mixed.

In the mixture of the components of the permeable concrete according to the invention, the materials in the form of particles other than cement may be introduced as premix or dry premix of diluted or concentrated aqueous powders or suspensions.

The permeable concrete block is preferably obtained by pouring the permeable concrete into a mold or formwork and possibly by compacting the surface of the fresh permeable concrete. The surface settlement of the permeable concrete can be achieved by any type of tool, including a ruler, a paver, a roller, a vibrator, in one or more steps.

The manufacture of the concrete block may include a step of curing the concrete block to protect the concrete against drying too fast during its setting and the first days of hardening. The step of curing the concrete block is performed after pouring the concrete, preferably after the step of compacting the surface of the concrete block. For example, the surface of the concrete can be kept wet by watering or protection by means of mats, wet bags or impermeable tarpaulins. For example, after the pouring step, the surface of the fresh concrete can be covered with waterproof tarpaulins for a few hours or several days. Depression can be achieved by using a suitably shaped mold in which the permeable concrete is poured in the fresh state. Depression can also be achieved by making a cut in the hardened permeable concrete block. In operation, the filtering system according to the invention is intended to receive water at least at the depression. A filtering action is exerted on the water received by both the plants disposed in the depression and the permeable concrete block. The water escaping from the permeable concrete block is thus at least partially freed of polluting agents that it contains. For example, the filtering system according to the invention can be disposed on a permeable soil. The water filtered by the filtering system according to the invention can then be supplied to the underlying soil. The filtering system according to the invention can be arranged at parking areas, pedestrian crosswalks, road borders, etc. Examples, illustrating the invention without limiting its scope, will be described in relation to the following figures, in which: FIG. 1 represents a schematic perspective view of an example of a concrete slab for an example of a filtration system according to the invention; Figure 2 shows a schematic cross section of the slab of Figure 1; and Figure 3 shows a schematic perspective view of another example of filtration system according to the invention.

EXAMPLES The present invention is described by the following nonlimiting examples. In these examples, the materials used are available from the following suppliers: Components: Suppliers: Lafarge Portland cement, Saint Pierre La Cour France Fly ash Carling thermal power plant, France 6/10 Lafarge gravel site of Cassis, France CHRYSOPIast 209TM superplasticizer Chryso Le Portland cement (St. Peter's cement yard) has a D10 of 2 μm and a D90 of 44 μm and an average particle size of 15 μm. It is a CEM 152.5 N type cement according to the EN 197-1 standard. Adjuvant CHRYSOPIast 209TM is a plasticizer and corresponds to a lignosulfonate.

Concrete formulations Concrete formulations (1) and (2) used to perform the tests are described in Tables 1 and 2 below: Table 1: Concrete formulation (1) Component Proportion (in kg) per 1 m3 of fresh concrete St Pierre cement La Cour 200 Carling fly ash 31 Cassis gravel 6/10 1570 CHRYSOPIast 209TM admixture 0.693 Total water 93.36 (including 80.8 effective water) The concrete has an effective water-to-bind ratio of 0.35. The volume of dough is 25 158 liters per cubic meter of fresh concrete. The air content of the concrete is 249 liters per cubic meter of fresh concrete.

Table 2: Formulation (2) of concrete Component Proportion (in kg) for 1 m3 of fresh concrete Saint Pierre Cement The Court 260 6/6 Cassis gravel 1325 Adjuvant CHRYSOPIast 209TM 0,693 Total water 93,36 (of which 80,8 effective water) Concrete has an effective water-to-bond ratio of 0.3. The volume of dough is 160 liters per cubic meter of fresh concrete. The air content of the concrete is 345 liters per cubic meter of fresh concrete.

Method of preparing a concrete according to the formulations (1) and (2) - Put the chippings in a mixer; - At T = 0 seconds: start mixing and add one third of the dampening water at the same time; - At T = 30 seconds: introduction of the binder (cement and fly ash) and further mixing; - At T = 60 seconds: (TO for the rheology maintenance test): introduction of the remaining two thirds of the wetting water and further mixing; At T = 3 minutes and 30 seconds: stopping the mixing; At T = 90 minutes: pouring of the concrete element into a mold; - At T = 24 hours: demolding of the concrete element and saturation in water for 6 days; - At T = 7 days: drying of the concrete element in the air.

Laser Particle Size Method The D10 and D90 values and average particle sizes for the different powders are obtained from the particle size curves of the curves determined using a Malvern MS2000 laser particle size analyzer. The measurement is carried out in a suitable medium (for example, in an aqueous medium); the particle size should be from 0.02 μm to 2 mm. The light source consists of a red He-Ne laser (632 nm) and a blue diode (466 nm). The optical model is that of Fraunhofer, the calculation matrix is of polydisperse type. A background measurement is first performed with a pump speed of 2000 rpm, an agitator speed of 800 rpm and a noise measurement over 10 s, in the absence of ultrasound. It is then verified that the laser light intensity is at least 80%, and that a decreasing exponential curve is obtained for the background noise. If this is not the case, the lenses of the cell should be cleaned. A first measurement is then carried out on the sample with the following parameters: pump speed of 2000 rpm, agitator speed of 800 rpm, absence of ultrasound, obscuration limit between 10 and 20%. The sample is introduced to have a darkness slightly above 10%. After darkening stabilization, the measurement is made with a time between immersion and the measurement set at 10 s. The measurement time is 30 s (30,000 diffraction images analyzed). In the granulogram obtained, it must be taken into account that part of the population of the powder can be agglomerated. Then a second measurement (without draining the tank) with ultrasound. The pump speed is raised to 2500 rpm, agitation at 1000 rpm, ultrasound is emitted at 100% (30 watts). This regime is maintained for 3 minutes, then it returns to the initial parameters: pump speed of 2000 rpm, agitator speed of 800 rpm, absence of ultrasound. After 10 s (to evacuate the possible air bubbles), a measurement of 30 s (30,000 images analyzed) is carried out. This second measurement corresponds to a deagglomerate powder by ultrasonic dispersion.

Each measurement is repeated at least twice to check the stability of the result. The apparatus is calibrated before each working session by means of a standard sample (silica Cl0 Sifraco) whose grain size curve is known. All the measurements presented in the description and the ranges announced correspond to the values obtained with ultrasound.

Measurement method of the compressive strength The measurement is carried out on a cylindrical specimen 15 cm in diameter and 10 cm in height according to the method described in standard NF 12390-3 "Resistance to the compression of specimens".

Method for measuring the permeability of a permeable concrete element The measurement is carried out on a cylindrical specimen 15 cm in diameter and 10 cm in height according to the method described in standard NF EN 12697-19 "Bituminous mixtures - Methods of test for hot hydrocarbon mixture - Part 19: permeabilities of test pieces ".

Measurement method of the porosity of a permeable concrete element The porosity of the concrete is determined by weighing according to the method described in document RMCAO T040 "Test method for porosity measurements of Portland pervious concrete". By measuring the mass, the volume and the apparent density, we deduce the porosity of the concrete. This method does not distinguish between open porosity and non-accessible porosity.

Method of determining the filtration efficiency In order to determine the filtration efficiency, the water infiltrating through the filtration system according to the invention is recovered and analyzed. Each week, 1 liter of water, with a pollutant load (see Table 3) representative of the concentrations that can be found in the runoff of an urban area, is poured on the receiving face of the filtration system which measures 1 m2 at a time the first day of the week.

Table 3: Concentration of pollutants applied Week Parameter Concentration 1 Total Phosphorus 0.48 mg / L 2 Total Nitrogen 5.26 mg / L 3 Lead 0.2 mg / L 4 Copper 0.12 mg / L 5 Zinc 1.26 mg / L 6 Oil 3 g / m2 A device makes it possible to recover the filtered water by the filtration system in a collecting tank. Regular monitoring of the recovery tanks with total hydrocarbon analyzes (by infrared spectrometry according to the AFNOR T90-114 method), total nitrogen (using a total organic carbon and total nitrogen analyzer), phosphorus (by spectrometry). inductively coupled plasma atomic emission) and heavy metals (by inductively coupled plasma atomic emission spectrometry) of the recovered water is realized.

EXAMPLE 1 A concrete according to the formulation (1) was prepared. The concrete was poured into a mold to form a parallelepiped slab. The free surface of the concrete in the mold was packed until a slab 10, as shown in FIG. 1, was formed in the shape of a rectangular parallelepiped having a length of 60 cm, a width of 40 cm and a height of 15 cm. The large face 12 of the slab 10 corresponds to the water receiving face of the filtration system and the large opposite face 13 of the slab 10 corresponds to the filtered water supply face. The face 12 comprises a rectangular parallelepiped shaped imprint 14 having a length of 40 cm, a width of 20 cm and a depth of 2 cm. The compressive strength at 28 days of the slab is 8.9 MPa. The permeability of the slab 10 is 7.1 mm / s. The porosity of the slab is 30%. FIG. 2 represents an exemplary embodiment of a filtration system 5 according to the invention comprising the slab 10 for which gravel 15 and voids 16 are shown schematically. A film 17 of a geotextile (membrane marketed by the Soprema company under the name soprafiltre) was arranged in the footprint 14. The film 17 was covered with a layer 18 of 2 cm thick universal potting soil. A turf (composed of fescue and rye grass), marketed under the name of rustic grass by the Vilmorin company was planted in the soil layer 18. It was sown 5 kg of seeds for a surface 200 m2. In FIG. 2, the plants obtained 20 are schematically represented.

EXAMPLE 2 A concrete according to the formulation (1) was prepared. The concrete was poured into a mold to form a parallelepiped slab. The free surface of the concrete in the mold was packed until a slab having the shape of a rectangular parallelepiped having a length of 60 cm, a width of 40 cm and a height of 15 cm. Two cylindrical openings were made in the slab. Each cylindrical opening has a diameter of 10 cm and a depth of about 5 cm. The compressive strength at 28 days of the slab is 8.9 MPa. The flexural strength at 28 days of the slab is 1.25 MPa. The permeability of the slab 10 is 7.1 mm / s. The porosity of the slab is 30%.

A layer of a geotextile (membrane marketed by the company Soprema under the name soprafiltre) was placed in each cylindrical opening. The geotextile layer was covered with a layer of 2 cm thick universal potting soil.

An ivy plant, marketed under the name hedera helix by the botanic society, was planted in one of the openings. A plant of Sedum, marketed under the name sedum acre by the botanic society was planted in the other cylindrical opening. The plants grew for 6 months from May to October.

EXAMPLE 3 FIG. 3 shows another embodiment of a filtration system 25 according to the invention. A concrete according to the formulation (2) has been prepared. The concrete was poured into molds to form three parallelepipedal slabs each having the shape of a rectangular parallelepiped having a length of 200 cm, a width of 120 cm and a height of 15 cm. Each slab was covered after pouring a plastic tarpaulin for 2 days. Each slab 30 does not include an imprint on the upper face 32. The compressive strength at 28 days of the slab is 8.9 MPa. The permeability of the slab 30 is 7.1 mm / s. The porosity of the slab is 30%. For each slab 30, a wooden frame 34 has been placed on the upper face 32 of the slab 30. A layer 36 of 2 cm thick of universal potting soil has been distributed on the upper face 32 in the frame 34. first slab, 9 plants of Sedum, marketed under the name sedum of Kamchatka by Cerdys company were planted. In Figure 3, there is shown schematically the plants obtained 38. For the second slab, 9 blue fescue plants, marketed under the name Festuca glauca "Elijah blue" by the Cerdys company were planted. No plants were planted for the third slab.

The plants were allowed to grow for 3 weeks. For the second slab, blue fescue has not resisted although it is an outdoor plant that is suitable for dry soil and hot and dry climate. The method of determining the filtration efficiency described above has been implemented for the first and third slabs.

Claims (9)

REVENDICATIONS1. A water filtration system (5; 25) comprising: - a block (10; 30) of permeable concrete comprising a water receiving face (12; 32) and a water supply face (13) filtered; a layer of a substrate (18; 36) covering at least part of the reception face; and at least one plant (20; 38), the roots of which extend at least in part in the layer of the substrate, chosen from the group comprising the genus sedum, lolium, sorghum, hordeum and trifolium. The filtration system of claim 1, wherein the plant (20; 38) is selected from the group consisting of lolium, sorghum, hordeum and trifolium. The water filtration system according to claim 1 or 2, wherein the water receiving face (12) comprises a recess (14), the substrate layer (18) being disposed at least partly in the depressing. The water filtration system of claim 1 or 2, including a border (34) surrounding the layer of the substrate (36). 5. Filtration system according to any one of claims 1 to 4, wherein the permeable concrete comprises for a cubic meter of fresh concrete: from 100 kg to 400 kg of a hydraulic binder; and 1300 kg to 1800 kg of a gravel or a mixture of gravel having an average size of 3 to 20 mm. The filtration system of any one of claims 1 to 5, wherein the permeable concrete has a density in the cured state of 1500 to 2200 kg / m3. 10 15 20 25 30 15 The filtration system of any one of claims 1 to 6, wherein the permeable concrete has a hardened porosity of 10 to 40% by volume. The filtration system of any one of claims 1 to 7, wherein the permeable concrete has a compressive strength after 28 days greater than or equal to 6 MPa. 9. Filtration system according to claim 5, wherein the permeable concrete comprises for one cubic meter of fresh concrete: from 60 kg to 400 kg of Portland cement; from 0 kg to 180 kg of at least one particulate material or a mixture of particulate materials having an average particle size of less than 100 μm; from 0.3 kg to 3 kg of a plasticizer; from 1300 kg to 1800 kg of the gravel or mixture of gravel; and from 40 kg to 200 kg of water.