FR3102985A1 - FORMULATION FOR CONCRETE, PROCESS FOR PREPARING THE CONCRETE, OBTAINED CONCRETE AND APPARATUS FOR THE PREPARATION OF THIS CONCRETE - Google Patents

Abstract

FORMULATION FOR CONCRETE, METHOD FOR PREPARING CONCRETE, CONCRETE OBTAINED AND APPARATUS FOR PREPARING THIS CONCRETE This formulation for concrete comprising: a granular skeleton comprising: a sandy fraction (S); and a gravel fraction (G); cement (C); and water (E) to ensure the hydration of the cement and the hardening of the concrete, characterized in that the granular skeleton also comprises a fraction of fines (F), which is in the form of an aqueous slurry , or of a partially dehydrated aqueous sludge in the form of cakes, the water of said aqueous sludge or of said partially dehydrated aqueous sludge forming part of the water (E) to ensure the hydration of the cement and the hardening of the concrete.

Description

FORMULATION FOR CONCRETE, METHOD FOR PREPARING CONCRETE, CONCRETE OBTAINED AND APPARATUS FOR PREPARING THIS CONCRETE

The present invention relates to a formulation for concrete, a process for the preparation of concrete from this formulation, the concrete obtained as well as an apparatus for the preparation of this concrete.

The concrete according to the invention has the particularity of incorporating as part of the granular skeleton fines in particular in the form of aqueous sludge, which come from the treatment of washing / hydrocycloning of land or consist of marine or river sediments . The water content of this sludge depends on its origin, knowing that it may have been reduced, for example, by settling or by treatment on filter presses, belt filters or centrifuges.

The treatment of washing / hydrocycloning of the land aims to separate the different particle size fractions, including fine particles, which fix the pollutants in a majority way, vis-à-vis the coarser fractions, such as sand and gravel. These fine particles are, in the land washing/hydrocycloning treatment process which will be described below, obtained in the form of aqueous sludge.

River or marine sediments, the discharge of which into rivers and the sea, is increasingly constrained by environmental regulations (including the London Protocol (1996) at the international level and the circular of June 14, 2000 relating to conditions of use of the GEODE standard for the quality of marine or estuarine sediments present in the natural or port environment for the national regulatory framework), are aqueous sludges which therefore need to be treated. Various solutions have been proposed for this treatment, these solutions aiming to transform this sludge into a solid material. One of them consists of treating the sludge with quicklime. Another – according to French patent application 2,937,266 – consists in treating the sludge with a sulpho-aluminous binder and at least one of a source of sulphate and a catalyst for the hydration reactions of the sulpho-aluminous binder. aluminous.

All the solutions proposed for the treatment of sludge by solidification thereof are in practice complicated, time-consuming and labor-intensive.

The applicant company has sought to resolve these difficulties and, to this end, proposes to introduce aqueous fines sludge directly during the preparation of a concrete, the water from this sludge constituting all or part of the mixing water. concrete.

It appeared surprisingly that the concretes obtained in this way can find advantageous applications because their mechanical compressive strengths have proven to be those of conventional concretes such as C25/30 concretes according to the concrete standard NF EN 206/CN. These resistances are of the order of 10-50 MPa at 28 days on cubic specimens of 15 x 15 x 15cm, being increased in particular by 30% at 90 days in the case of the use of a slag-based cement .

In addition, there is proposed according to the present invention a particularly interesting process for the preparation of these concretes, this particular process comprising a washing of earth allowing the formulation of the concrete without addition of external granular materials, with a view to a complete recycling of the earth. , which represent large volume waste: excavation soil, cuttings, ….

In this regard, it can be emphasized that the use of the fines according to the invention surprisingly leads to inert concretes – within the meaning of the Order of December 12, 2014 – despite the fact that these fines contain pollutants.

The present invention therefore firstly relates to a formulation for concrete comprising:

• a granular skeleton comprising:
  • a sandy fraction (S); And
  • a gravel fraction (G);
• cement (C); And
• water (E) to ensure the hydration of the cement and the hardening of the concrete,

characterized in that the granular skeleton also comprises a fraction of fines (F), which is in the form of an aqueous sludge, or of a partially dehydrated aqueous sludge in the form of cakes, the water of the said aqueous sludge or said partially dehydrated aqueous slurry forming part of the water (E) to ensure the hydration of the cement and the hardening of the concrete.

The water to ensure the hydration of the cement and the hardening of the concrete, called effective water, consists of the sum:

• an external supply of water; And
• moisture surrounding the sandy (S) and gravelly (G) fractions.

Indeed, in practice, the sands and gravel have a humidity apart from the grains which is generally at most and including 5% by mass of the mass of sand and gravel.

In other words, the effective water is equal to the difference between the total quantity of water contained in the fresh concrete and the quantity of water absorbable by the sand and gravel.

According to the invention, the water of the aqueous fines sludge, optionally partially dehydrated, is part of the effective water and, depending on the water content of the fines sludge, forms the external water supply which does not require additional water (in particular in the case of high water contents, the aqueous sludge being able to flow), or even forms an external supply of water which must be supplemented by an additional supply (in particular in the case of low water contents, the sludge having been put in the form of cakes, for example to facilitate handling).

In particular, the aqueous sludge may be in a flowable state and have a dry matter content of 10 to 50% by mass, in particular 20 to 40% by mass, in particular 25 to 35% by mass. , or may be in the partially dehydrated state, in the form of cakes, and have a dry matter content of 50 to 95% by mass, in particular 50 to 70% by mass.

Fines can be fines from silty-clay mineral materials, such as soils and raw marine or river sediments.

In accordance with a particularly advantageous embodiment, the aqueous sludge comes from a washing/hydrocycloning treatment of land, the sandy fraction (S), the gravelly fraction (G) and the aqueous fines sludge (F) possibly coming from of the same land washing/hydrocycloning treatment aimed at obtaining sand, gravel and an aqueous slurry of fines.

The fines can have a particle size of less than 400 μm, in particular less than 63 μm.

The gravel fraction (G) can be a 6/20 mm, 6/30 mm, 6/60 mm, 6/80 mm fraction, and the sandy fraction (S) can be a 0/6 mm, 0/4 mm fraction .

The cement (C) is advantageously chosen from:

• cements based on CEM III type blast furnace slag, and more particularly CEM/III type C; And
• oversulphated cements.

CEM/III cements are defined by the European standard for common cements, NF-EN 197-1, and oversulphated cements, by the European standard NF-EN 15743.

For CEM/III type C cement, the cement standard NF EN 197-1 sets the following proportions:

• blast furnace slag: 81-95% by mass
• Portland clinker: 19–5% by mass

gypsum may be present up to 5% by mass of blast furnace slag + Portland cement.

For oversulphated cement, standard NF EN 15743 sets the following proportions:

• Blast Furnace Slag, S: S >75%
• Calcium Sulfate, Cs: 5%≤ Cs ≤ 20%
• Portland Clinker, K: 0%≤ K ≤ 5%
• Secondary constituents, A: 0%≤ A ≤ 5%

The formulation according to the invention may also advantageously comprise at least one superplasticizer – high water reducer, in particular of the polycarboxylate type, such as the MasterGlenium ACE 550 adjuvant from BASF, for example.

Other admixtures conventionally used in concrete, such as setting accelerators, can also be added.

The constituents (S), (G), (F), (C) and (E) of the formulation may be present per 100 parts by mass of all these constituents, at the rate of:

• 10 - 30 parts by mass of sandy fraction (S);
• 35 - 65 parts by mass of gravel fraction (G);
• 5 – 25 parts by mass of fines (F), as dry matter;
• 10 - 25 parts by mass of cement (C); And
• 4 - 14 parts by mass of water (E);

at least one superplasticizer - high water reducer which can advantageously be added, in particular at a rate of up to 4 parts by mass relative to the mass of the cement (C).

The formulation of a concrete must set the effective water/cement ratio [(E)/(C)] at a value varying between 0.45 and 0.65, fixed by the different classes of exposure of concretes defined by the Standard. European of Concretes NF-EN 206-1/CN.

The present invention also relates to a concrete obtained from the formulation as defined above. This concrete is suitable for recycled concrete applications.

The present invention makes it possible to obtain, with the concrete formulations which are the subject of it, concretes having:

• a mechanical resistance in compression according to Standard NF EN 12390-3 June 2019 on a 15x15x15 cm cube, 10 - 50 MPa at 28 days in the case of using a CEMIII/C cement, and 5 - 45 MPa at 28 days in the case of an oversulphated cement; And
• a class S4 rheology within the meaning of standard NF EN 206 CN.

The present invention also relates to a process for preparing a concrete whose formulation is as defined above, characterized in that, in a concrete mixing tool, such as a concrete plant or truck mixer or concrete mixer , we successively introduce:

• aqueous fines slurry (F);
• the gravel fraction (G);
• the sandy fraction (S);
• cement (C); And
• where appropriate at least one superplasticizer - water reducer as defined above,

water (E) to ensure the hydration of the cement and the hardening of the concrete comprising, as added water, water from the aqueous fines slurry (F) to which additional water is optionally added before or after the introduction of the aqueous slurry of fines (F).

In particular, the process for preparing concrete according to the present invention may advantageously comprise the following steps:

(a) removal of macro-waste, such as pieces of wood, metal, concrete, electrical cables, plastic material, from land;

(b) dry screening to pass a mixture of gravel, sand and fines;

(c) washing/screening of this mixture by high pressure water jets to obtain:

• on the one hand, a gravel fraction (G); And
• on the other hand, a sandy pulp containing, in water, sand and fines;

(d) hydrocycloning the sandy pulp to obtain, in overflow, a sandy fraction (S) and, in overflow, an aqueous slurry of fines (F); Or

(d1) first hydrocycloning of the sandy pulp to obtain:

• underflow, a watery mud of sand and fines; And
• overflowing, an aqueous slurry of fines (F);

(d2) second hydrocycloning of the aqueous sand and fines slurry resulting from the first hydrocycloning to obtain:

• on the one hand, a sandy fraction (S); And
• on the other hand, an aqueous slurry of fines (F);

(e) if necessary, decantation of the aqueous fines sludge(s) (F) to reduce the water content and/or

(f) partial dehydration for example by pressing or centrifugation of the aqueous sludge(s) of fines (F); And

(g) preparation of a concrete from at least a part of the gravelly fraction (G), at least a part of the sandy fraction (S) and at least a part of the aqueous sludge(s) of fines (F ) if necessary partially dehydrated, with a possible addition of water to the fines sludge water (F).

It is possible to choose to carry out a single cycloning (d) or two cyclonings (d1 and d2) for example depending on the content of fines in the aqueous sludge. By way of example, a single cycloning (d) can be carried out in the case of a fines content of less than 15% by mass in the raw earth, and two successive cyclonings (d1 and d2) in the case of a fines content in the raw earth 15 to 40% by mass.

In step ©, the gravel fraction (G) obtained, for example, can be washed under high pressure water jets in a paddle scrubber, a small aqueous fraction of fines then being obtained, which can also be used in the manufacture of concrete according to the invention.

In step (d1), the aqueous slurry of sand and fines obtained in the underflow can be sent to at least one attrition cell to clean the sand of fine clay particles stuck to it, before sending this sludge to the second hydrocycloning (d2).

Finally, the subject of the present invention is an apparatus for the preparation of concrete from the formulation as defined above, characterized in that it comprises:

• a screen, such as a star screen, allowing a mixture of gravel, sand and fines to pass while retaining the coarse fraction of the land to be treated;
• a washer-screener comprising a set of high-pressure water jets to fragment said mixture, followed by a first sieve retaining an aqueous slurry of gravel and fines and a second sieve retaining a sandy pulp made of sands and fines, with, where appropriate, the interposition of an intermediate sieve, said sieves being driven by vertical movements to disperse the material and break up the agglomerates; And
• a device for washing said slurry of gravel and fines, such as a device comprising two endless screws rotating in opposite directions and high-pressure water jets, or a paddle sludge, making it possible to create shearing forces to obtain a gravelly fraction (G);
• a hydrocyclone making it possible to separate, from the sandy pulp, an underflow of a sandy fraction (S) and an overflow of an aqueous slurry of fines (F); Or
• a first hydrocyclone for separating, from the sandy pulp, an aqueous sludge of sands and fines and an aqueous sludge of fines (F);
• a second hydrocyclone for separating, from the aqueous mud of sand and fines from the first hydrocyclone, a sandy fraction (S) and an aqueous mud of fines (F),

at least a part of the gravelly fraction (G), at least a part of the sandy fraction (S) and at least a part of the aqueous sludge(s) entering into the composition of the formulation for concrete.

The apparatus according to the invention may also further comprise a fines aqueous sludge settling silo (F) for recovering fines sludge with a reduced humidity rate from the underflow, and/or at least one filter press, and / or at least one belt filter and/or at least one centrifuge, to recover fines aqueous sludge cakes.

The following examples illustrate the present invention without however limiting its scope.

Example 1

Making concrete from earth

The following process was carried out:

(a) Pre-treatment of soil to be treated

The macro-waste is extracted from the earth to be treated, which contains a percentage of fines of 30%.

(b) Dry screening/scalping

Dry screening of the soil obtained in (a) is carried out to retain the coarse fraction, greater than 80 mm and let the fractions of smaller particle size pass.

(c) Screening/sieving under water

Thanks to the superposition of three sieves (60 mm, 22 mm and 6 mm), a screen-washer separates the fragments of material into two parts (6/60mm and 0/6mm).

The 22mm sieve is only used as an intermediate “protection” sieve, avoiding too rapid and sudden arrival of the middle fraction on the 6mm sieve. The high-pressure water jets placed upstream of the screener exert shearing forces on the material and thus promote the separation of the fines. While the vertical movements of the sieves allow the material to be dispersed and the agglomerates to be broken up, the advancement component ensures the progress of the products towards their outlet.

The gravel (G) (6/60mm) is sent to a paddle sludge remover while a sandy pulp made up of sand and fines (0/6mm) is sent to a first hydrocyclone.

Consisting of two shafts resembling endless screws rotating in opposite directions, the paddle sludge remover completes the washing of gravel (G). Passing under high-pressure water jets creates shear forces on the material and thus promotes the separation of fines and their transfer into the water. The fines are then pumped to the sludge pond. The clean gravel (G) obtained at the outlet is stored in the dedicated area.

The paddle sludge remover also makes it possible to evacuate floating materials (light elements, plastics, porous carbonaceous material, etc.). These floats are then stored in the dedicated area.

(d1) First stage of hydrocycloning

The sandy pulp obtained at the outlet of the washing screen is sent to a first hydrocyclone. Hydrocycloning separates the relatively clean sand fraction from the fines.

The principle of operation of a hydrocyclone is based on the difference in mass of the particles. It is fed tangentially in its upper part by the mixture of water + sands + fines (<63μm). The centrifugal force created within the cell forms two spiral-shaped movements. While the first movement (downward) precipitates coarse particles (sand) towards the overflow, the second (ascending) sucks lighter particles such as fines and a large part of the water towards the overflow of the hydrocyclone.

At the end of this stage, the sand evacuated in the underflow still contains a significant portion of fines (mixture obtained in the underflow: 80% sand, 20% fines). It is therefore routed to attrition cells.

The aqueous fines sludge obtained as an overflow is sent to the sludge recovery basin.

(d2) Second hydrocycloning

Attrition cells improve the final quality of the sand by removing a large quantity of fines. Each cell has a rotating shaft fitted with two blades of specific shape allowing the sand suspension to be stirred vigorously. During their successive passage through the cells, the sand particles undergo significant frictional forces against each other. These forces have the effect of detaching the fine clay particles that remained.

The suspension obtained at the outlet of the last cell feeds a second hydrocyclone which, like the first, makes it possible to separate the fraction of sand (S) from the aqueous sludge of fines.

The clean sand (S) obtained at the outlet of the second hydrocyclone then passes over a vibrating table allowing it to be wrung out. At the end of this treatment, it comes out clean with a residual fines concentration of 3-4% and a water content of 5%. It is then moved and stored in a dedicated area.

The fines-laden water is collected throughout the process (at the paddle sludge level, the two hydrocycloning stages) and is sent to the sludge recovery basin. The moisture content of the mud in the basin is 90 to 95%.

(e) Settling of the aqueous sludge of fines

The water from the sludge recovery basin is then pumped to a settling silo. In order to speed up the settling process within the silo, a flocculant can be added. This flocculant is injected into the solution via a process called in-line homogenization, i.e. the flocculant is injected at several points in the pipe which brings the solution to the top of the settling silo. The fines settling time in the silo is about 120s. This extremely fast speed explains the continuous filling of the clear water basin at the outlet of the silo.

In the settling silo, the fines are recovered by underflow towards a sludge basin supplying the filter presses, while the clean water is evacuated by overflow into the clear water basin before being reinjected after filtration into the process. The moisture content of the sludge collected in the sludge pond is around 60%.

(f) Filtration of sludge on filter presses

The sludge stored in the sludge pond is then routed to filter presses to reduce the moisture content from 50% to 30%.

A filter press consists of several chambers arranged next to each other. The fines are injected at the inlet with a pressure of 12 bars (pressure which will be kept constant during the filtration). The fines are injected into each chamber by central injection. Small holes in the walls of each chamber allow the evacuation of water.

The water evacuated by the filtration leaves the filter and flows along a recovery gutter. At the outlet of this gutter, a probe measures in real time the flow of water evacuated. When this flow rate has become sufficiently low, the filtration is complete. The probe sends the information to the automaton which controls the dismantling of the plates. The moisture content of the filter cakes at the process outlet is 30%.

The cycle time of filter presses can vary, depending on the nature of the fines, between 45 minutes and 4 hours.

The filter cakes are stored in the dedicated tent shed pending their transfer by a specialized company.

From 1000 tons of soil, we were able to obtain 300 tons of 6/60 mm gravel, 400 tons of 0/6 mm sand and 300 tons of fines; these gravels, this sand and these fines obtained in the form of sludge were used in the preparation of concretes.

Example 2

Formulation of a concrete from an aqueous slurry of fines

A concrete was prepared, the formulation of which is given below in kg/m ³ , the fines being introduced as aqueous slurry at 60% by mass of water, and the sands and gravel having a humidity of 5% in mass. No additional water was used.

Sand fraction 0/6 mm 550

Gravel fraction 6/60 mm 1270

63 µm fines of particle size 200

Cement CEM III /C 400

Aggregate water 90

Fine mud water 120

Water efficient 210

Effective water/cement 0.53

Superplasticizer admixture 2% of the mass of the cement

The aqueous slurry of fines, the gravel fraction, the sandy fraction and the cement to which the superplasticizer was added were successively introduced into a concrete mixer.

A cube of 15 cm x 15 cm x 15 cm was cast.

The measured compressive strength of this concrete is 38 MPa at 28 days and 49 MPa at 90 days.

Example 3

Formulation of a concrete from an aqueous slurry of fines

A concrete was prepared, the formulation of which is given below in kg/m ³ , the fines being introduced as aqueous slurry at 60% by mass of water, and the sands and gravel having a humidity of 5% in mass. No additional water (supplied water) was used.

Sand fraction 0/6 mm 480

Gravel fraction 6/60 mm 1130

63 µm fines of 360 particle size

Cement CEM III/C 460

Aggregate water 80

Fine mud water 215

Effective Water 295

Effective water/cement 0.64

Superplasticizer admixture 2% of the mass of the cement

We proceeded as in Example 2.

The measured compressive strength of this concrete is 28 MPa at 28 days and 36 MPa at 90 days.

Example 4

Formulation of a concrete from an aqueous slurry of fines

A concrete was prepared, the formulation of which is given below in kg/m ³ , the fines being introduced as aqueous sludge at 30% by mass of water, and the sands and gravel having a humidity of 5% in mass.

Sand fraction 0/6 mm 540

Gravel fraction 6/60 mm 1265

63 µm fines of 170 particle size

Supersulfated cement 460

Fine Mud Water 50

Aggregate water 90

Added water 70

Water efficient 210

Effective water/cement 0.46

Superplasticizer admixture 2.5% of the mass of the cement

The procedure was as in Example 2, adding the additional water at the same time as the fines sludge.

The measured mechanical compressive strength of this concrete is 36 MPa at 28 days and 47 MPa at 90 days.

Claims (17)

Concrete formulation comprising:

• a granular skeleton comprising:
  • a sandy fraction (S); And
  • a gravel fraction (G);
• cement (C); And
• water (E) to ensure the hydration of the cement and the hardening of the concrete,

characterized in that the granular skeleton also comprises a fraction of fines (F), which is in the form of an aqueous sludge, or of a partially dehydrated aqueous sludge in the form of cakes, the water of the said aqueous sludge or said partially dehydrated aqueous sludge forming part of the water (E) to ensure the hydration of the cement and the hardening of the concrete. Concrete formulation according to Claim 1, characterized in that the aqueous sludge is in a flowable state and has a dry matter content of 10 to 50% by mass, in particular 20 to 40% by mass, in particular from 25 to 35% by mass, or may be in the partially dehydrated state, in the form of cakes, and have a dry matter content of 50 to 95% by mass, in particular from 50 to 70% by mass. Formulation for concrete according to one of Claims 1 and 2, characterized in that the fines are fines originating from silty-clayey mineral materials, such as earth and raw marine or river sediments. Formulation for concrete according to one of Claims 1 to 3, characterized in that the aqueous sludge is derived from a washing/hydrocycloning treatment of earth, the sandy fraction (S), the gravelly fraction (G) and the sludge aqueous fines (F) which can advantageously come from the same washing/hydrocycloning treatment of land aimed at obtaining sand, gravel and an aqueous slurry of fines. Concrete formulation according to one of Claims 1 to 4, characterized in that the fines have a particle size of less than 400 µm, in particular less than 63 µm. Formulation for concrete according to one of Claims 1 to 5, characterized in that the gravel fraction (G) is a 6/20 mm, 6/30 mm, 6/60 mm, 6/80 mm fraction and the sandy fraction (S) is a fraction 0/6 mm, 0/4 mm. Formulation for concrete according to one of Claims 1 to 6, characterized in that the cement (C) is chosen from:

• cements based on CEM III type blast furnace slag, and more particularly CEM/III type C; And
• oversulphated cements.

Formulation for concrete according to one of Claims 1 to 7, characterized in that it also comprises at least one superplasticizer – high water reducer. Formulation for concrete according to one of Claims 1 to 8, characterized in that the constituents (S), (G), (F), (C) and (E) of the formulation are present per 100 parts by mass of all these constituents, on the basis of:

• 10-30 parts by mass of sandy fraction (S);
• 35 - 65 parts by mass of gravel fraction (G);
• 5 - 25 parts by mass of fines (F), in the form of dry matter;
• 10 - 25 parts by mass of cement (C);
• 4 - 14 parts by mass of water (E);

at least one superplasticizer - high water reducer which can advantageously be added, in particular at a rate of up to 4 parts by mass relative to the mass of the cement (C). Concrete obtained from the formulation as defined in one of claims 1 to 9. Process for preparing a concrete whose formulation is as defined in one of Claims 1 to 9, characterized in that, in a concrete mixing tool, such as a concrete plant or truck mixer or concrete mixer, introduces successively:

• aqueous slurry of fines (F);
• the gravel fraction (G);
• the sandy fraction (S); And
• cement (C),
• where appropriate at least one superplasticizer - water reducer,

water (E) to ensure the hydration of the cement and the hardening of the concrete comprising, as added water, water from the aqueous fines slurry (F) to which additional water is optionally added before or after the introduction of the aqueous slurry of fines (F). Method according to claim 11, characterized by the fact that it comprises the following steps:
(a) removal of macro-waste, such as pieces of wood, metal, concrete, electrical cables, plastic material, from land;
(b) dry screening to pass a mixture of gravel, sand and fines;
(c) washing/screening of this mixture by high pressure water jets to obtain:

• on the one hand, a gravel fraction (G); And
• on the other hand, a sandy pulp containing, in water, sand and fines;

(d) hydrocycloning the sandy pulp to obtain, in overflow, a sandy fraction (S) and, in overflow, an aqueous slurry of fines (F); Or
(d1) first hydrocycloning of the sandy pulp to obtain:

• in underflow, an aqueous mud of sand and fines; And
• in overflow, an aqueous sludge of fines (F);

(d2) second hydrocycloning of the aqueous sand and fines slurry resulting from the first hydrocycloning to obtain:

• on the one hand, a sandy fraction (S); And
• on the other hand, an aqueous slurry of fines (F); And

(e) if necessary, decantation of the aqueous fines sludge(s) (F) to reduce the water content and/or
(f) partial dehydration for example by pressing or centrifugation of the aqueous sludge(s) of fines (F); And
(g) preparation of a concrete from at least a part of the gravel fraction (G), at least a part of the sandy fraction (S) and at least a part of the aqueous sludge(s) of fines (F ) if necessary partially dehydrated, with a possible addition of water to the fines sludge water (F). Process according to Claim 12, characterized in that a single cycloning (d) is carried out in the case of a fines content of less than 15% by mass in the raw earth, and two successive cyclonings (d1 and d2) in the case of a fines content in the raw earth of 15 to 40% by mass. Process according to one of Claims 12 and 13, characterized in that in step (c), washing is carried out under high-pressure water jets of the gravelly fraction (G) obtained, for example, in a sludge with vanes, a small aqueous fraction of fines being then obtained, which can also be used in the manufacture of concrete. Process according to one of Claims 12 to 14, characterized in that in step (d1), the aqueous slurry of sand and fines obtained in the underflow is sent to at least one attrition cell to clean the sand fine clay particles stuck to it, before sending this sludge to the second hydrocycloning (d2). Apparatus for the preparation of a concrete from the formulation as defined in one of claims 1 to 9, characterized in that it comprises:

• a sieve, such as a star sieve, allowing a mixture of gravel, sand and fines to pass while retaining the coarse fraction of the earth to be treated;
• a washer-screener comprising a set of high-pressure water jets to fragment said mixture, followed by a first sieve retaining an aqueous slurry of gravel and fines and a second sieve retaining a sandy pulp made of sands and fines, with, where appropriate, the interposition of an intermediate sieve, said sieves being driven by vertical movements to disperse the material and break up the agglomerates; And
• a device for washing said slurry of gravel and fines, such as a device comprising two endless screws rotating in opposite directions and high-pressure water jets, or a paddle sludge, making it possible to create shearing forces to obtain a gravel fraction (G);
• a hydrocyclone making it possible to separate, from the sandy pulp, an underflow of a sandy fraction (S) and an overflow of an aqueous sludge of fines (F); Or
• a first hydrocyclone making it possible to separate, from the sandy pulp, an aqueous sludge of sands and fines and an aqueous sludge of fines (F);
• a second hydrocyclone for separating, from the aqueous mud of sand and fines from the first hydrocyclone, a sandy fraction (S) and an aqueous mud of fines (F),

at least a part of the gravelly fraction (G), at least a part of the sandy fraction (S) and at least a part of the aqueous sludge(s) entering into the composition of the formulation for concrete. Apparatus according to claim 16, characterized in that it further comprises a fines aqueous sludge settling silo (F) for recovering fines sludge with a reduced humidity rate from the underflow, and/or at least one filter -press, and/or at least one belt filter and/or at least one centrifuge, to recover fines aqueous sludge cakes.