aqueous geopolymer composition based on dredged sediments, a geopolymer material obtained from said aqueous geopolymer composition, and their applications, particularly in the field of ecological concretes

Abstract

The present invention relates to an aqueous geopolymer composition based on dredged sediments, a geopolymer material obtained from said aqueous geopolymer composition, the use of said aqueous geopolymer composition as a binder for the manufacture of concrete, grout, concrete pavement, compacted road layer, bricks, retaining wall, quay wall, or precast concrete, and concrete comprising said geopolymer material. Figure to be published: Figure 1

Description

Title of the invention: aqueous geopolymer composition based on dredging sediments, a geopolymer material obtained from said aqueous geopolymer composition, and their applications in particular in the field of ecological concretes

[0001] The present invention relates to an aqueous geopolymer composition based on dredged sediments, a geopolymer material obtained from said aqueous geopolymer composition, the use of said aqueous geopolymer composition as a binder for the manufacture of concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a quayside breakwater, or pre-cast concrete, and a concrete comprising said geopolymer material.

[0002] The present invention falls within the scope of the recovery of non-immersible dredging sediments in ecological concretes for applications in public works.

[0003] Water is an agent of physical and chemical erosion of the rocks and soils it drains. Mineral and / or organic particles in suspension accumulate, thanks to the processes of flocculation or gravitation, in the bottom of river and sea waterways and ports; this is the natural process of sedimentation. In seaports and waterways, it is necessary to dredge the bottoms in order to maintain navigability (river traffic) and / or prevent flood risks. The concept of dredging also includes the operations of digging new ports, in particular marinas, or access channels for boats with increasingly deep drafts, the extension of existing ports, and port maintenance work (pleasure, commercial, industrial, fishing), often estuary ports which have a natural tendency to silting up.The dredged materials are diverse, ranging from stone blocks to silt (more or less compacted) through sands of various grain sizes, without forgetting the waste thrown into the sea. Their degree of pollution is also variable, depending on the nature of the pollutant and its quantity, whether the dredging is carried out for the opening of a new site in a natural environment or for maintenance or expansion in an existing port with polluting activities, more or less old.

[0004] Dredged sediments are a mixture of sands, silts and clays. Traditionally, all or almost all marine sediments, regardless of their level of contamination, were "slammed" off the coast, in pits dedicated to their immersion. However, in order to preserve the environment, and more particularly aquatic environments, several decrees of June 14, 2000, August 9, 2006, and of December 23, 2009 prohibited the immersion of sediments that were too heavily contaminated, for example with metallic elements, polycyclic aromatic hydrocarbons (PAHs), tributyltin (TBT), and / or polychlorinated biphenyls (PCBs); with predefined thresholds NI, N2 and SI; and then imposes on-land management. In France, 50 million m3 of sediments are dredged every year, with 90% of this volume submerged within the framework of the regulations for marine and estuarine environments. The remaining 10%, once removed from the waters, is managed on land.

[0005] A first strategy for storing sediments consists of depositing the sediments by pumping them into basins dug on the ground. However, the characteristics of the sediments change under the influence, in particular, of contact with air, which causes oxidation of the environment, of temperature differences, which influence microbial activity, and of a reduction in water content, which causes dehydration of the environment. The sediment is in fact capable of adsorbing and transforming contaminants and transferring them to the soil or water tables. Trace element contamination of soils is likely to disrupt biological activity and therefore to have harmful long-term consequences on the overall functioning of the ecosystem.The presence of inorganic or organic contaminants (TBT, PCB, PAH) can also cause long-term effects, particularly for species at the end of the food chain due to the bio-accumulative and / or bio-amplifiable nature of these substances.

[0006] A second strategy for storing sediments consists of storing / burying them in waste storage facilities. On-land sediment recovery channels have been the subject of growing interest from port and waterway managers in France due to regulations that make it increasingly difficult to "sludge" dredged sediments, the downward revision of management thresholds, the main consequence of which is to increase the volumes that must be treated on land, and the financial aspect, since the recovery of sediments would allow managers to transform a material currently considered waste into a material with a use value, a source of savings or even profits. There are many on-land sediment recovery channels.However, their implementation on an industrial scale is not so simple and most often requires pre-treatment and / or treatment of the dredged sediments to sort them and reduce the pollutant levels to make them acceptable.

[0007] Pretreatment may include dehydration and separation of the different layers to reduce volume, control contamination levels, and guide subsequent treatment. The treatment generally allows. The treatment may be a biological treatment (bioremediation, biowashing / bioleaching, spreading, composting), a physicochemical treatment (physicochemical extraction such as flotation or chemical washing), thermal treatment (thermal desorption, pyrolysis, wet oxidation, molten salt baths), immobilization treatment (platforms, in situ decantation, for drying), or a mixture thereof. The recovery channels for dredged sediments include leveling, beach nourishment, dune or bank reinforcement, backfilling (landscaped mounds, banks, earthworks or polder), construction materials in the construction sector (concrete, bricks, road and road materials).

[0008] By way of example, international application WO2016 / 198176 describes an additional cementitious material for use in association with a bearing cement as a hydraulic binder. The additional cementitious material is obtained from dredged sediments comprising sorting the sediments for recovery of the fine part, contacting the fine part with portlandite (Ca(OH)2, CaO), dehydration and then heat treatment (calcination).

[0009] However, treatment costs are high, particularly due to the considerable volumes to be treated and the complexity of some of the processes. Furthermore, a 2016 decree provides that in 2025 new thresholds will apply (Leroy Law), implying new volumes of sediment to be managed on land. Finally, industrializable recovery operations remain relatively rare and with difficulty in scaling up.

[0010] Consequently, there is a need to find a way of recovering dredged sediments that can address the social, technical and environmental issues that their management represents. In particular, there is a need for new ways of recovering dredged sediments that are easy to implement, industrializable, that can be freed from treatment and / or pretreatment processes and that lead to one or more materials with good mechanical performance for use in construction materials.

[0011] The invention relates firstly to an aqueous geopolymer composition, characterized in that it comprises dredging sediments, at least one alkali silicate and at least one metakaolin, and in that the aqueous geopolymer composition is free of alkaline base and the metakaolin represents at least 15% by mass relative to the total mass of the aqueous geopolymer composition.

[0012] The aqueous geopolymer composition of the invention makes it possible, on the one hand, to recover dredging sediments and, on the other hand, to produce a geopolymer material which has good characteristics in terms of mechanical properties so that it can be used in construction materials. Furthermore, the presence of at least 15% by mass of metakaolin and the absence of alkaline base introduced into the aqueous geopolymer composition contribute to obtaining good mechanical properties while reducing CO2 emissions (balance between the mass of CO2 emitted and compressive strength in MPa).

[0013] The aqueous geopolymer composition of the invention thus provides a common response to the problems of sediment management and the need for public works to develop new materials using local and renewable resources to limit the carbon impact of concrete production and material transport. Indeed, concrete is the most consumed material in the world after water and cement, one of its main constituents, and is responsible for 5 to 7% of global CO2 emissions. This alarming figure is not expected to decrease, because by 2030, global demand for cement is expected to increase by 216%. The invention proposes the reuse of dredging sediments in new low-CO2 mortars while ensuring proximity of production and ease of supply to limit transport.

[0014] The aqueous composition is capable of geopolymerizing (i.e. polycondensing) to form a geopolymer material.

[0015] In particular, dredged sediments are precursors of geopolymerization and participate in the geopolymerization reaction to form a geopolymer material.

[0016] In the present invention, the geopolymer composition is an aqueous composition. In other words, it comprises water.

[0017] Preferably, the aqueous geopolymer composition comprises from 15 to 40% by mass approximately of water, particularly preferably from 17 to 30% by mass approximately of water, and more particularly preferably from 20 to 25% by mass approximately of water, relative to the total mass of the aqueous geopolymer composition.

[0018] The water content is thus sufficient to allow the geopolymerization reaction without creating too much porosity in the final geopolymer gel which could then lead to shrinkage or contraction.

[0019] The water preferably comes mainly, and even more preferably only, from recovered dredging sediments and alkali silicate which can be in the form of an aqueous solution.

[0020] The water content of dredged sediments can be determined according to standard NF P94-047. It then makes it possible to determine the water content of the aqueous geopolymer composition.

[0021] In the invention, sediments are materials resulting from the erosion of rocks by water, wind and other erosion agents, and which, depending on their origin, can be fluvial, glacial, lacustrine or marine.

[0022] Sedimentation or landfall is the deposit of alluvial materials (pebbles, gravel, sand, silt, fines, etc.) eroded upstream and deposited by the watercourse in certain areas downstream (particularly during flood phases) or accumulated at the edge of sea ​​by ocean currents.

[0023] According to a particularly preferred embodiment, the dredged sediments (used in the aqueous geopolymer composition) are untreated. In other words, the dredged sediments used in the composition have not undergone any chemical or thermal treatment(s). They are therefore used as is without prior chemical or thermal treatment(s). In this embodiment, the dredged sediments used in the aqueous geopolymer composition are therefore in a natural state.

[0024] The aqueous geopolymer composition preferably comprises from 25 to 65% by mass approximately of dredged sediments, particularly preferably from 30 to 45% and particularly preferably from 30% to 40% by mass of dredged sediments, relative to the total mass of the aqueous geopolymer composition.

[0025] Preferably, the dredging sediments have a particle size of at most approximately 100 μm, and particularly preferably of at most approximately 60 μm. In other words, the dredging sediments used in the composition preferably correspond to a fine fraction of dredging sediments.

[0026] The dredged sediments used in the aqueous geopolymer composition are preferably muddy silty sediments.

[0027] Muddy silty sediments are characterized by a high content of SiO2 and / or Al2O3.

[0028] In a particularly preferred manner, the dredged sediments comprise at least approximately 25% by mass of SiO2, and more particularly preferred at least approximately 40% by mass of SiO2, relative to the total mass of the dredged sediments.

[0029] In a particularly preferred manner, the dredged sediments comprise at least approximately 8% by mass of A12O3, and more particularly preferred at least approximately 10% by mass of A12O3, relative to the total mass of the dredged sediments.

[0030] According to a preferred embodiment of the invention, the dredged sediments comprise silicon and aluminum, so that the Si / Al molar ratio is greater than or equal to 2, particularly preferably ranging from 2.1 to 4.0, and more particularly preferably ranging from 2.8 to 3.1.

[0031] The dredging sediments used in the aqueous geopolymer composition may comprise from 65% to 80% by mass approximately of silt, and preferably from 68% to 75% by mass approximately of silt, relative to the total mass of the dredging sediments. This is also referred to as the silt fraction.

[0032] The dredging sediments used in the aqueous geopolymer composition may comprise at least approximately 2% by mass of clay, preferably at least approximately 3% by mass of clay, and even more preferably from 4% to 10% by mass. approximately mass of clay, relative to the total mass of dredged sediments. This is also referred to as the clay fraction.

[0033] Depending on the clay content of the dredged sediments, the mechanical properties of the geopolymer material may vary and / or not be reproducible.

[0034] The aqueous geopolymer composition of the invention makes it possible to guarantee good reproducibility of mechanical performance and / or stable mechanical performance regardless of the clay content of the dredged sediments.

[0035] In the aqueous geopolymer composition, the dredging sediments preferably comprise at most approximately 30% by mass of sand, and particularly preferably from approximately 10% to 25% by mass of sand, relative to the total mass of the dredging sediments. This is also referred to as the sandy fraction or sandy particles.

[0036] Beyond 30% by mass of sand, the sand grains are too large to be able to bind to the geopolymer matrix, creating areas of voids, microcracks and a heterogeneous geopolymer material.

[0037] In the invention, the content of silt, clay, and sand in the dredged sediments can be determined using the laser granulometry method.

[0038] The dredged sediments may further comprise organic matter. Depending on the organic matter content of the dredged sediments, the mechanical properties of the geopolymer material may vary and / or not be reproducible. The organic matter content of the dredged sediments may be determined by a thermal calcination test at 450°C according to standard XP P94-0947.

[0039] The aqueous geopolymer composition of the invention makes it possible to guarantee good reproducibility of mechanical performance and / or stable mechanical performance regardless of the organic matter content of the dredged sediments.

[0040] Preferably, the dredged sediments comprise at least approximately 3000 mg of organic matter, more preferably approximately 4000 to 15000 mg of organic matter, and even more preferably approximately 6000 to 14000 mg of organic matter, per kg of sediment.

[0041] The sediments preferably have a specific surface area ranging from 0.200 m2 / g to 0.700 m2 / g, and particularly preferably from 0.450 m2 / g to 0.700 m2 / g.

[0042] In the invention, the specific surface area is preferably measured by the BET method.

[0043] The alkali silicate may be a sodium or potassium silicate and preferably a sodium silicate.

[0044] According to a preferred embodiment of the invention, the alkali silicate has a Si / alkali metal molar ratio ranging from 1 to 2, and particularly preferably from 1.2 to 1.7. This thus makes it possible to further improve the compressive strength of the geopolymer material formed.

[0045] The aqueous geopolymer composition preferably comprises from 5 to 20% by mass approximately of alkali silicate, and particularly preferably from 7 to 12% by mass approximately of alkali silicate, relative to the total mass of the aqueous geopolymer composition.

[0046] The aqueous geopolymer composition comprises at least 15% by mass of metakaolin, preferably from 20 to 40% by mass approximately of metakaolin, and particularly preferably from 30 to 38% by mass approximately of metakaolin, relative to the total mass of the aqueous geopolymer composition.

[0047] Below 15% by mass, mechanical properties such as compressive strength are not sufficient. Above 40% by mass, ecological performances (e.g. CO2 emissions) are not interesting compared to the use of a cement.

[0048] In the invention, the expression "metakaolin" means a dehydroxylated aluminosilicate. It is preferably obtained by dehydration of a kaolin or a kaolinite. This dehydration is conventionally obtained by calcination.

[0049] According to one embodiment of the invention, the metakaolin is a kaolin calcined at a temperature ranging from approximately 750°C to approximately 850°C.

[0050] Metakaolin can be analyzed by differential thermal analysis (DTA) [absence or presence of a crystallization point or peak], nuclear magnetic resonance (NMR) [27 Al NMR spectrum], and / or X-ray diffraction (XRD).

[0051] The aqueous geopolymer composition can be characterized by a water / solid mass ratio (dredging sediments, alkali silicate, metakaolin) ranging from approximately 0.30 to 0.45, and preferably ranging from approximately 0.30 to 0.35.

[0052] According to a preferred embodiment of the invention, the alkali silicate, the metakaolin, and the dredged sediments are defined by a mass ratio of alkali silicate / (metakaolin + dredged sediments) ranging from approximately 0.08 to 0.30, and particularly preferably ranging from approximately 0.10 to 0.20.

[0053] The aqueous geopolymer composition may further comprise one or more additives, such as recycled aggregates (sand, gravel, gravel) or crushed concrete; alkaline reagents (glass powder, rice husk ash, silica fume), additional highly aluminosilicate cementitious fluxes such as fly ash or silica fume.

[0054] The second subject of the invention is a geopolymer material, characterized in that it is obtained by polycondensation and / or hardening of an aqueous geopolymer composition in accordance with the first subject of the invention.

[0055] Geopolymers are essentially mineral chemical compounds or mixtures of compounds comprising silico-oxide (-Si-O-Si-O), silico-aluminate (-Si-O-Al-O), ferro-silico-aluminate (-Fe-O-Si-O-Al-O), or alumino- phosphate (-A1-0-P-0-), created by a geopolymerization process (i.e. polycondensation). The most common geopolymers are those based on aluminosilicates referred to as “poly(sialate)”.

[0056] In the present invention, the geopolymer obtained from the aqueous geopolymer composition is an aluminosilicate geopolymer.

[0057] The aluminosilicate geopolymer preferably results from the polycondensation of oligomers of the oligo(sialate) type formed from a mixture of at least one aluminosilicate, an alkaline reagent (eg. alkali metal silicate) and water.

[0058] In the present invention, the geopolymer may have the following formula: Mn[-(Si-O2)z-Al-O]n.wH2O in which M is an alkali metal ion, and n represents the degree of polycondensation, w is the number of chemically bonded water molecules, and z is the number of silicon atoms that constitute a single oligomeric aluminosilicate chain. The latter depends, in turn, on the molar ratio of SiO2 / Al2O3 contained in the geopolymer. The choice of this ratio varies depending on the desired setting time and strength. As this value gradually increases from 1 to 3, a sialate, i.e., Mn(-Si-O-Al-O-)n, a sialatesiloxo, i.e., Mn(Si-O-Al-O-Si-O-)n, or a sialate disiloxo, i.e., Mn(-Si-O-Al-O-Si-O-Si-O)n, will be formed, respectively.

[0059] The aluminosilicate geopolymer of the invention preferably has an Si / Al atomic ratio ranging from 2.5 to 3.5.

[0060] The aqueous geopolymer composition makes it possible to form a geopolymer material having little shrinkage, better dimensional stability, better compressive strength at more than 28 days, and preferably at 90 days, better durability and a reduced setting time.

[0061] The geopolymer material of the invention preferably has a compressive strength beyond 28 days of at least approximately 6 MPa, particularly preferably of at least approximately 6.5 MPa, and particularly preferably of at least approximately 7 MPa.

[0062] In the invention, the compressive strength can be determined according to standard NF EN 1015-11, in particular using an electromechanical press with a capacity of 100 kN at a constant loading speed of 0.6 mm / min.

[0063] The third subject of the invention is the use of an aqueous geopolymer composition in accordance with the first subject of the invention, as a binder for the manufacture of concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a quayside dike, or prefabricated concrete.

[0064] The aqueous geopolymer composition based on dredged sediments of the invention is used as a binder (geopolymer binder).

[0065] In the invention, the term "binder" means a compound which serves to agglomerate solid particles in the form of powder or aggregates.

[0066] In the aqueous geopolymer composition of the invention, the dredging sediments are precursors of geopolymerization and react with the alkali silicate and the metakolin, to form a binder which will make it possible to bind the granular elements of the concrete and provide mechanical resistance.

[0067] The binder can be used in the fields of public works and construction. This allows a 45% reduction in CO2 emissions, with higher performance than that obtained with Portland cement.

[0068] The fourth subject of the invention is a concrete, characterized in that it comprises a geopolymer material in accordance with the second subject of the invention.

[0069] Reusing dredged sediments as a raw material for the design of concrete directly on the dredging site would allow companies to simplify onshore management, reduce costs and environmental impact and place their consumption model in a circular economy.

[0070] The present invention is illustrated by the following exemplary embodiments, to which it is however not limited. Brief description of the drawings

[0071] The invention is illustrated by the following figures and examples.

[0072] [Fig-1] [Fig. 1] shows the compressive strength of a geopolymer material in accordance with the invention and of materials not in accordance with the invention.

[0073] [Fig.2] [Fig.2] shows the porosity characteristics of a geopolymer material in accordance with the invention and of a material not in accordance with the invention.

[0074] [Fig.3] [Fig.3] shows scanning electron microscopy (SEM) images of a geopolymer material in accordance with the invention and of a material not in accordance with the invention.

[0075] Examples

[0076] The raw materials used in the examples are listed below: - dredged sediments in their natural state from the Garonne, which come more specifically from the port of Bordeaux, - sodium silicate, “Xatico Benelux France”, “Géosil B47T”, SiO2 / Na2O molar ratio = 1.7, density = 1.57 g / cm3, 43.80% by mass of Na2O, 37.70% by mass of SiO2 and 10.20% by mass of Al2O3, - metakaolin, “Argeco”, obtained by flash calcination of kaolinitic clay, - “CEM I 52.5 N PM”, “Calcia” cement (64% by mass of CaO, 19.9% ​​by mass of SiO2 and 3.9% by mass of A12O3), - blast furnace slag, “Ecocem” (43.8% by mass of CaO, 37.7% by mass of SiO2 and 10.2% by mass of A12O3).

[0077] Unless otherwise indicated, all materials were used as received from the manufacturers, without purification.

[0078] Example 1: characterization of the dredging sediments used in the composition of the invention

[0079] In this example 1, dredged sediments from the Garonne were selected. The Garonne estuary is mainly composed of two distinct granulometric fractions: sediments with a strong sandy tendency upstream of the estuary and silty-muddy sediments downstream. The silty-muddy sediments were recovered at Pauillac and left to evaporate in tanks perforated with a geotextile for 1 to 3 months. Drying was carried out by infiltration and evaporation of the water. All fractions of the sediment were recovered.

[0080] The recovered dredged sediments comprise 71% by mass of silt, 24.5% by mass of sand, and 4.5% by mass of clay, relative to the total mass of dredged sediments. They have a particle size according to the NF P94-056 and NF P94-057 standards ranging from 2 to 50 μm. The analysis of the methylene blue value, carried out in accordance with the NF P94-068 standard, and the Atterberg limits NF P94-051, confirmed the silty-clayey nature of the dredged sediments with low plasticity.

[0081] The dredged sediments were also subjected to environmental tests in accordance with the decree of 9 August 2006 and the GEODE guide which determines the reference levels in France. No trace of contamination by heavy metals, PAHs and PCBs was observed. Indeed, the levels of contaminants measured were low and below the N1 and N2 thresholds.

[0082] The recovered dredged sediments comprise 41.38% by mass of SiO2, and 14.19% by mass of Al2O3. They have a Si / Al molar ratio of 2.91.

[0083] The recovered dredged sediments comprise approximately 10500 mg of organic matter per kg of sediment.

[0084] The recovered dredged sediments have a water content of 145% by mass, relative to the total mass of sediments and water, then 30% by mass, relative to the total mass of sediments and water after drying in the tanks.

[0085] Example 2: preparation of a geopolymer material in accordance with the invention

[0086] 620g of dredged sediment in water as recovered and described in Example 1 (477 g of dredging sediment in 143 g of water) and 477 g of metakaolin are introduced into a mixer sold by the company "CV Equipement", then mixed for 10 seconds. Once the resulting mixture is homogenized, 310 g of an aqueous solution of alkali silicate (139.5 g of alkali silicate in 170.5 g of water) is added and then the resulting composition is mixed at low speed 62 rpm for 90 seconds. The mixer was then stopped to remove the resulting aqueous geopolymer composition adhering to the walls and bottom of the bowl and then the resulting composition is mixed at high speed 125 rpm for 60 seconds.

[0087] The aqueous geopolymer composition is defined in Table 1 below:

[0088] [Tableauxl] Sediments (g) Water (g) Sodium silicate (g) Metakaolin (g) 477 313.5 139.5 477

[0089] After curing for 28 days, a geopolymer material in accordance with the invention MG is obtained having a compressive strength of 7 MPa.

[0090] In the invention, the compressive strength can be determined according to standard NF EN 1015-11, in particular using an electromechanical press with a capacity of 100 kN at a constant loading speed of 0.6 mm / min.

[0091] The compressive strength of the geopolymer material of the invention was compared with that of several comparative materials not in accordance with the invention in which the metakaolin was replaced by cement (“CEM I 52.5 N PM”) (MOI), blast furnace slag (M02), the metakaolin was removed and not replaced (M03), or the amount of metakaolin used was less than 15% by mass and an alkaline base was added (M04).

[0092] MOI is obtained from an aqueous composition comprising 60% by mass of dredging sediment, 7% by mass of cement, 27% by mass of water and 6% by mass of sodium silicate. MOI is not part of the invention.

[0093] M02 is obtained from an aqueous composition comprising 60% by mass of dredged sediments, 7% by mass of blast furnace slag, 27% by mass of water and 6% by mass of sodium silicate. M02 is not part of the invention.

[0094] M03 is obtained from an aqueous composition comprising 67% by mass of dredged sediments, 27% by mass of water and 6% by mass of sodium silicate. M03 is not part of the invention.

[0095] M04 is obtained from an aqueous composition comprising 60% by mass of dredged sediments, 7% by mass of metakaolin, 27% by mass of water, and 6% by mass of sodium silicate. M04 is not part of the invention.

[0096] [Fig.l] shows the compressive strength of the different materials MG, MOI, M02, M03, and M04. Only the material according to the invention MG is viable in terms of durability. In particular, the value of 7 Mpa is largely satisfactory for the development of applications in public works.

[0097] [Fig.2] shows the porosity characteristics of the MG and M04 materials, measured using a device sold under the trade name “AutoPore V” by the company “MICROMERITICS”. [Fig.2] shows a refinement of the porosity for M04 compared to MG. The x-axis represents the porosity size diameters in pm.

[0098] [Fig.3] shows scanning electron microscopy (SEM) images of MG and M04 materials taken with a device sold under the trade name “SEM-FEG Zeiss Ultra55” by the company “ZEISS Groupe”.

[0099] According to [Fig.3], the geopolymer material MG has a more ordered and smoother structure indicating a more complete geopolymerization.

Claims

Claims

1. Aqueous geopolymer composition, characterized in that it comprises dredged sediments, at least one alkali silicate and at least one metakaolin, and in that the aqueous geopolymer composition is free of alkaline base and the metakaolin represents at least 15% by mass relative to the total mass of the aqueous geopolymer composition.

2. Composition according to claim 1, characterized in that it comprises from 25 to 65% by mass of dredging sediments relative to the total mass of the aqueous geopolymer composition.

3. Composition according to claim 1 or 2, characterized in that the alkali silicate has a Si / alkali metal molar ratio ranging from 1 to 0

4. Z. Composition according to any one of the preceding claims, characterized in that the dredged sediments are untreated.

5. Composition according to any one of the preceding claims, characterized in that the dredging sediments comprise at most 30% by mass of sand, relative to the total mass of the dredging sediments.

6. Composition according to any one of the preceding claims, characterized in that the dredged sediments comprise silicon and aluminum, so that the Si / Al molar ratio is greater than or equal to 2, and preferably ranges from 2.1 to 4.

0.

7. Composition according to any one of the preceding claims, characterized in that the alkali silicate, the metakaolin, and the dredging sediments are defined by a mass ratio of alkali silicate / (metakaolin + dredging sediments) ranging from 0.08 to 0.

30.

8. Composition according to any one of the preceding claims, characterized in that it comprises from 20 to 40% by mass of metakaolin, relative to the total mass of the aqueous geopolymer composition.

9. Composition according to any one of the preceding claims, characterized in that it comprises from 15 to 40% by mass of water, relative to the total mass of the aqueous geopolymer composition.

10. Composition according to any one of the preceding claims, characterized in that it comprises from 5 to 20% by mass of alkali silicate, relative to the total mass of the aqueous geopolymer composition.

11. Geopolymer material, characterized in that it is obtained by polycondensation and / or hardening of an aqueous geopolymer composition as defined in any one of the preceding claims.

12. Use of an aqueous geopolymer composition as defined in any one of claims 1 to 10, as a binder for the manufacture of concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a quayside dike, or pre-cast concrete.

13. Concrete, characterized in that it comprises a geopolymer material as defined in claim 11.

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