Aqueous geopolymer composition based on dredging sediments, geopolymer material obtained from the aqueous geopolymer composition, and uses thereof in particular in the field of eco concretes

Abstract

The present invention relates to an aqueous geopolymer composition based on dredging sediments, to a geopolymer material obtained from the aqueous geopolymer composition, to the use of the aqueous geopolymer composition as a binder for producing a concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a dock breakwater, or a precast concrete, and to a concrete comprising the geopolymer material.

Description

Aqueous geopolymer composition based on dredged 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 is part 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. Suspended mineral and / or organic particles accumulate, through flocculation or gravitation processes, in the bottom of river and sea ports and rivers; this is the natural process of sedimentation. In sea ports and waterways, it is necessary to dredge the bottoms in order to maintain navigability (river traffic) and / or prevent flooding risks. The concept of dredging also encompasses the digging of new ports, particularly 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.The dredged materials are diverse, ranging from stone blocks to silt (more or less compacted) through sands of various grain sizes, not forgetting 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 sand, silt and clay. Traditionally, all or almost all marine sediments, regardless of their level of contamination, were "slammed" offshore, 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 December 23, 2009 have prohibited the immersion of sediments that are 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 impose onshore management. In France, 50 million m 3 of sediment is dredged every year, with 90% of this volume submerged as part 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 sediment storage consists of depositing the sediments by pumping them into basins dug on the ground. However, the characteristics of the sediments change under the influence of contact with air, which leads to oxidation of the environment, temperature differences, which influence microbial activity, and a decrease in water content, which leads to dehydration of the environment. The sediment is in fact capable of adsorbing and transforming contaminants and transferring them to the soil or groundwater. Trace element contamination of soils is likely to disrupt biological activity and therefore have long-term harmful consequences for 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 is to store / bury them in waste storage facilities. Onshore sediment recovery options have been the subject of growing interest from French port and waterway managers due to regulations that make it increasingly difficult to "sludge" sediments. dredged, the downward revision of management thresholds, the main consequence of which is to increase the volumes to be treated on land, and the financial aspect, since the recovery of sediments would allow managers to transform a material currently considered as waste into a material with a use value, a source of savings or even profits. There are many ways to recover sediments on land. However, their implementation on an industrial scale is not so simple and most often requires the pre-treatment and / or treatment of dredged sediments to sort them and reduce the pollutant levels to make them acceptable.

[0007] Pretreatment may include dewatering and separating the different layers to reduce volume, control contamination levels, and guide subsequent treatment. Treatment generally allows. Treatment may be biological treatment (bioremediation, biowashing / bioleaching, land spreading, composting), physicochemical treatment (physicochemical extraction such as flotation or chemical washes), thermal treatment (thermal desorption, pyrolysis, wet oxidation, molten salt baths), immobilization treatment (platforms, in situ decantation, for drying), or a mixture thereof. Dredged sediment recovery processes include reclamation, beach nourishment, dune or bank reinforcement, backfilling (landscaped mounds, banks, embankments or polders), construction materials in the construction industry (concrete, bricks, road and road materials).

[0008] For example, international application WO2016 / 198176 describes a supplementary cementitious material for use in combination with a portlandite cement as a hydraulic binder. The supplementary 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, processing costs are high, particularly due to the considerable volumes to be processed and the complexity of some of the process. 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, industrialized recovery operations remain relatively rare and difficult to scale up.

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

[0011] The first subject of the invention is 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 the 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 impact Carbon footprint of concrete production and material transportation. 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, as by 2030, global demand for cement is expected to increase by 216%. The invention proposes the reuse of dredged sediments in new low-CO2 mortars while ensuring proximity of production and ease of supply to limit transportation.

[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 geopolymeric 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 about 15 to 40% by mass of water, particularly preferably from about 17 to 30% by mass of water, and more particularly preferably from about 20 to 25% by mass 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 dredged 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 the NF P94-047 standard. This 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 agents of erosion, 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 seaside by marine 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. They are, for example, different from calcined sediments, mine tailings and / or foundry sludge. The first materials have undergone a high-temperature heat treatment which removes a large portion of organic matter; the second and third materials are loaded with metals. Conversely, the dredged sediments come from the sea and are controlled in terms of pollution (e.g.metal thresholds defined by the ministerial decree of August 9, 2006 and the decree of December 23, 2009). The dredging sediments used in the composition of the invention have in particular metal contents lower than these thresholds.

[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 dredged sediments have a particle size of at most about 100 μm, and particularly preferably at most about 60 μm. In other words, the dredged sediments used in the composition preferentially correspond to a fine fraction of dredged sediments.

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

[0027] The muddy silty sediments are characterized by a high content of SiO2 and / or AI2O3. X-ray diffraction analyses preferentially show similar mineralogies consisting mainly of quartz (SiC), Albite (NaAlSisOs) and Muscovite (KAl2(AISi30io)(OH,F)2).

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

[0029] Particularly preferably, the dredged sediments comprise at least approximately 8% by mass of AI2O3, and more particularly preferably at least approximately 10% by mass of AI2O3, 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 SiC / AkC mass ratio is greater than or equal to 2, particularly preferably ranges from 2.1 to 4.0, and more particularly preferably ranges from 2.8 to 3.1.

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

[0032] The dredging sediments used in the aqueous geopolymer composition may comprise at least about 2% by mass of clay, preferably at least about 3% by mass of clay, and even more preferably from about 4% to 10% by mass of clay, relative to the total mass of dredged sediments. 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 approximately 10% to 25% by mass of sand, relative to the total mass of the dredging sediments. This is also referred to as the sand fraction or sand 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 dredged sediments can be determined using the laser granulometry method.

[0038] Dredged sediments may also contain 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 dredged sediments can be determined by a thermal calcination test at 450°C according to 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] Sediments preferably have a specific surface area ranging from 0.200 m 2 / g at 0.700 m 2 / g, and particularly preferably 0.450 m 2 / g at 0.700 m 2 / g. This specific surface area reflects the quantity of gas that can be adsorbed to completely cover the surface of the sediments.

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

[0043] The alkali silicate can 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 of metakaolin approximately, and particularly preferably from 30 to 38% by mass of metakaolin approximately, 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 performance (e.g. CO2 emissions) is not interesting compared to the use of 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 materials 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-AI-O), ferro-silico-aluminate (-Fe-O-Si-O-AI-O), or alumino-phosphate (-AI-OPO-) units, created by a geopolymerization process (i.e. polycondensation). The most common geopolymers are those based on aluminosilicates designated under the term “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 oligo(sialate) type oligomers formed from a mixture of at least one aluminosilicate, an alkaline reagent (e.g. alkali metal silicate) and water.

[0058] In the present invention, the geopolymer may have the following formula: Mn [-(Si-O2)z-AI-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 make up a single oligomeric aluminosilicate chain. The latter depends, in turn, on the molar ratio of SiC / AkOs contained in the geopolymer. The choice of this ratio varies depending on the desired setting time and strength. As this value increases progressively from 1 to 3, a sialate, i.e., Mn(-Si-O-AI-O-)n, a sialatesiloxo, i.e., M n (Si-O-AI-O-Si-O-) n , or a disiloxo sialate, i.e. M n (-Si-O-AI-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 with little shrinkage, better dimensional stability, better compressive strength at more than 28 days, and preferably at 90 days, better durability and 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 a press electromechanical 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 quay dike, or pre-cast concrete, or for the manufacture of concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a quay dike, or pre-cast concrete (i.e. use of the aqueous geopolymer composition in accordance with the first subject of the invention as such).

[0064] The composition can in particular be used directly to make concrete without adding additives.

[0065] The aqueous geopolymer composition based on dredged sediments of the invention is used as a binder (geopolymer binder).

[0066] In the invention, the term "binder" means a compound which serves to agglomerate solid particles in the form of powder or aggregates.

[0067] In the aqueous geopolymer composition of the invention, the dredged 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.

[0068] The binder can be used in public works and construction, reducing CO2 emissions by 45% and achieving higher performance than Portland cement.

[0069] 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.

[0070] In one embodiment, the concrete does not include natural aggregates (sand, gravel, gravel) other than those present in the dredged sediments.

[0071] The concrete may be made of a geopolymer material in accordance with the second subject of the invention.

[0072] Reusing dredged sediment as a raw material for concrete design directly at the dredging site would allow companies to simplify onshore management, reduce costs and environmental impact and integrate their consumption model into a circular economy.

[0073] The present invention is illustrated by the following exemplary embodiments, to which it is however not limited.

[0074] Brief description of the drawings

[0075] The invention is illustrated by the following figures and examples.

[0076] Figure 1 shows the compressive strength of a geopolymer material in accordance with the invention and of materials not in accordance with the invention.

[0077] Figure 2 shows the porosity characteristics of a geopolymer material in accordance with the invention and of a material not in accordance with the invention.

[0078] Figure 3 shows scanning electron microscopy (SEM) images of a geopolymer material in accordance with the invention and a material not in accordance with the invention.

[0079] Examples

[0080] 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”, SiOz / NazO molar ratio = 1.7, density = 1.57 g / cm 3 , 43.80% by mass of NazO, 37.70% by mass of SiÛ2 and 10.20% by mass of AkCh, - metakaolin, “Argeco”, obtained by flash calcination of kaolinitic clay, - “CEM I 52.5 N PM” cement, “Calcia” (64% by mass of CaO, 19.9% ​​by mass of SiO2 and 3.9% by mass of AI2O3), - blast furnace slag, “Ecocem” (43.8% by mass of CaO, 37.7% by mass of SiO2 and 10.2% by mass of AI2O3).

[0081] Unless otherwise stated, all materials were used as received from the manufacturers, without purification.

[0082] Example 1: characterization of the dredged sediments used in the composition of the invention

[0083] In this example 1, dredged sediments from the Garonne were selected. The Garonne estuary is mainly composed of two distinct particle size fractions: sediments with a strong sandy tendency upstream of the estuary and silty-muddy sediments downstream. The silty-muddy sediments were recovered in Pauillac and left to evaporate in tanks perforated with a geotextile for 1 to 3 months. Drying was achieved by infiltration and evaporation of the water. All fractions of the sediment were recovered.

[0084] 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 grain 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.

[0085] The dredged sediments were also subjected to environmental tests in accordance with the decree of August 9, 2006 and the GEODE guide, which determines 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 NI and N2 thresholds.

[0086] The recovered dredged sediments comprise 41.38% by mass of SiO2, and 14.19% by mass of AI2O3. They have a SiO2 / AI2O3 mass ratio of 2.91.

[0087] The recovered dredged sediments comprise approximately 10,500 mg of organic matter per kg of sediment.

[0088] The recovered dredged sediments have a water content of 145% by mass, relative to the total mass of sediment and water, and then 30% by mass, relative to the total mass of sediment and water after drying in the tanks.

[0089] Example 2: preparation of a geopolymer material in accordance with the invention

[0090] 620g of dredged sediment in water as recovered and described in Example 1 (477g of dredged sediment in 143g of water) and 477g of metakaolin are introduced into a mixer sold by the company "CV Equipement", then mixed for 10 seconds. Once the resulting mixture is homogenized, 310g of an aqueous solution of alkali silicate (139.5g of alkali silicate in 170.5g 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.

[0091] The aqueous geopolymer composition is defined in Table 1 below:

[0092] [Table 1]

[0093] After curing for 28 days, a geopolymer material in accordance with the invention MG is obtained with a compressive strength of 7 MPa.

[0094] 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.

[0095] 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 (MO2), the metakaolin was removed and not replaced (MO3), or the amount of metakaolin used was less than 15% by mass and an alkali base was added (MO4).

[0096] MOI is obtained from an aqueous composition comprising 60% by mass of dredged 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.

[0097] M02 is obtained from an aqueous composition comprising 60% by mass of dredging 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.

[0098] M03 is obtained from an aqueous composition comprising 67% by mass of dredging sediment, 27% by mass of water and 6% by mass of sodium silicate. M03 is not part of the invention.

[0099] MO4 is obtained from an aqueous composition comprising 60% by mass of dredged sediment, 7% by mass of metakaolin, 27% by mass of water, and 6% by mass of sodium silicate. MO4 is not part of the invention.

[0100] Figure 1 shows the compressive strength of the different materials MG, MOI, MO2, MO3, and MO4. 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.

[0101] Figure 2 shows the porosity characteristics of MG and M04 materials, measured using a device sold under the trade name “AutoPore V” by the company “MICROMERITICS”. Figure 2 shows a refinement of the porosity for M04 compared to MG. The x-axis represents the pore size diameters in pm.

[0102] Figure 3 shows scanning electron microscopy (SEM) images of MG and M04 materials taken with a device sold under the trade name “MEB-FEG Zeiss Ultra55” by the company “ZEISS Group”.

[0103] From Figure 3, the MG geopolymer material has a more ordered and smoother structure indicating more complete geopolymerization.

Claims

Claims 1. Aqueous geopolymer composition, characterized in that it comprises dredging sediments, at least one alkali silicate and at least one metakaolin, 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, and in that the dredging sediments are untreated.

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 2.

4. Composition according to any one of the preceding claims, characterized in that the dredging sediments comprise at least 3000 mg of organic matter, per kg of sediments.

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 dredging sediments comprise silicon and aluminum, so that the SiC / AkOs mass 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 breakwater, or a pre-cast concrete, or for the manufacture of concrete, a filling grout, a concrete pavement, a compacted road layer, bricks, a retaining wall, a quayside breakwater, or a pre-cast concrete.

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

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