Low-carbon cement comprising raw earth

Abstract

Cement comprising: - at most 94% clinker; and - at least 6% of a mixture of raw earth comprising at least 10% phyllosilicates with at least one limestone filler and / or at least one pozzolan, said mixture comprising at least 20% raw earth.

Description

[0001] LOW CARBON CEMENT CONTAINING RAW EARTH

[0002] The present invention relates to a new low-carbon cement comprising raw earth.

[0003] The manufacture of binders, particularly hydraulic binders, and especially cements, essentially consists of calcining a mixture of carefully selected and measured raw materials, also known as "raw material." Firing this raw material produces an intermediate product, clinker, which, when ground with calcium sulfate and possibly added minerals, yields cement. The type of cement produced depends on the nature and proportions of the raw materials as well as the firing process. Several types of cement are distinguished: Portland cements (which represent the vast majority of cements produced worldwide), aluminous cements (or calcium aluminate cements), natural quick-setting cements, sulfoaluminate cements, sulfobelic cements, and other intermediate varieties.

[0004] The most common cements are Portland cements. Portland cements are made from Portland clinker, which is produced by clinkerizing a raw material rich in calcium carbonate in a kiln at a temperature of around 1450°C. The production of one tonne of Portland clinker results in the emission of significant quantities of CO2 (approximately 0.8 to 0.9 tonnes of CO2 per tonne of cement in the case of clinker).

[0005] However, in 2014, the quantity of cement sold worldwide was approximately 4.2 billion tons (source: French Cement Industry Association - SFIC). This figure, which is constantly increasing, has more than doubled in 15 years. The cement industry is therefore currently searching for a viable alternative to Portland cement, that is to say, cements with at least the same strength and quality characteristics as Portland cement, but which, during their production, emit less CO2.

[0006] During the production of clinker, the main component of Portland cement, CO2 emissions are linked to:

[0007] - up to 40% for heating the cement kiln, grinding and transport;

[0008] - up to 60% of this is due to so-called chemical CO2, or decarbonation. Decarbonation is a chemical reaction that occurs when limestone, the main raw material for the manufacture of Portland cement, is heated to a high temperature. The limestone is then transformed into quicklime and CO2 according to the following chemical reaction:

[0009] The natural carbonation of cement-based materials, particularly concrete, is a potential way to reduce the carbon footprint associated with cement manufacturing and use. However, although concrete made from these cements naturally recarbonates during its service life, accounting for 15% to 20% of the CO2 emitted during manufacturing, the overall carbon balance associated with Portland cement production remains positive. Therefore, it remains necessary to reduce CO2 emissions during Portland cement production and / or improve the processes for recycling concrete at the end of its life.

[0010] To reduce CO2 emissions related to Portland cement production, several approaches have been considered so far:

[0011] - the adaptation or modernization of cement processes in order to maximize the efficiency of heat exchange;

[0012] - the development of new "low carbon" binders such as sulfo-aluminous cements prepared from raw materials less rich in limestone and at a lower firing temperature, which allows a reduction in CO2 emissions of approximately 35%;

[0013] - or even the (partial) substitution of clinker in cements by materials that limit CO2 emissions.

[0014] Among the approaches mentioned above, the (partial) substitution of clinker in cements has been the subject of much development.

[0015] Among the substitute materials used, limestone filler (i.e., an inactive material) is a notable example. This substitution of clinker with limestone filler is now widely used but will face availability issues, particularly due to the need to preserve natural resources, the environment, and biodiversity. Materials derived from industrial recycling, such as fly ash from coal-fired power plants, can also be mentioned. However, the closure of coal-fired power plants is causing a shortage of good-quality fly ash. Furthermore, the development of activated natural pozzolans requires activation temperatures lower than those used to fire Portland clinker, especially with activated clays in LC3-type binders.

[0016] As of the date of the present invention, it therefore remains necessary to identify new substitute materials that will significantly reduce CO2 emissions during cement production while maintaining acceptable mechanical properties of construction materials prepared from these cements, in particular medium and long-term compressive strengths, at levels that allow their use.

[0017] The use of "raw" earth, that is to say uncalcined earth, and more specifically raw clays, for the preparation of building materials, particularly concrete, has been the subject of numerous developments.

[0018] Thus, "earth concrete" is a building material made from raw clayey earth, more commonly known as rammed earth or cob. These concretes nevertheless have limited mechanical properties and require organic additions (e.g., reinforcement of the concrete with plant fibers "macro-composites", mixing with organic substances "micro-composites", etc.) and / or inorganic additions (e.g., stabilization of the raw earth with quicklime or geopolymers, etc.).

[0019] International patent application WO-A-2020 / 141285 describes the use of raw clay as a substitute cementitious material without specifying the composition of the clays used. Furthermore, the use of a deflocculating agent is essential to obtain acceptable mechanical strength, which significantly increases the production cost of the material, both due to the cost of the agent itself and the complexity of the production process required.

[0020] However, it has now been found, quite surprisingly, that certain raw earths can be used as a substitute material for clinker in cements, thus making it possible to significantly lower the carbon footprint of the construction material finally prepared without reducing the mechanical properties, and in particular the medium and long-term compressive strengths of said material compared to materials prepared with the addition of limestone filler or pozzolana, and without the need for the addition of admixtures, deflocculating agents or activating agents.The use of these raw earths as a substitute material for clinker in cements therefore makes it possible to lower the carbon footprint associated with the production of the construction material by significantly reducing the amount of clinker to be produced to obtain said construction material, without requiring the use of additives or activating agents and while limiting the amount of limestone filler or pozzolana used.

[0021] Thus, the present invention relates to a cement comprising:

[0022] - at most 94% clinker; and at least 6% of a mixture of raw earth comprising at least 10% phyllosilicates with at least one limestone filler and / or at least one pozzolana, said mixture comprising at least 20% raw earth.

[0023] The use of raw earth as a substitute for clinker in cements according to the invention therefore makes it possible to lower the carbon footprint associated with the production of the construction material by significantly reducing the amount of clinker to be produced to obtain said construction material, without requiring the use of additives or activating agents and while limiting the amount of limestone filler or pozzolana used.

[0024] Within the scope of the present invention:

[0025] - The term "raw earth" means any uncalcined or uncooked earth. Preferably, "raw earth" means any uncalcined or uncooked earth containing at least 35% silt. Even more preferably, "raw earth" means any uncalcined or uncooked earth containing at least 35% silt and less than 25% clay. Most preferably, "raw earth" means any uncalcined or uncooked earth containing at least 35% silt, less than 25% clay, and less than 40% sand;

[0026] - The term "clinker" refers to any clinker, including Portland clinker as defined in standard EN 197-1, natural rapid cements as defined in standard NF P15-314, and sulfoaluminate clinker. Preferably, "clinker" refers to clinker comprising: o 1% to 67% C3S; o 10% to 32% C2S; o 0.5% to 18% C4AF; and o 0% to 11% C3A.

[0027] - The term "limestone filler" means any limestone filler as defined in standards NF EN 197-5 and 197-1, i.e., a filler with the following characteristics: o the calcium carbonate (CaCO3) content calculated from the calcium oxide content must be at least 40%; o the sum of the calcium carbonate and magnesium carbonate (CaCO3 and MgCO3) contents calculated from the calcium oxide and magnesium oxide content must be at least 75%; o the clay content determined by the methylene blue test is less than or equal to 1.20 g / 100 g of limestone filler; and o the total organic carbon (TOC) content is less than 0.50%;

[0028] - The term "pozzolan" means any pozzolan as defined in standard NF EN 197-1. A pozzolan can be natural (e.g., a material of volcanic origin or sedimentary rocks with an appropriate chemical and mineralogical composition), activated (e.g., a material of volcanic origin, clays, shales or sedimentary rocks, thermally activated) or a mixture of both. Preferably, the content of reactive SiC>2 is greater than or equal to 25%;

[0029] - The term "phyllosilicates" refers to all minerals formed by the stacking of tetrahedral layers where the tetrahedra share three out of four vertices, and the fourth vertex is connected to an octahedral layer occupied by different cations (notably Al, Mg, and Fe). Examples of phyllosilicates include 1:1 group phyllosilicates such as kaolinite or serpentine; 2:1 group phyllosilicates such as talc, muscovite, illite, or montmorillonite; and 2:1:1 group phyllosilicates such as chlorites;

[0030] - the term "tectosilicates" refers to all minerals formed by the association of tetrahedral elementary motifs [SiC ] 4 'by all their peaks. As an example of tectosilicates, we can notably cite the minerals of the quartz group, feldspathoids, feldspars or zeolites;

[0031] - The term "carbonates" refers to all minerals containing the carbonate ion [CO3] 2- Examples of carbonates include calcite, dolomite, magnesia, ankerite, vaterite, and aragonite;

[0032] - the term "adjuvant" means any adjuvant as defined in standard NF EN 934-2+A1, including plasticizers / water reducers, superplasticizers / high water reducers, water retainers, air-entraining adjuvants, setting accelerators, hardening accelerators, setting retarders or mass water repellents;

[0033] - The term "activating agent" refers to any agent that activates a precursor such as blast furnace slag, fly ash, or metakaolin, resulting in the hardening of the mixture. Examples of activating agents include alkali activators such as sodium or potassium hydroxide, sodium or potassium silicate, sodium or potassium carbonate, or sodium or potassium sulfate;

[0034] - The term "flocculating agent" refers to any agent that allows the dissociation of aggregates and colloids in aqueous suspension; and

[0035] - The term "building material" refers to mortar or concrete.

[0036] In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement:

[0037] - C represents CaO;

[0038] - A represents AI2O3;

[0039] - F represents Fe2Û3;

[0040] - S represents SiC>2; and

[0041] - $ represents SO3.

[0042] In the context of the present invention, "total organic carbon" or "TOC" corresponds to the amount (% w / w) of carbon that is not in inorganic form contained in an entity (e.g., raw earth) relative to the total weight of carbon contained in said entity (e.g., said raw earth). TOC includes, in particular, carbon contained in organic compounds and adsorbed CO2.

[0043] The COT value of an entity is determined according to the following formula:

[0044] COT=CT-CIT in which

[0045] "CT" denotes the quantity (% w / w) of total carbon of the entity

[0046] "CIT" denotes the quantity (% w / w) of total inorganic carbon of the entity.

[0047] Organic carbon (OCT) values ​​can be obtained by elemental analysis using a carbon analyzer, either by the difference between total carbon (TC) and total organic carbon (CIT) content (the latter being obtained after prior calcination of the sample to be analyzed at 500°C), or using a carbon analyzer that allows for a gradual temperature increase and temperature plateaus to separate the different carbon species in a sample. In the context of the present invention, the "methylene blue value" refers to the amount of methylene blue that can be adsorbed by a material suspended in water. The methylene blue value is directly proportional to the 0 / 50 mm fraction in the case of soil analysis (VBS) according to standard NF EN 17542-3.The value of methylene blue is expressed in grams of dye adsorbed per kilogram of the granular fraction in the case of aggregate analysis (MB or MB F) according to the standard NF EN 933-9 used to define a limestone filler in the standard EN 197-1.

[0048] In the context of the present invention, "specific surface area" means the total surface area (internal and external surface) of a sample divided by its mass determined by measuring the amount of gas physically adsorbed on the surface of a sample according to the Bunauer, Emmett and Teller (BET) method according to ISO 9277:2010.

[0049] In the context of the present invention, "dgo" corresponds to the diameter below which 90% of the total mass of the particles in the sample under consideration lies. This can be determined by any method known to those skilled in the art, in particular by the wet particle size distribution method described in standard NF EN ISO 17892-4.

[0050] In the context of the present invention, "d25" corresponds to the diameter below which 25% of the total mass of the particles in the sample under consideration lies. This can be determined by any method known to those skilled in the art, in particular by the wet particle size distribution method described in standard NF EN ISO 17892-4.

[0051] In the context of the present invention, "dso" corresponds to the diameter below which 50% of the total mass of the particles in the sample under consideration lies. This can be determined by any method known to those skilled in the art, in particular by the wet particle size distribution method described in standard NF EN ISO 17892-4.

[0052] In the context of the present invention, "dgo" corresponds to the diameter below which 90% of the total mass of the particles in the sample under consideration lies. This can be determined by any method known to those skilled in the art, in particular by the wet particle size distribution method described in standard NF EN ISO 17892-4.

[0053] Finally, within the framework of the present invention, the proportions expressed in % correspond to mass percentages relative to the total weight of the entity (e.g. cement, earth, etc.) considered.

[0054] The present invention therefore relates to a cement containing raw earth and having the aforementioned technical characteristics. Preferably, the cement according to the invention has the following characteristics, chosen alone or in combination: the cement comprises at most 80% clinker, preferably at most 65% clinker, most preferably at most 50% clinker; the cement comprises at least 10% clinker, preferably at least 20% clinker, most preferably at least 30% clinker; the cement comprises at least 20% of the raw earth mixture with at least one limestone filler and / or at least one pozzolan, preferably at least 35% of said mixture, most preferably at least 50% of said mixture; the raw earth mixture with at least one limestone filler and / or at least one pozzolan contains at least 30% raw earth, preferably at least 50% raw earth;The cement comprises a mixture of raw earth, at least one filler, and at least one pozzolan; the raw earth contains from 10% to 70% phyllosilicates, preferably from 10% to 65% phyllosilicates, most preferably from 15% to 60% phyllosilicates. The raw earth contains from 5% to 85% tectosilicates, preferably from 10% to 80% tectosilicates; the raw earth contains less than 74% carbonates, preferably less than 70% carbonates, most preferably less than 65% carbonates; the specific surface area of ​​the raw earth varies from 1 m². 2 / g at 45 m 2 / g; preferably still 2 m 2 / g at 40 m 2 / g; in a completely preferred manner of 3 m 2 / g at 35 m 2 / g; and / or the TOC of the raw earth is less than 0.8%, preferably less than 0.7%, most preferably less than 0.6%. The particle size distribution (dgo) of the raw earth is less than or equal to 200 µm, preferably less than or equal to 175 µm, preferably less than or equal to 150 µm, most preferably less than or equal to 100 µm; the particle size distribution (chs) of the raw earth is greater than or equal to 2 µm, preferably greater than or equal to 2.5 µm, preferably greater than or equal to 3 µm, most preferably greater than or equal to 4 µm; the particle size distribution (dso) of the raw earth is greater than or equal to 3 µm, preferably greater than or equal to 4 µm, most preferably greater than or equal to 5 µm; the particle size distribution of the raw earth is less than or equal to 200 pm, preferably less than or equal to 175 pm, preferably even less than or equal to 150 pm, most preferably less than or equal to 125 pm;the blue value of the raw earth is less than or equal to 6.00 g of dye per 100 g of earth, preferably less than or equal to 5.00 g of dye per 100 g of earth, preferably less than or equal to 4.00 g of dye per 100 g of earth, most preferably less than or equal to 3.50 g of dye per 100 g of earth; the blue value of the raw earth is greater than or equal to 0.100 g of dye per 100 g of earth, preferably 0.200 g of dye per 100 g of earth, preferably greater than or equal to 0.300 g of dye per 100 g of earth; the raw earth contains from 1% to 40% CaO, preferably from 3% to 37% CaO, most preferably from 5% to 35% CaO; raw earth contains from 5% to 90% SiO2, preferably still 10% to 85% SiO2; raw earth contains from 1% to 30% A Os, preferably from 2% to 25% ALOs; raw earth is free from adjuvant, flocculating agent and / or activating agent;and / or the raw earth is excavated or uncovered earth.

[0055] The cement according to the present invention is thus obtained from clinker and a mixture of raw earth with at least one limestone filler and / or at least one pozzolan. The raw earths used in the context of the present invention can be used without prior treatment or obtained by crushing or grinding to achieve the desired particle size. In this respect, any process known to those skilled in the art can be implemented. The low-carbon cement according to the present invention can be used to prepare a construction material. Thus, the present invention also relates to a construction material comprising a cement as defined above. The present invention can be illustrated, without limitation, by the following examples.

[0056] Example 1 - Raw earth

[0057] Different types of raw soil are obtained by drying followed by crushing, sieving and / or grinding in order to obtain the desired particle size.

[0058] The compositions and characteristics of the raw earths used (Earths 1 to 3) are reported in the following Table 1, in comparison with a limestone filler usually used in the cement industry.

[0059]

[0060] Table 1 - Composition and characteristics of raw earth according to the invention 2 - Cements according to the invention

[0061] Different reference cements are mixed with different quantities of raw earth from example 1 and / or filler according to the following proportions: cement 1: 70% CEM I 52.5 R + 30% earth 1; cement 2: 70% CEM I 52.5 R + 30% earth 2;

[0062] - cement 3: 70% CEM ll / B-LL 42.5 R + 30% earth 1; cement 4 70% CEM ll / B-LL 42.5 R + 30% earth 2;

[0063] - cement 5: 70% CEM IV / A (P) 42.4 R + 30% earth 1; cement 6: 70% CEM IV / A (P) 42.4 R + 30% earth 2; cement 7: 45% CEM I 52.5 R + 40% earth 1 + 15% activated pozzolan; cement 8: 60% CEM I 52.5 R + 20% earth 1 + 20% limestone filler (betocarb HP OMYA);

[0064] - Ref.1: CEM I 52.5 R;

[0065] - Ref.2: CEM ll / B-LL 42.5 R;

[0066] - Ref.3: CEM IV / A(P) 42.4 R;

[0067] Ref.4: CEM I 52.5 R + 30% limestone filler (Ref.);

[0068] - Ref. 5: CEM II / B-LL 42.5 R + 30% limestone filler (Ref.); and

[0069] - Ref.6: CEM IV / A(P) 42.4 R + 30% limestone filler (Ref.).

[0070] The compositions of the cements thus obtained are reported in Tables 2.1 and 2.2 below.

[0071]

[0072] Table 2.1 - Cements according to the invention

[0073] Table 2.2 - Reference cements Example 3 - Mechanical performance of cements 1 to 6

[0074] The compressive strength of cements 1 to 6 obtained in example 2 was measured on pure paste at different time intervals (1, 2, 7 and 28 days).

[0075] To do this, the binder is mixed with demineralized water in a water / binder ratio of 0.5 using a paddle mixer for 2 minutes at 1200 rpm. The resulting pure paste is placed in modified acrylonitrile styrene acrylate cubes (2x2x2 cm). 3 The cubes were stored for 24 hours in a humid room (100% humidity at 20°C) and then in dry containers with a saturated relative humidity (RH) at 20°C. Mean and standard deviation compressive strengths were obtained from 4 cubes per time period. The results are reported in Tables 3.1 (cements according to the invention) and 3.2 (reference cements) below.

[0076] Table 3.1 - Compressive strength of cements according to the invention

[0077] Table 3.2 - Compressive strength of reference cements

[0078] We note a decrease in the mechanical performance of the cements of the invention compared to reference cements 1 to 3 (i.e. reference cements without the addition of filler), although these remain acceptable.

[0079] On the other hand, we observe that: the mechanical performance of cements 1 & 2 of the invention is similar to that obtained with reference cement 4 (i.e. reference cement with added filler); the mechanical performance of cements 3 & 4 of the invention is similar to that obtained with reference cement 5 (i.e. reference cement with added filler); and the mechanical performance of cements 5 & 6 of the invention is similar to that obtained with reference cement 6 (i.e. reference cement with added filler).

[0080] The raw earth according to the invention therefore constitutes a credible alternative to the limestone fillers classically used, without the need for the addition of adjuvants or activating agents.

[0081] Example 4 - Mechanical performance of construction materials prepared from cements 7 and 8

[0082] Concretes are prepared from cements 7 and 8 of example 2.

[0083] The concrete compositions thus obtained are reported in the following Table 4.

[0084] Table 4 - Concretes according to the invention

[0085] The compressive strength of Concretes 1 and 2 was measured on 11 x 22 cm cylindrical specimens at 28 days according to standard NF EN 12390-3 with a water / cement ratio of 0.45.

[0086] The observed resistances were respectively 26.5 MPa and 33.0 MPa for Concretes 1 and 2 compatible with the concrete category C25 / 30.

Claims

DEMANDS 1. Cement comprising: - at most 94% clinker; and at least 6% of a mixture of raw earth comprising at least 10% phyllosilicates with at least one limestone filler and / or at least one pozzolana, said mixture comprising at least 20% raw earth.

2. Cement according to claim 1, characterized in that it comprises at most 80% clinker.

3. Cement according to claim 2, characterized in that it comprises at most 65% clinker.

4. Cement according to any one of claims 1 to 3, characterized in that it comprises at least 20% of the raw earth mixture with at least one limestone filler and / or at least one pozzolana.

5. Cement according to claim 4, characterized in that it comprises at least 35% of the raw earth mixture with at least one limestone filler and / or at least one pozzolan 6. Cement according to any one of claims 1 to 5, characterized in that the raw earth mixture with at least one limestone filler and / or at least one pozzolana contains at least 30% earth.

7. Cement according to any one of claims 1 to 6, characterized in that the raw earth contains from 15% to 60% phyllosilicates.

8. Cement according to any one of claims 1 to 7, characterized in that the raw earth contains from 5% to 85% tectosilicates.

9. Cement according to any one of claims 1 to 8, characterized in that the raw earth contains less than 74% carbonates, 10. Cement according to any one of claims 1 to 9, characterized in that the specific surface area of ​​the raw earth varies from 1 m 2 / g at 45 m 2 / g.

11. Cement according to any one of claims 1 to 10, characterized in that the total organic carbon (TOC) content of the raw earth is less than 0.8%.

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