Use of raw earth as a substitute material for clinker

Abstract

USE OF RAW EARTH AS A CLINKER SUBSTITUTION MATERIAL Use of raw earth with a particle size d90 less than or equal to 200 µm and a particle size d25 greater than or equal to 2 µm, and with a blue value less than or equal to 6.00 g of dye per 100 g of earth as a clinker substitute material.

Description

Title of the invention: Use of raw earth as a substitute material for clinker

[0001] The present invention relates to the use of raw earth as a substitute material for clinker.

[0002] 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.

[0003] The most common cements are Portland cements. Portland cements are obtained 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 is accompanied by 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).

[0004] 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 seeking a viable alternative to Portland cement, that is, cements with at least the same strength and quality characteristics as Portland cements, but which release less CO2 during their production.

[0005] During the production of clinker, the main constituent of Portland cement, CO2 emissions are linked to:

[0006] - up to 40% for heating the cement kiln, grinding and transport;

[0007] - up to 60% of so-called chemical CO2, or decarbonation.

[0008] 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] [Chem.l] CaCCh 4 GaO > COz

[0010] The natural carbonation of cement-based materials, particularly concrete, is a potential means of reducing the carbon footprint associated with the manufacturing process and the use of cement. However, although concrete made from these cements naturally recarbonates during the service life of the structures, 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 end-of-life concrete.

[0011] To reduce CO2 emissions related to the production of Portland cement, several approaches have been considered so far:

[0012] - the adaptation or modernization of cement processes in order to maximize the efficiency of heat exchange;

[0013] - the development of new "low carbon" binders such as sulfo- cements aluminous products prepared from raw materials less rich in limestone and at a lower cooking temperature, which allows a reduction in CO2 emissions of approximately 35%;

[0014] - or even the (partial) substitution of clinker in cements by materials allowing to limit CO2 emissions.

[0015] Among the above approaches, that of (partial) substitution of clinker in cements has been the subject of numerous developments.

[0016] Among the substitute materials used, limestone filler (i.e., an inactive material) can be mentioned in particular. This substitution of clinker with limestone filler is now widely used but will encounter problems of availability, notably due to the need to preserve natural resources as well as the environment and biodiversity.

[0017] As of the date of the present invention, it therefore remains necessary to identify new substitute materials that make it possible to significantly reduce CO2 emissions during the production of cement while maintaining the acceptable mechanical properties of construction materials prepared from these cements, in particular the medium and long-term compressive strengths, at levels allowing their use.

[0018] The use of "raw" earths, i.e. uncalcined, and more specifically of raw clays, for the preparation of construction materials, in particular concretes, has been the subject of numerous developments.

[0019] Thus, "earth concrete" is a building material based on raw clayey earth, better known as rammed earth or cob. These concretes nevertheless have limited mechanical properties and require organic additions (e.g., fiber 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.).

[0020] International patent application WO-A-2020 / 141285 describes the use of raw clay as a substitute cementitious material. However, the use of a deflocculating agent is essential to obtain acceptable mechanical strengths, which significantly increases the production cost of the material, both due to the cost of the agent and the complexity of the production process that must be implemented.

[0021] However, it has now been discovered, quite surprisingly, that certain raw earths can be used as a substitute for clinker in cements, thus significantly reducing the carbon footprint of the final construction material without compromising its mechanical properties, particularly its medium- and long-term compressive strength, compared to materials prepared with the addition of limestone filler, and without the need for admixtures, deflocculating agents, or activators. The use of these raw earths as a substitute for clinker therefore reduces the carbon footprint associated with the production of the construction material by significantly decreasing the amount of clinker required to obtain said construction material, without necessitating the use of limestone filler, admixtures, or activators.

[0022] Thus, the present invention relates to the use of raw earth having a particle size d90 less than or equal to 200 pm and a particle size d25 greater than or equal to 2 pm, and having a blue value less than or equal to 6.00 g of dye per 100 g of earth as a substitute material for clinker.

[0023] The use of raw earth with these technical characteristics as a substitute for clinker 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 limestone filler or additives or activating agents.

[0024] Within the scope of the present invention:

[0025] - the term "raw earth" means any earth that has not been calcined or cooked;

[0026] - The term "clinker substitute material" means any composition capable of to partially replace clinker in the preparation of a cementitious composition while allowing for an increase in the performance of the cementitious binder resulting from this combination;

[0027] - the term "phyllosilicates" refers to all minerals formed by 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;

[0028] - the term "tectosilicates" refers to all minerals formed by association tetrahedral elementary motifs [SiO4]4 at all their vertices. Examples of tectosilicates include minerals from the quartz group, feldspathoids, feldspars, and zeolites;

[0029] - the term "carbonates" refers to all minerals containing the carbonate ion [CO3]2 Examples of carbonates include calcite, dolomite, magnesia, ankerite, vaterite, aragonite;

[0030] - 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;

[0031] - The term "activating agent" means any agent that enables the activation of a precursor such as blast furnace slag, fly ash or metakaolins causing the mixture to harden. 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;

[0032] - The term "deflocculating agent" means any agent that allows the dissociation of aggregates and colloids in aqueous suspension; and

[0033] - "construction material" means mortar or concrete.

[0034] In the context of the present invention, the following notations are adopted for to identify the mineralogical components of cement:

[0035] - C represents CaO;

[0036] - A represents A12O3;

[0037] - F represents Fe2O3;

[0038] - S represents SiO2; and

[0039] - $ represents SO3.

[0040] In the context of the present invention, "total organic carbon" or "TOC" corresponds to the quantity (% 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.

[0041] The COT value of an entity is determined according to the following formula:

[0042] COT=CT-CIT

[0043] in which - "CT" denotes the quantity (% w / w) of total carbon of the entity - "CIT" refers to the quantity (% w / w) of total inorganic carbon of the entity.

[0044] Organic carbon content values ​​TOC can be obtained by elemental analysis with a carbon analyzer either by difference of carbon content TC and IT, the latter being obtained after prior calcination of the sample to be analyzed at 500°C, or with the help of a carbon analyzer allowing a gradual temperature rise and temperature plateaus in order to separate the different carbon species of a sample.

[0045] In the context of the present invention, the "methylene blue value" refers to the quantity 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 methylene blue value 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 standard NF EN 933-9, which is used to define a limestone filler in standard EN 197-1.

[0046] 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.

[0047] In the context of the present invention, "d90" 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.

[0048] 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 a person skilled in the art. in particular by the wet particle size distribution method described in standard NF EN ISO 17892-4.

[0049] 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., land) considered.

[0050] The present invention therefore relates to the use of raw earth with a particle size d90 of 200 µm or less and a particle size d25 of 2 µm or more, and a blue value of 6.00 g of dye per 100 g of earth or less, as a substitute material for clinker. Preferably, the raw earth has the following characteristics, chosen alone or in combination: - the d90 particle size of the raw earth is less than or equal to 175 pm, preferably less than or equal to 150 pm, most preferably less than or equal to 100 pm; - the particle size d25 of the raw earth is greater than or equal to 2.5 pm; preferably greater than or equal to 3 pm, most preferably greater than or equal to 4 pm; - the blue value of the raw earth is 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; - 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 1% to 30% Al2O3, preferably 2% to 25% Al2O3; - raw earth contains 5% to 70% phyllosilicates, preferably 10% to 65% phyllosilicates, most preferably 15% to 60% phyllosilicates. - raw earth contains from 5% to 85% tectosilicates, preferably still from 10% to 80% tectosilicates; - raw earth contains less than 74% carbonates, preferably even less than 70% carbonates, most preferably less than 65% carbonates; - the specific surface area of ​​raw earth varies from 1 m2 / g to 45 m2 / g; preferably from 2 m2 / g to 40 m2 / g; most preferably from 3 m2 / g to 35 m2 / g; - the TOC of raw earth is less than 0.8%, preferably even less than 0.7%, most preferably less than 0.6%; - the raw earth is free of additives, flocculating agents and / or activating agents; and / or - raw earth is earth from excavation or discovery.

[0051] The raw earth used in the context of the present invention can be used without prior treatment or obtained by optional drying followed by crushing, sieving and / or grinding to obtain the desired particle size. In this respect, any process known to those skilled in the art can be implemented.

[0052] The present invention can be illustrated in a non-limiting way by the following examples. Example 1 - Raw earth

[0053] Different raw earths are obtained by drying followed by crushing, sieving and / or grinding in order to obtain the desired particle size.

[0054] 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.

[0055] [Tables] Composition (% (w / w)) / Characteristics Raw Earth 1 (Earth 1) Raw Earth 2 (Earth 2) Raw Earth 3 (Earth 3) Limestone Filler (Ref.) SiO2 59.32 54.78 22.51 3.68 Al2O3 15.6 17.85 7.12 1.2 Fe2O3 5.86 5.74 2.69 0.62 CaO 5.5 3.99 33.28 51.57 MgO 1.85 4.04 2.02 0.67 SO3 0.01 0.05 0.30 0.42 k2O 2.47 3.59 1.91 0.38 Na₂O 1.13 2.03 0.10 0.03 SrO₂ 0.03 0.01 0.09 0.03 TiO₂ 0.77 1.00 0.37 0.06 p₂O₅ 0.2 0.33 0.08 0.02 MnO₂ 0.13 0.15 0.04 0.01 Cl₂ 0.012 0.007 0.004 0.021 Loss on ignition (950°C) (%) 6.69 6.15 29.49 41.11 Methylene blue value (g / 100 g of soil) 1.0 2.8 2.6 0.5 Specific surface area (m² / g) 7.8 5.9 22.6 12.2 TOC (%) 0.23 0.13 0.22 0.25 Phyllosilicates (% (w / w)) 45.8 63.8 21.1 1.3 Tectosilicates (% (w / w)) 45.6 33.2 15.6 1.8 Carbonates (% (w / w)) 8.7 2.6 62.4 96.9 d9o(pm) 90 70 48 322 d25(pm) 4.5 8.0 2 3.6

[0056] Table 1 - Composition and characteristics of raw earth according to the invention Example 2 - Cements according to the invention

[0057] 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; cement 3: 70% CEM II / B-LL 42.5 R + 30% earth 1; cement 4: 70% CEM II / B-LL 42.5 R + 30% earth 2; 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 pozzolana; - Cement 8: 60% CEM I 52.5 R + 20% earth 1 + 20% limestone filler (betocarb) HP OMYA); Ref. 1: CEM I 52.5 R; Ref.2: CEM IVB-LL 42.5 R; Ref.3: CEM IV / A(P) 42.4 R; Ref.4: CEM I 52.5 R + 30% limestone filler (Ref.); Ref. 5: CEM IVB-LL 42.5 R + 30% limestone filler (Ref.); and Ref.6: CEM IV / A(P) 42.4 R + 30% limestone filler (Ref.).

[0058] The compositions of the cements thus obtained are reported in Tables 2 and 3 below.

[0059] [Tables2] Cement (% w / w) 1 2 3 4 5 6 7 8 Cement used Clinker Portland 65.1 65.1 49.7 49.7 49.9 49.9 41.9 55.8 Limestone filler 0 0 15 15 0 0 0 20 Natural pozzolan 0 0 0 0 13.2 13.2 0 0 Activated pozzolan 0 0 0 0 0 0 15 0 Secondary constituents 0.7 0.7 0.7 0.7 2.6 2.6 0.4 0.6 Calcium sulfate (EN 197-1) 4.2 4.2 4.6 4.6 4.3 4.3 2.7 3.6 Additions Earth 1 30 0 30 0 30 0 40 20 Earth 2 0 30 0 30 0 30 0 0

[0060] Table 2 - Cements according to the invention

[0061] [Tables3] Cement (% w / w) Ref.1 Ref.2 Ref.3 Ref.4 Ref.5 Ref.6 Cement used Clinker 93.1 71.1 71.3 65.1 49.7 49.9 Limestone filler 0 21.5 0 0.0 15.0 0 Natural pozzolan 0 0 18.8 0.0 0 13.2 Activated pozzolan 0 0 0 0.0 0 0 Secondary constituents 0.9 0.9 3.8 0.7 0.7 2.6 Calcium sulfate (EN 197-1) 6.0 6.5 6.1 4.2 4.6 4.3 Added limestone filler 0 0 0 30 30 30

[0062] Table 3 - Reference cements

[0063] Example 3 - Mechanical performance of cements 1 to 6

[0064] The compressive strength of cements 1 to 6 obtained in example 2 was measured on pure paste at different time points (1, 2, 7 and 28 days).

[0065] 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 cm³). The cubes were stored for 24 hours in a humid room (100% humidity at 20°C) and then stored in dry containers at saturation relative humidity (RH) at 20°C. The mean and standard deviation of the compressive strengths were obtained from 4 cubes per time period.

[0066] The results obtained are reported in the following Tables 4 (cements according to the invention) and 5 (reference cements).

[0067] [Tables4] Cement 1 2 3 4 5 6 Rc (in MPa) at 1 day 16.0+1.0 19.5 + 0.7 12.3 + 0.2 13.2 + 0.3 8.5 + 0.2 9.8 + 0.2 Rc (in MPa) at 2 days 25.2+1.7 28.7 + 1.8 18.9+1.3 18.7 + 0.7 15.2 + 0.7 15.6 + 1.9 Rc (in MPa) at 7 days 33.5 + 2.2 32.7 + 2.4 23.0+1.0 23.2+1.3 23.6 + 2.7 23.5 + 1.5 Rc (in MPa) at 28 days 41.1+2.3 41.3 + 2.5 25.4 + 1.9 25.8 + 0.8 34.4 + 3.9 29.1 + 2.0

[0068] Table 4 - Compressive strength of cements according to the invention

[0069] [Tables5] Cement Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ref. 5 Ref. 6 Rc (in MPa) at 1 day 23.3 + 2.3 20.0 + 0.6 13.5 + 0.8 16.8 + 0.6 12.8 + 0.6 10.6 + 0.4 Rc (in MPa) 45.4 + 1.1 29.7 + 3.7 27.4 + 1.1 23.4 + 1.0 18.6 + 0.7 17.2 + 0.7 2-day Rc (in MPa) 7-day Rc 47.6 + 3.9 37.5 + 1.2 33.4 + 1.5 36.4 + 1.1 25.2 + 0.6 28.0 + 1.4 28-day Rc (in MPa) 65.1 + 9.3 41.4 + 1.2 46.2 + 1.2 40.6 + 2.6 27.9 + 0.4 32.0 + 2.0

[0070] Table 5 - Compressive strength of reference cements

[0071] A decrease in the mechanical performance of the cements of the invention is noted in comparison with reference cements 1 to 3 (i.e. reference cements without the addition of filler), although these remain acceptable.

[0072] 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 addition of filler).

[0073] 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.

[0074] Example 4 - Mechanical performance of prepared construction materials from cements 7 and 8

[0075] Concretes are prepared from cements 7 and 8 of example 2.

[0076] The concrete compositions thus obtained are reported in the following Table 6.

[0077] [Tableauxô] Ingredients Concrete 1 Concrete 2 Cement 7 350 kg / m3 - Cement 8 - 300 kg / m3 Sand 0 / 4 695 kg / m3 737 kg / m3 Gravel 4 / 11 367 kg / m3 389 kg / m3 Gravel 11 / 22 774 kg / m3 821 kg / m3 Admixture (Tempo 11) 0.9% 0.7% Total water content: 158 kg / m³ 135 kg / m³

[0078] Table 6 - Concretes according to the invention

[0079] The compressive strength of Concretes 1 and 2 was measured on cylindrical specimens 11 x 22 cm at 28 days according to standard NF EN 12390-3 with a water / cement ratio of 0.45.

[0080] The observed resistances were respectively 26.5 MPa and 33.0 MPa for Concretes 1 and 2 compatible with concrete category C25 / 30.

Claims

Demands

1. Use of raw earth having a particle size d90 less than or equal to 200 pm and a particle size d25 greater than or equal to 2 pm, and having a blue value less than or equal to 6.00 g of dye per 100 g of earth as a substitute material for clinker.

2. Use according to claim 1, characterized in that the particle size d90 of the raw earth is less than or equal to 175 pm.

3. Use according to claim 1 or 2, characterized in that the particle size d25 of the raw earth is greater than or equal to 2.5 pm.

4. Use according to any one of claims 1 to 3, characterized in that the blue value of the raw earth is less than or equal to 5.00 g of dye per 100 g of earth.

5. Use according to any one of claims 1 to 4, characterized in that the blue value of the raw earth is greater than or equal to 0.100 g of dye per 100 g of earth.

6. Use according to any one of claims 1 to 5, characterized in that the raw earth contains from 1% to 40% CaO.

7. Use according to any one of claims 1 to 6, characterized in that the raw earth contains from 5% to 90% SiO2.

8. Use according to any one of claims 1 to 7, characterized in that the raw earth contains from 1% to 30% Al2O3.

9. Use according to any one of claims 1 to 8, characterized in that the raw earth contains from 5% to 70% phyllosilicates.

10. Use according to any one of claims 1 to 9, characterized in that the raw earth contains from 5% to 85% tectosilicates.

11. Use according to any one of claims 1 to 10, characterized in that the raw earth contains less than 74% carbonates,

12. Use according to any one of claims 1 to 11, characterized in that the specific surface area of ​​the raw earth varies from 1 m2 / g to 45 m2 / g.

13. Use according to any one of claims 1 to 12, characterized in that the TOC of the raw earth is less than 0.8%,