USE OF MARL FOR THE PREPARATION OF A POZZOLANIC MATERIAL

Abstract

USE OF A MARL FOR THE PREPARATION OF A POZZOLANIC MATERIAL The present invention relates to the use of a marl comprising: more than 45% calcite; and at least 1% kaolinite; for the preparation of a pozzolanic material.

Description

Title of the invention: USE OF MARL FOR THE PREPARATION OF A POZZOLANIC MATERIAL

[0001] The present invention relates to the use of a marl for the preparation of a pozzolanic material.

[0002] The manufacture of hydraulic binders, and in particular that of cements, consists essentially of calcining a mixture of carefully chosen and measured raw materials, also referred to as "raw". The firing of this raw material produces an intermediate product, clinker, which, when ground with possible mineral additions, will produce cement. The type of cement produced depends on the nature and proportions of the raw materials as well as the firing process. There are several types of cement: Portland cements (which represent the vast majority of cements produced in the world), aluminous cements (or calcium aluminate cements), natural quick-setting cements, sulfo-aluminous cements, sulfo-belitic cements and other intermediate varieties.

[0003] The most widespread cements are Portland cements. Portland cements are obtained from Portland clinker, obtained after clinkering at a temperature of around 1450°C a raw material rich in calcium carbonate in a kiln. The production of one tonne of Portland cement is accompanied by the emission of very large quantities of CO2 (approximately 0.8 to 0.9 tonnes of CO2 per tonne of cement in the case of a CEM I).

[0004] However, in 2019, the quantity of cement sold worldwide was around 4.1 billion tonnes (source: Syndicat Français de l'Industrie Cimentière - SFIC). This figure, which is constantly increasing, has more than doubled in 15 years. The cement industry is therefore today looking for a valid alternative to Portland cement, i.e. cements with at least the same strength and quality characteristics as Portland cements, but which, during their production, release less CO2.

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

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

[0007] - up to 60% to 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: CaCCfe CaO + CO2

[0009] To reduce CO2 emissions linked to the production of Portland cement, several approaches have been considered so far:

[0010] - the adaptation or modernization of cement processes in order to maximize the heat exchange efficiency;

[0011] - the development of new “low carbon” binders such as sulfo-cements aluminous prepared from raw materials with less lime content and at a lower firing temperature, which allows a reduction in CO2 emissions of around 35%;

[0012] - or even the (partial) substitution of clinker in cements by materials to limit CO2 emissions.

[0013] Among the above approaches, that of the (partial) substitution of clinker in cements has been the subject of numerous developments. Two avenues have been mainly explored: the substitution of clinker by limestone filler and the substitution of clinker by so-called "pozzolanic" materials.

[0014] The substitution of clinker by limestone filler is limited due to its low chemical reactivity. Such a substitution therefore leads to a dilution effect which is accompanied by a significant drop in resistance for high levels of substitution.

[0015] On the other hand, the substitution of clinker by active or “pozzolanic” materials is accompanied by a much smaller reduction in resistance and for some of them by an increase in resistance.

[0016] A pozzolanic material generally designates any material having “pozzolanic properties”, that is to say capable of combining at room temperature and in the presence of water with lime or portlandite formed during the hydration of cement to give very slightly soluble hydrates capable of generating additional resistance in the long term.

[0017] Portland cement is in fact mainly made up of two types of anhydrous phases: calcium silicates (C3S and C2S - in which C represents CaO and S represents SiO2) and calcium aluminates (C2A and C4AF - in which C represents CaO, A represents A12O3 and F represents Fe2O3). It also contains a small amount of free lime.

[0018] It is the hydration of the silicate phases which generates the resistances thanks to the formation of gel-type hydrates: the hydrated calcium silicates CSH according to the following equations (not balanced): CsS + H-> CSH + CH CaS + H -> CSH + CH

[0019] in which C represents CaO, S represents SiO2 and H represents H2O.

[0020] Portlandite “CH” is a co-product of the hydration of calcium silicates. It represents between 15 and 20% by mass of the fully hydrated cement in the case of a CEMI.

[0021] Pozzolanic material is a source of amorphous and highly reactive silica and / or alumina. When mixed with cement, it will react with portlandite to form new hydrates: AtS + CH -> CASH

[0022] in which A represents A12O3, C represents CaO, S represents SiO2 and H represents H2O.

[0023] The pozzolanic reaction, slower and later, therefore allows the portlandite to be consumed to form secondary or late CSHs which are generally richer in alumina than the CSHs from silicates; they are generally referred to as CASHs for this reason. Like CSHs, CASHs are hydrates which are little or not crystallized and which close the porosity and generate an increase in resistance in the longer term.

[0024] At the date of the present invention, different pozzolanic materials are used:

[0025] - so-called “natural” pozzolans which are volcanic rocks rich in silica and naturally amorphous alumina;

[0026] - fly ash from electricity production in power plants coal-fired thermal plants, consisting mainly of silica, alumina and iron oxide;

[0027] - silica fume from the reduction of quartz by carbon during the production of silicon and iron / silicon alloys;

[0028] - blast furnace slag, obtained in the steel industry during the production of cast iron, almost entirely amorphous, consisting of silica, alumina but also calcium and magnesium oxide; and

[0029] - calcined clays which are synthetic pozzolans obtained by the calcination at temperatures ranging from 600°C to 900°C of clays, in particular kaolinitic, illitic or montmorillonitic clays.

[0030] The pozzolanicity of these materials nevertheless remains variable, and the resistance of construction materials prepared from pozzolanic materials is sometimes significantly lower than that of construction materials prepared from conventional Portland cements. It therefore remains interesting to identify new pozzolanic materials allowing the preparation of construction materials having a medium and long-term resistance comparable to that of construction materials prepared from Portland cements, while significantly limiting CO2 emissions during their preparation.

[0031] At the date of the present invention, the use of clays for the preparation of synthetic pozzolan by calcination is probably the strategy for reducing the carbon footprint of cements and concretes with the greatest potential. However, the use of large quantities of clay will pose problems of availability of the raw material.

[0032] Alternative solutions have thus been studied, such as the use of marls for the preparation of synthetic pozzolan by calcination.

[0033] Marl is a sedimentary rock, mainly composed of a mixture of calcite (CaCO3) and clay.

[0034] In their publication “Micro structure and ore composition of Roman cements produced

[0035] at defined calcination conditions », Materials Characterization, 58, 2007, pages 1217-1228, J. Weber et al. study in particular the pozzolanic properties of calcined marls. The marls studied contain respectively 71% and 63% by weight of calcite and are free of kaolinite. The authors note that if the (very) long-term resistances obtained with these calcined marls are satisfactory, the short-term or medium-term resistances are insufficient.

[0036] Similarly, in their publication “Calcareous smectite clay as a pozzolanic alternative to kaolin”, European Journal of Environmental and Civil Engineering, 2019, D. Tanner et al. also study the pozzolanic properties of calcined marls. The first marl studied contains 47% by weight of kaolinite and is free of calcite. The second marl studied comprises 8% by weight of kaolinite and 25% of calcite. Beyond 20% substitution of Portland cement by these calcined marls, the short-term resistances observed for the construction material thus prepared appear insufficient.

[0037] To aim for a strong substitution of cements, in particular Portland, by pozzolans in construction materials, and consequently obtain a substantial environmental impact, it is therefore still necessary to identify materials capable of being used for the preparation of pozzolanic materials which can themselves be used in high proportions in construction materials while maintaining mechanical properties, and in particular short-term resistances compatible with the implementation and use of said construction material.

[0038] Now, it has now been found, quite surprisingly, that calcite-rich marls containing kaolinite can, once calcined, be used as a pozzolanic material in construction materials, and this in significant proportions, up to 50% or even more of the construction material, while maintaining a short-term resistance of the construction material thus prepared compatible with its use. The construction materials thus prepared also have medium and long-term resistance comparable to that of construction materials prepared from conventional Portland cements, and can be prepared while significantly limiting CO2 emissions.

[0039] Thus, the subject of the present invention is the use of a marl comprising: - more than 45% calcite; and - at least 1% kaolinite;

[0040] for the preparation of a pozzolanic material.

[0041] Against all expectations, marls having high calcite contents and containing kaolinite can, once calcined, be used as pozzolanic material in construction materials, and this in proportions of up to 25% or even 50% of the construction material while maintaining a short-term resistance of the construction material thus prepared compatible with its use. The construction materials thus prepared also have medium and long-term resistances comparable to those of construction materials prepared from conventional Portland cements, and can be prepared while significantly limiting CO2 emissions.

[0042] In the context of the present invention:

[0043] - “calcite” means a polymorph of calcium carbonate CaCO3;

[0044] - "kaolinite" means the mineral of the phylosilicate family of formula Al 2Si2O5(OH)4 ;

[0045] - “marl” means any sedimentary rock composed mainly of polymorphs of calcium carbonate and / or magnesium carbonate, and of clay phases, in particular kaolinite, illite and / or montmorillonite phases;

[0046] - "montmorillonite" means the mineral of the phylosilicate family of formula (Na,Ca)0j3(Al,Mg)2Si4Oio(OH)2 • n H2O;

[0047] - “illite” means the mineral of the phyllosilicate family of type 2:1 with potassium as an interlayer cation, also including muscovite-type micas, of formula (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10;

[0048] - “pozzolanic material” means any material having properties pozzolanic within the meaning of European standard NF EN 197-1, i.e. capable of combining at room temperature and in the presence of water with lime or Portlandite formed during the hydration of cement to give very slightly soluble hydrates capable of generating additional resistance in the long term; and

[0049] - “construction material” means cement, concrete, mortar.

[0050] In the context of the present invention, the median diameter or d50 corresponds to the diameter below which 50% of the total volume of the particles is found. the sample considered. This can be determined by any method known to those skilled in the art, in particular by dry or wet laser granulometry.

[0051] Finally, in the context of the present invention, the proportions expressed in % correspond to mass percentages relative to the total weight of the entity considered.

[0052] The present invention therefore relates to the use of a marl having the mineralogical characteristics described above for the preparation of a pozzolanic material. Preferably, the present invention relates to the use of a marl as defined above for the preparation of a pozzolanic material, said marl having the following characteristics, chosen alone or in combination: - the marl contains at least 50% calcite, more preferably the marl contains at least 55% calcite, most preferably the marl contains at least 60% calcite; - the marl contains at least 1.5% kaolinite, more preferably the marl contains at least 2% kaolinite, most preferably the marl contains at least 2.5% kaolinite; - the marl also contains montmorillonite, more preferably the marl contains at least 3% montmorillonite, most preferably, the marl contains at least 5% montmorillonite; - the marl also contains illite, more preferably the marl contains at least 3% illite, most preferably the marl contains at least 5% illite; - the marl also contains quartz, more preferably the marl contains at least 3% quartz, most preferably the marl contains at least 7% quartz; and / or - the marl also contains chlorite, dolomite, microcline, albite, ankerite, orthoclase, pyrite, siderite, anatase and / or celestine.

[0053] The marl described above can therefore be used to prepare a pozzolanic material by calcination. Thus, the present invention also relates to a process for preparing a pozzolanic material from the marl described above, said process comprising the following steps: - possible drying then possible grinding of the marl; - calcination of the material obtained at a temperature between 650°C and 900°C; and - possible deagglomeration of the calcined marl obtained, for example by grinding, until reaching a median diameter of 5 pm to 20 pm.

[0054] When the marl is possibly ground before calcination, this is preferably carried out with a view to obtaining a powder of 100% passing at 2 mm.

[0055] The calcination step can be carried out using a rotary calciner, in which it lasts approximately 30 to 90 minutes. However, a "flash calciner" can also be used to calcine the marl to obtain a pozzolanic material, in which case the calcination step is very brief (1 to 2 seconds or less). The fact that a flash calciner can be used makes it possible to considerably reduce the energy required for calcination and preparation of the pozzolanic material.

[0056] When the calcined marl is possibly crushed, this is carried out until a median diameter of less than or equal to 25 μm is reached, preferably less than or equal to 20 μm, and most preferably less than or equal to 15 μm.

[0057] The present invention may be illustrated in a non-limiting manner by the following examples. Example 1 – Calcination of marl 1.1 - Composition of the marl

[0058] A raw marl having the mineralogical composition reported in the following Table 1 is used.

[0059] [Tables 1] Phase % (w / w) Albite 0.5 Ankerite 1.6 Calcite 60.1 Chlorite 1.8 Dolomite 0.8 Kaolinite 2.8 Microcline 2.6 Montmorillonite 8.5 Illite 8.1 Orthoclase 1, Pyrite 0.6 Quartz 10.8 Siderite 0.4 Anatase 0.3 Celestine 0.5

[0060] Table 1 - Mineralogical composition of the marl before calcination

[0061] The above marl has the chemical composition (in % (w / w)) reported in the Table 2 below.

[0062] [Tables2] A12O3 7.6 CaO 30.5 Cl 0.01 Fe2O3 3, k2o 2.3 MgO 2, MnO 0.05 Na2O 0.1 p2o5 0.1 SiO2 24.3 SO3 0.4 SrO 0.1 TiO2 0.4 Sulfides 0.3 Loss on ignition 950°C 28.6

[0063] Table 2 - Chemical composition of marl before calcination 1.2 - Calcination of the marl

[0064] The marl described above is dried for 12 hours at 105°C and then ground in a ring mill to a median diameter of 30 to 40 μm. The powder thus prepared is fired in a laboratory oven in batches of 200 g at 800°C for 1 h 00 with charging and hot defrosting. The calcined marl thus obtained (calcined marl AC-1) is then lightly ground again in a planetary mill (15 seconds, 700 rpm) to deagglomerate it and obtain a median diameter of 20 μm.

[0065] 1.2.3 - Mineralogical composition

[0066] The calcined marl thus obtained is analyzed. The mineralogical composition (in % (w / w)) of this is reported in the following table 3.

[0067] [Tables3] Phase AC-1 Periclase 1.5 Quartz 15.0 Anhydrite 1.0 Calcite 23.2 Gehlenite 0.1 Microcline 1.3 Orthoclase 1.0 Illite 6.6 Hematite 0.8 Bredigite 1.4 Amorphous 45.6

[0068]

[0069] Table 3 - Mineralogical composition of a calcined marl AC-1 Example 2 - Mortar composition according to the invention Preparation

[0070] A reference mortar (hereinafter Mortar 1) is prepared from a Portland cement CEM I 52.5 R according to standard EN 196-1. The composition of mortar 1 is as follows: - 450g of CEM I 52.5 R cement; - 1350g of standardized sand; and - 225g of water.

[0071] Similarly, mortars 2 to 4 are respectively prepared from a mixture: - 88% CEM I 52.5 R / 12% limestone filler (mortar 2); - 79% CEM I 52.5 R / 21% limestone filler (mortar 3); and - CEM I 52.5 R / 15% limestone filler / 30% AC-1 (mortar 4). Mechanical resistance

[0072] The mechanical resistance of mortars is measured in accordance with standard EN 196-1 on prismatic mortar specimens 4x4x16 cm3 prepared at 20°C.

[0073] The performance index characterizes the performance of the pozzolanic material when used at x% substitution. It is defined as the ratio of the compressive strengths (measured as indicated above) of a cement mortar consisting of 100-x% of a reference cement and x% of the pozzolanic addition considered, and of a mortar prepared with 100% of reference cement. / jp £ [ — -------------— -------------

[0074] The results of the compressive strength (Rc) measurements are reported in the following Table 4.

[0075] [Tables4] Mortar 1 (ref.) Mortar 2 Mortar 3 Mortar 4 Resistance to compression (MPa) 2 days 44 32 21 30 7 days 52 46 33 41 28 days 61 54 40 47 Performance index (in %) 2 days - 73 48 68 2 days - 88 63 79 28 days - 90 65 77

[0076] Table 4 - Compressive strengths

[0077] The mortar according to the invention (mortar 4) has medium and long-term compressive strengths higher than expected and acceptable performances compared to those observed for the reference CEM I (mortar 1) and compatible with the intended uses.

[0078] Furthermore, the mortar according to the invention (mortar 4) has short, medium and long term compressive strengths equivalent to those of mortar 2 (which only comprises 12% filler) and significantly higher than those of mortar 3 (containing 21% filler). The addition of calcined marl therefore allows a CEM I substitution rate significantly higher than the substitution rate obtained using limestone filler alone.

Claims

Claims

1. Use of a marl comprising: - more than 45% by weight of calcite; and - at least 1% by weight of kaolinite; for the preparation of a pozzolanic material by calcination of said marl at a temperature between 650°C and 900°C.

2. Use according to claim 1, characterized in that the marl contains at least 50% by weight of calcite.

3. Use according to claim 2, characterized in that the marl contains at least 55% by weight of calcite.

4. Use according to any one of claims 1 to 3, characterized in that the marl contains at least 2% by weight of kaolinite.

5. Use according to claim 4, characterized in that the marl contains at least 2.5% by weight of kaolinite.

6. Use according to any one of claims 1 to 5, characterized in that the marl also contains montmorillonite.

7. Use according to any one of claims 1 to 6, characterized in that the marl additionally contains illite.

8. Use according to any one of claims 1 to 7, characterized in that the marl additionally contains quartz.

9. Use according to any one of claims 1 to 8, characterized in that the marl additionally contains chlorite, dolomite, microcline, albite, ankerite, orthoclase, pyrite, siderite, anatase and / or celestine.