WO2025108539A1

WO2025108539A1 - Method to carbonate clinker and manufacture a binder

Info

Publication number: WO2025108539A1
Application number: PCT/EP2023/082669
Authority: WO
Inventors: Maria del Carmen AVITU GONZALEZ; Victoria UBICI; Javier CRUZ CANTU; Davide Zampini
Original assignee: Cemex Innovation Holding Ag
Current assignee: Cemex Innovation Holding Ag
Priority date: 2023-11-22
Filing date: 2023-11-22
Publication date: 2025-05-30
Anticipated expiration: 2026-05-22
Also published as: WO2025109100A1

Abstract

The present invention relates to a method for manufacturing a binder. Particularly, the present invention relates to a method to carbonate clinker by means of adding CO₂ and steam to said clinker to produce a binder.

Description

METHOD TO CARBONATE CLINKER AND MANUFACTURE A BINDER

DESCRIPTION

Technical field of the invention

The present invention relates to a method for manufacturing a binder. Particularly, the present invention relates to a method to carbonate clinker by means of adding CO2 and steam to said clinker to produce a binder.

State of the art

Current cement needs about 20-30% of traditional additions (Slag, Fly ash and Limestone) to produce a binder that fulfils the norms and standards specified by certification bodies. Typical additions such as fly ash and slag will scarce or disappear soon due to change of technology used for its production.

Cement is the world’s most produced material with nearly 2 billion tones manufactured globally per year, which creates 1 .6 billion tons of CO2 and makes cement production a significant contributor to greenhouse gas emissions. The cement industry is focused on reducing by 45% its CO2 emissions by 2030 and reach net zero by 2050, as called for in the Paris Agreement. To do so, one of the approaches under study is the so-called carbon capture and storage or utilization, whereby CO2 is captured at the flue stack and then stored in saline aquifers, depleted oil and gas reservoirs or in the deep ocean, or used for mineral carbonation, for example, wherein the CO2 is reacted with minerals to form carbonate minerals.

In recent years, there has been extensive research on the topic of C-S-H carbonation, in which CO2 reacts with calcium silicate hydrate (C-S-H), the main binder in concrete, responsible for giving concrete its strength and durability, as seen for example in Li et al. (Carbonation of the synthetic calcium silicate hydrate (C-S-H) under different concentrations of CO2: Chemical phases analysis and kinetics, Journal of CO2 Utilization, Volume 35, January 2020, Pages 303-313) [1] or in Morandeau et al. (Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties, Cement and Concrete Research Volume 56, February 2014, Pages 153-170) [2], among others.

The field of carbonation of C-S-H is a rapidly growing area of research. Nevertheless, when CO2 reacts with C-S-H it forms different phases of calcium carbonate (CaCOs) such as vaterite, aragonite or calcite, weakening the concrete and making it more susceptible to damage. The carbonation of C-S-H will lead to the degradation of concrete materials and sometimes even structures, as pointed by Liu et al. (Carbonation behaviour of calcium silicate hydrate (C-S-H): Its potential for CO2 capture, Chemical Engineering Journal, Volume 431 , Part 3, 1 March 2022, 134243) [3],

Another promising topic is the carbonation of recycled concrete or concrete fines to produce supplementary cementitious materials. For example, EP4155278 [4] discloses a method to manufacture supplementary cementitious materials by subjecting waste concrete to carbonation; EP3581257 and EP3744700 [5, 6] disclose methods to produce supplementary cementitious materials through the carbonation of concrete fines.

Another approach is the carbonation of cement pastes or concrete. EP3362237 [7] discloses a carbonation process of pre-dried concrete, which has lost 25 to 60% of their initial water content, by feeding CO2 gas into a closed air-tight chamber. EP4197982 [8] also produces a supplementary cementitious material wherein a powder made of oxides of calcium, magnesium and silica is mixed with water and this paste is placed in a reactor containing CO2, where it is left carbonating. In another embodiment, the grinding step is carried out in the presence of CO2 and the obtained powder is then mixed with water to form a paste.

EP4059905 [9] converts a starting material containing calcium silicon (hydr)oxide phases and calcium aluminium (hydr)oxide phases into an SiC>2 rich supplementary cementitious material and a calcium carbonate additive by mixing the starting material with water and passing this slurry through a gravity separation reactor together with CO2. EP3694818 [10] discloses a method for manufacturing a building element (a precast concrete part or concrete good) from a binder, this binder is mixed with water and optionally one or more of aggregate, additives, and admixtures to obtain a binder paste, which is then hydrated and carbonated until the amount of additionally bound carbon dioxide is at least 150 % of the initially bound water mass and/or the strength exceeds 2 MPa while still keeping the bound water at least 50 % of the initially bound water.

EP4155279 [11] also discloses a method to produce a supplementary cementitious material from the carbonation of a hydrate product. The method characterized in a hydrothermal treatment of a feedstock to provide a hydrate product, wherein the feedstock comprises silicate, aluminate, and/or aluminosilicate materials, and a source of calcium ions, and has a maximum content of hydrated cement paste of 10 wt.-%. The hydrate product is then carbonated to provide a pozzolanic product.

EP4119518 [12] discloses the carbonation of calcium sulphate containing waste in the presence of a high proportion of alkali metal ions, wherein calcium carbonate is formed while sulphate ions precipitate.

Although prior-art on carbonation of C-S-H, concrete waste, or fines to produce supplementary cementitious materials, cement pastes or pre-dried concrete is widely available, carbonation of clinker to produce a binder is a less explored topic. The idea behind this new approach is to replace the traditional hydration of cement with cement clinker carbonation for concrete production.

Chen et al. (Carbonation of CaO Clinkers and Improvement of Their Hydration Resistance, Journal of the Ceramic Society of Japan, 110, 512-517) [13], studied a carbonation treatment of CaO to improve CaO hydration resistance for usage in refractory. Two kinds of CaO clinkers, one with 70% (low) density and another with 95% (high) density were produced, both clinkers treated at 500-800°C in a carbon dioxide atmosphere.

In Ye et al. (Study on Effect of Carbonation Curing for Cement Minerals and Clinker, Key Engineering Materials, 477, 79-84) [14], cement minerals and clinker pastes were carbonated in an autoclave. They observed higher early compressive strength of clinker with carbonation curing vs natural curing. Similarly, Bao Lu et al. (Strength and microstructure of CO2 cured low-calcium clinker, Construction and Building Materials 188 (2018) 417-423) [15], produced low calcium clinker pastes and cured them under CO2. The compressive strength and CO2 curing degree of low calcium clinkers were increased with increasing the carbonation curing time, with the low calcium clinkers showing a denser microstructure after carbonation curing.

Zajac et al. (CO2 mineralization of Portland cement: Towards understanding the mechanisms of enforced carbonation, Journal of CO₂ Utilization 38 (2020) 398-415) [16], suspended clinker in a basic solution and bubbled the CO2 into it. They concluded that carbonation can be significantly faster than hydration.

Although these publications start to investigate the potential of clinker carbonation for the cement industry, they refer to research done at a lab scale, failing to provide methods that can be implemented by the industry.

Description of the invention

The present invention overcomes the drawbacks of the prior art by providing a method to carbonate clinker to produce cementitious binder, which can be used by the cement industry in mortar and concrete production as a highly blended cement without losing strength development capabilities. Furthermore, the method according to the invention enables to recapture part of the CO2 emitted by the calcination of the limestone from the raw meal.

The present invention relates to the production of a novel binder with embedded addition without the need to add supplementary cementitious materials to the cement obtained from grinded clinker. The invention modified the production of the current cement in 2 parts: first by a modification of the raw meal chemistry and the particle size distribution of said raw meal to produce cement clinker, secondly one adds the step of mineralization using a mix of H2O/CO2 enriched gas which will produce reactive additions. The novel binder presents better (+10%) or same reactivity than traditional ordinary portland cement (OPC) with lower C3S content and about 10 to 50% more reactivity than equivalent cement with traditional additions with the advantage to fix more that 50% of the CO2 emissions coming from the raw materials.

An objective of the present invention is therefore a method to produce a cementitious binder containing C2S, C3S and calcium carbonate, wherein said method comprises the steps of: a. Providing a raw meal comprised of calcium, silicate, aluminate, and/or aluminosilicate materials with the following traditional modulus: i. LSF (lime saturation factor): from 100 to 125, preferably from 102 to 120; ii. SM (silica Modulus) from 1 .0 to 3.0; iii. IM: (iron module) from 1 to 3.0; b. Burning or sintering the raw meal in a kiln at a temperature ranging from 1 100°C to 1 500°C to produce a sintered clinker; c. Cooling the sintered clinker in a cooler; d. Optionally storing the cooled clinker, for instance in a silo; e. Optionally transporting the clinker to the grinding mill; f. Grinding the clinker in a mill together with at least one sulfate source to obtain a cementitious binder; g. Optionally storing the cementitious binder, for instance in a cement silo; and wherein the method further comprises at least one carbonation step (OST) carried out after step b).

According to a particular embodiment of the method of the present invention, the calcium carbonate is aragonite.

According to a particular embodiment of the method of the present invention, in the clinker cooler, the temperature of the cooler drop from the sintering temperature (about 1 100°C to 1 500°C) to a temperature ranging from 150°C to 200°C, preferably to a temperature ranging from 80°C to 150°C.

According to a particular embodiment of the method of the present invention, the grinding step f), for example carried out by friction, raises the temperature of the clinker + sulfate source (for instance gypsum) to more than about 100 to 150°C.

According to a particular embodiment of the method of the present invention, the at least one carbonation step (CST) is carried out at a temperature ranging from 60°C to 250°C, using a carbonation gas containing CO2 and water steam. For example, the at least one carbonation step (CST) can be carried out during and/or between at least one of the steps c), d), e), f) and/or g). According to another particular embodiment of the method of the present invention, more than one CST can be used at different stages of the invention after step b). For instance, according to a first embodiment, 4 steps of carbonation according to the invention can be done, respectively at the end of the cooling step c) and during the grinding milling step f), and between step c) and d), and during step d). Any sequence involving one or more carbonation steps (in particular up to 3 carbonation steps) can be done during and/or between any of steps a. to f..

According to a particular embodiment of the method of the present invention, the method further comprises before step f) a clinker pre-grinding step located after c) but prior to the at least one carbonation step, to increase the specific surface of the clinker to be carbonated in increase the carbonation kinetics.

The raw meal chemistry in step a. of the method of the present invention is described by a Lime saturation Factor (LSF) located from 100 to 125, preferably from 102 to 120; a silica modulus (SM) located between 1.0 to 3.0, preferably between 2.0 to 2.4; and an iron module (IM) located between 1.0 and 3.0. preferably between 2.1 and 2.8.

A clinker that would be produced with raw meal modulus outside these ranges will stabilize other phases that cannot be carbonated effectively under the conditions disclosed in this invention. In a normal OPC clinker, the Lime saturation Factor (LSF) would be located from 93 to 98, because for a conventional clinker the goal is to minimize the residual calcium oxide CaO that will form in the clinker to avoid various detrimental effects (swelling, reactive phases depletion, etc.). Such clinker could not be optimally carbonated, and the resulting cement would not enable to achieve resistances to be used as a binder.

The raw meal typically contains:

- a calcium main source obtained from, but not limited to, limestone, fly ash, ground granulated blast furnace slag, silica fume, etc. Synthetic or natural;

- A silica main source obtained from clay, fly ash, slag, sand;

- An alumina main source obtained mainly from clay;

- Various additional components like gypsum, iron ore.

In another particular embodiment of the method of the present invention, the raw meal in step a. further comprises magnesium and other minor elements that will present in the raw materials.

The raw meal in step a. does not need to have a specific particle size. Nonetheless, the raw meal may be ground to a particle size D90 between 40 pm and 100 pm.

The grinding step can be carried out in a ball mill, vertical roller mill, high pressure grinding roll, Raymond mill, attrition mill, semi-wet mill or any mill that is suitable for grinding such material. For a conventional raw meal to produce clinker, the D90 would be located between 75 and 90 microns. The raw meal of step a) is significantly different from a raw meal to produce a normal clinker. For instance, the selected values for the Lime Saturation Factor LSF are selected in a range that would not be recommended for producing a normal clinker.

Step b. of the method of the present invention can be for instance carried out using a conventional clinker manufacturing line comprising a pre-heater, optionally a separate calciner, a rotary kiln and a clinker cooler as schematically presented in Figure 1 .

The raw meal (1) is introduced into the pre-heater (2) and is then optionally calcined in the calciner (3) using temperatures ranging from 850°C to 950°C, and finally burned or sintered in the rotary kiln (6) at temperatures ranging from 1 100°C to 1 500°C.

In step c. of the method of the present invention, the sintered clinker is then discharged from the kiln (6) to enter the clinker cooler (7), where its temperature is reduced using air blowers (8) to a temperature ranging from 20°C to 250°C, preferably from 150°C to 200°C, more preferably from 80°C to 150°C, depending on the cooler length and the velocity of clinker transportation in the cooler. Typically, the cooling conditions can be adjusted so that the temperature of the clinker in the last part of cooler reached the temperature conditions as per the carbonation step (60°C to 250°C) so the last part of the cooler, or a cooler extended in length can be used as the carbonation reactor to meet the residential time for carbonation (15 to 60 min).

The air (9) from the cooler (7) is typically returned back into the calciner (3).

Hot gases containing CO2 (4) are extracted from the preheater (2) and guided to the chimney (5).

The cooler clinker is then carbonated in a reactor (10), for instance placed after the clinker cooler (7) or part of the clinker cooler. In a preferred embodiment, gases (11 , 12, 13) are extracted from the chimney (5), the pipe leading the gases to the chimney (4), the precalciner (3) or the calciner (3) and introduced into the clinker carbonation reactor (10) together with water steam (15) obtained typically from a water steam generator (not shown). The carbonation reactor is typically thermally insulated to maintain the required carbonation temperature according to the invention, and optionally is equipped with heating device, for instance electrical resistances in the CST directly or to heat up the CGM. The CO2 rich gases and the steam are typically preheated (not shown) to ensure the proper required temperature in the carbonation reactor (10), before being re -introduced (16) into the carbonation reactor (10).

The gases leaving (17) the carbonation reactor (10), can be reintroduced into the preheater (2) the calciner (3) directly or via the duct (9). Alternatively, the carbonation gases (17) can be recirculated and re-introduced into the reactor (18). According to another particular embodiment of the method of the present invention, a rich CO2 gases sources (19) can be used to regulate the CO2 level in the reactor (10).

Finally, the carbonated clinker is discharged (14) to be stored for instance in a silo (not shown) before it is transported to the grinding mill (not shown).

The process can be easily automated by installing all the steered gas valves, by-pass valves, heating devices, ventilators, temperature O2 and CO2 measurement devices, using a conventional PLC (not shown) and regulation devices.

The process allows to ensure the development of the targeted composition and phases formation in the clinker so the final cement derived from the clinker will have a high reactivity with water and develop high strength.

Typically, the produced and cooled clinker is stored in one or many clinker silos (step dj, prior to be transported (step e.) to be post-processed, typically by a milling/grinding in step f..

In step f. the clinker grinding mill is typically a single or multi-chambers ball mill equipped with a separator, or any type of grinding mill like vertical mills, roll mills, etc.). In step f. a sulfate source, in form of gypsum for instance, is added to the clinker at a dosage of typically 5%. Additionally, other supplementary cementitious materials can be added like slag, ground granulated blast furnace slag, natural pozzolans, fly ashes, limestone, etc. The outcome product of step f. is cement.

The carbonation step (CST) of the method of the present invention is carried out using water or water steam and CO2. Preferably, steam and CC>2-containing gas (CG), together referred as the carbonation gas mixture (CGM), are introduced together. Alternatively, water steam can be introduced before the CO2-containing (CG). The carbonation step CTS does not require to use pressure vessel and be operated at or slightly above atmospheric pressure to enable the carbonation gases to circulate through the clinker bed in the reactor.

Temperatures used during the carbonation step CST are located between ranging from 60°C to 250°C, preferably between 80°C and 120°C. The carbonation step CST, in the conditions defined by the present invention has a duration located between 15 min and 60 min, preferably for a duration of about 20 minutes.

The CO2 in the mixture of gases CGM (mixture of the carburizing gas CG and water vapor) is selected to be located from 10% (v/v) to 50% (v/v), and the water steam selected to be located from 50% (v/v) to 90% (v/v). In another particular embodiment of the method of the present invention, the carbonating gas (CG) (carbonating gas) contains from 25% (v/v) to 99.9% (v/v) CO2.

The CC>2-containing gas (CG) may be selected from pure CO2 gas, any CO2- containing effluent gas from an industry. For example, the CO2-containing gas may be the effluent gas from the clinker production process (from a cement plant). In this case, the CO2-containing gas can be recirculated from any point before or after the preheater (12) or from the main flue gas chimney (13) of the cement production line (Figure 1). According to a preferred embodiment of the method according to the invention, the CO2-containing gas (CG) has a CO2 content from 25% (v/v) to 60% (v/v) depending on the CO2 enrichment (Figure 1).

Typically, CGM is recirculated at its composition is regulated using CO2 sources and water steam to maintain the carbonation conditions defined in the invention.

According to another particular embodiment of the method of the present invention, the carbonation step CST is carried out in a separate continuous reactor located after the clinker cooler. Alternatively, the carbonation step CST can be carried out in any separate static or continuous reactor using the conditions defined by the present invention.

The carbonation step CST can be carried out during and/or between any of the steps c.-to g..

For example, a dedicated continuous semi-continuous or batch reactor can be placed after the clinker cooler in step c) or can be designed as an extension of the clinker cooler. The carbonation step CST can also be done directly inside the clinker cooler, by injecting the CGM as part or complement of the cooling fluid in the part of the cooler where the clinker has reached the appropriate temperature conditions as per the invention.

Alternatively, the carbonation step CST can be carried out in a clinker silo in step d. Indeed, sintered clinker out of the cooler can be stored in a vertical silo (step d.). As the sintered clinker already has a temperature in the range of the carbonation conditions (60- 250°C), the silo can be thermically insulated and if needed, equipped with additional heating (either by heating the CO2-containing gas to the appropriate temperature or by any other means.

The carbonation CST can also be done during the transportation of the clinker (step e.) from the clinker silo (step d.) to the grinding mill in step the grinding mill of step f..

Regarding step f., the sintered clinker normally enters the grinding at room temperature after cooling and storage. However, the fringing operation itself (shear, friction) generates an important temperature increase between 100°C and 200°C of the material being milled, depending on the operating conditions, which also enables the carbonation step to be carried out. The temperature in the mill if the mill is used as CST can be regulated by cooling or heating the CG with heat exchangers or cooling the mill with water and/or heating the mill with electrical resistances.

A carbonation continuous or batch reactor according to the invention is typically a thermally insulated horizontal or vertical container, containing the clinker to be carbonated, having various inlets for the CGM to reach the clinker, and one or many outlets to collect the CGM after being in contact with the clinker. The carbonation reactor may be heated using for instance electrical resistance. The temperature in the reactor is measured by conventional thermo-couples and the CO2 may be measured using for instance an Infra- Red gas measurement device.

Continuous reactors will be equipped with a system to transport the clinker through the reactor (band, belt, vibration), whereas static or batch reactors will be equipped with means to fill in and discharge the reactor.

In another particular embodiment of the method of the present invention, the CGM can be looped from the outlet to the inlet of the reactor using a pump or a blower. The CO2 content of the CGM can be regulated by adding a CO2 rich corrector gas (CRCG 15 in Figure 1), so the CO2 content in the reactor can be modified and kept constant at given set values, as can be seen in Figure 1.

The CGM after carbonation can for instance be connected back to the clinker production starch or any location of the preheater, calciner or in the return air from the clinker cooler to calciner or preheater.

Definitions

Admixture: Chemical species used to modify or improve concrete's properties in fresh and hardened state. These could be air entrainers, water reducers, set retarders, superplasticizers and others.

Alumina module (AM): The ratio of alumina oxide (AI2O3) to iron oxide (Fe2Os). It is calculated as follows: AM = A12O31 Fe2Os.

Binder: Material with cementing properties that sets and hardens due to hydration even under water. Hydraulic binders produce calcium silicate hydrates also known as CSH.

C3S: C3S, or tricalcium silicate, is a mineral compound in Portland cement. It is responsible for the early strength development of concrete. C3S is formed when limestone and clay are heated to a high temperature in a kiln.

C2S: C2S, also known as dicalcium silicate, is one of the four main compounds in Portland cement. It is a white, odorless powder that is formed when limestone and clay are heated to a high temperature in a kiln. C2S is responsible for the long-term strength and durability of concrete. C3A: Tricalcium aluminate (C3A) is one of the four main components of Portland cement clinker, along with tricalcium silicate (C3S), dicalcium silicate (C2S), and tetracalcium aluminoferrite (C4AF). C3A is a very reactive compound, and it plays an important role in the early hydration and setting of cement.

C4AF: Tetracalcium aluminoferrite (C4AF) is one of the four main compounds found in Portland cement clinker, the other three being tricalcium silicate (C3S), dicalcium silicate (C2S), and tricalcium aluminate (C3A). C4AF is formed when limestone, clay, and other raw materials are heated to a high temperature in a cement kiln.

Carbonation: Carbonation is the reaction between carbon dioxide gas and a solid (for example, minerals) or liquid (for example, water).

Cement: It is a binder that sets and hardens and brings materials together. The most common cement is the ordinary Portland cement (OPC) and a series of Portland cements blended with other cementitious materials.

Cement paste: Mixture of cement, + fly ash + slag + silica fume + water + entrained air.

Clinker: A hard, nodular material produced by heating limestone and clay to a high temperature in a kiln. It is the main ingredient in Portland cement, which is the most common type of cement used in construction.

Coarse Aggregates: Manufactured, natural or recycled minerals with a particle size greater than 8 mm and a maximum size lower than 32 mm.

Concrete fines: Concrete fines are a recycled product made from recycled concrete aggregate. It is a typical substitute for natural stone aggregates and ranges from 3/8" to a fine powder. Its compact nature makes it a great sub-base material, and it is generally used as a base for pavers, roads, parking areas, and building foundations.

Fibers: Material used to increase concrete's structural performance. Fibers include: steel fibers, glass fibers, synthetic fibers and natural fibers.

Fly ash: A byproduct of coal combustion in power stations. It is a fine gray powder composed of spherical, glassy particles that rise with the flue gases. It has pozzolanic properties, meaning that it can react to form cementitious compounds.

Greenhouse gas: A gas that contributes to the greenhouse effect by absorbing infrared radiation. Carbon dioxide and chlorofluorocarbons are examples of greenhouse gases.

Hydration: It is the mechanism through which OPC or other inorganic materials react with water to develop strength. Calcium silicate hydrates are formed and other species like ettringite, mono-sulfate, Portlandite, etc. Hydraulic binder: It is a material with cementing properties that sets and hardens due to hydration even under water. Hydraulic binders produce calcium silicate hydrates also known as CSH.

Iron module: The ratio of alumina oxide (AI2O3) to iron oxide (Fe2Os). It is calculated as follows: AM = A12O31 Fe2Os.

Kiln: A long, cylindrical furnace that is used to produce clinker, the main ingredient in cement.

Lightweight aggregate: Have a particle density between 20 kg/m³ and 2000 kg/m³, for example expanded shale, expanded clay, expanded slate, foamed slag, exfoliated vermiculite, expanded perlite, pumice, expanded glass, expanded polystyrene beads or a combination thereof, according to the norm EN 13055.

Lime saturation factor: A measure of the proportion of lime in the clinker in relation to other components. It is calculated as follows: LSF = CaO I (2.8 SiC>2 + 1.2 AI2O3 + 0.65 Fe2Os)

Limestone: A hard sedimentary rock, composed mainly of calcium carbonate or dolomite, used as building material and in the making of cement.

Mineralization: Concrete mineralization is a process that chemically transforms carbon and permanently stores it. Carbon mineralization methods involve capturing CO2 and injecting it into fresh concrete, where it becomes permanently embedded and actually helps to improve its strength.

Mill: A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Most cement is currently ground in ball mills and also vertical roller mills which are more effective than ball mills.

Mortar: Mortar is made from cement, sand, and sometimes lime or admixtures, and is used for bonding bricks, stones, and other materials.

Pozzolan: Pozzolan is a siliceous or silico-aluminous material that reacts with calcium hydroxide to form compounds having cementitious properties

Ordinary Portland cement: Hydraulic cement made from grinding clinker with gypsum. Portland cement contains calcium silicate, calcium aluminate and calcium ferro-aluminate phases. These mineral phases react with water to produce strength.

Pre-dried concrete: Pre-dried concrete is a type of concrete that is partially dried before it is placed. This can be done using a variety of methods, such as heating the concrete, or by exposing it to a vacuum.

Raw meal: Cement raw meal is a mixture of ground limestone, clay, and other materials that is used to produce cement clinker. Clinker is the main ingredient in cement, and it is produced by heating raw meal to a high temperature in a kiln.

Sand: Manufactured, natural or recycled minerals with a particle size lower than 4mm. Silica fume: Source of amorphous silicon obtained as a byproduct of the silicon and ferrosilicon alloy production. Also known as micro-silica.

Silica Modulus: The ratio of silica (SiC>2) to alumina (AI2O3) and iron oxide (Fe2Os) in cement raw meal or clinker. It is calculated as follows: SM = SiC>21 (AI2O3 + Fe2Os)

Silicate: Generic name for a series of compounds with formula Na2O.nSiC>2. Fluid reagent used as alkaline liquid when mixed with sodium hydroxide. Usually, it comprises sodium silicate but can also comprise potassium and lithium silicates. The powder version of this reagent is known as metasilicates and could be pentahydrates or nonahydrates.

Slag: Slag is a byproduct of metal smelting or refining. It is a mixture of oxides, silicates, and sulfides of various metals, including iron, calcium, silicon, aluminum, and magnesium. Slag is typically formed as a molten liquid, but it can also be solid or granular.

Specific surface: The surface area per unit mass or volume of a material. It is a measure of the amount of surface area that is available for physical and chemical processes to occur

Steam: The gaseous state of water. It is produced when water is heated to its boiling point, which is 100 degrees Celsius at sea level.

Strength development - setting I hardening: The setting time starts when the construction material changes from plastic to rigid. In the rigid stage the material cannot be poured or moved anymore. After this phase the strength development corresponding to the hardening of the material.

Supplementary cementitious materials: Materials that are added to concrete to improve its properties, such as strength, durability, and workability. SCMs are typically used in conjunction with Portland cement, but they can also be used to replace Portland cement partially or fully.

Brief description of the figures

Figure 1 is a schematic representation of the invention based on a conventional clinker production line.

EXAMPLES

The burning of a raw meal and sintering of clinker in a clinker manufacturing line is normally designed to provide the following phases in the clinker: C3S: - 55-70% C2S: 18-22% C4AF: 10-12% C3A: 1-2% CaO: less than 1 .5%

Clinker with a good reactivity will normally fully depend on the quantity of C3S that is formed and the main objective in the cement industry is to maintain a high C3S content and a very low CaO content.

Exposing a clinker to water steam with or without CO2 will deplete the C3S and C2S contents and would normally be completely excluded from good practices in the cement industry.

Experimental

The various clinkers in the following examples were prepared by milling and mixing raw meals using a planetary ball mill to reach a fineness typically ranging from 40 urn to 50 pm.

The raw meal samples were pelletized and burned sintered in an electrical furnace in air at temperatures ranging from 1 100°C to 1 500°C.

The chemical compositions of the samples were determined using XR-fluorescence, and the phases identification and quantification were done using X-Ray diffraction and Rietveld quantification.

After chemical and phases analysis, the obtained clinker pellets were used for the carbonation experiments.

The carbonation step was carried out using a batch container-based reactor connected to a CO2 gas sources (CG) and a steam generator to form the carburizing gas mixture CGM.

Temperature in the reactor was controlled using a thermometer and regulated using an electrical furnace.

Blanks or refences (uncarbonated and regular clinkers) as well as carbonated samples were milled together with an 5% % of sulfate in a planetary ball mill to obtain a fineness of 45 pm.

Mortars samples according to EN 196-1 , using 450 g weight% of cement, 1350 g weight % of sand and with a water/cement ratio of 0.5 weight/weight were prepared for mechanical resistance testing and cured at 25°C and > 98% relative humidity.

Strength measurements were done in compression after 2 days, 7 days, and 28 days of curing.

Table 1 shows some of the typical clinkers prepared to highlight the invention.

Table 1 : various clinkers prepared

Clinker A is an example of a clinker prepared according to the invention.

Clinker B is an example of a conventional clinker prepare to compare with the clinker (as cements) according to the invention Clinker C is a clinker showing similar composition as the clinker according to the invention yet prepared out of the regular clinker B with limestone additions to meets the compositions obtained in the carbonated clinker, though without carbonation.

The strength development at 2, 7 and 28 days show how reactive the cements obtained from the respective clinkers are. Strength results are compared to the convention cement made out of conventional, clinker B.

Table 2: Results obtained according to the invention for the 3 clinkers of table 1 , with or without carbonation, as well as the reference clinkers (A not carbonated), B (not carbonated) and C.

Table 3: Results obtained with experimental conditions outside the scope of the invention, including 2 clinkers D and E prepared with LSF outside the claimed range of the invention.

From the results in tables 2 and 3, only the clinkers as per the invention (LSF from 102 to 120 irrespective of the carbonated conditions provides the expected results.

Carbonation in all cases produce 20 points drop of the most reactive phase C3S, whereas the C2S content is less affected by the carbonation, and free lime CaO completely disappears. Phases that form during carbonation on table 3 are CaCCh in 3 main allotropes (calcite, aragonite and vaterite)

Comparing the strength results in table shows that the simulated clinker C develops much less strength at 28 days than the carbonated samples A, although it shows higher contents of the reactive phases C2S and C3S. This evidences the fact that the CaCCh formed during carbonation of the clinker A phases are much more reactive and provides a much higher finally strength. Results in table 2 also shows that the carbonated clinker A enables to reach higher final 28 days strength that a conventional cement obtained from a conventional clinker B containing much higher content of C3S and C2S.

Carbonation of the clinker performed under the conditions provided by the invention, together with the raw meal lime saturation factor LSF enables to increase the final strength of the corresponding cement, although, traditional clinker and cement chemistry will suggest the opposite effect due to the depletion of the reactive phases C3S and C2S.

Finally, the results presented in figure 3 shows that selecting carbonation temperatures below or above the claimed range of 60 °C - 250 °C or selecting carbonation conditions with high CO2 contents or high-water contents does not provide the strength enhancement observed if the conditions are selected according to the invention.

Similarly, tables 3 shows that clinkers prepared with LSF values outside the conditions defined by the invention do not produce and strength enhancement effect. Table 3 also shows that the formation of aragonite as a product of the carbonation plays a key role in the high strength development of the carbonated clinker type A as per the invention.

It is thus another purpose of the invention is to define the operative conditions to enable a carbonation of the clinker, maximizing the CO2 uptake of the clinker, while ensuring that the CaCCh formed by carbonation using a mix of CO2 containing gases and water vapor is mainly in the form of aragonite, that will participate to the hydraulic enhancement of the carbonated clinker in order to maximize the mechanical properties of the cement derived from the carbonated clinker according to the invention.

The advantages of the invention are obvious from the results as the process enables to enhance the strength resistance while have a significant amount of CaCCh in the clinker.

In addition, another advantages of the method according to the invention is to enable to capture a large part of the CO2 emitted during the clinker manufacturing process. This CO2 uptake, expressed as carbonation % representing the amount of weight % CO2 absorbed by the clinkers during carbonation is not limited to the results presented in tables 2 and 3.

Additional experiments performed on crushed clinker or on cements produced from the carbonated clinkers A according to the conditions defined by the invention enable to significantly increase the carbonation level up to 20 weight % CO2 with no significant deterioration of the strength development, maintaining the final strength levels in the range of those achieved with conventional clinker B.

The method of the invention is also very simple to implement and provides high versatility and flexibility offering a wide set of alternatives depending on the cement plant condition, layout and available sources of CO2. Flue gases can be easily managed by returning them to the main clinker manufacturing equipment, offering a CO2 uptake of creased CO2 emissions that is much higher that any known processes so far, specifically those processes using CO2 carbonation during in the final fresh mortars or concrete that remain limited to some weight % CO2 uptake and in most cases required pressuring vessels with all the inherent disadvantages.

As a result, the blended cementitious binder obtained by the carbonation process according to the invention can be used as a cement or can be mixed with various aluminosilicates (e.g., slag, silica fume, flay ash, natural or synthetic pozzolans, additional CaCCh or the mix of any of them), to be used as mortars or concrete for any applications. Final application will also depend on mix design of the mortars or concrete (quantities and type of cement, of additions, of lightweight of dense sand, of medium and coarse sized lightweight or dense aggregates of admixtures of any additions like accelerators, retarders, fibers, or any ingredient that enters the composition of mortars concrete.

List of references

1. Li et al., Carbonation of the synthetic calcium silicate hydrate (C-S-H) under different concentrations of CO2: Chemical phases analysis and kinetics, Journal of CO2 Utilization, Volume 35, January 2020, Pages 303-313

2. Morandeau et al. (Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties, Cement and Concrete Research Volume 56, February 2014, Pages 153-170

3. Liu et al., Carbonation behaviour of calcium silicate hydrate (C-S-H): Its potential for CO2 capture, Chemical Engineering Journal, Volume 431 , Part 3, 1 March 2022, 134243

4. EP4155278

5. EP3581257

6. EP3744700

7. EP3362237

8. EP4197982

9. EP4059905

10. EP3694818

11. EP4155279

12. EP4119518

13. Chen et al., Carbonation of CaO Clinkers and Improvement of Their Hydration Resistance, Journal of the Ceramic Society of Japan, 110, 512-517

14. Ye et al., Study on Effect of Carbonation Curing for Cement Minerals and Clinker, Key Engineering Materials, 477, 79-84

15. Bao Lu et al., Strength and microstructure of CO2 cured low-calcium clinker, Construction and Building Materials 188 (2018) 417-423

16. Zajac et al., CO2 mineralization of Portland cement: Towards understanding the mechanisms of enforced carbonation, Journal of CO₂ Utilization 38 (2020) 398-415)

Claims

1) Method to produce a cementitious binder containing C2S, C3S and calcium carbonate, wherein said method comprises the steps of: a. Providing a raw meal comprised of calcium, silicate, aluminate, and/or aluminosilicate materials with the following traditional modulus: b. i. LSF (lime saturation factor): from 100 to 125, preferably from 102 to 120; ii. SM (silica Modulus) from 1 to 3; iii. IM: (iron module) from 1 to 3.0; c. Burning the raw meal in a kiln at a temperature ranging from 1 100°C to 1 500°C to produce a sintered clinker; d. Cooling the sintered clinker in a cooler; e. Optionally storing the cooled clinker, for instance in a silo; f. Optionally transporting the clinker to the grinding mill; g. Grinding the clinker in a mill together with at least one sulfate source to obtain a cementitious binder; h. Optionally storing the cementitious binder, for instance in a cement silo; and wherein the method further comprises at least one carbonation step (OST) carried out after step b).

2) Method according to claim 1, wherein the calcium carbonate is aragonite.

3) Method according to claim 1 or 2, wherein steps a) to g) are carried out.

4) Method according to any of claims claim 1 to 3, wherein the at least one carbonation step is carried out during and/or between step c., d., e., f. and/or g..

5) Method according to any of claims 1 to 4, wherein the method further comprises a pre-grinding step before step f. and after step c., but prior to any carbonation step.

6) Method according to any of claims 1 or 5, wherein the raw meal in step a. further comprises magnesium.

7) Method according to any of claims 1 to 6, wherein step b. is carried out at a temperature ranging from 850°C to 950°C, then from 1 100°C to 1 500°C. 8) Method according to any of claims 1 to 7, step c. is carried out at a temperature ranging from 20°C to 250°C, preferably ranging from 80°C to 150°C.

9) Method according to any of claims 1 to 8, wherein the sulfate source is added in step f. at a dosage of 5%.

10) Method according to any of claims 1 to 9, wherein step f. is carried out at a temperature ranging from 100°C to 150°C.

11) Method according to any of claims 1 to 10, wherein the raw meal is ground in step f. at a particle size D90 ranging from 40 pm to 100 pm, preferably ranging from 75 pm to 90 pm.

12) Method according to any of claims 1 to 11 , wherein the at least one carbonation step is carried out at a temperature ranging from 60°C to 250°C.

13) Method according to any of claims 1 to 12, wherein the at least one carbonation step is carried out using 10% (v/v) to 50% (v/v) CO2 and 50% (v/v) to 90% (v/v) water stream.

14) Method according to any of claims 1 to 12, wherein the at least one carbonation step is carried out using carbonation gases (CG), optionally enriched in CO2, from the chimney, the preheater and/or the calciner of the clinker production line.

15) Method according to claim 14, wherein the at least one carbonation step is carried out using carbonation gases (CG) containing from 25% (v/v) to 60% (v/v) CO2.