Cementitious composition including carbonated biochar

Abstract

CEMENTATION COMPOSITION COMPRISING CARBONATE BIOCHAR Cement composition comprising at least 1% carbonate biochar, construction material comprising said cement composition and use of carbonate biochar as a cementitious addition.

Description

Title of the invention: Cementitious composition comprising carbonated biochar

[0001] The present invention relates to new low carbon balance cementitious compositions containing carbonated biochar, as well as the use of carbonated biochar as a cementitious additive.

[0002] The manufacture of hydraulic binders, and in particular cements, essentially consists of calcining a mixture of carefully selected and measured raw materials, also referred to as "raw material." Firing this raw material produces an intermediate product, clinker, which, when ground with possible mineral additions, 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 approximately 0.8 to 0.9 tonnes of CO2.

[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] CaCO₃ CaO + GO2

[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, releasing 15% to 20% of the CO2 emitted during production, 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 sulfoa- cements luminous 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] Carbon capture and storage technologies have also been developed to limit CO2 emissions from cement plants or coal-fired power plants. International patent application WO-A-2019 / 115722 describes a process that simultaneously cleans exhaust gases containing CO2 and manufactures an additional cementitious material.The described process involves using recycled concrete fines, including supplying recycled concrete fines with a d90 value < 1000 pm in stockpiles or a silo as a starting material, rinsing the starting material to provide a carbonaceous material, removing the carbonaceous material and the cleaned exhaust gas, and deagglomerating the carbonaceous material to form additional cementitious material. It also involves using stockpiles or a silo containing a starting material of recycled concrete fines with a d90 value < 1000 pm for cleaning exhaust gas containing CO2 and simultaneously producing additional cementitious material. However, this process is complex to implement and requires drying the carbonaceous product before it can be used.

[0016] As of the date of the present invention, it remains necessary to identify new substitute materials that will significantly reduce CO2 emissions during cement production while maintaining the 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 term “biochar” is an abbreviation of “bio-charcoal,” in which the prefix “bio” designates biological origin and “charcoal” corresponds to the English term for charcoal. Thus, “biochar” refers to a charcoal of plant origin obtained by the pyrolysis of organic matter from various sources such as plants, including wood, straw, and agricultural or green space residues, or organic compounds such as sewage sludge, also known as “WWTP sludge.”

[0018] Biochar differs from charcoal by its use as a fertilizer rather than as a fuel and by its environmental impact, since it acts as a carbon sink (or CO2 sink) rather than releasing CO2 into the atmosphere when burned.

[0019] Biochar is therefore interesting for two reasons:

[0020] - it concentrates a large amount of biogenic carbon (between 40 and over 80%); and - its structure develops a large specific surface area capable of adsorbing large quantities of CO2.

[0021] Biochar is thus classically used in agriculture to increase soil quality, and therefore its productivity. However, although carbon sequestration in the soil by burying biochar has been practiced for many years to combat soil acidification and increase fertility, losses and emissions of carbon in the form of CO2 have been identified when the chemical balances of the soil (pH, leaching, burial depth, etc.) vary.

[0022] International patent application WO-A-2018 / 203829 describes the use of biochar as a substitute sand for the preparation of concrete or mortar-type construction materials. However, this patent application does not describe the use of biochar as a cementitious additive.

[0023] In the publication “The use of Biochar to reduce the carbon footprint of cement-based materials,” Procedia Structural Integrity, 26 (2020), 199–210, the authors Suarez-Riera et al. describe the use of biochar as a cementitious additive (or filler) to reduce the carbon footprint of both cement production and the building material prepared from it. According to the authors, the optimum rate of cement substitution by biochar is 2%, which remains relatively low.

[0024] However, it has now been found quite surprisingly that the use of carbonated biochar as a cementitious addition made it possible to significantly increase the rate of substitution of cement compared with biochar, thus making it possible to significantly lower the carbon footprint of the construction material finally prepared while maintaining mechanical properties, and in particular compressive strengths in the medium and long term compatible with the intended uses.

[0025] Thus, the present invention relates to a cementitious composition comprising at least 1% of carbonated biochar.

[0026] The addition of carbonated biochar in the compositions of the invention makes it possible to significantly increase the rate of substitution of cement compared to biochar, and therefore to significantly lower the carbon footprint of the construction material finally prepared from said composition, while maintaining mechanical properties, and in particular compressive strengths in the medium and long term compatible with the intended uses.

[0027] Within the scope of the present invention:

[0028] - "Biochar" means any material obtained by pyrolysis of biomass organic matter of various origins such as plants, including wood, straw and agricultural or green space residues, or organic compounds such as sewage treatment plant sludge known as "STEP sludge";

[0029] - The term "carbonate biochar" means any biochar which, after being brought into contact with a gaseous flow enriched in CO2, retains some of it in its porous structure, and therefore contains adsorbed CO2;

[0030] - the term "aluminous cement" means any cement, amorphous or not, obtained by cooking of a mixture of limestone and bauxite and containing at least 5% monocalcium aluminate CA;

[0031] - The term "natural quick-setting cement" means any hard, setting hydraulic binder Rapid cement conforming to standard NF P 15-314: 1993 in force at the date of the present invention. Preferably, "natural rapid cement" means a cement prepared from a clinker comprising:

[0032] • from 0% to 20% of C3S;

[0033] • 40% to 60% of C2S; • 7% to 12% of C4AF; • 2% to 10% of C3A; • 10% to 15% CaCO3 (calcite); • 10% to 15% of Ca5(SiO4)2CO3 (spurrite); • 3% to 10% sulfate phases: yeelimite C4Al3$, langbeinite (K2Mg2(SO4)3, anhydrite (CaSO4); and • 10% to 20% of lime, periclase, quartz and / or one or more amorphous phases;

[0034] - "Portland cement" means any cement based on classified Portland clinker as EMC (I, II, III, IV or V) according to the NF EN 197-1 standard;

[0035] - "sulfoaluminate cement" means any cement prepared from clinker sulfoaluminous containing 5% to 90% of 'yeelimite' C4A3$ phase, a sulfate source, and, optionally, a limestone addition;

[0036] - The term "cementitious composition" means any composition based on cement or alkali-activated binder that can be used for the preparation of a construction material;

[0037] - "construction material" means cement, concrete, mortar; and

[0038] In the context of the present invention, the "rate of CO2 adsorbed" corresponds to the quantity (% w / w) of adsorbed CO2 contained in the carbonated biochar relative to the total weight of the carbonated biochar.

[0039] To determine the rate of CO2 adsorbed, different methods can be used such as, for example, a combination of calcination at different temperatures and elemental carbon analysis allowing to distinguish organic carbon, inorganic carbon and with certain devices to determine carbon in other forms.

[0040] The use of a BET analyzer can also determine the amount of CO2 adsorbed in the porosity of the biochar. Finally, Raman and infrared spectroscopies are complementary techniques to the previous ones for detecting adsorbed CO2.

[0041] Thus, to determine the rate of CO2 adsorbed, the following procedure can in particular be implemented:

[0042] - place an alumina crucible on a balance and tare it; - fill the crucible with the powder (biochar or cementitious material) to be analyzed spreading it out and weighing the test sample; - introduce the filled crucible into the CHS elemental analyzer; - enter the value of the sample mass; - note the total carbon (TC) content measured by the device; - then, to determine the inorganic carbon (ITC), start by calcining the powder (biochar or cementitious material) at 500°C and then repeat the previous steps.

[0043] 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 relative to the total weight of carbon contained in said entity. TOC includes, in particular, carbon contained in organic compounds and adsorbed CO2.

[0044] The COT value of an entity is determined according to the following formula:

[0045] COT=CT-CH

[0046] in which

[0047] - "CT" denotes the quantity (% w / w) of total carbon of the entity obtained through to an elemental analysis with a carbon / sulfur (CS) analyzer on a raw sample; and - "CIT" refers to the quantity (% w / w) of total inorganic carbon of the entity obtained by calcining the sample to be analyzed at 500°C before proceeding with a new determination of elemental carbon by a CS analyzer.

[0048] In the context of the present invention, the median diameter or d50 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 dry or wet laser granulometry.

[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. clinker or cement) considered.

[0050] The present invention therefore relates to a cementitious composition comprising at least 1% carbonated biochar. Preferably, the present invention relates to a cementitious composition as defined above having the following characteristics, chosen alone or in combination:

[0051] - the composition comprises at least 2% of carbonated biochar; preferably the composition comprises at least 3% of carbonated biochar; even more preferably the composition comprises at least 4% of carbonated biochar; most preferably the composition comprises at least 5% of carbonated biochar; - the composition includes up to 30% carbonated biochar; preferably the composition includes up to 25% carbonated biochar; most preferably the composition includes up to 20% carbonated biochar; - Carbonate biochar contains at least 1% adsorbed carbon; preferably carbonate biochar contains at least 3% adsorbed carbon; preferably still carbonate biochar contains at least 5% adsorbed carbon; most preferably carbonate biochar contains at least 7% adsorbed carbon; - the composition contains from 70% to 99% of cement or alkali-activated binder; preferably the composition contains from 75% to 98% of cement or alkali-activated binder; preferably still the composition contains from 80% to 97% of cement or alkali-activated binder; most preferably the composition contains from 80% to 95% of cement or alkali-activated binder; - the composition contains an aluminous cement, a natural quick-setting cement, a Portland cement or a sulfoaluminate cement; and / or - the composition also contains a filler or a cementitious addition according to standard EN 197-1.

[0052] The cementitious composition according to the present invention can be prepared according to any

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[0063] process known to the person skilled in the art. By way of example, the composition according to the present invention can in particular be prepared by simply mixing in a mill or mixer a cement or an alkali-activated binder with the carbonated biochar or by mixing in a mill or mixer clinker, gypsum (and optionally limestone filler or any known additive) and carbonated biochar. The cementitious composition according to the present invention is therefore obtained from clinker, an alkali-activated binder or cement, and a carbonated biochar. The carbonated biochar can be obtained by any process known to those skilled in the art. By way of example, a process for preparing carbonated biochar may include the following steps: - introduction of biochar into a rotary drum, mixer, container or fluidized bed type reactor; - bringing the biochar into contact with a CO2 source such as the exhaust gases from a cement plant or a thermal power station; and - stopping the gas injection and recovering the resulting carbonated biochar. The cementitious composition 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 cementitious composition as defined above. Finally, the carbonated biochar described above can therefore be used as a cementitious additive. Thus, the present invention also relates to the use of a carbonated biochar as a cementitious additive. The present invention can be illustrated in a non-limiting way by the following examples. Example 1 - Carbonate biochar Carbonate biochar is obtained by placing approximately 500g of biochar obtained by pyrolysis of wood in a container which is itself placed in a hermetically sealed glass reactor. The reactor is equipped with a cup containing water to regulate the relative humidity in the reactor. This cup is placed at the bottom of the reactor under the tray containing the biochar. The reactor lid is fitted with a glass stopper with 2 holes that allow the injection and evacuation of gas. The gas injected for 65 hours is 100% CO2. The biochar thus carbonated has the following characteristics (Table 1).

[0064] [Tables 1] Biochar (before introduction into the reactor) Carbonate biochar Mass (in g) 501.6 502.5 TOC (%) 77.02 84.7

[0065] Table 1 - Biochar / carbonated biochar

[0066] Example 2 - Cementitious compositions according to the invention

[0067] A reference Portland cement of class CEM I 52.5 R is mixed with different quantities of powder of the carbonated biochar obtained in Example 1 or with the powder of the non-carbonated biochar used in Example 1.

[0068] The biochar powder is obtained by grinding biochar in which all particles are less than 2 mm and the d50 is 43 µm. Once ground in a ring mill, the biochar has a d50 of 1 µm.

[0069] The composition of the cementitious compositions 2, 4 and 6 (compositions according to the invention) and 3, 5 and 7 (cementitious compositions prepared from a non-carbonate biochar) thus obtained is reported in the following Table 2.

[0070] [Tables2] Cementitious Composition 1 (Reference) 2 3 4 5 6 7 CEM I 52.5 (% w / w) 100 97 97 95 95 90 90 Carbonate Biochar (% w / w) 0 3 0 5 0 10 0 Biochar (% w / w) 0 0 3 0 5 0 10 TOC (%) 0.23 1.98 1.94 3.57 3.38 7.76 7.41

[0071] Table 2 - Cementitious compositions 1 to 7

[0072] The CO2 emission gain for cement compositions 2 to 7 compared to the reference cement composition 1 is reported in the following Table 3.

[0073] [Tables3] Composition of the column 2 3 4 5 6 7 CO2 gain compared to the reference (KgCO2 eq / t) 135 134 207 205 385 382

[0074] Table 3 - CO2 Gain for Cementitious Compositions 2 to 7 Example 3 - Mechanical Performance

[0075] The compressive strength of the cementitious compositions 1, 2, 4, 6 and 7 obtained in Example 2 was measured on prismatic specimens of standardized mortar (4x4x6cm3), at different intervals (1, 2, 7 and 28 days) according to standard EN 196-1.

[0076] The results obtained are reported in the following Table 4.

[0077] [Tables4] Cementitious composition 1 2 4 6 7 Rc (in MPa) at 1 day 29.3 25.9 25 23.3 22.1 Rc (in MPa) at 2 days 41.7 37.8 35.3 35.1 31.7 Rc (in MPa) at 7 days 52.9 49.8 47.1 48.7 43.7 Rc (in MPa) at 28 days 61.6 60.1 58 56.8 54

[0078] Table 4 - Compressive strengths of cementitious compositions 1, 2, 4, 6 and 7

[0079] The cementitious compositions according to the invention (i.e. 2, 4 and 6) exhibit acceptable performance with regard to those observed for the reference CEM I at all deadlines.

[0080] The cementitious compositions according to the invention (i.e. 2, 4 and 6) exhibit acceptable performance compared to that observed for the reference CEM I at all deadlines.

[0081] Conversely, a decrease in the mechanical performance of composition 7 containing 10% non-carbonated biochar is observed, whereas for composition 6 containing carbonated biochar in the same proportions, mechanical performance is maintained at an acceptable level in the short, medium, and long term. The addition Therefore, 10% carbonated biochar allows us to maintain a higher level of resistance than that observed for the composition containing the same amount of non-carbonated biochar.

Claims

Demands

1.

2. Cementitious composition comprising at least 5% carbonated biochar. Cementitious composition according to claim 1, characterized in that it comprises up to 30% carbonated biochar.

3. Cementitious composition according to claim 2, characterized in that it comprises up to 25% carbonated biochar.

4. Cementitious composition according to any one of claims 1 to 3 characterized in that the carbonated biochar contains at least 1% adsorbed carbon

5. Cement composition according to any one of claims 1 to 4, characterized in that it contains from 70% to 95% cement or alkali-activated binder.

6. Cement composition according to any one of claims 1 to 5, characterized in that it contains an aluminous cement, a natural rapid cement, a Portland cement or a sulfoaluminous cement.