Use of carbonated biomass ash as a substitute cementitious material

Abstract

The invention relates to the use of carbonated biomass ash as a substitute cementitious material.

Description

[0001] USE OF CARBONATED BIOMASS ASH AS A MATERIAL

[0002] SUBSTITUTION CEMENT

[0003] The present invention relates to the use of carbonated biomass ash as a substitute cementitious material.

[0004] 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". The firing of this raw material produces an intermediate product, clinker, which, when ground with calcium sulfate and possible mineral additions, produces 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.

[0005] The most widely used cements are Portland cements. Portland cements are made from Portland clinker, obtained after clinkerization at a temperature of around 1450°C of a raw material rich in calcium carbonate in a kiln. 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).

[0006] However, in 2014, the quantity of cement sold worldwide was around 4.2 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, that is, cements with at least the same strength and quality characteristics as Portland cements, but which, during their production, release less CO2.

[0007] During the production of clinker, the main constituent of Portland cement, the release of CO2 is linked to:

[0008] - up to 40% for heating the cement kiln, grinding and transport;

[0009] - up to 60% to so-called chemical CO2, or decarbonation. Decarbonation is a chemical reaction that takes place 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:

[0010] Natural carbonation of cement-based materials, particularly concrete, is a potential way to reduce the carbon footprint associated with the manufacturing process and use of cement. However, although concretes prepared from these cements naturally recarbonate during the lifetime of the structures to the extent of 15% to 20% of the decarbonation CO2 emitted during manufacturing, the carbon footprint associated with the production of Portland cement remains positive. It is therefore still necessary to reduce CO2 emissions during the production of Portland cement and / or to improve the processes for reusing end-of-life concrete.

[0011] To reduce CO2 emissions linked 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 exchanges;

[0013] - the development of new “low carbon” binders such as sulfo-aluminous cements prepared from raw materials with less limestone and at a lower firing temperature, which allows a reduction in CO2 emissions of around 35%;

[0014] - or the (partial) substitution of clinker in cements with materials that limit CO2 emissions.

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

[0016] Examples of alternative materials include blast furnace slag and fly ash from coal-fired power plants. However, the closure of coal-fired power plants is causing a shortage of good-quality fly ash. Furthermore, replacing clinker with limestone filler (i.e., an inactive material) essentially has a diluting effect and is accompanied by a significant drop in strength, which is problematic. 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 for both cleaning CO2-containing exhaust gases and producing additional cementitious material.The method described involves using recycled concrete fines comprising providing recycled concrete fines with dgo 1000 pm in stockpiles or a silo as a feedstock, rinsing the feedstock to provide carbonaceous material, removing the carbonaceous material and cleaned exhaust gas, and deagglomerating the carbonaceous material to form the additional cementitious material, and using stockpiles or a silo containing a recycled concrete fines feedstock with dgo 1000 pm for cleaning CO2-containing exhaust gas and simultaneously manufacturing additional cementitious material. However, this method requires drying the carbonated product before it can be used.

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

[0018] Biomass ash, i.e. ash obtained from the combustion of biomass such as wood, so-called annual plants, agricultural residues, paper and sewage treatment plant sludge (or WWTP sludge) is recovered through its use in various fields. Thus, it is noted that biomass ash is used in particular to stabilize foundation soils, for the treatment of liquid effluents or as a secondary raw material in ceramic products or as a mineral filler in bituminous coatings.

[0019] The use of carbonated biomass ash in the form of monoliths as a substitute for lightweight aggregates was studied by Hills Colin et al. in their publication "Valorisation of agricultural biomass-ash with CO2", Scientific Reports, vol.10, n°1, 1 December 2020. The use of such ash as a cement substitute, or, more generally, as a binder substitute, is never mentioned by the authors. Furthermore, the solution presented in this document only reduces the carbon footprint associated with the production of the construction material due to the capture of CO2 by the aggregate used to prepare it (the production of said aggregates does not produce (or produces little) CO2).

[0020] The use of biomass ash as an alternative to coal fly ash as a substitute material in cementitious compositions has also been evaluated. However, several authors, such as Ivana Carevic et al., “Correlation between physical and chemical properties of wood biomass ash and cement composites performances”, Construction and Bulling Materials, Vol.256, 30 September 2020, 119450, have found that the use of these ashes in cements or concretes leads to a loss of workability which makes the processing of cement or concrete difficult. Workability can be partially restored by increasing the amount of mixing water, but this increase in the W / C ratio results in a loss of mechanical strength.

[0021] This workability issue is also reported in Japanese patent application JP-A-2021-155720. The subject of this patent application is the provision of a method for preparing a construction material capable of capturing / immobilizing CO2 quickly. A method for preparing a construction material comprising a step of carbonating an alkaline solid containing calcium and then mixing it with a cement is notably described. It is nevertheless explained that the use of an alkaline solid containing calcium in cements is associated with workability problems and that the use of coal ash (i.e. fly ash) should be preferred in order to limit this effect.

[0022] However, it has now been found, quite surprisingly, that the carbonation of biomass ash allows its use as a cementitious additive without reducing the workability of the cement or concrete finally prepared. In addition, it has also been observed that carbonated biomass ash does not behave as simple fillers but participates in the increase in performance of the cement binder, which makes it possible to significantly increase the substitution rate of cement compared to conventional filler, thus making it possible to significantly reduce the carbon footprint of the finally prepared construction material while maintaining mechanical properties, and in particular medium and long-term compressive strengths compatible with the intended uses.The use of carbonated biomass ash as a substitute cementitious material therefore makes it possible to reduce the carbon footprint associated with the production of the construction material not only by capturing CO2 by the biomass ash, but also by significantly reducing the quantity of clinker to be produced to obtain said construction material.

[0023] Thus, the subject of the present invention is the use of carbonated biomass ash as a substitute cementitious material.

[0024] The use of carbonated biomass ash makes it possible to significantly increase the cement substitution rate compared to conventional fillers, and therefore to significantly reduce the carbon footprint of the construction material finally prepared from said cement, while maintaining workability and mechanical properties, and in particular medium and long-term compressive strengths compatible with the intended uses.

[0025] In the context of the present invention:

[0026] - “biomass ash” means any mainly basic residue from the combustion of various natural, non-fossil, plant-based organic materials such as wood, so-called annual plants, agricultural residues, paper and sewage treatment plant sludge (or WWTP sludge) containing less than 11% total carbon, less than 4% inorganic carbon, and at least 1% Na2 <D équivalent. De préférence, les cendres de biomasse contiennent en outre au moins l’une des phases suivantes : whitlockite, hydroxyapatite, tremolite et / ou phosphate tricalcique ;

[0027] - “carbonated biomass ash” means any biomass ash which, after being brought into contact with a gas flow enriched in CO2, retains part of it and contains more than 4% inorganic carbon;

[0028] - “aluminous cement” means any cement, amorphous or not, obtained by cooking a mixture of limestone and bauxite and containing at least 5% monocalcium aluminate CA;

[0029] - “quick-setting natural cement” means any hydraulic binder with rapid setting and hardening in accordance with standard NF P 15-314: 1993 in force on the date of the present invention. Preferably, “quick-setting natural cement” means a cement prepared from a clinker comprising: from 0% to 20% of C3S; from 40% to 60% of C2S; from 7% to 12% of C4AF; from 2% to 10% of C3A; from 10% to 15% of CaCOs (calcite); from 10% to 15% of Cas(SiO4)2CO3 (spurrite); from 3% to 10% of sulfate phases: yeelimite C4A3$, langbeinite (K2Mg2(SO4)3, anhydrite (CaSO4); and from 10% to 20% of lime, periclase, quartz and / or one or more amorphous phases;

[0030] - “Portland cement” means any Portland clinker-based cement classified as CEM (I, II, III, IV or V) according to standard NF EN 197-1;

[0031] - “sulfoaluminous cement” means any cement prepared from a sulfoaluminous clinker containing from 5% to 90% of the C4A3$ 'yeelimite' phase, a sulfate source, and, optionally, a limestone addition;

[0032] - "cementitious composition" means any composition based on cement or alkali-activated binder and free from aggregates, preferably any composition comprising an aluminous cement, a quick-setting natural cement, a Portland cement and / or a sulfo-aluminous cement and free from aggregates, capable of being used for the preparation of a construction material;

[0033] - “substitute cementitious material” means any composition capable of partially replacing a cementitious composition in the preparation of a construction material while contributing to the increase in performance of the cementitious binder resulting from this combination;

[0034] - we mean by "Na2 <D équivalent » ou « Na2<D eq. » la teneur en alcalis d’un ciment calculé selon la formule suivante : % Na2<D eq. = (% Na2<D + 0.658 % K2O) soluble dans l'acide ;

[0035] - "loss on ignition" means the cumulative content of bound water, organic matter, CO2 in carbonates (limestone fillers and carbonate part of the material) and any oxidizable elements. Loss on ignition is determined by calcination in air at a temperature of (950 + / - 25°C) according to the method described in standard NF EN 196-2 (classification index P 15-472) - Test methods for cements - Part 2: Chemical analysis of cements; and

[0036] - “construction material” means a mortar or concrete. In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement:

[0037] - C represents CaO;

[0038] - A represents AI2O3;

[0039] - F represents Fe2Os;

[0040] - S represents SiC>2; and

[0041] - $ represents SO3.

[0042] In the context of the present invention, the “inorganic carbon content” or “CIT” corresponds to the quantity (% w / w) of inorganic carbon contained in an entity (e.g. carbonated biomass ash) relative to the total weight of said entity (e.g. said carbonated biomass ash).

[0043] To determine the inorganic carbon content, different methods can be used, such as a previously calibrated Carbon Hydrogen Sulfur (CHS) elemental analyzer. To do this, approximately 250 mg of the product to be analyzed is placed in a nickel boat. This boat is then introduced into a quartz tube furnace, allowing a gradual increase in temperature and temperature plateaus to separate the different carbon species in a sample.It is thus possible to determine: the “TOC”, i.e. the quantity (% w / w) of total organic carbon of the entity determined by analysis of the signal obtained between 100°C and 400°C with a plateau at 400°C; the “C”, i.e. the quantity (% w / w) of elemental carbon of the entity determined by analysis of the signal obtained between 400°C and 600°C with a plateau at 600°C; and the “CIT”, i.e. the quantity (% w / w) of total inorganic carbon of the entity determined by analysis of the signal obtained between 600°C and 1000°C with a plateau at 1000°C.

[0044] Total carbon “CT” corresponds to the sum of these three values: CT = COT+C+CIT

[0045] Finally, in the context of the present invention, the proportions expressed in % correspond to mass percentages relative to the total weight of the entity (e.g. ash) considered. The present invention therefore relates to the use of carbonated biomass ash as a substitute cementitious material. Preferably, the carbonated biomass ash has the following characteristics, chosen alone or in combination: the carbonated biomass ash contains at least 4.5% inorganic carbon; preferably the carbonated biomass ash contains at least 5% inorganic carbon; most preferably the carbonated biomass ash contains at least 5.5% inorganic carbon; the carbonated biomass ash contains less than 10% lime; preferably the carbonated biomass ash contains less than 5% lime;most preferably, the carbonated biomass ash contains less than 3% lime; the carbonated biomass ash contains more than 2% carbonates; preferably the carbonated biomass ash contains more than 15% carbonates; most preferably, the carbonated biomass ash contains more than 25% carbonates; the carbonated biomass ash contains less than 60% SiC>2; preferably the carbonated biomass ash contains less than 40% SiC>2; most preferably, the carbonated biomass ash contains less than 30% SiC>2; the carbonated biomass ash contains less than 40% ALOs; preferably the carbonated biomass ash contains less than 30% A Os; most preferably, the carbonated biomass ash contains less than 20% AI2O3;the carbonated biomass ash contains calcite, kalcinite, carbo-hydroxyapatite and / or hydrocalumina; and / or the carbonated biomass ash has a loss on ignition of at least 5%; preferably the carbonated biomass ash has a loss on ignition of at least 15%; most preferably the carbonated biomass ash has a loss on ignition of at least 20%;

[0046] The carbonated biomass ash according to the present invention makes it possible to achieve substitution rates of up to 45% of the cementitious composition, preferably up to 40% of the cementitious composition, most preferably up to 35% of the cementitious composition, while maintaining mechanical properties, and in particular medium and long-term compressive strengths of the construction material finally prepared, compatible with the intended uses.

[0047] The carbonated biomass ash used in the context of the present invention may be obtained according to any method known to those skilled in the art. By way of example, mention may in particular be made of a method for preparing carbonated biomass ash comprising the following steps: introducing the biomass ash into a reactor of the rotating drum, mixer, container or fluidized bed type; bringing the ash into contact with a source of CO2 such as exhaust gases from a cement plant or a thermal power plant; and recovering the carbonated biomass ash obtained.

[0048] The present invention may be illustrated in a non-limiting manner by the following examples.

[0049] Example 1 - Carbonated biomass ash

[0050] Different carbonated biomass ashes are obtained by placing a mixture of approximately 250 g of ashes obtained by combustion of different biomasses and 15% by mass of water ashes in a hermetically sealed bowl which is itself fixed on the base of a heating mixer robot.

[0051] The compositions and characteristics of the biomass ash used (Ash 1 to 4) before carbonation are reported in the following Table 1, in comparison with the composition and characteristics of the fly ash (non-carbonated) usually used in the cement industry.

[0052]

[0053] Table 1 - Composition and characteristics of biomass ash before carbonation

[0054] The reactor is equipped with a cup containing water to regulate the relative humidity in the reactor.

[0055] The bowl temperature is maintained at 55°C. The bowl lid is equipped with two holes that allow gas to be injected and evacuated. The gas is injected during a mixing time of 1 hour and is 100% CO2.

[0056] Carbonated biomass ash has the following characteristics (Table 2), compared to non-carbonated biomass ash.

[0057] Table 2 - Ash / carbonate ash

[0058] Example 2 - Cementitious compositions according to the invention A reference Portland cement of class CEM I 52.5 R is mixed with different quantities of non-carbonated or carbonated ash from example 1.

[0059] The compositions of cementitious compositions 2 to 5 (compositions according to the invention) and 6 to 9 (cementitious compositions prepared from non-carbonated ash) thus obtained are reported in Tables 3.1, 3.2 and 3.3 below.

[0060]

[0061] Table 3.1 - Cementitious compositions 1 to 9

[0062]

[0063] Table 3.2 - Cementitious compositions 1 to 9 (phase composition)

[0064] Table 3.3 - Cementitious compositions 1 to 9 (elemental analysis)

[0065] The CO2 emission gain for cement compositions 2 to 5 compared to the reference cement composition 1 is reported in Table 4 below.

[0066] Table 4 - CO2 gain for cement compositions 2 to 5 Example 3 - Workability (spreading)

[0067] A spreading measurement was carried out in accordance with standard EN 1015-3 on 3 mortars manufactured according to standard 196-1 by mixing 450g of binder 1, 4 or 8, 1350g of sand and 225g of water.

[0068] The results are reported in the following Table 5.

[0069] Table 5 - Spreading measurement for cement compositions 1, 3 and 8

[0070] As these results show, the use of a mixture of cement and non-carbonated ash leads to a loss of almost 30% of workability. Carbonating the ash before mixing it with the cement limits the loss of rheology and maintains it at an acceptable level for good implementation.

[0071] Example 4 - Mechanical performance

[0072] The compressive strength of the cementitious compositions obtained in example 2 was measured on prismatic specimens of standardized mortar (4x4x16cm3), at different times (1, 2, 7 and 28 days) according to standard EN 196-1.

[0073] The results obtained are reported in the following Table 6.

[0074] Table 6 - Compressive strength of cementitious compositions 1 and 4 to 9

[0075] The cementitious compositions according to the invention (i.e. compositions 4 and 5) exhibit acceptable performances compared to those observed for the reference CEM I at all timescales. We thus note a maintenance of mechanical performances in the short, medium and long term at an acceptable level.

[0076] On the other hand, there is a significant decrease in the mechanical performance of cement compositions containing non-carbonated biomass ash.

[0077] Example 5 - Comparative Examples

[0078] 5.1 - Cement composition based on coal-type fly ash

[0079] The coal-type fly ash whose composition is reported in Table 1 is carbonated according to the protocol of Example 1.

[0080] Cement composition 10 is obtained by mixing a reference Portland cement of class CEM I 52.5 R with the carbonated ash thus obtained in a proportion (% w / w) 75 / 25. 5.2 - Carbonated cement composition after addition of non-carbonated ash

[0081] Cement composition 11 is obtained by carbonation according to the protocol of example 1 of a 75 / 25 (% w / w) mixture of a reference Portland cement of class CEM I 52.5 R with paper ash no. 4 of example 1 (non-carbonated ash).

[0082] 5.3 - Comparative results

[0083] 5.3.1 - Maneuverability (spread)

[0084] The workability of cement composition 11 is evaluated according to the protocol of example 3.

[0085] The mortar prepared from cement composition 11 is too dry and therefore does not spread, making it impossible to use.

[0086] 5.3.2 - Compressive strength

[0087] The compressive strength of cement compositions 10 and 11 is evaluated according to the protocol of example 4.

[0088] The results obtained are reported in the following Table 7.

[0089] Table 7- Compressive strength of cement compositions 10 and 11

[0090] The compressive strengths of cementitious compositions prepared from fly ash from coal combustion are significantly lower than the compressive strengths of cementitious compositions prepared from carbonated biomass ash at 2, 7 and 28 days. The results obtained for cementitious composition 11 are extremely low (loss of more than 50% of performance compared to the 100% Portland reference) and make it unusable.

Claims

DEMANDS 1. Use of carbonated biomass ash as a substitute cementitious material.

2. Use according to claim 1, characterized in that the carbonated biomass ash contains at least 4.5% inorganic carbon.

3. Use according to claim 2, characterized in that the carbonated biomass ash contains at least 5% inorganic carbon.

4. Use according to claim 3, characterized in that the carbonated biomass ash contains at least 5.5% inorganic carbon.

5. Use according to any one of claims 1 to 4, characterized in that the carbonated biomass ash contains less than 10% lime.

6. Use according to any one of claims 1 to 5, characterized in that the carbonated biomass ash contains more than 2% carbonates.

7. Use according to any one of claims 1 to 6, characterized in that the carbonated biomass ash contains less than 60% of SiC>2.

8. Use according to any one of claims 1 to 7, characterized in that the carbonated biomass ash contains less than 40% ALOs.

9. Use according to any one of claims 1 to 8, characterized in that the carbonated biomass ash contains calcite, kalcinite, carbo-hydroxyapatite and / or hydrocalumine.

10. Use according to any one of claims 1 to 9, characterized in that the carbonated biomass ash has a loss on ignition of at least 5%.

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