Patent Application
20250154056
The present invention relates to the use of carbonated biomass ash as a cementitious material substitute.
The manufacture of binders, in particular the hydraulic binders, and in particular that of cements, essentially consists in calcining a mixture of carefully selected and dosed raw materials, also called «raw-mix». The cooking of this raw material produces an intermediate product, the clinker, which, when milled with calcium sulfate and possible mineral additions, will produce cement. The type of manufactured cement depends on the nature and proportions of the raw materials as well as the cooking method. There are several types of cements: Portland cements (which represent most of cements produced in the world), aluminous cements (or calcium aluminate), natural quick setting cements, sulpho-aluminous cements, sulfo-belitic cements and other intermediate varieties.
The most widely used cements are the Portland type cements. The Portland cements are obtained from Portland clinker, obtained after clinkering at a temperature in the range of 1450° C. from a raw-mix material rich in calcium carbonate in a furnace. The production of one ton of Portland clinker is accompanied by the emission of significant quantities of CO2 (about 0.8 to 0.9 tons of CO2 per ton of cement in the case of a clinker).
Yet, in 2014, the amount of cement sold worldwide was around 4.2 billion tons (source: French Trade Union for the Cement Industry—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 to say cements having at least the same strength and quality features as Portland cements, but which, during their production, emit less CO2.
During the production of clinker, the main constituent of Portland cement, the release of CO2 is linked to:
The decarbonation is a chemical reaction that takes place when limestone, the main raw material for the manufacture of Portland cement, is heated at high temperatures. The limestone is then transformed into quick lime and CO2 according to the following chemical reaction:
CaCO3→CaO+CO2
The natural carbonation of cement-based materials, particularly concretes, is a potential way to reduce the carbon footprint linked to the manufacturing process and use of cement. However, although concrete prepared from these cements are naturally recarbonated during the life of the structures to the tune of 15% to 20% of the CO2 emitted during the manufacturing, the carbon balance associated with the production of Portland cement remains positive. It therefore remains necessary to reduce CO2 emissions during the production of Portland cement and/or to improve end-of-life concrete recovery methods.
To reduce the CO2 emissions related to the production of Portland cement, several approaches have been considered so far:
Among the above approaches, that of (partial) substitution of clinker in cements has been the subject of numerous developments.
Among the used substitute materials, it can notably cited slag from blast furnaces and fly ash from coal-fired power stations. However, the closure of coal-fired power stations is causing a shortage of good quality fly ash. Furthermore, the substitution of clinker with limestone filler (that is to say an inactive material) essentially has a dilution effect and is accompanied by a significant drop in strength, which is problematic.
Carbon capture and storage technologies have also been developed to limit the CO2 emissions from cement plants or coal-fired power plants. International patent application WO-A-2019/115722 describes a method allowing both the cleaning of CO2-containing exhaust gases and the manufacture of additional cementitious material. The described method involves using recycled concrete fines comprising the provision of recycled concrete fines with d90≤1000 μm into stocks or a silo as a starting material, rinsing the starting material to provide a carbonaceous material, the removal of the carbonaceous material and the cleaned exhaust gas, and the deagglomeration of the carbonaceous material to form the additional cementitious material, as well as the use of stocks or a silo containing a starting material of recycled concrete fines with d90≤1000 μm for cleaning CO2-containing exhaust gases and the simultaneous manufacture of an additional cementitious material. However, this method requires drying the carbonated product before it can be used.
At the date of the present invention, it therefore remains necessary to identify new substitute materials making it possible to significantly reduce the CO2 emissions during the production of cement while maintaining the mechanical properties of the construction materials prepared from these cements, in particular medium and long-term compressive strengths, at levels allowing their use.
The biomass ash, that is to say the ash obtained from the combustion of biomass such as wood, so-called annual plants, agricultural residues, paper and wastewater treatment plant sludge (or STEP sludge) are valued through their use in different fields. Thus, it is noted that biomass ash are used in particular to stabilize foundation soils, for the treatment of liquid effluents or even as a secondary raw material in ceramic products or as a mineral filler in bituminous coatings.
The use of carbonated biomass ash in the form of monoliths as a substitute for light aggregates was studied by Hills Colin et al. in their publication «Valorisation of agricultural biomass-ash with CO2», Scientific Reports, vol. 10, no 1, 1 Dec. 2020. The use of such ash as a cementitious substitute, or, more generally, as a binder substitute, is never mentioned by the authors. Moreover, the solution presented in this document only makes it possible to reduce 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 little) CO2.
The use of biomass ash as alternatives to coal fly ash as a substitute material in cementitious compositions was also evaluated. However, several authors, such as Ivana Carević et al., «Correlation between physical and chemical properties of wood biomass ash and cement composites performances», Construction and Building Materials, Vol. 256, 30 Sep. 2020, 119450, have found that the use of these ash in cements or concretes leads to a loss of workability which makes the implementation of the cement or concrete difficult. The 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.
This workability issue is also reported in Japanese patent application JP-A-2021-155720. The purpose of this patent application is to provide a method for preparing a construction material capable of capturing/immobilizing the CO2 quickly. A method for preparing a construction material comprising a step of carbonating an alkaline solid containing calcium then a mixing with a cement is described in particular. It is nevertheless explained that the use of alkaline solids 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.
Yet, it has now been found quite surprisingly that the carbonation of biomass ash allows their use as a cementitious addition without this reducing the workability of the cement or concrete finally prepared. Furthermore, it has also been observed that carbonated biomass ash do not behave like simple fillers but contribute to increasing the performance of the binder, which makes it possible to significantly increase the substitution rate of said binder compared to conventional filler, thus making it possible to significantly reduce the carbon footprint of the construction material finally prepared 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 cement substitute therefore makes it possible to lower the carbon footprint associated with the production of the construction material not only by the capture of CO2 by the biomass ash, but also by the significant reduction in the amount of clinker to be produced to obtain said construction material.
Thus, the present invention relates to the use of carbonated biomass ash as a cementitious material substitute.
The use of carbonated biomass ash makes it possible to significantly increase the cement substitution rate compared to conventional fillers, and therefore to significantly lower the carbon footprint of the construction material finally prepared from said binder, and while maintaining a workability and mechanical properties, and in particular medium and long-term compressive strengths compatible with the intended uses
In the context of the present invention:
the term «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; 20
In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement:
In the context of the present invention, the «inorganic carbon rate» or «CIT» corresponds to the amount (% 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).
To determine the level of inorganic carbon, different methods can be used, such as for example 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 tubular quartz furnace allowing a gradual rise in temperature and stages in temperature in order to separate the different carbon species in a sample. It can thus be determined:
The total carbon «CT» corresponds to the sum of these three values: CT=COT+C+CIT
Finally, in the context of the present invention, the proportions expressed in % correspond to weight percentages relative to the total weight of the considered entity (e.g. ash).
The subject of the present invention is therefore the use of carbonated biomass ash as a cementitious material substitute. Preferably, the carbonated biomass ash possess the following characteristics, selected alone or in combination:
The carbonated biomass ash according to the present invention make 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.
The carbonated biomass ash used in the context of the present invention can be obtained by any method known to those skilled in the art. By way of example, it can in particular be cited a method for preparing carbonated biomass ash comprising the following steps:
The present invention can be illustrated in a non-limiting manner by the following examples.
Different carbonated biomass ash are obtained by placing a mixture of approximately 250 g of ash obtained by combustion of different biomasses and 15% by mass of water ash in a hermetically sealed bowl which is itself fixed on the base of a heated mixing robot.
The compositions and features of the used biomass ash (Ash 1 to 4) before carbonation are reported in Table 1 below, in comparison with the composition and features of fly ash (non-carbonated) usually used in the cement industry.
The reactor is equipped with a cup containing water to regulate the relative humidity in the reactor.
The temperature of the bowl is maintained at 55° C. The bowl cover is equipped with 2 orifices which allow the injection of a gas and its evacuation.
The gas is injected for a mixing time of 1 hour and is made up of 100% CO2.
The biomass ash thus carbonated have the following features (Table 2), in comparison with non-carbonated biomass ash.
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.
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 the following Tables 3.1, 3.2 and 3.3.
The gain in CO2 emissions for the cement compositions 2 to 5 compared to the reference cement composition 1 is reported in the following Table 4.
A spreading measurement was carried out in accordance with standard EN 1015-3 on 3 mortars manufactured according to standard 196-1 by mixing 450 g of binder 1, 4 or 8, 1350 g of sand and 225 g of water.
The results are reported in the following Table 5.
As these results show, the use of a mixture of cement and non-carbonated ash leads to a loss of almost 30% in workability. Carbonating the ash before mixing with the cement makes it possible to limit the loss of rheology and maintain it at an acceptable level for a good implementation.
The compressive strength of the cementitious compositions obtained in Example 2 was measured on prismatic specimens of standardized mortar (4×4×16 cm3), at different time periods (1, 2, 7 and 28 days) according to standard EN 196-1.
The obtained results are reported in the following Table 6.
The cementitious compositions according to the invention (i.e. compositions 4 and 5) present acceptable performances with regard to those observed for the reference CEM I at all deadlines. It is thus noted that mechanical performance is maintained in the short, medium and long term at an acceptable level.
On the other hand, there is a sharp reduction in the mechanical performance of cementitious compositions containing non-carbonated biomass ash.
The coal-type fly ash whose composition is reported in Table 1 are carbonated according to the protocol of Example 1.
The cementitious 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 Cementitious Composition after Addition of Non-Carbonated Ash
The cementitious composition 11 is obtained by carbonation according to the protocol of Example 1 of a 75/25 mixture (% w/w) of a reference Portland cement of class CEM I 52.5 R with paper ash No. 4 of Example 1 (non-carbonated ash).
The workability of the cementitious composition 11 is evaluated according to the protocol of Example 3.
The mortar prepared from the cementitious composition 11 is too dry and therefore does not spread, making its implementation impossible.
The compressive strength of cementitious compositions 10 and 11 is evaluated according to the protocol of Example 4.
The obtained results are reported in the following Table 7.
The compressive strengths of the cement compositions prepared from fly ash from coal combustion are significantly lower than the compressive strengths of the cementitious compositions prepared from carbonated biomass ash at 2, 7 and 28 days. The obtained results for cementitious composition 11 are extremely low (loss of more than 50% of performance compared to the 100% Portland reference) and render it unusable.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR22/01386 | Feb 2022 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2023/050208 | 2/16/2023 | WO |
