Hydraulic binder

Abstract

The invention relates to a hydraulic binder comprising 50 to 85% by weight of a source of calcium sulfate, 5 to 35% by weight of biomass ash and 0 to 30% by weight of a pozzolanic material.

Description

Title of the invention: Hydraulic binder

[0001] The invention relates to the field of construction materials. It relates more particularly to hydraulic binders as well as to dry mortar compositions comprising said hydraulic binders.

[0002] Dry mortar compositions are generally powdered mixtures comprising a hydraulic binder and aggregates. After mixing ("mixing") with water, a paste (wet or fresh mortar) is obtained which can be shaped and then hardened to form a hardened mortar. Such mortars can have various applications: facade coatings, tile adhesives, flooring products such as screeds, jointing mortars, masonry mortars and many others.

[0003] Depending on the intended applications, dry mortar compositions must meet a large number of requirements, relating both to their ability to be implemented (spreadability, workability, workability, pumpability, rheology, etc.) and to the hardened mortar (in particular its mechanical strength, for example compressive strength).

[0004] For flooring products in particular, such as screeds, several properties are important. The spread of the fresh mortar must be high in order to obtain self-leveling properties. The mortar must also be able to harden quickly in order to reduce construction times. The compressive strength must also be high. The dimensional stability of the mortar is also important, during hardening, but also afterwards, for example if the hardened mortar comes into contact with water.

[0005] Hydraulic binders for soil products based on Portland cement are known. The environmental footprint of these binders is, however, high because the Portland clinker manufacturing processes require decarbonation, calcination and clinkerization operations by heating, particularly at very high temperatures of around 1450°C. Portland cements, for example, are responsible for emissions of around 800 kg of CO2 per tonne of cement produced. They also consume energy and natural resources.

[0006] The invention aims to overcome these drawbacks by proposing a hydraulic binder with a low environmental footprint and suitable for obtaining mortars, in particular for flooring products, by having self-leveling properties, rapid hardening and good dimensional stability, in particular after exposure to water.

[0007] For this purpose, the invention relates to a hydraulic binder comprising 50 to 85% by weight of a source of calcium sulfate, 5 to 35% by weight of biomass ash and 0 to 30% by weight of a pozzolanic material.

[0008] The source of calcium sulfate is preferably chosen from hemihydrate, gypsum and anhydrite, alone or in a mixture.

[0009] Biomass ash is ash formed by the combustion of biomass, used for example to produce electricity, steam and / or heat. The biomass may come from, for example, agricultural products, forestry products, household and municipal waste, the paper or pulp industry and / or crops for energy production.

[0010] Preferably, the biomass ash comprises, or even consists of, ash obtained by combustion of waste (or residues, or by-products) from the paper or pulp industry. This ash has proven to be particularly reactive. For example, this waste may be produced during the production of paper or cardboard from recycled paper or cardboard. This waste may, for example, be recovered during the pulping step, during which water and chemicals such as hydrogen peroxide, sodium hydroxide and sodium silicate are added to the shredded paper in order to separate the cellulose fibers, and / or during the screening steps.

[0011] According to other embodiments, the biomass ash comprises, or consists of, ash obtained by combustion of wood and residues from the paper or pulp industry. According to other embodiments, the biomass ash comprises, or consists of, wood ash. The wood ash is generated by combustion of wood or forest products. The wood ash is in particular obtained by combustion of forest waste, wood waste (bark, sawdust), wood residues or residues from the paper or wood pulp industry. The biomass can for example be produced during logging activities for the paper pulp industry or other wood-related industries and during forest clearing for forest fire prevention.For example, biomass ash may include, or consist of, fly ash obtained by burning wood, bark, forest residues and / or wood residues. The wood is, for example, selected from pine and eucalyptus. The wood may also come from demolition sites or household wood waste.

[0012] Regardless of the biomass source, combustion is preferably carried out by fluidized bed combustion, particularly by bubbling fluidized bed combustion. Other combustion methods are fixed bed combustion or circulating fluidized bed combustion.

[0013] Regardless of the combustion process, the biomass ash used in the present invention is preferably recovered from the flue gases (e.g., by filtration), as opposed to ash recovered from the bottom of the boiler, which frequently contains undesirable materials such as heavy metals.

[0014] Biomass ashes can exhibit different reactivities depending on their chemical and / or mineralogical composition, which depends on the type of biomass as well as the combustion technology. For example, a high temperature (at least 700 or 800°C) allows the production of interesting mineralogical phases, in particular when the residence time of the biomass in the boiler is long. Some biomass ashes thus exhibit a very high reactivity, sometimes higher than that of Portland cement.

[0015] Preferably, the biomass ash comprises, or consists of, biomass ash having a chemical composition by weight comprising 5-35%, in particular 9-30% of SiO2, 3-20%, in particular 5-15% of Al2O3, 0-5%, in particular 0.5-3% of Fe2O3 and 30-70%, in particular 40-65% of CaO. Such biomass ash is very reactive and will be referred to as "highly reactive biomass ash" in the present text. The biomass ash of the hydraulic binder according to the invention preferably comprises at least 60% by weight, in particular at least 70% and even at least 80% or at least 90%, or even 100%, of such highly reactive biomass ash. Examples of such biomass ash are those obtained by burning waste or residues from the paper and pulp industry, particularly when they have been heated to high temperatures (e.g. at least 700 or 800°C).

[0016] Other, less reactive biomass ashes have an average chemical composition comprising (by weight) 38-55% SiO2, 5-12% Al2O3, 1-7% Fe2O3, 6-30% CaO and 1-7% K2O. Such a composition comprises in particular 40-50% SiO2, 8-10% Al2O3, 2-5% Fe2O3, 10-30% CaO and 2-8% K2O. Such biomass ashes will be referred to as "moderately reactive ashes" in the present text. The weight content of moderately reactive ashes is preferably less than 40%, in particular less than 30% or less than 20%, even less than 10%, or even 0%, relative to the total weight of biomass ashes. Examples of such moderately reactive ashes are certain wood ashes.

[0017] The loss on ignition of the biomass ash is preferably less than 20% by weight, in particular less than 15% and even less than 10% or 5%.

[0018] The biomass ash may be a mixture of different biomass ashes. In particular, the biomass ash may be a mixture of ashes highly reactive ash and moderately reactive ash, for example to adjust the setting and hardening characteristics of the binder. Preferably, the weight ratio between highly reactive ash and moderately reactive ash is at least 60:40, in particular at least 70:30, even at least 80:20 or at least 90:10.

[0019] The biomass ash preferably comprises at least 10% by weight of hydraulic phases, more particularly at least 15%, even at least 20%, relative to the total weight of biomass ash. This content is even advantageously at least 25% or even at least 30%. It is preferably at most 60% and even at most 50%. The hydraulic phases are preferably chosen from calcium silicates, calcium aluminates, free lime (CaO) and mixtures thereof. The calcium silicates and calcium aluminates preferably comprise one or more of the following phases: C2S, C3S, C3A, C4AF, C2A2S, CA, C12A7 and CA2. The biomass ash preferably comprises at least 10% by weight of C2S phases, at least 5% by weight of C2A2S phases and at least 1% by weight of C3A phases, relative to the total weight of biomass ash.The C3S phase content is preferably at most 1% by weight, or even zero, because it prevents the formation of aluminate phases during hydration. The free lime content in the biomass ash is preferably at least 5% by weight, even at least 10%, for example 5 to 18%.

[0020] The biomass ash may also comprise amorphous phases, in particular comprising CaO, Al2O3 and SiO2, in contents allowing the dissolution of these elements. The quantity of amorphous phase is for example 10 to 25% by weight.

[0021] The biomass ash may comprise free (metallic) aluminum, but preferably in an amount of at most 3% by weight relative to the total weight of biomass ash, since this compound can cause expansion of the mortar during curing. In some embodiments, the free aluminum content is at most 1% by weight, or even zero.

[0022] The biomass ash may comprise additional reactive phases, such as carbonates (especially calcite), sulfates (e.g., calcium sulfate) or aluminosilicates. The calcite content is preferably 10 to 40% by weight, relative to the total weight of biomass ash.

[0023] In terms of particle size, the D50 (based on volume distribution) of the biomass ash is preferably 8 to 50 pm, in particular 10 to 30 pm, for example about 15 pm. The maximum size (Dmax) is preferably less than or equal to 200 pm. These dimensions are generally measured by laser particle size analysis.

[0024] The pozzolanic material is preferably chosen from fly ash, calcined clays, silica fumes, calcined shales and natural or calcined pozzolans. The calcined clay is advantageously metakaolin. The pozzolanic material helps reduce dimensional variations of the mortar after exposure to water. However, its presence is optional.

[0025] Preferably, the total content of calcium sulfate source, biomass ash and pozzolanic material is at least 80% by weight, in particular at least 85% by weight, or even at least 90% by weight, and even at least 95% by weight (relative to the total weight of hydraulic binder). According to one embodiment, the hydraulic binder consists of the calcium sulfate source, biomass ash and pozzolanic material. According to another embodiment, the hydraulic binder consists of the calcium sulfate source and biomass ash.

[0026] Preferably, the binder comprises little or no cement. The cement content is advantageously less than 5% by weight, and preferably the cement content is zero. The cements include in particular Portland cements, belitic cements, aluminous cements, and sulfoaluminous cements. The term "cement content" means the total content of cements possibly contained in the binder.

[0027] The content of calcium sulfate source is preferably between 55 and 80% by weight, in particular between 60 and 75% by weight, or even between 65 and 72% by weight.

[0028] The biomass ash content is preferably between 8 and 30% by weight, in particular between 10 and 25% by weight, or even between 15 and 22% by weight.

[0029] The content of pozzolanic material is preferably between 5 and 25% by weight, in particular between 10 and 20% by weight, or even between 12 and 18% by weight.

[0030] All combinations between these preferred content ranges are of course possible, even if they are not all listed here for reasons of brevity. As a preferred example, the binder may advantageously comprise 55 to 80% by weight of a calcium sulfate source, 8 to 30% by weight of biomass ash and 5 to 25% by weight of a pozzolanic material. According to another preferred example, the binder comprises 60 to 75% by weight of a calcium sulfate source, 10 to 25% by weight of biomass ash and 10 to 20% by weight of a pozzolanic material.

[0031] The invention also relates to a dry mortar composition comprising a hydraulic binder according to the invention and aggregates.

[0032] The composition is designated as dry since the majority, if not all, of these constituents are in powder form. The percentages of each of the constituents are given as mass percentages relative to the totality of the components of said composition.

[0033] The aggregates generally used in mortar compositions have a diameter of less than 8 mm, preferably less than 4 mm, or even less than 3 mm, which distinguishes mortar compositions from concrete compositions, which contain coarse aggregates. The aggregates may comprise fillers, which are finely ground inert mineral materials, generally of the calcareous or siliceous type. Preferably, the aggregates comprise sands, in particular siliceous sands and / or fillers, in particular calcareous or dolomitic fillers. The aggregates may also comprise lightweight aggregates chosen from perlite, vermiculite, expanded glass beads, expanded polystyrene beads, cenospheres, expanded silicates, aerogels and mixtures thereof.

[0034] The total content of aggregates is preferably between 40 and 90%, in particular between 50 and 80%, or even between 60 and 75% by weight relative to the dry mortar composition.

[0035] The dry mortar composition may also comprise one or more additives, chosen from rheological agents, plasticizing or superplasticizing agents, water-retaining agents, air-entraining agents, thickening agents, biocidal protective agents, dispersing agents, pigments, setting or hardening accelerators and / or retarders, polymeric resins and anti-foaming agents. The total content of additives and adjuvants preferably varies between 0.001 and 5% by weight relative to the total weight of the dry composition.

[0036] The dry mortar composition preferably comprises an expansion-inhibiting agent, in particular chosen from lithium salts (in particular lithium nitrate and sodium sulfate), nitrates (in particular sodium or potassium nitrates) and carboxylic acids (in particular oxalic acid and citric acid). The total content of expansion-inhibiting agent is preferably between 0.5 and 3.0%, in particular between 1.0 and 2.5% relative to the weight of hydraulic binder.

[0037] Preferably, in particular for application as a floor product, the dry composition comprises superplasticizing agents and retarders. The retarder is preferably a carboxylic acid or a carboxylic acid salt, in particular tartaric acid.

[0038] The presence of these different additives makes it possible, in particular but not exclusively, to adapt the setting time or the rheology of the wet mortar composition, that is to say after mixing with water, so as to meet expectations depending on the desired product.

[0039] The invention also relates to a method for obtaining a floor product comprising mixing with water a dry mortar composition according to the invention to obtain a wet mortar and depositing said wet mortar on a substrate.

[0040] The weight content of added water, relative to the total weight of hydraulic binder, is preferably between 0.4 and 0.7, in particular between 0.5 and 0.6.

[0041] The floor product is in particular a self-leveling screed. Floor products will traditionally be obtained by curing in air and at room temperature the mortar obtained after mixing. For example, screeds are obtained by mixing the dry mortar composition with water, then pouring the resulting liquid onto a substrate so as to obtain a layer which is then left to harden in air and at room temperature. The substrate is for example a concrete slab or floor.

[0042] The hydraulic binder is however not limited to obtaining floor products, but can also be advantageously used in all types of mortar compositions, such as facade coatings, tile adhesives, jointing mortars, repair mortars or even masonry mortars.

[0043] Examples

[0044] The following examples illustrate the invention in a non-limiting manner.

[0045] Dry mortar compositions were obtained by mixing the components indicated in Table 1 below (contents in weight percentages relative to the weight of dry mortar composition).

[0046] [Tables 1] Cl 1 2 [3-hemihydrate 25 25 25 Portland cement 7 0 0 Biomass ash 1 0 7 0 Biomass ash 2 0 0 7 Metakaolin 5 5 5 Limestone filler 13 13 13 Silica sand 50 50 50 Superplasticizer 0.4 0.6 0.6 Retarder 0.06 0.02 0.0.1

[0047] Example C1 is a comparative example using Portland cement instead of biomass ash.

[0048] Biomass ash 1 was an ash resulting from the combustion of waste from the paper industry. It comprised as main elements 11% SiO2, 11% A12O3, 1% Fe2O3, 57% CaO, 2% MgO. In terms of mineralogical composition, it comprised 13% by weight of C2S phase, 6% of C2A2S phase, 2% of C3A phase, 5% of CaO, 4% of Ca(OH)2, 38% of calcite and 23% of amorphous phase.

[0049] Biomass ash 2 was an ash from the combustion of wood panel waste. Its main components were 43% SiO2, 9% A12O 3.4% Fe2O3, 26% CaO, 1% Na2O, 5% K2O and 3% MgO. In terms of mineralogical composition, it comprised 47% by weight of amorphous phase, 13% quartz, 9% calcio-olivine, 6% akermanite, 4% albite and 6% Ca(OH)2.

[0050] The setting and hardening retardant was tartaric acid.

[0051] The mixing of the compositions was carried out by adding water, in an amount such that the ratio between the amount of water and the total weight of binder and fillers was 0.4.

[0052] Table 2 below indicates for each of the wet mortars, the spreading value as well as the setting time, the spreading value, expressed in mm corresponding to an average of 3 measurements taken after 3 minutes, using a ring 68 mm in diameter and 35 mm in height.

[0053] [Tables2] Cl 1 2 Spread (mm) 219 214 220 Setting time (min) 76 94 101

[0054] These results show that the binder according to the invention behaves in a very acceptable manner in terms of rheology and hardening kinetics.

[0055] The dimensional stability and mechanical strength of the hardened mortars were evaluated after immersion in water at 5°C.

[0056] Examples 1 and 2 showed no dimensional variation, even after 150 days of immersion. On the other hand, comparative example Cia showed very strong swelling, with a very strong dimensional variation, greater than 5 mm / m after 5 days of immersion, and 20 mm / m after 30 days of immersion, leading to the destruction of the sample.

[0057] In terms of compressive strength, the examples according to the invention had strengths greater than 5 MPa after 3 months of immersion (8 MPa for example 1, and 6 MPa for example 2). The compressive strength even increased over time, a sign of continued hydration of the binder. On the other hand, the compressive strength of comparative example C1 was less than 3 MPa already after 1 month of immersion, and close to 0 after 3 months.

[0058] The binder according to the invention therefore makes it possible to obtain rapid-setting mortars, exhibiting high spreadability, and retaining very good properties even after immersion in cold water.

Claims

Claims

1. A hydraulic binder comprising 50 to 85% by weight of a calcium sulfate source, 5 to 35% by weight of biomass ash and 0 to 30% by weight of a pozzolanic material.

2. Hydraulic binder according to claim 1, in which the source of calcium sulfate is chosen from hemihydrate, gypsum and / or anhydrite, alone or in a mixture.

3. Hydraulic binder according to one of the preceding claims, in which the pozzolanic material is chosen from fly ash, calcined clays, silica fumes, calcined schists and natural or calcined pozzolans.

4. Hydraulic binder according to one of the preceding claims, wherein the total content of calcium sulfate source, biomass ash and pozzolanic material is at least 80% by weight, and even at least 95% by weight.

5. Hydraulic binder according to one of the preceding claims, in which the cement content is less than 5% by weight, and preferably in which the cement content is zero.

6. Hydraulic binder according to one of the preceding claims, in which the content of calcium sulfate source is between 55 and 80%, in particular between 60 and 75% by weight.

7. Hydraulic binder according to one of the preceding claims, in which the biomass ash content is between 8 and 30%, in particular between 10 and 25% by weight.

8. Hydraulic binder according to one of the preceding claims, in which the content of pozzolanic material is between 5 and 25%, in particular between 10 and 20% by weight.

9. Dry mortar composition comprising a hydraulic binder according to one of the preceding claims and aggregates.

10. A method of obtaining a floor product comprising mixing with water a dry mortar composition according to the preceding claim to obtain a wet mortar and depositing said wet mortar on a substrate.