A mortar or concrete composition

Abstract

The invention relates to a mortar or concrete composition comprising aggregates and a mineral binder, said mineral binder comprising activated clay particles made by subjecting powdered clay to a treatment with an acidic solution, then to a washing step, and then to a calcination step.

Description

A mortar or concrete composition

[0001] The invention relates to a mortar or concrete composition. More specifically, it relates to a composition comprising a binder that comprises activated clay particles.

[0002] A mortar composition is a pulverulent mixture comprising a hydraulic binder and aggregates (such as sands and fillers). After mixing with water, it forms a paste, called wet mortar, that can be applied on various substrates before setting and hardening, finally forming a hardened mortar. Mortars can for example be used as renders, plasters, flooring compounds, masonry mortars, tile adhesives, grouts etc. or to make constructions elements by additive manufacturing. A concrete composition is similar to a mortar composition, the main difference being that the aggregates contain coarser particles, such as crushed rock or gravels.

[0003] The hydraulic binder used in such compositions is often cement, especially Portland cement (OPC), the production of which requires huge amounts of energy and releases large amounts of CO2in the atmosphere. There is in consequence a need to provide compositions that have a much lower CO2footprint while still meeting the requirements for the intended use. To this end, many substitutes for cement have been proposed, including industrial by-products such as fly ashes or slags.

[0004] For some applications, the aesthetics of the final mortar or concrete, especially its color, is important. In such cases, white cement, such as white Ordinary Portland Cement (WOPC) is mainly used. It can be used in combination with pigments if specific color, other than white, is required. In such cases, many conventional substitutes for cement cannot be used because they impart a strong coloration.

[0005] A goal of the invention is to propose compositions where the use of white cement is reduced, so as to reduce its carbon footprint, while maintaining the required color.

[0006] To this end, an object of the invention is a mortar or concrete composition comprising aggregates and a mineral binder, said mineral binder comprising activated clay particles made by subjecting powdered clay to a treatment with an acidic solution, then to a washing step, and then to a calcination step.

[0007] Another object of the invention is a method for making such a mortar or concrete composition, comprising subjecting powdered clay to a treatment with an acidic solution, then to a washing step, and then to a calcination step to obtain activated clay particles, and mixing said activated clay particles with aggregates.

[0008] The inventors have discovered that clays, even when they are initially colored, for example gray, brown or red, can become white or off-white and show a good reactivity as a binder, by using a specific activation process that comprises an acid attack followed by washing and calcination. As explained in more details in the present specification, the activated clay can replace a large part of white cement or other hydraulic binders while keeping acceptable performances for the final product. The invention therefore makes it possible to use any kind of clays, whatever their initial color. It has also been observed that the acid treatment allowed to reduce the calcination temperature needed to achieve the same mechanical properties for the hardened product.

[0009] Throughout this specification, the term “powdered clay” will be used to designate the initial product, i.e., a raw clay in powdered form, while the term “activated clay” will be used to designate the clay that has been treated by an acidic solution, washed and calcined.

[0010] A clay is understood as a pulverulent material predominantly comprising at least one clay mineral. Clay may consist of one clay mineral or of a plurality of clay minerals. Alternatively, clay may contain, in addition to one or more clay minerals, other minerals such as, for example, quartz, feldspar, mica, etc. This is particularly the case when the clay is obtained by crushing a clay-bearing rock. Clay may also come from excavated soils, in particular as a result of construction work. Clay may also be recovered as wastes from different industries (construction industry, ceramic industry, production of construction materials, etc.).

[0011] Clay minerals are hydrated aluminosilicates of the phyllosilicate family. The clay (especially before the calcination step, so the powdered clay or raw clay) may for example comprise a mineral selected from kaolinite, smectite (in particular montmorillonite, saponite or beidellite), illite, hectorite, laponite and chlorite. Fibrous clay minerals such as sepiolite and attapulgite (also known as palygorskite) may also be used but are not preferred, in particular because they may comprise hazardous materials such as asbestos.

[0012] The clay is preferably a kaolinitic clay. In other words, the main mineral is a clay mineral from the kaolin group, especially kaolinite. The kaolin group also comprises dickite, halloysite and nacrite. The amount of mineral from the kaolin group in the clay is preferably at least 30wt%, even at least 40wt%, especially at least 50wt%. Kaolinite and other clay minerals of the kaolin group have a different structure than other clay minerals. Especially, minerals of the kaolin group are 1:1 clays, where the layers are uncharged and bonded by hydrogen bonds, while minerals of the smectite and illite groups are 2:1 clays, where the layers have a net negative charge and are bonded by individual cations. The acid treatment has proven particularly useful for kaolinitic clays.

[0013] It is known to calcine kaolinite-rich minerals to produce metakaolin, that shows pozzolanic activity. Calcination results in a dehydroxylation of the kaolinite and results in an amorphous mineral. Other clay minerals such as illite or smectite cannot however been activated by calcination only. For such minerals, EP2226363 has proposed to perform an acid treatment before calcination, said acid treatment removing the cations (such as calcium) present between the layers of the clay mineral and creating additional phases, for example calcium sulfate. No washing step is performed in order to preserve such phases in the activated clay, which is orange in color.

[0014] The particle size distribution in volume of the powdered clay (i.e., the initial product) is preferably such that the D50 is 1-15 µm, preferably 2-10 µm. Such distribution can be determined by laser granulometry. As conventional in the technique, D50 corresponds to the median diameter. To this end, raw clay may be crushed and / or milled.

[0015] The powdered clay is preferably not white, for example brown, gray or dark red (before the acidic treatment). Typically, the lightness L* in reflection is less than 70, even less than 60, for example between 30 and 55. The absolute value of the parameters a* and / or b* is preferably more than 5, even more than 10 or more than 15, for example between 10 and 30. The values of L*a*b* are defined by the CIE 1976 standard and may be calculated from a spectrum in reflection.

[0016] Before the treatment by an acidic solution or before milling, the clay may be dried, in order to evaporate the excess water. It can be done for example at temperatures between 80 and 150°C, for durations of 1 hour to 5 days.

[0017] The treatment by an acidic solution preferably involves the contact between the powdered clay and an aqueous solution of an acid at a concentration of 1 to 10 mol / L, especially 2 to 8 mol / L, even 3 or 4 to 6 mol / L. It has been observed that a low concentration does not always make it possible to obtain a white or off-white color.

[0018] The acid is preferably selected from sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid and acetic acid.

[0019] The treatment by an acidic solution may be made in a reflux system to improve the contact between the powdered clay and the acidic solution. The duration of the contact is preferably 10 minutes to 10 hours, especially 1 to 8 hours, even 2 to 6 hours. The treatment by an acidic solution may be made at room temperature, or at temperatures between 30 and 120°C, especially between 80 and 110°C. The amount of powdered clay compared to the volume of acidic solution is preferably 10-10000 g / L, especially 50-500 g / L.

[0020] After the treatment by an acidic solution, the treated clay is washed, for example using water, to eliminate acid residues and impurities (especially coloring impurities) extracted by the acid treatment. It may then be dried.

[0021] The calcination step is preferably carried out at a temperature of 200 to 700°C, especially of 300 to 600°C or 350 to 550°C, even of 400 to 500°C. It has been observed that good reactivities could be obtained at calcination temperatures lower than the temperatures normally used for the production of metakaolin (650-800°C). The duration of the calcination step is preferably 0.1 to 10 hours, especially 0.2 to 5 hours, even 0.5 to 2 hours. Alternatively, the calcination may be a flash calcination, with a duration of a few seconds, typically 1 to 10 seconds.

[0022] The calcined clay particles may then be quickly milled to deagglomerate them. The particle size distribution in volume of the activated clay is preferably such that the D50 is 10-30 µm, preferably 12-20 µm.

[0023] The clay particles are preferably not mixed with alkaline earth (such as lime) between the treatment with an acidic solution and the calcination step. The production process of the activated clay particles normally consists of the treatment with an acidic solution, the washing step and the calcination step, and optionally drying and milling steps.

[0024] The activated clay particles are usually white or off-white, whatever the initial color of the clay. Especially, their lightness L* in reflection is preferably more than 70, even more than 75 or more than 80.

[0025] The mortar composition is preferably a dry mortar composition, i.e., a composition consisting of dry powders. The mortar or concrete composition preferably comprises 5-60wt% of mineral binder and 20-90wt% of aggregates. In a preferred embodiment, the mortar composition comprises 10-20wt% of mineral binder and 75-90wt% aggregates, which is especially useful for plasters and renders. In another preferred embodiment, the mortar composition comprises 15-40wt% of mineral binder and 55-85wt% aggregates, which is especially useful for adhesives and basecoats for ETICS (External Thermal Insulation Composite Systems). In another preferred embodiment, the mortar composition comprises 20-50wt% of mineral binder and 55-80wt% aggregates, which is especially useful for tile adhesives. In another preferred embodiment, the mortar composition comprises 5-20wt% of mineral binder and 70-90wt% aggregates, which is especially useful for masonry mortars. In another preferred embodiment, the mortar composition comprises 5-20wt% of mineral binder and 60-85wt% aggregates, which is especially useful for flooring compounds, such as floor screeds. All these amounts are given with respect to the total weight of mortar or concrete composition.

[0026] The mineral binder preferably comprises 10-95wt% of activated clay particles and 5-90wt% of an activator, with respect to the weight of mineral binder. The activator makes it possible to increase the reactivity of the binder. The amount of activated clay particles in the mineral binder is preferably 20-90wt%, especially 30-80wt%, even 40-70wt%, with respect to the weight of mineral binder.

[0027] The activator is preferably selected from Ordinary Portland Cement (OPC), calcium aluminate cement, calcium sulfoaluminate cement, belite cements, lime (such as hydrated or hydraulic lime), alkali silicates (such as sodium metasilicate), calcium salts (such as calcium formate, calcium sulfate, calcium nitrate), alkali sulfates, alkali thiosulfates, alkali thiocyanates, alkali (poly)phosphates (such as sodium tripolyphosphate), alkali phosphonates, chlorides (such as sodium chloride, potassium chloride, calcium chloride or magnesium chloride), carboxylic acids, ultrafine calcium carbonate, slags (such as blast furnace slag, ladle slag, alumina slag), fly ashes, silica fumes, spent FCC catalysts, metakaolin, biomass ashes, amines (such as alkanolamines, for example monoethanolamine, diethanolamine, triethanolamine, triisopropanolamine or diethanol-isopropanolamine), sodium aluminates, aluminum sulfates and mixtures thereof. The OPC is preferably a white OPC. The activated clays may therefore replace 75% of white cement and even more.

[0028] The mineral binder preferably comprises (or consists of) a mixture of activated clays and white OPC. The weight ratio between clay and white OPC is preferably 20:80 to 90:10, especially 30:70 to 80:20, even 40:60 to 70:30.

[0029] The aggregates are preferably selected from siliceous aggregates, calcareous aggregates, dolomitic aggregates and mixtures thereof. Examples are ground limestone or dolomite, and silica sand. The aggregates preferably comprise sands (size 0-5 mm), and possibly fillers (size 0-0.1 mm). The aggregates preferably comprise (or even consist of) silica sand. A mixture of silica sand and limestone is also possible. Alternatively, or cumulatively, the aggregates may comprise lightweight aggregates, i.e. aggregates having an apparent density of at most 600 kg / m3, such as hydrophobic expanded perlite, thermosetting polymer powder (for example micronized rubber powder), hollow silicate particles (for example expanded glass beads and / or cenospheres) and mixtures thereof. When the mortar is used as a tile adhesive, the maximum size of the aggregates is preferably 2 mm, even 1 mm. The aggregates may also comprise fibers.

[0030] The mortar or concrete composition preferably comprises one or more additive chosen from redispersable polymer powders, accelerators, retarders, rheological modifiers, pigments, defoamers, stabilizers, thickeners, shrinkage-reducing agents, hydrophobic agents, plasticizers, and superplasticizers. The total amount of such additives is preferably 0.1 to 15.0wt%, especially 0.5 to 5.0wt% with respect to the amount of mortar or concrete composition.

[0031] Retarders are for example carboxylic acids such as tartaric or citric acids or their salts. The total amount of retarders is preferably 0.01 to 1.0wt% with respect to the amount of mortar or concrete composition.

[0032] Thickeners and water-retention agents are for example cellulose ethers and / or starch ethers. Their total amount is preferably 0.1 to 0.6wt%, especially 0.2 to 0.5wt% with respect to the amount of dry mortar composition. These additives make it possible to improve the workability of the wet mortar.

[0033] The redispersable polymer powder preferably comprises at least a polymer based on one or more monomers selected from the group including vinyl esters (especially vinyl esters of unbranched or branched alkylcarboxylic acids having from 1 to 15 carbon atoms), methacrylates and acrylates (especially (meth)acrylates of alcohols having from 1 to 10 carbon atoms), methacrylic acid, acrylic acid, vinyl aromatics, olefins (such as ethylene or propylene), dienes and vinyl halides. The amount of redispersable polymer powder is preferably 0.2 to 8.0wt%, especially 0.5 to 6.0wt%, with respect to the amount of mortar or concrete composition.

[0034] The ratio of water to the mortar or concrete composition (“water ratio”) preferably ranges from 0.10 to 0.50 by weight, in order to get the right consistency for the wet mortar or concrete. This corresponds to a water dosage of 10 to 50% (added to 100% of dry mortar or concrete).

[0035] Another object of the invention is the use of a mortar composition according to the invention as a façade render or plaster, as a flooring compound, as a tile grout, as an adhesive or basecoat for External Thermal Insulation Composite Systems, as a masonry mortar, or in a 3D-printing process for manufacturing construction elements.

[0036] Another object of the invention is a construction element, such as a board or a tile, made by mixing with water a mortar composition according to the invention, wherein the aggregates comprise fibers, and hardening the obtained mixture. Such construction elements are especially fiber-cement boards or (corrugated) fiber-cement roof tiles.

[0037] Examples

[0038] The following examples illustrate the invention in a non-limiting manner.

[0039] Two clays have been studied: a kaolinite clay (called A, gray color) and a clay from industrial waste (called B, a by-product of a sand manufacturing process, red color, mainly containing kaolinite as well as polymorphs – dickite, halloysite and nacrite). These clays have been dried at 105°C for 2 days to evaporate excess water and then crushed and milled in a vibratory disc mill for 60 seconds. Table 1 shows the particle size distribution in volume and the colorimetric parameters L*a*b* (CIE 1976) of the clays after milling.

[0040] ClayABD10 (µm)1.21.4D50 (µm)3.96.0D90 (µm)46.229.8L*51.046.6a*2.516.9b*7.317.3

[0041] The clays have then been submitted to an acidic treatment. To this end, 30 g of clay has been treated in 300 mL of sulfuric acid (5M) in a reflux system at 105°C for 4 hours. After washing with water and filtering under vacuum to remove the acidic residues, the clays have been dried at 40°C overnight and calcined at 500°C for 1 hour, and then deagglomerated by milling in a vibratory disc mill for 5 seconds. Table 2 shows the particle size distribution in volume and the colorimetric parameters L*a*b* (CIE 1976) of the activated clays after treatment.

[0042] ClayABD10 (µm)2.12.9D50 (µm)15.714.5D90 (µm)117.616.5L*81.271.9a*-0.51.2b*1.41.9

[0043] These results show that after treatment the clays are white or off-white. In other tests, the acid concentration was 1M and 10M. A concentration of 10M showed similar results, while a concentration of 1M was less efficient.

[0044] In a comparative experiment, clays A and B have been calcined at 500°C and 800°C for 1 hour, but without the preliminary acidic treatment. Table 3 show the results in terms of color.

[0045] ClayAB500°CL*60.055.0a*13.018.6b*25.925.1800°CL*59.057.0a*17.520.3b*29.826.6

[0046] The pozzolanic activity of treated clays A and B was evaluated and compared with the activity of the raw (untreated) clays. The pozzolanic activity of untreated clay B according to ASTM C1897 (isothermal calorimetry) was 74 J / g after 3 days and 160 J / g after 7 days, while the activity of the treated clay was 163 J / g after 3 days and 222 J / g after 7 days. The pozzolanic activity was also evaluated according to Brazilian Standard NBR15895. The activity was 243 mgCa(OH2) / g for untreated clay A and 600 mgCa(OH2) / g for treated clay A. For clay B, it was 493 mgCa(OH2) / g (untreated) and 1034 mgCa(OH2) / g (treated).

[0047] Mortars have been prepared by mixing 18wt% of a binder with 81.9wt% of sand and 0.1wt% of cellulose ether. The binders were mixtures of white OPC with treated clays. Four mixtures were tested, with OPC:clay weight ratios of respectively 100:0 (comparative example), 75:25, 50:50 and 25:75. All mortars showed acceptable hardening performances.

[0048] The compression strength of some mortars after 7 days of curing has been measured for the 50:50 ratios. Table 4 shows the results, the compression strength being expressed in MPa. As a comparison, the table also gives the results for the untreated clays, i.e., clays before acidic treatment and calcination.

[0049] ComparativeABTreated6.84.27.7Untreated1.20.9

[0050] In terms of color, these mortars were white, with L*a*b* values of (85.0; -0.1; 3.0) for the mortar using the clay A and (80.5; 1.1; 4.1) for the mortar using the clay B.

[0051] Other mortars have been prepared by mixing 18wt% of a binder with 81.9wt% of sand and 0.1wt% of cellulose ether. In a first comparative sample C1, the binder was composed of white Portland cement. In a second comparative example C2, the binder was composed of 54.9wt% white Portland cement, 13.6wt% dolomite filler, 1.5wt% gypsum and 30wt% metakaolin (i.e. kaolin calcined at high temperature, without acid treatment). In the inventive example 1, metakaolin was replaced by the treated clay A as described before. The water ratio was 20wt%. Table 5 gives the adhesive and compressive strength of the mortars, measured after 28 days according to Brazilian standard NBR 14081 / 2012.

[0052] ExampleAdhesive strength (MPa)Compressive strength (MPa)C10.595.81C20.672.5710.643.60

[0053] These results show that the mechanical strength of the mortar using the treated clay according to the invention is similar to, or even better than, the mechanical strength of a mortar using metakaolin, even though the calcination temperature was much higher for metakaolin.

Claims

A mortar or concrete composition comprising aggregates and a mineral binder, said mineral binder comprising activated clay particles made by subjecting powdered clay to a treatment with an acidic solution, then to a washing step, and then to a calcination step.The mortar or concrete composition according to claim 1, wherein the clay comprises a mineral selected from kaolinite, smectite, illite, hectorite, laponite and chlorite.The mortar or concrete composition according to the preceding claim, wherein the main mineral of the clay is a clay mineral from the kaolin group, especially is kaolinite.The mortar or concrete composition according to any one of the preceding claims, wherein the treatment by an acidic solution involves the contact between the powdered clay and an aqueous solution of an acid at a concentration of 1 to 10 mol / L.The mortar or concrete composition according to the preceding claim, wherein the acid is selected from sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid and acetic acid.The mortar or concrete composition according to any one of the preceding claims, wherein the washing step is done by using water.The mortar or concrete composition according to anyone of the preceding claims, wherein the calcination step is carried out at a temperature of 200 to 700°C, especially 300 to 500°C.The mortar or concrete composition according to any one of the preceding claims, wherein the activated clay particles are white, especially their lightness L* in reflection is more than 70.The mortar or concrete composition according to any one of the preceding claims, which comprises 5-60wt% of mineral binder and 20-90wt% of aggregates.The mortar or concrete composition according to anyone of the preceding claims, wherein the mineral binder comprises 10-95wt% of activated clay particles and 5-90wt% of an activator, with respect to the weight of mineral binder.The mortar or concrete composition according to the preceding claim, wherein the activator is selected from Ordinary Portland Cement, calcium aluminate cement, calcium sulfoaluminate cement, belite cements, lime, alkali silicates, calcium salts, alkali sulfates, alkali thiosulfates, alkali thiocyanates, alkali (poly)phosphates, alkali phosphonates, chlorides, carboxylic acids, ultrafine calcium carbonate, slags, fly ashes, silica fumes, spent FCC catalysts, metakaolin, biomass ashes, amines, sodium aluminates, aluminum sulfates and mixtures thereof.A method for making a mortar or concrete composition according to any one of the preceding claims, comprising subjecting powdered clay to a treatment with an acidic solution, then to a washing step, and then to a calcination step to obtain activated clay particles, and mixing said activated clay particles with aggregates.The method according to the preceding claim, wherein the treatment by an acidic solution involves the contact between the powdered clay and an aqueous solution of an acid at a concentration of 1 to 10 mol / L.The method according to any one of claims 12 and 13, wherein the acid is selected from sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid and acetic acid.The method according to any one of claims 12 to 14, wherein the calcination step is carried out at a temperature of 200 to 700°C, especially 300 to 500°C.The use of a mortar composition according to any one of claims 1 to 11 as a tile adhesive, as a façade render or plaster, as a flooring compound, as a tile grout, as an adhesive or basecoat for External Thermal Insulation Composite Systems, as a masonry mortar, or in a 3D-printing process for manufacturing construction elements.A construction element, such as a board or a tile, made by mixing with water a mortar composition according to any one of claims 1 to 11, wherein the aggregates comprise fibers, and hardening the obtained mixture.