Adjuvant to increase the short-term mechanical strength of a hydraulic composition with reduced clinker content

Abstract

Adjuvant for increasing the short-term mechanical strength of a hydraulic composition with reduced clinker content. The present invention relates to the use, for improving the mechanical strength of a hydraulic composition based on a cementitious composition comprising: - 20 to 64% by weight of clinker, - 5 to 60% by weight of activated clay, - 0 to 35% by weight of limestone, - 0 to 10% by weight of calcium sulfate, the proportions being, relative to the dry weight of the cementitious composition, 0.2 to 5.0% by weight, preferably 0.2 to 1.0% by weight, relative to the dry weight of the cementitious composition, of at least one adjuvant comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or a mixture thereof. Figure for the abstract: None

Description

Title of the invention: Adjuvant for increasing the short-term mechanical strength of a hydraulic composition with reduced clinker content

[0001] The present invention relates to the use of an adjuvant to improve the mechanical resistance, particularly in the short term, for example up to 2 days, of a hydraulic composition based on a cementitious composition comprising a high proportion of activated clay and a reduced clinker content, an adjuvanted cementitious composition and its uses.

[0002] Common cementitious compositions include a significant proportion of clinker. For example, a cementitious composition according to standard NF EN 197-1 (April 2012) "Composition, specifications and conformity criteria for common cements" includes at least 65% by weight of clinker.

[0003] The aim is to lower the clinker content of cementitious compositions in order to reduce their carbon footprint, while maintaining their mechanical and rheological properties. New cementitious compositions in which part of the clinker is replaced by activated clays and limestones are beginning to emerge, as described in particular in the provisional standard prEN 197-5 (September 2020) “Cernent - Part 5: Portland-composite cernent CEM II / CM and Composite cernent CEM VI”.

[0004] Patent application WO 2010 / 130511 describes a cementitious composition comprising activated clay.

[0005] However, the acquisition of mechanical resistances, especially in the short term, preferably mechanical resistances at 2 days, is not facilitated.

[0006] Most of the adjuvants known to improve the mechanical strength of a hydraulic composition based on a cementitious composition with a usual clinker content are not efficient enough to improve the mechanical strength of a hydraulic composition based on a cementitious composition with a reduced clinker content.

[0007] Application WO 2019 / 094060 describes a cementitious composition comprising: - from 30 to 95% by weight of hydratable cement, limestone or mixtures thereof, - 5 to 70% by weight of calcined clay comprising 1 to 15% by weight of Fe2O3, - from 0.002 to 0.200% by weight of a tertiary alkanolamine,

[0008] the proportions being relative to the dry weight of the cementitious composition. The tertiary alkanolamine improves the pozzolanic reactivity of the activated clay.

[0009] There is a need to develop alternative methods to improve the mechanical resistance, preferably in the short term (e.g. 2 days), of hydraulic compositions based on cementitious compositions with reduced clinker content.

[0010] Another objective is to provide a cementitious composition with low clinker content and comprising activated clays to obtain a hydraulic composition with good mechanical properties, in particular mechanical strength, especially in the short term, for example at 2 days.

[0011] According to a first object, the invention relates to the use, for improving the mechanical strength of a hydraulic composition based on a cementitious composition comprising:

[0012] - from 20 to 64% by weight of clinker,

[0013] - from 5 to 60% by weight of activated clay,

[0014] - from 0 to 35% by weight of limestone,

[0015] - from 0 to 10% by weight of calcium sulfate,

[0016] the proportions being relative to the dry weight of the cementitious composition,

[0017] from 0.2 to 5.0% by weight, relative to the dry weight of cementitious composition, preferably from 0.2 to 1.0% by weight, relative to the dry weight of cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or their mixture.

[0018] The hydraulic composition according to the invention is preferably a concrete, mortar or screed composition. In addition to the cementitious composition of water, it comprises an aggregate and optionally one or more mineral additions.

[0019] The term "aggregates" refers to a collection of mineral grains with an average diameter between 0 and 125 mm. Depending on their diameter, aggregates are classified into one of the following six categories: fillers, fine sands, sands, gravels, crushed stone, and ballast (in standard NF P 18-545 (September 2011) "Aggregates - Elements of definition, conformity and coding"). The most commonly used aggregates are:

[0020] - fillers, which have a diameter of less than 2 mm and for which at least 85% of the aggregates have a diameter of less than 1.25 mm and at least 70% of the aggregates have a diameter of less than 0.063 mm,

[0021] - sands with a diameter between 0 and 4 mm (in standard NF EN 13242+A1 (March 2008) "Aggregates for materials treated with hydraulic binders and materials untreated materials used for civil engineering works and for road construction (diameter up to 6 mm).

[0022] - bass drivers with a diameter greater than 6.3 mm,

[0023] - gravel with a diameter between 2 and 63 mm.

[0024] Sands are therefore included in the definition of aggregate according to the invention.

[0025] The fillers may in particular be of calcareous or dolomitic origin.

[0026] The term “mineral additions” refers to pozzolanic materials (as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria for common cements” paragraph 5.2.3), fly ash (as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria for common cements” paragraph 5.2.4), calcined shale (as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria for common cements” paragraph 5.2.5), limestone (as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria for common cements” paragraph 5.2.6) or silica fume (as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria of common cements” paragraph 5.2.7) or their mixtures.Other additions, not currently recognized by the NF EN 197-1 standard (April 2012) "Composition, specifications and conformity criteria for common cements", may also be used. These include metakaolins, such as type A metakaolins conforming to the NF P 18-513 standard (August 2012) "Flash Metakaolin" or calcined clays, siliceous additions, such as Qz mineralogy siliceous additions conforming to the NF P 18-509 standard (September 2012) "Additions for hydraulic concrete", aluminosilicates, particularly inorganic geopolymers, and aluminosilicates containing iron oxides such as bauxite residues, norites or aphthae from excavations.The proportions and nature of mineral additions may also conform to the provisional standard prEN 197-5 (September 2020) "Cernent - Part 5: Portland-composite cernent CEM II / CM and Composite cernent CEM VI", which defines CEM II / CM cements comprising between 50 and 64% by weight of clinker and 36 to 50% by weight of blast furnace slag and CEM VI cements comprising 35 to 49% by weight of clinker, 31 to 59% by weight of blast furnace slag and 6 to 20% by weight of mineral additions as defined above.

[0027] The additive, in the proportions used, advantageously provides a hydraulic composition with good mechanical strength, particularly in the short term. Short-term mechanical strength refers to the mechanical strength at 16 hours, 1 day, and 2 days, preferably at 2 days. These strengths Mechanical properties are measured according to standard NF EN 196-1 (September 2016) "Test methods for cements - Part 1: Determination of strengths - Test methods for cements". Preferably, the admixture provides a mechanical strength gain of at least 9% compared to the cementitious composition without admixture, preferably at least 15%, preferably 20 to 45%, preferably 25 to 35%, at 2 days.

[0028] The admixture is generally used in a proportion of 0.2 to 5.0% by weight, in particular 0.5 to 1.0% by weight, preferably 0.6 to 1.0% by weight, the proportions being by weight relative to the dry weight of the cementitious composition.

[0029] The adjuvant according to the invention can be used during the grinding of the cementitious composition or during the preparation of the hydraulic composition, preferably in the mix.

[0030] Preferably the alkaline salt is a potassium salt or a sodium salt or a lithium salt, preferably a potassium salt or a sodium salt.

[0031] Preferably, the alkali salt is chosen from alkali salts of formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate or a mixture thereof.

[0032] Preferably, the alkali salt is chosen from potassium or sodium or lithium salts, preferably potassium or sodium salts, of formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate or a mixture thereof.

[0033] The cementitious composition according to the invention comprises:

[0034] - from 20 to 64% by weight, preferably from 35 to 60% by weight, of clinker,

[0035] - from 5 to 60% by weight of activated clay,

[0036] - from 0 to 35% by weight of limestone,

[0037] - from 0 to 10% by weight of calcium sulfate,

[0038] the proportions being in weight relative to the dry weight of the cementitious composition.

[0039] Such a cementitious composition is unusual in that its proportion of clinker is low and its proportion of activated clay is high. The cementitious composition is notably of type LC3 (“limestone calcined clay cement” in English, as described in the article by Karen Scrivener et al., Calcined clay limestone cements (LC3), Cement and Concrete Research, Volume 114, December 2018, Pages 49-56), and / or it may be a CEM II / CMQ-L or CEM II / CMQ-LL of the provisional standard prEN 197-5 (September 2020) “Cement - Part 5: Portland-composite cement CEM II / CM and Composite cement CEM VI”.

[0040] The clinker is in particular Portland clinker, preferably Portland clinker as defined in the book "Cernent Chemistry". Harry FW Taylor. Edition, 2nd, Academy Press, 1990).

[0041] The cementitious composition comprises from 0 to 35% by weight, preferably from 10 to 30% by weight of limestone, the proportions being in weight relative to the dry weight of the cementitious composition.

[0042] Limestone is preferably as defined in standard NF EN 197-1 (April 2012) “Composition, specifications and conformity criteria for common cements” paragraph 5.2.6.

[0043] The cementitious composition comprises from 0 to 10% by weight, preferably from 1.0 to 5.0% by weight of calcium sulfate, the proportions being by weight relative to the dry weight of the cementitious composition.

[0044] Calcium sulfate can be in dehydrated form, hydrated form, or a mixture thereof. Hydrated calcium sulfate can be monohydrated, dihydrated, or a mixture thereof. Dihydrated calcium sulfate, with the formula CaSO4.2H2O, is gypsum. Gypsum is therefore an example of calcium sulfate.

[0045] By "activated clay" is meant a clay that has undergone dehydroxylation. As used here, the term "dehydroxylation" refers to the loss of one or more hydroxyl (OH) groups in the form of water (H2O) from a clay.

[0046] Preferably, the activated clay is an activated kaolinitic clay. "Kaolinitic clay" means a clay that contains kaolinite. "Activated kaolinitic clay" is a kaolinitic clay in which at least some of the kaolinite has been dehydroxylated to metakaolin, preferably no longer containing kaolinite. For example, when the clay mineral kaolinite is heated from 300 to 600°C, water is lost according to the following reaction.

[0047] AI2Si2O5(OH)4 -> AI2Si2O7 + 2H2O

[0048] Thus, an activated kaolin clay comprises, or is even composed of, metakaolin. Metakaolin is very reactive in the presence of water and portlandite to form hydrated phases, notably hydrated calcium aluminous silicates (CASH) and strâtlingite.

[0049] For the purposes of this application, the activated kaolin clay may contain residual kaolinite (which was not dehydroxylated during activation) in a quantity, as measured by thermogravimetric analysis (TGA), typically by heating to between 30 and 900°C, with, for example, a heating rate of 10°C / min, which allows for quantification of the mass loss corresponding to the water released by the clay. This residual kaolinite content is generally less than or equal to 50% by weight, typically less than or equal to 40% by weight, in particular less than or equal to 30% by weight, preferably less than or equal to 20% by weight, and particularly preferably less than or equal to 10% by weight, relative to the weight of the activated clay, the proportions being expressed by weight relative to the dry weight of the cementitious composition. The kaolinitic clay having been activated may be free of kaolinite (the dehydroxylation was then total).

[0050] Dehydroxylation can be carried out by thermal, mechanical and / or chemical treatment.

[0051] The mechanical treatment can for example be that described in the article by Aleksandra Mitrovié et al. Preparation of pozzolanic addition by mechanical treatment of kaolin clay, International Journal of Mineral Processing, Volume 132, 2014, 59-66.

[0052] The heat treatment is calcination, generally at a temperature between 400 and 700°C (dehydroxylation temperature). This is referred to as calcined kaolin clay.

[0053] Calcination is most often carried out in a rotary kiln into which the clay is introduced. The kaolin is transformed, at least partially, into an amorphous and reactive phase with high pozzolanic properties, called metakaolin. The calcined clay is then ground. Calcination can also be carried out by the "flash" method, where the clay is ground and the fine particles are calcined in a few seconds in a kiln.

[0054] Regardless of the activation method used (in particular mechanical or thermal), the activated clay can undergo further chemical activation through compounds capable of complexing cations, preferably compounds capable of complexing calcium.

[0055] The kaolin clay that has been activated can for example be IMERYS METASTAR 501.

[0056] Preferably, within the cementitious composition, the mass ratio of the weight of activated clay to the weight of limestone is 1 / 2 to 5 / 1, preferably 1 / 1 to 3 / 1, particularly preferably 3 / 2 to 5 / 2.

[0057] Preferably, within the cementitious composition, the mass ratio of the weight of clinker to the weight of activated clay is 1 / 4 to 4 / 1, in particular 1 / 1 to 3 / 1, preferably 3 / 2 to 5 / 2.

[0058] Preferably, within the cementitious composition, the mass ratio of the weight of clinker to the weight of limestone is from 1 / 1 to 10 / 1, in particular from 3 / 1 to 5 / 1.

[0059] Preferably, the cementitious composition contains:

[0060] - from 5.0 to 25% by weight, preferably from 6.0 to 20% by weight, of Al2O3,

[0061] - 25 to 55% by weight, preferably 40 to 50% by weight, of CaO,

[0062] - 20 to 40% by weight, preferably 22 to 35% by weight, of SiO2,

[0063] - from 2.0 to 10% by weight, preferably from 2.0 to 5.0% by weight of SO3, and / or

[0064] - from 0.1 to 10% by weight, preferably from 0.5 to 8.0% by weight, of Fe2O3,

[0065] compared to the sum of the dry weights of clinker, activated clay, limestone and calcium sulfate.

[0066] Other additives may be used within the scope of the present invention in addition to the additives mentioned above. These additives may be selected by those skilled in the art from among the typical additives used in cementitious and hydraulic compositions. Examples include alkanolamines, glycols, glycerols, water-reducing and high-reducing water-reducing additives, surfactants, carboxylic acids or their salts such as acetic, adipic, gluconic, formic, oxalic, citric, maleic, lactic, tartaric, malonic acids and mixtures thereof, antifoaming additives, air-entraining additives and / or grinding agents, and setting retarders.

[0067] In the context of the present invention, setting retardants include setting retardants based on sugar, molasses or vinasse.

[0068] Preferably, water-reducing and high-reducing adjuvants are chosen from:

[0069] - Sulfonated salts of naphthalene and formaldehyde polycondensates, commonly called polynaphthalene sulfonates or naphthalene-based superplasticizers;

[0070] - Sulfonated salts of melamine and formaldehyde polycondensates, called commonly melamine-based superplasticizers;

[0071] - Lignin derivatives such as lignosulfonates;

[0072] - Sodium gluconate and sodium glucoheptonate;

[0073] - Polyacrylates;

[0074] - Polyaryl ethers (PAE);

[0075] - Products based on polycarboxylic acids, in particular copolymers polycarboxylate combs, which are branched polymers whose main chain bears carboxylic groups and whose side chains are composed of polyether-type sequences, in particular polyethylene oxide, such as poly[(meth)acrylic acid - grafted - polyethylene oxide]. The superplasticizers from the CHRYSO®Fluid Optima, CHRYSO®Fluid Premia and CHRYSO®Plast Omega ranges marketed by CHRYSO can be used in particular;

[0076] - Products based on polyalkoxylated polyphosphonates, in particular those described in the patent EP 0 663 892 (for example CHRYSO®Fluid Optima 100).

[0077] Preferably, the cementitious composition does not include alkanolamine.

[0078] The hydraulic composition may also include other additives known to those skilled in the art, for example a mineral addition and / or additives, by example an anti-air entrainment additive, an anti-foaming agent, a setting accelerator or retarder, a rheology modifying agent, another fluidifier (plasticizer or superplasticizer), in particular a superplasticizer, for example a CHRYSO®Fluid Premia 180 or CHRYSO®Fluid Premia 196 superplasticizer.

[0079] According to a second object, the present invention also relates to an additive cementitious composition comprising:

[0080] - from 20 to 64% by weight of clinker,

[0081] - from 5 to 60% by weight of activated clay,

[0082] - from 0 to 35% by weight of limestone,

[0083] - from 0 to 10% by weight of calcium sulfate,

[0084] the proportions being in relation to the dry weight of the cementitious composition,

[0085] and from 0.2 to 5.0% by weight, in relation to the dry weight of the cementitious composition, preferably from 0.2 to 1.0% by weight, in relation to the dry weight of the cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or their mixture.

[0086] Preferably, the alkali salts and the quantity of its salts are as described above.

[0087] For the purposes of the application, "cementitious composition with additives" means a composition comprising the cementitious composition as defined above and the additive, and "cementitious composition" means the cementitious composition free of additives.

[0088] The embodiments defined above for the cementitious composition are applicable for the cementitious composition with admixture.

[0089] The admixed cementitious composition may further include a grinding agent or be free of one.

[0090] According to a third object, the present invention also relates to a method for improving the short-term mechanical resistance of a hydraulic composition based on a cementitious composition comprising 20 to 64% by weight of clinker, 5 to 60% by weight of activated clay, 0 to 35% by weight of limestone, 0 to 10% by weight of calcium sulfate, the proportions being relative to the dry weight of the cementitious composition, said method comprising the addition of 0.2 to 5.0% by weight, relative to the dry weight of the cementitious composition, preferably 0.2 to 1.0% by weight, relative to the dry weight of the cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or a mixture thereof to the hydraulic composition.

[0091] Preferably, the alkali salts and the quantity of its salts are as described above.

[0092] Preferably, the additive increases mechanical strength by at least 9%, preferably by 15 to 45% after 2 days. Preferably, the additive increases mechanical strength by at least 20%, preferably by 25 to 35%, compared to the mechanical strength obtained for the same hydraulic composition without the additive.

[0093] The admixture can be added to the cementitious composition during a grinding step or during the preparation of the hydraulic composition.

[0094] The adjuvant can be added:

[0095] - During the co-grinding of at least two constituents of the cementitious composition, of preferably clinker and calcium sulfate or activated clay and limestone;

[0096] - And / or during the grinding of one of the constituents of the cementitious composition during that it is a separate grinding, preferably when grinding activated clay, more preferably when grinding clinker;

[0097] - And / or during the mixing of components of the cementitious composition;

[0098] - And / or during the preparation of the hydraulic composition, in particular during the mixing of the cementitious composition.

[0099] According to a fourth object, the invention also relates to a hydraulic composition comprising (or even being made up of) the cementitious composition defined above, water, an aggregate and optionally one or more mineral additions, and 0.2 to 5.0% by weight, relative to the dry weight of the cementitious composition, preferably 0.2 to 1.0% by weight, relative to the dry weight of the cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or a mixture thereof.

[0100] Hydraulic compositions are prepared in a conventional manner by mixing the aforementioned constituents. The admixture is added during the mixing or grinding of the cementitious composition.

[0101] The invention is illustrated in the following examples.

[0102] Example 1: Description of cementitious compositions

[0103] The oxide contents and total alkali equivalent (Na2Oeq) of LC3 type cement compositions 1 and 2 were determined by X-ray fluorescence and the kaolinite and amorphous phase contents of LC3 type cement compositions 1 and 2 were determined by X-ray diffraction / Rietveld refinement as detailed in Table 1.

[0104] [Tables 1] Chemical composition of cementitious composition 1 (mass %) Chemical composition of cementitious composition 2 (mass %) SiO2 (X-ray fluorescence) 26.6 26.5 Al2O3 (X-ray fluorescence) 13.4 17.2 Fe2O3 (X-ray fluorescence) 2.74 2.06 CaO (X-ray fluorescence) 43.1 41.7 Na2O (X-ray fluorescence) 0.03 0.04 K2O (X-ray fluorescence) 0.71 0.48 SO3 (X-ray fluorescence) 3.11 3.09 Na2Oeq. (= Na2O + 0.658 K2O) (X-ray fluorescence) 0.50 0.36 Kaolinite Al2Si2O5(OH)4 (X-ray diffraction / Rietveld refinement) 2.1 0.0 Amorphous phases (X-ray diffraction / Rie Tveld refinement) 15.0 27.8

[0105] The 2-day compressive mechanical strengths of LC3 type hydraulic compositions were compared without additives and in the presence of 1.0% by weight of the claimed additives, relative to the dry weight of the cementitious composition.

[0106] Example 2:

[0107] A hydraulic composition 1 was prepared from the cementitious composition 1. According to the protocol of standard NF EN 196-1 (September 2016) "Test methods for cements - Part 1: Determination of strengths - Test methods for cements" with a water-to-cement ratio of 0.5. The admixture was added during mixing. The admixtures of the invention evaluated are sodium formate, potassium carbonate, sodium hydroxide, potassium hydroxide, sodium chloride, potassium chloride, sodium oxalate, sodium sulfate, and potassium sulfate. The dosages are expressed as a percentage of the dry weight of the cementitious composition. In comparison, sodium chloride, calcium chloride, and diethanolisopropanolamine were evaluated at 0.02% by weight (the usual dosage in cement admixtures).The 2-day compressive strengths were evaluated according to standard NF EN 196-1 (September 2016) "Test methods for cements - Part 1: Determination of strengths - Test methods for . cements”. The results are presented in Table 2 (Mechanical compressive strengths at 2 days evaluated according to standard NF EN 196-1 (September 2016) “Methods of test for cements - Part 1: Determination of strengths - Methods of test for cements”, gain in mechanical compressive strength at 2 days compared to the control without additive and relative gain at 2 days compared to the control without additive for the different hydraulic compositions 1 with additives).

[0108] [Tables2] Hydraulic Composition 1 Mechanical compressive strength at 2 days (MPa) Gain in mechanical compressive strength at 2 days compared to the control without additive (MPa) Relative gain at 2 days compared to the control without additive (%) Hydraulic Composition 1 + 1.0 wt% sodium formate (invention) 20.5 + 2.5 + 14 Hydraulic Composition 1 + 1.0 wt% potassium carbonate (invention) 22.7 + 4.8 + 26 Hydraulic Composition 1 + 1.0 wt% sodium hydroxide (invention) 25.9 + 7.9 + 44 Hydraulic Composition 1 + 1.0 wt% potassium hydroxide (invention) 19.6 + 3.8 + 24 Hydraulic Composition 1 + 0.2 wt% sodium chloride (invention) 19.7 + 3.5 + 22 Hydraulic composition 1 + 1.0% by weight of sodium chloride (invention) 23.7 + 5.7 + 32 Hydraulic composition 1 + 1.0% by weight of potassium chloride (invention) 21.9 + 6.1 + 39 Hydraulic composition 1 + 1.0% by weight of sodium oxalate (invention) 21.9 + 3.9 + 22 Hydraulic composition 1 + 1.0% by weight of sodium sulfate (invention) 23.3 + 5.7 + 32 Hydraulic composition 1 + 1.0% by weight of potassium sulfate (invention) 19.5 + 3.7 + 23 Hydraulic composition 1 + 1.0% by weight of lithium sulfate (invention) 22.2 + 4.6 + 26 Hydraulic composition 1 + 1.0% by weight of sodium nitrate (invention) 19.1 + 2.9 + 18 Hydraulic composition 1 + 1.0% by weight of calcium hydroxide (comparative of the effect of the nature of the salt) 18.9 + 0.9 + 5 Hydraulic composition 1 + 0.02% by weight of chloride of sodium (compared to the usual dosage) 16.4 + 0.2 + 1 Hydraulic composition 1 + 0.02 wt% of diethanolisopropanolamine (compared to the usual dosage) 18.6 + 0.6 + 3 Hydraulic composition 1 + 0.03 wt% of cement additive (amine base) 18.8 + 0.9 + 4

[0109] The hydraulic compositions of the invention have yielded compressive strengths at 2 days ranging from 2.5 to 7.9 MPa, compared to 0.2 to 0.9 MPa for the comparative examples. The improvement in compressive strength at 2 days provided by the additives of the invention varies from 14 to 44%. These results show the greater effectiveness of alkali salts compared to calcium and of the claimed dosage range compared to usual dosage ranges (0.02%).

[0110] Example 3:

[0111] A hydraulic composition 2 was prepared from the cementitious composition 2 in a conventional manner according to the manufacturing protocol for mortars representative of the C25 30 concrete application according to standard NF EN 206 / CN (December 2014) "Concrete - Specification, performance, production and conformity" at a water-to-cementitious composition ratio of 0.6. The admixture is added during mixing. The admixtures of the invention, assessed at 1.0% by dry weight of the cementitious composition, are sodium formate, potassium carbonate, sodium hydroxide, sodium chloride, sodium oxalate, and sodium sulfate. The compressive strengths at 2 days were evaluated on 4x4x16 cm³ specimens.The results are presented in Table 3 (Mechanical compressive strengths at 2 days evaluated on specimens of size 4 x 4 x 16 cm3, gain in mechanical compressive strength at 2 days compared to the control without additive and relative gain at 2 days compared to the control without additive for the different hydraulic compositions with additives).

[0112] [Tableaux3] Hydraulic Composition 2 Compressive Strength at 2 Days (MPa) Gain in Compressive Strength at 2 Days Compared to the Control Without Adjuvant (MPa) Relative Gain at 2 Days Compared to the Control Without Adjuvant (%) Hydraulic Composition 2 + 1.0 wt% of sodium formate (invention) 11.0 + 1.3 + 13 Hydraulic Composition 2 + 1.0 wt% of potassium carbonate (invention) 11.2 + 1.5 + 15 Hydraulic Composition 2 + 1.0 wt% of h 13.8 + 4.1 + 42 Sodium hydroxide (invention) Hydraulic composition 2 + 1.0% by weight of sodium chloride (invention) 10.5 + 0.8 + 9 Hydraulic composition 2 + 1.0% by weight of sodium oxalate (invention) 12.4 + 2.7 + 28 Hydraulic composition 2 + 1.0% by weight of sodium sulfate (invention) 12.4 + 2.7 + 28

[0113] The additives of the invention made it possible to increase the compressive strength of the material at 2 days from 0.8 to 4.1 MPa, i.e. a gain of 9.0 to 42% compared to the control without additive.

Claims

Demands

1. Use of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate, or nitrate, or a mixture thereof, for improving the mechanical strength of a hydraulic composition based on a cementitious composition comprising: - 20 to 64% by weight of clinker, - 5 to 60% by weight of activated clay, - 0 to 35% by weight of limestone, - 0 to 10% by weight of calcium sulfate, the proportions being, relative to the dry weight of the cementitious composition, the mass ratio of the weight of activated clay to the weight of limestone being 3:2 to 5:2, the mass ratio of the weight of clinker to the weight of limestone being 3:1 to 5:1, said admixture being present in a proportion of 0.2 to 1.0% by weight, relative to the dry weight of the composition cemetery.

2. Cementitious composition with admixture comprising: - 20 to 64% by weight of clinker, - 5 to 60% by weight of activated clay, - 0 to 35% by weight of limestone, - 0 to 10% by weight of calcium sulfate, the proportions being in relation to the dry weight of the cementitious composition, the mass ratio of the weight of activated clay in relation to the weight of limestone is 3 / 2 to 5 / 2, the mass ratio of the weight of clinker in relation to the weight of limestone is 3 / 1 to 5 / 1, and 0.2 to 1.0% by weight, in relation to the dry weight of the cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or a mixture thereof.

3. A method for improving the mechanical strength, particularly the short-term mechanical strength, of a hydraulic composition based on a cementitious composition comprising - 20 to 64% by weight of clinker, - 5 to 60% by weight of activated clay, - 0 to 35% by weight of limestone, - 0 to 10% by weight of calcium sulfate, the proportions being in relation to the dry weight of the cement composition, the mass ratio of the weight of activated clay in relation to the weight of limestone is 3 / 2 to 5 / 2, the mass ratio of the weight of clinker in relation to the weight of limestone is 3 / 1 to 5 / 1, including the addition to said hydraulic composition of 0.2 to 1.0% by weight, in relation to the dry weight of cement composition, of at least one admixture comprising at least one alkali salt chosen from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or their mixture.

4. Hydraulic composition comprising - a cementitious composition comprising: • 20 to 64% by weight of clinker, • 5 to 60% by weight of activated clay, • 0 to 35% by weight of limestone, • 0 to 10% by weight of calcium sulfate, the proportions being, in relation to the dry weight of the cementitious composition, the mass ratio of the weight of activated clay to the weight of limestone is 3 / 2 to 5 / 2, the mass ratio of the weight of clinker to the weight of limestone is 3 / 1 to 5 / 1, - 0.2 to 1.0% by weight, in relation to the dry weight of the cementitious composition, of at least one admixture comprising at least one alkali salt selected from the alkali salts of formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate or a mixture thereof, - At least one aggregate and - optionally one or more mineral additions.

5. Use according to claim 1, wherein the adjuvant is selected from sodium or potassium or lithium salts, preferably sodium or potassium salts, preferably lithium salts formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate or a mixture thereof.

6. Cementitious composition according to claim 2 wherein the admixture is selected from sodium or potassium or lithium salts, preferably sodium or potassium salts, preferably formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate salts or a mixture thereof.

7. A method according to claim 3, wherein the adjuvant is selected from sodium or potassium or lithium salts, preferably sodium or potassium salts, preferably formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate salts or a mixture thereof.

8. Hydraulic composition according to claim 4, wherein the additive is selected from sodium or potassium or lithium salts, preferably sodium or potassium salts, preferably formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate salts or a mixture thereof.