Patent Application
20240262749
The present invention relates to the use of an admixture for improving the mechanical strength, particularly the short short-term strength for example of up to 2 days, of a hydraulic composition based on a cement composition comprising a high proportion of activated clay and a reduced content of clinker, and to an admixed cement composition and uses thereof.
Usual cement compositions comprise a high proportion of clinker. For example, a cement composition in accordance with standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements» comprises at least 65% by weight of clinker.
It is sought to lower the clinker content of cement compositions to reduce the carbon footprint thereof, whilst maintaining their mechanical and rheological properties. New cement compositions in which part of the clinker is replaced by activated clays and limestone are emerging, as described in particular in the provisional standard prEN 197-5 (September 2020) «Cement—Part 5: Portland-composite cement CEM II/C-M and Composite cement CEM VI».
Patent application WO 2010/130511 describes a cement composition comprising activated clay.
However, the acquiring of mechanical strength in particular short-term strength and preferably mechanical strength at 2 days is not facilitated.
Most admixtures known to improve the mechanical strength of a hydraulic composition based on a cement composition with usual clinker content do not perform sufficiently well to improve the mechanical strength of a hydraulic composition based on a cement composition having a reduced clinker content.
Patent WO 2019/094060 describes a cement composition comprising:
There is a need to develop alternative methods for improving mechanical strength, preferably over the short-term (for example 2 days) of hydraulic compositions based on cement compositions having a reduced clinker content.
A further objective is to provide a cement composition with low clinker content and comprising activated clays allowing the obtaining of a hydraulic composition having good mechanical properties, mechanical strength in particular, and in particular over the short-term for example at 2 days.
A first subject of the invention, to improve the mechanical strength of a hydraulic composition based on a cement composition, comprising:
Preferably, the hydraulic composition of the invention does not comprise calcium chloride.
The hydraulic composition of the invention is preferably a composition of concrete, mortar or cement creed. In addition to the cement composition it comprises water, an aggregate and optionally one or more mineral additions.
By «aggregates», it is meant an assembly of mineral grains having a mean diameter of between 0 and 125 mm. Depending on their diameter, the aggregates are classified in one of the six following families: fillers, fine sand, coarse sand, gravel sand, gravel and ballast (in standard NF P 18-545 (September 2011) «Aggregates—Defining elements, conformity and coding». The aggregates that are most used are the following:
Sands are therefore included in the definition of aggregate according to the invention.
Fillers can be of lime or dolomitic origin in particular.
The expression «mineral additions» designates pozzolanic materials (such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements» paragraph 5.2.3), fly ash (such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements» paragraph 5.2.4), burnt shale (such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements» paragraph 5.2.5), limestones (such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and common criteria for common cements» paragraph 5.2.6) or silica fume (such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements«paragraph 5.2.7), or mixtures thereof. The expression «mineral additions» also designates slags (such as defined in cement standard NF EN 197-1(2012) paragraph 5.2.2), basic oxygen furnace slag (BOF). Other additions not currently recognized by standard NF EN 197-1 (April 2012) «Composition, specifications and common criteria for common cements», can also be used. These particularly concern metakaolins such as type A metakaolins conforming to standard NF P 18-513 (August 2012), «Metakaolin Flash» or calcined clays, siliceous additions such as siliceous additions of Qz mineralogy conforming to standard NF P 18-509 (September 2012) «Additions for concrete», aluminosilicates in particular of inorganic geopolymer type, aluminosilicates containing iron oxides such as bauxite residues, norite or aplite from excavation work. The proportions of mineral additions and their type can also conform to the provisional standard prEN 197-5 (September 2020) «Cement—Part 5: Portland-composite cement CEM II/C-M and Composite cement CEM VI>, which defines CEM II/C-M cements comprising between 50 and 64% by weight of clinker and from 36 to 50% by weight of blast furnace slag, and CEM VI cement comprising from 35 to 49% by weight of clinker, from 31 to 59% by weight of blast furnace slag and from 6 to 20% by weight of mineral additions such as defined above.
The admixture, in the proportions used, advantageously allows the obtaining of a hydraulic composition having good mechanical strength, short-term strength in particular. By short-term mechanical strength it is meant to designate mechanical strength at 16 hours, 1 day and 2 days, preferably at 2 days. Such mechanical strength is measured in accordance with standard NF EN 196-1 (September 2016) «Methods of testing cement—Part 1: Determination of strength». Preferably the admixture allows the obtaining of a gain in mechanical strength of at least 9% compared with the cement composition without admixture, preferably of at least 15%, preferably from 20 to 45%, preferably from 25 to 35%, at 2 days.
Therefore, and preferably, the present application, to improve the mechanical strength at 2 days by at least 9%, preferably by at least 15%, preferably by 20 to 45%, preferably by 25 to 35% compared with a cement composition without admixture, of a hydraulic composition based on a cement composition comprising:
Preferably, the hydraulic composition of the invention does not comprise calcium chloride.
The admixture is generally used in a proportion of 0.2 to 5.0% by weight, in particular of 0.5 to 1.0% by weight, preferably from 0.6 to 1.0% by weight, the proportions being by weight relative to the dry weight of the cement composition.
The admixture of the invention can be used when grinding the cement composition or else when preparing the hydraulic composition, preferably when mixing with water.
Preferably, the alkali metal salt is a potassium salt or a sodium salt or a lithium salt, preferably a potassium salt or a sodium salt.
Preferably, the alkali metal salt is chosen from among alkali metal formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate salts, or a mixture thereof.
Preferably, the alkali metal salt is chosen from among potassium or sodium or lithium salts, preferably potassium or sodium formate, carbonate, chloride, hydroxide, oxalate, sulfate or nitrate salts, or a mixture thereof.
The cement composition of the invention comprises:
Preferably, the hydraulic composition of the invention does not comprise calcium chloride.
Said cement composition is not usual in that it has a low proportion of clinker and a high proportion of activated clay. The cement composition is in particular of LC3 type («limestone calcined clay cement» such 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 can be CEM II/C-M-Q-L or CEM II/C-M-Q-LL according to provisional standard prEN 197-5 (September 2020) «Cement—Part 5: Portland-composite cement CEM II/C-M and Composite cement CEM VI».
The clinker is particularly Portland clinker, preferably Portland clinker such as defined in the work «Cement Chemistry». Harry F. W. Taylor. Edition, 2, Academic Press, 1990).
The cement composition comprises from 0 to 35% by weight, preferably from 10 to 30% by weight of limestone, the proportions being by weight relative to the dry weight of the cement composition.
The limestone is preferably such as defined in standard NF EN 197-1 (April 2012) «Composition, specifications and conformity criteria for common cements» paragraph 5.2.6.
The cement 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 cement composition.
The calcium sulfate can be in dehydrate or hydrate form, or mixture thereof. The calcium sulfate hydrate can be a monohydrate, dihydrate or mixture thereof. The calcium sulfate dihydrate of formula CaSO4.2H2O is gypsum. Gypsum is therefore an example of calcium sulfate.
By «activated clay», it is meant a clay that has been subjected to dehydroxylation. Such as used herein, the term «dehydroxylation» refers to the loss by a clay of one or more hydroxy groups (OH) in water form (H2O).
Preferably, the activated clay is a kaolinic clay (also called kaolinitic) that has been activated. By «kaolinic clay», it is meant a clay which comprises kaolinite. A «kaolinic clay that has been activated» is a kaolinic clay in which at least part of the kaolinite has been dehydroxylated to metakaolin, preferably no longer including any kaolinite. For example, when heating clayey mineral kaolinite to 300 to 600° C., some water is lost according to the following reaction:
Al2Si2O5(OH)4→Al2Si2O7+2H2O
Therefore, a kaolinic clay that has been activated comprises and is even composed of metakaolin. Metakaolin is highly reactive in the presence of water and portlandite to form hydrate phases, in particular calcium alumina silicate hydrate (C-A-S-H) and strätlingite.
In the meaning of the application, kaolinic clay that has been activated may comprise residual kaolinite (which was not dehydroxylated during activation) in an amount such as measured by thermogravimetric analysis (ATG), typically by temperature rise between 30 and 900° C., at a heating rate for example of 10° C./min, which allows quantification of the loss of mass corresponding to the water released by the clay. This content of residual kaolinite 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 most preferably less than or equal to 10% by weight relative to the weight of the activated clay, the proportions being by weight relative to the dry weight of the cement composition. Kaolinic clay that has been activated can be free of kaolinite (in which case dehydroxylation was complete).
Dehydroxylation can be conducted by thermal, mechanical and/or chemical treatment.
Mechanical treatment for example can be the treatment described in the article by Aleksandra Mitrović et al., Preparation of pozzolanic addition by mechanical treatment of kaolin clay, International Journal of Mineral Processing, Volume 132, 2014, 59-66.
Thermal treatment is by calcining, generally at a temperature of between 400 and 700° C. (dehydroxylation temperature). In this case, it is known as kaolinic clay that has been calcined.
Calcining is most often carried out in a rotary kiln in which the clay is charged. The kaolin is at least partially converted to an amorphous and reactive phase having strong pozzolanic properties, called metakaolin. The calcined clay is then milled. Calcining can be conducted using the «flash» method whereby the clay is milled and the fine particles are calcined within a few seconds in a kiln.
Irrespective of the activation method used (in particular mechanical or thermal), the activated clay can be subjected to additional activation via chemical route by means of compounds capable of complexing cations, preferably compounds capable of complexing calcium.
The kaolinic clay that has been activated can be IMERYS METASTAR 501 for example.
Preferably, the cement composition comprises more than 30% by weight of calcined clay and up to 60% by weight of calcined clay, preferably from 35 to 60% by weight of calcined clay, the proportions being by weight relative to the dry weight of the cement composition.
Preferably, in the cement composition, the weight ratio of activated clay weight relative to the weight of limestone is from 1:2 to 5:1, preferably from 1:1 to 3:1, most preferably from 3:2 to 5:2.
Preferably, in the cement composition, the weight ratio of clinker weight relative to the weight of activated clay is from 1:4 to 4:1, in particular from 1:1 to 3:1, preferably from 3:2 to 5:2.
Preferably, in the cement composition the weight ratio of clinker weight relative to limestone weight is from 1:1 to 10:1, in particular from 3:1 to 5:1.
Preferably, the cement composition contains:
Other admixtures can be used in the present invention in addition to the above-mentioned admixtures. These admixtures can be chosen by skilled persons from among typical admixtures of cement compositions and hydraulic compositions. Particular mention can be made of alkanolamines, glycols, glycerols, water-reducing and high-range water-reducing admixtures, surfactants, carboxylic acids and salts thereof such as acetic, adipic, gluconic, formic, oxalic, citric, maleic, lactic, tartaric, malonic acids and mixtures thereof, defoaming additives, air-entraining additives and/or grinding agents, set retarding agents.
In the present invention, among set retarding agents, particular mention can be made of sugar-, molasses- or vinasse-based set retarders.
Preferably the water reducing and high-range water reducing admixtures are chosen from among:
Preferably, the cement composition does not comprise an alkanolamine.
The hydraulic composition may also comprise other additives known to skilled persons, for example a mineral addition and/or additives such as an air-entraining additive, a defoaming agent, a set accelerator or retarder, a rheology-modifying agent, another fluidizer (plasticizer or superplasticizer), in particular a superplasticizer such as a CHRYSO®Fluid Premia 180 or CHRYSO®Fluid Premia 196 superplasticizer.
A further subject of the invention concerns an admixed cement composition comprising:
Preferably, the alkali metal salts and the amount of these salts are such as described above.
In the meaning of the application, by «admixed cement composition» it is meant a composition comprising the cement composition such a defined above together with the admixture, and by «cement composition» it is meant the cement composition free of admixture.
The embodiments defined above for the cement composition apply to the admixed cement composition.
The admixed cement composition may or may not further comprise a grinding agent.
A third subject of the invention concerns a method for improving the short-term mechanical strength of a hydraulic composition based on a cement composition comprising from 20 to 64% by weight of clinker, from 5 to 60% by weight of activated clay, from 0 to 35% by weight of limestone, from 0 to 10% by weight of calcium sulfate, the proportions being relative to the dry weight of the cement composition, said method comprising the addition of 0.2 to 5.0% by weight relative to the dry weight of the cement composition, preferably from 0.2 to 1.0% by weight relative to the dry weight of the cement composition, of at least one admixture comprising at least one alkali metal salt chosen from alkali metal formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate salts, or a mixture thereof, to the hydraulic composition.
Preferably, the alkali metal salts and the amount of these salts are such as described above.
Preferably, the admixture allows an increase in mechanical strength of at least 9%, preferably of 15 to 45% at 2 days. Preferably the admixture allows mechanical strength to be increased by at least 20%, preferably by 25 to 35% compared with the mechanical strength obtained for the same hydraulic composition free of admixture.
The admixture can be added to the cement composition at the grinding step or else when preparing the hydraulic composition.
The admixture can be added:
The embodiments defined above for the cement composition are applicable for the method of the invention.
A fourth subject of the invention concerns a hydraulic composition comprising (even composed of) the cement composition defined above, water, an aggregate and optionally one or more mineral additions, and from 0.2 to 5.0% by weight relative to the dry weight of the cement composition, preferably from 0.2 to 1.0% by weight relative to the dry weight of the cement composition, of at least one admixture comprising at least one alkali metal salt chosen from alkali metal formate, carbonate, chloride, hydroxide, oxalate, thiocyanate, silicate, sulfate or nitrate salts, or a mixture thereof.
The hydraulic compositions are prepared conventionally by mixing the above-mentioned constituents. The admixture is added at the time of mixing with water, or when grinding the cement composition.
The embodiments defined above for the cement composition apply to the hydraulic composition.
The invention is illustrated in the following examples.
The oxide contents and total equivalent alkalinity (Na2Oeq) of cement compositions 1 and 2 of LC3 type were determined by X-ray fluorescence, and the contents of kaolinite and amorphous phases of cement compositions 1 and 2 of LC3 type were determined by X-ray Diffraction/Rietveld Refinement as detailed in Table 1.
The compressive mechanical strength at 2 days of the hydraulic compositions of LC3 type were compared without admixture and in the presence of 1.0% by weight of the claimed admixtures, relative to the dry weight of cement composition.
Different hydraulic compositions were prepared from a mixture of CEM I, activated clay and limestone, with different quantities of each of the constituents.
The compressive mechanical strength at 2 days was evaluated in accordance with standard NF EN 196-1 (September 2016) «Methods of testing cement—Part 1: Determination of strength—Methods for testing cement». The results are given in Table 2 (Compressive mechanical strength at 2 days evaluated according to standard NF EN 196-1 (September 2016) «Methods of testing cement».
These tests show that at an equivalent clay/limestone ratio, the increase in clay concentration in the hydraulic composition leads to a major loss in mechanical strength at 2 days.
A hydraulic composition 1 was prepared from cement composition 1 following the protocol of standard NF EN 196-1 (September 2016) «Methods of testing cement—Part 1: Determination of strength—Methods of testing cement», with a water-to-cement composition ratio of 0.5. The admixture was added when mixing with water. The evaluated admixtures of the invention were sodium formate, potassium carbonate, sodium hydroxide, potassium hydroxide, sodium chloride, potassium chloride, sodium oxalate, sodium sulfate and potassium sulfate. The dosages are expressed as % relative to the dry weight of the cement composition. For comparison, the sodium chloride, calcium chloride and diethanolisopropanolamine were evaluated at 0.02% by weight (usual dosage of admixtures for cement). The compressive mechanical strength at 2 days was evaluated in accordance with standard NF EN 196-1 (September 2016) «Methods of testing cement—Part 1: Determination of strength—Methods of testing cement». The results are given in Table 3 (Compressive mechanical strength at 2 days evaluated according to standard NF EN 196-1 (September 2016) «Methods of testing cement—Part 1: Determination of strength—Methods of testing cement», gain in compressive mechanical strength at 2 days compared win the reference without admixture, and relative gain at 2 days compared with the reference without admixture for the different admixed hydraulic compositions 1).
The hydraulic compositions of the invention allowed the obtaining of compressive mechanical strengths at 2 days ranging from 2.5 to 7.9 MPa compared with 0.2 to 0.9 MPa for the comparative examples. The gain in compressive mechanical strength at 2 days afforded by the admixtures of the invention varied from 14 to 44%. These results show the greater efficacy of the alkali metal salts compared with calcium, and of the range of claimed dosages compared with usual dosage ranges (0.02%).
A hydraulic composition 2 was prepared from cement composition 2 in conventional manner following the manufacturing protocol for mortars representative of concrete application C25 30 in accordance with standard NF EN 206/CN (December 2014) «Concrete—Specification, performance, production and conformity» with a water-to—cement composition ratio of 0.6. The admixture was added at the time of mixing with water. The admixtures of the invention evaluated at 1.0% relative to the dry weight of the cement composition were sodium formate, potassium carbonate, sodium hydroxide, sodium chloride, sodium oxalate and sodium sulfate. The compressive mechanical strength at 2 days was evaluated on test specimens of size 4×4×16 cm3. The results are given in Table 4: Compressive mechanical strength at 2 days evaluated on test specimens of size 4×4×16 cm3, gain in compressive mechanical strength at 2 days compared with the reference without admixture, and relative gain at 2 days compared with the reference without admixture for the different admixed hydraulic compositions 2).
The admixtures of the invention allowed an increase in the compressive strength of the materials at 2 days of 0.8 to 4.1 MPa, i.e. a gain of 9.0 to 42% compared with the reference without admixture.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2106078 | Jun 2021 | FR | national |
This application is the US national stage of PCT/EP2022/065652, filed Jun. 9, 2022 and designating the United States, which claims the priority of FR 2106078, filed Jun. 9, 2021. The entire contents of each foregoing application are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/065652 | 6/9/2022 | WO |
