WO2008068322A1

WO2008068322A1 - Coated alkaline-earth metal carbonate particles, use of such particles in the production of construction materials and construction materials compositions containing such particles

Info

Publication number: WO2008068322A1
Application number: PCT/EP2007/063479
Authority: WO
Inventors: Roberto Rosa; Karine Cavalier
Original assignee: Solvay (Société Anonyme)
Priority date: 2006-12-08
Filing date: 2007-12-06
Publication date: 2008-06-12

Abstract

This invention relates to alkaline-earth metal carbonate particles at least partly coated with a coating agent comprising a polyacrylic acid, or a polyacrylic acid derivative or a mixture thereof, with a content with respect to the uncoated alkaline-earth metal carbonate of at least 0.2% by weight and at most of 10% by weight, to the use of such particles in the production of construction materials and to construction materials containing such particles.

Description

Coated alkaline-earth metal carbonate particles, use of such particles in the production of construction materials and construction materials compositions containing such particles

The present invention is related to coated alkaline-earth metal carbonate particles, to the use of such particles in the production of construction materials and to construction materials compositions containing such particles.

Construction materials, in particular plaster, stucco, cement render, mortar and concrete can be in the form of pasty construction materials that harden on drying and are extensively used in the construction industry i.e. for coating walls, floors, ceilings and partitions, for sticking bricks or for making building parts. They can be used outside and inside buildings. Such construction materials usually contain a binder such as cement, lime or gypsum and a mineral aggregate such as sand, gravel or a lightweight mineral aggregate, and water.

The binder acts as an adhesive between the smaller particles of the mineral aggregates (rock and sand) which coalesce into a solid mass. Other additives can be added to such mixtures in order to control properties of fresh or hardened materials: setting and hardening rate, consistence, porosity, corrosion, fungicidal properties, insecticide or germicidal resistance, permeability, pigmentation, etc. Depending on their use, the hardened materials must exhibit numerous properties like high mechanical resistance (to fissuring and scratch, for instance), high heat resistance, high thermal insulation, high sound insulation, high sound absorption, high anti-humidity effect (anti salts rising), high permeability to water vapor but low permeability to liquid water, good surface aspect, resistance to ultraviolet light, to mention only a few.

Calcium carbonate is used in the preparation of construction materials. French patent application FR 2 866 330 describes an ultra-high-performance, self compacting light colored concrete containing uncoated calcium carbonate particles. Although the hardened concrete exhibits besides its light color, an excellent compression resistance, it is not satisfying other properties like workability, abrasion resistance, water and vapor permeability, sound absorption properties, etc. It is difficult to obtain simultaneously several of such properties. It is the aim of this invention to provide alkaline-earth metal carbonate particles which could improve simultaneously such properties of construction materials. The invention relates then to alkaline-earth metal carbonate particles at least partly coated with a coating agent comprising a polyacrylic acid, a derivative of a polyacrylic acid or a mixture thereof, wherein the content of the polyacrylic acid, the polyacrylic acid derivative or the mixture thereof with respect to the uncoated alkaline-earth metal carbonate is at least of 0.2% by weight and at most of 10% by weight.

By "coated" alkaline-earth metal carbonate particles, one intends to denote "surface treated" alkaline-earth metal carbonate particles.

In the coated alkaline-earth metal carbonate particles according to the invention, the alkaline-earth metal is preferably selected from magnesium, calcium, strontium, barium and mixtures thereof. Calcium is more preferred.

The alkaline-earth metal carbonate particles of the invention can be particles of natural or synthetic alkaline-earth metal carbonate. Natural magnesium carbonate can be natural magnesite or hydromagnesite. Natural calcium carbonate can be natural calcite or aragonite, chalk or marble. Natural magnesium and calcium carbonate can occur as calcium-magnesium carbonate containing minerals like huntite and dolomite. Natural barium and calcium carbonate can occur as barium-calcium carbonate containing minerals like alstonite, barytoclacite and parastonite. Natural magnesium and barium carbonate can occur as barium-magnesium carbonate containing minerals like norsethite. Natural strontium, barium and calcium carbonate can occur as strontium-barium-calcium carbonate containing minerals like olekminskite. Natural strontium carbonate can be natural strontianite. Natural barium carbonate can be natural witherite. Synthetic alkaline-earth metal carbonates are preferred. Synthetic precipitated alkaline-earth metal carbonates are more preferred. Synthetic precipitated calcium carbonate is the most preferred. By particles, one intends to denote primary particles and clusters of primary particles. Primary particles are defined as the smallest discrete particles that can be seen by Electron Microscopy analysis. In the coated alkaline-earth metal carbonate particles according to the invention, the alkaline-earth metal carbonate of the invention may be substantially amorphous or substantially crystalline. The term "substantially amorphous or crystalline" is intended to mean that more 50%, in particular more than 75% and preferably more than 90% by weight of the alkaline-earth metal carbonate is in the form of amorphous or crystalline material when analyzed by the X-ray diffraction technique. Substantially crystalline alkaline-earth metal carbonates are preferred. Substantially crystalline calcium carbonate is more preferred.

When the alkaline-earth metal carbonate is magnesium carbonate, the magnesium carbonate may consist of barringtonite, nesquehonite, lansfordite or of a mixture of at least two of these crystallographic varieties.

When the alkaline-earth metal carbonate is strontium carbonate, the strontium carbonate may consist of aragonite type.

When the alkaline-earth metal carbonate is barium carbonate, the barium carbonate may consist of aragonite type. When the alkaline-earth metal carbonate is calcium carbonate, the calcium carbonate may consist of calcite, of vaterite or of aragonite or of a mixture of at least two of these crystallographic varieties. Calcium carbonate particles presenting at least partly a calcite crystallographic structure are preferred. The calcium carbonate particles presenting the calcite crystallographic structure amount generally for at least 20% by weight of the total calcium carbonate particles, often for at least 50%, frequently for at least 80% and most specifically for at least 95%.

The coated alkaline-earth metal carbonate particles of the invention can exhibit various morphologies. The particles can have the form of needles, scalenohedra, rhombohedra, hexagons, pseudo-cubes, pseudo-spheres, platelets or prisms.

The coated calcium carbonate particles of the invention can exhibit various morphologies. The particles can have the form of needles, scalenohedra, rhombohedra, pseudo-cubes, pseudo-spheres, platelets or prisms. The corners and edges of several of such forms, for instance rhombohedra and pseudo-cubes can be rounded. These forms are determined by means of Scanning Electron

Microscopy. The scalenohedra and rhombohedra forms are preferred. Calcium carbonate particles presenting a rhomboedral morphology are more preferred.

The calcium carbonate particles presenting the rhomboedral morphology amount generally for at least 20% by number of the total calcium carbonate particles, often for at least 50% frequently for at least 80% and most specifically for at least 95%. The % by number can be obtained from Scanning Electron

Microscopy measurements.

The coated alkaline-earth metal carbonate particles according to the invention have a BET specific surface area generally greater than or equal to

0.1 m²/g, often greater than or equal to 1 m /g, frequently greater than or equal to - A -

5 m²/g, more often greater than or equal to 10 m²/g and in particular greater than or equal to 15 m Ig. The BET specific surface area of the particles is generally less than or equal to 300 m²/g, often less than or equal to 150 m²/g and frequently less than or equal to 100 m²/g. A specific surface area of less than or equal to 70 m²/g gives also good results. The specific surface area is measured by the standardized BET method (standard ISO 9277-1995).

The coated alkaline-earth carbonate particles of the invention have generally a mean primary particle size (dp) higher than or equal to 0.010 μm, often higher than or equal to 0.030 μm, frequently higher than or equal to 0.050 μm, specifically higher than or equal to 0.060 μm The mean primary particle size is generally lower than or equal to 20 μm, frequently lower than or equal to 10 μm, often lower than or equal to 1 μm, most often lower than or equal to 0.75 μm and more specifically lower than or equal to 0.100 μm.. The mean primary particle size is measured according to a method derived from standard NF Xl 1-601 - 1974 (Lea & Nurse method) with a permeable porosity (ε) value around 0.45 and using the equation of Carman and Malherbe and a final conversion of the surfacic diameter (ds) to the particle diameter by the relation : dp = ds exp[-3.2 ((measured ε) - 0.45)] The size distribution of the coated alkaline-earth metal carbonate particles according to the invention is obtained by Gravitational Liquid Sedimentation Methods (standard ISO 13317-3-2001).

The average size of the coated particles (equal to the value of D₅₀ defined below) is commonly higher than or equal to 0.030 μm, often higher than or equal to 0.050 μm, frequently higher than or equal to 0.070 μm, specifically higher than or equal to 0.100 μm and most specifically higher than or equal to

0.150 μm. The average size of the particles is generally lower than or equal to 20 μm, frequently lower than or equal to 10 μm, often lower than or equal to 5 μm, specifically lower than or equal to 3 μm and most specifically lower than or equal to 2 μm. D₅₀ is the particle size value which expresses that 50 % by vol of the particles have a size value lower than or equal to D₅₀.

The coated alkaline-earth metal carbonate particles of the invention can occur as clusters of primary particles, which highest dimension is generally higher than or equal to 10 nm, often higher than or equal to 20 nm, frequently higher than or equal to 50 nm, specifically higher than or equal to 80 nm and in particular higher than or equal to 140 nm. That highest dimension is generally lower than or equal to 40 μm, often lower than or equal to 4 μm and frequently lower than or equal to 0.3 μm. Those clusters exhibit a smallest dimension which is generally higher than or equal to 5 nm, often higher than or equal to 10 nm, frequently higher than or equal to 25 nm, specifically higher than or equal to 40 nm and in particular higher than or equal to 70 nm. That smallest dimension is generally lower than or equal to 10 μm, often lower than or equal to 0.7 μm and frequently lower than or equal to 0.2 μm. Those dimensions can be obtained by measuring the highest and lowest dimensions of the clusters on photographs obtained by Scanning Electron Microscopy.

The alkaline-earth metal carbonate particles of the invention are at least partly coated with a coating agent comprising a polyacrylic acid, a derivative of a polyacrylic acid or a mixture thereof.

By polyacrylic acid one intends to denote homopolymers of acrylic acid, homopolymers of substituted acrylic acids like methacrylic acids, copolymers of acrylic acid with substituted acrylic acids and copolymers of acrylic acid and/or substituted acrylic acids with other vinyl monomers. Homopolymers of acrylic acid are more preferred.

By polyacrylic acids derivatives, one intends to denote esters or salts of the polyacrylic acids defined before.

Polyacrylic acids may be partially esterified with alcohol terminated polyethers, like polyethylene oxide for instance. (Neomere^® TECH 305008 and Neomere^® TECH 305062 (Chryso) and Melpers^® 040, Melpers^® 4100 and Melpers^® VP4335 N. D (Degussa) are examples of such polyacrylic acid derivatives. They may be partially neutralized, i.e., in the form of salts of polyacrylic acid. They may also be partially esterified and neutralized. Salts are more preferred derivatives. The salt may be an alkaline earth metal salt, i.e. a calcium, magnesium, strontium or barium salt of the polyacrylic acid or an alkaline metal salt, i.e., lithium, sodium, potassium, rubidium or cesium of the polyacrylic acid, or mixtures thereof. Sodium salts are more preferred. The molecular weight of the polyacrylic acid is generally higher than or equal to 500 g/mol, preferably higher than or equal to 700 g/mol and most preferably higher than or equal to 1 000 g/mol. That molecular weight is usually lower than or equal to 15 000 g/mol, ideally lower than or equal to 10 000 g/mol and in particular lower than or equal to 5 000 g/mol. When a mixture of a polyacrylic acid and a polyacrylic acid derivative is used, the weight ratio between the acid and the acid derivative is generally of at least 10 %, often of at least 25% and frequently of at least 45%. This ratio is generally of at most 100%, often of at most 75 % and frequently of at most 55%. When the polyacrylic acid derivative is a salt, those ratios can be obtained by partially neutralizing a polyacrylic acid with a base or by mixing a not neutralized polyacrylic acid with a fully neutralized polyacrylic acid.

It is preferred that the coating agent comprises a polyacrylic acid salt. It is more preferred that the polyacrylic acid salt is a sodium salt.

The content of the polyacrylic acid, the polyacrylic acid derivative or the mixture thereof, with respect to the uncoated alkaline-earth metal carbonate is of at least 0.2% by weight, preferably of at least 0.4% by weight and more preferably of at least 0.5% by weight and most preferably of at least 0.7% by weight. That content is of at most 10% by weight, preferably of at most 5% by weight, more preferably of at most 1% by weight, especially below 1% by weight, and most preferably of at most 0.8% by weight. The content of the coating agent is generally higher than or equal to 0.2% by weight of uncoated alkaline-earth metal carbonate particles and often higher than or equal to 0.4% by weight. That content is generally lower than or equal to 20% by weight of uncoated alkaline-earth metal carbonate particles and often lower than or equal to 15% by weight. The free flowing density of the coated alkaline-earth metal carbonate particles of the invention is generally of at least 140 kg/m³, preferably of at least 200 kg/m³ and more preferably of at least 220 kg/m³. The free flowing density of the coated alkaline-earth metal carbonate particles of the invention is generally of at most 270 kg/m³, preferably of at most 250 kg/m³ and more preferably of at most 235 kg/m³. The free flowing density is measured according to standard ISO 903.

The density after tamping of the coated alkaline-earth metal carbonate particles of the invention is generally of at least 250 kg/m³, preferably of at least 300 kg/m³ and more preferably of at least 350 kg/m³. The free flowing density of the coated alkaline-earth metal carbonate particles of the invention is generally of at most 450 kg/m³, preferably of at most 400 kg/m³ and more preferably of at most 375 kg/m³. The density after tamping is measured according to standard ISO 787-11.

According to a first embodiment, the process for manufacturing the coated particles of the invention comprises the following steps: (a) Contacting a powder, a moist cake or an aqueous suspension of alkaline-earth metal carbonate particles with the coating agent or with a solution or with a suspension or with an emulsion of the coating agent in a solvent, such as to obtain a coating medium, (b) Heating and stirring the coating medium, such as to coat the alkaline-earth metal carbonate particles at least partly with the coating agent.

According to a first variant of that first embodiment, the process comprises an additional step (c) after step (b):

(c) Eliminating at least a fraction of the solvent from the coating medium of step (b) in order to obtain a concentrated coating medium or wet coated alkaline- earth metal carbonate particles.

According to a second variant of that first embodiment, the process comprises an additional step (d) after step (c):

(d) Drying the concentrated coating medium or the wet coated alkaline-earth metal carbonate particles of step (c).

The alkaline-earth metal carbonate particles can be obtained by any process. They can be powders, moist cakes or suspension of alkaline-earth metal carbonate particles obtained by any known method.

Natural alkaline-earth metal carbonates can be processed by mechanically crushing and grading alkaline-earth metal carbonates containing ores to obtain particles adjusted to the desired size.

Synthetic alkaline-earth metal carbonate particles are usually prepared by precipitation.

Precipitated magnesium carbonates may be prepared by reacting magnesium hydroxide with carbon dioxide at high pressure.

Precipitated calcium carbonate may be manufactured by first preparing a calcium oxide (quick lime) by subjecting limestone to calcination by burning a fuel, such as coke, a petroleum fuel (such as heavy or light oil), natural gas, petroleum gas (LPG) or the like, and then reacting the calcium oxide with water to produce a calcium hydroxide slurry (milk or lime), and reacting the calcium hydroxide slurry with the carbon dioxide discharged from a calcination furnace for obtaining the calcium oxide from limestone to obtain the desired particle size and shape precipitated calcium carbonate (carbonation process). Precipitation of calcium carbonate can also be carried out by adding an alkali metal carbonate starting with lime water (causticisation method) or precipitation by the addition of an alkali metal carbonate starting with solutions containing calcium chloride or by urea decomposition when heating solutions containing urea and calcium chloride. Other processes for obtaining precipitated calcium carbonate are also possible like the Pattinson process. Precipitated calcium carbonate obtained from the carbonation process is preferred. Strontium and barium carbonates may be prepared by precipitating the carbonates from strontium or barium sulfide solutions with carbon dioxide. Barium carbonate may also be prepared by precipitating the carbonate from barium sulfide solutions with sodium carbonate.

By powder one intends to denote a dry solid, i.e. a solid with a water content usually lower than or equal to 10% by weight. This content is preferably lower than or equal to 3% by weight and more particularly lower than or equal to 1% by weight.

By moist cake, one intends to denote a solid with a water content normally greater than 10 % by weight, more specifically greater than or equal to 30% by weight. This content is generally lower than or equal to 70% by weight and preferably lower than or equal to 50% by weight.

The solid content of the aqueous suspension of alkaline-earth metal carbonate particles in step (a) is usually higher than or equal to 25 g/L, frequently higher than or equal to 50 g/L, and often higher than or equal to 100 g/L. That content is usually lower than or equal to 350 g/L, frequently lower than or equal to 300 g/L, and often lower than or equal to 250 g/L.

The coating agent can be used in any form as a solid, a liquid or a gas, or as a solution, a suspension or an emulsion in a solvent. The solvent can be an organic or an inorganic solvent. The solvent is preferably inorganic and is more preferably water.

According to a second embodiment, especially, useful when the alkaline- earth metal carbonate particles are precipitated alkaline-earth metal carbonate particles, the coating agent is present in the precipitation medium before the precipitation of the alkaline-earth metal carbonate particles occurs. The process comprises the following steps:

(A) Obtaining a precipitation medium by mixing a alkaline-earth metal containing compound or a carbonate containing compound, and the coating agent in a solvent, and

(B) Adding respectively a carbonate or a alkaline-earth metal containing compound to the precipitation medium of step (A) so as to precipitate alkaline-earth metal carbonate particles and coat at least partly the precipitated particles with the coating agent, in a coating medium.

According to a first variant of that second embodiment, the process comprises an additional step (C) after step (B): (C) Eliminating at least a fraction of the solvent from the coating medium of step (B) in order to obtain a concentrated coating medium or wet coated alkaline- earth metal carbonate particles.

According to a second variant of that second embodiment, the process comprises an additional step (D) after step (C): (D)Drying the concentrated coating medium or the wet coated alkaline-earth metal carbonate particles of step (C).

This process is particularly well suited when the precipitated alkaline-earth metal carbonate is calcium carbonate.

The solvent can be an organic solvent or an inorganic solvent or a mixture thereof. It is preferred to use an inorganic solvent, preferably water.

Any alkaline-earth metal containing compound can be used. For calcium, it is preferred to use quick lime.

Any carbonate containing compound can be used. It is preferred to use carbon dioxide. The coating agent may contain a crystallization controller i.e. a substance able to control the crystallographic phase, the morphology and/or the size of the precipitated alkaline-earth metal carbonate particles.

The coated alkaline-earth metal carbonate particles obtained of steps (b) or (B) can be separated from the coating medium by any separation methods, for instance by filtration, centrifugation. Filtration is preferred.

The drying of the coated alkaline-earth metal carbonate particles obtained in steps (c) or (C) can be carried out by any methods like for instance microwave drying, oven drying, fluid or moving bed drying. Moving bed drying is preferred. The invention also relates to the use of the coated alkaline-earth metal carbonate particles of the invention for the production of construction materials. The construction materials are defined as materials used in the building of works of civil engineering, of public works or of architecture.

More specifically, the construction materials include plaster, stucco, cement render, mortar and concrete, and the resulting hardened materials. Such hardened materials can be of any shape like for instance sealants, coatings, blocks, bricks and panels. Generally the construction materials contain at least one inorganic binder like for instance cement, hydraulic lime, aerial lime and gypsum, at least one mineral aggregate like for instance sand and lightweight mineral aggregates, optionally at least one coloring compound selected from pigments and dyes, water, and optionally at least one other additive selected from polymeric resins, surface- active agents, colloids, thickeners, alkali agents, co-solvents, wetting and dispersing agents, biocides, foaming agents, anti- foaming agents, anti- settling agents, fibers and organic binders.

The inorganic binder is selected from cement, hydraulic lime, aerial lime, gypsum and mixtures thereof. Cement, hydraulic lime and mixtures thereof are preferred.

By gypsum, one intends to designate any composition containing as major components calcium sulfate (CaSO₄), calcium sulfate hemihydrate (CaSO₄.1/2H₂O) or any mixture thereof, as described in "Wirsching Franz, Gebruder Knauf Westdeutsche Gipswerke, Iphofen, Federal Republik of

Germany, Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A4, Page 555, Calcium Sulfate."

By cement, one intends to designate any composition containing as major components calcium silicates (tri- and dicalcium silicates), calcium aluminates and calcium aluminoferrites, calcium oxide and silicon oxide as defined in the standard UNI EN 197-1-2001. The various types of cement such as those described in "Siegbert Sprung, Forschungsinstitut der Zementindustrie, Dϋsseldorf, Federal Republic of Germany, Ullmann's Encyclopedia of Industrial Chemistry, Sixth, Completely Revised Edition, Volume 7, Page 1, Cement and Concrete, Chapter 1." can be convenient. They include but are not limited to Standardized Common cements like Portland Cement, Portland composite cement (Portland slag cement, Portland silica fume cement, Portland pozzolanic cement, Portland fly ash cement, Portland shale cement, Portland limestone cement), Blast-furnace cement, Pozzolanic cement and Composite cement and Standardized Special cements like Sulfate-resistant cements, Low-heat cements, Low-alkali cements, calcium aluminate cement and Special cements like Supersulfated cements, Water-repellent cements, Oil-well cements, Regulated set cements, Expanding cements and Masonry cements. Portland type cements are more particularly preferred. The cement can be obtained by known processes as such described in

"Siegbert Sprung, Forschungsinstitut der Zementindustrie, Dϋsseldorf, Federal Republic of Germany, Ullmann's Encyclopedia of Industrial Chemistry, Sixth, Completely Revised Edition, Volume 7, Page 1, Cement and Concrete, Chapter 1."

By hydraulic lime (HL), one intends to designate any composition containing calcium hydroxide (Ca(OH)₂), calcium silicate and aluminates as major components according to the standard UNI EN 459-1. This means that the content of Ca(OH)₂ in weight percent of the HL composition is higher than the weight percent of any other component. It is preferable to use hydraulic lime where the content of Ca(OH)₂ is higher than or equal to 50 wt %, preferably higher than or equal to 75 wt %, more preferably higher than or equal to 90 wt %, still more preferably higher than or equal to 95 wt % and most preferably higher than or equal to 99 wt % of the total weight of the composition. Calcium hydroxide (Ca(OH)₂) can be obtained by any known method, for instance by making quicklime (CaO) by thermal decomposition of limestone and by further slaking quick lime with water. For the various production processes of manufacturing, it can be referred to "Tony Oates, Limetec Consultancy Services, Buxton, Derbyshire, United Kingdom, Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A 15, Page 317, Lime and Limestone, Chapter 4". Cement, hydraulic lime and mixture thereof are preferred. Mixtures of cement and hydraulic lime are known as bastard lime (BL).

The cement content in the mixture of cement and hydraulic lime is usually higher than or equal to 10 wt %, preferably higher than or equal to 20 wt %, more preferably higher than or equal to 30 wt %, still more preferably higher than or equal to 40 wt % and most preferably higher than or equal to 45 wt % of the total weight of the mixture. It is generally lower than or equal to 90 wt %, preferably lower than or equal to 80 wt %, more preferably lower than or equal to 70 wt %, still more preferably lower than or equal to 60 wt % and most preferably lower than or equal to 55 wt % of the total weight of the mixture. The calcium hydroxide content in the mixture of cement and hydraulic lime is usually higher than or equal to 10 wt %, preferably higher than or equal to 20 wt %, more preferably higher than or equal to 30 wt %, still more preferably higher than or equal to 40 wt % and most preferably higher than or equal to 45 wt % of the total weight of the mixture. It is generally lower than or equal to 90 wt %, preferably lower than or equal to 80 wt %, more preferably lower than or equal to 70 wt %, still more preferably lower than or equal to 60 wt % and most preferably lower than or equal to 55 wt % of the total weight of the mixture.

Other compounds can be present in the construction material according to the invention. Those compounds are usually used for the preparation of plaster, cement render, mortar, concrete or other materials for construction. They include but are not limited to sand, lightweight materials, polymeric resins (i.e. polyvinyl acetate), surface- active agents (i.e. polymeric wetting agents, colloids (i.e., methyl cellulose), pigments, dyes, thickener, alkali agent, co-solvents, wetting and dispersing agents, biocide, foaming agent, anti-foaming agent, anti-settling agent, fibers, organic binder and water.

By pigments, one intends to denote a water insoluble coloring organic or inorganic substance. Inorganic substances different from the alkaline-earth metal carbonate particle used in the invention are preferred. They can be selected from metal oxides (like iron oxides, chromium oxides, titanium oxide for instance), clays, natural earths, other inorganic compounds (cobalt blues, bismuth vanadate, chrome yellows, molybdate reds for instance). Organic pigments are also well known in the construction industry and involve among others: carbon black, monoazo pigments, isoindolinone pigments, naphthalene tetracarboxylic acid pigments, dibromanthanthrone pigments, perylene tetracarboxylic acid pigments, anthraquinone pigments, quinacridone pigments, heterocyclic Ni-complex pigments, dioxazine pigments, indanthrone pigments, phthalocyanines, disazo pigments, isoindoline pigments, azo condensation pigments, manganese salts of monoazo dyes and thiazine pigments. By dyes, one intends to denote a water soluble coloring organic or inorganic substance. Examples of such substances are methane dyes (triphenylmethane dyes in particular), azo dyes, nitro dyes, nitroso dyes, phthalein dyes, indigoid dyes, antraquinone dyes, alizarine dyes, aniline dyes, methylene blue and reactive dyes.

Pigments are preferred. Inorganic pigments are more preferred.

Sand is a loose material consisting of small mineral particles or rock and mineral particles distinguishable by the naked eye. Grain vary from almost spherical to angular, with diameter range from 1/16 mm to 2 mm. Sand is often the principal component of the mineral aggregate used in the preparation of concrete. By sand, one intends to denote any composition which contains silicon dioxide as the major component. The content of silicon dioxide is generally higher than or equal to 50% by weight, preferably higher than or equal to 75% and most preferably higher than or equal to 90%. Silicon dioxide is preferably in the form of quartz. The quartz content of silicon dioxide is generally higher than or equal to 50% by weight, preferably higher than or equal to 75% and most preferably higher than or equal to 90%. Such sand composition is found in inland continental settings and non-tropical coastal settings. Sand can also contain other constituents such as iron, feldspar and gypsum.

By lightweight mineral aggregates, one intends to denote inorganic solid materials with a bulk density lower than or equal to 1 g/cm³, preferably lower than or equal to 0.5 g/cm³, and most preferably lower than or equal to 0.2 g/cm³. The definition of the bulk density and the method of measurement is defined in "Rouquerol, J., D. Avnir, C. W. Fairbridge, D. H. Everett, J. H. Haynes, N. Pernicone, J. D. F. Ramsay, K. S. W. Sing, and K. K. Unger, "Recommendations for the Characterization of Porous Solids," Pure Appl. Chem., 66, 1739 (1994) ». Such materials are generally porous. Example of such materials are pumice, perlite and vermiculite. The alkaline-earth metal carbonate content in the construction material according to the invention is usually higher than or equal to 0.15 wt %, preferably higher than or equal to 0.5 wt %, more preferably higher than or equal 1 wt %, yet more preferably higher than or equal to 2 wt %, still more preferably higher than or equal to 4 wt %, in particular more preferably higher than or equal to 5 wt % and most preferably higher than or equal to 6 wt % of the total weight of the construction material excluding water. It is generally lower than or equal to 65 wt %, preferably lower than or equal to 50 wt %, more preferably lower than or equal to 40 wt %, still more preferably lower than or equal to 30 wt %, yet more preferably lower than or equal to 20 wt %, in particular more preferably lower than or equal to 10 wt % and most preferably lower than or equal to 8 wt %.

The binder content in the construction material according to the invention is usually higher than or equal to 1 wt %, preferably higher than or equal to 2 wt %, more preferably higher than or equal to 5 wt %, still more preferably higher than or equal to 10 wt % and most preferably higher than or equal to 20 wt % of the total weight of the construction material excluding water. It is generally lower than or equal to 90 wt %, preferably lower than or equal to 70 wt %, more preferably lower than or equal to 50 wt %, still more preferably lower than or equal to 30 wt % and most preferably lower than or equal to 25 wt %. The pigment content in the construction material according to the invention is usually higher than or equal to 0.01 wt %, preferably higher than or equal to 1 wt %, more preferably higher than or equal to 10 wt %, still more preferably higher than or equal to 30 wt % and most preferably higher than or equal to 40 wt % of the total weight of the construction material excluding water. It is generally lower than or equal to 90 wt %, preferably lower than or equal to 70 wt %, more preferably lower than or equal to 60 wt %, still more preferably lower than or equal to 50 wt % and most preferably lower than or equal to 45 wt %.

The skilled man will know the amount of water to be added to the construction material to obtain the desired rheological properties required by the application.

It has surprisingly been found that when in construction materials, coated alkaline-earth metal carbonate particles as described here before are used, improved workability, abrasion resistance, water and vapor permeability are obtained. After hardening, the construction material according to the invention exhibits an improved resistance to abrasion. That resistance (Taber abrasion test) is measured according to the standard ISO 7784-2: 1997. The construction material according to the invention is applied on a fiber-cement support (area 100 cm²) to give a coating thickness of 0.1 - 5 cm. The coating support is dried until constant weight. The dried coating is then submitted to abrasion resistance test with a sand paper P60 disk rotating at 60 ± 2 tr/min for 50 - 1000 cycles. The abrasion resistance is measured by the weight loss of the dried coating. The weight loss is usually lower than or equal to 100 wt %, preferably lower than or equal to 70 wt %, more preferably lower than or equal to 50 wt %, still more preferably lower than or equal to 30 wt % and most preferably lower than or equal to 10 wt %. The weight loss is usually higher than or equal to 0 wt %, preferably higher than or equal to 1 wt %, more preferably higher than or equal to 2 wt %, still more preferably higher than or equal to 5 wt % and most preferably lower than or equal to 8 wt %. After hardening, the construction material according to the invention exhibits an increased permeability to water vapor and a decreased permeability to liquid water. Without wishing to be bound by any theory, it is believed that the permeability properties are related to the porosity of the cured material. The permeability to water vapour is obtained by measuring the vapour permeability coefficient according to the standard UNI EN 1015-19:2002. The vapour permeability coefficient (μ) is usually higher than or equal to 0.01, preferably higher than or equal to 0.1, more preferably higher than or equal to 1, still more preferably higher than or equal to 10 and most preferably higher than or equal to 20. It is generally lower than or equal to 100, preferably lower than or equal to 50, more preferably lower than or equal to 40, still more preferably lower than or equal to 30 and most preferably lower than or equal to 25.

The permeability to liquid water is measured by the standard UNI EN ISO 1015-18: 2004. The permeability is usually higher than or equal to 0.01 kg/(m² min⁰⁵), preferably higher than or equal to 0.05 kg/(m² min⁰⁵), more preferably higher than or equal to 0.1 kg/(m² min⁰⁵), still more preferably higher than or equal to 0.5 kg/(m² min⁰⁵) and most preferably higher than or equal to 1 kg/(m² min⁰⁵). It is generally lower than or equal to 50 kg/(m² min⁰⁵), preferably lower than or equal to 10 kg/(m² min⁰⁵), more preferably lower than or equal to 5 kg/(m² min⁰⁵), still more preferably lower than or equal to 3 kg/(m² min⁰⁵) and most preferably lower than or equal to 2 kg/(m² min⁰⁵). Before hardening, the construction material according to the invention exhibits a consistence assessed using an internal method. To test the consistence an Abrams like cone (dimension: ri = 2.5 cm, r₂ = 5 cm, h = 15 cm) was used. The procedure consists of filling the cone with the mixture, lifting the cone immediately, and measuring the extent to which the mixture has subsided after two minutes. A higher value of subsidence corresponds to a better consistence. The subsidence is usually higher than or equal to 0.1 cm, preferably higher than or equal to 0.5 cm, more preferably higher than or equal to 1 cm, still more preferably higher than or equal to 3 cm and most preferably higher than or equal to 5 cm. It is generally lower than or equal to 15 cm, preferably lower than or equal to 12 cm, more preferably lower than or equal to 10 cm, still more preferably lower than or equal to 7 cm and most preferably lower than or equal to 5 cm.

The following examples further illustrate the invention but are not to be construed as limiting its scope. The average size of the particles D₅₀ have been obtained with a Sedigraph

5000 instrument from Micromeritics after preparation of the samples with a MasterTech 5100 of Micromeritics. Typically, 2.5 g of sample are dispersed in 50 mL of a hexametaphosphate solution (2 g/L in distilled water), stirred at high speed for 210 s and treated with ultra- sound for 180 s (starting time for ultra- sound treatment, 30 s after starting time of stirring) at full power of the MasterTech 5100. Example 1 (not according to the invention) - Preparation of precipitated calcium carbonate (PCC)

Two batches of precipitated calcium carbonate (IA and IB) were prepared as follows. An aqueous suspension containing precipitated calcium carbonate particles was obtained by carbonating 1 L of a milk of lime suspension containing 148 g

Ca(OH)₂ with a flow of 300 L/h of air containing 30% vol of carbon dioxide, at a temperature of 18⁰C for 2 h. The suspension contained 200 g of CaCO₃ZL. The precipitated calcium carbonate was filtered and dried at 105⁰C for 24 h. In both batches, the dried precipitated calcium carbonate particles exhibited a calcite crystallographic structure, a rhombic morphology, a BET specific surface area of 20 m /g, a dp of 0.070 μm and a D₅₀ of 1.2 μm.

Example 2 (according to the invention) - Preparation of precipitated calcium carbonate coated with polyacrylic acid 1 L of a suspension of precipitated calcium carbonate particles obtained according to example 1 (batch IB) before the filtration step and containing 200 g of CaCθ₃/L, was mixed with 1.82 g of a polyacrylate suspension

(Bevaloid 6778, supplier Kemira, 55 wt/wt % in water) and the resulting mixture was stirred for 45 minutes at 65⁰C. The resulting mixture was filtrated and the resulting filtrated solid was dried.

The dried coated precipitated calcium carbonate particles contained 5 g of polyacrylate/kg of uncoated calcium carbonate.

Example 3 (according to the invention) - Preparation of precipitated calcium carbonate coated with polyacrylic acid

The same procedure as in example 2 was used, except that PCC from batch IA was used and that the amount of the polyacrylate suspension was

2.54 g.

The dried coated precipitated calcium carbonate particles contained 7 g of polyacrylate/kg of uncoated calcium carbonate.

Example 4 (according to the invention) - Preparation of precipitated calcium carbonate coated with polyacrylic acid

The same procedure as in example 2 was used, except that the amount of the polyacrylate suspension was 3.64 g. The dried coated precipitated calcium carbonate particles contained 10 g of polyacrylate/kg of uncoated calcium carbonate. Example 5 (according to the invention) - Preparation of precipitated calcium carbonate coated with polvacrylic acid

The same procedure as in example 2 was used, except that the amount of the polyacrylate suspension was 7.27 g. The dried coated precipitated calcium carbonate particles contained 20 g of polyacrylate/kg of uncoated calcium carbonate.

Example 6 (according to the invention) - Preparation of precipitated calcium carbonate coated with polyacrylic acid

The same procedure as in example 2 was used, except that the amount of the polyacrylate suspension was 10.91 g.

The dried coated precipitated calcium carbonate particles contained 30 g of polyacrylate/kg of uncoated calcium carbonate. Example 7 (not according to the invention) - Ground calcium carbonate (GCC)

A natural Ground Calcium Carbonate (Durcal 1 from OMYA) has been used. The particles exhibit a BET specific surface area of 5 m²/g and a D₅₀ of 1.8 μm.

Example 8 (according to the invention) - Preparation of coated ground calcium carbonate

The same procedure was used as in example 2 except that the suspension of precipitated calcium carbonate of example 1 has been replaced by a suspension of the natural ground calcium carbonate of example 7 (200 g of CaCC"₃/L) and that the amount of the polyacrylate suspension used was 0.7 g.

The dried coated ground calcium carbonate particles contained 2 g of polyacrylate/kg of uncoated calcium carbonate. Example 9 (according to the invention) - Preparation of coated ground calcium carbonate

The same procedure was used as in example 8, except that that the amount of the polyacrylate suspension used was 2.4 g.

The dried coated ground calcium carbonate particles contained 7 g of polyacrylate/kg of uncoated calcium carbonate.

Examples 10 to 18 (according to the invention) - Preparation of hydraulic lime based mortar compositions containing calcium carbonate

Mortar compositions containing the calcium carbonates of examples 1 to 9 were prepared. Compositions containing 56.35 weight % of sand (fluvial sand 0-0.5 mm),

19.95 weight % of water, 18.00 weight % of hydraulic lime and 5.70 weight % of calcium carbonate, were obtained by mixing the various components.

All the compositions were prepared using a concrete mixer (according to standard EN 196-1:1991). During the hardening time (28 days), the samples were maintained at temperature in the range of 15 to 3O⁰C and relative humidity in the range of 30 to 70% .

Example 19 (not according to the invention) - Preparation of a hydraulic lime based mortar composition without calcium carbonate

A mortar composition without calcium carbonate was also prepared following the procedure of examples 10 to 18, except that no calcium carbonate was added. The mortar compositions containing 62.05 weight % of sand (fluvial sand 0-0.5 mm), 19.95 weight % of water and 18.00 weight % of hydraulic lime, so that the calcium carbonate was replaced by sand, were obtained by mixing the various components.

Examples 20 to 24 (according to the invention) - Preparation of cement based mortar compositions containing calcium carbonate

Mortar compositions containing the calcium carbonates of examples 1, 3 and 7 to 9 were prepared.

Compositions containing 59.60 weight % of sand (fluvial sand 0-0.5 mm), 17.70 weight % of water, 19.40 weight % of cement (type Portland 32.5) and 3.30 weight % of calcium carbonate, were obtained by mixing the various components.

All the compositions were prepared using a concrete mixer (according to standard EN 196-1:1991). During the hardening time (28 days), the samples were maintained at temperature in the range of 15 to 3O⁰C and relative humidity in the range of 30 to 70 %.

Example 25 (not according to the invention) - Preparation of a cement based mortar composition without calcium carbonate

A mortar composition without calcium carbonate was also prepared following the procedure of examples 20 to 24 except that no calcium carbonate was added. The mortar compositions containing 62.90 weight % of sand (fluvial sand 0-0.5 mm), 17.70 weight % of water and 19.40 weight % of cement (type Portland 32.5), so that the calcium carbonate was replaced by sand, were obtained by mixing the various components.

The mortar compositions based respectively on hydraulic lime and cement are summarized in Table 1 and the results of the tests are reported in Table 2 for hydraulic lime based mortars and Table 3 for cement based mortars. Table 1

Table 2

Table 3

n.m.: not measured

Claims

C L A I M S

1. -Alkaline earth metal carbonate particles at least partly coated with a coating agent comprising a polyacrylic acid, a derivative of a polyacrylic acid or a mixture thereof, wherein the content of the polyacrylic acid, the polyacrylic acid derivative or the mixture thereof with respect to the uncoated alkaline earth metal carbonate is of at least 0.2 % by weight, preferably at least 0.4% by weight and of at most 10 % by weight, preferably at most of 5 % by weight, more preferably at most 1% by weight, and especially below 1% by weight.

2. - Coated alkaline earth metal carbonate particles according to claim 1 wherein the polyacrylic acid is a homopolymer of acrylic acid with a molecular weight of at least 500 g/mol and of at most 15 000 g/mol.

3. - Coated alkaline earth metal carbonate particles according to claim 1 or 2 wherein the polyacrylic acid derivative is selected from polyacrylic acid salts and esters.

4. - Coated alkaline earth metal carbonate particles according to claim 3 wherein the polacrylic acid derivative is sodium polyacrylate.

5. - Coated alkaline earth metal carbonate particles according to any of claims 1 to 4, wherein the alkaline-earth metal is selected from magnesium, calcium, strontium, barium and mixtures thereof, and preferably calcium.

6. - Coated alkaline-earth metal carbonate particles according to any of claims 1 to 5 wherein the alkaline-earth metal carbonate particles exhibit at least one of the following characteristics :

(a) The alkaline-earth metal carbonate is precipitated alkaline-earth metal carbonate

(b) When the alkaline-earth metal is calcium, the calcium carbonate presents at least partly a calcite crystallographic structure

(c) When the alkaline-earth metal is calcium, at least 20 % by number of the particles presents a rhomboedral morphology (d) The BET specific area of the particles is higher than or equal to 1 m²/g and lower than or equal to 300 m /g

(e) The mean primary particle size measured by air permeation (dp) is higher than or equal to 0.010 μm and lower than or equal to 20 μm.

(f) The average particle size measured by sedigraphy (D₅₀) is higher than or equal to 0.030 μm and lower than or equal to 20 μm.

7. - Process for manufacturing coated alkaline-earth metal carbonate particles according to any of claims 1 to 6, comprising the following steps :

(a) Contacting a powder, a moist cake or an aqueous suspension of alkaline-earth metal carbonate particles with the coating agent or with a solution or with a suspension or with an emulsion of the coating agent in a solvent, such as to obtain a coating medium,

(b) Heating and stirring the coating medium, such as to coat the alkaline-earth metal carbonate particles at least partly with the coating agent,

(c) Eliminating at least a fraction of the solvent from the coating medium of step (b) in order to obtain a concentrated coating medium, or wet coated alkaline- earth metal carbonate particles, and

8. - Process for manufacturing coated alkaline-earth metal carbonate particles according to any of claims 1 to 6 comprising the following step :

(A) Obtaining a precipitation medium by mixing an alkaline-earth metal containing compound or a carbonate containing compound, and the coating agent in a solvent,

(B) Adding respectively a carbonate or an alkaline-earth metal containing compound to the precipitation medium of step (A) so as to precipitate alkaline-earth metal carbonate particles and coat at least partly the precipitated particles with the coating agent, in a coating medium, (C) Eliminating at least a fraction of the solvent from the coating medium of step (B), in order to obtain a concentrated coating medium or wet coated alkaline- earth metal carbonate particles, and

(D)Drying the concentrated coating medium or the wet coated alkaline-earth metal carbonate particles of step (C).

9. - Use of alkaline-earth metal carbonate particles according to any of claims 1 to 6, for the production of construction materials.

10. - Construction material compositions comprising at least one construction material component selected from plaster, stucco, cement render, mortar and concrete, or mixtures thereof and the coated alkaline-earth metal carbonate particles according to any of claims 1 to 6.