FR3042494A1 - HYDRAULIC COMPOSITION HAVING ENHANCED CARBONATION RESISTANCE - Google Patents

Abstract

The present invention relates to the use of at least one crosslinked polyacrylamide, in the form of a particle powder having an average size of from 300 μm to 2000 μm, said crosslinked polyacrylamide having a nitrogen level greater than or equal to 4% by weight relative to the mass of said polyacrylamide, in combination with at least one hydraulic binder in a hydraulic composition, for reducing and / or preventing carbonation within said hydraulic composition, said at least one crosslinked polyacrylamide (s) ) being present in said hydraulic composition in a weight ratio polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%.

Description

HYDRAULIC COMPOSITION HAVING ENHANCED CARBONATION RESISTANCE

The present invention relates to the field of construction materials, and more particularly to a new hydraulic composition having improved durability, in particular a better resistance to carbonation.

The durability of hydraulic composites is a major concern. Indeed, a work must withstand over time to the various aggressions or solicitations (physical, mechanical, chemical, ...), that is to say to the loads to which it is subjected, as well as wind, to the rain, cold, heat or environment. Exposure to the ambient atmosphere can cause the carbonation of a hydraulic composition. Atmospheric CO2 diffuses into the hydraulic composition by its porosity and reacts with the hydrates of the cement, in particular with portlandite, to form calcium carbonate. This results in a drop in pH, which generally goes from a value of 13 in the non-carbonated zone to a value generally less than 9 in the carbonated zone. The pH of the hydraulic composition drops and initiates corrosion of the steels in a humid environment and in the presence of oxygen.

In case of corrosion, rust develops around the steel bars and breaks up the hydraulic coating composition, which is a problem. The hydraulic composition is damaged and the corrosion is all the more accelerated as the metal frames are exposed.

The carbonation of the hydraulic compositions is in particular a major problem for hydraulic compositions with a low rate of clinker. Indeed, these hydraulic compositions are very sensitive to carbonation because of their low rate of Portlandite (phase created during the hydration of a clinker, in particular Portland), this phase playing a buffer role in the progression of carbonation.

In order to meet the requirements of users, it has become necessary to find a means to reduce or prevent carbonation, and thus the corrosion of metal elements when they are present, in hydraulic compositions, particularly hydraulic compositions having a low level. clinker and comprising mineral additions.

Also the problem to be solved by the invention is to provide a means for reducing or preventing carbonation, and thus the corrosion of metal elements when present, in hydraulic compositions, particularly hydraulic compositions having a low level. clinker and comprising mineral additions. It should be noted that the present invention seeks to reduce or prevent carbonation at a given stage of the hydration, which is characterized by the same mechanical resistance in compression (iso-resistance). Without being bound by theory, it would seem that carbonation is strongly linked to the progress of hydration.

More specifically, the present invention relates to the use of at least one crosslinked polyacrylamide, in the form of a particle powder having an average size of from 300 μm to 2000 μm, said crosslinked polyacrylamide having a degree of nitrogen greater than or equal to 4% by weight relative to the mass of said polyacrylamide, in combination with at least one hydraulic binder in a hydraulic composition, for reducing and / or preventing carbonation within said hydraulic composition, said polyacrylamide (s) ( s) crosslinked being present in said hydraulic composition in a weight ratio polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%.

Unexpectedly, the inventors have demonstrated that the use of one (or more) crosslinked polyacrylamide added directly to the mass of a hydraulic composition makes it possible to reduce and / or prevent the carbonation of the composition in the cured state. and thus to improve the durability of the hydraulic composition and to reduce the corrosion of the metal reinforcements.

The present invention provides access to an improved durability hydraulic composition which has one or more of the following characteristics: - the hydraulic composition has improved resistance to carbonation; the metal reinforcements present in the hydraulic composition are not or only slightly corroded; - the corrosion of metal reinforcements can be delayed when this occurs; the coating (as defined in standard NF EN 1992-1-1 of October 2005, paragraph 4.4.1.1) of the reinforcements becomes less critical and the positioning of the reinforcements in the thickness of the hydraulic composition is facilitated; the hydraulic composition may comprise a reduced rate of clinker, without this promoting the corrosion of the metal reinforcements; the hydraulic composition makes it possible to form a barrier to gases other than CO2 (for example radon, chlorine, and oxygen), as well as a liquid barrier.

Conventionally, the term "hydraulic binder" means a dry material that takes and hardens by hydration. The setting is the transition from liquid or pasty state to solid state. The setting is followed or accompanied by a curing phenomenon during which the material acquires mechanical properties. Hardening usually occurs after the end of setting, especially for cements.

A hydraulic binder generally comprises a clinker, calcium sulfate, and one or more mineral additions, in particular as detailed below.

A hydraulic composition according to the invention preferably further comprises water.

Conventionally, the term "hydraulic composition" a composition comprising a hydraulic binder, water, optionally metal elements, optionally aggregates and optionally adjuvants. Preferably, the hydraulic composition of the invention is a concrete.

The amount of water is such that the water / binder mass ratio is preferably from 0.4 to 1.2 and preferably from 0.4 to 0.7.

A hydraulic composition according to the invention includes both the compositions in the fresh state and in the cured state, for example a cement slurry, a mortar or a concrete.

Crosslinked polyacrylamides

The hydraulic composition according to the invention comprises at least one crosslinked polyacrylamide.

More specifically, it is a crosslinked non-water soluble polyacrylamide said superabsorbent.

This "superabsorbent" property describes the ability of polyacrylamides to absorb water. These superabsorbent polymers have already been implemented in many fields of application to take advantage of these swelling capacities.

The crosslinked polyacrylamides according to the invention are capable of swelling in a hydraulic composition by absorbing water.

As is clear from the examples described below, the presence of one or more crosslinked polyacrylamide (s) in a hydraulic composition is particularly beneficial to reduce the carbonation rate of said composition.

Thus, the hydraulic composition of the invention, which incorporates at least one crosslinked polyacrylamide, has a greater resistance to carbonation than a reference hydraulic composition free of crosslinked polyacrylamide, which makes it possible to improve the durability of said hydraulic composition and of reduce the corrosion of any metal reinforcements.

In the context of the present invention, the term "polyacrylamide" is intended to cover a polymer formed solely of monomeric acrylamide units (H2C = CH-C (O) -NH2), also called homopolymer, and also a polymer comprising one or more other monomeric entities different from acrylamide monomer units, also called copolymer.

According to one embodiment, a polyacrylamide that is suitable for the invention may comprise amide units and anionic, cationic or nonionic units, different from the amide units.

This type of polyacrylamide can be obtained by polymerization of a monomer mixture comprising acrylamide monomer units and anionic, cationic or nonionic comonomers, different from the acrylamide monomers.

The nonionic monomer units may for example be chosen from vinyl acetate and vinyl alcohol.

The anionic monomer units may for example be selected from the group consisting of alkali or ammonium salts of methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, or maleic acid.

The cationic monomer units can be, for example, chosen from the group consisting of (meth) acrylamidoethyltrimethylammonium chloride and (meth) acrylamidopropyltrimethylammonium chloride.

According to one variant, a polyacrylamide that is suitable for the invention may comprise amide units and carboxylic acid and / or carboxylate units. By "carboxylate" is meant in particular alkali metal carboxylate, particularly sodium or potassium, or ammonium carboxylate.

These carboxylic acid or carboxylate units can be generated from the acrylamide monomeric units by hydrolysis. In this case, the polyacrylamides are obtained by polymerization of acrylamide monomers and then by hydrolysis.

These carboxylic acid or carboxylate units can also come from monomeric units acrylic acid or acrylate. In this case, the polyacrylamides are obtained by copolymerization of acrylamide monomers and acrylic acid and / or acrylate monomers.

Preferably, a polyacrylamide comprises amide units and carboxylic acid and / or carboxylate units in an amide / (acrylic and / or acrylate) molar ratio of from 0.20 to 9.0.

In the context of the present invention, the term "crosslinked polyacrylamide", a homopolymer or copolymer of acrylamide as described above, obtained by polymerization of a mixture comprising at least one acrylamide monomer and at least one crosslinking agent.

The presence of a crosslinking agent in the mixture makes it possible to connect the polyacrylamide chains to one another and to create a three-dimensional network of polyacrylamide chains. A crosslinked polyacrylamide thus consists essentially of linear segments, crosslinked with each other, some of whose carbon atoms carry an amide group (optionally hydrolysed), contributing to the hydrophilic nature of the crosslinked polyacrylamide.

The degree of crosslinking of a crosslinked polyacrylamide increases with the proportion of crosslinking agent in the monomer mixture. The crosslinked polyacrylamides according to the invention are preferably obtained from monomer mixtures comprising from 0.1% to 20%, preferably from 1% to 10%, advantageously from 2% to 5% of crosslinking agent (s). (s) by weight relative to the total weight of the monomer mixture.

In contrast to linear (non-crosslinked) polyacrylamides, the crosslinked polyacrylamides are hydrophilic but non-water-soluble gels, and this hydrophilic nature results in superabsorbent properties advantageously used in the context of the present invention.

More particularly, as crosslinked polyacrylamide adapted to the implementation of the invention, mention may be made of acrylamide / alkali metal acrylate copolymers, such as, for example, acrylamide / sodium or potassium acrylate copolymers, in particular polyacrylamide Aquasorb 3005. Max from the SNF company.

The nitrogen content of a polyacrylamide may be variable and is generally greater than or equal to 4% by weight relative to the mass of said polyacrylamide.

The nitrogen dosage of a polyacrylamide can be measured by a NOT-meter with a solid combustion chamber. Polyacrylamide is first oxidized to form nitrogen oxides. These oxides are then reduced to NO. This NO is sent to a reaction chamber containing ozone O3 in excess; there is then light emission proportional to the concentration of nitric oxide. The emitted light is measured by a photomultiplier and a signal, observable in the form of a peak, is obtained.

The crosslinked polyacrylamide (s) suitable for the implementation of the invention have a nitrogen content greater than or equal to 4% by weight relative to the weight of said polyacrylamide.

Preferably, the nitrogen content is from 4% to 18%, advantageously from 9% to 15% by weight relative to the weight of said polyacrylamide.

The crosslinked polyacrylamide (s) of the invention is (are) in the form of a powder of polymer particles having an average size of from 300 .mu.m to 2000 .mu.m, preferably from 300 .mu.m to 300 .mu.m. 1000 μm, and preferably from 350 μm to 600 μm.

The size of the crosslinked polyacrylamide particles is generally measured by sieving or laser particle size. This is called the maximum particle size.

The industrial production of the crosslinked polyacrylamide particles generally comprises the following steps: a step of copolymerization of at least two monomers (generally acrylic acid and acrylamide) in the presence of a crosslinking agent. A spray drying step for inverse emulsion polymerization; or a drying, grinding and sieving step for bulk polymerization.

The copolymerization is carried out in bulk or in inverse emulsion. The crosslinking agent may be glyoxal, 1,1,2,2-ethanetetrol, Ν, Ν'-methylenebisacrylamide, piperazine diacrylamide, Ν, Ν'-bisacrylylcystamine, or Ν, Ν'-diallyltartradiamide. . The molecular weight of the polymers obtained is very high (> 10,000,000 g / mol).

The crosslinked polyacrylamides according to the invention are preferably obtained by mass polymerization according to the method described above.

The crosslinked polyacrylamide (s) is (are) present in the hydraulic composition in a weight ratio of from 0.01% to 5.0% relative to the weight of the binder.

Preferably, the weight ratio of crosslinked polyacrylamide (s) relative to the binder is from 0.05% to 2.0%, from 0.05% to 1.0%, or else from 0.05% at 0.75%.

Preferably, the weight ratio of crosslinked polyacrylamide (s) relative to the binder is from 0.1% to 0.50%, or from 0.1% to 0.35%.

The composition of the invention may comprise a mixture of several crosslinked polyacrylamide (s), having different nitrogen levels or different particle sizes.

clinker

The clinker used according to the present invention may be a Portland clinker, a sulfo-aluminous clinker, an aluminous clinker, a belitic clinker, a sulpho-belitic clinker and mixtures thereof, preferably a Portland clinker.

A Portland clinker is obtained by high temperature clinkerisation of a mixture comprising in particular limestone and clay. For example, a Portland clinker is a clinker as defined in standard NF EN 197-1 of February 2001.

The mass proportion of clinker in the hydraulic binder may be from 0% to 100% relative to the weight of the binder, preferably from 5% to 95%, more preferably from 30% to 85%.

As mentioned above, the invention is particularly advantageous for hydraulic compositions having a low clinker content.

For the purposes of the invention, a low clinker ratio means a clinker mass content in the hydraulic binder less than 85%.

Thus, the reduced amount of clinker is usually compensated in the hydraulic binder by mineral additions, such as a limestone filler described below.

Mineral addition

Mineral additions are generally materials that can be used as partial or total substitution for clinker.

The mineral additives suitable for the hydraulic binder according to the invention may be chosen from slags (for example as defined in standard NF EN 197-1 of February 2001, paragraph 5.2.2), natural or artificial pozzolans (for example such as defined in standard NF EN 197-1 of February 2001, paragraph 5.2.3), fly ash (for example as defined in standard NF EN 197-1 of February 2001, paragraph 5.2.4), calcined schists (For example as defined in standard NF EN 197-1 of February 2001, paragraph 5.2.5), mineral additions based on calcium carbonate, for example limestone (for example as defined in standard NF EN 197 1 February 2001, paragraph 5.2.6), silica fumes (for example as defined in standard NF EN 197-1 of February 2001, paragraph 5.2.7), metakaolins, biomass ash (for example ashes of rice husks) and mixtures thereof.

The mineral additions used according to the invention may also be ash from the combustion of plants, such as for example the ashes from the combustion of rice balls.

The mineral additions used according to the invention may also be zeolites.

Flying ash is usually a powdery particle in the flue gases of coal-fired power plants. It is usually recovered by electrostatic or mechanical precipitation.

The chemical composition of a fly ash depends mainly on the chemical composition of the burned coal and the process used in the thermal power plant from which it originated. It is the same for its mineralogical composition. The fly ash used according to the invention may be of siliceous or calcic nature.

Preferably, the fly ash used according to the present invention is chosen from those as described in European Standard NF EN 197-1 of February 2001.

Slags are generally obtained by rapidly cooling the molten slag from the smelting of iron ore in a blast furnace.

The slags used according to the present invention may be chosen from granulated blast furnace slags according to the European Standard NF EN 197-1 of February 2001, paragraph 5.2.2.

The silica fumes used according to the present invention may be a material obtained by the reduction of high purity quartz by charcoal in electric arc furnaces used for the production of silicon and ferrosilicon alloys. The silica fumes are generally formed of spherical particles comprising at least 85% by mass of amorphous silica.

Preferably, the silica fumes used according to the present invention are chosen from silica fumes according to the European standard NF EN 197-1 of February 2001, paragraph 5.2.7.

The pozzolanic materials used according to the present invention may be natural siliceous or silico-aluminous substances, or a combination thereof. Pozzolanic materials include natural pozzolans, which are generally materials of volcanic origin or sedimentary rocks, and calcined natural pozzolans, which are materials of volcanic origin, clays, shales or rocks. sedimentary, thermally activated. The pozzolanic materials used according to the invention may be chosen from pumice, tuffs, slag or mixtures thereof.

Preferably, the pozzolanic materials used according to the present invention are chosen from pozzolanic materials according to European Standard NF EN 197-1 of February 2001, section 5.2.3.

Preferably, the mineral additives used according to the invention are materials containing calcium carbonate, for example limestone (also called limestone filler).

The calcined clays used according to the present invention can result from the calcination of a clay, kaolinite, associated with different minerals (phyllosilicates, quartz, iron oxides) in varying proportions depending on the deposits. They can be obtained either by grinding calcination or by grinding calcination in production units with rotary kilns, trays or so-called "flash" calcination, for example. They are essentially composed of amorphous alumina silicate particles.

Preferably, the calcined clays used according to the present invention may be chosen from metakaolins according to the preliminary draft standard PR NF P 18-513 of December 2011.

According to one variant, the hydraulic binder of the invention may further comprise calcium sulphate.

The calcium sulphate used includes gypsum (calcium sulfate dihydrate, CaSO4.2H2O), hemihydrate (CaSO4.1 / 2H2O), anhydrite (anhydrous calcium sulphate, CaSO4) or a mixture thereof. Gypsum and anhydrite exist in their natural state. It is also possible to use a calcium sulphate which is a by-product of certain industrial processes.

In general, the hydraulic binder of the invention comprises from 3% to 28% by weight of calcium sulphate relative to the weight of clinker.

A high content of calcium sulphate is generally adopted for aluminous and sulphoaluminous cements. The chemical nature (gypsum, hemihydrate or anhydrite) and the calcium sulphate dosage are advantageously adjusted depending on the cement to prevent swelling of the hydrates.

In the case where the clinker is a Portland clinker, the hydraulic binder of the invention comprises from 1% to 8%, preferably from 2% to 5% by mass of calcium sulphate relative to the mass of clinker.

A binder according to the invention is generally obtained by co-grinding a clinker and calcium sulphate.

Metallic elements

A hydraulic composition according to the invention may comprise metal elements, such as reinforcements, in particular reinforced concrete reinforcements according to European Standard NF EN 1992-1-1 of October 2005.

The frames can be in the form of bars, welded mesh or assembly of bars, reinforcement. The junctions of the bars may be provided by overlapping, splicing, soldering, ligation, crimping or any other means.

According to a variant of the invention, the metal elements are drawn steel fibers completely or partially replacing ordinary metal reinforcements in certain applications (pavements, shotcrete or repair concrete).

aggregates

A hydraulic composition according to the invention may comprise aggregates.

The aggregates optionally used in the composition according to the invention include sand (whose particles generally have a maximum size (Dmax) less than or equal to 4 mm), and possibly chippings (whose particles generally have a minimum size (Dmin) greater than 4 mm and preferably a Dmax less than or equal to 20 mm). The aggregates used in the composition according to the invention are generally in accordance with European Standard NF EN 12620 of August 2003, and are of natural or artificial origin. Aggregates can also be wood.

admixtures

A hydraulic composition according to the invention may comprise conventional adjuvants subject to their compatibility with the crosslinked polyacrylamide (s) required according to the invention.

The adjuvants that can be used in the hydraulic composition according to the invention can for example be one of those described in European standards NF EN 934-2 of September 2002, NF EN 934-3 of November 2009 or NF EN 934-4 of August 2009. Advantageously, the hydraulic composition according to the invention comprises at least one adjuvant for hydraulic composition: an accelerator, an air-entraining agent, a viscosifying agent, a retarder, an inerting clays, an antifoaming agent, a plasticizer and / or a superplasticizer.

Preferably, the hydraulic composition according to the invention comprises at least one antifoam agent avoiding the entrainment of air in the composition.

Inerting clays are compounds that reduce or prevent the harmful effects of clays on the properties of hydraulic binders. Inerting clays include those described in WO 2006/032785 and WO 2006/032786.

The term "superplasticizer" as used in the present specification and accompanying claims is to be understood to include both water reducers and superplasticizers as described in the book entitled "Concrete Admixtures Handbook, Properties Science". and Technology, "VS Ramachandran, Noyes Publications, 1984.

A water reducer is defined as an adjuvant which typically reduces the amount of mixing water of a concrete for a given workability from typically 10% to 15%. Water reducers include, for example, lignosulfonates, hydroxycarboxylic acids, carbohydrates and other specialized organic compounds, for example glycerol, polyvinyl alcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein.

Superplasticizers belong to a new class of water reducers, chemically different from normal water reducers and able to reduce water amounts by about 30%. Superplasticizers were broadly classified into four groups: sulfonated condensates of naphthalene formaldehyde (SNF) (usually a sodium salt); sulphonated condensates of melamine formaldehyde (SMF); modified lignosulfonates (MLS); And the others. More recent superplasticizers include polycarboxylic compounds such as polycarboxylates, for example polyacrylates. A superplasticizer is preferably a new generation superplasticizer, for example a copolymer containing a polyethylene glycol as a grafted chain and carboxylic functions in the main chain as a polycarboxylic ether. Sodium polycarboxylate polysulfonates and sodium polyacrylates can also be used. Phosphonic acid derivatives, sodium polycarboxylate polysulfonates and sodium polyacrylates may also be used. The required amount of superplasticizer usually depends on the reactivity of the cement. The lower the reactivity, the lower the required amount of superplasticizer. To reduce the total amount of alkaline salts, the superplasticizer can be used as a calcium salt rather than as a sodium salt. Other additives may be incorporated in the composition according to the invention, for example an antifoaming agent (for example polydimethylsiloxane, triisobutylphosphonate). Antifoam agents also include silicones in the form of a solution of. solid or preferably in the form of resin, oil or emulsion, preferably in water. More particularly suitable are the silicones comprising (RSi () 0.5) and (R2SiO) groups.

In these formulas, the R radicals, which may be the same or different, are preferably a hydrogen atom or an alkyl group of 1 to 8 carbon atoms, the methyl group being preferred. The number of patterns is preferably from 30 to 120.

The amount of such an agent in the final cement is generally at most 5 parts by weight relative to the cement.

According to a preferred embodiment, a hydraulic composition according to the invention comprises: a hydraulic binder comprising a Portland clinker, calcium sulphate, optionally a calcareous filler or other mineral addition, the mass proportion of clinker in the binder being comprised of 30% to 85%, at least one crosslinked polyacrylamide in the form of a particle powder having an average size of from 300 μm to 2000 μm, said crosslinked polyacrylamide having a nitrogen content greater than or equal to 4% by weight relative to the weight of the polyacrylamide, in a weight ratio of polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%, water, in a proportion such that the weight ratio water / binder is included from 0.4 to 1.2, preferably from 0.3 to 0.7, optionally a granulate such as sand, optionally a superplasticizer, and optionally an antifoaming agent.

A hydraulic composition according to the invention may be prepared by bringing into contact at least one hydraulic binder, at least one crosslinked polyacrylamide in the form of a powder of particles having an average size of from 300 μm to 2,000 μm, said crosslinked polyacrylamide having a nitrogen content greater than or equal to 4% by mass relative to the weight of the polyacrylamide, in a weight ratio of polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%, and of the water.

According to a preferred embodiment, the crosslinked polyacrylamide (s) is (are) used in the form of a powder.

Preferably, the hydraulic binder and the crosslinked polyacrylamide (s) are (are) previously brought into contact in dry form, advantageously in the form of a powder, before the mixture obtained is brought into contact with water.

The hydraulic composition according to the invention can be used directly on site in the fresh state and cast in a formwork adapted to the intended application, or used in prefabrication plant.

The mixing of the hydraulic composition can be carried out according to methods known to those skilled in the art.

A hydraulic composition according to the present invention can be shaped to produce, after hydration and hardening, a shaped object for the field of construction.

Objects shaped for the field of construction include, for example, a floor, a screed, a foundation, a wall, a partition, a ceiling, a beam, a worktop, a pillar, a bridge stack, a cinder block, a pipe, a pole, a staircase, a panel, a comiche, a mold, a road element (for example a curb), or a covering (for example of road or wall).

In the present description, including the accompanying claims, the percentages are by mass unless otherwise specified.

The following examples illustrate the embodiment of the invention.

EXAMPLES

Example 1 - Preparation of mortar specimens

Mortar specimens were prepared from a hydraulic composition comprising a hydraulic binder with a low clinker content (35% substituted with a calcareous material). The water / binder ratio is equal to 0.55 and the TiBP (defoaming agent) dosage is 0.09% / binder.

The composition of the specimens is shown in Table 1 and the characteristics of the cement and sand are shown in Tables 2 and 3.

Table 1

Table 2: Characteristics of the CEM 152.5 N CE CP2 NF, Saint Pierre The Court

Table 3: Characteristics

standardized sand (EN 12620)

The crosslinked polyacrylamides used (supplied by SNF) are described in Table 4 below:

Table 4

Protocol for preparing test specimens

The sand was put into the bowl of a Perrier type 32 mixer with prewetting water. Mixing started and was maintained at low speed for 1 minute.

The kneading was then stopped for 4 minutes.

The hydraulic binder (cement + filler) and the cross-linked polyacrylamide powder were added and kneading was resumed at low speed for 1 minute. The mixing water, comprising the adjuvants (antifoam and plasticizer), was then added in 30 seconds while mixing at low speed.

The mixture was kneaded at high speed for 1 minute to obtain a mortar.

The formulations prepared are described in the following Table 5:

Table 5

The mortar was then poured into polystyrene molds measuring 4 cm x 4 cm x 16 cm (without vibration) to obtain 6 concrete specimens (demolded after 24 h at 20 ° C at 100% relative humidity). ).

Example 2 - Measurement of carbonation of the mortar specimens

Measurement protocol

The mortar specimens were then placed under accelerated carbonation conditions.

After 6 days of curing in a wet cabinet at 100% relative humidity and 20 ° C., the test pieces were placed in a carbonation box (rectangular HDPE tank, with a capacity of 576 liters, equipped with a tight-fitting lid). whose atmosphere has been enriched with CO2 (10% +/- 0,5% of CO2 in the air volume of the chamber), 20 ° C +/- 1 ° C and 65% +/- 5% of relative humidity.

The temperature regulation was ensured by the fact that the box was placed in a laboratory regulated at 20 +/- 1 ° C. The relative humidity was regulated by a tray filled with ammonium nitrate salt saturated with water, this tray being positioned at the bottom of the box, over the entire available surface. For CO2, the box was connected to a network fed by bottles filled with a mixture of 50% CO2 / 50% nitrogen under pressure. An expansion unit has enabled the mixture to be delivered at 1 bar of relative pressure in the network. The introduction of the gas was managed automatically by a gaseous CO2 analyzer which continuously analyzed the atmosphere of the box (ABISS wall scanner, model LMP 320, supplied by the company PBI Datasensor). At each gas introduction, another solenoid valve was opened to evacuate excess gas to a crawl space outside the laboratory, in order to avoid any overpressure in the box. A fan operated continuously to have a homogeneous distribution of CO2 gas in the atmosphere of the box. At different times, the specimens were taken out of the carbonation box and split with a hydraulic cutter to determine the depth of carbonation.

Resistance to carbonation was estimated by measuring the carbonation depth of the specimens. This depth was measured after different periods of exposure of the specimens in the chamber enriched in CO2 gas.

The higher this depth, the less resistant the concrete is to carbonation, and the greater the risk of structural reinforcement corrosion. The material is said to be carbonated when its pH is less than or equal to 9. This is visualized by spraying a solution of 0.5% phenolphthalein diluted in a mixture composed of 50% demineralised water and 50% ethanol. Phenolphthalein is a colored indicator that changes to purple pink when the pH is above 9 and remains colorless when the pH is below 9. The carbonated concrete zones are therefore those that remain colorless after spraying the phenolphthalein suspension. The depths of carbonate concrete and mortar were measured in several zones. The arithmetic mean of the values obtained was calculated. Results

The results of the measurement of carbonation depth (in mm) as a function of time (in days) as a function of the type of crosslinked polyacrylamide are indicated in the following Table 6:

Table 6

The crosslinked polyacrylamides led to significantly reduced carbonation depths compared to the non-crosslinked polyacrylamide control.

Claims (10)

Use of at least one crosslinked polyacrylamide, in the form of a particle powder having an average size of from 300 μm to 2000 μm, said crosslinked polyacrylamide having a nitrogen content greater than or equal to 4% by weight with respect to the mass of said polyacrylamide, in combination with at least one hydraulic binder in a hydraulic composition, for reducing and / or preventing carbonation within said hydraulic composition, said at least one crosslinked polyacrylamide (s) being present ( s) in said hydraulic composition in a weight ratio polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%. 2. Use according to claim 1, wherein the hydraulic composition further comprises water, preferably in a weight ratio water / binder of 0.4 to 1.2. 3. Use according to claim 1 or 2, wherein the hydraulic composition further comprises metal elements, preferably reinforcements. 4. Use according to any one of the preceding claims, wherein the crosslinked polyacrylamide (s) is (are) obtained by polymerization from a mixture comprising at least one acrylamide monomer and at least one crosslinking agent. . 5. Use according to any one of the preceding claims, wherein the crosslinked polyacrylamide (s) is a copolymer comprising acrylamide monomer units and acrylic acid and / or acrylate monomer units, preferably acrylamide monomeric units. and / or alkali metal acrylate monomer units. 6. Use according to any one of the preceding claims, wherein the hydraulic binder comprises at least one clinker, preferably a Portland clinker. 7. Use according to the preceding claim, wherein the mass proportion of clinker in the hydraulic binder is from 30% to 85% relative to the mass of said binder. 8. Use according to any one of the preceding claims, wherein the weight ratio polyacrylamide (s) crosslinked (s) / binder is from 0.05% to 2.0%. 9. Use according to any one of the preceding claims, wherein the hydraulic binder further comprises at least one mineral addition, which is preferably selected from the group consisting of slags, pozzolans, fly ash, calcined schists, calcium carbonate materials, silica fumes, metakaolins, biomass ash and mixtures thereof. 10. A hydraulic composition comprising: a hydraulic binder comprising a Portland clinker, optionally a limestone filler or other mineral addition, the mass proportion of clinker in the binder being from 30% to 85%, at least one crosslinked polyacrylamide in the form of a particle powder having an average size of from 300 μm to 2000 μm, said crosslinked polyacrylamide having a nitrogen content greater than or equal to 4% by mass relative to the weight of the polyacrylamide, in a weight ratio of polyacrylamide (s) crosslinked (s) / binder of 0.01% to 5.0%, water, in a proportion such that the weight ratio water / binder is 0.4 to 1.2, preferably 0, 4 to 0.7, optionally a granulate such as sand, optionally a superplasticizer, and optionally an antifoaming agent.