WO2013174899A1

WO2013174899A1 - Improvement of the mechanical strengths of a hydraulic composition

Info

Publication number: WO2013174899A1
Application number: PCT/EP2013/060568
Authority: WO
Inventors: Anthony PEUCHLESTRADE; Mylène MARTIN; Elise BONY; Arnaud Schwartzentruber; Blandine ALBERT
Original assignee: Lafarge SA
Current assignee: Lafarge SA
Priority date: 2012-05-24
Filing date: 2013-05-23
Publication date: 2013-11-28
Anticipated expiration: 2014-11-24
Also published as: FR2990939A1; FR2990939B1

Description

IMPROVEMENT OF THE MECHANICAL STRENGTHS OF A HYDRAULIC

COMPOSITION

The present invention relates to the use of an admixture containing boron in hydraulic compositions comprising a Portland clinker and a mineral addition.

The main problem of hydraulic compositions comprising a mineral addition as a partial substitution of the Portland clinker is the decrease of mechanical compressive strengths, in particular measured 28 days after the hydraulic composition has been mixed. This decrease is, in particular, due to the reduction of the quantity of clinker relative to the total quantity of binder, given that the binder generally comprises clinker and mineral additions.

Several solutions exist to improve the mechanical compressive strengths measured 28 days after hydraulic compositions have been mixed but none of these solutions comprise an admixture containing boron.

An example of an admixture containing boron is borate. Borate is known as a set- retarding agent for hydraulic binders and hydraulic compositions. It is therefore not known as a means to improve the development of mechanical compressive strengths.

In order to meet user requirements it has become necessary to find a means of improving the mechanical compressive strengths measured 28 days after hydraulic compositions comprising a Portland clinker and a mineral addition have been mixed.

Therefore, the problem which the invention seeks to solve is to provide a means to improve the mechanical compressive strengths measured 28 days after hydraulic compositions comprising a Portland clinker and a mineral addition have been mixed.

Unexpectedly, the inventors have shown that it is possible to use an admixture containing boron to improve the mechanical compressive strengths measured 28 days after hydraulic compositions comprising a Portland clinker and a mineral addition have been mixed.

The present invention relates to a use of an admixture containing boron, which comprises a boron oxide, boric acid or a borate, before or during the mixing, to improve the compressive mechanical strength of a hydraulic composition, comprising a Portland clinker and a mineral addition, said compressive mechanical strength being measured 28 days after the hydraulic composition has been mixed.

Preferably, the admixture containing boron is a borate. The borate is preferably a borate salt. More preferably, the borate is selected from a metaborate, a tetraborate, a pentaborate, a perborate, a pyroborate and a biborate, even more preferably a metaborate and a tetraborate, most preferably a metaborate. Preferably, the borate comprises a salt of a mono- or di-valent cation. More preferably, the borate comprises an alkali metal salt, an alkaline earth metal salt or a poor metal salt. Most preferably, the borate comprises an alkali metal salt or an alkaline earth metal salt.

A poor metal is a metal element in the p block of the Periodic Table of Elements, generally aluminium, gallium, indium, thallium, tin, lead and bismuth.

Preferably, the cation is selected from sodium, potassium, barium, calcium and strontium.

The borate is preferably selected from sodium metaborate, potassium metaborate, barium metaborate, calcium metaborate, calcium tetraborate and mixtures thereof.

More preferably, the borate is selected from sodium metaborate, potassium metaborate, barium metaborate, calcium metaborate and mixtures thereof.

Most preferably, the borate comprises barium metaborate.

Preferably, the borate is in a hydrated form.

The admixture containing boron may be added, for example:

- at the same time as and/or in the mixing water;

- directly to at least one of the components of a hydraulic composition before the addition of the mixing water; or

- during the mixing.

Generally, the more the quantity of admixture containing boron increases, the more the mechanical compressive strengths increase 28 days after the hydraulic composition has been mixed.

Preferably, the quantity of admixture containing boron is from 1 to 5 % by mass of B₂0₃-equivalent relative to the mass of binder. The binder comprises the clinker, the mineral addition and the admixture containing boron.

Preferably, the quantity of admixture containing boron is less than or equal to 10 % by mass relative to the mass of binder.

Portland clinker is obtained by clinkering at high temperature a mixture comprising limestone and, for example, clay. For example, a Portland clinker is a clinker as defined in the NF EN 197-1 Standard of February 2001 .

Portland clinker is generally co-ground with calcium sulphate to produce a cement. Calcium sulphate used according to the present invention includes gypsum (calcium sulphate dihydrate, CaS0₄.2H₂0), hemi-hydrate (CaS0₄.1/2H₂0), anhydrite (anhydrous calcium sulphate, CaS0₄) or a mixture thereof. The gypsum and anhydrite exist in the natural state. Calcium sulphate produced as a by-product of certain industrial processes may also be used. Mineral additions are for example slags (for example as defined in the "Cement" NF EN 197-1 Standard of February 2001 , paragraph 5.2.2), natural or artificial pozzolans (for example as defined in the "Cement" NF EN 197-1 Standard of February 2001 , paragraph 5.2.3), fly ash (for example as defined in the "Cement" NF EN 197-1 Standard of February 2001 , paragraph 5.2.4), calcined shale (for example, as defined in the « Cement » NF EN 197-1 Standard, paragraph 5.2.5), mineral additions comprising calcium carbonate, for example limestone (for example as defined in the" Cement" NF EN 197-1 Standard paragraph 5.2.6) silica fume (for example as defined in the "Cement" NF EN 197-1 Standard of February 2001 , paragraph 5.2.7), metakaolins, biomass ash (for example rice husk ash) or mixtures thereof.

Preferably, the mineral addition comprises a pozzolan, a slag, a fly ash or mixtures thereof. More preferably, the mineral addition comprises a fly ash. The mineral addition may also comprise a mineral addition comprising calcium carbonate, for example limestone.

The effect of the admixture containing boron on the mechanical compressive strengths measured 28 days after the hydraulic composition has been mixed increases as the fineness of a particular mineral addition increases: fly ash.

Fly ash generally comprises pulverulent particles contained in fume in thermal power plants fed with carbon. It is generally recovered by electrostatic or mechanical precipitation.

Preferably, the fly ash is as described in the EN 197-1 Standard of February 2001

(type V or W) and in the ASTM C 618 Standard (class F or C).

A fly ash of type V comprises less than 10.0 % by mass of reactive CaO, at most

1 .0 % by mass of free CaO and at least 25.0 % by mass of reactive Si0₂. The reactive CaO is the total CaO of the binder minus the CaO coming from the CaC0₃, calculated on the basis of the measured content of C0₂, and minus the CaO coming from the CaS0₄, calculated on the basis of the measured content of S0₃ minus the S0₃ carried by the alkali metal salts.

A fly ash of type W comprises at least 10.0 % by mass of reactive CaO. A fly ash of type W which comprises from 10.0 and 15.0 % of reactive CaO also comprises at least 25.0 % by mass of reactive Si0₂.

A fly ash of class C comprises at least 50.0 % of Si0₂ + Al₂0₃ + Fe₂0₃, at most 5.0 % of S0₃ and a loss on ignition of at most 6.0 %.

A fly ash of class F comprises at least 70.0 % of Si0₂ + Al₂0₃ + Fe₂0₃, at most 5.0 % of S0₃ and a loss on ignition of at most 6.0 %.

A hydraulic binder is a material which sets and hardens by hydration, for example a cement. A cement generally comprises clinker and calcium sulphate. The clinker may in particular be a Portland clinker. For example, the cement may be:

- a Portland cement, which is generally a cement of type CEM I according to the NF EN 197-1 Standard of February 2001 , in particular Table 1 , page 12 of the Standard;

- a pozzolanic cement, which is generally a cement of type CEM IV according to the NF EN 197-1 Standard of February 2001 , in particular Table 1 , page 12 of the Standard; or

- a blended cement, which is generally a cement of type CEM II, CEM III or CEM V according to the NF EN 197-1 Standard of February 2001 , in particular Table 1 , page 12 of the Standard.

Preferably, the hydraulic composition comprises 20 to 80 % by mass of Portland clinker and 80 to 20 % by mass of a mineral addition relative to the mass of clinker and mineral addition.

It is to be understood that the partial substitution of the clinker by a mineral addition makes it possible to reduce emissions of carbon dioxide (produced during the production of the clinker) by reducing the quantity of clinker, whilst obtaining the same mechanical strengths.

A hydraulic composition generally comprises a hydraulic binder and water, optionally aggregates, and optionally admixtures. Hydraulic compositions include both fresh and hardened compositions, for example a cement slurry, a mortar or a concrete. The hydraulic composition may be used directly on the jobsite in the fresh state and poured into formwork adapted to a given application, used in a pre-cast plant or used as a coating on a solid support.

The quantity of water is preferably such that the water/binder ratio is from 0.2 to 0.7, more preferably from 0.4 to 0.6. The binder comprises the clinker, the mineral additions and the admixture containing boron.

The aggregates used include sand (whose particles generally have a maximum size

(Dmax) less than or equal to 4 mm), and coarse aggregates (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 include calcareous, siliceous, and silico-calcareous materials. They include natural, artificial, waste and recycled materials. The aggregates may also comprise, for example, wood.

The hydraulic composition may also comprise an admixture, for example one of those described in the EN 934-2, EN 934-3 or EN 934-4 Standards, respectively of September 2002, November 2009 and August 2009. Preferably, the hydraulic composition also comprises an admixture for a hydraulic composition, for example, an accelerator, an air- entraining agent, a viscosity-modifying agent, a retarder, a clay-inerting agent, a plasticizer and/or a superplasticizer. In particular, it is useful to include a superplasticizer, e.g. a polycarboxylate superplasticizer, in particular from 0.05 to 1.5 %, preferably from 0.1 to 0.8 % by mass.

Clay-inerting agents are compounds which permit the reduction or prevention of the harmful effects of clays on the properties of hydraulic binders. Clay-inerting agents include those described in the patent applications WO 2006/032785 and WO 2006/032786.

The term "superplasticizer" as used in the present description and the accompanying claims is to be understood as including both water reducers and superplasticizers as described in the Concrete Admixtures Handbook, Properties Science and Technology, V.S. Ramachandran, Noyes Publications, 1984.

A water reducer is defined as an additive which reduces the amount of mixing water of concrete for a given workability by typically 10 - 15 %. Water reducers include, for example lignosulphonates, hydroxycarboxylic acids, glucides 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 the older water reducers and capable of reducing water contents by about 30 %. The superplasticizers have been broadly classified into four groups: sulphonated naphthalene formaldehyde condensate (SNF) (generally a sodium salt); sulphonated melamine formaldehyde condensate (SMF); modified lignosulfonates (MLS); and others. More recent superplasticizers include polycarboxylic compounds, for example, polycarboxylates, e.g. polyacrylates. A superplasticizer is preferably a new generation superplasticizer, for example a copolymer containing polyethylene glycol as graft chain and carboxylic functions in the main chain such as a polycarboxylic ether. Sodium polycarboxylate-polysulphonates and sodium polyacrylates may also be used. Phosphonic acid derivatives may also be used. The amount of superplasticizer required generally depends on the reactivity of the cement. The lower the reactivity, the lower the amount of superplasticizer required. In order to reduce the total alkali salt content, the superplasticizer may be used as a calcium salt rather than a sodium salt.

Preferably, the components of the hydraulic composition to which the admixture containing boron may be added comprise aggregates, fibres, a hydraulic binder, a slag, silica fume, a fly ash, a mineral addition comprising calcium carbonate, a siliceous filler, a pozzolan, an admixture, the mixing water and/or the pre-wetting water of the aggregates.

The mixing of the hydraulic composition may be carried out, for example by known methods.

According to an embodiment of the invention, the binder is prepared during a first step, and the optional aggregates and the water are added during a second step. The hydraulic composition may be shaped to produce, after hydration and hardening, a shaped article for the construction field. Such shaped articles that comprise a hydraulic composition as obtained according to the process of the invention also constitute a feature of the invention. Shaped articles for the construction field include, for example, a floor, a screed, a foundation, a wall, a partition wall, a ceiling, a beam, a work top, a pillar, a bridge pier, a block of concrete, optionally foamed concrete, a pipe, a post, a stair, a panel, a cornice, a mould, a road system component (for example a border of a pavement), a roof tile, a surfacing (for example of a road or a wall), or an insulating component (acoustic and/or thermal).

The Dv97 is the 97^th percentile of the size distribution of the particles, by volume; that is, 97 % of the particles have a size that is less than or equal to the Dv97 and 3 % of the particles have a size that is greater than the Dv97.

Particle size distributions and particle sizes less than approximately 200 μηη are measured using a Malvern MS2000 laser granulometer. Measurements are carried out in ethanol. The light source consists of a red He-Ne laser (632 nm) and a blue diode

(466 nm). The optical model is that of Mie and the calculation matrix is of the polydisperse type.

The apparatus is calibrated before each working session by means of a standard sample (Sibelco C10 silica) for which the particle size distribution is known.

Measurements are carried out with the following parameters: pump speed 2300 rpm and stirrer speed 800 rpm. The sample is introduced in order to establish an obscuration between 10 and 20 %. The measurement is carried out after stabilisation of the obscuration. Ultrasound at 80 % is first applied for 1 minute to ensure the de-agglomeration of the sample. After about 30 seconds (for possible air bubbles to clear), a measurement is carried out for 15 seconds (15000 analysed images). Without emptying the cell, the measurement is repeated at least twice to verify the stability of the result and elimination of possible bubbles.

All values given in the description and the specified ranges correspond to average values obtained with ultrasound.

Particle sizes greater than 200 μηη are generally determined by sieving.

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

The following non-limiting examples illustrate embodiments of the invention. EXAMPLES

The tested hydraulic composition was a mortar, the formulation of which is described in the various tables herein below. The standardized sand was a siliceous sand conforming with the EN 196-1 Standard of April 2006, the supplier of which is Societe Nouvelle du Littoral.

The cement was a CEM I 52.5 R cement having a Dv97 of approximately 19 μηη, it came from the Lafarge cement plant of Saint Pierre La Cour.

The admixture containing boron was:

- sodium metaborate, Ν3Β0₂·4Η₂0 (CAS 10555-76-7), comprising 25.3 % by mass of B₂0₃-equivalent;

- potassium metaborate, ΚΒ0₂·1 ,5Η₂0 (CAS 13709-94-9), comprising 32.0 % by mass of B₂0₃-equivalent

- barium metaborate, Ba(B0₂)₂ ^«H₂0 (CAS 13701-59-2), comprising 28.9 % by mass of B₂0₃-equivalent; or

- calcium metaborate, Ca(B0₂)₂ ^«2H₂0 (CAS 13701 -64-9), comprising 43.0 % by mass of B₂0₃-equivalent.

The fly ash was fly ash from a thermal power plant in Sundance in the United States having an initial fineness without grinding (FA1 -1 ), a Dv97 of approximately 25 μηη (FA1 -2) or a Dv97 of approximately 10 μηη (FA1 -3), or fly ash coming from a thermal power plant in Le Havre in France having an original fineness without grinding (FA2-1 ), a Dv97 of approximately 25 μηη (FA2-2) or a Dv97 of approximately 10 μηη (FA2-3).

The pozzolans were pozzolans from Cameroon (Pozzl ) or from Mylos in Greece (Pozz2).

The slag was a slag from Fos Sur Mer in France having an initial fineness without grinding.

The mineral addition comprising calcium carbonate was limestone commercialised under the brand name of BL200 (Supplier: Omya).

The mortar was produced according to the procedure described herein below:

1 ) introduce the standardized sand into the vessel of a Perrier mixer;

2) from 0 to 30 seconds: begin mixing at low speed (140 rpm) and add the pre- wetting water in 30 seconds;

3) from 30 seconds to 1 minute: mix the aggregates + pre-wetting water;

4) from 1 minute to 5 minutes: leave to rest;

5) from 5 minutes to 6 minutes: add the cement and mineral additions;

6) from 6 minutes to 7 minutes: mix at low speed;

7) from 7 minutes to 7 minutes and 30 seconds: add the mixing water and optionally the admixture containing boron whilst mixing at low speed;

8) from 7 minutes and 30 seconds to 9 minutes and 30 seconds: mix at high speed

(280 rpm). The mechanical compressive strengths were measured 28 days after the hydraulic composition was mixed on samples of hardened mortar in the form of a paving stone with the following dimensions: 40 mm x 40 mm x 160 mm.

The samples of mortar had been moulded immediately after the preparation of the mortar. The mould was attached to a shock table. The mortar was introduced into the mould in two layers (each layer of mortar weighing approximately 300 g). The first layer of mortar, then the second layer of mortar were placed by 60 shocks on the shock table. The mould was removed from the shock table and levelled to remove excess mortar. A plate of glass of 210 mm x 185 mm and 6 mm thickness was placed on the mould. The mould, covered by the glass plate, was placed in a humid enclosure. The mould was removed from the enclosure and the sample of hardened mortar was demoulded 24 hours after the hydraulic composition was mixed, then it was submerged in water at 20°C ± 1 °C. The sample of hardened mortar was removed from the water 15 minutes maximum before the measurement of the mechanical compressive strength. The sample of hardened mortar was dried then covered with a damp cloth until the measurement was taken.

An increasing load was applied on the lateral sides of the samples of hardened mortar at a speed of 2 400 N/s ± 200 N/s for the measurement of the mechanical compressive strength, until breaking of the sample.

Each of the tested formulations in the examples herein below comprised:

- 1350 g of sand;

225 g of water;

180 g of cement; and

180 g of fly ash, pozzolans or slag.

Example 1 : Hydraulic compositions comprising fly ash

The effect of the barium metaborate on the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed was tested on several hydraulic compositions comprising fly ash. Tests 1 , 5, 7, 14, 16 and 18 were the control compositions because the compositions tested in these trials did not comprise barium metaborate.

Table 1 a and Table 1 b herein below present the tested compositions and the results obtained for the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. FA1-1 FA1-2 FA1-3

1 2 3 4 5 6 7 8 9 10 11 12 13

Limestone (g) 90 72 63 36 90 63 90 89 88 87 86 85 63

Barium

0 18 27 54 0 27 0 1 2 3 4 5 27

Meta borate (g)

% B₂0₃eq /

0.0 1.2 1.7 3.5 0.0 1.7 0.0 0.1 0.1 0.2 0.3 0.3 1.7 binder

% B₂0₃eq / FA 0.0 2.9 4.3 8.7 0.0 4.3 0.0 0.2 0.3 0.5 0.6 0.8 4.3

28-day Cs (MPa) 21.8 34.9 37.3 30.8 24.7 42.8 24.0 25.4 26.0 26.7 27.5 27.6 46.6

Table 1a: Hydraulic compositions comprising fly ash FA1-1, FA1-2 or FA1-3

Table 1b: Hydraulic compositions comprising fly ash FA2-1, FA2-2 or FA2-3 28-day Cs is to be understood as the mechanical compressive strengths measured

28 days after the hydraulic composition was mixed.

According to Table 1 a and Table 1 b herein above, by comparing the formulae comprising barium metaborate and their respective control compositions, which did not comprise barium metaborate, the addition of barium metaborate improved the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. For example, the mechanical compressive strength measured 28 days after the composition of Test 4 was mixed was 30.8 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 1 was mixed was 21 .8 MPa.

Generally, the effect of the admixture containing boron on the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed was better when the fly ash was finer. For example, the mechanical compressive strength measured 28 days after the composition of Test 15 was mixed was 28.9 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 14 was mixed was 21 .8 MPa. The gain of mechanical compressive strength measured 28 days after the hydraulic composition was mixed was 7.1 MPa for the FA2-1 fly ash, which had a standard fineness. Likewise, the mechanical compressive strength measured 28 days after the composition of Test 19 was mixed was 43.3 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 18 was mixed was 23.6 MPa. The gain of mechanical compressive strength measured 28 days after the hydraulic composition was mixed was 19.7 MPa for the FA2-3 fly ash, which had a Dv97 of approximately 10 μηη. The increase of the mechanical compressive strength measured 28 days after the hydraulic composition was mixed was therefore greater for the finer fly ash. The same finding was made for the FA1 fly ash.

Example 2: Hydraulic compositions comprising pozzolans

The effect of the barium metaborate on the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed was tested on several hydraulic compositions comprising pozzolans. Tests 1 and 5 were the control compositions because the compositions tested in these trials did not comprise barium metaborate.

Table 2 herein below presents the tested compositions and the results obtained for the mechanical compressive strengths measured 28 days after the hydraulic compositions were mixed.

Table 2: Hydraulic compositions comprising pozzolans Pozzl or Pozz2 28-day Cs is to be understood as the mechanical compressive strengths measured

28 days after the hydraulic composition was mixed.

According to Table 2 herein above, by comparing the formulae comprising barium metaborate and their respective control compositions, which did not comprise barium metaborate, the addition of barium metaborate improved the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. For example, the mechanical compressive strength measured 28 days after the composition of Test 2 was mixed was 31 .1 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 1 was mixed was 21 .6 MPa.

Example 3: Hydraulic compositions comprising slag

The effect of the barium metaborate on the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed was tested on several hydraulic compositions comprising slag. Test 1 was the control composition because the composition tested in this trial did not comprise barium metaborate.

Table 3 herein below presents the tested compositions and the results obtained for the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. Slag

1 2 3 4

Limestone (g) 90 72 63 36

Barium Metaborate (g) 0 18 27 54

% B₂0₃eq / binder 0.0 1.2 1.7 3.5

% B₂0₃eq / slag 0.0 2.9 4.3 8.7

28-day Cs (MPa) 37.6 40.8 42.1 40.1

Table 3: Hydraulic compositions comprising slag

28-day Cs is to be understood as the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed.

According to Table 3 herein above, by comparing the formulae comprising barium metaborate and their control compositions, which did not comprise barium metaborate, the addition of barium metaborate improved the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. For example, the mechanical compressive strength measured 28 days after the composition of Test 3 was mixed was 42.1 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 1 was mixed was 37.6 MPa.

Example 4: Hydraulic compositions comprising different admixtures containing boron

Different admixtures containing boron were tested on hydraulic compositions comprising the FA1 -1 fly ash. Test 0 was the control composition because the composition tested in this trial did not comprise an admixture containing boron.

The tested admixtures containing boron were barium metaborate, calcium metaborate, potassium metaborate and sodium metaborate.

Table 4 herein below presents the tested compositions and the results obtained for the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed.

Table 4: Hydraulic compositions comprising different admixtures containing boron 28-day Cs is to be understood as the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed.

According to Table 4 herein above, by comparing the formulae comprising an admixture containing boron and their control compositions, which did not comprise an admixture containing boron, the addition of this admixture improved the mechanical compressive strengths measured 28 days after the hydraulic composition was mixed. For example, the mechanical compressive strength measured 28 days after the composition of Test 5 was mixed (comprising potassium metaborate) was 28.7 MPa, whilst the mechanical compressive strength measured 28 days after the composition of Test 0 was mixed (not comprising an admixture containing boron) was 21 .8 MPa.

Claims

1 - A use of an admixture containing boron, which comprises a boron oxide, boric acid or a borate, before or during the mixing, to improve the compressive mechanical strength of a hydraulic composition, comprising a Portland clinker and a mineral addition, said compressive mechanical strength being measured 28 days after the hydraulic composition has been mixed.

2- The use according to claim 1 , wherein the quantity of admixture containing boron is less than or equal to 10 % by mass relative to the mass of binder.

3- The use according to claim 1 or claim 2, wherein the quantity of admixture containing boron is from 1 to 5 % by mass of B₂0₃-equivalent relative to the mass of binder. 4- The use according to any one of claims 1 to 3, wherein the admixture containing boron is selected from metaborates and tetraborates.

5- The use according to any one of claims 1 to 4, wherein the admixture containing boron is selected from sodium metaborate, potassium metaborate, barium metaborate, calcium metaborate and mixtures thereof.

6- The use according to any one of claims 1 to 5, wherein the admixture containing boron is barium metaborate. 7- The use according to any one of claims 1 to 6, wherein the mineral addition comprises a pozzolan, a slag, a fly ash or mixtures thereof.

8- The use according to any one of claims 1 to 7 wherein the mineral addition comprises a fly ash.

9- An shaped article for the construction field comprising a hydraulic composition as obtained according to any one of claims 1 to 8.