OA20512A

OA20512A - Method for grinding a hydraulic binder

Info

Publication number: OA20512A
Application number: OA1202100387
Authority: OA
Inventors: Hüseyin OYTUN YAZAN; Laurent Guillot; Pascal Boustingorry
Original assignee: Chryso
Priority date: 2019-02-25
Filing date: 2020-02-25
Publication date: 2022-09-30

Abstract

The application concerns a method for grinding a hydraulic binder, comprising: a) introducing: - a hydraulic binder, and - a composition B comprising at least one grinding aid B into the first chamber (12) of a horizontal grinder (11) comprising several chambers (12, 14), including a first chamber (12) and a last chamber (14), each chamber (12) being separated from the adjacent chamber (14) by a diaphragm (17), whereby a composition p comprising the hydraulic binder and composition B is obtained in the first chamber (12), b) grinding composition p in the horizontal grinder (11), whereby composition B moves from the first chamber (12) to the last chamber (14) and a ground composition C is obtained at the outlet of the last chamber (14), characterised in that, at the grinding step, it comprises introducing into the last chamber (14) a composition A comprising at least one grinding aid A comprising an aminoalcohol, and the grinding unit intended for implementing same

Description

Mandataire : Cabinet BONNY & Associés, LAW FIRM, B.P. 869, YAOUNDE (CM).

Φ Titre : Method for grinding a hydraulic binder.

O Abrégé :

The application concerns a method for grinding a hydraulic binder, comprising:

a) introducing:

- a hydraulic binder, and

- a composition B comprising at least one grinding aid B into the first chamber (12) of a horizontal grinder (11) comprising several chambers (12, 14), including a first chamber (12) and a last chamber (14), each chamber (12) being separated from the adjacent chamber (14) by a diaphragm (17), whereby a composition p comprising the hydraulic binder and composition B is obtained in the first chamber (12),

b) grinding composition p in the horizontal grinder (11), whereby composition B moves from the first chamber (12) to the last chamber (14) and a ground composition C is obtained at the outlet of the last chamber (14), characterised in that, at the grinding step, it comprises introducing into the last chamber (14) a composition A comprising at least one grinding aid A comprising an aminoalcohol, and the grinding unit intended for implementing same.

O.A.P.I. - B.P. 887, YAOUNDE (Cameroun) - Tel. (237) 222 20 57 00-Site web: http:/www.oapi.int- Email: oapi@oapi.int

METHOD FOR GRINDING A HYDRAULIC BINDER

The présent invention concems a method for grinding a hydraulic binder such as cernent. The method for prepahng a hydraulic binder inciudes grinding to reduce the particle size of the binder, thereby increasing reactivity and imparting desired rheologica! properties thereto.

The use ofa grinding aid allows improved yield of hydraulic binder grinding. Grinding aids allow:

an increase in production when grinding, for one same energy consumption and one same fineness, or an increase in frneness, for one same energy consumption.

When a horizontal grinding mill is used having several grinding chambers for grinding a hydraulic binder, the grinding aid(s) is(are) injected into the first chamberofthe grinding mill together with the hydraulic binder to be ground, or separately.

There is a need to develop a method for grinding a hydraulic binder allowing improved quality of the ground hydraulic binder (in particular Bfaîne fineness and/or particle size distribution) and/or improved grinding yield to reduce costs.

For this purpose, a first subject ofthe invention is a method for grinding a hydraulic binder, comprising:

a) introducing:

a hydraulic binder, and a composition B comprising at least one grinding aid B, into the first chamber of a horizontal grinder comprising several chambers, including a first chamber and a fast chamber, each chamber being separated from the adjacent chamber by a diaphragm, whereby a composition β comprising the hydraulic binder and composition B is obtaîned in the first chamber,

b) grinding composition β in the horizontal grinder, whereby composition β moves from the first chamberto the last chamber, and a ground composition C is obtained atthe outlet ofthe last chamber, characterised in that, at the grinding step, it comprises introducing into the last chamber a composition A comprising at least one grinding aid A comprising an aminoalcohoî, composition A differing from composition β.

The method uses a horizontal grinder comprising several chambers (sometimes called « compartments »), including a first chamber and a last chamber, each chamber being separated from the adjacent chamber by a dîaphragm. in general, the ch a m bers hâve the same diameter and/or the last chamber is îonger than the first chamber. Preferably, the grinding charge (métal balls...) differs in size from one chamber to the next.

The first chamber is the chamber receiving the hydrauiic binder to be ground. The last chamber is the chamber from which the ground composition C leaves the grinder. The ground composition C comprises the ground hydrauiic binder, grinding aid A and grinding aid B.

Throughout grinding, the hydrauiic binder moves from the first chamber to the adjacent chamber until reaching the last chamber. The dîaphragm separating two adjacent chambers oniy allows particies of hydrauiic binder to pass that are of sufficient reduced size for finer grinding in the following adjacent chamber. The particle size of the hydrauiic binder is therefore iargesi in the first chamber and smallest in the last chamber.

Typically, the grinder only has two chambers: the first chamberand the last chamber (which is then the second chamber), these being separated by a dîaphragm.

The grinder is generally a bail mlll. The mean bail diameter in the first chamber is generally greater than the mean bail diameter in the last chamber.

The method comprises a step a) to intmduce a hydrauiic binder and a composition B comprising at feast one grinding aid B into the first chamberofthe grinder.

By the term « hydrauiic binder » it is meant any compound having the property of becoming hydrated in the presence of water, the hydration of which allows a solid to be obtained having mechanical characteristics. The hydrauiic binder can be a cernent conforming to standard EN 197-1 of 2012, and în particular a cernent oftype OEM I, OEM II, CEM II!, CEM IV or CEM V in accordance with cernent standard NF EN 197-1 of 2012. The cernent can therefore particutariy comprise minerai additions.

The expression « minerai additions » désignâtes slag (such as defined in cernent standard NF EN 197-1 of 2012 paragraph 5.2.2), steelmaking slag, pozzolanic materials (such as defined în cernent standard NF EN 197-1 paragraph 5.2.3), fly ash (such as defined in cernent standard NF EN 197-1 paragraph 5.2.4), calcined schists (such as defined in cernent standard NF EN 197-1 paragraph 5.2.5), limestone such as defined in cernent standard NF EN 197-1 paragraph 5.2.6) or fumed sîlicas (such as defined in cernent standard NF EN 197-1 paragraph 5.2.7) or the compositions thereof. Othsr additions, currently not recognized by cernent standard NF EN 197-1 (2012), can also be used. These are chiefly metakaolins, such as type A metakaolîns conforming to standard NF P 18-513 de 2012, and siliceous additions of Qz mineralogy conforming to standard NF P 18-509 of 2012.

In a first embodiment, grinding aid B comprises a potyol, preferably selected from among:

a diol such as an alkylene glycol preferably having 1 to 20 carbon atoms, in particular 1 to 10 carbon atoms, the alkylene group thereof possibly carrying a methyl and typically being selected from among 2-methyl-1,3-propanediol, monoethylenegiycol, diethyleneglycol, triethyleneglycol, tetraethyleneglycol, propylene glycol and a mixture thereof, a triol, preferably glycerol, tetraol, preferably erythritol, and a mixture thereof.

Grinding aid B for example comprises an alkylene glycol, or a mixture of alkylene glycols and optionally g ty ce roi, the glycerol preferably being conta in ed in a proportion of 0 to 5 % by weight relative to the weight ofthe assembly (glycerol and alkylene glycol(s)).

Grinding aid B (and composition B) are then preferably free of aminoalcohoi, in particular of one of those listed below.

In a second embodiment, grinding aid B comprises an aminoalcohoi or one of the salts thereof, said aminoalcohoi preferably comprising:

from 2 to 8 carbon atoms, in particular 4 to 6 carbon atoms, and/or

1,2 or 3 alcohol tunctions, selected for example from among N-methyldietha no lamine (MDEA), diisopropanolamine (DIPA), triisopropanolamine (TIPA), triethanolamine (TEA), ethanol-diisopropanolamine (EDJPA), diethanolisopropanolamine (DEIPA) and a mixture thereof. For example, grinding aid B comprises triisopropanolamine (TIPA), triethanolamine (TEA) or a mixture thereof. The preferred aminoalcohoi salts are hydrochlorides such TEA.HCl, TIPA.HCI, EDIPA.HCi and DEIPA.HCI.

In this second embodiment, grinding aid B (and composition B) are preferably free of polyol, and in particular of one of those listed above.

This second embodiment is particularly adapted for grinding a soft hydraulic binder on which polyols could indues agglomération harmfui for grinding, and should therefore be avoided.

In a third embodiment, grinding aid B comprises a polyol and aminoalcohoi.

In the second and third embodiments (when grinding aid B comprises an aminoalcohoi), grinding aid B may comprise a carboxylic acid or sait thereof, selected for example from among acetic acid and one of the salts thereof, formic acid or one ofthe salts thereof, or a mixture thereof. Grinding aid B then comprises an aminoalcohoi, a carboxylic acid or sait thereof and optionally a polyol. The sait can be the sait formed between the aminoafcohoi and carboxylic acid. Carboxyiic acid generally allows adjustment of the dïspersing force of composition δ, this force sometimes being too intense when aminoafcohoî is used without carboxyiic acid.

Grinding aid B îsthe active material of composition B. Composition B may comprise one or more grinding aids B.

in addition to grinding aid B, composition B may comprise a solvent, generally water. Composition B can be composed of an aqueous solution of at least one grinding aid B (this aid preferably being constituted of one or more polyols, one or more aminoalcohols or a mixture thereof, and optionally one or more carboxylic acids or a sait thereof when the grinding aid comprises and aminoalcohol), even of a mixture of water and grinding aid B.

The proportion of grinding aid B introduced into the first chamber at step a) is typically from 50 to 2500 g, in particular from 75 to 500 g, preferably from 90 to 250 g per tonne of hydraulic binder fed into the first chamber at step a). Beîow this value, the efficiency ofthe grinding aid decreases, and above this value costs become too high. The proportion relates to the « dry » grinding aid without taking into account any solvent or optional other additives in composition B. When composition B comprises several grinding aids B, it îs the sum of their proportions that is taken into considération.

The feedtng of the hydraulic binder and composition B may or may not be simultaneous. In addition, the feeding ofthe hydraulic binder and composition B can be made via separate inlets of the first chamber or via one same inlet. For example, the First chamber can be charger! with composition β comprising the hydraulic binderand composition B (introducing the hydraulic binder and composition B simultaneously via one same inlet). Preferably, composition B and the hydraulic binder are introduced simultaneously via one same inlet of the first chamber. Typically, composition B is dispersed in the hydraulic binder in the feed hopper ofthe hydraulic binder, for example via a spray ramp or a pipe releasing drops onto a hydraulic binder feed hopper. In this case, it is therefore composition p, which is introduced into the first chamber ofthe horizontal grinder.

The method comprises a step b) to grind composition β in the grinder, whereby composition β moves from the first chamberto the last chamber, and a ground composition C is obtained at the outlet of the last chamber. The mean particle size of composition C is therefore smallerthan that of composition β. Measurement of particle size can be performed by laser particle size measurement giving a size distribution, or by sieving under pressure which typically gives a mass proportion of rejects on adefined screen mesh typically 32.45 and/or 63 pm (on the understanding that the same measuring method must be used for size comparison).

At grinding step b) of the method of the invention, a composition A comprising at teast one grinding aid A comprising an aminoalcohoi is injeded into the iast chamberofthe grinder, Typically, composition A is injected into the iast chamber:

either at the diaphragm separating the Iast chamber from the adjacent chamber, or into the enciosure of the last chamber in a zone generally doser to the diaphragm, separating the îast chamber from the adjacent chamber, than to the outlet of the last chamber, or at the outlet of the last chamber, typically at the discharge grate equipping the outlet of the last chamber.

The method employs at least two grinding aids A and B which are introduced into different points of the grinder: one into the first chamber, the other into the last chamber.

The inventors hâve shown that the grinding aids A and B are not distributed in the same manner within the grinding unit the dosage of a grinding aid along the grinding unit varies as a fonction ofthe type ofgrinding aid. When the grinding aids are both introduced into the first chamber as in the prior art:

the quantity of grinding aid found on the particles of hydraulîc binder is essentialiy govemed by the spécifie surface area of the hydraulîc binder particles as soon as they leave the first chamber of the grinder;

inside the first chamber of the grinder, when grinding aid B comprises an alkylene glycol, it is more abundant per unit surface area of hydraulîc binder than grinding aid A comprising an aminoalcohoi, the quantity of grinding aid per unit surface area of hydraulîc binder stabilises in the second chamberofthe grinder, and thedifférence between the two grinding aids decreases in the last chamber.

Grinding aid A, comprising an aminoalcohoi, generally has good capability of fluidifying the flow of particles, which is not frie case of a grinding aid comprising an alkylene glycol. Without wishing to be bound by any particular theory, in the iight ofthe following examples, the inventors assume that the grinding aids are conveyed by the hydraulîc binder particles of large spécifie surface area, and hence by the small size particles;

this effect would be amplifié if the grinding aid has a fiuidifying effect, which is the case for grinding aid A comprising an aminoalcohoi, which increase the flow rate of hydrauiic binder particles of small size. Grinding aid A comprising an aminoalcohoi is therefore less abundant in the first grinding chamber which comprises hydraulîc binder particles of iarge size.

This démon strates the advantage of introducing the two grinding aids at different points on the grinding line: grinding aid B in the first chamber to allow a sufficiently long résidence time ofthe hydraulic binder in the grinder, and grinding aid A comprising an aminoalcohol in the last chamber, to remove smali-sized particles from the grinder and/or to fluidify the partiales ofthe ground composition C thereby improving subséquent processability thereof and facilitating any subséquent séparation (second alternative described below).

Composition A differs from composition β. In other words, composition A injected into the last chamber is not the composition undergoing grinding in the grinder.

Grinding aid A comprises at least one aminoalcohol preferably comprising:

from 2 to 8 carbon atoms, in particular 4 to 6 carbon atoms, and/or

1,2 or 3 alcohol fonctions,

e.g. selected from among N-methyldiethanolamine (MDEA), diisopropanolamine (DIRA), triisopropanoiamine (TIRA), triethanoîamine (TEA), éthanol diisopropanolamine (EDIPA), dîeth an olisopropa nota mine (DEIPA) and a mixture thereof. For example, grinding aid A comprises triisopropanoiamine (TIPA), triethanoîamine (TEA) or a mixture thereof.

Grinding aid A may comprise a carboxylic acid or sait thereof, selected for exampie from among acetic acid orone ofthe salts thereof, formic acid orone ofthe salts thereof, or a mixture thereof. Grinding aid A therefore comprises an aminoalcohol and a carboxylic acid or a sait thereof. The sait can be the sait formed between the aminoalcohol and carboxylic acid. Carboxylic acid generally allows adjustment of the dispersing force of composition A, this sometimes being too intense when aminoalcohol is used without carboxylic acid.

in one embodiment, grinding aid A is the same as grinding aid B. Composition A can be the same as composition B.

in another embodiment, grinding aid A differs from grinding aid B. Composition A differs from composition B.

Grinding aid A is the active material of composition A. Composition A may comprise one or more grinding aids A.

In addition to grinding aid A, composition A may comprise a solvent, generally water. Composition A can be constituted of an aqueous solution of at least one grinding aid A, even of a mixture of water and grinding aid A.

The proportion of grinding aid A injected into the last chamber at step b) is typically from 50 to 2500 g, In particular from 75 to 500 g, preferably from 90 to 250 g per tonne of hydraulic binder fed into the first chamber at step a). Below this value the efficiency ofthe grinding aid decreases, and above this value the costs become too high. This proportion reiates to the « dry » grinding aid without taking into account any solvent and optional other additives to composition A. When composition A comprises severai grinding aids A, it is the sum of their proportions that is taken into considération.

At grinding step b), air can be circulated from the first chamber towards the iast chamber. Air enfers via the first chamber and leaves via the iast chamber. This air aliows displacement of the most volatile particies of composition β undergoing grinding. The method may then comprise, after step b):

i) fiftering the air ieaving the Iast chamber, whereby the most volatile ground particies of hydraulic binder are recovered; then ii) grouping the recovered most volatile particies with the ground composition C, generally via flow under an air stream.

In a first alternative, after step b) the method comprises a step bl) to recover the ground composition C. Ground composition C then has the desired size/specific surface area. The method can then be implemented by continuous, semî-continuous or batch process.

In this first alternative, the main advantage of injecting composition A comprising at least one grinding aid A comprising an aminoalcohol into the Iast chamber is to obtain fluidification of the ground composition C, which improves subséquent processability thereof since ground composition C is more fluid facilitating the fiow thereof for example in a silo or when loading or unloading a truck, in general, the required dosage of grinding aid A comprising an aminoalcohol to obtain suitable fluidity of the ground composition C is higherthan the dosage required for efficient grinding of the hydraulic binder. It is therefore of advantage to inject grinding aid A into the Iast chamber of the grinder, including in the embodiment in which grinding aid A is injected at the outlet of the Iast chamber typîcally at the discharge grate equipping the outlet of the Iast chamber.

!n a second alternative, the method after step b) comprises:

c) separating, by a separator, composition C ground into fines and separator rejects, where the mean particle size of the separator rejects is greater than that of the fines;

d) recovering the fines;

e) retuming the separator rejects to the first chamber of the horizontal grinder.

In this second alternative, the method comprises a séparation step c) between composition C ground into fines and separator rejects.

The inventera hâve shown that:

séparation is more efficient the greater the quantîty of grinding aid A or B, until limit efficacy is reached;

séparation efficacy is dépendent on the grinding aid used. Séparation is more efficient with grinding aid A comprising an aminoaicohoî than with a grinding aid comprising a polyol.

Therefore, injectrng grinding aid A comprising an aminoalcohoi into the last chamber of the grinderallows better fluidification ofthe ground composition C at the time of séparation and makes séparation more efficient.

Additionally, the introduction of composition A comprising at least one grinding aid A comprising an aminoalcohoi into the last chamber also has the advantage of fluidifying the ground composition C, and the recovered fines, which improves the subséquent processability thereof since the fines hâve more fluid flow e.g. in a silo or when îoading or unloading a truck. In general, the required dosage of grinding aid A comprising an aminoalcohoi to obtaîn acceptable fiuidity of recovered fines is greater than that required for efficient grinding ofthe hydraulic binder, in this second alternative, steps i) and it) defined above, when performed, are preferabiy foîlowed by a step iii) to retum the partiales grouped with ground composition C backto the separator. Steps i), it) and iii) are implemented between steps b) and c).

In this second alternative, the fines are recovered at step e). It is the composition of hydraulic binder ground to the desired size/specific surface area which is obtained with the method. Typicaily, when the hydraulic binder is cernent, the spécifie surface area of the fines measured with the Blaine method is of the order of 3200 to 4500 cm²/g.

The separator rejects comprise particies that are too large for the desired size. They are retumed to the first grinding chamber to be re-ground. Therefore, composition β contained in the first chamber comprises, even consists of, the hydraulic binder, separator rejects and composition B (bearing in mind that the rejects comprise hydraulic binder, grinding aid A and grinding aid B).

in general, in this second alternative, the grinding method is a continuous process.

A second subject of the invention is a grinding unit intended to implement the method of the invention, comprising:

a source of hydraulic binder;

a source of composition B comprising at least one grinding aid B;

a source of composition A comprising ai least one grinding aid A comprising an aminoalcohoi;

a horizontal grinder comprising several chambers, including a first chamber having at least one inlet and a last chamber having an ouflet, each chamber being separated from the adjacent chamber by a diaphragm, characterized in that the last chamber is equipped with an inlet connected to the source of composition A.

The above-described embodiments, in particular those for the grinder, are applicable.

In general, the last chamber extends from the diaphragm separating the last chamber from the adjacent chamberas far as the discharge grate, which is able to let ground composition C be discharged from the grinder. Typically, the inîet of the last chamber connected to the source of composition A is positioned:

erther at the diaphragm separating the last chamber from the adjacent chamber;

or in the enclosure ofthe last chamber in a zone generally doser to the diaphragm, separating the last chamber from the adjacent chamber, than ta the outlet of the last chamber;

or at the outlet ofthe last chamber, typically at the discharge grate equipping the outlet of the last chamber.

If the grinder is a bail grinder, the outlet of the last chamber is generally equipped with a discharge grate configured to prevent ihe grinding balls from leaving the grinder.

Typically, the grinder has only two chambers: the first chamber and last chamber (which is then the second chamber), these being separated by a diaphragm.

The grinder is typically configured so that air is able to circulate from an inlet ofthe first chamber towards the outlet of the second chamber. The unit comprises a filter connected to the outlet of the last chamber and configured to filter air and to recover the most volatile partîcles of ground hydraulic binder.

In a first alternative, the grinding unitdoes not hâve a separator. This first alternative ofthe grinding unit allows impiementation ofthe firstalternative ofthe method described above. In this first alternative of the unit, the filter if any is configured to filter air, to recover the most volatile partîcles of the ground hydraulic binder and to retum these to the ground composition C.

In this first alternative, the first chamber is:

either equipped with a single inlet connected to the source of hydraulic binder and to the source of composition B, or equipped with two inlets, the first inlet being connected to the source of hydraulic binder and the second inlet being connected to the source of composition B.

In a second alternative, the grinding unit comprises a separator. The separator is typically a dynamic air or cyclonic separator with rotating chamber or a static fîîter separator, or a combination thereof. The outlet of the last chamber of the grinder is then generally connected to the inlet of a separator able to separate the partîcles according to size and provided with two outlets, one ofthe outlets being connected to an inlet ofthe first chamber ofthe horizontal grinder. This second alternative ofthe grinding unit allows impiementation ofthe second alternative ofthe above-described method. The grinding unitthen comprises a closed circuit since the outlet of the last grinding chamber is connected to the iniet of the separator of which one of the outlets is connected to the first chamber of the grinder.

In this second alternative, the first chamber is:

either equipped with a single iniet connected to the source of hydraulic binder, to the source of composition B and to an outlet of the separator;

or equipped with two înlets, the first iniet being connected to the source of hydraulic binder and source of composition B, the second iniet being connected to an outlet of the separator;

or equipped with three inlets, the first iniet being connected to the source of hydraulic binder, the second iniet being connected to the source of composition B and the third iniet being connected to an outlet of the separator.

in this second alternative of the unit, the filter if any is positioned between the last chamber of the grinder and the separator. The filter is configured to filter air, to recover the most volatile partiales of hydraulic binder and to return these to the separator.

The invention is illustrated in connection with the following examples and appended Figures.

FtGURES

[Fig 1] Figure 1: Schematic of a grinding unît according to the second alternative of the invention.

[Fig 2] Figure 2; Schematic of a prior art grinding unit and such as used in Example 1, indicating the sampüng points 1,2, 3, 4 5 and 6 for Example 1.

[Fig 3] Figure 3: Example of a Tromp curve. Percentage of separator rejects retumed to the grinder as a function of particle size in pm.

[Fig 4] Figure 4: Efficiency C of the separator as a function of the quantity of grinding aid entering the separator for each grinding aid and each dosage of grinding aid measured in m² of cernent. The values indicated in the graphs correspond to the initiai dry dosages in ppm of grinding aid relative to cernent weight. The crosses correspond to grinding aid A comprising an aminoalcohoi and the circles to grinding aid B comprising an alkyiene glycoE [Fig 5J Figure 5: Slope β of the separator fish-hook as a function of the quantity of grinding aid entering the separator for each grinding aid and each dosage of grinding aid measured in m² of cernent. The crosses correspond to grinding aid A comprising an aminoalcohol and the circles to grinding aid B comprising an alkyiene glycol. The values indicated in the graphs correspond to the initial dry dosages in ppm of grinding aid relative to cernent weight.

[Fig 6] Figure 6: Dosage of grinding aid (in dry g) measured per m² of cernent in the chambers of the grinder and at different points of the unît where samples were taken. The crosses correspond to grinding aid A comprising an aminoalcohoi and the circies to grinding aid B comprising an alkylene glycol.

[Fig 7] Figure 7: Reiationship between the quantity of grinding aid (in dry g) measured per tonne of cernent on the samples and the spécifie surface area of the cernent in cm²/g. The crosses correspond to grinding aid A comprising an aminoalcohoi and the circies to grinding aid B comprising an alkylene glycol.

[Fîg 8] Figure 8: Schematic of a grinding unit according to the second alternative and positions of sampling points in Example 2.

[Fig 1] Figure 1 illustrâtes a grinding unit according to the second alternative of the invention, in the case in which the grinding unit comprises a fîlter. A horizontal grinder 11 comprising two chambers:

a first chamber 12 equipped with a first iniet 13; and a second chamber (last chamber) 14 equipped with an inIet 15 and outiet 16, the first chamber 12 being separated from the second chamber 14 by a diaphragm 17. The inlet 13 of the first chamber 12 is connected to a hydrautic binder source 18, to a source 19 of composition B, and to an outiet 24 of the separator 23. The inlet 15 of the second chamber 14 is connected to the source 20 of composition A. The grinder 1 is configured so that air is able to circulate from the inlet 13 of the first chamber towards the outiet 16 of the second chamber 14. The outiet 16 of the second chamber 14 is connected to:

a fîlter 21 configured to fîlter air and to retum the filtered particles to the inlet 22 of a separator 23; and the inlet 22 ofthe separator 23 able to separate the particles according to particie size and equipped with two outlets: an outiet 24 connected to the inlet 13 of the first chamber 12 and an outiet 25.

The points 1,2, 3, 4, 5 and 6 do not correspond to éléments of the unît but indicate the different points where samples are taken, with reference to the following examples.

EXAMPLES

In the following examples, the grinding aids A and B hâve been fed in varying methods, either into the first chamber 12 via inlet 13, or at the discharge grate equîpping the outiet 16 ofthe second chamber, or at both these points. The experiments conducted evidence the distribution of grinding aid A comprising an aminoalcohoi or of grinding aid B comprising an alkylene glycol, and the impact thereof on particle size and cernent flow, as well as the flow rates of materiai in the method, and show the advantage of injecting grinding aid A into the second chamber 14 ofthe horizontal grinder 11.

EXAMPLE 1

Materials

The tested cernent was of CEM 142.5R type (94 % clin ken 5.5 % gypsum; 5.5 % limestone). The grinding aids were specifically formulated for the study. Their compositions are given in Table 1 below;

Table 1 : Composition ofthe grinding aids A and B used in Exampie 1

[Table 1]

	Compounds	Active material (%)
Grinding aid A comprising an aminoalcohol	Water
Triethanolamine	8.33
T riisopropanolamine (diluted)	33.33
Grinding aid B comprising an alkylene glycol	Waater
Diethylene glycol	22.70
Glyceroi (diluted)	12.09

The grinding unit used is such as illustrated in Figure 2.

The horizontal grinder 11 comprised two chambers separated by a diaphragm 17.

For a cernent without grinding aid, and for cements each containing grinding aids at different concentrations, samples were taken at different points on the circuit shown in Figure 2, once the State of equilibrium had been reached on the grinding line.

Also, for cements containing grinding aids, samples were taken every 1.2 m m the first chamber 12 ofthe horizontal grinder 11 and at every métré in the second chamber.

In this first example, the grinding aid in liquid form was injected dropwise into the feed hopper of the hydraulic binder. The mixture of hydraulic binder and grinding aid was fed into the intet 13 of the horizontal grinder 1.

Table 2 below summarises the different analysed samples

Table 2 Samples taken along the grinding line - initial dosages

ΓΓαΜη Tt £ I QMIÇ *,J

Test	Grinding aid	initial dosage (ppm)	Dry * dosage (ppm)	Reference given to dosage	Samples taken in the grinder	Samples taken along the circuit (Points 2, 3, 4, 5. 6)
T3 (ref)	None	0	0		X	X
T4	Grinding aid A comprising an aminoalcohol	250	104	D1		X
T5	350	146	D2		X
T6	450	187	D3	X	X
T7	Grinding aid B comprising an alkylene glycol	300	104	DI		X
T8	400	139	D2		X
T9	500	174	D3	X	X

* Dosage of active materis! without taking water into account.

Test T3, without grinding aid, is the reference for the study. The different initiai dosages are called D1, D2 and D3 hereafter

Methods

Mixing:

A Kenwood Chef Elite mixer KVC5305S was used to mixthe cernent and ultrapure -water with the desired water/cement ratio (« W/C » hereafter). 400 g of cernent were added to ultrapure water prepared in the bowl ofthe mixer, following the sequence indicated in Table 3:

Table 3 Mixing protocol

[Table 3J

Time	Speed (rpm)	Action
0~30”	43	Pouring of powder
30”-1 '	96	Mixing
T-1’30	0	Scraping edges
1 '30-2’30	96	Mixing

if there were many coarse particles in the cernent, mixing was performed manually, The cernent was added to the ultrapure water for 30 s after which the paste was mixed with a spatuta fcr2 min.

Assay of grinding aids:

Assay of grinding aids was obtained by washing the cernent and measuring the carbon concentration in the cernent grout.

The cernent was mixed with ultrapure water following the above-descnbed mixing protocol, then left to stand for 30 min. After manuat homogénisation, the grout was filtered through a Büchner, and the ffitrate collected in a haemoiysistube after 0.2 pm filtration, and acidified to overcome any carbonatation. These solutions were passed through a Total Organic Carbon analyzer (« TOC » hereafter) to détermine the carbon concentrations.

The amount of carbon in the cernent without grinding aid wasdeducted from measurements taken on the cements containing a grinding aid.

To verify that the grinding aid had no absorption isotherm on the solid phase in water, measurements were taken with two water/cement W/C ratios: 0.4 and 0.6, on sam pies of fine particles taken at outlet 25 of the W/C separator (tests T3, T6, T9, point (6) on the grinding circuit). In the absence of an absorption isotherm, the ratio of carbon in solution/cement is not depenbent on the initial W/C ratio, anb the entirety ofthe grinding aid is assayed.

Measurement of Total Organic Carbon (TOC) was performed on the acidified filtrâtes using a SHIMADZU TOC-VCPN analyzer. TOC was calcuiated by the différence between the quantity of total carbon (obtained by carbonisation ofthe solution and measurement ofthe quantity of COs released under infrared) and the quantity of inorganic carbon (obtained by acidification of the solution to pH < 1 and release of dissoîved CO? by bubbling with synthetic air). A calibration curve foreach ofthe grinding aids ailowed détermination ofthe concentration thereof in the cernent grouts. It is expressed in g/L.

Results

The quantifies of grinding aid are expressed in ppm (g dry weight of grinding aid per tonne of cernent) or in g/m² (g dry weight of grinding aid per square mètre of cernent surface area).

TOC calibration

The calibration curves obtained for grinding aid A comprising an aminoalcohol and for grinding aid B comprising an alkylene glycol showed a coefficient of corrélation of 1, and were therefore able to be used to caiculate the quantity of grinding agent from the quantîty of TOC measured in the sampies.

The concentration of grinding aid A (Ca) comprising an aminoalcohol was therefore calculated from the TOC value according to:

Cà= 0Ό019 * TOC + 0.0115

The concentration of grinding aid B (Cb) comprising an alkylene glycol was therefore calculated from the TOC value according to:

C₈= 0.0026 * TOC + 0.0111

Vérification of cernent washing

To ensure the absence of absorption isotherm of the grinding aids on the cernent, TOC measurements were taken with two W/C ratios. 0.4 and 0.6, for tests T6 and T9, at points (6) and the resutts were as follows:

Table 4 Effïcacy of cernent washing -TOC value as a fonction of W/C ratio

[Table 4]

Test	TOC value atW/C 0.4 (ppm)	TOC value at W/C 0.6 (ppm)
T6(6)	149	146
T9(6)	132	137

The resuIts show that the TOC values are not substantially dépendent on the W/C ratio. The grinding aids are not adsorbed on the surface of the cernent particles, and washing is therefore efficacîous for determining the quantity of grinding aid in the different sampies.

For the experiments described below, the cements were analysed with a W/C ratio of 0.4, to obtain a stronger concentration of carbon in solution.

TOC on sampies not containinq a grinding aid - Test T3

TOC was measured at points (2), ¢3), (4), (5) and (6) on the grinding line and inside the horizontal grinder 11, on sampies ground without grinding aid (reference). The TOC values related to cernent weight are given in Tables 5 to 7:

Table 5 : TOC values on the different sampies taken outside the grinder

[Table 5]

Point on grinding line	TOC (ppm of cernent)
(2) Grinder surplus	2.8
(3) Fiiter	4.6
(4) Separator feed	3
(5) Separator rejects retumed to the grinder	2.4
(6) Fines leaving the separator	3.5

Table 6: TOC Inside the grinder, 1^st chamber

[Table 6]

Distance from inlet (m)	TOC (ppm of cernent)
0	1.3
1.2	4.2
2.4	2.1
3.6	1.9

Table T: TOC inside the grinder, 2^IK1 chamber

[Table 7]

Distance from diaphragm 17 (m)	TOC (ppm de ciment)
0	2.2
1	3.1
2	2.5
3	2.8
4	5.0
5	2.5
5.9	3.1

The cernent ofthe sampies in the tests conducted without grinding aid contained less than 5 ppm TOC along the grinding line.

In the corresponding sampies containing grinding aid in the experiments described below, this quantity was deducted so as only to take into account the grinding aid.

TOC on sampies ground with grinding aids

The results are expressed in dry dosage of grinding aid per tonne of cernent or ppm.

1Û Influence of initial dosage

Each grinding aid was fed at three initia! dosages D1, D2 or D3 (Table 2). The quantities of grinding aid measured in the different cernent sampies are given in Table 8 below.

Table 8: Active material by weight of cernent for each ofthe samples

[Table 8]

	!πi*iâi dGSayG GÎ grinding 3ïd A comprising an aminoaicohoi	Initial dosage of grinding aid B comprising an alkylene gîycol
D1	D2	D3	DI	D2	D3
Active material by weight of cernent (g/t, BWOC)	(2) Grinder surplus	65	80	97	61	64	84
(3) Filter	134	108	150	97	92	120
(4) Separator feed	72	86	107	52	63	85
(5) Separator rejects retumed to grinder	33	35	44	32	37	40
(6) Fines leaving separator	92	108	142	93	99	123

It was observed that:

The quantity of grinding aid in the cernent at different points along the grinding line increases with initial dosage, with the exception of the filter 21 in which the dosage measured for dosage D1 is higher than that measured for dosage D2, irrespective of grinding aid.

In the fîîter 21, for grinding aid A comprising an aminoaicohoi at dosage D1, the quantity of grinding aid measured in the cernent is higher than the initiai dosage. The inventors assume that this excess could be due to the quantity ofgrinding aid on the surface ofthe partîcles of separator rejects reinjected into the grinding line, or to absorption of grinding aid in suspension in the circuit.

The dosage of grinding agent on large partîcles (those of separator rejects retumed to the horizontal grinder 11 ) is tower than on the partîcles of small size (Fines leaving the separator). More specifically, the inventors hâve observed that, for both grinding aids, the quantity of active material of the grinding aids measured in the different samples is correlated with the spécifie surface area of the cernent particles, as per the following équation:

quantîty of active material (in g/t) =

0.0329 * (spécifie surface area ofthe cernent (in cm²/g)) - 1.637 with a coefficient of corrélation R² of 0.9528.

The measured quantifies of grinding aid were therefore related to the spécifie surface area ofthe particles and are given in Table 9 below.

Tofifo O ' Λ J rtar rru λ F /va τΠΛηί FA>· ù*irvh λ f C / aiyio nuuvç tiiaicjÎia) m ui Lrcrt/l jl/î σαυπ Ut ύα/ιί/^ίνύ

[Table 9]

	Initial dosage of grinding aid A comprising an aminoalcohoi	Initia! dosage of grinding aid B comprising an alkylene glycol
D1	D2	D3	D1	D2	D3
Active material (g) per m² of cernent	(2) Grinder surplus	2.0	2.5	3.2	2.1	2.5	3.0
(3) Filter	2.5	2.4	3.1	2.4	2.3	2.9
(4) Separator feed	2.1	2.5	3.3	1.7	2.0	2.9
(5) Separator rejects returned to grinder	1.9	2.3	3.0	1.8	2.2	2.7
(6) Fines leaving the separator	2.3	2.7	3.6	2.4	2.6	3.3

Expressed in g per m² of cernent, the différence between the quantifies of grinding aid at the different points ofthe circuit decreases for one same initial dosage: the spécifie surface area ofthe cernent particles and hence their particle size governs the interactions between the grinding aids and the cernent.

Separator dfiC'Qi'cy = ffs/r-ftooii (h) and bypsss cOuiplOÎtîSirÎ (C)

The Tromp curve describes the efficacy of a separator. It is caiculated for each particle size class as the ratio between the flow of separator rejects (retumed to the horizontal grinder 11 ) and the flow of separator feed. In the case of perfect separator efficacy, the percentage of rejects would be zéro up until the maximum acceptable particle size is reached, and then 100 %. In actual cases, the Tromp curve ofthe separator has the shape given in Figure 3.

Bypass évidences that there exists, for every class of particle size, a fraction of particies that is always reinjected into the horizontal grinder 11. Separator efficiency is described by;

C = 1-bypass the separator is ail the more efficient the higher the value of C

The « Fîsh Hook » is that part of the curve at which particle size is smaller than that corresponding to the bypass, and évidences escape of fines towards the horizontal grinder 11. The gentlsrthe sîope (β) the lesserthe quantity of fines returned to the horizontal grinder 11 and the betterthe efficiency ofthe separator.

The resutts given in Figure 4 and Figure 5 show that separator efficiency is dépendent on the grinding aid used :

C is always higher and β îower with grinding aid A comprising an aminoalcohoi;

exhîbits non-monotone variation with the initial dosage of grinding aid B comprising an alkylene glycol, and decreases monotone fashion when the initial dosage of grinding aid A comprising an aminoalcohoi increases.

limit separatorefficiency is reached on and afterthe intermediate dosage of grinding aid A comprising an aminoalcohoi (C no longer varies, ; stabilises) Inside the grinder- Tests T6 and T9

Samples were taken every 1.2 m in the first chamber 12, and every métré in the second. The dosages of grinding aid per m² of cernent are given in Figure 6.

For grinding aid B comprising an alkylene glycol, the quantity decreases siightly in the first chamber 12 and then drops and stabilises in the second chamber 14. For grinding aid A comprising an aminoalcohoi, this quantity increases in the first chamber 12 and stabilises in the second chamber 14.

in the first chamber 12 of the horizontal grinder 11, the quantity of grinding aid by weight of cernent does not progress linearly with the spécifie surface area of the cernent. This relaitonship becomes true as from the second chamber, as illustrated in Figure 7.

Inside the horizontal grinder 11, the two grinding aids differ in the first chamber 12, grinding aid B comprising an alkylene glycol being more abondant per unit surface area than grinding aid A comprising aminoalcohoi. The quantity of grinding aid per unit surface area of cernent stabilises in the second chamber ofthe horizontal grinder 11, and the différence between the two grinding aids decreases.

EXAMPLE 2

Materials

The studied cernent was of CEM i 42.5R type (94 % clinker; 5.5 % gypsum; 5.5 % limestone).

The grinding aids were specificaliy formulated for Exampie 2. Their compositions are given in Table 10 below. Grinding aid B1 is of same type as grinding aid A. Grinding aid B2 differs. Table 10: Composition of grinding aids A, B1 and δ 2 used in Example 2.

[Table 10]

	Compounds	Active material (%)
Grinding aid A comprising an aminoalcohol	Water
Triethano lamine	8.33
T riisopropanolamine (diiuted)	33.33
Grinding aid B1 comprising an aminoalcohoi	Water
Triethanolamine	8.33
Triisopropanolamine (diiuted)	33.33
Grinding aid B2 comprising an alkyiene gfycoî	Water
Diethylene giycoî	22.70
Giycerol (diiuted)	12.09

The grinding unit used was such as illustrated in Figure 8. Figure 8 is identical to Figure 1 except that:

the sampling points 2 to 6 are shown in Figure 8;

the iniet 15 of the second chamber 14, that is connected to the source 20 of composition A, is positioned atthe discharge grate equipping the outlet 16 of the second chamber. The iniet 15 and outlet 16 are therefore at the same position.

The horizontal grinder 11 used comprised two chambers separated by a diaphragm 17. în this second example, the advantage is shown of injecting grinding aids into each of the two chambers.

Different cases were tested:

either no grinding aid was injected (reference - test T1);

or grinding aid B1 was injected into iniet 13 ofthe first chamber and no grinding aid was injected into the second chamber (comparative - tests T2, T3 and T4);

or no grinding aid was injected into the first chamber and grinding aid A was injected at the dîscharge g rate equipping the outiet 16 ofthe second chamber (comparative - tests T5 and T6);

or grinding aid B2 was injected via inlet 13 of the first chamber and no grinding aid 5 was injected into the second chamber (comparative - test T8);

or grinding aid B was injected via inlet 13 of the first chamber and grinding aid A was injected atthe discharge grate equippingthe outiet 16 ofthe second chamber, via an injection tube on the axis ofthe discharge grate (invention - tests T7, T9 and T10), with two distinct cases:

- either grinding aid B is B1 (same as grinding aid A) and the grinding aids injected into the first and second chamber are therefore of same type (test T7), or grinding aid B is B2 (differing from grinding aid A) and the grinding aids injected into the first and second chambers are of different type (tests T9 and T10).

Samples were taken at different points 2, 3. 4. 5 and 6 ofthe circuit illustrated in Figure 8. 15 once the State of equilibrium was reached on the grinding line.

Table 11 summarises ail the tests conducted, initial dosages and points of injection.

[Table 11]

	1st chamber	2n<» chamber	Samples ta ken in the grinder	Samples taken at points 2, 3, 4, 5, 6
Test	Dosage of aid B1 (ppm)	Dosage of aid B2 (Ppm)	Dosage of aid A (ppm)
T1 (ref)	0	0	0	X	X
T2 (comp)	250	0	0		X
T3 (comp)	350	0	0		X
T4 (comp)	450	0	0	X	X
T5 (comp)	0	0	262		X
T6 (comp)	0	0	350		X
T7 (inv)	250	0	138		X
T8 (comp)	0	300	0		X
T9 (inv)	0	300	113		X
T10 (inv)	0	300	199	X	X

The different flows were recorded at the sampling points of the circuit and percentage circulating load was caiculated as the ratio between the flow of fresh material entering the 5 circuit (here 48 tonnes/h in ail tests) and the flow of material retumed by the separatorfrom outlet 24. This percentage measures the manner in which the process becomes saturated with material i.e. its relative congestion, and dïnectly impacts efficiency. It is therefore sought to reduce this percentage so that it is possible to increase the flow rate of the method.

Particle size analyses on samples also aliowed measurementofthe fineness ofthe cernent obtained at the outlet via rejects on 45 pm screen. The smaller the rejects the finer the cernent.

The bypass values ofthe separator were also measured during the tests. The higherthe value of parameier C, the better the quaiity of filtration at the separator.

Flow rate at the filter was also measured. The filter 21 can easily be saturated since it becomes charged with fine particles. It is therefore preferred to hâve a low flow rate at the 5 filter 21.

AH measurements are grouped together in Table 12.

[Table 12]

Test	Percentage circulating load	C =1-Bypass	Rejects at 45 pm	Flow at filter 21 (tonnes/h)
T1 (ref)	44.56%	94%	5.0	19.73
T2 (comp)	86.67%	90%	4.2	8.28
T3 (comp)	136.96%	83%	2.8	13.53
T4 (comp)	244.75%	73%	1.0	7.25
T5 (comp)	97.02%	89%	3.2	13.38
T6 (comp)	114.58%	87%	2.0	13.74
T7 (inv)	98.83%	89%	2.0	3.53
T8 (comp)	68.04%	91%	3.4	16.86
T9 (inv)	77.96%	90%	4.0	8.61
T10 (inv)	71.79%	91%	2.8	11.00

The injection of grinding aid B1 into the first chamber without any injection into the second 10 chamber (tests T2 to T4) allows a fine cernent to be obtained (smalier rejects than for reference T1) but ieads to a strong increase in circulating load and to strong dégradation of fiitering quaiity at the separator as shown by parameter C.

Injection of grinding aid A into the second chamber without an injection into the first chamber (tests T5 and T6),

- or by injecting grinding aid B1 into the first chamber (test T7), allows easing of the methou with lower circulating loads and better séparation factors C than those obtained in tests T2 to T4.

Injection of grinding aid B2 into the first chamber (test T8) allows a lower circulating load and good fiitering quaiity at the separator. Nonethefess, the flow rate at the filter 21 is the 20 highest. Test T8 places a heavier load on this filter than tests T9 and T10, meaning that the iatter offer a better compromise.

The most efficient combination is injection of grinding aid B2 into the first chamber and of grinding aid A into the second chamber (tests T9 to T10), for which the lowest circulating loads, highest séparation factors C and cements of acceptable fineness are obtained. The circulating loads and flow rates at the grinder outlet filter measured in tests T9 and T10 allow an increase in feed flow rate henca in the general productivity ofthe method without risk of saturating the method.

Conclusion

These results show that:

the quantity of grinding aid found on the cernent particles is essentially governed by the spécifie surface area of the cernent particles as soon as they leave the first chamber 12 ofthe horizontal grinder 11 ;

The more the initial dosage of grinding aid is increased, the more the quantity of grinding aid increases along the grinding line. However, for grinding aid A comprising an aminoalcohol, at an intermediate dosage D2, there is a greater quantity of grinding aid than initially added. This différence coutd be due to the tact that the filter 21 setects the particles of smallest size for which the concentration of grinding aid js the highest further to the developed area effect.

The loss of grinding aid along the grinding line increases with initial dosage, which could resuit from gas-solid adsorption at dynamic equiiibrium in the horizontal grinder 11. To tlmit this loss, lower dosages should be used but the grinding aid would then not allow optimization ofthe parameters ofthe horizontal grinder 1 to reach the desired fineness.

Inside the horizontal grinder 1, the two grinding aids differ in the concentrations thereof in the first chamber 12, grinding aid B comprising an alkyîene glycol being the most concentrated.

At the separator, grinding aid A comprising an aminoatcohol has a more favourable effect on the fish hook slope (β) and on bypass complément (C) than grinding aid B comprising an alkyîene glycol. The intermediate dosage D2 of grinding aid A comprising and aminoalcohol already allows an efficiency plateau to be reached in the separator, contrary to grinding aid B comprising an alkyîene glycol.

Injection of grinding aid A into the second chamber and of grinding aid B2 into the first chamber ailowed obtaining ofthe best compromise between separator efficacy, circulating load, cernent fineness and flow rate at the filter, compared with:

- injection of grinding aid B1 into the first chamber without injecting any grinding aid into the second chamber;

- injection of grinding aid B1 into the first chamber and of grinding aid B2 into the second chamber.

These results show the advantage of injecting the two grinding aids at different points along the grinding line: grinding aid B at the inlet 13 ofthe horizontal grinder 11 to allow a sufficiently long résidence tsme ofthe cernent in the horizontal grinder 11 without removing fines too rapidly, and grinding aid A comprising an aminoalcohol în the second chamber 14 ofthe horizontal grinder 11 for better fluidification ofthe powder în the separator line.

Claims

1,2 or 3 alcohoi fonctions, the aminoaicohol preferabiy being N-methyldiethanolamine (MDEA), diisopropanolamine (DIPA), triisopropanolamine (T1PA), triethanolamine (TEA), ethanol-dilsopropanolamine (EDIPA), diethanolisopropa no lamine (DEIPA) or a mixture thereof.

1,2 or 3 alcohot fonctions, the aminoalcohoi preferabiy being N-methyldiethano!amine (MDEA), diisopropanolamine (DIRA), triisopropanolamine (T1PA), triethanolamine (TEA), ethanol-diisopropanolamine (EDiPA), diethanolisopropanolamine (DEIPA) or a mixture thereof, and optionally a carboxylic acid or sait thereof, selected for example from among acetic acid or one ofthe salis thereof, formic acid or one ofthe saits thereof, or a mixture thereof.

1. A method for grinding a hydraulic binder, comprising:

a) introducing:

a hydraulic binder, and a composition B comprising at ieast one grinding aid B, into the first chamber (12) of a horizontal grinder (11) comprising several chambers (12, 14), including a first chamber (12) and a last chamber (14), each chamber (12) being separated from the adjacent chamber (14) by a diaphragm (17), whereby a composition β comprising the hydraulic binder and composition B is obtained in the first chamber (12), b) grinding composition β in the horizontal grinder (11), whereby composition β moves from the first chamber (12) to the last chamber (14) and a ground composition C is obtained at the outlet ofthe last chamber (14), characterised in that, at the grinding step, it comprises introducing into the last chamber (14) a composition A comprising at least one grinding aid A comprising an aminoalcohol, composition A differing from composition β.

2. The method for grinding a hydraulic binder according to claim 1, comprising afterstep b):

c) separating, by a separator (23), composition C ground into fines and separator rejects, where the mean size of the particles of the separator rejects is greater than that of the particles of the fines;

d) recovering the fines;

e) retuming the separator rejects to the first chamber (12) ofthe horizontal grinder (11).

3. The method for grinding a hydraulic binder according to claim 1 or 2, wherein the horizontal grinder (11) only has two chambers (12,14).

4. The method for grinding a hydraulic binder according to any of daims 1 to 3, wherein the hydraulic binder is cernent optionally comprising minerai additions.

5. The method for grinding a hydraulic binder according to any of daims 1 to 4, wherein the grinding aid B comprises a polyol, preferably selected from among:

a dioi such as an alkylene glycol preferably having 1 to 20 carbon atoms, in particular 1 to 10 carbon atoms, the alkylene group possibiy carrying a methyl and typically being selected from among 2-methyl-1,3-propanedioi, le monoethyleneglycol, diethyleneglycol, triethyleneglycol, tetraethyleneglycol, propylene glycol and a mixture thereof, a trio}, preferabiy glycerol, and a tetraol, preferabiy erythritol, or a mixture thereof, preferabiy the grinding aid B comprises an alkylene glycol preferabiy having 1 to 20 carbon aioms, or a mixture thereof, and option a liy glycerol.

6. The method for grinding a hydraulîc binder according to any of claims 1 to 5, wherein grinding aid B comprises:

an aminoalcohoi or one ofthe saits thereof, said aminoaicohol particularly comprising:

from 2 to 8 carbon atoms, in particular 4 to 6 carbon atoms, and/or

7. The method for grinding a hydraulîc binder according to any of claims 1 to 6, wherein the aminoalcohoi of grinding aid A comprises:

from 2 to 8 carbon atoms, in particular 4 to 6 carbon atoms, and/or

8. The method for grinding a hydraulîc binder according to any of claims 1 to 7, wherein composition A is injected into the last chamber;

either atthe diaphragm separating the last chamber from the adjacent chamber, or into the enciosure of the iast chamber in a zone preferabiy doser to the diaphragm, separating the last chamber from the adjacent chamber, than to the outlet of the last chamber, or at the outlet of the last chamber, preferabiy at the dischargs grate equipping the outlet ofthe last chamber.

9. A grinding unit intended to implement the method according to any of daims 1 to 8, comprising:

a source (18) of hydraulîc binder, a source (19) of composition B comprising at least one grinding aid B, a source (20) of composition A comprising at îeast one grinding aid A comprising an aminoalcohol, a horizontal grinder (11) comprising severa! chambers (12,14), inoluding a first chamber (12) equipped with at least one inlet (13) and a test chamber (14) equipped with 5 an outlet (16), each chamber (12) being separated from the adjacent chamber (14) by a dtaphragm (17), characterized in that the test chamber (14) is equipped with an inlet (15) connected to the source (20) of composition A.

10. The grinding unit according to claim 9, wherein the outlet (16) ofthe test

10 chamber (14) is connected to the inlet (22) of a separator (23) able to separate particles according to their particle size and equipped with two outlets (24,25), one of the outlets (24) being connected to an inlet (13) ofthe firstchamber(12) ofthe horizontalgrinder(11).