WO2009001263A1

WO2009001263A1 - Process for the manufacturing of cement-and-fibre products, comprising the use of a pozzolanic material, and acqueous suspension of pozzolanic material used in said process

Info

Publication number: WO2009001263A1
Application number: PCT/IB2008/052443
Authority: WO
Inventors: Alessandro Quadrio Curzio
Original assignee: Petracem S.R.L.
Priority date: 2007-06-22
Filing date: 2008-06-20
Publication date: 2008-12-31
Also published as: EP2173682A1; ITMI20071269A1

Abstract

The invention concerns a method for manufacturing cement items, comprising at least one phase of mixing cement with strengthening fibres, water, additives and mineral admixtures, wherein among said mineral admixtures a first fraction of micronised pozzolanic material is comprised, wherein the percentage of particles having a size below 1 μm by dry weight is greater than 12%, preferably of 16%, and even better of 20%. 90% of the particles of said fraction are below 14 μm, preferably below 9 μm, and even better below 5 μm. A second fraction of pozzolanic material having an average solid particle size ranging between 12 μm and 40 μm is further comprised. The invention further concerns the aqueous suspension containing said first and second fraction of pozzolanic material.

Description

PROCESS FOR THE MANUFACTURING OF CEMENT-AND-FIBRE PRODUCTS, COMPRISING THE USE OF A POZZOLANIC MATERIAL, AND ACQUEOUS

SUSPENSION OF POZZOLANIC MATERIAL USED IN SAID PROCESS

* * * * * The present invention concerns a process for the manufacturing of cementitious products made of cement and fibres wherein a material having pozzolanic properties is employed. The invention also comprises an aqueous suspension of the material exhibiting pozzolanic properties used in said process. As known, up until about 15 years ago, the manufacture and use of products made of "asbestos-cement" employing asbestos fibres sunk in a cement-based matrix was largely widespread in Italy. The properties of the asbestos fibres, as construction material to be used for the manufacture of cement manufactured products, were really outstanding, and they were paired with a very low cost, both factors having determined the above-said wide diffusion.

However, after many years of use, it was discovered that asbestos fibres are in actual fact highly toxic and carcinogenic, more so to operators in the manufacturing industry thereof, but also - even though to a lower degree - to the users of said manufactured items, especially due to the fact that asbestos fibres are extraordinarily thin and light, so that minute fragments of the same may be easily inhaled and hence absorbed in the deepest areas of the respiratory apparatus, where they develop their pathogenic action. As a consequence of this discovery, Italy was among the first countries (with law no. 257/92), but later the majority of the most industrialised countries followed, to ban or dramatically curb asbestos use in building materials and, in particular, in the manufacturing of cement items .

In truth asbestos use is still allowed in a certain number of countries, among the least sensitive to health and safety and environmental issues, but such material in any case is going to be no longer used on a global scale within a short time. In order to be able to keep manufacturing items having characteristics similar to those of asbestos-cement, some of the asbestos-manufacturing companies have changed over time and have developed technologies for manufacturing a new composite material containing cement and fibres, replacing that asbestos- cement, so-called "fibre-cement" or "green fibre-cement" (in the following simply "fibre-cement") .

In actual fact fibre-cement, having to use less effective and less cement-compatible strengthening fibres than asbestos, both from the point of view of the mechanical and elastic properties, and due to its potential for causing the various layers of which fibre-cement consists to adhere to one another

(generally 5-7 layers) , as well as due to the lower ability thereof to bind with the cement matrix, is manufactured with far greater difficulties than asbestos-cement and requires the use of some other material and of manufacturing skill to be able to nevertheless produce good quality fibre-cement.

Getting ready the new technologies necessary for the manufacture of fibre-cement has certainly not been simple and, in certain cases, some of the technologies initially used have proved not valid or not fully valid over time, especially due to durability problems and to problems of three-dimensional stability of the manufactured items obtained therewith.

Other technologies have instead proved valid and are used on a large scale and with optimal results for the manufacture of fibre-cement. Among these technologies there are, for example, those employing both cellulose fibres (moreover, sometimes used in the past also with asbestos) , essentially used as process auxiliaries, and PVA (polyvinyl-alcohol) fibres, used as strengthening elements, but other fibre technologies may also be used.

A further additional component, the so-called "admixture mineral", of critical importance for the manufacture of items made of fibre-cement, is silica fume. Silica fume is a by-product of the electric-arc manufacture of silica, silica-iron and other silica-based metallic alloys. The main features of silica fume are the extremely high fineness and the high pozzolanic properties thereof: it consists almost exclusively of amorphous silica highly reactive with cement.

These features have made it, in general, a first-class building material, since:

- due to its high degree of fineness, it fills the pores between a cement grain and the other;

- due to its "vitreous" form, it chemically reacts with the lime that is released during the cement hydration phase, forming calcium hydrosilicates .

Silica fume has proved of fundamental importance also in the manufacture of fibre-cement, where it is used mixed with cement, in amounts which generally vary between 3% and 12% of cement weight, especially because it allows to obtain good mutual adhesion of the various layers which make up the fibre- cement manufactured items (flat sheets, corrugated sheets, pipes and other special pieces) without which it is not possible to obtain good-quality fibre-cement. Thereby the limits are compensated which currently-used fibres have over asbestos, with which, instead, no particular mineral admixture was necessary, such as silica fume, to obtain the necessary adhesion between the layers .

In addition to this, the above-said chemical reaction developed by silica fume in contact with lime determines the formation of stable bonds, so that also the mechanical properties and the durability over time of fibre-cement benefit from it.

The fineness of the individual silica fume particles is, in theory, generally comprised between 0.05 μm and 0.5 μm. In practice, however, the silica fume particles tend to aggregate, probably due to electrostatic reasons, forming particle aggregates (sort of clusters) which, for practical purposes, tend to behave as an individual particle. For this reason, mechanical actions are generally performed also on silica fume to disperse the particles of such aggregates. The dispersion of these aggregates does not require high amounts of work and energy such as in the case of proper milling, but work is nevertheless necessary. Moreover, after the mechanical dispersion operation, silica fume has a particularly high amount of very fine particles (or smaller aggregates) below 1 μm. Silica fume is a product having definitely unique features both in terms of fineness and of pozzolanic reactivity and, for this reason, the fields of application thereof keep growing ever more in various sectors: manufacture of special concretes, refractory concretes, prefabrication, etc. Over the last few years this has determined a reduced availability of this material - which, as said, is a by-product of other manufacturing processes and hence, as such, is not manufactured per se - and, consequently, a dramatic increase of the price thereof. Moreover, various other types of materials exhibiting pozzolanic properties exist, of both natural and artificial origin. The name pozzolana comes from Pozzuoli, i.e. from where the Romans seem to have taken the first pozzolanic material used as building binder alongside with lime. Pozzolana is a mainly siliceous or siliceous-aluminous material which, in its powder form, is capable of hardening, mixed with water and lime, producing hydrated calcium silicates and aluminates, very similar to those obtained in the hydration of Portland cement. The pozzolanic properties depend on various factors, among which the chemical characteristics, the temperature reached during the natural or thermal process and the cooling speed, the reactive surface, the fineness, etc.

Various types of materials hence exist having more or less pronounced pozzolanic properties and, in various countries, rules exist which regulate the use thereof as building materials, generally for the manufacture of cements and concretes. None of these materials, moreover, has properties comparable with those of silica fume, which, as a matter of fact, is considered the material with the most marked pozzolanic properties and is treated as a special, unique material even in the various industry-specific technical rules. The same Applicant, with Italian patent application MI2001A 000736 as well as other studies, had suggested the opportunity of treating, through wet milling, various types of materials, among which materials having pozzolanic properties, so as to increase the reactivity thereof and to manufacture therefrom building materials having properties similar to silica fume. However, in none of these studies and inventions was a very restricted and precise field of granulometric characteristics specifically identified, so that these materials may be found suitable to replace silica fume in the manufacture of fibre- cement .

The main object of the present invention is hence to identify a material which is apt to replace silica fume in the manufacture of fibre-cement, such as to allow the manufacture of a fibre-cement having a suitable performance, but characterised by greater market availability, and hence of a decidedly lower price than silica fume.

Another object of the invention is that of devising a manufacturing method having a limited cost and of easy execution for the manufacture of such new mineral admixture .

A further object of the invention is finally that of providing a new method for the manufacture of fibre-cement, characterised by a lower cost and by a greater consistency of the characteristics of the manufactured items obtained using, as partial replacement of the cement component, the same replacement material identified above, treated in the same plant with a different process.

These objects are achieved, according to the present invention, through a fibre-cement manufacturing method, comprising the mixing of cement with strengthening fibres, additives, mineral admixtures and any other known components, characterised in that one of said mineral admixtures is a micronised material with pozzolanic properties, wherein the percentage of particles having a size below 1 μm is greater than 12%, preferably greater than 16% and even more preferably greater than 20%. According to a feature of the invention, the itiicronised material having pozzolanic properties is used in the form of an aqueous suspension.

A further opportunity, according to the present invention, is to use the above material with pozzolanic properties, suitably milled, for partially replacing (between 15% and 50%) the cement component. In this case it is convenient to perform milling, either dry or wet, up to an average solid particle fineness comprised between 12 μm and 40 μm. This fineness range is the one which characterises also the cements normally available on the market and among these also pozzolanic cements, as well as fly ash which are residues of coal combustion: nothing new in such respect. However, the invention identifies the opportunity for optimising costs and efficiency of the fibre-cement manufacturing process through the co-manufacture of a non-micronised material having pozzolanic properties, but more coarsely milled, according to specific granulometric features, with the advantage of a content of pozzolanic substances having more controlled and more stable chemical-physical features and of accomplishing scale economies using all or part of the same plant used for micronisation, mentioned before, also for manufacturing such material.

A further, advantageous feature of the invention is that of being able to use treatment waters coming from the same fibre- cement manufacturing process for the preparation of the aqueous suspension of micronised pozzolanic material, following the possible addition to said waters of suitable additives and fluidisers .

Further features and advantages of the invention will in any case be more evident from the following detailed description of a preferred embodiment, also with reference to the accompanying drawings - and to the table of fig. 21, which summarises the data of the granulometric measurements concerning the diagrams of figs. 1 to 20 - wherein: figs. 1 to 6 are diagrams showing granulometric curves of various silica fume samples with different granulometric features which have been successfully used industrially for fibre-cement manufacture: they display important granulometric differences, since some fibre-cement manufacturers require higher granulometric fineness measures and others less so; Figs. 7 to 20 show the granulometric curves of various samples of pozzolanic materials wet-milled in microsphere mills. These are mainly natural pozzolanas coming from central and southern Italy (figs. 7, 8, 9, 10, 11, 12, 15, 16, 17, 18, 19, 20) and fly ash coming from coal combustion (figs. 13 and 14). The present invention is based on the assumption that in the traditional manufacture of fibre-cement it is precisely the particles with a size below 1-2 μm that have a highly positive effect, for the purpose of the mutual adhesion of the fibre- cement layers. Starting from this assumption and after a series of studies and trials on different possible replacement materials of silica fume, the Applicant has finally identified the opportunity for advantageously replacing silica fume using materials having pozzolanic properties, provided these materials have a high percentage of particles sized below 1 μm or 2 μm. Among the materials which may be successfully used for this purpose, both natural pozzolanas (of volcanic or clastic origin) and the artificial pozzolanic materials often consisting of byproducts of industrial processes may be included, such as, for example, the ash left over from coal combustion, or from the combustion of wheat husks or rice hulls, baked clay and other ceramic and/or vitreous materials. All these materials will be synthetically defined in the following as "alternative pozzolanic materials".

Various types of alternative pozzolanic materials are available on the market, with various degrees of reactivity, and with different physical, chemical, mineralogical features and colours. For the choice of the most suitable type, it is useful to proceed to a verification phase taking into account the above factors as well as local ones, such as material availability, transportation costs, consistency of characteristics etc. In this respect, it must be underlined that the more pronounced the pozzolanic properties, the greater the benefit, especially in terms of the mechanical resistances of fibre- cement. In terms of characteristics, alternative pozzolanic materials will be preferably such as to be able to be considered suitable, according to the UNI EN and/or American ASTM standards, for the use thereof in cement or in concrete.

What has been ascertained as essential for the purpose of good-quality fibre-cement manufacturing is the fact that these alternative pozzolanic materials, before being used in the fibre-cement manufacturing process, are very finely milled (micronised) and, in particular, with a granulometric fineness which encompasses a high amount of particles of a size below 1-2 μm, similar to the one found in the silica fume currently used for such manufacture .

More in detail - even though for indicative purposes - as a matter of fact, figures 1 to 6 have differentiated granulometric curves of wet-milled silica fume (in these granulometric curves, performed with a wet laser granulometer, particle aggregates are identified a single, larger-sized particle) and used for manufacturing fibre-cement from various manufacturers: in all the drawings it can be detected how silica fume has, even though with differentiated granulometric features, a characteristic minimum point at about 1 μm and a relatively large proportion of particles of a size below lμm.

The importance of particle fineness is presumably due to the fact that the very fine component (below 1-2 μm) is the one most significantly affecting the adhesion of the various layers of which fibre-cement consists: if the adhesion of the various layers is good, the fibre-cement is of good quality also, while if adhesion is poor, the fibre-cement is unsuitable. As said, this adhesion is strongly affected by the very fine component. As a matter of fact, in such respect, various fibre-cement manufacturers take care that also the silica fume is as fine as possible, but they have never identified the opportunity and the way to effectively replace it with a product having poorer pozzolanic properties, provided it is micronised at clearly-set degrees .

As a matter of fact, tests carried out by the Applicant have shown that the granulometric features of certain milled silica fume and of some pozzolanas, also wet ground, are significantly different: as a matter of fact, while silica fume easily has a high amount of particles having a size below 1 μm

(it essentially being a disaggregation of particles, rather than proper milling) , in order to obtain the same amount of particles below 1 μm with pozzolanas it is necessary instead to push milling much further.

Figures 7 to 20 show granulometric curves of wet pozzolanas micronised in different ways and times. Natural pozzolanas have all been milled in two steps: the first step with ball mills to reduce size, generally below 100-300 μm, the second step to perform the more extreme milling with microsphere mills wherein it is unsuitable to introduce particles having a size larger than 100-300 urn.

Aqueous suspensions have generally been prepared with concentrations ranging between 40% and 60% of dry substance. In order to improve dispersion and increase concentration (important for transport costs) , fluidisers and/or dispersant which are easily found on the market and are compatible with the manufacturing of fibre-cement have sometimes been used. Figures 1 to 4 show the granulometric curves of silica fume which, despite not being particularly fine, i.e. having a remarkable amount of particles sized above 2 μm, were suitable for the manufacturing of good-quality fibre-cement. Figures 5 to 6 show instead the granulometric curves of finer silica fume destined to a more demanding fibre-cement manufacturer, and suitable for this second fibre-cement manufacturer.

Some first experiments of fibre-cement manufacturing using micronised pozzolanas having granulometric curves on average rather similar to those reported in figs. 1 to 4 were carried out with the pozzolanas shown in figures 18 to 20: the result was negative: the fibre-cement layers did not have good adhesion and the plates were hence unsuitable.

The experiments were hence continued with pozzolanas subjected to more extreme milling treatments and positive results were obtained with the pozzolanic materials displaying the features reported in figs. 7 to 14. With the materials shown in granulometric curves 15 to 17, the results were partly positive and partly negative. The initial assumptions were hence confirmed, i.e. that it is necessary to obtain an alternative pozzolanic material from milling with a high amount of particles sized below 1-2 μm.

In order to obtain fibre-cements performances comparable to those obtained with silica fume having a granulometric curve of the type shown in figs. 5 to 6, it was hence necessary to use pozzolanas having the granulometric characteristics illustrated in figs . 7 to 9.

The main data of all the granulometric measurements carried out are reported in the table of fig. 21. All the granulometric measurements reported in figures 1 to 21 were performed with a granulometer-laser of the "Mastersizer Micro Ver. 2.17" type by the company "Malvern Instruments Ltd.".

In order to further deepen and assess the quality of the results, a wider experimentation can certainly be carried out.

In conclusion, it is suitable for micronised pozzolanas to have an amount of particles sized below 1 μm equal to at least 12%. More preferably equal to at least 16%. Even more preferably equal to at least 20%. As highlighted by the experiments carried out, better results are obtained the narrower the distribution curve of particle size. It is hence preferable for alternative pozzolanic materials to have an amount of particles of a size below 2 μm equal to at least 30%. More preferably equal to at least 36%. Even more preferably equal to at least 42%. As a consequence of the fact that the desired fineness IS obtained through extreme milling, also the fraction of larger-sized particles is nevertheless generally smaller-sized than that typical of the granulometric curves of silica fume. Preferably hence 90% of the particles will have a size below 14 μm, preferably below 9 μm and more preferably below 5 μm.

Such finely-milled pozzolanic materials allow to manufacture fibre-cement manufactured items having sufficiently high mechanical properties to be able to meet the standards provided by reference standards.

As mentioned above, in order to manufacture the finely micronised pozzolanic material, the solution identified as the most suitable one is that of wet milling in an aqueous suspension. As a matter of fact, this milling procedure has proved by far more efficient than dry milling: through wet milling, a much higher degree of fineness at a relatively low cost and in a short time may be obtained. On the contrary, through dry milling enormously longer times are required. As aqueous phase, the same process water of fibre-cement manufacturing may be used, at least in part, previously treated with suitable fluidisers and additives.

The most suitable equipment identified for the crucial milling phase, i.e. the most extreme one, are microsphere mills (by "microsphere" bodies having a size generally varying between 0.5 and 3 mm are understood) . Where pozzolanas to be milled are coarse (understanding by "coarse" size values generally above 100-500 μm) a preliminary granulometric-reduction process will be necessary, so that the particles be reduced to a size preferably below 100-300 μm before being sent to the wet milling phase by microsphere mill. The preliminary granulometric reduction phase may be performed regardlessly through various known dry or wet milling technologies.

The cost of the pozzolanic materials obtained from wet micronisation may generally vary, between 1/6 and 1/2.5 with respect to the cost of silica fume and this depends mainly on the local availability of good-quality alternative pozzolanic materials and on the costs of silica fume, in addition to other factors such as the quantities dealt with, the cost of electric energy, the labour cost, etc. The amount of micronised alternative pozzolanic material necessary to fully or partly replace silica fume will have to take into account a volume replacement of dry material and the difference will hence have to be considered between the absolute specific weight of the pozzolana which one intends to use (generally, materials having pozzolanic properties with specific weights ranging between 2.2 and 2.85 g/1 exist) with respect to the silica fume (2.2 - 2.3 g/1) . After which the optimal amount will have to be established, generally empirically, with a possible oscillation which may generally be of about ± 25% by weight. A detail which may prove useful in choosing the silica-fume alternative pozzolanic material and which may positively affect fibre-cement properties is the fact that this material, the micronisation degree being equal, be chosen among those having a larger specific surface, i.e., due to its own mineralogical characteristics, a more rugged surface. This characteristic does not emerge from the measurements performed with a laser granulometer, which performs readings detecting the outermost profile of the individual particles as if they were all small spheres, and it must hence be identified by other methods or instruments .

As said previously, fibre-cement is manufactured by using a mixture of various components among which cement, fibres, mineral admixtures, etc. Compared to the other cement-based products, fibre-cement is a very difficult product to obtain, therefore it is fundamental for the raw materials to have certain characteristics and for said characteristics to be consistent .

For the purpose of obtaining good-quality fibre-cement it is important that also the cement and the mineral admixtures have clearly-established characteristics of fineness and reactivity. Moreover, cement facilities have large plants which are generally not willing to manufacture differentiated and particular batches. In these plants "mixture cements" are produced using mineral ingredients often coming from different sources, which generate different performances with not particularly precise fineness characteristics. All that is particularly deleterious for fibre-cement manufacture, even though in compliance with the UNI EN cement standard.

For this reason it appears interesting to be able to replace a proportion of cement with a pozzolanic material coming from a single and controlled source, which hence has a satisfactory level of consistency of its characteristics, and which can be milled directly by the user to the best-suited granulometric fineness. In such respect, hence, should one intend to start a manufacturing business for the micronisation of a pozzolanic material alternative to silica-fume, for fibre- cement manufacturing - which activity it would be sensible to accomplish at the same fibre-cement manufacturing plant - with the same plant with which micronised pozzolana or part thereof is manufactured, a less-finely milled (50% of particles ranging between 12 μm and 40 μm) pozzolana may also be manufactured - in an extremely convenient way, both in terms of cost and quality - to manufacture the "pozzolanic component" of the mixture cement, hence avoiding to purchase on the market a significant proportion of cement. This can be conveniently done taking into account how the milling plant will be structured globally, both by varying some elements which determine the milling efficiency of the microsphere mills, such as the size of the milling bodies and the transit speed of the aqueous suspension pumped into the same, and, if the preliminary milling phase is performed with equipment suited to achieve the results (D50 12 μm-40 μm) such as ball mills or bar mills, avoiding to mill pozzolanas in microsphere mills.

In any case it is convenient for this second portion also of less-fine pozzolanic materials to be prepared and used in the form of aqueous suspension.

Claims

1) Fibre-cement manufacturing method, comprising at least one phase of mixing cement with strengthening fibres, water, additives and mineral admixtures, characterised in that among said mineral admixtures a first fraction of micronised pozzolanic material is comprised, different from silica fume, wherein the percentage of particles having a size below 1 μm, by dry weight, is greater than 12%.

2) Fibre-cement manufacturing method as claimed in claim 1) , wherein said first fraction of micronised pozzolanic material is used in the form of aqueous suspension.

3) Fibre-cement manufacturing method as claimed in claim 2) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 1 μm, by dry weight, is greater than 16%.

4) Fibre-cement manufacturing method as claimed in claim 2) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 1 μm, by dry weight, is greater than 20%.

5) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 4) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm, by dry weight, is equal at least to 30%.

6) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 4) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm, by dry weight, is equal at least to 36%.

7) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 4) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm, by dry weight, is equal at least to 42%. 8) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 7) , characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles have a size below 14 μm, by dry weight.

9) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 7) , characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles have a size below 9 μm, by dry weight.

10) Fibre-cement manufacturing method as claimed in any one of the preceding claims 1) to 7), characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles have a size below 5 μm, by dry weight.

11) Fibre-cement manufacturing method as claimed in any one of the preceding claims 2) to 10), characterised in that the aqueous suspension of said first fraction of pozzolanic material is obtained through a wet milling treatment. 12) Fibre-cement manufacturing method as claimed in claim 11) , characterised in that the wet milling treatment during the most extreme milling phase is performed in microsphere mills, with spheres having a size ranging between 0.5 and 3 mm.

13) Fibre-cement manufacturing method as claimed in any one of the preceding claims 2) to 12) , characterised in that in the preparation of the aqueous suspension of said first fraction of micronised pozzolanic material, stabilising additives, dispersants, and water reducers (fluidisers) are used.

14) Fibre-cement manufacturing method as claimed in claim 13) , wherein the aqueous phase of said suspension consists, at least in part, in the treatment waters of fibre-cement manufacturing .

15) Fibre-cement manufacturing method as claimed in any one of the preceding claims, characterised in that it further comprises a second fraction of pozzolanic material having an average solid particle fineness ranging between 12 μm and 40 μm. 16) Fibre-cement manufacturing method as claimed in claim

15) , characterised in that said second fraction of pozzolanic material replaces a proportion of the cement necessary for fibre-cement manufacturing. 17) Fibre-cement manufacturing method as claimed in claim

16) , wherein said proportion of cement ranges between 15% and 50% of the cement required for fibre-cement manufacturing.

18) Fibre-cement manufacturing method as claimed in any one of the preceding claims 15) to 17) , wherein said second fraction of pozzolanic material is used in the form of aqueous suspension.

19) Aqueous suspension used as mineral admixture in a fibre-cement manufacturing method comprising at least one phase of cement mixing with strengthening fibres, water, additives and mineral admixtures, characterised in that it comprises a first fraction of micronised pozzolanic material, other than silica fume, wherein the percentage of particles having a size below 1 μm, by dry weight, is greater than 12%.

20) Aqueous suspension as claimed in claim 19) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 1 μm, by dry weight, is greater than 16%.

21) Aqueous suspension as claimed in claim 19) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 1 μm, by dry weight, is greater than 20%.

22) Aqueous suspension as claimed in any one of the preceding claims 19) to 21) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm, by dry weight, is equal to at least 30%.

23) Aqueous suspension as claimed in any one of the preceding claims 19) to 21) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm, by dry weight, is equal to at least 36%.

24) Aqueous suspension as claimed in any one of the preceding claims 19) to 21) , characterised in that in said first fraction of micronised material having pozzolanic properties the percentage of particles having a size below 2 μm by dry weight is equal to at least 42%.

25) Aqueous suspension as claimed in any one of the preceding claims 19) to 24) , characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles has a size below 14 μm by dry weight.

26) Aqueous suspension as claimed in any one of the preceding claims 19) to 24) , characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles has a size below 9 μm by dry weight.

27) Aqueous suspension as claimed in any one of the preceding claims 19) to 24) , characterised in that in said first fraction of micronised material having pozzolanic properties at least 90% of the particles has a size below 5 μm by dry weight. 28) Aqueous suspension as claimed in any one of the preceding claims 19) to 27) , characterised in that it further comprises a second fraction of pozzolanic material having an average fineness of the solid particles ranging between 12 μm and 40 μm. 29) Fibre-cement manufacturing method as claimed in any^¬ one of the preceding claims, wherein the pozzolanic material, the milling fineness being equal, is chosen among those having a larger specific surface.