EP2582642A1

EP2582642A1 - Cellulose fibres for fibre-reinforced cement products

Info

Publication number: EP2582642A1
Application number: EP11722390.9A
Authority: EP
Inventors: Benoît de Lhoneux; Ruben Bordin
Original assignee: Redco NV SA
Current assignee: Etex Services NV
Priority date: 2010-06-15
Filing date: 2011-05-24
Publication date: 2013-04-24
Also published as: WO2011157516A1

Abstract

The invention concerns cellulose fibres for the manufacture of fibre-reinforced cement products, and more particularly cellulose fibres comprising a first and a second fraction of cellulose fibres obtained by fractionation of the same parent cellulose pulp followed by separate refining treatment of the first and second fraction to a different refining level. The invention also relates to a process for the manufacture of fibre-reinforced cement products comprising the fractionation of parent cellulose pulp to obtain a first and a second fraction of cellulose fibres, followed by separate refining treatment of each of the first and second fraction of cellulose fibres to a different refining level, and blending the first and the second fraction of cellulose fibres before their introduction into the slurry feeding unit of the fibre-reinforced cement production line. Other objects of the present invention are fibre-reinforced cement products comprising said cellulose fibres and fibre-reinforced cement products obtained by said process.

Description

CELLULOSE FIBRES FOR FIBRE-REINFORCED CEMENT PRODUCTS

Field of the invention

The invention concerns cellulose fibres for the manufacture of fibre-reinforced cement products, and more particularly cellulose fibres comprising a first and a second fraction of cellulose fibres obtained by fractionation of the same parent cellulose pulp followed by separate refining treatment of the first and second fraction to a different refining level.

The invention also relates to a process for the manufacture of fibre-reinforced cement products comprising the fractionation of parent cellulose pulp to obtain a first and a second fraction of cellulose fibres, followed by separate refining treatment of each of the first and second fraction of cellulose fibres to a different refining level, and blending the first and the second fraction of cellulose fibres before their introduction into the slurry feeding unit of the fibre-reinforced cement production line. Other objects of the present invention are fibre-reinforced cement products comprising said cellulose fibres and fibre- reinforced cement products obtained by said process.

State of the art

Shaped fibre-cement products are manufactured starting from an aqueous suspension comprising hydraulic binders, fibres, and possibly fillers and additives. This aqueous suspension is mixed in order to obtain a uniform distribution of the components. The suspension is then dewatered. The so obtained green fresh product can be shaped into a flat sheet, a corrugated sheet or a tube. The green shaped product is then hardened under atmospheric conditions or under specific pressure and temperature conditions.

The Hatschek process is most widely known for the manufacturing of fibre-cement products. It was initially applied to the asbestos-cement, and is exhaustively described in the book "Asbestzement" by Harald Klos (Springer Verlag, 1 967). Other manufacturing pro- cesses known by the man skilled in the art which can be cited are Magnani, Mazza, Flow- on, extrusion and injection.

The Hatschek technique consists in forming a sheet comparable to a paper, by filtration using a fluid aqueous suspension obtained by mixing essentially cement, fibres and water. The sheet, or a superposition of sheets, is then drained of water by suction and/or pressure. The fibres hold to the filter (or sieve), forming an additional screen, the mesh cells of which have a size suitable for retaining the particles, even fine particles, of cement or of other binder or additive, together with an important amount of water which contributes to the cohesion of the thick layer being formed on the screen. The retention on the sieve can be further enhanced by the addition of flocculants. The filter (or sieve) consists of a drum covered with a filter cloth installed in a tank containing the suspension; since the drum rotates in the tank, the hydrostatic pressure forces some of the water to pass through the filter cloth, whereas the solids, that is to say notably the fibres, the cement particles and other additives, build up on the screen of the drum as a thin layer whose thickness increases with the rotation of the drum. This layer is transferred, usually by means of a felt belt and further dewatered by suction through the belt, to a forming roll, onto which generally several layers are superposed until the desired thickness of sheet material has been reached .

The sheet on the forming drum is then cut manually with a knife following a groove in the cylinder or automatically with a steel blade incorporated in the forming drum or with a wire, after which it is subjected to a forming step, which consists of putting it between templates, for instance metal templates which have been oiled. Afterwards, it is submitted to a hardening stage at room temperature (air curing). For applications requiring high strength and good dimensional stability, the air curing step is followed by autoclaving (steam-curing under specific pressure and temperature conditions). For certain applications the green product is compressed between the forming and the curing stage to increase its density (post- compression).

The reinforcing fibres used in the manufacture of fibre-cement products are from synthetic and/or natural origin. Among synthetic reinforcing fibres, poly(vinylalcohol), polypropylene and polyacrylonitrile fibres can be mentioned. As natural reinforcing fibres, cellulose fibres have replaced since years the asbestos fibres. In the case of autoclaved fibre-cement pro^¬ ducts, cellulose fibres are usually the sole source of reinforcing fibres.

Suitable cellulose fibres are selected from but not limited to vegetable fibres such as jute, flax, cotton, straw, hemp, bagasse, ramie, and abaca, waste wood pul ps and wood pulps for paper making processes.

The l iterature descri bes several methods to i mprove the properties of the cellulose fibres used in fibre-reinforced cement products.

EP-A-0297857 describes fibre-reinforced products which have improved flexural strength and toughness relative to prior known cellulose fibre-reinforced products at constant fibre addition level through the use of softwood fibres having an en hanced level of summerwood fibres. However, EP-A-0297857 does not provide for the use of the remaining fraction with a lower content of summerwood and is economically not feasible.

Further attempts have been made to optimize the cel lulose fibres in order to enhance the properties of fibre-reinforced cement products. AU-A-5 1 51 5 1 describes fibre-reinforced cement articles comprising cellulose fibres whereof at least a proportion of the fibres are uniformly or variously refined to an average freeness value of from 250 CSF to 600 CSF. Refining is a well known mechanical treatment d uring which the cellulose fibres are fibri l- lated thereby increasing their water uptake and consequently affecting their filtration behaviour and retention ability on the sieve. The drainability of a pulp suspension in water or its freeness is determined according to two common methods : Schopper-Riegler (SR) and Canadian Standard Freeness (CSF). These methods are specified respectively in ISO 5267- 1 and ISO 5267-2 , and the results are expressed respectively in °SR and ml CSF.

The use of a blend of refined and unrefined cellulose fibres for the manufacture of fibre- reinforced cement prod ucts with i mproved mechanical properties belongs to commonly known practices as well and is described in e.g. JP06-340460, JP07- 1 65456 and GB-A- 21 37977. Summary of the invention

The invention relates to cellulose fi bres for the production of fibre-reinforced cement products comprising a first and a second fraction of cellulose fibres obtained by fractiona- tion of the same parent cellulose pulp followed by separate refining treatment of the first and second fraction to a different refining level , characterized in that

- before refining treatment, the cellulose fibres of the first fraction have an average length which is longer than the average length of the u nrefined cellulose fibres of the parent cel^¬ lu lose pulp, and the cellulose fibres of the second fraction have an average length which is shorter than the average length of the unrefined cellulose fibres of the parent cellulose pulp,

- the cellulose fibres of the first fraction have a refining degree lower than 25 °SR, and the cellulose fibres of the second fraction have a refining degree of at least 25 °SR but lower than 70 °SR.

According to the present invention and contrary to the state of the art, the longest fibres are first separated from the parent pulp; the shorter fibres are submitted to extensive re^¬ fining while the longest fibres are only slightly refined or even unrefined . This process of selective refining wherei n the longest cellulose fibres are first extracted from the parent pulp before exhaustive refining (which implies si mu ltaneous cutting and damaging), allows to take the full benefits of the longest cellulose fibres which provide the reinforcing, and hence the mechanical properties. Moreover, this method is economically feasible as both fractions obtained from the same parent pul p are used for the manufacture of the fibre- reinforced cement prod uct characterized by mechanical properties which are superior to those obtained by the use of the parent cellulose fibres and which even exceed those ob- tained by blending the unrefined parent cellulose fibres and a refined proportion of the latter. Also, it does not require the addition of parent unrefined cellulose fibres nor the use of fillers to obtain good filterability during prod uction of the fibre-cement product on a Hatschek or flow-on line. Moreover, the cellulose fibres according to the present invention obtained by fractionation from any parent cellulose pul p have enhanced reinforcing proper- ties compared to the parent pulp cellulose fibres refined to the same level. This is i m- portant from the fibre-cement producer's point of view as the availability of cellulose fibres providing satisfactory reinforcing properties without the use of other reinforcing synthetic fibres is limited. The process to manufacture fibre-cement products comprising a step of fractionation to obtain the cellulose fibres according to the present invention allows to manufacture a large variety of tailor-made blends of long reinforcing (first fraction) and short processing (second fraction) cellulose fibres to satisfy the particular needs for the production of a wide range of fibre-cement products.

The cellulose fibres according to the present invention are easy to be used in the manufacture of fibre-reinforced cement products, and have a high reinforcing capacity. They are particularly suited for the manufacture of autoclaved fibre-reinforced cement products and at a cost which is not prohibitive.

The two fractions of cellulose fibres according to the present invention are characterized by a different refining level.

The first fraction of cellulose fibres is characterized by a refining degree lower than 25 °SR. If the first fraction of cellulose fibres has a °SR of at least 25 , the fibre-cement product does not have superior mechanical properties. Preferably the first fraction of cellulose fibres is characterized by a °SR which is lower than 1 5.

The second fraction of the cellulose fibres according to the present invention is characterized by a °SR of at least 25, more preferably of at least 30. Preferably the cellulose fibres of the second fraction have a °SR lower than 70. A second fraction characterized by a °SR lower than 25, leads to a considerable amount of fine mineral particles which are lost through the rotating sieve and pollute the process water. If the second fraction has a °SR of 70 or higher, filtration problems due to slow dewatering occur during production of the fibre-cement product. A second fraction with a °SR in the range of from 30 to 50 is preferred. Particularly preferred is a second fraction characterized by a °SR in the range of 35 to 45.

Preferably, the difference in SR refining degree between the two fractions of cellulose fibres is at least 1 0, more preferably at least 1 5. A difference in SR refining degree of the two fractions of at least 20 is particularly suitable, and said difference of at least 25 being most preferred. According to a preferred embodiment, the intensity of the refining treatment of the first fraction of the cellulose fibres of the present invention is lower than for the second fraction. The refining intensity is determined according to TAPPI TIP 0508-05. Preferably, the first fraction is refined using an intensity which is lower than 1 Ws/ m. A refining intensity for the first fraction lower than 0.8 Ws/m is particularly preferred.

Preferably, the second fraction is refined at an intensity of at least 1 Ws/ m for energy efficiency reasons. The length of the cellulose fibres in the parent cellulose pulp, the first fraction or the second fraction can be measured according to different methods such as but without being limited to projection (according to TAPPI T232), classification (according to TAPPI T233) and automated optical analyzer (according to TAPPI T271 ). The preferred apparatus to determine the length of the cellulose fibers of the parent pulp, the first fraction or the second fraction is the Kajaani apparatus based on the ability of the fiber to change the direction of light polarization (according to TAPPI T271 ). A Kajaani FS300 equipped with a CCD camera and image analysis is particularly preferred.

The cellulose fibres according to the present invention are fractionated in a manner such that the content of cellulose fibres with a length shorter than 20 μιη in the first fraction as determined by a Kajaani FS300 Fiber Analyzer, is preferably lower than 0.8 % expressed in length-weighted fraction. If the content of fibres with a length shorter than 20 μιη in the first fraction is at least 0.8 expressed in length-weighted fraction, the difference in average length of the cellulose fibres in the first and second fractions is insufficient, and the beha- viour of the cellulose fibres fed as re-blend to the fibre-cement plant will be quite similar to a blend of refined and unrefined cellulose fibers of the same refining degree.

The average refining degree of the blend of the two cellulose fractions is preferably in the range of from 1 8 to 35 °SR, more preferably in the range of from 20 to 30 °SR. If the refin- ing degree of the blend is lower than 1 8 °SR, the weight loss of solids on the sieve of the Hatschek machine or the felt in case of the flow-on process is too high. If the refining degree of the blend is higher than 35 °SR, the drainage on the sieve of the Hatschek machine or the felt in case of a flow-on line will be too slow.

The cellulose fibres according to the present invention are preferably obtained from wood pulp, more preferably from chemical wood pulp. Kraft pulp is particularly preferred. The cellulose fibres can be bleached or unbleached. Suitable pulps are processed from softwood, e.g. Pinus Radiata, or from hardwood. Good results were obtained with cellulose fibres from unbleached, softwood kraft pulp. Cellulose fibres characterized by a Kappa number in the range of 20 to 40, more particularly in the range of 20 to 30 are especially preferred. The parent unfractionated cellulose fibres are characterized by a Schopper-Riegler degree which is usually in the range of 1 2 to 1 5. Preference is given to parent cellulose fibres with a length determined according to TAPPI method T271 in the range of from 0.8 to 4 mm. Cellulose fibres with an alkali soluble content as measured according to TAPPI method T21 2 below 3.5 wt% are suitable.

The cellulose fibres according to the present invention can be subjected to additional fibre treatments, including but not limited to sizing, loading, bleaching and biocide treatment.

The present invention also provides a fibre-reinforced cement product comprising the claimed cellulose fibres.

Fibre-reinforced cement products comprising from 0.5 to 1 5 wt% of cellulose fibres according to the present invention are preferred. Particularly preferred fibre-cement products comprise from 1 to 1 2 wt% of cellulose fibres according to the present invention. Good results were obtained with compositions comprising from 1 to 1 0 wt% of cellulose fibres according to the present invention.

The fibre-reinforced cement product according to the present invention possibly also comprises unfractionated cellulose fibres, such as but not limited to bleached cellulose fibers. Fibre-reinforced cement products comprising cellulose fibres according to the present invention are preferably autoclaved.

Fibre-reinforced cement products comprising cellulose fibres according to the present invention have enhanced mechanical properties, such as work of flexural rupture, compared to fibre-cement products comprising the same amount of the parent cellulose fibres and refined to the same degree.

Another embodiment of the present invention is a process for the manufacture of fibre- reinforced cement products comprising fractionation of parent cellulose pulp to obtain a first and a second two fraction of cellulose fibres, followed by separate refining treatment of the first and second fraction of cellulose fibres to a different refining level, and blending the first and second fraction of cellulose fibres before their introduction into the slurry feeding unit of the fibre-reinforced cement production line.

The present invention concerns more particularly a process for the manufacture of fibre- reinforced cement products wherein the first and second fraction of cellulose fibers are characterized in that

- before refining treatment, the cellulose fibres of the first fraction have an average length which is longer than the average length of the unrefined cellulose fibres of the parent pulp, and the cellulose fibres of the second fraction have an average length which is shorter than the average length of the unrefined cellulose fibres of the parent pulp

Particular embodiments of the present invention are processes for the manufacture of fi- bre-reinforced cement products wherein the fractionation is selected from a single or multi-step fractionation, centrifugal fractionation, fractionation in pressurized screeners or a combination thereof.

A process wherein the first fraction has a content of cellulose fibres characterized by a length shorter than 20 μιη which is lower than 0.8 % (expressed in length-weighted frac- tion) is particularly preferred. A process for the manufacture of fibre-reinforced cement products wherein the fractionation is carried out such that the mass split ratio of the first to the second fraction is in the range of 65 /35 to 35 /65, more particularly in the range of 50/ 50 to 35 /65 is preferred. Preference is given to a process wherein the parent cellulose pulp is wood pulp, more particularly wood pulp obtained by a chemical pulping process such as but not limited to kraft wood pulp.

Brief description of the drawing

The invention will be explained in detail below, referring to the accompanying drawing in which :

Figure 1 is an example of flow chart of a typical pressure screen single-step fractionation process, including pressure screw dewatering steps and refining units.

The figure is not drawn to scale. A typical fractionation process together with the pre- and post-treatment (including de- watering and refining) steps of the pulp is depicted in figure 1 . Parent cellulose (a) arrives at the fibre-cement plant as sheets which are pulped (1 ) after the addition of water (b) to obtain a consistency in the range of from 50 to 1 00 g /l. This parent cellulose pulp is then submitted to a purification step (2) to remove impurities such as sand, metal particles, pol- ymeric contaminants..., which can be carried out using a variety of state-of-the-art systems such as hydrocyclones, sieves, ... and their combinations. After dilution to a consistency in the range of from 4 to 35 g/l, the pulp is subject to fractionation (3) which can be performed with equipment including but not limited to pressure screening systems, centrifugal fractionation (hydrocyclones), vibrating sieves and their combinations. A pres- sure screening unit wherein the diluted slurry of fibres is forced through a cylindrical wedge wire screening basket is preferred. Fractionation can be performed in one or several steps and segregates the parent pulp feed into a rejected (4) and an accepted fraction (5). The parent pulp material can be length-fractionated, fractionated according to the fibre coarseness or to a combination thereof. Preferably, fractionation is performed according to length-separation. The geometry of the fractionation equipment and the operating condi- tions can be adjusted to focus on the fibre length as the selection parameter during the fractionation. The first fraction of cellulose fibers according to the present invention corresponds to the rejected fraction (4), while the second fraction of cellulose fibers according to the present invention corresponds to the accepted fraction (5). A suitable mass split ratio of first to second fraction is in the range of 65 /35 to 35 /65. This mass split ratio is more preferably in the range of 50/ 50 to 35 /65.

In one embodiment, the rejected fraction (4) is then discharged into the mixer (6).

As shown in figure 1 , according to an alternative mode of execution to manufacture the cellulose fibres of the invention, the first fraction (4) is slightly refined (7) to a degree lower than 25 °SR before discharge into the mixer (6). According to a preferred mode of execution, the first fraction (4) is submitted to a refining treatment using an intensity which is lower than for the second fraction (5).

The second fraction (5) is transported to the refining unit (8) where it is refined until a °SR of at least 25 is achieved, and consecutively transported to the mixer (6) where both frac- tions are blended and afterwards conveyed to the slurry feeding unit of the fibre-cement plant. According to a mode of execution of the present invention, the refined second (5) and unrefined or slightly refined first (4) fractions are recombined in their entirety into the fibre-reinforced cement product. According to another embodiment, only a part of the second (5) fraction is used in the manufacture of the fibre-reinforced cement product of the present invention.

Detailed description of particular embodiments

. The invention is described hereafter in a detailed way using particular examples of em- bodiment. EXAMPLES

Two different SUKP (softwood unbleached kraft pulp) , A and B, have been used as parent cellulose pulps.

The characteristics of these parent cellulose fibres are given in table I.

The SUKP pulps have been fractionated on a pilot equipment in a two step mode using a pressure screening unit, provided on the inside with a rotor and pulsation elements and wherein the diluted slurry of fibres is forced through a cylindrical wedge wire screening slotted basket.

The dimensions of the screen are as follows :

Profiling (P) = 0.6 mm

Opening (S) = 0.2 mm

Wedge wire width (W) = 2.3 mm,

The mass flow split of first (reject)(long fibres)/second (accept) (short fibres) fibres is 50/ 50 or 35 /65.

SUKP A and B were obtained in a drum pulper at a consistency of 1 5%, and then diluted at a consistency of 4.5- 5.5 g/l before fractionation. Finally, pulp fractions were dewatered in a wire press to a dry content of 20-30%.

The Schopper-Riegler freeness has been measured according to the method described in ISO 5267- 1 .

The characteristics of the fractions are summarized in table 1 . The unrefined SUKP first (i.e. long) fraction from pulp A has a °SR of about 1 2. Refining has been performed using a single disc 1 2 inches Sprout-Waldron laboratory refiner at a SEL (Specific Edge Load) of below 1 Ws/ m. The blend of 50% unrefined SUKP first fraction and 50% SUKP second frac- tion refined to 40 °SR (example 1 ) and the blend of 60% SUKP first fraction refined to 20 °SR and 40% SUKP second fraction refined to 30 °SR (example 4) have an average refining degree of 25 °SR.

The length of the cellulose fibres and the fines (expressed in length-weighted fraction and defined as cellulose fibres with a length shorter than 20 μιη) are measured by a Kajaani FS300 Fiber Analyzer. The compositions of the cellulose fibres as used in the examples (ex.) and comparative examples (C.Ex.) are also given in table I.

Table I

Preparation of the blends and production on Mini-Hatschek machine (MiH) Cementitious products were manufactured by the Hatschek technique, according to a pilot method reproducing the main characteristics of the products obtained by industrial methods. The compositions which have been used after strong dilution with water, are as follows (concentrations of solids expressed in weight % with respect to the total dry matter) : Cement : 37.5 wt%

AI(OH)₃ : 4 wt%

Quartz : 50.5 wt%

Cellulose : 8 wt%

The sheets were hardened during 24 hours at 20°C under water saturated atmosphere, and afterwards autoclaved at 1 0 bar during 7 hours.

Measurement of flexural resistance

The flexural resistance is determined by a flexural test on three points using an apparatus UTS, a span of 1 46 mm and a test speed of 20 mm/minute on wet saturated MiH samples of 50*1 60 mm. Twenty samples are measured in the two directions (machine direction and direction perpendicular to this), 2 weeks after the production. The apparatus records the stress /strain curve and the SMOR (maxi mum stress expressed in MPa) and iMOR (work of fracture expressed in J / m²) are determined.

The results of the measurements mentioned in table II are the average of the measure^¬ ments in both directions and are expressed in % compared to comparative example 1 as reference for the comparative examples 2 -3 and the examples 1 -4, and compared to comparative example 4 as reference for comparative example 5 and example 5.

Table II

The values in table II show that autoclaved fibre-cement products comprising the cellulose fibres according to the present invention have improved mechanical properties compared to fibre-cement products comprising parent cell ulose fibres (comparative example 1 and comparative example 4) and to fibre-cement products comprising only the first refined fraction of the cellulose fibres (comparative example 2 resp. comparative example 5). Moreover, fibre-cement products comprising cellulose fibres according to the invention have mechan ical properties which exceed those obtained with the blend of unrefined pa^¬ rent cellulose fibres and refined parent cellulose fibres (comparative example 3).

The fibre-cement products obtained in the examples 1 to 3 have superior mechanical properties compared to those obtained in comparative example 2. Comparative example 2 can be considered as an example according to the invention described in EP-A-0297857. The comparison between example 1 and comparative example 3 shows that better results are obtained by using an unrefined fraction of the longest fi bres and a second fraction re^¬ fined to 40 °SR rather than using a blend of unrefined (unbeaten) parent (virgin) pulp and pulp refined to 40 °SR. Comparative example 3 can be considered as an example according to the state of the art of blending refined and unrefined cellulose fibres. The comparison between example 1 and example 2 shows that better flexural properties are obtained with a higher ratio of the first/second fraction in the blend.

Fractionation at a lower mass split first/second fraction (i.e. selecting longer cellulose fibres) enhances the flexural properties of the fibre-cement product at the same blending ratio of first/second fraction cellulose fibres (example 3 versus example 2).

Claims

1 . Cellulose fibres for the production of fibre-reinforced cement products comprising a first and a second fraction of cellulose fibres obtained by fractionation of the same parent cellulose pulp followed by separate refining treatment of the first and second fraction to a different refining level, characterized in that

- before refining treatment, the cellulose fibres of the first fraction have an average length which is longer than the average length of the unrefined cellulose fibres of the parent cellulose pulp, and the cellulose fibres of the second fraction have an average length which is shorter than the average length of the unrefined cellulose fibres of the parent cellulose pulp,

2. Cellulose fibres according to claim 1 , wherein the first fraction of cellulose fibres has a content of cellulose fibres characterized by a length shorter than 20 μιη which is lower than 0.8 % (expressed in length-weighted fraction).

3. Cellulose fibres according to any of the preceding claims wherein the fractionation is such that the mass split ratio of the first/second fraction is in the range of 65 /35 to 35 /65.

4. Cellulose fibres according to any of the preceding claims, wherein the fractionation process is selected from centrifugal fractionation, fractionation in pressurized screeners or a combination thereof.

5. Cellulose fibres according to any of the preceding claims, wherein the fractionation is selected from a single or a multi-step fractionation.

6. Cellulose fibres according to any of the preceding claims, wherein the parent cellulose pulp material is wood pulp.

7. Cellulose fibres according to any of the preceding claims, wherein the parent cellu- lose pulp material is obtained by a chemical pulping process.

8. Process for the manufacture of fibre-reinforced cement products comprising a fractionation of parent cellulose pulp to obtain a first and a second fraction of cellulose fibres, followed by a separate refining treatment of the first and second fraction of cellulose fibres to a different refining level, and blending the first and second frac tion of cellulose fibres before their introduction into the slurry feeding unit of the fibre-reinforced cement production line, and characterized in that

9. Process for the manufacture of fibre-reinforced cement products according to claim 8 wherein the first fraction of cellulose fibres has a content of cellulose fibres char acterized by a length shorter than 20 μιη which is lower than 0.8 % (expressed in length-weighted fraction).

1 0. Process for the manufacture of fibre-reinforced cement products according to claim 8 or 9, wherein the fractionation is such that the mass split ratio of the first/second fraction is in the range of 65 /35 to 35 /65.

1 1 . Process for the manufacture of fibre-reinforced cement products according to any of the claims 8 to 1 0, wherein the parent cellulose pulp material is obtained by a chemical pulping process.

1 2. Process for the manufacture of fibre-reinforced cement products according to any of the claims 8 to 1 1 , wherein the cellulose fibres are cellulose fibres according to any of the claims 4 to 6.

1 3. Fibre-reinforced cement product comprising cellulose fibres according to any of the claims 1 to 7. Fibre-reinforced cement product obtained by the process according to any of the claims 8 to 1 2.