NL8403247A - SHEET MATERIAL OF FIBER REINFORCED CEMENT. - Google Patents

Description

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Fiber reinforced cement sheet material.

The invention relates to fiber reinforced cement sheet material, which may be flat or have a profiled cross section, for example a corrugated (corrugated) cross section. Such material 5 is suitable for use as building boards, for example as a roofing material. The flat material is particularly suitable for use as roofing slates.

Cement sheet materials reinforced with asbestos fibers have been known for many years and provide a lightweight roofing material which is both weather resistant and fire resistant. It is now necessary to replace asbestos as a component of such materials, but the product obtained as a result of such replacement must be substantially equivalent in all desirable properties thereof to existing asbestos-cement materials. The materials must also be capable of being fabricated on existing asbestos cement equipment in order to avoid the capital investment of replacing or drastically altering such equipment.

The use of glass fibers as a substitute for asbestos fibers in such equipment has been the subject of extensive research over the past 10-15 years. The initial difficulties which have been described, for example, in British Pat. No. 1,543,951, have been overcome to such an extent that it is now possible to formulate glass fiber-containing cement suspensions which can be used on asbestos cement machines, for example, by the measures described in British Patent Specification 30 1,543,951. This possibility is not necessarily accompanied by the formation of a product 8403247 · 2 - having suitable properties for a special purpose.

Sheets or sheets for construction use are generally required to have an average -2 breaking modulus (flexural strength) of at least 16 N.mm and a density of at least 1.3 g / cm 2. The requirements for roofing slates are even more stringent. The currently available asbestos cement roofing slates, also known as compressed asbestos cement slates, have a smooth surface, generally bearing an acrylic coating of the desired color, and according to current U.K. standard specifications have an average minimum mean breaking modulus 22 (MOR) of 22.5 N.mm. A minimum density of -3 1.8 g.cm is advisable to avoid porosity, which could result in frost damage on roofing slates.

A simple replacement of the asbestos content of asbestos cement sheet materials with chopped strand glass fibers does not give materials of equivalent appearance because the chopped strands tend to be visible in or protruding from the surface resulting in a surface finish which is either unacceptable when the usual amount of coating has been applied or requires so much decoration material to form an acceptable coating that an unacceptable increase in cost is caused. Furthermore, such simple replacement of the asbestos by chopped strand glass fibers does not allow to obtain equivalent strength with economical amounts of glass fibers due to an uneven distribution of the glass fibers in the cement and a deterioration of the glass fibers by alkaline materials in the cement. . British Patent 1,543,951 discloses a process for the manufacture of an asbestos-free fiber-reinforced composite cement material from an aqueous cement suspension comprising both chopped strands of glass fibers and single filaments of inorganic non-crystalline contains material, the latter ma- o .................

8403247 * 3 - material can be formed from continuous filaments baked glass fiber strands which separate or break up (filament) into filaments upon contact with the cement slurry. When glass fiber in such a single 5-fold filament form, obtained from filamentized chopped strands, is used as the sole fibrous reinforcement, a smooth surface finish can be obtained.

However, the difficulties in strength are exacerbated because the single filaments are open to attack by the alkaline materials in the cement, while difficulties also arise in obtaining an appropriate bond (bond) between the fiber and the matrix.

To improve the strength of glass fiber reinforced cement products, several proposals have been made for the inclusion of reactive silicon oxide in various forms. For example, British Patent 1,402,555 (NRDC) relates to a glass fiber reinforced "pozzolanic" cement product comprising a cement matrix containing at least 10% by weight of a pzzolana (which is a glassy silicate material, which can react with calcium hydroxide and thereby hardens to a hard strong material), and fibers of an alkali-resistant silica / zirconia glass containing at least 6 mole percent ZrC 2 - The above-mentioned British patent mentions that a very desirable Increase in the strength of the compositions can be achieved by a controlled heat treatment, which accelerates the achievement of stable properties and ultimate strength, and which can take the form of holding at least 2 days underwater at a temperature of Example 60-80 ° C. One of the described preferred pozzo-lana's is powdered fuel ash (PFA), which is used in amounts of 15-40% by weight. British Patent 1,421,556 (TAC Construction Materials Limited) describes the manufacture of cement board products reinforced with a mixture of long and short alkali resistant glassy staple fibers, for example, chopped glass fiber strands and ground 840 324 7 & Mineral fibers, with cellulose fibers and sufficient silica, for example in the form of diatomite, to react with the free lime released during the hydration of the cement. The plate products are autoclaved 5 to promote the reaction. European Patent Application 68,742 (Cape Boards & Panels Limited) relates to molded articles, such as sheets and sheets for cladding and roofing purposes, and describes a manufacturing method using an aqueous suspension containing 50-90% cement on a dry weight basis , 5-40% highly reactive pozzolanic silica and 5-15% cellulose fibers. Curing in the air causes a reaction between the cement and the silicon oxide.

Said patent literature states that mixtures of highly reactive pozzolanic silicon oxides, for example volatilized silica and diatomite, can be used and that glass fibers can be included in addition to the cellulose fibers. The British patent. 2,048,330b (Rockwool International A / S) describes a process for the preparation of a fiber reinforced cementitious board from an aqueous suspension of cement and fibers selected from the group of synthetic mineral fibers, natural organic fibers and mixtures thereof, wherein a fine material (more particularly, a filter dust material, obtained as a by-product in the preparation of silicon or silicon alloys by an electrothermal process and consisting essentially of volatilized silicon oxide) with an average particle size lower than that of the cement particles, is included in the slurry to reduce the loss of fine cement particles and neutralize the alkaline products in the mixture, thus preventing the alkaline degradation of the mineral fibers. It is stated that the amount of fine particles should preferably not exceed 15 wt%, based on the weight of the cement, because high concentrations of fine particles increase the rate at which excess water is released from the slurry 840 324 7% .................

«-5- deleted, reduce. Finally, British Patent 1,565,823 describes the use of reactive silica in the form of powdered fuel ash (PFA) or a fine silica flower, such as diatomite or ELKEM 5 silica, which is a volatilized silicon oxide have been found to have a synergistic effect with the special finishing (sizing) compositions described in this British patent for the application to alkali resistant glass fibers for cement reinforcement. Amounts of 10-40% of the reactive silicon oxide have been found to effect a further improvement in the durability of the finished glass fiber strands incorporated in the cement. The reactive silicon oxide is believed to assist in bonding the glass fibers into the cement matrix as well as in the reaction with the alkaline materials in the matrix.

Recent recent investigations have shown that the varying forms of reactive silicon oxide have different effects on the initial (early) strength and on the long-term strength of the composite materials. This is especially the case when glass fiber in a single filament form is used for reinforcement. Our own investigations have shown that when using filamentized dispersible glass fiber strands as the only fibrous reinforcing material, it is essential to use a mixture of two different reactive silicon oxides, namely powdered fuel ash and volatilized silica, within specific ranges to to manufacture flat sheet material, suitable for use as building boards, on the existing asbestos cement machinery, with both good initial strength and good long-term durability, which may even be accompanied by an increase of the strength above the initial strength. The use of the volatilized silica without the pulverized fuel ash gives good initial strength, but when exposed to simulated aging tests, the material shows a marked drop in strength. Powdered fuel ash on its own without the volatilized silicon oxide gives good initial strength and poor overall matrix strength.

According to the invention, there is therefore provided a sheet material formed from a fiber-reinforced cement product, containing by weight percentages of the solids:

Ordinary Portland cement 50-71% 10 Powdered fuel ash 14-40%

Volatilized silica 5-12% (containing at least 86 wt% SiC2). Filamentized chopped glass 2-7% fiber strands, these components forming at least 90 wt% of the solid components of the product and where, when the cement product contains less than 8 wt% volatilized silica, the volatilized silicon oxide is of a quality containing more than 86 wt% SiC> 2, and when the cement product contains only 5 wt% volatilized silica, the volatilized silicon oxide of a quality containing at least 94 wt% Si00, the sheet material having a minimum -2 mean breaking modulus of 16 N.mm and a minimum -3 density of 1.3 g / cm.

The combination of powdered fuel ash and volatilized silica in the amounts (ratios) indicated above results in a product of satisfactory initial strength and long-term durability, accompanied by an increase in strength to above initial strength after curing. The use of filamentized glass fibers provides a smooth surface, as required when a coating is to be applied, by preventing the appearance of protruding strand ends as would occur if integral chopped strands were used.

The term "volatilized silicon oxide" 8403247 - 7 - *%> is used here to designate the material (also known as micro-silica or fumed silica) which is formed in the art as a by-product during the preparation of silicon or silicon / metal alloys via an electro-5 metallurgical process. Its chemical composition may vary slightly depending on the properties of the process and of the main product, but it usually contains at least 86 wt% SiO2 and 0.1-0.7% SiC. Lower purity grades are not suitable for use in the present invention, because the amount required then causes difficulties in dewatering the cement-sheet material. Purer grades of relatively carbon-free volatilized silica, containing at least 94%

SiO2 and about 0.1% SiC are available. It has been found that these more pure grades have a higher surface activity and thus can be used in smaller amounts than the normal grades in the present invention. Therefore, if the amount of volatilized silicon oxide used in the sheet material of the invention is less than 8 wt%, the volatilized silicon oxide must be of a quality containing more than 86 wt% SiO2 and when the minimum amount of 5% is volatilized silicon oxide is used, the latter must contain 94 wt.% SiO2.

The preferred percentage of the filamentized chopped glass fiber strands in the sheet material is 3-4%. Although the percentage may be as low as 2%, difficulties can be encountered in handling the green (i.e., uncured) sheet in this case. At rates between 4% and 7%, difficulties can be experienced in ensuring uniform dispersion of the glass fibers in the cement matrix.

The remainder of the product may comprise up to 4% by weight of cellulose pulp, which is included as a process aid to aid drainage. Up to 5% by weight of a plasticizer (plasticizer), for example, ball clay, 8403247 * 9 * - 8 - bentonite or talc, may also be included to improve the plasticity of the material before it is cured. Small amounts of conventional dispersants and flocculants can also be used.

The filamentized strands are preferably made from an alkali-resistant glass mixture containing at least 6 mol% ZrC> 2 · For example, the glass fiber strands may be of the type described and claimed in British Patent 1,290,528 and is marketed by Fiberglass Limited under the trademark

Cem-FIL, and its composition in mol% can be substantially:

Si02 69%

Zr02 9% 15 Na20 15.5%

CaO 6.5%

The invention further provides a flat sheet material suitable for use as roofing slates formed from a fiber reinforced cement product containing 20 percent solids by weight:

Ordinary Portland cement 50-70%

Powdered fuel ash 20-40%

Volatilized silicon oxide 8-12% (containing at least 86 wt% SiO2) 25 Filamentized chopped glass 2-5% fiber strands with these components forming at least 98 wt% of the solids of the product while the remainder (if present) consists of compatible ingredients, the sheet material having a minimum mean breaking modulus of 20 -2-3 N.mm and a minimum density of 1.8g.cm, and having a smooth surface for receiving a coating.

Tests on roofing slates made of such material have shown that they exhibit significantly better resistance to repeated freezing and thawing and generally to weathering than conventional asbestos cements. slates.

The invention also relates to a process for the manufacture of a fiber reinforced cement sheet material comprising the steps of mixing an aqueous suspension, the solid content of which comprises: Portland ordinary cement 50-70%

Powdered fuel ash 14-40%

Volatilized silica 5-12% (containing at least 86 wt% S102) 10 Dispersible chopped glass fiber strands 2-7% with these components making up at least 90 wt% of the solids content of the slurry and where when the slurry is less than Contains 8% by weight of volatilized silica, the volatilized silicon oxide is of a quality containing more than 86% by weight of SiCl, and when the slurry contains only 5% by weight of volatilized silicon oxide, the volatilized silicon oxide is of a quality least 94 wt%

SiO2, wherein mixing is carried out such that the chopped glass fiber strands are dispersed into single filaments, depositing a layer (lamina) from the slurry on a perforated surface, superimposing a plurality of these layers (laminae) to build up a sheet of cementitious material, and to cure the sheet.

In order to prevent mechanical damage to the glass fibers during processing (treatment), the slurry mixing can be carried out by first mixing the cement, the powdered fuel ash and silica with water in a high shear mixer 30 and then dispersible chopped glass fiber strands under low shear mixing conditions. Alternatively, the slurry mixing can be performed by first mixing the cement and the powdered fuel ash and optionally a small amount of the silica with water in a high shear mixer and then the silica or the remainder of the silica 8403247 - 10-h »or the remainder of the silica with the dispersible chopped glass fiber strands under low shear mix conditions.

The deposition of the lamina and the build-up of the sheet can be carried out on an asbestos cement machine of the Bell or Hatschek type.

Before being cured, the sheet can be formed into a desired cross-sectional profile, for example to provide it with adjacent or spaced ridges (wrinkles). For example, the sheet can be shaped by using a vacuum profiling head of a known type, or by placing it on a former plate, the top surface of which has the desired cross-sectional profile, and collapsing the sheet into contact with this surface. In the latter case, a second former sheet can be placed on the sheet to complete the shaping.

The sheet can be cured at a temperature in the range of 60-90 ° C and preferably 70-80 ° C for 24 hours and then stored at ambient temperature for at least 7 days to complete the curing. Such high temperature initial curing is conducive to ensuring the long term durability of the finished product, while the presence of the pulverized fuel ash and the volatilized silicon oxide allows the filamentized glass fibers to cure in survive a sufficient amount to provide suitable amplification.

The sheet may be compressed to dehydrate it before effecting curing, for example, by placing a stack of such sheets with interleaved plates in a press and subjecting the stack to pressure to expel the water.

For the manufacture of roofing slates 35, the shapes of the roofing slates are preferably stamped from the sheet before effecting compression and curing and the slates are separated from each other after curing.

Specific embodiments of the invention will now be described in greater detail by way of example.

Sheet material of the invention, suitable for the manufacture of roofing slates, can be manufactured on conventional asbestos cement machines of either the Bell type, as described in published British Patent Application 2,059,867A, or the well known

Hatschek type. In both these machines, several layers (laminae) (typically eight) are superimposed to form a sheet of glass fiber reinforced cement 4-5mm thick after compression. In the case of the Bell machine, a glass fiber-containing aqueous cement slurry is transferred to a moving web or belt via a scraper roller system, whereupon it is dewatered by suction to a water content of about 25%. The layer (lamina) thus formed is transferred from the belt to a rotating drum. When enough layers (laminae) have been superimposed on the drum to build up a sheet of the desired thickness, the sheet is cut from the drum. In the case of the Hatschek machine, the layer (lamina) is deposited on a rotary screen and then transferred to a belt and from there onto a drum. The sheet is cut off the drum again once a sufficient number of layers have been applied to each other to build up the desired thickness.

The subsequent treatment (processing) 30 is substantially the same in each case. A cutting machine is used to punch the shape of several flat rectangular roofing slates with their mounting holes on the sheet. The slates may have standard dimensions of, for example, 600 x 300 mm or 500 x 250 mm. The 35 sheet is placed on a steel insert plate and transferred to a stack of analog sheets. When a full 840 324 7 «- 12 -

When the number of stamped-out sheets has accumulated in the stack, it is passed to a press, in which the sheets are further dewatered under pressure to a final water content of about 20%. The insert plates are then removed and the sheets are placed at 80 ° C for 24 hours

hardened and finally stored at ambient temperature for 7 days. The individual roofing slates can then be detached from one another and are ready for cladding if desired.

The following specific examples I and II

relate to the manufacture of roofing slates in a Bell machine as described above.

Example I

An aqueous suspension was formulated with the following composition, expressed as parts by weight of solid:

Regular Portland cement 61%

Powdered fuel ash 25%

Volatilized Silicon Oxide (86 wt% SiC ^) 9% 20 Filamentized Chopped Strands of 3% Alkali Resistant Fiberglass As Sold Under the Trademark "Cem-FIL" by Fiberglass Limited

Cellulose Pulp 2%. Conventional dispersants, flocculants, etc., may also be incorporated in known amounts in small amounts (less than 0.1%).

The glass fiber strands had a length of approximately 3 mm, were constructed of filaments with a diameter of approximately 20 µl, and were impregnated with a sizing composition, which was formulated to ensure that the strands disperse or filamentate in contact with the slurry. Examples of such sizing agents are disclosed in U.S. Pat. No. 3,948,673.

35 The composition of the glass fiber was in mole%: 840 324 7% - 13 -

Si02 69%

Zr02 9% Ν & 20 15.5%

CaO 6.5% 5 After curing as described above at 80 ° C for 24 hours and storage for 7 days at ambient temperature, the slates were examined to determine their bending strengths in both the longitudinal and transverse directions with respect to the direction of movement from belt 10 of the Bell machine; they were also examined for impact strength. Further sample slates were subjected to accelerated aging by full immersion in water at 70 ° C for 16 days, simulating approximately 30 years of natural weather, after which the slates were re-examined. The results obtained are shown below

Table 1

Length.- Cross- Average 20__direction direction__

Immediate Proportionality _2 limit (N.mm) 22.9 12.6

Breaking modulus na (N.mm 25.8 15.1 20.5 25 Shock strength _2 hardening (Nmm.mrn) - - 3.2

Proportionality

After limit (N.mm 28.7 16.0 30 Breaking modulus accelerated (N.mm 29.7 17.3 23.5

Shock strength _2 aging (Nmm.mrn) - - 2.4 1 -3 8403247

Density of slates: 1.95 g.cm - 14 -

It turns out that the mean fracture modulus is -2

was greater than 20 N.mm and increased after aging. Example IX

Roofing slates were prepared in the manner described above from an aqueous cement slurry of the following composition, expressed as weight percentages of the solid content:

Regular Portland cement 61%

Powdered fuel ash 24.5% 10 Volatilized silicon oxide 9% (86 wt% SiOj)

Filamentized chopped glass 3.5% fiber strands (as in Example I)

Cellulose pulp 2% 15 Dispersants, flocculants, etc. <0.1%

The slates obtained were examined in the manner described in Example I, yielding the following results: Table 2

Length- Cross- Average ___ direction direction_

Proportionality -2 25 Immediate Limit (N.mm) 24.6 15.9

Breaking modulus -2 na (N.mm) 25.8 16.5 21.2

Shock strength _2 cure (Nmm.mm) - - 2.9 30 ___ -3

Density of slates: 1.90 g.cm Example III

Roofing slates were prepared from an aqueous suspension in the manner described in Examples I and IX with the following solids contents (in wt%): 840 324 7 - 15 -

Ordinary Portland cement 70%

Powdered fuel ash 14%

Volatilized Silicon Oxide (86% w / w SiC ^) 11% Filamentized Chopped Fiberglass- 3.5% 5 Strands (as in Example I)

Processing aids (cellulose 1.5% pulp, dispersant, flocculant)

Comparative Example IV

For comparison, a further set of slates was made from a slurry prepared as described in Example III, however, the powdered fuel ash was replaced with limestone flour (CaCO2).

Comparative example V

For further comparison, roofing slates were made from a slurry with the following solids content (in wt%):

Ordinary Portland cement 69% 20 Powdered fuel ash 6%

Volatilized silicon oxide (86 wt% SiC ^) 20%

Filamentized chopped fiberglass 3% strands (as in Example I)

Processing aids (cellulose 2% 25 pulp, dispersant, flocculant)

The results of the tests on the roofing slates of Example III and Comparative Examples IV and V are shown below: 1 8403247-16 Table 4

Close LOP MOR Shock Specific _ness _MOR_ III Immediately after curing 1.7 12.3 15.1 3.8 8.9

After accelerated aging 1.7 16.0 17.0 2.7 10.1 10 IV Immediate after curing 1.7 12.6 15.4 4.0 9.1

After accelerated aging 1.7 11.1 11.4 1.0 6.7 V Immediately after curing 1.5 8.7 11.8 8.0 7.9 20 ______________

It turns out that the replacement of the pulverized fuel ash with limestone flour in Example IV gave a considerably reduced strength after aging, while Example V with too much silicon oxide and insufficient pulverized fuel ash gave poor strength, even ineffective after curing.

Example VI

This example relates to the manufacture of a flat sheet of glass fiber reinforced cement on a Hatschek machine for use as a building board, for which a minimum mean breaking modulus (MOR) of -2-26 N.mm and a minimum density of 1.3 g.cm can be specified.

The aqueous suspension had the following composition in parts by weight: 8403247 ¢ - - 17 -

Portland ordinary cement 60.5%

Powdered fuel ash 24.5%

Volatilized Silicon Oxide 8.0% (86 wt% SiO2) 5 Dispersible Chopped Glass 3.5% Fiber Strands

Processing aids (cellu 3.5% lose pulp, dispersant, flocculant) The glass fiber strands were those described in detail above in Example I.

Sheets were conventionally formed on the Hatschek machine. Some of these sheets were profiled (ie, corrugated) using a conventional profiling head and deposited on a molding plate of a corresponding shape for curing. Other sheets were pressed together to dehydrate them to a water content of 20% before effecting curing. In either case, the sheet was then cured at 80 ° C for 24 hours and then stored at ambient temperature for 7 days. Samples cut from the sheet were examined in the manner described above to determine their bending strengths in both the longitudinal and transverse directions with respect to the movement of the Hatschek machine cylindrical screen and belt. They were also examined for impact strength. The results obtained are shown below.

Table 4 1 2 3 4 5 6 8403247

Profiled uncompressed sheet: Dry density 1.4 g.cm ^ 2

Length direction Transverse direction Average LOP 13.8 12.6 13.2 3 MOR 22.4 16.7 19.6 4

Shock - - 3.7 5 .....-.....- - ---- - - -—- 3 - 6

Compressed flat sheet. Dry density 1.7 g.cm

Length direction Transverse direction Average LOP 18.7 16.9 17.8 MOR 31.8 19.8 25.8 _Shock_- _-_ 3.5 - 18 -

Further tests were conducted in the laboratory to investigate the range of possible sheet material compositions for the manufacture of roofing slates. In such laboratory tests with normal equipment, it is difficult to obtain as dim a product as on the machines for manufacturing on a technical scale and it is not possible to build the slates as a series of layers (laminae) or the same obtain product density. The results obtained are useful in a comparative sense, although the absolute values obtained cannot be directly translated into values that would be obtained using analog recipes when run on a technical scale on a Bell or Hatschek machine. The laboratory tests were performed; 15 by forming a slate of 30 cm square and 8 mm thick and dewatering thereof by simultaneous application of a pressure and suction. The slate was then cured at 60 ° C for 24 hours and the strengths were determined as described in the previous examples. The results are shown in Table 5, which also lists the composition of each slate, the length of the glass filaments used, and a break modulus value corrected for the lower slate density as opposed to that to be expected for a slate obtained from the same composition in an embodiment or technical scale. In all of these examples, volatilized silica having an SiO 2 content of at least 86% by weight was used. 1 8403247 i - 19 - <u (• i <u -2? M ό yy— oocor ^ oi'-itNcnr ^ va'a · r \ u Lj Lj Lj cl Ti - ** - - * * · - - ^ ^ <1) (1) 0ίΜ <ϋθυΉ Γ- ΟΙ * - · Γ- OO <X> 0> O 'O' D | Tl OO 0) O -Η φ ** τ4 * 4 mms o θ '> ϋ Λ

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Of the ten samples tested, samples 1 and 10 were included only as comparative samples, which are outside the scope of the invention, because they do not contain volatilized silica or powdered fuel ash, respectively. Sample 4 is also outside the scope of the invention because the volatilized silica content is too low to use a material having a SiCl 2 content of only 86% by weight. The strengths obtained could be increased by increasing the curing temperature and would certainly be increased in the engineering scale due to the better distribution of the glass fibers resulting from the formation of individual layers (laminae) on the Bell- and Hatschek machines. ,

Table 5 shows that if the volatilized silica is not present (Sample 1), the overall strength of the matrix is poor compared to that of the samples containing more than 8% of the volatilized silica. Sample 10 shows that in the absence of powdered fuel ash, the initial strength is low compared to that of samples containing equivalent amounts of volatilized silica; the products made from such a composition, when exposed to an artificial aging, show a further decrease in strength. The strength of sample 42 would be significantly increased if volatilized silica having a SiCl 2 content of 94% was used in accordance with the invention.

In order to demonstrate the importance of using volatilized silica with a SiC> 2 content of 94% instead of an SiC 2 content of 86%, where the amount of volatilized silicon oxide in the material is relatively low, it was produced a series of samples, differing only in the type and amount of volatilized silica, in the laboratory and tested for the LOP and MOR to give the results indicated below. Two grades of volatilized 8403247-21 silica, containing 86% SiC> 2, and one grade containing 94% SiO2, labeled as grades 1, 2 and 3, were used.

Table 6A

5 _

_LOP MOR

81% Volatilized Silicon Oxide (86% SiO2) (Grade 1) 12.6 15.3 61% "" "" 11.1 13.4 10 51% _ ^ _ "_10.4 12.4

Table 6B

81% Volatilized Silicon Oxide (86% SiO2) (Grade 1) 10.6 13.2 15 81% "" "(Grade 2) 10.8 13.6 61%" "" 10.3 12.5 51% _ ” 8.6 11.4

Table 6C

20 _ 81% Volatilized Silicon Oxide (86% SiC ^) (Grade 1) 10.6 12.2 81% "" "(Grade 3) 9.6 12.5 25 61%" "9.4 12.0 51% 9.5 9.5.0

The results obtained show that the reduction of the silicon oxide content from 8.5% to 5.5% was accompanied by a significant loss in strength when volatilized silicon oxide with an SiO2 content of 86% was used, but that the use of volatilized silica with a SiO 2 content of 94% did not result in a significant loss of strength.

8403247

Claims (18)

A sheet material formed from a fiber-reinforced cement product, characterized in that the product, in percentages by weight of the solids, comprises: A sheet material according to claim 1, characterized in that the weight percentage of the filament chopped glass fiber strands is 3-4%. A sheet material according to claims 1 or 2, 25, characterized in that the remainder of the product comprises up to 4% by weight of cellulose pulp. A sheet material according to one or more of the preceding claims, characterized in that the filamentized chopped glass fiber strands are made of an alkali-resistant glass mixture containing at least 6 mol. & ZrO 2. A sheet material according to claim 4, characterized in that the composition of the glass fiber strands in mol% is substantially: SiO 2 69% ZrO 2 9% Na 2 O 15.5% CaO 6.5%. 8403247 ♦ - 23 - 5 Ordinary Portland cement 50-71% Powdered fuel ash 14-40% Volatilized silicon oxide (containing 5-12% at least 86 wt% SiO2) Filamented chopped glass 2-7% 10 fiber strands with these components at least 90 wt % of the solids of the product and where, when the cement product contains less than 8 wt% volatilized silica, the volatilized silicon oxide is of a quality containing more than 86 wt% SiO2, and when the cement pro contains only 5% by weight of volatilized silicon oxide, the volatilized silicon oxide is of a quality containing at least 94% by weight of SiO 2, and the sheet material has a ά-2 minimum mean break modulus of 16 N. ram and a mini-3 20 male density of 1.3 g.cm. 6. A flat sheet material suitable for use as roofing slates, formed from a fiber-reinforced cement product, characterized in that the product comprises in percentages by weight of solids; 5 ordinary Portland cement 50-70% pulverized fuel ash 20-40% volatilized silica (containing 8-12% the at least 86 wt% SiOj) filamentated chopped fiberglass -2-5% 10 strands with these components at least 98% by weight of the solids of the product form, the remainder (if any) consists of compatible ingredients, and the sheet material -2 has a minimum mean breaking modulus of 20 N.mm and a -3 minimum density of 1.8g .cm has a smooth surface for receiving a coating. 7. A method of manufacturing a fiber reinforced cement sheet material, characterized in that said method comprises the steps of mixing an aqueous suspension, the solid contents of which comprise; ordinary Portland cement 50-71% powdered fuel ash 14-40% volatilized silica (containing 5-12% the at least 86 wt% SiC2) 25 dispersible chopped fiberglass 2-7% strands with these components at least 90 wt.% Of the solids contents of the slurry and wherein, when the slurry contains less than 8 wt.% Volatilized silica, the volatilized silicon oxide is of a quality containing more than 86 wt. & SiO2, and when the suspension contains only 5% by weight of volatilized silica, the volatilized silica is of a quality containing at least 94% by weight of SiCl, the mixing being carried out such that the chopped glass fiber strands disperse into single filaments, depositing a layer (lamina) of the suspension 8403247 Jf - 24 - n sion on a perforated surface, placing a plurality of these layers on top of each other to build up a sheet of cementitious material and curing the t sheet. 8. Process according to claim 7, characterized in that the mixing of the slurry is carried out by first mixing the cement, the powdered fuel ash and the silica with water in a high-shear mixer and then adding the dispersible chopped glass fiber strands. to be added under mixing under low shear conditions. 9. Process according to claim 7, characterized in that the mixing of the slurry is carried out by first mixing the cement and the powdered fuel ash and optionally a small amount of the silica with water in a high-shear mixer and then adding the silica or the remainder of the silica with the dispersible chopped glass fiber strands under mixing under low shear conditions. 10. Method according to claims 7-9, characterized in that the deposition of the layers and the construction of the sheet are carried out on an asbestos cement machine of the Bell or Hatschek type. 11. Method according to claims 7-10, characterized in that the sheet is formed into a desired cross-section profile 25 before the curing is effected. A method according to claim 11, characterized in that the sheet is formed into a shape by applying a vacuum profiling head of a known type. 13. Method according to claim 11, characterized in that the sheet is formed into a shape by placing it on a former plate, the top surface of which has the desired cross-sectional profile, and collapsing the sheet in contact with this surface. Method according to claim 13, characterized in that a second former sheet with said profile is placed above this sheet. 840 324 7 J - 25 - 15. Process according to claims 7-14, characterized in that the sheet is cured at a temperature in the range of 60-90 ° C for 24 hours and then stored at ambient temperature for 7 days in order to complete the curing . A method according to claim 15, characterized in that the sheet is cured at a temperature in the range of 70-80 ° C. 17. Method according to claims 7-16, characterized in that the sheet is compressed in order to dewater it before effecting the curing. 18. Method according to claim 17 for the production of roofing slates, characterized in that the shapes of the roofing slates are stamped out of the sheet before it is pressed and cured and the slates are separated after curing. 1 8403247