EP2705938A1

EP2705938A1 - Filter assembly

Info

Publication number: EP2705938A1
Application number: EP12183880.9A
Authority: EP
Inventors: Clemens Hauswirth; David Collinge; Andrew Beswick; Richard Ward
Original assignee: SGL Carbon SE
Current assignee: SGL Carbon SE
Priority date: 2012-09-11
Filing date: 2012-09-11
Publication date: 2014-03-12

Abstract

A multilayer-structured filter assembly (9) for press mould (1) for manufacturing cementitious products comprising a perforated plate (10), a first layer-structure (11) attached to the perforated plate (10) and a second textile layer-structure (12) attached on top of the first layer-structure (11). The provided filter assembly (9) allows dehydrating a concrete slurry mix without passing particulate material and ensures smooth surfaces or defined dimple effects on the manufactured product without producing shadow marks or high pressure stress to the filter-assembly. The provided filter assembly is intended to be used as face and/or back filters in press moulds (1).

Description

The present invention relates to a filter assembly for a press mould for manufacturing cementitious products, a process for manufacturing cementitious products, products made by this process and a cementitious product or concrete-forming apparatus.
Cementitious products such as concrete blocks or paving slabs are typically made using a press mould. A press mould normally comprises a mould cavity, in which a slurry mix of water, sand, cement and stone aggregate is poured. The mould has a closed bottom, often positioned in a revolving table, and closed sides and is open at the top to allow the slurry mix to enter. A hydraulic ram-plate is positioned above the mould, which is moved toward the closed bottom to apply a high compressive pressure on the poured slurry mix. Thereby, the slurry mix is compacted, shaped to the shape of the mould and dispensable water is pressed out by the hydraulic ram-plate but also by vacuum suction. In order to release the squeezed out water, without passing the particulate material such as cement particles and stone aggregates, a face filter can be provided covering the closed bottom of the mould in the revolving table and a filter may also be provided covering the hydraulic ram-plate. Classical water-permeable filters are made of paper and loosely provided at the contact borders between the slurry mix and the mould and the slurry mix and the hydraulic ram-plate, respectively. As the filters made of paper have to be removed with the moulded concrete product, they are generally not reusable. To avoid this wastage of filter material different textile filters have been proposed ( WO 94/25236 , GB 2365368 and GB 2376654 ).
Some textile filters carry the disadvantage that they imprint their structure pattern on the final cementitious product during the pressing preventing a smooth surface of the final cementitious product. While some textile filters allow the formation of defined dimple effects on the surface of the final cementitious product, the formation of dimples can be disturbed by the uneven dissipation of water during pressing, as the water takes the line of least resistance to the large suction drain holes/water channels provided in the bottom of the mould in the revolving table or the hydraulic ram-plate. This non-uniform dissipation of water also promotes the formation of damp marks near the drain holes on the product surface during the pressing step. Further, this uneven dissipation of water also exposes the perforated plastic plate to pressure stress around the holes.
Therefore, it is an object of the present invention to provide a reusable and stable textile filter for press moulds for manufacturing cementitious products, wherein the final cementitious product has a smooth surface or a defined sharp dimple effect, but no damp marks.
The above object of the present invention is achieved by a multilayer-structured filter assembly according to claim 1.
A multilayer-structured filter assembly for a press mould used for manufacturing cementitious products comprises:

a perforated plate,
a filter with at least two layers comprising:
- a first layer-structure attached to the perforated plate, and a second textile layer-structure for contacting a cementitious slurry attached to the surface of the first layer-structure on the other side of the first layer structure opposite to the perforated plate.

Preferably, such cementitious products are products made of or comprising cement or concrete, e.g. concrete blocks.
In preferred aspects of the invention, the first layer-structure could comprise a non-woven textile, a woven textile or a foam and the second textile layer-structure comprises a woven textile, a knitted textile, or a spun bonded non-woven textile or similar structure.
Preferably, the perforated plate is a plastic plate, which is easier to produce and cheaper than plates made of metal. It is also preferred that the first layer-structure is a textile structure, although other materials such as foams are also advantageous.
The combination of at least two layers has been found to be sufficiently permeable enough to allow the water to pass in a rapid manner. At the same time, for the layer combinations of the invention, the water passage through the layer is evenly distributed so as to avoid channel-formation, which can occur in highly water-permeable materials. The filter assembly prevents water dispersing only in the least resistance direction of the large suction drain holes in the hydraulic ram-plate onto which the filter assembly is mounted and thereby avoids damp marks on the final cementitious product. Non-uniform water dispersion can also lead to direct channelling of the water to the perforation holes in the perforated plate around the suction drain holes, such that the perforation holes are blocked and the plastic plate is lifted from the back plate. The provided filter assembly decreases the pressure stress exerted to the perforated plate by ensuring quick and even dispensing of the water. The reduction of pressure stress exerted on the plate increases the durability of the perforated plate. The uniform flow of the dispersed water also has the advantage that an increased flow through perforation holes around the suction drain holes does not influence the formation of an unacceptable dimple effect on the surface of the cementitious product in the vicinity of the suction drain holes.
Preferably the air porosity of the inventive multi-layer filter assembly is between 150 and 300 ml/s, more preferably between 200 and 250 ml/s and most preferably between 200 and 220 ml/s.
Furthermore, the filter assembly provided in this invention does not transfer a visible pattern imprint onto the surface of the cementitious product. When required, the filter assembly can also provide a defined dimple effect to the surface of the cementitious product.
The filter assembly provided in this invention ensures smooth surfaces or surfaces with a defined dimple effect of the final cementitious product, but avoids damp marks on the surface of the cementitious product and increases the durability of the perforated plate and thereby also of the filter assembly.
The use of multiple layers in the filter assembly also increases the filter stability, durability and therefore the number of recycling steps.
For the multilayer-structured filter assembly, any combination of textile of the first and the second textile layer-structure is possible. For example, a knitted textile layer-structure of the second textile layer-structure can be combined with a non-woven or woven layer-structure of the first layer-structure, respectively. The use of a knitted textile layer-structure in the second textile layer-structure allows for very smooth surfaces of the cementitious product and defined dimple effects, while the non-woven or woven layer-structure, preferably a non-woven layer-structure or foam, of the first layer-structure allows for even dissipation of water.
If the first layer-structure is a foam, then polyurethane foams are preferred.
Also, a woven textile layer-structure of the second textile layer-structure can be combined with a woven or non-woven textile layer-structure or foam of the first layer-structure. If both layers are woven textiles, preferably, the woven textile of the first layer-structure has a higher mass per unit area than the woven textile of the second textile layer-structure.
The combination of a woven and a non-woven layer-structure or the combination of two different woven layer-structures as described above both allow for smooth surfaces of the cementitious products and even dissipation of water, thus preventing damp marks on the final product.
In addition, the combination of a spunbonded non-woven textile layer-structure of the second textile layer-structure and a non-woven textile of a first layer-structure is a low-priced variation of the present invention, still achieving good surfaces of the final product, even dissipation of water and increased filter durability.
In particular, these filter layer combinations can be less expensive to produce than single layer knitted structures.
Preferably, if the first layer-structure comprises a textile, it comprises hydrophobic fibres with a melting point which is lower than 350 °C, more preferably polypropylene. The use of such hydrophobic fibres leads to improved filtering properties for water, while holding back particulates. The presence of hydrophobic fibres also increases the durability of the textile layer-structures used in the filter assembly increasing the number of potential pressing cycles.
Preferably, the mass per unit area of the first layer-structure is between 100 and 700 g/m², more preferably between 100 and 400 g/m². If the mass per unit area of the first layer-structure is too high the first layer-structure will not allow water to pass through. If the mass per unit area of the first layer-structure is too low, the first layer-structure is not stable enough during pressing. If the first layer-structure has this mass per unit area range, the density and resilience of the first layer-structure is optimal for ensuring stability while maintaining quick and even water dissipation during pressing the slurry.
In addition, porosity values must be improved for optimal passage of water. The porosity values in this context mean air porosity or permeability values which are also a reasonable estimation for the penetration of the water/cementitious mixture through the filter.
For best results, the first layer structure has preferably an air porosity value between 300 ml/s and 400 ml/s, more preferably between 340 ml/s and 360 ml/s to achieve good fluid penetration.
Preferably, the non-woven textile of the first layer-structure may comprise a reinforcing scrim within the non-woven layer-structure further increasing stability, filter durability and improving uniformity of water dissipation during pressing the slurry. The scrim is not considered to be a layer structure in the sense of the invention, since the scrim is inserted into a textile layer to reinforce the stability.
Preferably, the textile of the second textile layer-structure comprises polypropylene and/or polyester yarns leading not only to good filtering properties for water, but not for particulates. This also increases robustness, shape retention, crease resistance, stability and water transporting properties.
Preferably, the mass per unit area of the textile of the second textile layer-structure is between 50 and 300 g/m². More preferably the mass per unit area is between 100 and 300 g/m², which gives even better results in this respect. Best results are obtained if the mass per unit area is between 150 and 250 g/m². If the second textile layer-structure has this mass per unit area range, a smooth surface of the final cementitious product is ensured while a good quality of filtering cementitious and stone aggregates is achieved, simultaneously.
In addition, it was found that the air porosity of the second textile layer-structure has preferably an air porosity value between 300 ml/s and 380 ml/s, more preferably between 330 ml/s and 350 ml/s, to achieve good fluid penetration.
Preferably, the combined mass per unit area of the first layer-structure and the second textile layer-structure is between 150 and 1000 g/m², more preferably between 200 and 600 g/m². If the combination of the first layer-structure and the second textile layer-structure has this mass per unit area range, the final quality of the cementitious product is ensured, while a good quality of filtering cementitious and stone aggregates is achieved and the water is dispersed evenly and quickly, simultaneously. If the mass per unit area of the first layer-structure is too high the first layer-structure will not allow water to pass through. If the mass per unit area of the first layer-structure is too low, the first layer-structure is not stable enough during pressing.
In addition it was found, that the combined air porosity of the first layer-structure and the second textile layer-structure has preferably an air porosity value between 100 ml/s and 300 ml/s, more preferably between 200 ml/s and 220 ml/s to achieve good water penetration.
Preferably, if the first layer-structure comprises a textile, the fibres have a dtex value between 5dtex and 50dtex. If the fibres in the first layer-structure range from 5dtex to 50dtex, the dissipation of the water over the entire surface of the first layer-structure is ensured avoiding damp marks and increasing durability of the filter assembly. In this embodiment of the invention it is preferred that the first layer-structure is a non-woven textile comprising hydrophobic fibres.
Preferably, the first layer-structure is bound to the perforated plate by a discontinuous dot adhesive layer or by sealing the first layer-structure onto the back of the perforated plate with double sided tape or by heat welding techniques, thus, improving the attachment of the first layer-structure to the perforated plate maintaining stability and durability of the filter assembly while not constraining water permeability. Especially, bounding the first layer-structure to the perforated plate by a discontinuous dot adhesive layer prevents creasing of the first layer-structure.
Preferably, the second textile layer-structure is attached to the first texture layer-structure using a discontinuous dot adhesive layer further improving the attachment of the first layer-structure to the second textile layer-structure which increases stability and durability of the filter assembly while not constraining water permeability. Further, bonding the second textile layer-structure to the first layer-structure by a discontinuous dot adhesive layer prevents creasing of the second textile layer-structure and the first layer-structure, respectively preventing irregularities of the filtering process and thereby avoiding damp marks and uneven surfaces of the cementitious product.
A further aspect of the invention is a process for manufacturing cementitious products comprising: pouring a cementitious slurry into a press mould (1), which is open at the top, to allow the slurry to enter; form-pressing and dehydrating the cementitious slurry using a compression plate by moving the compression plate on which a multilayer-structured filter assembly (9) as described herein is attached towards the cementitious slurry; lifting the compression plate away from the cementitious slurry; and removing the manufactured cementitious product from the press mould (1).
Preferably, in the above process, the filter assembly is employed on the compression plate as a head filter. However, in preferred embodiments, the filter assembly may also be employed as a face filter at the bottom press plate of the press mould.
In this process, typically the cementitious slurry will be a concrete slurry for the formation of concrete products.
The invention will be described in more detail in the following describing specific variants and preferred aspects of the invention.

Measurement conditions:

The air permeability was measured by BS EN ISO 9237:1995 which replaced the previous standard BS 5636. The apparatus used was a SDL Atlas (Shirley) Air Permeability Tester, Model SDL 21, which can be used to the standard above.
Round test area of sample: 5.07 cm²; 2.54 cm diameter (1 inch diameter).
Pressure range 0-25 mm water gauge (0 to 1 inch).
The four rotameters cover a flow range of 0.04 to 350 ml/s.
In operating the apparatus according to standard BS EN ISO 9237:1995 the guard ring was kept closed to give maximum air flow.
In deviation from the standard, for which the mean air flow is calculated and expressed in ml/s and divided by the size of the test area specimen, the figures quoted herewithin are direct readings which are not equated to the size of the sample area but expressed as ml/s at 0.98 mbars.
The test therefore provides an air flow reading of a fabric that is relevant to determine air flow values that are suitable to cement filtration.

Figure 1 is a diagrammatic sectional side view of a cementitious-product or concrete forming apparatus.
Figure 2a is a diagrammatic sectional side view of the filter assembly intended to be preferably used as face filter 7.
Figure 2b shows an alternative variant of the above figure with a diagrammatic sectional side view of a filter assembly intended to be used as face filter 7 or head filter 8.

Fig. 1, shows an arrangement such as can be employed to form cementitious products from the corresponding slurry. Typically, these are concrete products. A diagrammatic sectional side view of the cementitious-product-forming apparatus is shown in which a cementitious-product-forming apparatus comprises a press mould 1 having side walls 3 which define the form of mould cavity open at the top. Typical shapes are square, rectangular or round-shaped filters. The cementitious-product-forming apparatus described in this embodiment is preferably intended to be used for manufacturing concrete products. The mould cavity may have any other form appropriate for the forming of the manufactured cementitious product.
The bottom surface of the press mould 1 is closed by a bottom press plate 2.The bottom press plate 2 is provided with a series of suction holes and water channels 6 to allow the excessive liquid to drain there through from the mould cavity during pressing. The cementitious-product-forming apparatus further comprises a die head attached to a movable compression plate 5 positioned above the press mould 1, configured to move downwardly towards the cementitious slurry 4 positioned in the mould cavity for compressing the cementitious slurry 4 in order to shape e.g. a concrete slab or any other product. The compression plate 5 slides into the open top of the mould cavity. The compression plate 5 is provided with a series of suction holes and water channels 6 to allow the excessive liquid to drain there through from the mould cavity during pressing.
The bottom press plate 2 is covered on top by a face filter 7, while the die head is covered by a head filter 8. The filter assembly 9 according to this invention can be used as a face filter 7 as well as a head filter 8 or both in the same cementitious-product-forming apparatus.
As shown in Fig. 2a and Fig. 2b, the filter assembly 9 comprises a perforated plate 10, a first layer-structure 11 and a second textile layer-structure 12. The perforate plate 10 is preferably formed from a plastic material and comprises a plurality of perforations or openings which are preferably arranged in an array of rows and columns. The openings have preferably a size of 3 mm in diameter. The perforated plate 10 has between 15 and 40%, preferably 33%, open space per square surface and the angle between a row of openings and the opening in the next adjacent row and column is between 20 and 60°, preferably 60°. Other diameters of the openings, percentages of open space per square surface and the angle between a row of openings and the opening in the next adjacent row and column may be adopted. The perforated plate 10 is arranged to be a close fit in the mould cavity.
As shown in Figs. 1, Fig. 2a and Fig. 2b, the first layer-structure 11 is attached on top to the perforated plate 10 and a second textile layer-structure 12 is attached on top to the first layer-structure 11 facing the cementitious slurry 4 in a filter assembly 9 intended to be used as face filter 7. In case the filter assembly 9 is intended to be used as head filter 8, the filter assembly 9 is attached upside down to the die head /compressing plate 5 such that the second textile layer-structure 12 faces the cementitious slurry 4 and the perforated plate 10 is attached to the die head/compressing plate 5. The second textile is wrapped preferably around the edges of the perforated plate 10. Form and size of the first layer-structure 11 and the second textile layer-structure 12 are adapted to the size and shape of the press mould 1 and the manufactured cementitious product.
It is also possible to have an arrangement in which the second textile layer-structure 12 does not wrap around the other layers and the perforate plate 10, but rather lies on top of the other layers as shown in Fig. 2b in a simple layered arrangement.
As shown in Fig. 2a and Fig. 2b, the first layer-structure 11 and the second textile layer-structure 12 permits passage of water there through, but restricts the passage of particulate material.
The first layer-structure 11 preferably comprises a non-woven textile, a woven textile or a foam. The first layer-structure 11 is porous, stable and has a sufficient density and thickness to impart resilience. Preferably, the first layer-structure 11 comprises a non-woven textile. Preferably, the non-woven textile of the first textile layer-structure 11 comprises hydrophobic fibres with a melting point lower than 350°C, preferably between 100°C and 200°C. The hydrophobic fibres used in the non-woven textile of the first layer-structure 11 have dtex values between 5dtex and 50dtex. Preferably, the non-woven textile of the first textile layer-structure 11 comprises polypropylene, but it may also comprise polyester, polyvinylchloride or nylon or a mix of fibres. Preferably, the mass per unit area of the non-woven textile of the first layer-structure 11 ranges from 100 to 700 g/m², more preferably from 100 to 400 g/m². Preferably, at least some fibres in the non-woven textile of the first layer-structure 11 are located at least partially in a vertical direction. The non-woven first layer-structure 11 is porous, stable, dense, and thick enough to impart resilience to diffuse the pressure of the hydraulic ram-plate sideways to the total surface area of the filter assembly 9 pressing surfaces such that the water is pushed out through the filter quickly and evenly. The non-woven textile layer-structure preferably comprises a reinforcing scrim within the structure. The scrim may be a non-woven or woven textile layer-structure, preferably a woven one made of nylon, polypropylene, polyester or a similar structure, preferably of nylon. Preferably a 40 to 50 g/m², most preferably a 46 g/m² scrim is employed. The woven scrim comprises warp and weft component respectively. The staple fibres are needle punched through the scrim so that the scrim provides a reinforcing for the first layer-structure of the filter assembly 9, but it is embedded in the centre of the thickness of the first layer-structure. The scrim may be made more stable by weaving it by means of leno weaving. The non-woven textile of the first layer-structure 11 may also be heat stabilised and needled.
Referring to Fig. 2a and Fig. 2b, the filter material for the second textile layer-structure 12 may be any material, which is capable of permitting fluid to pass there through during pressing while preventing the passage there through of particulate material above a predetermined size. Accordingly, textile structures may be used, preferably woven, knitted or light mass per unit area spun-bonded non-woven layer-structures of simple but even and smooth structure. The preferred second textile layer-structure 12 is a knitted or a woven textile, wherein any pattern of the textile layer-structure is suitable. The used textile layer-structure is preferably porous, stable and has a fine flat surface not transferring visible imprints of a pattern onto the surface of the final cementitious product. Preferably, the second textile layer-structure 12 comprises a woven textile. Preferably, the woven textile of the second textile layer-structure 12 comprises hydrophobic yarns, such as polypropylene and/or polyester yarns, but also nylon fibres, PVC fibres or a blend of fibres may be used. A combination of polypropylene and polyester yarns is particularly preferred. The mass per unit area of the woven textile of the second textile layer-structure 12 is between 50 and 300 g/m², preferably between 100 and 300 g/m² and most preferably between 150 and 250 g/m². The second textile layer-structure 12 preferably comprises hydrophobic yarns on its surface to enable an easy peel away from the surface of the final pressed cementitious product. The second textile layer-structure 12 may also be knitted, preferably on a raschel warp-knitting machine being preferably a fall plate type structure as described in detail in the patent application WO 94/25236 or needled. In a further modification to the present invention, the weaving, knitting or needling procedures can be varied to increase or decrease the porosity and permeability of the textile structure.
The mass per unit area of the combination of the first layer-structure 11 and the second textile layer-structure 12 is between 150 and 1000 g/m², preferably between 200 and 600 g/m².
Preferably, the first layer-structure 11 as shown in Fig. 2a and Fig. 2b is bound to the perforated plate 10 by a discontinuous dot adhesive layer or by sealing the first layer-structure 11 onto the back of the perforated plate 10 with double sided tape or by heat welding techniques. Preferably, the second textile layer-structure 12 is attached to the first textile layer-structure using a discontinuous dot adhesive layer. A discontinuous dot adhesive layer is described in UK Patent Application No. 8730127 . The adhesive is provided in the form of a discontinuous coating on one face of a substrate. The substrate is in the form of a roll, but the two faces of the substrate have a different release effect so that, as the substrate is unrolled, the entire adhesive is on one face of the substrate. The discontinuous adhesive coating is applied to the substrate in the form of discrete particles. Particles are preferably applied in a pattern of column and rows, which covers the entire surface of the substrate.
The first layer-structure 11 and the second textile layer-structure 12 are positioned face-to-face in contact with the substrate, which is then cut to the same size as the first layer-structure 11 and the second textile layer-structure 12, respectively. The second textile layer-structure 12 and the first layer-structure 11 are pressed together with the substrate, respectively. When a particular piece of the first layer-structure 11 and/or the second textile layer-structure 12 is to be used, the substrate is peeled off leaving the pattern of adhesive particles transferred onto the reverse face of the first layer-structure 11 and/or the second textile layer-structure 12, respectively. The first layer-structure 11 is then pressed with its reverse face against the top face of the perforated plate 10 or the underside of the perforated plate 10 to cause the filter material to adhere to the perforated plate 10. Accordingly, the second textile layer-structure 12 is then pressed with its reverse face against the first layer-structure.
It has been found that the air porosity can be employed as an important measure for the suitability of a filter for the above described purposes. The porosity must not be too high or else channel-formation can ensue during pressing. On the other hand, low porosity inhibits water penetration. A balance must be struck, which is best achieved with inventive multi-layer structures with an air porosity between 150 and 300 ml/s.
The method of using the cementitious-product-forming apparatus shown in Fig. 1 will now be described. A quantity of cementitious slurry 4 is placed into the press mould 1. The compressing plate is operated to move downwardly into the mould compressing the cementitious slurry 4 between the filter assemblies 9 of the face filter 7 and the head filter 8 leading to expression of water from the cementitious slurry 4. The drained water passes the filter assembly 9 of the head filter 8 and the face filter 7 but cement, sand and other particulates are retained by the filter assemblies 9 of the head filter 8 and the face filter 7, respectively. After passing the filter assemblies 9 of the head filter 8 and the face filter 7, the drained water passes the perforations and openings of the bottom press plate (2) or compression plate (5) and exits the press mould 1 by suction holes and water channels 6, preferably by vacuum suction. The slurry mix takes up the shape of the final cementitious product defined by shape of the mould cavity. The compression plate is withdrawn from the press mould 1 and the final cementitious product is removed from the mould by moving the bottom press plate 2 through the mould. The final cementitious product is then removed.
The invention thus also relates to a cementitious-product-forming apparatus comprising: a compression plate having suction holes or water channels; a mould for inserting a cementitious slurry having a bottom and sidewalls; and at least one multilayer-structured filter assembly (9) according to any one of claims 1 to 11, wherein the filter assembly (9) is positioned on the bottom of the mould and/or is attached on the compression plate. In such cases, the filter is employed e.g. as either a head filter 8 and/or a face filter 7, both having an orientation that the second textile layer-structure faces the cementitious slurry to be pressed.
Finally, the inventive filter and process employing the filter give rise to well-formed standard paving slabs which correspond to existing norms or are improved in certain properties.
The exact microscopic structures of the manufactured cementitious products are not readily determinable, but the products can be achieved by the processes mentioned above.
The invention therefore also concerns a cementitious product or concrete product formed by a process for manufacturing cementitious products e.g. as described above, preferably comprising: pouring a cementitious slurry in a press mould, which is open at the top, to allow the slurry to enter; form-pressing and dehydrating the cementitious slurry using a compression plate by moving the compression plate on which a multilayer-structured filter assembly) according to any one of claims 1 to 11 is attached towards the cementitious slurry; lifting the compression plate away from the cementitious slurry; and removing the manufactured cementitious product from the press mould.

Reference list

1 press mould
2 bottom press plate
3 side walls
4 cementitious slurry
5 compression plate
6 suction holes/ water channels
7 face filter
8 head filter
9 filter assembly
10 perforated plate
11 first layer-structure
12 second textile layer-structure

Claims

A multilayer-structured filter assembly (9) for a press mould (1) used for manufacturing cementitious products comprising:
a perforated plate (10),

a filter with at least two layers comprising:
a first layer-structure (11) attached to the perforated plate (10), and

a second textile layer-structure (12) for contacting a cementitious slurry attached to the surface of the first layer-structure (11) on the other side of the first layer structure opposite to the perforated plate (10).
The multilayer-structured filter assembly (9) according to claim 1,
wherein the first layer-structure (11) comprises a non-woven textile, a woven textile or a foam and
the second textile layer-structure (12) comprises a woven textile, a knitted textile, or a spun-bonded non-woven textile.
The multilayer-structured filter assembly (9) according to claim 1 or 2, wherein
the the first layer-structure (11) comprises hydrophobic fibres having a melting point lower than 350 °C, preferably of polypropylene.
The multilayer-structured filter assembly (9) according to claim 1 to 3, wherein
the the second textile layer-structure (12) comprises polypropylene and/or polyester yarns.
The multilayer-structured filter assembly (9) according to any one of claims 1 to 4, wherein
the mass per unit area of the second textile layer-structure (12) is between 50 and 300 g/m².
The multilayer-structured filter assembly (9) according to any one of claims 1 to 5, wherein
the mass per unit area of the first layer-structure (11) is between 100 and 700 g/m².
The multilayer-structured filter assembly (9) according to any one of claims 1 to 6, wherein
the combined mass per unit area of the first and the second layer-structures is between 150 and 1000 g/m².
The multilayer-structured filter assembly (9) according to any one of claims 1 to 7, wherein
the first layer-structure (11) comprises fibres that have a dtex value between 5dtex and 50dtex.
The multilayer-structured filter assembly (9) according to any one of claims 1 to 8, wherein
the first layer-structure (11) comprises a non-woven textile and a reinforcing scrim within the first layer-structure (11).
The multilayer-structured filter assembly (9) according to any one of claims 1 to 9, wherein
the first layer-structure (11) is bound to the perforated plate (10) by a discontinuous dot adhesive layer or by sealing the first layer-structure (11) onto the back of the plate with double sided tape or by heat welding techniques.
The multilayer-structured filter assembly (9) according to any one of claims 1 to 10, wherein
the first layer-structure (11) is attached to the second texture layer-structure (12) using a discontinuous dot adhesive layer.
Use of a multilayer-structured filter assembly (9) according to any one of claims 1 to 11 in a press mould (1) for manufacturing cementitious products.
A process for manufacturing cementitious products comprising:
pouring a cementitious slurry into a press mould (1), which is open at the top, to allow the slurry to enter;

form-pressing and dehydrating the cementitious slurry using a compression plate by moving the compression plate on which a multilayer-structured filter assembly (9) according to any one of claims 1 to 11 is attached towards the cementitious slurry;

lifting the compression plate away from the cementitious slurry; and

removing the manufactured cementitious product from the press mould (1).
A cementitious-product-forming apparatus comprising:
a compression plate having suction holes or water channels;

a mould for inserting a cementitious slurry having a bottom and sidewalls; and

at least one multilayer-structured filter assembly (9) according to any one of claims 1 to 11, wherein

the filter assembly (9) is positioned on the bottom of the mould and/or is attached on the compression plate.
A cementitious or concrete product formed by a process for manufacturing cementitious products comprising:
pouring a cementitious slurry in a press mould (1), which is open at the top, to allow the slurry to enter;

form-pressing and dehydrating the cementitious slurry using a compression plate by moving the compression plate on which a multilayer-structured filter assembly (9) according to any one of claims 1 to 11 is attached towards the cementitious slurry;

lifting the compression plate away from the cementitious slurry; and

removing the manufactured cementitious product from the press mould (1).