IE911652A1

IE911652A1 - Inset for asphalt layers

Info

Publication number: IE911652A1
Application number: IE165291A
Authority: IE
Original assignee: Hoechst Ag
Priority date: 1990-05-15
Filing date: 1991-05-14
Publication date: 1991-11-20
Also published as: JPH04228706A; DE4015504A1; PT97652A; EP0457227A1

Abstract

There is described a liner which is particularly employed in the renovation of old bituminous road surfaces as an intermediate layer between the old and new road surface. The liner is a non-woven material containing hollow fibres or consisting of hollow fibres or a composite of such a non-woven material and a woven fabric, knitted fabric, stitch-bonded material or other fabric of defined yarn position. A liner is preferred in which the non-woven material and the fabric of defined yarn position are bonded by the weft-laying Raschel technique. The liner described has particularly advantageous reinforcing and sealing properties and is distinguished by good laying ability.

Description

Description Inset for asphalt layers The invention relates to an inset for asphalt layers for 5 use in particular in road construction. Textile materials have for many years been used in the renovation of worn bituminous pavements in the form of an interlayer between the old and the new pavement. However, textiles can also be used in the building of new roads, as inset between the pavement and the base-course. The functioning and the advantages of such insets were discussed at a conference from March 8, 1989 to March 10, 1989 in Li^ge, Belgium (Reflective Cracking in Pavements, Assessment and Control).

In practice, essentially two fundamental concepts have become established. One provides for the use of nonwovens which are customarily in the form of spunbondeds formed from continuous filaments and made of polypropylene or increasingly, owing to the higher melting point, poly20 ester (cf. for example Die AsphaltstraBe 1/88, p. 15ff, or Installation Guide for Paving Fabric in Asphalt Overlays from Hoechst Fibre Industries, USA). On the other hand lattice fabrics are used, formed from highstrength polyester yarns (cf. for example Bitumen, Teer, Asphalt, Peche, vol. 25, April 1974). A recent addition are grids, which comprise oriented perforated films formed from a cast or extruded plastic, usually polypropylene .

The inset is in general introduced by first applying a layer of an adhesive, for example a contact adhesive, Bitumen B 80 or an emulsion, for example a cationic bitumen emulsion, to the area to be repaired and then placing a length of inset material smoothly on top. Here the nonwoven acts as a crack-preventing layer in the - 2 manner of a buffer and as an absorbing layer for bitumen or contact adhesive. An important requirement is to obtain a permanent bond without voids or layers which slide over each other.

As mentioned earlier, the main advantage of a nonwoven placed between the pavement and the ground is a certain buffer effect which is intended to prevent, or at least delay, the formation and propagation of cracks, for example reflective cracks. In addition, the bitumen10 impregnated nonwoven acts as a water barrier which is intended to prevent the penetration of surface water into the base-course.

Even though lattice fabrics or grids, owing to their superior strength properties, are efficient at absorbing relative movements between the pavement and the basecourse and thus are superior in preventing crack formation and propagation, they have the disadvantage, however, that cracks can pass through the coarse mesh holes, which are from 20 to 40 mm in size. Another disadvantage is that they offer virtually no barrier to the penetration of surface water. Also, owing to their stiffness, such lattice fabrics and grids present laying problems, which frequently leads to inadequate bonding and thus to premature detachment of the asphalt layer.

It has also already been proposed to use a composite material formed from a nonwoven and a textile sheet material of defined yarn arrangement for the reinforcement of asphalt layers in road construction. Such a composite material does show increased resistance to crack formation and propagation, but it is also costly and impregnating it adequately requires a relatively large amount of bitumen.

DE-U-7,133,997 discloses a composite material formed from crimped polyamide fiber nonwoven and a needled-in con35 tinuous filament lattice fabric, which are held together by a water-resistant binder. This composite material is - 3 used as an erosion-preventing damming material in dyke and canal construction.

The present invention has for its object to provide an inset for asphalt layers in road construction which is particularly effective in preventing crack formation and propagation in the asphalt layers, which possesses a good sealing effect against the penetration of surface water, and is easy to lay, and which for the same application properties is lighter than existing materials and in general also requires a smaller amount of binder, for example bitumen, contact adhesive or bitumen emulsion, for adequate impregnation and which therefore is more economical and hence less costly to manufacture and use.

It has now been found, surprisingly, that this object is achieved and high inset requirements are met by nonwovens having a significantly lower basis weight and hence requiring considerably less material when the fiber material of the inset and in particular of the nonwoven present therein contains hollow fibers. A further advan20 tage of the inset of the present invention is that in many cases it permits a distinct saving in binder, for example bitumen, contact adhesive or bitumen emulsion, which likewise is a beneficial weight and cost saving measure.

Accordingly, the present invention provides an inset for asphalt layers which consists of or contains a synthetic fiber nonwoven which is composed at least in part of hollow fibers.

When an inset of the present invention consists of the synthetic fiber nonwoven, it is an inset whose sole textile component is the nonwoven which contains or consists of hollow fibers. In many cases, such an inset will be good enough for use in practice.

Particular application advantages are offered by an inset - 4 of the present invention which comprises a composite material consisting of two components, one of which is the nonwoven, composed at least in part of hollow fibers, while the other component, hereinafter also referred to as reinforcement, is a woven, knitted, laid or grid fabric, a Raschel material or some other sheetlike structure of defined yarn arrangement.

This second component may likewise contain or consist of hollow fibers.

As has been found, such a novel inset has a surprisingly high resistance to crack formation and propagation. This is likely to be due to a combination effect between the advantageous properties of its two components. In addition, the inset constructed according to the present invention has an excellent sealing effect which prevents the passage of water and thus also of organic and inorganic constituents .

The proportion of hollow fibers in the nonwoven which confers the desired combination of properties on the inset can in certain circumstances be surprisingly small.

Frequently, a marked economic and technical advantage is obtained even with an inset whose nonwoven contains only 10 % of hollow fiber.

In general, it is advantageous to use an inset whose nonwoven contains 50-100 % of hollow fiber, although to meet the very highest technical requirement profiles it may of course be necessary to use inset nonwovens which are 100 % hollow fiber. If a hollow fiber reinforcement is used, the above remarks concerning the hollow fiber content of the nonwoven apply in the same way. However, it is not necessary that the nonwoven and the reinforcement have the same hollow fiber contents.

The linear density of the synthetic fibers of the nonwoven of the inset of the present invention and of the reinforcement is within the range customary for geotextiles. The linear density is accordingly in general - 5 between 0.5 and 50 dtex, preferably within the range from 2 to 20 dtex.

It may in certain instances be advantageous to use mixed linear densities; more particularly, in those inset nonwovens which are not 100 % hollow fiber the hollow fibers and the non-hollow fibers can have different linear densities.

Similarly, the fiber linear densities of the nonwoven and the reinforcement may of course be different; they are selected and if necessary combined as required.

The synthetic fibers can be continuous filament fibers or staple fibers, advantageously with staple lengths of 2-20 cm.

However, it is also possible without reservation to use 15 insets which contain both continuous filament and staple fibers .

For instance, in many cases the desired combination of properties may be imparted to a continuous filament nonwoven by blending in a suitable proportion of hollow staple fibers.

Of course, it is also possible for mixtures of hollow and non-hollow staple fibers to be used to form a staple fiber web nonwoven.

The synthetic fibers present in the nonwovens of the 25 insets of the present invention can have one or more voids, and the voids can be short or very short in the direction of the fiber axis or they can extend along the entire fiber length. Accordingly, hollow fibers for the purposes of this invention include not only foam fibers but also hollow fibers with one or more voids which extend along major sections or the entire length of the fiber.

Preference is given to insets according to the present invention whose hollow fibers have voids which extend essentially along the entire fiber length or, for certain applications, also to insets with foam fibers.

Of crucial significance is the void content of the - 6 synthetic fibers. Of particular utility for the insets or the present invention are synthetic fibers whose void content is 3-40 % by volume, preferably 5-20 % by volume. Suitable synthetic fibers generally comprise spinnable polyamide, polyacrylonitrile, polyethylene, polypropylene or polyester.

Preference is given to synthetic fibers made of polyester, in particular polyethylene terephthalate, on account of their high temperature resistance.

The nonwovens of the insets of the present invention can in principle be consolidated in any known way. For instance, it is possible to consolidate the web with a binder with which the web is impregnated and which is subsequently cured, or the binder can be a thermobinder which is incorporated into the web for example in powder or filament form and which on heating consolidates the web into a nonwoven.

The consolidation of the web to a nonwoven can also be effected by calendering, partly to intermingle the filaments mechanically, partly to effect autogenous bonding at the crossing points.

Of particular advantage are those insets of the present invention which consist of or contain a nonwoven which has been mechanically consolidated. Mechanical consolid25 ation for the purposes of the present invention is for example needling or else for example hydromechanical consolidation as described for example in EP-A-0 108 621. The various consolidation techniques may if desired also be combined.

The basis weight of the inset nonwoven of the present invention does of course depend on the intended use. In general it ranges from 50 to 300 g/m2, preferably from 100 to 180 g/m2, but for particular service requirements, in particular when the nonwoven is the sole textile constituent of the inset, it may also be higher, for example up to 500 g/m2.

A further preferred embodiment of the insets of the present invention is based on a spunbonded nonwoven, in - 7 particular a spunbonded which has been consolidated by needling.

The choice of raw material for the second component of the composite material, for the woven fabric say, is similar to that in the case of the nonwoven. Particular preference is given to making the two components of the composite material from the same raw material, i.e. in particular from polyesters, irrespective of whether the composite material contains a woven, laid, lattice or knitted fabric or is constructed as a Raschel material.

The basis weight of the second component - the reinforcement - of the composite material is preferably within the range from 100 to 500 g/m2. The breaking strength of the second component of the composite material should be from 10 to 200 kN/m, preferably from 25 to 200 kN/m (the breaking strength in question being the breaking strength of a sheetlike structure 1 m in width). The breaking extension is preferably within the range between 5 and 35 %, in particular between 10 and %. Preferably, the composite material is constructed as a Raschel material in which the two components of the composite material are held together by the weft-insertion Raschel technique. A material produced by the weftinsertion technique with a web inlay exhibits a particularly strong bond between the two components of the composite material.

However, good results are also obtained on bonding together the two components of the composite material by needling, by adhering or by stitching. The bond between the two components must be sufficiently strong to ensure that the inset will not weaken due to delamination of the composite material.

In a particularly preferred embodiment, the nonwoven is a (R)Trevira spunbonded in which high-tenacity Trevira hochfest yarns have been integrated by the weft-insertion Raschel technique or which has been bonded to a woven fabric made of high-tenacity Trevira hochfest yarns by - 8 stitching.

Particular preference is also given to those embodiments of the inset which combine more than one of the abovementioned preferred features.

In composite materials the breaking strength of the second component of the composite material can be equated to the breaking strength of the composite material itself, since the nonwoven, owing in particular to its high extensibility, does not make any significant contri10 bution to the breaking strength.

The inset of the present invention is suitable in general for reinforcing asphalt layers, for example new pavements or roof coverings or crack-resistant insulation. An area where the inset of the present invention has particular advantages, in particular in respect of economy of material, is the abovementioned repair of damaged pavements, where the inset will act as a link between old and new asphalt layers .

The bond between the inset and the two asphalt layers is obtained with an adhesive, for example pure bitumen. On using other adhesives, the ultimate amount of adhesive must be determined beforehand. The amount of adhesive must correspond at least to the pore volume of the composite material and must allow for loss of adhesive into the (damaged) asphalt layers. The relevant requirements are summarized in the TASK FORCE 25 Specification Guide for Paving Fabrics.

As mentioned earlier, the composite material constructed according to the present invention exhibits a particu30 larly high resistance to crack formation and transmission. Here the nonwoven component ensures an optimal bond between the asphalt and the inset; it also prevents any passage of water and forms a buffer which absorbs the forces due to the cracks. Advantageously the composite material is used with the nonwoven on the underside.

In the event of larger cracks, due in particular to the - 9 demolition of adjoining buildings and/or ground movements, frost heaves or other stresses, the force is absorbed in particular by the high-strength second component of the composite material.

The present invention further provides a binder-filled inset comprising a synthetic fiber nonwoven and a binder, wherein the nonwoven is composed at least in part of hollow fibers and contains binder in an amount of BQ g/m2, BW where BQ = Pbinder x (T x 10,000 - - ) Pfiber In this formula, BQ is the binder quantity in g/m2, pbinder is the density of the binder in g/cm3, pfiber is the effective density of the fibers in g/cm3, BW is the basis weight of the nonwoven of the inset in g/m2 and T is the thickness of the nonwoven of the inset in cm.

The preferred binder for the binder-filled insets of the present invention is bitumen.

A preferred binder-filled inset contains one of the above-described novel composite materials comprising a hollow fiber nonwoven and another textile sheet material of defined yarn arrangement and binder in an amount BQ.

The present invention also provides a process for producing the inset of the present invention by depositing and synthetic continuous filament or staple fibers in a conventional manner on a moving surface, subsequent consolidation with or without combination with a textile material of defined yarn arrangement, which may likewise consist of or contain hollow fibers, wherein at least some of the laid synthetic fibers are hollow fibers.

To produce staple fiber nonwovens which according to the present invention contain a proportion of hollow fibers, a mixture of hollow and non-hollow staple fibers in the desired mixing ratio can be conventionally dry- or wet35 laid to form a web and then consolidated. - 10 However, it is also possible to produce nonwovens from continuous filament fibers and staple fibers by admixing the staple fibers in the course of the laying of the continuous filament fibers. In this case, either the continuous filament fibers or the staple fibers may be hollow fibers in whole or in part.

Similarly, if the nonwovens are produced by the spunbonding process it is possible to mix hollow and non-hollow fibers in the course of the laying. For instance, the hollow fibers can be produced separately and withdrawn from fiber reservoirs, e.g. bobbin creels, and fed by means of blowing nozzles into the stream of non-hollow fibers traveling in the direction of the moving surface, or the spinneret manifolds which are used for producing the web-forming filaments may in addition to openings for non-hollow fibers contain openings for hollow fibers, the ratio between the various openings and the ratio of the amounts of filament spun therefrom corresponding to the target ratio of hollow and non-hollow fibers in the nonwoven of the inset of the present invention.

In general, the proportion of deposited hollow fiber in an inset of the present invention is at least 10 %. Preferably, the proportion of deposited hollow fiber is from 50 to 100 %, and if maximum effects are to be achieved, 100 % of the deposited fibers are hollow fibers .

The web is consolidated to the nonwoven in a conventional manner using a binder, especially a thermobinder, or by calendering or preferably by mechanical means. However, it is also possible to employ a combination of various of these consolidation techniques.

Binders can be for example polymer solutions or dispersions or latices, which are applied to the web by impregnation or spraying and which, after the liquid phase has evaporated, leave tiny membranes stretched out at the crossing points of the filaments.

However, it is also possible to use thermosetting binders - u which harden with or without heating and stabilize the fibers at the crossing points. It can be similarly advantageous to use thermobinders, which are incorporated into the web for example in the form of powders or preferably in the form of fibers and which, as the web is heated to beyond their melting point, run together at the crossing points of the fibers and form bonding points which, on cooling, consolidate the web to give a nonwoven .

Similar consolidation can be obtained by autogenous bonding of the filaments at their crossing points by subjecting the web to calendering in the vicinity of the melting point of the filaments.

Preference is given to mechanical consolidation, for example by needling or by hydromechanical consolidation, as described for example in EP-A-0 108 621. This puts no chemical or thermal stresses on the filament material whatsoever, so that the advantageous physical properties which are imparted to the filaments from their manner of production, for example by high-speed spinning and drawing operations, are passed on in full to the nonwoven .

To produce insets according to the present invention from a combination of a nonwoven with a textile material of defined yarn arrangement, the nonwoven must be combined with the textile material in such a way as to prevent any weakening of the inset due to delamination. This requirement can be met if the components are joined together by needling, adhering or stitching.

Particular preference is given to producing the novel composite-based insets by the weft-insertion Raschel technique.

This is a form of warp knitting in which the nonwoven is reinforced in some directions by yarns, preferably high35 strength yarns with or without a hollow fiber content or made of hollow fibers. This warp-knitting technique is - 12 carried out on so-called Raschel machines. A particularly suitable Raschel machine for producing a composite material constructed according to the present invention is the RS 3 MSU-V model from Karl Mayer, Textilmaschinen5 fabrik GmbH, Obertshausen.

Claims

What Is claimed is:

1. An inset for asphalt layers which contains a nonwoven made of synthetic fibers, wherein this non5 woven is composed at least in part of hollow fibers.

2. The inset of claim 1, wherein the nonwoven is the sole textile constituent of the inset.

3. The inset of claim 1, comprising a composite material consisting of two components, one of which

4. The inset of at least one of claims 1 to 3, wherein 50-100 % of the synthetic fibers are hollow fibers. 5. The thickness of the nonwoven of the inset in cm. 5 two components are integrated with one another by the weft-insertion Raschel technique.

5. The inset of at least one of claims 1 to 4, wherein the void content of the hollow fibers is 3-40 % by

6. The inset of at least one of claims 1 to 5, wherein the basis weight of the nonwoven is within the range between 50 and 300 g/m 2 , preferably between 100 and 180 g/m 2 . 25

7. The inset of at least one of claims 1 to 6, wherein the nonwoven is a continuous filament spunbonded.

8. The inset of at least one of claims 1 to 7, wherein the synthetic fibers are made of polyester, preferably polyethylene terephthalate. - 14

9. The inset of at least one of claims 1 to 8, wherein the nonwoven has been mechanically consolidated. 10. Staple fibers in a conventional manner on a moving surface to form a web and subsequent consolidation with or without combination of the nonwoven with a textile material of defined yarn arrangement, which comprises using hollow fibers for at least some of

10. The inset of claim 3, wherein the composite material is constructed as a Raschel material in which the 10 is the nonwoven, composed at least in part of hollow fibers, while the second component is a woven, knitted, laid or grid fabric, a Raschel material or some other sheetlike structure of defined yarn arrangement which may likewise consist of or contain

11. The inset of claim 3, wherein the two components of the composite material are bonded together by needling, adhering or stitching. 10

12. The inset of at least one of claims 3 to 11, wherein the second component of the composite material comprises high-strength yarns.

13. The inset of at least one of claims 3 to 12, wherein the two components of the composite material are

14. The inset as claimed in at least one of claims 3 to 13, wherein the basis weight of the second component of the composite material is within the range between 100 and 500 g/m 2 .

15. The deposited synthetic fibers and, if required, a textile material of defined yarn arrangement which likewise consists of or contains hollow fibers. - 15 BQ is the binder quantity in g/m 2 , pbinder is the density of the binder in g/cm 3 , p£iber is the effective density of the fibers in g/cm 3 , BW is the basis weight of the nonwoven of the inset in g/m z and T is 15 made of the same raw material. 15 hollow fibers.

16. A binder-filled inset comprising a synthetic fiber 25 nonwoven and a binder, wherein the nonwoven is composed at least in part of hollow fibers and contains binder in an amount of BQ g/m 2 , BW where BQ = p binder x (T x 10,000 - -) Pfiber and

17. The binder-filled inset of claim 16, comprising an inset of claim 3 and binder in an amount BQ.

18. A process for producing the inset of claim 1 by depositing synthetic continuous filament and/or

19. The process of claim 18, wherein 50-100 % of the laid fibers are hollow fibers.

20. 20. The process of either of claims 18 and 19, wherein the web-to-nonwoven consolidation is effected mechanically. 20 15. The inset of at least one of claims 3 to 14, wherein the breaking extension of the second component of the composite material is within the range between 5 and 35 %. 20 volume.

21. The process of either of claims 18 and 19, wherein the nonwoven is bonded to the other textile material by the we ft-insertion Raschel technique.

22. 22.

23. 23.

24.

25. 24. 25. An inset as claimed in claim 1, substantially as hereinbefore described. A binder-filled inset as claimed in claim 16, substantial ly as hereinbefore described. A process as claimed in claim 18, substantially as hereinbefore described. An inset as claimed in claim 1, whenever produced by a process claimed in a preceding claim.