EP0018491B1 - Fibrous reinforcement for cement or bitumen bonded building elements and coverings - Google Patents

Abstract

A fibrous reinforcing means for cementitiously and bituminously bound composite structures and coatings comprises at least two various groups of fibrous articles. At least one of the groups consists of fibrous articles in the form of a closed filamentary net. The fibres thereof are resilient. They are added to the material to be mixed in a condensed shape such to expand during the mixing step of the preparation of the composite structure.

Description

The invention relates to a fibrous reinforcement for cement and bitumen-bonded components and coverings, with at least two different groups of fiber structures according to the preamble of claim 1.

The use of fibers for the reinforcement and reinforcement of materials, the so-called fiber reinforcement, is generally known. Currently, the following fibers in particular, in the form of monofilament fibers, are considered to be expedient for the use mentioned: steel fibers, glass fibers, plastic fibers (e.g. polypropylene, polyethylene, polyamide, aramid (highly aromatic polyamide), PVC, carbon fibers, asbestos fibers, Natural fibers.

An obvious requirement for reinforcement fibers is the uniform distribution of the same over the cross-section of the component reinforced with it, in order to improve its crack pattern. However, the known fibers usually have the disadvantage that they clump together in the material to be reinforced, for example due to electrostatic charging, and therefore there is no uniform distribution of the same. Thus, their dosage is chosen to be relatively high in cross-section and the introduction techniques, e.g. B. trickling, are probably feasible under laboratory conditions, but very expensive and in practice difficult, if at all, feasible. This means that economically viable solutions with regard to fiber reinforcement are extremely limited.

In DE-A-2 447 816 a reinforcement element has become known which is fiberized and forms a network. This mesh-shaped reinforcement element fulfills its task satisfactorily in the frame intended for it. However, the use of this reinforcement element together with other reinforcement elements to increase the quality of a body reinforced in this way was not feasible, because the mesh-shaped, but not the other reinforcement elements, of course, are incorporated into the material to be reinforced, e.g. B. Distributed concrete. In addition, it had been found that the simultaneous use of several different reinforcement elements did not result in a satisfactory increase in the quality of the respective body reinforced with them, because there was no teaching with regard to the mixture proportions of the individual different reinforcement elements.

The invention seeks to remedy this. For this purpose, the fibrous reinforcement is designed according to the characterizing part of claim 1. The distribution of the percentages of the groups of fiber structures of different fiber lengths is equal to the distribution of the percentages of the aggregates used of different grain sizes.

The advantages achieved by the invention are essentially to be seen in the fact that the reinforcement elements can be introduced into the mix together with the additives in calculable proportions, and thus an optimal effect of the reinforcement elements can take place.

The reinforcement elements, which are evenly distributed over the cross-section of the reinforced component, do not aggregate. They are so evenly distributed and proportionately present in the mix that they can be regarded as additional additives.

• Fig. 1 ein Bewehrungselement in Form eines Kunststoffasernetzes,
• Fig. 2 das Bewehrungselement der Fig. 1 in der Zustandsform vor dem Einbringen,
• Fig. 3 eine genormte Siebkurve für die Zuschlagstoffe zur Betonherstellung,
• Fig. 4 ein Diagramm der Verteilung des prozentualen Anteils verschiedener Bewehrungsfasern bezogen auf die Faserlänge, und
• Fig. ein Diagramm der Verteilung des prozentualen Anteils verschiedener Bewehrungsfasern bezogen auf der E-Modul.

The invention is explained in more detail below with reference to the drawings, for example. It shows

• 1 is a reinforcement element in the form of a plastic fiber network,
• 2 the reinforcement element of FIG. 1 in the state before insertion,
• 3 is a standardized sieve curve for the aggregates for concrete production,
• Fig. 4 is a diagram of the distribution of the percentage of different reinforcing fibers based on the fiber length, and
• Fig. A diagram of the distribution of the percentage of different reinforcement fibers based on the modulus of elasticity.

It has been mentioned in the introduction that one of the great difficulties of fiber reinforcements, e.g. B. the concrete is that in practice it is hardly economically possible to achieve a uniform distribution on the cross-section of the component to be reinforced in order to produce, among other things, a uniform cracking. This is due to the fact that the individual fibers clump together due to electrostatic attractive forces or due to other technical influences, e.g. B. different, specific weight, either sink to the bottom of a body that has just been cast, or float up on its surface.

In order to distribute these reinforcement elements consisting of individual fibers evenly over the cross-section, they are used seriously according to the inventive concept together with a specially designed reinforcement element, which is described below.

This reinforcement element has the shape of a closed fiber network made of polypropylene and is shown in FIGS. 1 and 2. This fiber network is a one-piece structure, two different fiber thicknesses being present in the embodiment shown. First fibers 1 are each connected to one another by second fibers 2, the cross section of the second fibers 2 being smaller than the cross section of the first fibers 1. This also applies to the mix added fiber nets now tend to adhere to one another, in particular due to the mixing, for example due to the static charging thereof, such that no uniform distribution would occur in the concrete. However, because the fine polypropylene fibers are resilient, for example all the second fibers 2 act as springs which keep the first fibers 1 at a distance from one another, overcoming the mutual attraction forces, so that the fibers self-distribute in the mix or in the concrete. In addition, individual fiber ends 3 loop around the grains of the material to be mixed, which additionally counteract the agglomeration of the fiber network during mixing and immediately afterwards. Obviously, the net-shaped reinforcement element in the final state does not describe the flat plane shown in FIG. 1, but is deformed in space in all three dimensions. _' a

The state of the reinforcement element before it is introduced into the mix is shown in FIG. 2. The reinforcement element is wound wound in a string, the number of turns being predetermined. To produce the reinforced component, the reinforcement element in the gathered form shown in FIG. 2 is entered together with the material to be mixed into the concrete mixing machine, and the mixing is then carried out in the usual manner and during the standardized period of time. During this period, the cord shape of the reinforcement element is opened and after this time period the reinforcement element is in the three-dimensionally distributed network form. As is well known, the mixing farmer is standardized in the production of concrete. Therefore, the number of turns of the cord piece to obtain a three-dimensional network after mixing can be determined exactly. If the mesh is not completely open after the mixing process has ended, its effect on the reinforcement is limited. If the mesh is fully open before mixing is complete, it will be torn apart during the remaining mixing period, take the form of the known split fibers, and also lose its effect as a reinforcement element. In the present gathered form according to FIG. 2, it is now possible to use the reinforcement element in practice without difficulty, since it does not require any additional devices for introducing it into the mix (in particular it does not have to be sprinkled in) and, in addition, there is no additional monitoring of time periods necessary. It must also be mentioned that the insertion form twisted into the cord is only pure, for example. The gathered form can be formed by other deformations, and water-soluble adhesives can also be arranged to hold the gathered form together.

It has already been mentioned that the fibrous reinforcements are required to be distributed evenly over the cross-section of the reinforced component, since finally the crack formation, the crack pattern, must be uniform.

Such a uniform distribution can now be achieved when using such self-distributing mesh reinforcement elements, this together, i. H. in combination with other known fibrous reinforcement elements in the form of individual fibers such. B. glass fibers, steel fibers, plastic fibers, carbon fibers, asbestos fibers, natural fibers etc. One or more of these types of fibers can be used together with the reticular reinforcement element, the fiber lengths can be different, as will be explained in more detail below. If reinforcing fibers, which are individual fibers, are introduced into the mix together with the fiber network, the fiber network self-distributing during mixing, the single fibers are evenly distributed by the spreading networks. The nets also prevent the individual fibers from clumping together, since the nets prevent the individual fibers from doing so purely mechanically. The individual fibers are thus guided through the networks in such a way that a uniform distribution of the individual fibers, and obviously also the fiber networks, is achieved in the reinforced concrete piece.

An exemplary embodiment is now described below in which mesh-like reinforcement elements made of polypropylene are combined with steel fibers in concrete.

A test specimen was first made from unreinforced concrete. A bending tensile strength of approximately 32 kg / cm ^{2 was} measured for this concrete body, which value is a common average value for concrete. Then another concrete test piece was produced, to which a calculated optimal amount of steel fibers, namely 144 kg, was added. A bending tensile strength of this concrete steel specimen, which was reinforced only with steel fibers, was measured at approximately 68 kp / cm ² . The steel fibers thus improved the bending tensile strength by approximately 36 kp / cm ^2. Another concrete test piece was produced in which a calculated optimal amount of 1 kg of the reticular polypropylene fiber reinforcement was added. A bending tensile strength of a concrete test piece reinforced with plastic mesh was measured at approximately 36 kp / cm ² . So the improvement in bending tensile strength was 4 kp / cm ^2.

Using plastic nets together with steel fibers would therefore result in an improvement in the bending tensile strength of 36 + 4 = 40 kp / cm ² , so a test specimen with both reinforcements would have a bending strength of 32 + 40 = 72 kp / cm2.

Now, however, the use of steel fibers according to the invention together with fiber nets produces an unexpected, significant improvement in the bending tensile strength due to the distributing effect of the fiber nets.

A concrete test specimen was now produced, which with 144 kg of the above steel fibers and with 1 kg of Fiber mesh was reinforced, and then the flexural strength was measured. The measured value was approximately 100 kp / cm ^2, which value is incomparably higher in comparison with the calculated 72 kp / cm ^z . These test results, along with other measured data, are shown in the table below:

This table shows that the actual data of the concrete obtained in the tests, which is reinforced with the different fibers mentioned, surprisingly deviates from the computationally to be expected.

The example above shows that reinforcing an m ³ concrete with 144 kg steel fibers and with 1 kg plastic fiber mesh results in a bending tensile strength of 100 kp / cm ² , the proportions of the different fibers having proven to be optimal.

Further tests were carried out with the following reinforcement elements: 67% »split fiber« (plastic fibers, in open mesh form), 29% plastic fibers of the above-mentioned, closed mesh form and 4% monofilament aramid fibers (aramid = highly aromatic polyamide). This combination resulted in a doubling of the bending tensile strength of the unreinforced concrete, again a result that was not calculated.

It is evident from the tests carried out with the above-mentioned exemplary embodiments that a compulsory, uniform distribution of the individual reinforcement fibers leads to an unexpected improvement in the quality of the reinforced concrete.

Returning to the unreinforced concrete, it must now be considered that the quality of the concrete also depends on the even distribution of the aggregates with different grain sizes. It is not only important how evenly a certain grain size (i.e., e.g. gravel bodies with a diameter of only 5 mm) is distributed in the poured concrete, but also what the proportions of the different grain sizes are.

It is known that the aggregates for the production of concrete have to follow certain rules, among other things with regard to the grain sizes. In particular, the aggregate grain build-up curve, i. That is, the so-called sieve curve lies within predetermined limits and demonstrates a predetermined course, as is stipulated in Switzerland, for example, in Article 2.02 of the SIA standards, which sieve curve also corresponds to the DIN standard 1045 with regard to the aggregates for concrete .

The sieve curve S drawn in FIG. 3, which is also called the granulation curve, prescribes the percentage distribution of the grain sizes to be aimed for according to SIA, that is to say the grain distribution.

In FIG. 3, A: denotes the residue in percent by weight, B: the mesh size or round hole size in mm, C: passage in percent by weight. For the sake of completeness, it should be mentioned that curve S indicates mean values with respect to permissible scatter ranges, which is known to the person skilled in the art. (The corresponding curve S according to DIN 1045 is defined as "particularly good".)

This sieve curve, which is based on purely technical facts and knowledge, determines the percentage distribution of the aggregates of different grain sizes in order to obtain a (unreinforced) high-quality concrete.

It has now been recognized that the same law also applies to fiber reinforcement.

One of the properties to consider is fiber length. Instead of using only a predetermined length of the respective fibers, fibers of the same material with different lengths are used, however, analogously to the different grain sizes of the additives. The percentage distribution of the amounts of the respective fiber lengths with respect to the grain sizes of the additives follows the recognized law.

This is shown in FIG. 4. D denotes the quantity in% and E the fiber length in mm. The curve T, the course of which is geometrically the same as the sieve curve S in the figure, can be referred to as a “length granulation curve”. According to this curve T, an optimal fiber length distribution has to be as follows:

In the aforementioned embodiment containing the polypropylene fiber network and the steel fibers, this means that different fiber lengths are used both in the fiber network and in the steel fibers, the percentage proportions of each fiber length corresponding to the "length granulation curve" T, so that the quality of the fiber-reinforced concrete is further improved is.

Another property to be considered for reinforcement fibers is the modulus of elasticity of the materials from which the fibers are made. This means that the fiber reinforcement not only has to consist of only two fiber groups according to the above (but which can also be used in practice), but the polypropylene network together with steel fibers and / or glass fibers and / or carbon fibers and / or asbestos fibers and / or other plastic fibers, e.g. B. aramid etc. is to be used.

Here, too, the known sieve curve S according to FIG. 3 forms the basis of the percentage quantity distribution of the fiber reinforcements with respect to the elastic modulus, as shown in FIG. 5. 5, F means the amount in%, G the modulus of elasticity in kp / cm ² , representing different substances, and curve U again corresponds to curve S in FIG. 3.

5 shows that an optimal distribution of the amounts of respective reinforcement elements with respect to the modulus of elasticity is as follows:

So the reinforcement fibers of different materials are to be used according to the above law.

For optimal reinforcement by means of the fibers, the regularity of the quantity distribution with respect to the fiber length according to curve T of FIG. 4 is now combined with the regularity of the quantity distribution with regard to the elastic modulus according to curve U of FIG. This means that predetermined proportions of fibers with regard to fiber length and modulus of elasticity of the different materials are selected for optimal reinforcement.

Because there is always at least one closed fiber network, which uniformly distributes all fibers during mixing and prevents agglomeration, the introduction of any fiber material and any fiber length can be carried out without any particular effort. No practical application procedures or mixing periods need to be taken into account.

Two exemplary embodiments of the introduction of the reinforcement fibers are now described below.

The fibers are usually produced by dividing or cutting a film (for example in the case of plastic fibers), so that either the closed fiber network, open fiber networks or individual fibers are produced, or continuously (for example in the case of steel fibers or glass fibers) manufactured wires are cut. As is already known for certain plastic fibers, the fiber structures can now be twisted before cutting to produce the fibers of a predetermined length (the wires are twisted before cutting or are connected to one another by means of adhesives), so that there are several cord-shaped structures different in terms of the material. All these cord-like structures are then twisted together again, so that a thicker cord made of the different reinforcement materials is present, which cord is then finally cut into individual pieces. Depending on the materials used, these pieces of cord retain their shape due to the pretension, friction etc. imparted during twisting, or water-soluble adhesives are used. The number of twists, the adhesive, etc. is predetermined from tests and selected such that the reinforcement cords can be entered into the concrete mixing machine together with the additives, and after the standardized concrete mixing time has ended due to the self-distributing fiber network that is always present, uniform over the Cross section of the reinforced concrete body are distributed.

In another embodiment, in which the concrete to be poured is conveyed through a pressure pipe in a known manner, only the closed fiber networks are entered into the concrete mixing machine together with the additives. Immediately before the end of the pressure pipe, the remaining reinforcing fibers are introduced into the concrete stream, in a likewise known manner by means of a jet pump arrangement. Here, too, the uniform distribution of the individual fibers is ensured because the fiber nets prevent the individual fibers from clumping, sinking or rising.

Although the above description is directed, for example, to the manufacture of a reinforced concrete body, it should be noted that the fiber reinforcement described also for tar and Bitumen coverings can be used to prevent large cracks from forming and to generate a crack pattern from fine cracks, into which cracks no water can enter and freeze therein, so that frost damage can largely be prevented on roads etc.

Claims (6)

1. Fibrous reinforcement for structures and coating bound by concrete and bitumen, including at least two different groups of fibre forms, which fibre forms have different fibre lengths and of which at least the one group comprises a plurality of individual fibre nets each in form of a closed fibre net of polypropylene of which the fibres are spring elastic and feature a first length, and which groups of fibre forms prior to their adding to the material to be mixed are jointly present in a condensed form, characterized in that the respective further group of fibre forms is present in form of individual fibres having a second fibre length or in form of a further plurality of individual fibre nets having a second fibre length, which second fibre length differs from the first one and in that the distribution in percent of the amount the fibre lengths of the fibre forms equals the distribution in percent of the amount of the grain sizes of the aggregates used.

2. Fibrous reinforcement according to claim 1, characterized in that the fibrous forms comprise various moduli of elasticity, and that the distribution of the in percent of the groups of fibre forms having various moduli of elasticity equals the distribution in percent of the amounts of the aggregates used having various grain sizes.

3. Fibrous reinforcement according to claim 1, characterized in that two groups of fibre forms are present, of which one group comprises the form of a closed fibre net of polypropylene with spring elastic fibres and the second group contains steel fibres.

4. Fibrous reinforcement according to claim 1, wherein one of the groups of fibre forms comprises the form of a closed fibre net of polypropylene of which the fibres are spring elastic, characterized in that at least one further group comprises glass fibres and/or steel fibres and/or plastic material fibres and/or carbon fibres and/or asbestos fibres and/or natural fibres.

5. Fibrous reinforcement according to claim 1, characterized in that prior to the adding thereof to the materials to be mixed all groups of fibre forms are joined to each other.

6. Fibrous reinforcement according to claim 1, characterized in that the fibre forms are twisted with each other.

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