EP0018491A2 - Fibrous reinforcement for cement or bitumen bonded building elements and coverings - Google Patents

Abstract

The reinforcement is intended to achieve an improved fine crack distribution and higher strength of the reinforced component by preventing individual fibers from clumping together and achieving an even distribution of the same even over the cross section of the component. The individual fibers are fed into the mixing machine together with a fiber network and the additives. Before being introduced, the fiber net has a gathered, cord-like shape and distributes itself during mixing. Fibers of different lengths and made of different materials are used. The relation quantities with regard to the fiber length and with respect to the elastic modulus of the fibers are selected in such a way that they follow the law that is given by the sieve curve with regard to the grain sizes of the aggregates in order to produce the optimal relative grain size distribution in the concrete.

Description

The invention relates to a fibrous reinforcement for cement and bitumen-bound components and coverings.

The use of fibers for the reinforcement and reinforcement of materials, the so-called fiber reinforcement, is generally known. The following fibers, in general, in the form of monofilament fibers, are currently considered to be particularly useful 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 even distribution of the same across 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 thereof. In this way, their dosage is selected to be relatively high in cross-section and the application techniques, e.g. Pouring in, probably feasible under laboratory conditions, but very complex and in practice difficult, if at all, feasible. As a result, economically viable solutions with regard to fiber reinforcement are extremely limited.

The invention seeks to remedy this. For this purpose, the fibrous reinforcement is selected such that at least two different groups of fiber structures are present, at least one of which is in the form of a closed fiber network, the fibers of which are resilient and have a gathered shape in the state before being introduced into the mix.

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. The reinforcement elements are evenly distributed over the cross-section of the reinforced component. Aggregations do not occur.

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

• Fig. 1 ein Bewehrungselement in Form eines Kunststofffasernetzes,
• 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. 5 ein Diagramm der Verteilung des prozentualen Anteils verschiedener Bewehrungsfasern bezogen auf der E-Modul.

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. 5 is 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 reinforcement, e.g. of the concrete is that in practice it is hardly economically feasible to achieve a uniform distribution of the same across the cross-section of the component to be reinforced, in order to produce, among other things, uniform crack formation. 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. different specific weights, either sink to the bottom of a body that has just been cast, or float on the surface at the top.

In order to distribute these reinforcement elements consisting of individual fibers evenly over the cross-section, According to the concept of the invention, they are first used 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. These fiber nets added to the mix now also tend to stick to one another, in particular due to the mixing, for example due to the static charging thereof, such that no uniform distribution in the concrete would occur. However, because the fine polypropylene fibers are resilient, for example all the second fibers 2 act as springs which keep the first fibers 1 apart 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 aggregation of the fiber network during and immediately after mixing. 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.

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 mix into the concrete mixing machine and the mixing is then carried out carried out in the usual manner and during the standardized period. 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 time in the production of concrete is standardized. Therefore, the number of turns of the cord piece in order to obtain a three-dimensional network after mixing can be precisely determined. 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 evenly distributed over the cross-section of the reinforced component, since ultimately the crack formation, the crack pattern, must be uniform.

Such a uniform distribution can now be achieved when using such self-distributing mesh-shaped reinforcement elements, this together, ie in combination with other known fibrous reinforcement elements in the form of individual fibers such as 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 mesh reinforcement element, whereby 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 individual 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 of 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 . Thus, the steel fibers caused the bending tensile strength to be improved by approximately 36 kp / cm ² . Another concrete test specimen was produced, in which a calculated optimal amount of 1 kg of the reticulated polypropylene fiber reinforcement of a plastic reticulated concrete test specimen of approximately 36 kp / cm ^{2 was} measured. So the improvement in bending tensile strength was 4 kp / cm ² .

The use of plastic nets together with steel fibers This would result in an arithmetical improvement in the bending tensile strength of 36 + 4 = 40 kp / cm ² , so a concrete test piece with both reinforcements would have a bending tensile strength of 32 + 40 = 72 kp / _cm ² .

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 piece was now produced, which was reinforced with 144 kg of the above steel fibers and with 1 kg of the fiber nets, and then the bending 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 ² . These test results, along with other measured data, are shown in the table below:

This table shows that the actual data of the concrete determined in the tests, which is reinforced with the different fibers mentioned, surprisingly deviates from the calculations 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 , whereby the proportions of the different fibers mentioned have 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 aforementioned 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.

As is known, the aggregates for the production of concrete have to follow certain rules, among other things, with regard to grain sizes. In particular, the curve the grain structure of the aggregates, ie the so-called sieve curve, lie within predetermined limits and demonstrate a predetermined course, as is defined, for example, in Switzerland in Art. 2.02 of the SIA standards, which sieve curve also follows the DIN standard l045 with regard to the Aggregates for concrete corresponds.

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, ie 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 conditions 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 identical to the sieve curve S in FIG. 3, can be called 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 plypropylene 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 the respective fiber lengths 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 in accordance with the above (but 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. 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. The diagram in FIG. 5 shows that an optimal distribution of the quantities 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 modulus of elasticity according to curve U of FIG. 5. This means that for optimal reinforcement, predetermined proportions of fibers are selected with regard to fiber length and modulus of elasticity of the different materials.

Because there is always at least one closed fiber network that 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 have 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 (e.g. in the case of plastic fibers) dividing or cutting a film, so that either the closed fiber network, open fiber networks or individual fibers are produced, or (e.g. in the case of steel fibers or glass fibers), continuously produced wires are cut. As is already known with 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 with different materials. All these cord-like structures are then twisted together again, so that a thicker cord made of the most varied reinforcement materials is present, which cord is then finally cut into individual pieces. will cut. 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 in such a way 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 reinforcement fibers are introduced into the concrete stream, likewise in a known manner by means of a jet pump arrangement. The uniform distribution of the individual fibers is also ensured here because the fiber networks prevent the individual fibers from clumping, sinking or rising.

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

Claims (14)

1. Fibrous reinforcement for cement and bitumen-bonded components and coverings, characterized in that at least two different groups of fiber structures are present, at least one of which has the shape of a closed fiber network, the fibers of which are resilient and have a gathered shape before being introduced into the mix . 2. Fibrous reinforcement according to claim 1, characterized in that two different groups of fiber structures have the shape of a closed fiber network with resilient fibers, the length of the fibers of one group being different from that of the other group. 3. Fibrous reinforcement according to claim 1, characterized in that the fiber structures have different fiber lengths. 4. Fibrous reinforcement according to claim 1, characterized in that the fiber structure is in the form of a closed fiber network made of plastic. 5. Fibrous reinforcement according to claim 1, characterized in that the plastic is polypropylene. 6. Fibrous reinforcement according to claim 1, characterized in that two different groups _F asergebil- de are present, of which the first group has the shape of the closed fiber network with resilient fibers and the second group contains steel fibers. 7. Fibrous reinforcement according to claim 1, characterized in that at least three different groups of fiber structures are present, of which the first group has the shape of the closed fiber network with resilient fibers, and of the other groups at least two fibers each made of the same material but different lengths and / or contain shapes. 8. Fibrous reinforcement according to claim 1, characterized in that more than two different groups of fibers made of different materials are present. 9. Fibrous reinforcement according to claim 8, characterized in that the more than two different groups have glass fibers and / or steel fibers and / or plastic fibers and / or natural fibers. 10. Fibrous reinforcement according to claim 1, characterized in that all groups of fiber structures are connected to one another before being introduced into the mix. ll. Fibrous reinforcement according to claim 10, characterized in that the groups are mechanically connected to one another. 12. Fibrous reinforcement according to claim 11, characterized in that the groups are twisted together. 13. Fibrous reinforcement according to claim 3, characterized in that the distribution of the percentages of the groups of fiber structures of different fiber lengths are equal to the distribution of the percentages of the aggregates used of different grain sizes. 14. Fibrous reinforcement according to claim 1, characterized in that the fiber structures have different elasticity modules, and that the distribution of the percentages of the groups of fiber structures with different elasticity modulus equal to the distribution of the percentages actual proportions of the aggregates used are of different grain sizes.

Images