Method for manufacturing shotcrete structures using a material having high impact resistance and optimum deformation properties

© Start of patent duration: Longest possible duration:

© Issued on:

© inventor:

1977 01 15

1977 10 10

SANDELL BERTIL IN HOVÄS (SWEDEN)

GOTH IN VÄXJÖ (SWEDEN).

LILJEGREN © Dependence:

OE 339194 © Pamphlets considered as delimiting from the state of the art:

DT-OS2337129, FR-PS2170403, US-PS2604068, US-PS 2910250, US-PS 3812749 - 2 -

Nr.339194

The invention relates to a device for the production of Betonstrufcturen means of a spray nozzle, wherein the concrete mixture crushed fiber or rod-shaped reinforcing material is added. Concrete structures produced in this way are characterized by high impact resistance and favorable deformation properties (low shrinkage and creep tendency, reduced cracking and improved crack distribution).

Attempts have already been made to reinforce concrete with fibers. It is essential to the orientation and arrangement of the fibers in the concrete. The various mixing methods developed for this purpose have not proven successful in practice, since the orientation and position of the fibers, ie their uniform distribution in the concrete, causes great difficulties. The fibers are here reverberated into larger units, which are reflected by their weight on the base layer of the structure. The mixing of fiber concrete is complicated by the fact that the result depends on the type of the amount, as well as length and thickness of the fibers of the fiber material used.

Attempts of admixture of fibers to concrete have shown that remarkably improved properties of the concrete can be achieved if the orientation and distribution of the fibers can be controlled.

The invention is therefore based on the object to provide a device for adding fibers into the concrete mixture, in which the balling of the fibers in the concrete mixture can be prevented. This is inventively achieved in that in the spray nozzle for the concrete mixture tangentially opens a line through which the fiber or rod-shaped reinforcing material is supplied by air.

It is already known from French Pat. No. 2,170,403 to mix two streams of material shortly before they hit one another on a base by crossing the streams. However, following this suggestion, to introduce steel fibers to a concrete stream, one encounters insuperable difficulties. The concrete mass must namely be transported with plenty of excess air (about 7 m³ / min at a rate of 20 to 801 / min), meaning that the fiber stream is deflected and the fibers do not mix with the concrete mass. If you try to transport the steel fibers with the same pressure as the concrete mass, the spraying process is no longer economical. In addition, it is deflected without a mixture between fibers and concrete mass, the concrete beam.

It was not until the knowledge that the fibers were forced to feed the concrete in the spray nozzle that it was possible, on the one hand, to prevent the balling effect of the fibers and, on the other hand, to obtain an absolutely uniform distribution of the fibers in the concrete stream, without the material stream escaping is derived, slowed down or otherwise obstructed, which is very important because it is very important in the application of shotcrete, that the concrete mass is applied perpendicular to the treatment surface.

Such fiber-reinforced concrete can be used to advantage when reinforcing ceilings and walls of tunnels, sewers, pipes, thin-walled shell structures, etc. An improved energy absorption capacity is obtained in these application areas, ie the impact resistance increases, as does the strength. The fibrous material, which should have high tensile strength and high coefficient of elasticity, can be used to advantage when producing tubes or molds which are to be a permanent part of the structure, etc. If not required, the tensile strength of the manufactured elements is particularly suitable polypropylene fibers can be used to advantage, resulting in greatly improved impact resistance. Other types of fibrous materials may also be used, for example natural or synthetic textile fibers.

In summary, it can be said that the main advantages of the fiber reinforced concrete are the increased energy absorbency and the improved integrity after cracking.

The invention will be explained in more detail with reference to an embodiment shown in the drawings. 1 shows a device according to the invention in which the reinforcing agent still has to be comminuted, and FIG. 2 shows a partial section of another device in which already comminuted reinforcing material is used to produce the concrete structure.

The spray nozzle -10-, shown schematically in FIG. 1, may be a nozzle known in the art except for the connecting sleeve -11-. Through a flexible pipe -12- or line is a mixture of a binder cement, lime, gypsum or the like. and aggregates, for example sand, by means of an air stream to the nozzle -10-, the home-annular passage -14- is mixed in the nozzle -10- through the connector --- 13- coming water.

The reinforcing material -15-, which may, for example, be wound around a cylinder or exposed, is directed to a cutting device -16-, where it is cut to a suitable length. The shredded fibers may be up to about 50 mm in length.

In Fig.l one type of cutting device is shown, in which the band or thread-like material is unwound from a storage cylinder by means of rollers. From here it is guided to a rotor, which is provided along its circumference with cutting teeth. By varying the speed of the rotor, the number and arrangement of the cutting teeth or the speed of the rollers, it is possible to vary the length of the portions of the reinforcing material as desired. In addition, the cutting teeth act as fan blades carrying the shredded reinforcing material to a supply port in a flexible conduit

-3No.339194 -17- move. This line connects the sleeve -11- of the nozzle -10- with a

Connector -18-. The end of an inlet tube 19, which can be connected to a compressed air source, extends into the connecting piece 18 or, if appropriate, also into the flexible line 17. The end is inserted so far that when compressed air is introduced through the inlet tube -9-, the reduced reinforcing material in the conduit - 17 - sucked by ejector action and in the

Concrete in the nozzle -10- is introduced by the air flow. The amount of fiber material in the concrete can be varied, and the content of fibrous material can be up to several percent by volume.

In experiments, it has been found that when using a spraying device of the type described above, such a distribution of the fibers is obtained that the individual fibers come to lie in planes which are substantially parallel to the surface or a frame or the like. on which the concrete is sprayed, whereby a high impact resistance is achieved.

The reference numeral -11'- indicates a different position for the sleeve for introducing the reinforcing material. The sleeve -11'- is arranged such that the reinforcing material is added to the mixture of, for example, cement and aggregates before water is added. This can be done because the mixture carried in the flexible tube 12 is carried by a stream of air and so can not form a solid column in the tube 12.

In cases where already comminuted reinforcing material is to be used, a vibrating and orienting device of the type schematically shown in Fig. 2 may be used instead of the cutting device of Fig. 1. In the apparatus of Figure 2, the reinforcing material, which may be formed in the present case of steel wire sections of appropriate length, placed in a funnel-shaped container, wherein the container or a part of the container is vibrated, so that the wire pieces on a get inclined plate on which they are aligned in the direction of an opening, which is formed by a connecting piece. The wire pieces are brought into the concrete spray nozzle via a flexible tube in the same manner as already explained above.

Since the comminuted reinforcing material will be aligned parallel to the surface to be sprayed using the device according to the invention, this is particularly suitable for the production of thin concrete components, which receive high impact resistance as a result of this orientation.