EP0183682A2

EP0183682A2 - Method of compacting concrete

Info

Publication number: EP0183682A2
Application number: EP85890293A
Authority: EP
Inventors: Heikki Ilmari Kankkunen
Original assignee: Rakennusvalmiste Oy
Current assignee: Rakennusvalmiste Oy
Priority date: 1984-11-29
Filing date: 1985-11-28
Publication date: 1986-06-04
Also published as: EP0183682A3; NO854779L; FI844686A0; DK550085A; FI844686L; DK550085D0

Abstract

This publication describes a method for compacting a concrete mix (1) in a casting mould (2...6). In accordance with the invention, at least a part of the walls (2, 3, 4) of the mold (2...6) which are in contact with the concrete mix (1) are moved in such a synchronized, simultaneously reciprocative manner which, due to acceleration and deceleration forces, causes an internal compacting friction in the concrete mix (1). The method in accordance with the invention facilitates the fabrication of thinner constructions than previously and improves the compactness of concrete surfaces.

Description

The present invention relates to a method in accordance with the preamble of claim 1 for compacting concrete in a mold.
Methods for fabrication of concrete elements by using different types of molds are known in prior art. The molds are generally fabricated of steel, wood, concrete, or some'other stiff plate material. The molds are dimensioned to withstand the casting pressure during concrete pouring and compaction without appreciable deformation. In addition, the molds must be capable of being dismantled after the concrete has set. When the molds are assembled and stiffly supported, the casting proper can be started. The casting is generally carried out by loading concrete into the mold in small quantities by vibrating the mold simultaneously or by using separate vibrators for compaction. Filling the mold is continued by adding concrete in small quantities until the mold is filled up to the rim and the upper surface can be smoothed. Various vibrating methods are applied in prior art casting procedures, according to mold size, shape and concrete mix stiffness.
Common vibrators are of the high-frequency vibrating type, which are stiffly mounted to the mold and integrally transfer the vibration energy to the cast concrete. Especially with molds of light construction, another conventional method is to use a high-frequency vibrator rod which is transported or transferred according to the progress of the casting process to the point where compaction is desired.
Combinations of the aforementioned methods are also used in prior art. Equally well known is the procedure of applying a method known as shock compaction in horizontally cast elements to compact concrete by sharp blows at a low repetition rate.
However, all the aforementioned methods and equipment suffer from the following drawbacks: In all vibrating methods, which utilize high-frequency vibration, the process generates high-intensity acoustic noise that is difficult to attenuate or eliminate. Also in the shock method, the noise level is high due to the high impact energy. In addition, the transfer of vibration energy from the vibrators to the concrete mix requires extremely stiff mold constructions to allow the vibration energy to spread sufficiently far into the mix, or when using molds of light construction, several vibrators must be used. All these arrangements result in high vibration forces, heavy mold constructions, and simultaneously a low efficiency of energy utilization in compaction. Furthermore, the high acoustic noise level exceeds generally accepted limit values if no acoustic damping countermeasures are provided, leading to health hazards.
The aim of the invention is to overcome the drawbacks of prior art techniques and to present an entirely new method of concrete compaction.
The method according to the invention is based on effecting concrete compaction by internal shear in concrete, produced by acceleration or deceleration forces generated by the movement of mold walls.
More specifically, the method in accordance with the invention is characterized by what is stated in the characterizing part of claim 1.
The method offers appreciable advantages. The method is applicable for casting both fluid and stiff concretes. Moreover, the invention facilitates the fabrication of thinner constructions than those previously achieved. The compactness of concrete surfaces is also improved.
In the following, the invention will be examined in more detail by means of the exemplifying embodiments in accordance with the attached drawings.

Figure 1 shows one embodiment of the principle of the compaction method in accordance with the invention.
Figure 2 shows another embodiment of the principle of the compaction method in accordance with the invention.
Figure 3 shows an application of the method to a beam mold.
Figure 4 shows an application of the method to a wall-shaped element mold.
Figure 5 shows an application of the method to a battery type row mold.
Figure 6 shows an application of the method to a flat mold, open from the top.
Figures 7a...7e describe the trajectories of the mold movement.

In a vertical mold of Figure 1, the compaction of a concrete mix 1 is achieved by a simultaneous, synchronized reciprocating movement of both mold walls 2 and 3 in the vertical direction. This arrangement conveys in the concrete mix 1 a changing kinetic energy causing the concrete mix to be subjected to an internal shear action and leading to compaction under internal pressure. When the concrete mix is poured into the mold, due to several physical factors (surface tension, cohesion, or mold surface roughness), a static friction is generated between the mold surface and the concrete mix, opposing the gliding of the concrete mix along the mold surface. In this situation, under the shear imposed by the mold surfaces which are moving in an accelerating or decelerating manner, the concrete mix shears (with internal displacements) rather than glides in respect to the surface.
Under the influence of the internal shear, the concrete mix starts effectively compacting under the pressure of its own weight. When required, the pressure can be augmented by various feeding means. The preferable amplitude of mold wall shear movement depends to a great extent on the stiffness of the cast concrete and the thickness of the cast structure. The preferable amplitude for applications in conjunction with conventional molds is in the order of 0.5...30 mm. The preferable shear movement frequency also depends on the stiffness of the concrete mix and, consequently, on its internal friction, because the acceleration or deceleration of the movement of mold walls 2, 3 must be sufficient to overcome the internal friction of the concrete mix to generate internal shear and displacement in the concrete mix. The applicable frequency range for casting concrete elements of conventional construction is in the range of 2...2000 strokes/second, preferably 4...300 strokes/s (2...150 Hz).
Figure 1 shows in schematic form the displacement caused in the concrete mix by acceleration or deceleration on the plane of the mold wall.
Figure 2 shows the corresponding displacement when the mold is plane mold, open from the top and its bottom 7 constructed for reciprocating movement in the horizontal direction.
In the embodiment of Figure 3 the displacement shear action compaction method is applied to a conventional pillar or beam mold. In long molds the compaction can be achieved by simply providing a simultaneous synchronized reciprocating movement of mold walls 2, 3 and 8.
Respectively, Figure 4 shows a mold with walls in which a combined longitudinal and transversal movement in the mold surface plane is advantageously applied.
The row mold of the battery mold type in Figure 5 has mold walls 2, 3, and 4 connected at one end of each wall, respectively, via jointed bars 12 and associated bearings 11 to a camshaft-type actuator 9, which is permanently fixed by bearings 10. When the actuator 9 rotates, all adjacent mold walls 2, 3, 4 perform simultaneous parallel movements in the direction of the walls,.causing the desired shear action in the concrete mix 1.
Figure 6 shows a flat one-sided mold in which all trajectories described above can be applied separately or in combinations.
The trajectory shown in Figure 7a is aligned to lie entirely in the longitudinal direction of the mold surface.
Figure 7b shows a combined movement in the longitudinal and transverse direction, essentially improving the shear action.
Correspondingly, Figure 7c shows the trajectory only in the transverse direction of the mold surface.
Figure 7d shows a combined trajectory which forms an annular movement in the plane of the mold surface. The annular trajectory can also differ from a circle to create local maxima of acceleration or deceleration (Figure 7e).
The mold trajectory can also be configured to include combinations of the aforementioned trajectories so that impulse-like discontinuities of high acceleration are added to the trajectory to exceed the internal friction of the concrete mix at these discontinuities.
The mold surface can also be roughened to eliminate glide between the surface and the concrete mix.

Claims

1. A method for compacting a concrete mix (1) in a casting mold (2...8), characterized in that at least a part of the mold walls (2, 3, 7) which are in contact with the concrete mix (1) are brought to a simultaneous, synchronized reciprocating movement which, due to acceleration and deceleration forces; causes an internal displacement with compacting shear action in the concrete mix (1).

2. A method as claimed in claim 1,
characterized in that the reciprocating movement takes place in the longitudinal direction of the mold.

3. A method as claimed in claim 1,
characterized in that the reciprocating movement takes place in the transverse direction of the mold.

4. A method as claimed in claim 1,
characterized in that the reciprocating movement takes place as a combination of movements in the directions of the longitudinal and transverse axes of the mold.

5. A method as claimed in claim 1,
characterized in that the frequency of the reciprocating movement is 1...1000 Hz, preferably 2...150 Hz.

6. A method as claimed in claim 1,
characterized in that the inner surfaces of the mold parts (2, 3, 4, 7) are roughened to improve the effect of friction.

7. A method as claimed in claim 1,
characterized in that the adjacent walls (2, 3, 4) of the mold are moved reciprocatively.

8. A method as claimed in claim 1,
characterized in that the bottom (7) of the mold is moved reciprocatively.