US3452406A - Forming concrete articles - Google Patents

Description

July 1, 1969 J. G. 0. MORGAN FORMING CONCRETE ARTICLES Filed Feb. 25, 1966 FIGZ United States Patent C FORMING CONCRETE ARTICLES John Guy David Morgan, London, England, assignor to Blaw Knox Limited, Kent, England, a British company Filed Feb. 25, 1966, Ser. No. 530,136

Claims priority, application Great Britain, Mar. 2, 1965, 8,969/65; Aug. 12, 1965, 34,580/65 Int. Cl. B28b 3/20 US. Cl. 25-11 1 Claim ABSTRACT OF THE DISCLOSURE An apparatus for forming concrete articles includes a forming means which can be moved relative to a base to cause concrete to flow onto the base and to be compacted simultaneously with the formation of the article. The forming means includes a plate and a curved member spaced from each other to define a streamline fiow path for concrete through the forming means. The curved member is adjustable along the axis of symmetry of a hyperbola defining the streamline flow of concrete through the forming means.

This invention relates to an apparatus for forming concrete articles having a uniform cross-section or, in the casewhere a strip of concrete having a uniform upper surface is laid on an uneven base, a uniform partial crosssection.

Existing apparatus for forming concrete articles of this nature are pavers for laying concrete on the ground to form road pavements, aerodrome runways and the like. The object of this apparatus is to place or spread the uncompacted concrete in the correct place or position on the ground and compact it to the correct cross section to provide a smoothly finished and dense article.

Present methods involve providing an excess of uncompacted concrete to the machine, the surplus being struck off and recirculated. The level of strike off must be closely controlled, in order to achieve an accurate finished surface. This is difiicult to achieve on account of density variations in the concrete. By the use of a deep surcharge which provides a hydrostatic pressure in the concrete, the concrete may be extruded rendering an improvement in finished surface. However such extrusion processes as are at present employed require a great deal of force and power for their execution, both to achieve extrusion and compaction. The present inventor considers that the process could be made considerably more efiicient by the use of a flow forming process, wherein the power required might be drastically reduced and more eflicient compaction achieved, without there being any need for a strike ofi of the uncompacted concrete or a recirculation of material.

The importance of compaction cannot be over-emphasised. Concrete prior to compaction may contain a fractional voidage of up to 25% by volume. Concrete containing a voidage of develops only 50% of its possible strength, and its durability in the face of adverse weather conditions is much reduced. As a requirement therefore, concrete laying machinery for use in public works must lay concrete having a fractional voidage at the surface of less than 2%.

In present machinery the compaction is mainly carried out by vibration, applied either at the surface by means of a vibrating beam or screed, or internally by means of immersed tubular vibrators.

Whilst the compaction requirements may be achieved by this method at the surface, in a deep slab it becomes progressively more difiicult to achieve compaction in the lower layers whilst maintaining a reasonable forward speed of travel.

In the apparatus according to the present invention compaction is achieved during the form of the concrete article and also in distinction to the method of operation employed in existing machines, spreading, recirculation and strike off are eliminated. The flow of concrete is thus controlled before it reaches the base on which it is being laid. Also compaction at all layers is greatly assisted by the flow patterns of the concrete.

Accordingly the present invention provides a process of forming a concrete article, wherein the concrete, being an aggregate suspension in a cement paste matrix, is passed under hydrostatic pressure onto a base, via a passage the shape of which allows substantially irrotational flow in the concrete and wherein the compaction of the concrete is effected simultaneously with the formation of the concrete article.

The necessary formation and compaction of the concrete laid by the apparatus according to the present invention is achieved by provision of suitably shaped forming or guide surfaces which ensure the desired conditions of flow. This is essentially an irrotational motion of the concrete.

The principle of irrotational flow is best explained by consider-ing the motion of an infinitesimally small cube of a fluid as the motion proceeds. In general the shape of the cube will change in a way which may or may not entail a mean rotation of the cube relative to its original position. If there is no such mean rotation, then the motion is said to be irrotational.

In FIGURE 1 the deformation of a rectangle of fluid, being a cross-section of a cube when the flow is two dimensional only, i.e., is parallel to a plane, is considered when the rectangle is following streamlines of flow around a corner. It will be seen that the shape of the rectangle is changed from one having a major vertical axis, through a square where it is opposite the corner to a rectangle having a horizontal major axis.

If the rectangle is considered to represent a block of cement paste containing irregular particles of aggregate it will be realised that, as the block follows a path of streamline flow, the following conditions will ensue.

Since the solid irregular particles cannot deform in the same manner as the cement paste, relative movement of the cement paste over the surface of the particles must take place leading to a release of the trapped air.

As the solid particles do not rotate to any great extent in this condition of flow, the energy required to produce this release of voidage is not so great as is required by other methods of compaction such as vibration applied at the surface or within the body of the concrete which rely on a different mechanism to achieve compaction, although vibrators are included in the embodiment of the present invention, their purpose is to retain the concrete in a fluid state for the purpose of flow forming rather than for direct air removal.

Thus compaction is achieved by applying the maximum amount of pure shear strain to the cement paste during its passage, but not in an amount or at a rate such that the cement paste is caused to fail.

Accordingly the present invention provides an apparatus for forming by a flow process concrete articles comprising forming and compacting means having an exit cross-section of the article to be formed, having an entry cross-section of an area larger than that of the exit cross-section and having sides defining a passage between the entry and exit cross-sections, which sides allow the concrete to pass through the passage in such a way that it flows in a substantially irrotational manner, whereby compaction of the concrete is achieved.

Preferably the apparatus additionally comprises one or more vibrators for vibrating the concrete in the compacting and forming means, and where the apparatus includes supply means such for example as a hopper vibrators may also be placed in such supply means. Vibrators preferably curved with the streamline may with advantage be placed in the passage and an external vibrator above and in contact with the upper forming means.

As mentioned above, the finite size of the aggregate particles contained in the cement paste matrix will prevent the flow from being purely irrotational. Nevertheless by the use of the apparatus according to the present invention, rotation is reduced to a minimum.

A particularly favourable flow forming condition has been found to be achieved when the forming means include, having regard to the intended direction of travel of the apparatus, a front surface, e.g., a front plate, which is steep and substantially straight, as indicated in FIGURE 2. The streamlines of flow in relation to an origin on the base, displaced a short distance opposite the direction of travel from the point of intersection of the plate and base, are hyperbolic curves.

The front forming plate could equally be inclined backwards to the direction of travel to form an acute angle, or the plate may be at right angles to the base.

The upper side or boundary wall of the passage and any other surfaces in the flow path such as vibrating vanes should with advantage be curved in accordance with the hyperbolic streamlines of flow in order that the conditions of flow given earlier may be achieved.

In order to accommodate undulations in the base on which the concrete strip is being laid and to ensure that the upper surface of the concrete remains at a chosen level it is desirable that the upper side or boundary of the passage should be adjustable relative to the other side of the passage.

Preferably the concrete is vibrated during its passage and adjustments to the nonbasal cross-section of the formed article is achieved by altering the quantity of rotational flow in the boundary layer adjacent to the upper side or boundary wall of the passage.

Accordingly assuming that the upper side or boundary of the passage is in the form of a plate then the position of such upper forming plate will be adjustable, and means will be provided for altering the position of said upper forming plate relative to the front forming plate. However, this adjustment must be performed in a manner such that there must not be any substantial deviations from the flow conditions given earlier.

In the particularly favourable flow forming condition already described, the condition is achieved by shaping the upper forming plate such that it conforms to the flow streamlines at its mean position, and substantially maintains the correct geometry by moving in the direction of the axis of the hyperbola,

In order to achieve accuracy of finished level an extrusion plate should be mounted to the rear of the top forming plate, as this will prevent concrete rising up behind the top forming plate in a surface Wave.

In order that the invention may be more clearly understood a preferred embodiment thereof will now be described, by way of example only, with reference to FIG- URE 2 of the accompanying drawings which shows diagrammatically in elevation an apparatus according to the present invention for forming a concrete strip.

The apparatus illustrated in FIGURE 2 and designated generally by the reference numeral 1 is adapted to stand on and to be moved forwardly (i.e., to the left as seen in the drawing) along a base 2 on which a strip of concrete is to be laid. The apparatus comprises forming means indicated generally by the reference numeral 3 such means consisting essentially of a plate 4 which is inclined forwardly in the directions of travel of the apparatus and has a curved lower border 5 the bottom edge of which rests on the base 2. The lateral edges of the plate 4 are joined to the leading edges of a pair of side plates 7 which latter are disposed in spaced parallel relation, the width of the plate 4 and the spacing of the sides 7 determining the width of the strip of concrete which will be laid. 9 denotes a hopper which is formed in the following manner: the leading end portions of the sides 7 are extended upwardly and outwardly to form hopper sides 10 while the plate 4 is extended upwardly to form a front wall 12, the rear wall of the hopper being formed by a backplate 13 which is joined between the hopper sides 10.

As will be seen the plate 4 and the two sides 7 define in conjunction with the base 2 a passage 14 which is closed at its upper sides by a curved member designated generally by 15 extending between the two sides 7. To ensure the desired flow the curved member 15 will be of the form hereinbefore described. The curved member 15 which is capable of movement relatively to the sides 7 to vary the dimensions of the passage 14 consists of upper and lower end portions 16 and 17 and a floating central section 18 which is resiliently attached to the upper and lower end portions 16 and 17 through the medium of rubber buffers 21 and 22. 20 denotes a vibrator device which is associated with the floating section. It will be appreciated that the entry cross-section of the passage 14 at its junction with the bottom of the hopper 9 is defined by the plate 4, the sides 7 and the upper end portion 16 of the curved member 15 while the exit cross section is defined by the trailing vertical edges of the sides 7, the horizontal trailing edge of the lower end portion 17 and the base 2.

A supporting bracket 23 is positioned above the curved member 15 such bracket being supported at its ends on the sides 7. A tie-bar 24 is fixed at its opposite ends to the upper and loWer end portions 16 and 17 respectively of said curved member. The tie-bar 24 carries two guide rods 25, 26 which pas slidably through appropriate apertures in the bracket 23. Movement of the tie-bar 24 relative to the bracket 23 and hence adjustment of the curved member 15 is effected by means of a screw 27. Clearly instead of such an adjusting screw it would be feasible to employ a fluid operated ram or some other appropriate device for effecting adjustment of the member 15.

Two vibrators 30 and 31 are positioned in the passage 14 while in the embodiment illustrated there is attached to the lower portion of the plate 4 a cable 32 which leads to a winch 33 whereby the apparatus may be drawn forwardly over or along the base 2, Instead of employing a winch and cable for effecting movement of the apparatus the latter may be so constructed as to be capable of being attached to a tractor and in such a case it may then be desirable to provide the apparatus with supporting wheels or the like. Again it may be feasible to mount the apparatus on wheels or tracks and to incorporated drive means so that it (the apparatus) will constitute a self-propelled unit.

When it is desired to lay a strip of concrete, a dry concrete mix consisting for example of four parts of coarse aggregate to two parts of sand to one part of cement 1s fed into the hopper 9 and the vibrators 30, 31 and 20 are set in operation. When the concrete has shaken down in the passage 14 and the hopper 9 replenished, the apparatus is caused to move forwardly over the base 2. In the embodiment illustrated this forward movement will be effected on operation of the winch 33 but as indicated above the apparatus may be moved by a tractor. As the apparatus is drawn over the base 2 a strip of concrete will be left behind, having a smooth finish and having been compacted inside the apparatus sufficiently for a man to walk on it immediately afterwards. In order for a continuous strip to be laid the hopper 9 must be replenished as necessary. Any necessary minor adjustments to the height or depth of the strip can be effected by appropriate manipulation of the screw 27 or of the hydraulic ram or other means which may be employed for effecting adjustment of the tie-bar 24 and hence of the curved member 15.

The very effective compaction of the concrete forming the strip issuing from the tail end of the apparatus is achieved because the configuration of the passage 14 allows the concrete mix to flow in a manner which is substantially irrotational and in which the stresses in the material are at a minimum. The qualification substantially is used because of the size of the particles of aggregate. Since different parts of particles of aggregate will be following slightly different streamlines of flow, some turning movement will be necessarily imparted to each particle and it is therefore inaccurate to speak of the flow of concrete mix in the passage as being completely irrotational. It may be pointed out here that in the performance of the invention the concrete will be compacted throughout the whole of its cross-section as it is fed through the passage 14. Furthermore the gravitational force developed by the vertical feeding of the concrete to the passage will be utilised to assist in the compaction in the general forming and shaping of the concrete mixture in the passage.

The shape of the vibrators 30, 31 is chosen to conform as closely as possible with the streamlines of flow in the passage 14. A straight vibrator by cutting across the curved streamline of flow and, therefore, possessing a considerable effective cross-sectional area would cause a disturbance in the flow of the concrete mix.

Possibly instead of employing vibrators such as are indicated at 30, 31 it may be feasible to employ one or more vibrators in the passage 14 which are curved in accordance with the requisite flow conditions, the or eachsuch vibrator being supported on an actuating arm projecting through a slot in the front plate 4 or being associated with the floating section 18 and vibrated therefrom.

I claim: 1. Apparatus for forming concrete articles onto a base comprising:

forming means adapted to be moved relative to the base for feeding and compacting a flow of concrete onto the base, said forming means having a passageway defining a streamline path of flow for concrete, said passageway being defined by (a) a plate means which extends transversely to the intended direction of movement of the forming means relative to the base, (b) side members joined to lateral edges of said plate means and extending rearwardly therefrom in parallel spaced relation, and (c) a curved member defining an upper boundary of the passageway through the forming means, said passageway further having an exit cross-section corresponding to the desired crosssection of the article to be formed, and an entry cross-section of an area larger than the area of the exit cross-section, and said curved member having a cross-section in the form of a hyperbola, and including an adjustment means which moves at least a portion of the curved member along the axis of symmetry of the hyperbola defined by the shape of the curve of said curved member, and (d) at least one vibrator means, substantially conforming in shape to the streamline path of flow, positioned in said passageway.

References Cited UNITED STATES PATENTS 166,104 7/1875 Holfhein 25-32 X 1,292,250 1/1919 Carr 2532 2,225,015 12/1940 Lebelle 25- 41 X 3,145,444 8/1964 Brown et al. 2541 X 3,176,371 4/1965 Patchen 26470 X 3,200,177 8/ 1965 Dodd 26470 3,274,906 9/1966 Worson et al.

3,281,903 11/1966 Ross 16428l X J. SPENCER OVERHOLSER, Primary Examiner.

R. D. BALDWIN, Assistant Examiner.

US. Cl. X.R.

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