GB2313145A - Slip forming - Google Patents

Abstract

A mobile slip forming machine comprises a hopper (15), a conforming chamber (19), a mould (17) and means to introduce at least one ligature such as a tensionable cable (27, 30) into the concrete mix (C) upstream of the mould (17). The machine is driven along track (13) at a rate that enables the concrete mix (C) to flow along conforming chamber (19) and through mould (17) with the cables (27, 30) being embedded in the drying concrete of structure (S). In order to enter the concrete mix (C), each cable (eg 27) is drawn off a storage drum (23), around a guide (28), before passing through wall (W) of the conforming chamber by way of a liquid seal (S1). Displacement of the concrete mix through the hopper (15) and conforming chamber (19) is facilitated by internal vibrators (VI - V3).

Description

SLIP FORMING This invention relates to slip forming. It is particularly concerned with the use of slip forming to produce an extended structure of concrete. A typical slip forming operation involves a production unit made up of a hopper for liquid concrete behind which is mounted a mould having an outlet cross section corresponding to the required section of the finished structure. The unit is driven forwardly on tracks or wheels while liquid concrete is fed into the hopper to flow downwardly and then out through the mould to be deposited in place as a continuous mass which is left to harden into the moulded structure. For as long as the unit moves forwardly and the hopper is supplied with concrete then the extended mass will continue to be formed on the path followed by the unit.

Slip forming is commonly used to form extended structure on motorways such as slot drains and crash barriers. The characteristics of the concrete supplied to the hopper is significant. The unhardened material must be capable of flow through the unit and out of the mould. However it must also provide for the generated slip formed section to be retained until the concrete has hardened to provide the finished monolithic profile.

It is known to incorporate structural members into a slip formed structure. These are rigid members of limited length say 5 to 12 metres. The introduction of such a member into a slip forming process raises operational, including quality control, problems. Being of limited length the members require the slip forming process to be periodically interrupted to enable a further member to be secured to one already substantially embedded in concrete. It has been found virtually impossible to ensure that such a structural member and more importantly a sequence of such members can be readily inserted into, or maintained in, a desired relative position within the still unhardened concrete mass. As a consequence it is not possible to guarantee the structural integrity of a structure incorporating rigid members without losing much of the benefits of continuous forming to be gained from the use of the slip forming process.

According to a first aspect of the present invention there is provided a slip forming process wherein a supply of flowable concrete is fed along a path from a hopper through a mould to provide for the generation downstream of the mould of a moulded structure of cross section established by the mould characterised by the introduction of at least one pre-tensioned ligature into the path upstream of the mould and providing for the or each ligature to pass through the mould incorporated in the moulded structure at a predetermined location relative to a mould datum.

According to a first preferred version of the first aspect of the present invention the, or at least one, ligature is a tensionable cable.

According to a second aspect of the present invention there is provided a slip forming machine comprising a mobile unit including a hopper, a mould having an inlet side linked to the hopper by a flow path upstream of the mould and an outlet side downstream of the mould, characterised in that the unit further incorporates at least one ligature storage means such as a drum, a ligature path extending from the storage means into the flow path upstream of the mould and then in the flow path through the mould and downstream thereof.

According to a first preferred version of the second aspect of the present invention the flow path between the hopper and the inlet side of the mould is defined at least in part by a wall member and the, or each, ligature path extends from the outside through the wall member into the flow path. Typically the, or each, ligature path extends through the wall member by way of a liquid sealing means.

According to a third aspect of the present invention there is provided an extended concrete structure including pre-stressed ligatures formed by the slip forming process of the first aspect of the first preferred version thereof.

According to a fourth aspect of the present invention there is provided an extended concrete structure including prestressed ligatures formed by means of slip forming machines according to the second aspect or any preferred version thereof.

An embodiment of the invention will now be described by way of example with reference to the accompanying line drawings of a slip forming unit and of pretensioned slip formed product produced thereby.

Figure 1 is a part sectioned side elevation of the unit; Figure 2 is a rear view of the unit of Figure 1 in direction of arrow II in Figure 1; Figure 3 is a front view of the unit of Figure 1 in direction of arrow III in Figure 1; Figures 4 and 5 are cross section of structures manufactured by means of the unit described in connection with Figures 1 to 3 of which Figure 4 is of a slot drain and Figure 5 is of a crash barrier.

FIGURES 1,2 AND 3 These show a slip forming unit 11 including a chassis 12 supported on tracks 13A, 13B (with corresponding tracks on the opposite side) by means of which the unit 11 can be propelled and steered along a desired path.

The chassis 11 supports a cab 14, a hopper 15 and a mould support 16 on to which is mounted a mould 17. The cab 14 serves as a control position for the direction of travel and for operation of the slip forming process.

The hopper 15 serves to store a wet concrete mix C. The lower section of the hopper 15 turns into the mould 17 by means of a conforming chamber 19. When required supplies of fresh concrete are periodically or continuously added to the mix C through open top 20 of the hopper 15. This serves to provide a driving head H for concrete mix 18 in the region of upstream side 21 of mould 17. Hopper 15 is provided with internal vibrators to provide for enhanced flow characteristics to mix 18 and compaction of the concrete mix which might otherwise be slowed by frictional resistance to flow of mix against the inside faces of the hopper 15 and conforming chamber 19.

The front of the hopper 15 serves to support a set of rope guides 23, 24, 25, 26 on each of which are wound continuous lengths of pre-tensioning cable of known type.

Cable on each drum is drawn off as will be described hereafter under a predetermined tension to provide for pre-tensioning of the structure formed by way of the mould 17. To this end cable 27 from drum 23 passes downwardly from the drum 23, around guide 28 and through the wall W of conforming chamber 19 by way of a seal S1 to enter the wet concrete mix 18 flowing along the conforming chamber 19 to and through the mould 17. The guide 28 is adjustable to provide for ready alignment of the cable 27 to ensure that the cable enters the concrete mix 18 so as to pass through the mould 17 at the correct position within to the formed product.

The cables 29, 30 and 31 from, respectively drums 24, 25, 26, are dealt with in a similar way to cable 27 from drum 23 having their own adjustable supports, respectively 29A, 30A, 31A.

The cross section of the structure S created by means of mould 17 in the unit 11 is shown in Figure 4. This is made up of a section 31 with a circular void 32 fed by way of slot 33 fed from inwardly sloping faces 34, 35. Locations A, B, C and D correspond to the positions in the cast product of, respectively, pre-tensioned cables 27, 29, 30 and 31 referred to earlier. The circular opening 32 is formed by means of an inflated tube T of plastics material in a known manner. The tube T is left in situ until the structure is stable and is then removed. The position and utilisation of the tube T are not described in any detail to avoid undue elaboration of the description of the present example of a unit.

For use the unit 11 is equipped with a mould 17 having an opening corresponding to the desired cross section shown in Figure 4. The unit 11 is then positioned at the starting position for the required structure which is to be fonned. Cables 27, 29, 30, 31 are drawn off their respective drums 23, 24, 25, 26 and led through seals (typically seal S1 for cable 27) in wall 29 and so into the conforming chamber 19. The cables 27, 28, 29, 30 are then passed through the mould 17 and out to an anchorage position A where they are secured on a layout corresponding to the required relative locations A, B, C, D shown in Figure 4. corresponding to the required location in the finished structure S.

Plastic tube T is located through the unit 11 and also anchored at position A to provide for the alignment of the circular opening 30 within the finished structure to serve as the drain culvert. The tube T is inflated to resist deformation by the flowing unhardened concrete mix having passed through mould 17.

Concrete mix C is then allowed to flow from hopper 15 down through conforming chamber 19 and out through mould 17. Displacement of concrete through the hopper 15 and the conforming chamber 19 is facilitated by internal vibrators V1 to V3. The unit 11 is then driven along the track of the required structure at a rate which enables concrete mix C in hopper 15 to flow downwardly along conforming chamber 19 and through mould 17 to deposit the structure S on the desired path. By feeding the cables 27, 29, 30, 31 into the mix as it flows through the mould 17 it has been found that an accurate alignment of the cables in the structure S is readily established and maintained. The concrete mix C is generated as a fairly dry mix so that having passed through the mould 17 the slip formed material hardens rapidly to maintain the finished form of the structure S without sagging or loss of shape.

The slip form process described can then be continued for as long as concrete mix is supplied and cables 27, 29, 30, 31 are available from their respective reels. In the event the one or more cables are near to running out then the unit 11 can be stopped and a fresh reel of cable added to replace each of the exhausted ones on the front of the hopper 15. The end of each fresh length of cable is secured to the end of each old embedded cable the new cable tensioned and the process of slip forming is then restarted.

The proposed slip forming process involving the use of pre-tensioned cable is capable of creating long lengths of structure measured in thousands of metres per day in which the pretensioned cables are accurately located in the structure. This contrasts with the existing methods using rigid members requiring joing at interveals of a few metres.

Figure 5 shows a crash barrier 50 which can be formed as a continuous structure in a similar way to that of the slot drain described in connection with Figure 4 by the use of an appropriate mould in place of mould 17 described earlier. The barrier 50 is made up of a concrete mass 51 having embedded in it five equi-spaced pre-tensioned cables 52 - 56. The manufacture of the crash barrier 50 is virtually identical, to that of forming the slot drain structure S described in connection with Figure 4. The main differences are that in this case the drums for the cable 52 - 56 are located on the front of the hopper and directed by supports to enter the hopper in a vertical line so as to pass through the mould embedded in drying concrete to form the required crash barrier structure. As before the structure dries around the pre-tensioned and aligned cables 52 - 56.

Apart from the structural benefit to be obtained from the use of pre-tensioned cables in a structure there is provided the further benefit that in the event the structure incorporating the cables is subject to impact damage then the cables which are intimately embedded in the concrete serve to anchor any broken pieces. In this way the broken pieces are prevented from being turned into projectiles . Such an anchoring characteristic is clearly of benefit in relating to crowded motorway or railway locations where a fast moving impacts with concrete structures involving substantial energy dissappation could lead to serious damage or injuries or both.

The provision by the invention of readily introducing pre-tensioned cables into a slip forming process provides for the creation of many types of structure without complicated setting up processes and with good quality control characteristics.

The example described above utilises reels of cable mounted on the front of the hooper with cable from them being drawn into the concrete mix in the conforming chamber by way of seals in the hopper wall. However as an alternative the reels of cable can be located elsewhere such as on chassis of the unit or a separate structure mounted thereon from where the cables are led upwardly above the open hopper before being directed dpwnwardly to enter the concrete mix through the open top of the hopper and down through the mix before being re-aligned by guides at the throat of the conforming chamber to pass through the mould in the correct relative alignment. By entering the cables through the open hopper the need for seals in the wall of the hopper is removed.

Claims (9)

1 A slip forming process wherein a supply of flowable concrete is fed along a path from a hopper through a mould to provide for the generation downstream of the mould of a moulded structure of cross section established by the mould characterised by the introduction of at least one pre-tensioned ligature into the path upstream of the mould and providing for the or each ligature to pass through the mould incorporated in the moulded structure at a predetermined location relative to a mould datum.

2 A slip forming process as claimed in Claim 1 wherein the, or at least one, ligature is a cable.

3 A slip forming machine comprising a mobile unit including a hopper, a mould having an inlet side linked to the hopper by a flow path upstream of the mould and an outlet side downstream of the mould, characterised in that the unit further incorporates at least one ligature storage means such as a drum, a ligature path extending from the storage means into the flow path upstream of the mould and then in the flow path through the mould and downstream thereof.

4 A slip forming machine as claimed in Claim 3 wherein the flow path between the hopper and the inlet side of the mould is defined at least in part by a wall member and the, or each, ligature path extends through the wall member.

5 A slip forming machine as claimed in Claim 4 wherein the, or each, ligature path extends through the wall member by way of a liquid sealing means.

6 An extended concrete structure including pre-stressed ligatures formed by the slip forming process of Claims 1 and 2.

7 An extended concrete structure including prestressed ligatures formed by means of the slip forming machines as claimed in Claims 3, 4 or 5.

8 A slip forming process as hereinbefore described with reference to the accompanying drawings.

9 A slip forming machine as hereinbefore described with reference to the accompanying drawings.