GB2382096A

GB2382096A - Debonding sheath for piles

Info

Publication number: GB2382096A
Application number: GB0128406A
Authority: GB
Inventors: Robert Arthur Merritt; Jimmy Elliott
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-27
Filing date: 2001-11-27
Publication date: 2003-05-21
Anticipated expiration: 2021-11-27
Also published as: GB0128406D0; GB2382096B

Abstract

A debonding sheath for use with reinforcing elements (13, 14) in concrete foundations, such as piles (10), has an upper section (16) formed from a plastic such as polyethylene and a lower portion (17) of polystyrene. In use, the sheath is placed around the reinforcing elements (13, 14) such that the junction (21) between the two materials is not below the plane (P) at which the pile reinforcing elements (13, 14) are cut. Once the element is cut, polystyrene (17) embedded in the concrete can be removed by heating or chemical solvents.

Description

Breaking/Dressing of Piles This invention relates to the breaking and/or dressing of reinforced concrete piles, diaphragm walls and barrette foundation elements, that is, the removal of the upper portion of such elements to a predetermined level to allow a superstructure to be built or erected thereon.

Foundation elements such as reinforced concrete piles and diaphragm walls providing ground support for a civil engineering structure are cast in holes or trenches pre-formed in the ground around a steel reinforcement framework or"cage"which is inserted in the hole or trench either before or after the concrete is poured. The upper ends of the cage members extend above the concrete for incorporation in the overlying structure to be supported. The upper region of the set concrete may be of inferior quality and strength, for example because it will contain mud or other debris from the bottom of the hole or trench and which "floats"on the surface of the concrete as it is poured, so it is necessary to remove the upper portion of the set concrete pile or diaphragm wall to an accurately-predetermined height to provide a full-strength support for the overlying structure at the required level. In this description and where appropriate, references to piles are to be understood as applying also to other foundation elements.

European Patent No. 0888481 describes one method for the breaking away and removing the upper portion of a reinforced concrete pile by treating the reinforcement which is to be within that portion of pile subsequently to be broken away so as to isolate it from the concrete cast around it, forming a transverse hole in the pile at the level where it is to be broken away and inserting oppositely-acting wedges within the hole so that, on forcing the wedges apart, they apply forces which act towards opposite ends of the pile to split the pile in a transverse plane. The upper portion may then be removed by lifting it away from the remainder of the pile, the isolation or"debonding"treatment enabling the upper portion to be thus separated from the reinforcement. The debonding material is typically polyethylene tubing, this material being sufficiently dense to withstand ingress of water and cement grout while being sufficiently flexible to withstand rough handling and to be compressed against the bars by tying wire ligatures to retain it in place.

In carrying out the method as described in said European Patent No. 0888481, the debonding material is either secured in position before the concrete is cast or, if the cage is inserted after the concrete is poured, is pre-applied to the upper parts of the reinforcement bars. However, this entails practical problems in that the actual position of lower end of the debonding material after placing the cage may not be precisely at the intended level,

with the result either that some debonding material remains in the body of the pile after removal of the upper portion or that the debonding material does not reach down to the intended level, this resulting in a pile break which is not clean and requires manual remedial work to make it flat at the required level. However, since polyethylene can be removed from set concrete only by laborious and time-consuming mechanical means, it has become the usual practice deliberately to apply the polyethylene"short", subsequent remedial work to render the pile flat being regarded as preferable to removal of polyethylene from set concrete.

The present invention provides means whereby the debonding material can be applied to the reinforcement cage with the lower end thereof at or below the intended level of removal of the upper part of the pile.

Accordingly, in one aspect the present invention provides debonding material for attachment to a reinforcement element in a concrete pile (as hereinbefore described) for isolating the element from concrete cast around it in a region of the pile subsequently to be removed, the debonding material comprising a sleeve member including a body portion formed from a foamed polyolefin plastics material having a lower (in use) end portion formed from a foamed polystyrene plastics material.

The polyolefin plastics material preferably comprises a polyethylene and the polyolefin body portion may be bonded to the polystyrene end portion to form a composite sleeve member. However, the respective portions may be merely assembled on the reinforcement element in juxtaposed relationship with suitable bonding to the reinforcement element.

The use of polystyrene for the end portion of the sleeve member of the present invention enables the sleeve member routinely to be placed with the lower end thereof in or slightly below the plane above which the upper region of the pile is to be removed, any polystyrene below the plane becoming embedded in and retained in the remaining lower part of the pile.

Any polystyrene thus retained can readily be removed, for example by chemical action or by application of heat, without damage or detriment to the integrity of the concrete of the pile.

It has been found that the polyolefin provides sufficient support to the polystyrene to enable it to withstand rough handling and, in particular, the pressures involved when the reinforcement cage with debonding material attached is urged downwardly through

previously-poured concrete to locate it in position in the wet concrete, provided that the polyolefin is adequately bonded or secured to the reinforcement bars.

The polystyrene cannot itself be secured to the reinforcement bars since it is brittle and cannot be compressed to provide a sufficiently tight union with the bars.

The length of the polystyrene lower portion will be variable depending on the dimensions of the sleeve overall but will typically be 300 mm in length.

The invention also provides in another aspect a reinforcement element for forming reinforced concrete, the element having applied thereto a debonding material comprising a sleeve member including a body portion formed from a foamed polyolefin plastics material having a lower (in use) portion formed from a foamed polystyrene plastics material.

In yet another aspect, the invention provides a method of breaking and/or dressing a reinforced concrete pile (as hereinbefore described) by removal of the upper portion above a predetermined transverse plane, the method comprising applying a debonding material to the reinforcement within that portion of pile to be removed, casting wet concrete to form the pile either before or after placing the reinforcement in position, allowing the concrete to set and removing the upper portion of the pile above said plane to leave exposed corresponding portions of the reinforcement, in which the debonding material comprises a sleeve member having a body portion formed from a foamed polyolefin plastics material having an end portion comprising a foamed polystyrene plastics material, the sleeve member being disposed on the reinforcement such that the end portion is lowermost and the predetermined plane lies within the longitudinal extent of the end portion.

The removal of the upper portion of the pile may entail the use of oppositely-acting wedges as described in European Patent No. 0888481 or by other means, such as by the use of a hydraulically-powered clamping collar with appropriate inwardly-directed tooth elements.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawing which is a longitudinal section through a concrete pile before removal of the head portion. The drawing shows a concrete pile 10 embedded in the ground 12. The pile has a steel reinforcement cage comprising rods 13,14. The pile has a lower end 11 and an upper or head portion 15 which is to be removed above a plane P. As illustrated, concrete has been cast, the cage has been inserted from above through the wet concrete and the concrete has hardened. The head is now ready to be removed, for example by carrying out the method as described in European Patent No. 0888481, once

the ground has been excavated around the pile down to just below plane P. In order to carry out the head removal method, the upper ends of the cage rods 13,14 are sheathed in debonding sleeves each consisting of a foamed polyethylene upper part 16 and a lower polystyrene part 17. The upper parts are securely attached to the rods by ligatures 18,19, the positioning of the sleeves being such that, after placing the cage and allowing for slight settlement, the lower end 20 of the sleeve is at or below plane P, provided that the junction 21 between the polyethylene and polystyrene is not below plane P. As illustrated, the lower ends of the sleeves are slightly below plane P.

In removing the upper or head portion 15 of the pile, a transverse passageway is formed at the level of plane P and oppositely-acting wedges are inserted to fracture the concrete cleanly in plane P. Alternatively, a hydraulically-acting collar may be used. The head portion can be bodily removed off the cage rods 13,14 using a crane, the debonding material acting as a dry lubricant between the concrete and rods. The lower most end regions of the parts 17 will be retained, embedded in the concrete of the portion of pile remaining in place, and can be removed either by application of heat or by chemical solvents without damaging the integrity of the concrete.

Because the polystyrene material of the lower part can be relatively easily removed, compared with polyethylene, the site engineer can with confidence locate the sleeving to ensure that it extends downwards at least as far as the plane in which the head portion of the pile is to be broken away, thus ensuring that the break is clean with no or minimum subsequent manual work being required to achieve a sufficiently flat upper end to the pile for subsequent construction work.

Claims

Claims 1. Debonding material for attachment to a reinforcement element in a concrete foundation element, for isolating the reinforcement element from concrete cast around it in a region of the foundation element subsequently to be removed, the debonding material comprising a sleeve member including a body portion formed from a foamed polyolefin plastics material having a lower end portion formed from a foamed polystyrene plastics material.
2. Debonding material according to claim 1, in which the polyolefin plastics material comprises a polyethylene.
3. Debonding material according to claim I or claim 2, in which the polyolefin body portion is bonded to the polystyrene end portion to form a composite sleeve member.
4. Debonding material according to any preceding claim, in which the foundation element comprises a concrete pile.
5. A reinforcement element for forming a reinforced concrete foundation element, the reinforcement element having applied thereto a debonding material comprising a sleeve member including a body portion formed from a foamed polyolefin plastics material having a lower portion formed from a foamed polystyrene plastics material.
6. A reinforcement element according to claim 5, in which the polyolefin plastics material comprises a polyethylene.
7. A method of breaking and/or dressing a reinforced concrete foundation element, by removal of the upper portion above a predetermined transverse plane, the method comprising applying a debonding material to the reinforcement which will be within that portion of pile to be removed, casting wet concrete to form the foundation element either before or after placing the reinforcement in position, allowing the concrete to set and removing the upper portion of the foundation element above said plane to expose portions of the reinforcement, in which the debonding material comprises a sleeve member having a body portion formed from a foamed polyolefin plastics material having an end portion comprising a foamed polystyrene plastics material, the sleeve member being disposed on the reinforcement such that the end portion is lowermost and the predetermined plane lies within the longitudinal extent of the end portion.
8. A method according to claim 7, in which the foundation element comprises a concrete pile.

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9. A concrete foundation element when formed and broken or dressed according to the method of claim 8.
10. A method of breaking and/or dressing a reinforced concrete foundation element, substantially as herein described with reference to the drawing.