WO1990008635A1

WO1990008635A1 - Process for the production of a concrete post, and concrete pile obtained

Info

Publication number: WO1990008635A1
Application number: PCT/NL1990/000012
Authority: WO
Inventors: Frederikus Adolf Joseph Grimbergen
Original assignee: Grimbergen Frederikus Adolf Jo
Priority date: 1989-02-01
Filing date: 1990-01-31
Publication date: 1990-08-09
Also published as: NL8900245A; AU5039190A

Abstract

A process is described for the production of a concrete post (1) in which prestressing elements (2) are connected to prefabricated concrete pieces (3; 4) and the prestressing elements (2) are tensioned and enclosed in that state in a mould by a concrete mixture which is allowed to set. The grade of the prefabricated concrete pieces (3; 4) differs from the grade of concrete in the remaining part of the concrete post (1), depending on the purpose for which it is to be used. In particular, the cubic compressive strength of the concrete of the concrete pieces (3; 4) is greater than the cubic compressive strength of the concrete in the remainder of the concrete post(1). A concrete pile obtained by the process according to the invention is also described.

Description

Process for the production of a concrete post, and concrete pile obtained.

The invention relates to a process for the production of a concrete post with prestressing elements in which: the starting point is one or more set, prefabricated concrete pieces, at least one of which is intended for one end of the subsequent concrete pile; said concrete pieces with prestressing elements attached thereto are placed in a mould to be used for shaping the concrete post; the prestressing elements are tensioned with a predetermined force and held under tension, and the mould is then filled with a concrete mixture; the concrete mixture is allowed to set, and the tension is then removed; the concrete pile is removed from the mould and finished off if necessary.

•Such a process is known from Dutch Patent 68008, which discloses, inter alia, that prefabricated concrete pieces with prestressing elements attached thereto are placed in a mould, tension is then produced in the prestressing elements by pulling on the concrete pieces, and this tension is maintained during the pouring of the concrete mixture to be used and the setting thereof. Such a process when used has the advantage that all prestressing elements can be pulled on simultaneously by means of the prefabricated concrete piece, which means that it is unnecessary to clamp all prestressing elements individually.

In order to obtain a concrete post with uniform properties, for the remaining part of the concrete post one uses a concrete mixture which after setting produces a concrete which is the same as the concrete of the prefabricated concrete pieces at the ends.

It has now been found that major advantages can be obtained if according to the invention the one or more prefabricated concrete pieces are made of a_..grade of concrete which differs from the grade of the concrete in the remaining part of the concrete post after setting of the concrete mixture used for it. Depending on the purpose for which the concrete post is being made and the manufacturing conditions, it appears advantageous to select different grades of concrete for the concrete of the concrete pieces and the concrete of the remaining part of the concrete post. For example, for a concrete post which is to be used in a corrosive environment, for example seawater, an ordinary grade of concrete can be selected for the two ends if they are placed in enclosing structures or, .for example, the seabed, while for the part of the concrete post which comes into contact with the seawater it is necessary to select a grade which has high seawater resistance.

If a concrete post is to be used as a pile, it is necessary to use in particular for the concrete piece intended for placing at an end of the concrete post a grade of concrete which has a higher cubic compressive strength than the concrete in the remaining part of the concrete post.

Where a concrete post is being used as a pile, great impact stress occurs at one end of the pile when it is being driven into the ground. On account of such impact stress, the concrete has to meet very high quality standards at the end of the pile coming into contact with a piling hammer, and in particular has to have a very high cubic compressive strength. The parts of such a pile lying outside the end region are tensioned less than the top end and can therefore be made of a concrete of lower cubic compressive strength. It is expedient in such a case to make the cubic compressive strength of a concrete piece provided at one or both ends of a concrete post at least 10% higher than the cubic compressive strength of the concrete in the remaining part of the ready concrete post.

In connection with the above, you are also referred to NEN standard 7053 of February 1980, in which the criteria which apply during the production of, for example, concrete piles and the requirements which a finished concrete pile has to meet are described. The prestressing elements used in the process according to the invention can in general be selected from the elements normally used for this purpose, such as bars, steel cables, plastic cables and the like.

In the process according to the invention the prestressing elements are tensioned and maintained under tension during filling of the mould and setting of the concrete. Where one or two set prefabricated concrete pieces are used, one of the prefabricated concrete pieces used is, for example, fixed to the mould used before the tensioning, while after the tensioning the other prefabricated, set concrete piece or some other retaining device for the prestressing elements is fixed to the mould. After the tensioning and fixing operation, the mould is filled with concrete mixture, and this concrete mixture is left to set. The part of the mould which is filled with a suitable concrete mixture is advantageously divided into several different lengthwise regions, and for each lengthwise region a concrete mixture selected for that region is used. This embodiment of the process makes it possible not only to select a grade of concrete for the end regions of the post which is different from the remaining part of the post, but the remaining part of the post can also be subdivided into regions of differing concrete quality. For example, in the region 4 directly adjacent to the top end region, which is formed by a concrete piece of great compressive strength, it is possible to select a concrete mixture of a compressive strength after setting which is lower than the compressive strength of the end concrete piece, but which is higher than the compressive strength of the concrete further away from the end. Great flexibility in the selection of the various grades of concrete for concrete posts is obtained in this way. The invention also relates to a concrete pile which is manufactured by means of the process according to the invention described above, and which is characterized in that, at least at the end coming into contact with a piling hammer during use thereof, the concrete pile contains a prefabricated concrete piece in which the concrete has a cubic compressive strength of at least 50 tfewton/mm , while the cubic compressive strength of the concrete in the remaining part of the concrete pile is lower than 45 Newton/mm 2. In this way the prefabricated concrete piece at the top end of the pile coming into contact with a piling hammer can have a cubic compressive strength of, for example, 60 Newton/mm . The remaining part of the pile can then have a cubic compressive strength of 45 Newton/mm^ or lower, for example 37.5 Newton/mm . Such a concrete pile in which at least the head coming into contact with the piling hammer is made of a strong concrete exhibits optimum performance, since damage to the head during the piling operation does not occur at all, or is rare, while the remaining part of the pile easily meets the standards which are set for a support. In connection with the cubic compressive strength described above you are referred to Dutch standard NEN 3861 (1974). As regards the various grades of concrete to be used, you are referred to the brochure "Betonkwaliteit, hoe krijgen we dat" (Concrete quality, how do we get it?); VNC 1989.

More detailed information can be found in the standard work: "Betontechnologie" (1989). Reference can also be made to the Dutch standard "Voorschriften Beton¬ technologie" NEN 5950 (1986).

The invention will now be explained with reference to the drawing, in which:

Fig. 1 shows a schematic cross-section of a concrete post according to the invention; and

Fig. 2 shows on an enlarged scale an -end part of a concrete post according to the invention with concrete piece bonded thereto.

In Fig. 1 a concrete post according to the invention is indicated by reference number 1; in this case the concrete post can be, for example, a concr.ete pile'. The post is provided with prestressing elements 2 which are, for example, in the form of prestressing bars. The lefthand end of the post has one end in the form of a prefabricated concrete piece 3, while the other end of the post is formed by a prefabricated concrete piece 4. In view of its use as a pile, the concrete piece 3 has a high cubic compressive strength, for example a cubic compressive strength of at least 50 Newton/mm². The concrete piece 9 lying between the two end parts 3 and 4 is made of a concrete with a lower cubic compressive strength, for example a cubic compressive strength of 45 Newton/mm², or less.

During the manufacture of such a post, for ^"example prior to the tensioning of the tensioning elements, the concrete piece 3 is fixed to the mould, is then tensioned, and the concrete piece 4 is then fixed to the mould, so that the tensile force of the prestressing elements is absorbed by the mould. The concrete is then poured to form the intermediate part 9; the setting concrete will show good adhesion both to the prestressing elements 2 and to the boundary faces 5 and 6 of the concrete pieces 3 and 4„

The top surface 7 of the concrete piece 3 can be a suitable rounded shape for the piling operation; the ends of the prestressing elements 2 can be finished in any suitable manner known in this specialist field, in order to ensure good anchoring.

Fig. 2 shows on an enlarged scale yet another embodiment of a concrete post end according to the invention. A concrete piece 3 which is connected to the remaining part of the post 9 is shown. The prestressing elements 2 in this case have a thickened end 2' resting in a recess 3' which is open from the side 7 of the concrete piece 3. The anchoring of the prestressing elements 2 in this case takes place mechanically, and differently from the situation of Fig. 1, in which the prestressing elements were also anchored in the concrete piece 3 through bonding to the concrete. It is also shown schematically that the concrete piece 3 can be fixed to the mould by means of a pulling element 10 being the shape o ^"a bolt with head 11 and an end 12 by means of which the fixing to the mould can take place. Additional reinforcement elements for reinforcement of the material of the concrete piece 3 are also shown in cross-section by reference number 14.

It is also pointed out that in the drawing the concrete pieces 3 and 4 have the same external dimensions as the remaining part 9 of the post. This is, of course, not necessary; the concrete pieces can also be of a shape and external measurement which differs from those of the part 9.

The thickened end 2' of the prestressing element 2 shown in Fig. 2, accommodated in the widened end 3', is shown here as a thickened part which has been produced by mechanical deformation.

Of course, a thickened part can also be formed in other ways, for example by providing the end of a prestressing element with screw thread onto which a suitable nut is screwed. After fitting, the nut can be welded fast, if desired; but means which prevent loosening of the nut can also be provided between nut and prestressing element. For fixing of the prestressing elements to the concrete piece 3, the prestressing element 2 can in that case be inserted through the through hole in the concrete piece 3 from the side which faces away from the recess 3' until the end of the prestressing element 2 projects beyond the concrete piece 3. The nut can then be fitted on the prestressing element 2 and tightened, and the prestressing element is then pulled back until the thickened end is accommodated in the recess 3' .

Claims

θC A I M S

1. Process for the production of a concrete post (1⁾ with prestressing elements (2) in which: the starting point is one or more set, prefabricated concrete pieces (3, 4), at least one of which is intended for one end of the subsequent concrete pile (1); said concrete pieces (3, 4) with prestressing elements (2) attached thereto are placed in a mould to be used for shaping the concrete post (1); the prestressing elements (2) are tensioned with a predetermined force and held under tension, and the mould is then filled with a concrete mixture; the concrete mixture is allowed to set, and the tension is then removed; the concrete pile is removed from the mould and finished off if necessary, characterized in that for the one or more prefabricated concrete pieces a grade of concrete is selected which differs from the grade of the concrete in the remaining part of the concrete post (1) after setting of the concrete mixture used for it.

2. Process according to Claim 1, characterized in that for a concrete piece (3, 4) intended for placing at one end of the concrete post (1) a grade of concrete which has a higher cubic compressive strength than the concrete in the remaining part of the concrete post is selected.

3. Process according to Claim 2, characterized in that the cubic compressive strength of a concrete piece (3, 4) is at least 10% greater than the cubic compressive strength of the concrete in the remaining part of the ready concrete post (1) .

4. Concrete pile which is manufactured by means of the process according to one or more of Claims 1 - 3, characterized in that at least at the end coming into contact with a piling hammer during use thereof, the concrete pile contains a prefabricated concrete piece (3, 4) in which the concrete has a cubic compressive strength of at least 50 N/mm², while the cubic compressive strength of the concrete in the remaining part of the concrete pile (1) is lower than 45 N/mm².