The present invention relates to encapsulating bars or pipes. In a preferred application the invention relates to a reinforcing bar for use in reinforced concrete structures, concrete structures incorporating such a reinforcing bar, and a method of reducing the incidence and/or severity of corrosion of reinforcing members embedded in concrete. BACKGROUND OF THE INVENTION

Conventional reinforced structures include reinforcing bars made from steel. These are normally provided with various protrusions to increase the keying or intimate contact between the bar and the concrete. Since the bar has substantially high tensile strength, and the concrete has poor tensile strength but high compressive strength, the combination of the two materials produces a much improved structure.

However, such structures suffer from a malaise which is sometimes termed "concrete cancer J This malaise occurs in the event that the steel reinforcing bar or bars within the concrete structure commence to rust at one or more locations. Such rust is often caused by water seeping into the concrete, for example through fine cracks in the concrete itself. Rusting of the bar often also commences whilst the bar is exposed to atmosphere prior to being embedded in the concrete. As the rusting steel turns from iron into iron oxide, the volume which the reinforcing bar occupies within the concrete expands thereby resulting in the concrete being cracked and substantially weakened. To date, the only affective cure known for concrete cancer is to remove the cracking concrete from around the rusting reinforcing bar, remove the rust from the reinforcing bar, coat the remaining portion of the bar with some rust preventative or similar chemical compound, and replace the concrete. This is both a time consuming and expensive procedure. It is also a common form of substantial maintenance expenditure on buildings older than approximately 15-20 years.

It is known to attempt to overcome the above-mentioned problem by the provision of paint or like chemical coatings over the outer surface of the reinforcing

bars or galvanising. However, this attempt at a mechanism which prevents the reinforcing bars rusting has not been entirely successful during to the rough handling of the reinforcing bars before reaching, and at, construction sites. This rough handling results in any such coating being chipped or cracked with a consequent loss of 5 effectiveness.

The present invention, at least in some of its preferred forms, seeks to ameliorate the above-mentioned difficulties. DISCLOSURE OF THE INVENTION

In accordance with the first aspect of the present invention there is disclosed a ι o bar or pipe comprising an elongate member of substantially high tensile strength having at least one layer of sheet plastics material intimately bonded thereto to substantially encapsulate said member.

In a preferred application the bar or pipe is a reinforcing bar for use in reinforced concrete structures. Preferably the member includes surface protrusions 15 and/or indentations to improve keying between said bar and any concrete in which said bar is embedded.

In accordance with the second aspect of the present invention there is disclosed a concrete structure incorporating the above-mentioned reinforcing bar.

In accordance with a third aspect of the present invention there is disclosed a 20 method of reducing the incidence and/or severity of corrosion of reinforcing bars embedded in concrete, said method comprising the step of: substantially encapsulating said member in at least one layer of sheet plastics material prior to said member being embedded in said concrete. BRIEF DESCRIPTION OF THE DRAWINGS 25 Embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 is a perspective view of a portion of a reinforcing bar in accordance with a first embodiment of the present invention,

Figs. 2-7 are each a schematic cross-sectional view of the bar of Fig. 1 illustrating in sequence the steps involved in encapsulating the bar,

Fig. 8 is a schematic perspective view illustrating a number of bars being simultaneously encapsulated, Fig. 9 is a schematic cross-sectional view of a reinforcing bar in accordance with a second embodiment of the present invention,

Fig. 10 is a schematic cross-sectional view of a reinforcing bar in accordance with a third embodiment of the present invention,

Fig. 11 is a schematic cross-sectional view of an insulated pipe in accordance with a fourth embodiment of the present invention,

Fig. 12 is a schematic cross-sectional view of an irregular shaped bar in accordance with a fifth embodiment of the present invention, and

Fig. 13 is a schematic cross-sectional view of an irregular shaped bar in accordance with a sixth embodiment of the present invention,

PREFERRED EMBODIMENTS OF THE INVENTION

As seen in Fig. 1 the reinforcing bar 1 of the first embodiment of the present invention has a generally circular cross-section with a longitudinally extending groove 2 which extends along the length of the bar. The round bar shown in Fig. 1 is solid steel. The invention is also equally applicable to encapsulating other metals and/or alloys including aluminium, brass and copper, in the form of solid bars, hollow tubes and other irregular shapes.

As indicated in Figs. 2-7, the bar 1 is encapsulated with thermoplastic sheet plastics material, the preferred form of which is APET. The sheet 4 is firstly softened by means of heating and then moved relative to the bar 1 so as to come into contact with the surface 5 thereof. Preferably the sheet 4 is drawn towards the bar 1 by a pressure differential such as a vacuum which effectively evacuates all moisture and air from between the sheet 4 and bar 1. The result is as illustrated in Fig. 3.

It is preferred that the surface 5 of the bar I can be provided with an adhesive such as a heat actuatable or pressure sensitive adhesive.

As soon as the formation cycle is completed the cooling cycle of sheet 4 should be accelerated by any conventional cooling apparatus such as air fans or water jets (not illustrated) so that the shrinkage of sheet 4 tensions the surface material and achieves intimate bonding to the bar. The bar is then trimmed so as to remove those portions of the sheet 4 not intimately bonded to the bar 1.

As indicated in Fig. 4, the trimmed bar is then rotated about its longitudinal axis through 180° and the process is repeated with a second sheet 14 as indicated in Figs. 5 and 6. The two sheets 4 and 14 overlap so as to fully encapsulate the bar. Again, the bar is trimmed so as to produce the final product as indicated in Fig. 7.

Fig. 8 illustrates a plurality of bars 10 being simultaneously partially encapsulated by a sheet 4. It will be apparent from Fig. 8 that since the longitudinal extent of the sheet 4 exceeds that of the reinforcing bars 10, the ends of the bars are also encapsulated in overlapping fashion.

Fig. 9 illustrates a second embodiment of the present invention in which bar 20 is provided with oppositely arranged ridges 21 and 22 and a series of arcuate ribs 24. It will apparent to those skilled in the concreting arts that the groove 2, ridges 21, 22 and ribs 24 all act to increase the degree of keying, or intimate adhesion between, the reinforcing bar and the surrounding concrete after the reinforcing bar has been embedded in the concrete.

Fig. 10 illustrates a third embodiment of the present invention in which the bar 20, similar to that illustrated in Fig. 9, is encapsulated by a single layer of thermoplastic sheet material 4 which overlaps itself to fully encapsulate the bar. Fig. 11 illustrates a fourth embodiment of the invention in which a hollow bar in the form of pipe 30 includes an external layer of insulation 32, which in the example shown is a layer of EPS. The pipe 30 and insulating layer 32 are then both encapsulated by sheet 4 and 14, as previously described. In other similar embodiments

(not shown) the bar is not hollow and various types of materials are placed between the bar and the layers 4 and 14.

Figs. 12 and 13 show fifth and sixth embodiments in which the sheets 4 and 4 and 14 respectively encapsulate irregular shaped bars 34 and 36. The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, although the illustrated embodiments only illustrate a single encapsulating layer, two or more layers can be sequentially applied in order to increase the thickness of the encapsulation and simultaneously increase the rigidity of the bar still further. Also plastic rather than metal ties can be used to hold the reinforcing in place.

Further, although the preferred material of the sheet 4 is APET (amorphous polyethylene terephthalate) and the preferred thickness is approximately 500 micron, other materials such as HIPS (high impact polystyrene), PET, recycled PET, vinyls, acetates including cellulose acetates, PVC, ABS and mixtures and blends thereof, and other typical thermoforming plastics can be used and a range of thicknesses of sheet material of the order of from about 200 micron to about 3.0 mm can also be used.

Finally, the plastics material of the sheet 4 can conveniently be colour coded in order to make it apparent immediately, not only that the reinforcing bar is encapsulated, but also depending upon the colour and the colour codes selected, the nature of the encapsulation or the grade, size, quality etc. of the bar. This is thought to be of substantial assistance in ensuring compliance with specified encapsulated reinforcing bars since if the reinforcing, prior to the pouring of the concrete, is not of a colour indicated by the correct colour code, then it is immediately clear to supervising personnel such as foremen and architects that the reinforcing which is about to be embedded in concrete, is not as specified. INDUSTRIAL APPLICABILITY

The advantages offered by the above-described arrangement are primarily two¬ fold. Firstly, the encapsulating sheet is impervious and quite tough in its own right.

As a consequence, moisture and oxygen excluded from the bar thereby preventing the bar rusting both before and after being embedded in concrete. The coating provided by the sheet(s) is also sufficiently tough to withstand rough handling on construction sites and during transport, without compromising the integrity of the encapsulation.

An unexpected second advantage of the above-described arrangement is that the encapsulation itself, because it is intimately bonded to the bar, increases the strength of the bar, with regard to the tensile strength, bending moment, torsional strength, rigidity and stiffness of the bar. As a consequence, the reinforcing action of the encapsulated bar is improved over a conventional bar of identical dimensions and profile.

A test was conducted on 12 mm diameter steel reinforcing bar having a lm span and a central load. The deflection of plain bar and the bar encapsulated in accordance with the present invention are as follows.

Load (kg) Deflection (mm)

Plain bar Encapsulated bar

5 9.0 8.0

10 14.5 11.0

15 18.5 13.0

20 23.0 15.0

26 28.0 17.5

As is evident from the above table the encapsulated bar is noticeably stronger than the plain bar. This permits designers to use thinner or hollow encapsulated bars in place of larger plain bars, representing a material saving.

It is also believed that encapsulating bars in accordance with the invention increases fatigue resistance as the covering disturbs the fatiguing harmonics and effectively damps vibration of the bar. The thickness and thereby mass of the covering is related to the resonant frequency which allows the designer to choose a particular thickness to cancel or minimise certain harmonics.

In the fourth embodiment of the invention shown in Fig. 11 the encapsulating sheets 4 and 14 tension the insulating layer 32 of the pipe 30 and improve the insulatory properties of the pipe.