NZ611894B - Indented tendons, processes of forming and uses thereof - Google Patents

Abstract

tendon comprising a plurality of indentations that have been cold-rolled into the tendon along the length and around the circumference thereof, each indentation having opposing edges which generally extend longitudinally and in parallel to a longitudinal centreline of the tendon, wherein, when the tendon is viewed in transverse cross-section through the indentation from one edge to the other, and an axis is projected from the longitudinal centreline of the tendon to bisect a chord that extends between the edges, a base of each indentation is defined by a radius which extends from a point on the axis which is near to but offset from the tendon centreline, with the radius being approximately equal to or less than a radius of the tendon at an unindented portion thereof. tendon is viewed in transverse cross-section through the indentation from one edge to the other, and an axis is projected from the longitudinal centreline of the tendon to bisect a chord that extends between the edges, a base of each indentation is defined by a radius which extends from a point on the axis which is near to but offset from the tendon centreline, with the radius being approximately equal to or less than a radius of the tendon at an unindented portion thereof.

Description

INDENTED TENDONS, PROCESSES OF FORMING AND USES THEREOF TECHNICAL FIELD Disclosed herein is a tendon that comprises a plurality of indentations that have been cold-rolled into the tendon, with the indentations being formed along the length and around the circumference of the tendon. A process of cold-forming such an indented tendon is also disclosed. The cold-rolling of the indentations can produce a tendon having high tensile resistance as well as a low relaxation characteristic. The tendon into which the indentations are cold-rolled may itself be cold-drawn. The cold- rolling can also allow for more precise control of volume and shape of the indentations.

The tendon may be employed as a reinforcing element and, as such, the indentations in the tendon may be configured to provide for an increased bond with material to be reinforced (e.g. concrete, rock, etc). The disclosure is to be broadly interpreted in that the tendon may also take the form of a rod or wire, or may comprise a plurality of rods or wires bundled to form a composite strand and/or cable (i.e. that comprises a plurality of strands). A reinforcing element comprising the one or more tendons may be used to reinforce, for example, concrete or rock structures, but it should be appreciated that its application is not so limited.

BACKGROUND ART Elongate reinforcing elements, such as wire, rod and bar, and combinations thereof, are used to reinforce materials with poor tensile strength such as cement, concrete and rock. To form such elongate reinforcing elements, either a hot-rolling or a cold-rolling process may be employed in which a metal element is roll formed between, for example, two or more work rolls. For certain reinforcing applications, the mechanical properties and residual stresses resulting from hot-rolling may not be suitable for purpose in comparison to reinforcing elements formed by cold-rolling.

When hot-rolling rod or bar to form a reinforcing element, the rod or bar is rolled at a temperature above the recrystallization temperature of the material (metal).

This enables grains within the metal rod or bar that are deformed during rolling to recrystallize, thereby preventing the metal from work hardening.

When the reinforcing element is to have ribs formed thereon by hot-rolling, a heated rod or bar is fed between work rolls that have been machined to have teeth thereon. The ribs are formed by an extrusion or flow of the hot metal into gaps between the teeth and, at the same time, the portions of the rod or bar located between adjacent ribs are squeezed by the apex of opposing roll teeth, whereby the diameter of the rod or bar is also reduced. When ribs are formed by hot-rolling, poor consistency in the height 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 of ribs moving along the rod or bar can result, as can variability in the depth of indentations between adjacent ribs moving along the rod or bar. Examples of bar and rod having ribs that are hot-rolled thereon are shown, for example, in each of GB 646,801 and EP 601,630.

In many applications of reinforcing bar and rod, consistency in rib height and consistency in indentation depth are not important considerations, so that a hot-rolled rod or bar may be suitable for such applications.

However, because the deformed grains of the hot roll-formed rod or bar are able to recrystallize, the rod or bar will have higher ductility but a lower tensile strength when compared to a cold-rolled rod or bar of the same material. Also, a hot-rolled rod or bar displays higher strain relaxation than a cold-rolled rod or bar. Hence, for certain reinforcing applications, hot roll-formed rod or bar can be unsuitable. More specifically, low relaxation, cold-drawn bars are most suitable to pre- and post- tensioning reinforcing applications.

In the cold-rolling of a metal rod or bar to form a reinforcing element, the rod or bar is usually rolled at room temperature, with the metal being worked by the rolls below its recrystallization temperature. The strength of the rod or bar is increased by strain hardening, occurring as a result of plastic deformation of the metal. Cold rolling is known to produce reinforcing elements with higher tolerances and less variability along the length of the rod or bar. Cold rolling also results in considerably less diameter reduction of the resultant rod or bar.

Both hot- and cold-rolled rod, bar and wire can be used to reinforce materials such as concrete slabs and vertical or horizontal rock structures to increase their tensile strength. The rod, bar or wire may also be formed into grid or mesh prior to being embedded in the slabs and structures.

Such components can assist with the transfer of loads applied to the material.

For example, rod, mesh and bar used in concrete slabs can provide increased tensile strength to complement the inherent compressive strength of the concrete. Similarly, a rock bolt can be inserted and grouted or adhered into a rock structure to provide tensile strength and resistance to shifting loads (e.g. to help prevent collapse of walls and ceilings of an underground wall, tunnel, etc). Further, to more effectively bond to the concrete or grout, the rod, bar or wire may be roughened, corrugated, ribbed or indented to provide additional surface area, as well as providing for “keying” of the bond between the rod, bar or wire and the concrete.

However, when reinforced concrete is to be used in load-bearing applications (e.g. in bridges, bearers, etc) the concrete may be ‘prestressed’. One way to prestress concrete is by pre-tensioning the reinforcing element, wherein concrete is poured and 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 cured around an elongate reinforcing element that is already under longitudinal tension.

Once the concrete has cured/set, the tensioning of the reinforcing element is released, whereby the element tends to contract, thus causing the concrete to be compressed (i.e. be placed into compressive stress). However, the concrete may also maintain the reinforcing element in a stressed tensile state.

In use, when a load is applied to the reinforced concrete, the tensed reinforcing element as well as the compressed concrete function in a composite manner, whereby the structure is able to absorb additional stress (e.g. through a reduction in the inherent compressive force in the concrete). Further, because the concrete is always under compression it is less subject to failure.

Another way to pre-stress concrete is by post-tensioning, which involves compressing the concrete to apply tension to a reinforcing element after the concrete has been poured and cured. Post-tensioned concrete may either be “bonded”, whereby tension is applied to the reinforcing elements after curing of the concrete and then e.g. grouted in place, or may be “un-bonded”, whereby each reinforcing element has freedom of movement relative to concrete (e.g. each element extends in its own sheath, with each sheath extending through the concrete). In either case, the reinforcing element can be tensioned by jacks, anchors or anchor plates located at opposing edges/ends of the concrete.

Because cold-rolled rod, bar or wire has a higher tensile strength and low relaxation (i.e. less tendency to lose strain when under tension) compared to hot-rolled rod or bar, when a cold-rolled reinforcing element is placed in a stressed tensile state (such as by pre- or post-tensioning) it is inherently better able to sustain, for the lifetime of the structure, the compressive load on material being reinforced (e.g. concrete, grout, etc) than is a hot-rolled product.

Further, where an effective bond between the cold-rolled reinforcing element and the reinforced material can be maintained, then such compressive load can be better sustained, and hence improved performance of the composite material can be achieved.

Thus, a cold-rolled reinforcing element can be more suited to certain load-bearing applications.

Rods, bars and wires having various dimensions and indentation patterns for use in reinforcing concrete are known in the art. For example, CN 201908391 discloses a large diameter steel wire having oblique surface indentations. The spacing between indentations is quite large, with only a small proportion of the wire being indented. The indenting of only a small proportion is to maintain the overall tensile strength of the wire.

In another example, CN 201908230 discloses the use of a combination of 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 indented and unindented wires to form a strand for use as a reinforcing element for prestressed concrete.

Similarly, CN 201339272 discloses the use of an indented reinforcing steel bar, in the form of three wires that are wound together to form a strand, for use in railway sleepers.

In a further example, CN 201678906 discloses a reinforcing steel bar for use in concrete slabs. The bars are laid in a grid-like manner and have indentations on their surface, similar to those described in CN201339272. A polyethylene plastic is cast onto its surface at locations where the bars overlap in the grid formation.

Alternatively, when reinforcing materials such as vertical or horizontal rock structures, rock bolts or cable bolts are placed into pre-drilled holes in the rock structure. Grouting may then be pumped into the hole, or adhesive (e.g. in pre-installed capsules) may be released to surround the bolt and secure it in place. In order to sufficiently bond the grout to the bolt, a number of wires or rods are often wound together to form a strand or tendon, and a number of strands or tendons can be used to form the bolt. The spacing between the wires or rods, and strands or tendons, provides additional surface area for the grout or adhesive to bond to. Roughening, corrugating, indenting or ribbing of the bolt surface (e.g. such as by forming a threaded bolt) to provide additional surface area for bonding between the bolt and the grout/adhesive is also known. For example, US 3,653,217, and WO 01/77493 each disclose rock bolts having various configurations, including indented or ribbed bars, as well as cables having a number of twisted wires wound together.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the tendon, rock bolt and forming process thereof, as disclosed herein.

SUMMARY OF THE DISCLOSURE Disclosed herein is a tendon comprising a plurality of indentations that have been cold-rolled into the tendon along the length and around the circumference thereof.

Cold-rolling of the tendon to form the indentations can produce a tendon having high tensile resistance as well as a low relaxation characteristic. The tendon into which the indentations are cold-rolled may itself be cold-drawn. Cold-rolling of the tendon can also enable each of the indentations to be formed with a high and consistent tolerance, and consistently along the length of the tendon, as well as allowing for more precise control of the volume and shape of each indentation, in comparison to the variability of hot rolling processes. Such characteristics can be desirable to an end user of the tendon, 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 and can make the “products” in which the tendons are employed more efficiently formed, and of increased composite strength and performance.

Each indentation can be cold-rolled into the tendon to have opposing edges which generally extend longitudinally, and in parallel, to a longitudinal centreline of the tendon.

In a first aspect of the disclosure, when the tendon is viewed in transverse cross- section through the indentation, from one edge to the other, and an axis is projected from the longitudinal centreline of the tendon to bisect a chord that extends between the edges, a base of each indentation can be defined by a radius which extends from a point on the axis which is near to but offset from the tendon centreline. The radius is approximately equal to or less than a radius of the tendon at an unindented portion thereof.

In other words, a base of each indentation is defined by a depth on the axis from the unindented portion and by a radius that is approximately equal to or less than a radius of the tendon at an unindented portion thereof.

In this first aspect, the base of each indentation which is defined by the offset radius can extend for a substantial proportion of the indentation base when the tendon is viewed in transverse cross-section. Thus, the base as defined by the offset radius may almost extend from one edge to the other. For example, the base defined by the offset radius may extend for greater than 95% and may approach up to 99% of the edge-to- edge extent of the indentation.

By way of further example, the extent of the base as defined by the offset radius may result in a corner radius at each of the opposing edges of the indentation that is less than half the depth of the indentation. A process for cold-forming such an indentation may accordingly be configured to produce such “tight” corners.

Maximising the extent of the base that is defined by the offset radius, as well as minimising the extent of the base that is affected by the corner radii, also maximises the resultant indentation volume, especially in comparison to prior art indentations of similar length and width.

Thus, when the tendon is used, for example, as a reinforcing element, the greater indentation volume allows more of the material being reinforced, or more of the filler/grout/adhesive, to extend into the indentations and bond with the tendon. Further, when such a reinforcing element is placed in a stressed tensile state (such as by pre- or post-tensioning) it is inherently better able to sustain a compressive load on the material being reinforced, and hence an improved performance of the composite material can be achieved.

In addition, notwithstanding the greater indentation volume, it has been 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 surprisingly observed that the target breaking load strength of the tendon can be maintained.

Here, it should be understood that the ability to more precisely and consistently form the indentations, each with a base of such extent, arise from the careful and unique control of a cold-forming process. Such precision would simply not be possible with a hot-rolling process.

In addition, having the base of each indentation defined in this manner means that the base has approximately the same curvature, but is offset from, the curvature of the tendon surface. This provides a more uniform depth across substantially the entire base of the indentation as compared with indentations previously achievable for cold- formed tendons (e.g. rod and wire), thus maximising the average (i.e. median) depth of a given indentation.

Thus, a cold-rolling process for producing the indentations in the tendon can be performed such that a very full extent of base as defined by the offset radius may result.

In this regard, feed tendon specification/tolerances, tendon feed speed and/or machining of the cold-work rolls may each be controlled to exceptionally high tolerances.

In a second aspect of the disclosure, when the tendon is viewed in transverse cross-section through the indentation, from one edge to the other, a chord ‘e’ can be defined as the straight line distance between adjacent edges of adjacent indentations.

The sum of each such chord, when moving one revolution around the centreline of the tendon, may produce a value in the range of 0.1 of the circumference of the unindented tendon. For example, a cold-rolling process for producing the indentations in the tendon can be controlled to result in tolerances whereby the sum of each such chord is 0.1 ± 0.01.

Again, such precise and consistent formation of the indentations on the tendon arises from the careful and unique control of the present cold-forming process.

There are a number of country-specific standards in place relating to the summation of chord lengths for a nominal wire diameter. This is generally referred to as the “Σe” (or “sum e”) value.

In Australia, for example, the use of steel prestressing materials is governed by the Australian Standard: AS4672, which dictates that Σe be less than 0.3 of the wire circumference. This is to ensure that a sufficient bond between the wire and surrounding material can be achieved. Currently available wires, such as those disclosed in CN201339272 and CN201078906, for example, have a Σe that is approximately equal to the value stipulated in the Australian Standard. To the contrary, CN 201908391 teaches a wire having a Σe value of more than 0.3 of the wire 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 circumference which would therefore prevent its use, in Australia, as a prestressing material. The present disclosure represents a significant reduction in Σe compared to values considered acceptable by Australian Standards [AS4672] and in comparison to known steel prestressing materials. Reduction of this Σe value therefore results in a higher proportion of the circumference of the tendon being indented, thus providing for a higher degree of bonding of the tendon with the surrounding material.

Thus, a cold-rolling process for producing the indentations in the tendon can be controlled whereby the Σe value (i.e. each chord length) can be reduced, whilst at the same time the formation of thin and weak steel fins on the tendon can be prevented, and a target breaking load strength of the tendon can be maintained.

In one form, for a given length of tendon, there can be a total circumferential surface area SA which is equal to the circumference of the tendon, at an unindented portion thereof, multiplied by the given length. The SA represents the total circumferential surface area of the indented tendon, but as if the tendon were unindented (i.e. the surface area that is “missing” due to the indentation is included in the total circumferential surface area). There is also an indented surface area SA which is that part of the total circumferential surface area SA which has been indented (i.e. that part of the total circumferential surface area that has been removed, or is missing/vacant, due to the indentation of the tendon). The indented surface area SA may be approximately equal to or greater than 50% of the total circumferential surface area SA . For example, the indented surface area SA may be between approximately tot i 50 to 75% of the total circumferential surface area SA , in order to prevent fins forming on the tendon and to maintain the strength of the tendon.

When the tendon is used as a reinforcing element, having an indented surface area approximately equal to or greater than 50% of the total circumferential surface area, this has been observed to greatly increase the surface area available for the tendon to bond to the surrounding material. For example, when the tendon is used as a reinforcing element for pre-tensioned concrete, the additional surface area can allow the tension to be released from the reinforcing element earlier than usual, because the material need not be cured for as long, or fully cured, and yet the same extent of bonding, locking and/or securement between the tendon and the concrete can be achieved.

Alternatively, a lower strength concrete may be used, in place of current higher strength concretes, due to the increased securement of the material as a result of the increased indentations.

In addition, the indented area may be maximised in a manner such that thin, weak steel fins are not formed on the tendon between the indentations. Accordingly, a 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 target breaking load strength of the tendon may be maintained.

For example, a cold-rolling process for producing the tendon can be controlled to result in such an increased indented surface area, along with a substantially constant depth of indentation, to thereby provide a tendon that is reliable and consistent when in use. Because the increase in indented surface area allows for a greater proportion of material to bond to the tendon, improved performance of the resultant composite material can result and this can also assist in preventing its failure in use.

In one form of the tendon, a depth of a given indentation, defined as the distance between an unindented surface of the tendon and a base of the indentation, may be substantially consistent for the entire base of the indentation, with a maximum variation of depth being approximately 10%. By ensuring a consistent, substantially uniform depth for a given indentation, a better and more uniform bonding between the surrounding material and the tendon can be achieved.

The Australian Standard AS4672 dictates that the maximum permissible depth variation for a given indentation is up to 50%. For example, a cold-rolling process for producing the tendon can be controlled to result in a significant reduction of depth variation, in a manner hitherto fore not contemplated, to thereby provide an indented tendon that behaves more consistently and that is less prone to the surrounding material pulling out of the indentation.

By way of comparison, rods or wires in the prior art can have an indentation base with a varying profile, which provides indentation regions that are more susceptible to withdrawal or to separation of material from the indentation (thus leading to failure of the rod or wire in use).

In one form, an average depth for a given indentation, defined as the average (i.e. median) distance between the base of the indentation and an unindented surface of the tendon, may be substantially consistent to the average depth of other indentations.

The maximum variation of average depth may be approximately 10%. For example, a cold-rolling process for producing such a tendon can be controlled to result in the average depth of indentations being consistently produced.

Having indentations that are of a substantially consistent profile also contributes to reliable performance of the tendon in-use. A consistent indentation depth for a given tendon may also provide a user with confidence in how the tendon will perform in use, whether it be a portion of the tendon (i.e. if the tendon has been cut to predetermined lengths for use in smaller sections), or the entire length of tendon (i.e. there can be consistency for the entire tendon length). Thus, the performance of a large section of reinforced material will be reliable, as will be smaller sections that may be cut from the larger (e.g. whole) section. 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 In one form, each indentation may have a volume such that the total volume for all indentations is approximately greater than or equal to 5% of the volume of a pre- indented tendon. The total volume of indentations can influence the ability of the tendon to bond with the material (i.e. it can maximise the volume of surrounding material that can bond with the tendon). Again, a cold-rolling process for producing such a tendon can be controlled to result in a consistent total volume of all indentations being produced.

Prior art rods often have a total indentation volume of as little as 1.5%. This is due, in part, to the need to minimise deformation of the rods to ensure that sufficient rod strength is maintained, such as is disclosed in CN 201908391 or CN 201678906.

However, when the cold-rolling process is carefully controlled to maximise total indentation volume, it has been observed that the strength of the tendon is not compromised in comparison to prior art rods.

The tendon as disclosed herein may take the form of a rod, bar or wire. When the tendon takes the form of a rod or wire, a number of rods or wires may be wound together to form a strand. Similarly, a number of strands may be wound together to form a cable or rope. Strands and/or cables may find particular use in applications such as rock bolting, ropes, lifting cables, mooring cables, road barriers, etc.

In one form, the process of cold-forming can produce a low-relaxation wire.

When indented, such low-relaxation wire may find particular use in concrete reinforcement and foundations, such as for railway sleepers, concrete bearers, bridges, buildings, causeways, dams or any other concrete structure. In an alternative form, the wire may take the form of a low carbon wire. The low carbon wire may find particular use in standard reinforced concrete applications, such as a wire meshing.

In one form, the tendon may be suitable for use as a reinforcing element. For example, the tendon may be used as a concrete reinforcing element, or may form part of a rock bolt or cable bolt.

The use of such a tendon, as defined above, as a reinforcing element is also disclosed. For example, the use of the tendon as a concrete reinforcing element, or as part of a rock bolt, etc, is disclosed.

Also disclosed herein is a process of cold-forming an indented tendon. The process comprises providing and then cold-rolling a first length of unindented tendon through a set of toothed rolls.

As mentioned above, cold-forming of the tendon can produce a tendon having high tensile resistance as well as a low relaxation characteristic (i.e. less tendency to 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 relax due to strain hardening), making the tendon highly suitable for material reinforcing applications. The unindented tendon into which the indentations are cold- rolled may itself be cold-drawn.

As set forth above, the cold-rolling process step can be controlled such that each of the indentations is formed with a high and consistent tolerance, and in a consistent manner along the length of the tendon, as well as providing for more precise control of the volume and shape of each indentation, in comparison to the variability of hot rolling processes.

For example, the process can be operated to ensure a high and consistent tolerance in the unindented “feed” tendon provided to the cold-rolling stage. In this regard, careful control may be exercised when e.g. cold-drawing the feed tendon.

In addition, the toothed rolls can be configured (e.g. carefully and closely machined) to cold-form the indentations with a high and consistent tolerance, and in a consistent manner along the length and around the circumference of the tendon.

Further, the tendon feed speed (roll speed) can be carefully controlled to further maximise consistency in the indenting of the tendon.

In one form of the process as disclosed herein, the cold-rolling can be controlled such that the sum of the volumes of each indentation is approximately greater than or equal to 5% of the volume of the tendon. Controlling the total indentation volume for a given length of tendon has been observed to produce a tendon that will perform consistently in use.

When a second length of unindented tendon, of the same given size as the first length of tendon, is cold-rolled through the set of toothed rolls, indentations can be created along the length and around the circumference of the second length of tendon.

The total volume of all indentations on the second tendon can be measured, as a % of the total tendon volume.

The process can be operated so as to ensure that the total volume of indentations on the second tendon varies from the total volume of indentations of the first tendon, as a % of total tendon volume, by less than 20%.

For example, where the total volume of indentations on the second tendon varies by more than 20% from the total volume of indentations for the first tendon, the second length of tendon can be discarded. Again, this can provide consistency to the processing of any given length of a tendon, including of subsequently rolled tendons.

Where a subsequently rolled tendon has a total indentation volume that falls within such controlled process parameters, this indicates to a user of such tendons that they may rely on the tendon’s integrity and performance characteristics in use, regardless of when the tendon was manufactured. Further, by operating the process to consistently monitor 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 for non-conformance with the specifications (e.g. total indentation volume), tuning or refining of drawing and rolling parameters such as by controlling diameter of an unindented tendon, adjusting the location/alignment of the toothed rolls, and replacement of the toothed rolls, can be implemented as required.

In a further form of the process as disclosed herein, rolling can be controlled such that, when the tendon is viewed in transverse cross-section through the indentation from one edge to the other and an axis is projected from the longitudinal centreline of the tendon to bisect a chord that extends between the edges of the indentation, a base of each indentation can be defined by a radius which extends from a point on the axis which is near to but offset from the tendon centreline. The radius can be approximately equal to or less than a radius of the tendon at an unindented portion thereof. A base of the indentation having a radius approximately equal to the radius of the tendon can result in a base that is substantially parallel to the arc of the circumference of the unindented portion of the tendon. The base may, in this regard, be considered to form an arc that is substantially concentric to the arc of the circumference of the unindented portion. The toothed rolls may be precision ground, during machining of the rolls, to accordingly cold-form such a base, and to the specific size of the intended product.

In yet another form of the process as disclosed herein, rolling of the tendon can be controlled such that, when the tendon is viewed in transverse cross-section through the indentation from one edge to the other, a chord ‘e’ can be defined as the straight line distance between adjacent edges of adjacent indentations, where each edge is defined as where each indentation commences. The sum of each such chord, when moving one revolution around the centreline of the tendon, can produce a value in the range of 0.1 of the circumference of the unindented tendon. The toothed rolls may accordingly be precision ground, during machining of the rolls, to be configured to reduce the Σe value (i.e. the summed value of chords ‘e’ moving one revolution around the tendon), whilst maintaining the integrity of the tendon. For example, a cold-rolling process for producing the indentations in the tendon can be controlled to result in tolerances whereby the sum of each such chord is 0.1 ± 0.01.

In yet another form of the process as disclosed herein, rolling can be controlled so that a depth of a given indentation, defined as the distance between an unindented surface of the tendon and a base of the indentation, is substantially consistent for the entire base of the indentation. The maximum variation of depth for a given indentation can be approximately 10%. When the variation in depth for a given indentation is more than 10%, the tendon may be discarded. This implementation of the process has been observed to establish strict quality control to ensure that users are provided with a consistent product that will perform in a consistent manner. 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 In one form, the rolling may be further controlled so that the average depth of a given indentation is substantially consistent with the average depth of other indentations. The maximum variation in average depth for indentations may be approximately 10%. Again, when the average depth of indentation varies by more than 10% between indentations, the tendon can be discarded. Ensuring consistency in the resultant tendon provides a reliable and dependable product.

In one form, the indented tendon formed by the process as disclosed herein may undergo further processing. The further processing may include heat treatment and/or loading of the tendon. Further processing may also include coating, polishing or roughening the tendon.

In one form, the tendon resulting from the process as disclosed herein may be cut to a predetermined length. The cut length of tendon may then be used as, for example, a reinforcing element.

Also disclosed herein is a rock bolt. The rock bolt comprises a plurality of straight tendons having at least one co-terminated end. The ends may be co-terminated by a member, such as a boss, that extends, in the finished rock bolt, beyond the outermost tendons to form a shoulder for abutment against the rock or a plate, to assist with anchoring the bolt to the rock. The co-terminated end eliminates the need to use, for example, an additional anchor head or clamp to secure the tendons together.

In one form, the tendons may be co-terminated such that a pre-determined spacing is maintained therebetween. Providing a spacing between the tendons at their co-terminated ends allows grout or filler, which is pumped into the bore hole in which the rock bolt is being positioned, or a pre-existing adhesive (e.g. in a capsule), to have an increased tendon surface area with which to bond. Spacing between the tendons can also simplify or make injection of the grout or filler, or the flow of adhesive, easier.

The tendon ends may be co-terminated by a head portion, which may be moulded, sagged, clamped, welded, cast or bolted to the ends. Intermediate spacers may be used to maintain the pre-determined spacing along the length of the tendons. Maintenance of the spacings along all, or part, of the length of the tendons ensures maximum volume between tendons for grout/adhesive to flow into, thus providing for additional securement of the rock bolt.

In one form, at least one of the tendons of the rock bolt may comprise a tendon that is formed as disclosed above. For example, the rock bolt may comprise up to eight such tendons, and two of the tendons may be as disclosed above. In another form, each of the tendons of the rock bolt may comprise a tendon as disclosed above. The use of such cold-formed indented tendon(s) as rock bolt tendons further increases the surface 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 area to which the grout, filler or adhesive can bond, and provides for additional securement by the interlocking of the grout, filler or adhesive with the indentations.

This helps to prevent pull-out of the tendons from the grout, filler or adhesive.

In one form, one or more of the tendons may be of a different length to the other tendons. A rock bolt may generally be positioned into a drilled hole in rock, and grout pumped into the hole to secure the bolt in the rock. Having tendons of differing lengths can assist with pumping of the grout into the hole, and ensuring that the tendons are adequately surrounded by the grout to provide adequate securement to the rock.

Further, tendons of different length can allow some parts to be stronger than other parts of the bolt.

In one form, one or more of the tendons may be in the form of a tube, having a hollow centre and indentations formed along the length and around the circumference of the tubular material. This can assist with pumping of the grout into the hole. For example, where grouting tubes are used in the tendon, they can be of different lengths to allow the grout to penetrate into different parts of the bore hole.

BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms which may fall within the scope of the tendon, rock bolt and forming process thereof as set forth in the Summary, specific tendon embodiments, rock bolt embodiments and forming processes thereof will now be described, by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a side schematic view of a tendon embodiment, in accordance with the present disclosure; Figure 2 shows a cross-sectional schematic view of the tendon shown in Figure 1, with Figure 2a showing a detail of Figure 2; Figure 3 shows a plan view of the circumferential surface area of the tendon shown in Figures 1 and 2; Figure 4 shows a side view of an embodiment of a rock bolt, in accordance with the present disclosure; Figure 5A to 5C respectively show side and plan views, and a cross-sectional detail, of a toothed roll suitable for implementing the process as disclosed herein to produce indented tendon as disclosed herein.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring firstly to Figures 1 and 2, a portion of a tendon, in the form of rod 10, is shown. The rod 10 may itself comprise a cold-drawn rod, the diameter of which has 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 been carefully formed in the preceding cold-drawing process stage. Indentations 20, 30 and 40 are cold-rolled into the rod 10 along the length and around the circumference of the rod.

The cold-drawing of the rod 10 and the cold-rolling of the indentations 20, 30 and 40 provides the rod 10 with high tensile resistance as well as a low relaxation characteristic. The cold-rolling of the indentations 20, 30 and 40 also enables each indentation to be formed with a high and consistent tolerance, as well as consistently along the length of the rod. The cold-rolling also allows for more precise control of the volume and shape of each indentation, especially when compared to hot rolled product.

The rod 10 is shown having a longitudinal centreline LC (e.g. central axis), a length L and a circumference C , which is the circumference of the rod if it were unindented (i.e. calculated using the radius R of an unindented portion of the rod 10, as taken from the longitudinal centreline LC). The indentations 20, 30, 40 are cold-formed around the circumference C of the rod 10 and are repeated along its length L. Each indentation 20, 30, 40 has opposing edges 22, 24; 32, 34; 42, 44, respectively, which edges generally extend longitudinally, and in parallel to the longitudinal centreline LC of the rod 10. Each indentation 20, 30, 40 has a base 26, 36, 46 which extends between the two opposing edges 22, 24; 32, 34; 42, 44.

The configuration of base 26 of indent 20 will now be described in detail, with reference to Figures 2 and 2a. Base 26 is configured to have a radius that is approximately equal to, or slightly less than, the radius R of an unindented portion of the rod 10. By way of example, if indentation 20 is considered, it will be seen that the radius R of the base 26 of indentation 20 extends from a point P on an axis B-B. i20 20 Axis B-B is the bisector of the chord C-C, which extends between the edges 22 and 24 of indentation 20, with axis B-B extending through the longitudinal centreline LC of the rod 10. It can be seen in Figure 2 that point P , from which the indentation radius R i20 extends, is near to but offset from the longitudinal centreline LC of rod 10. The point P is located on axis B-B on an opposite side of the longitudinal centreline LC of rod to the base 26.

It will also be seen that the distance that point P is offset from the longitudinal centreline LC on axis B-B is equivalent to (i.e. establishes) the depth D of the indentation 20. Further, it will be seen that the depth D is the average distance between the base 26 of indentation 20, and the circumference C of an unindented portion of rod 10 if it were to continue where the indent is located (i.e. see dotted circumference line in Figure 2).

While only the configuration of base 26 has been described above, bases 36 and 46 are of a similar configuration and thus a similar explanation to the above applies to 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 the bases 36 and 46 of indentations 30 and 40.

It can be clearly seen in Figure 2 that, due to radius R being approximately equal to, but offset from, radius R , the depth D of indentation 20 remains u i20 substantially constant across the base 26 and for a large edge-to-edge extent. This is also true for the bases 36, 46 of indentations 30, 40, whereby a maximum average depth variation between indentations is 10%. This results in a concentric circle-like arrangement of bases 26, 36, 46 with respect to the circumference C .

As also shown in Figure 2, the extent (i.e. edge-to-edge) of the base 26, 36, 46 of each indentation 20, 30 and 40, as defined by the offset radius R , represents a substantial proportion of the indentation when the tendon is viewed in transverse cross- section. For example, the extent of the base 26, 36 or 46 formed by the offset radius R usually extends for at least 95%, and can approach up to 99%, of the edge-to-edge extent of the indentation. This maximising of the extent of the base that is defined by the offset radius also maximises the resultant indentation volume, especially in comparison to prior art indentations of similar length and width.

More particularly, as revealed in the detail of Figure 2A, the high tolerance and precision cold-forming of the indentations, can result in a corner radius R at each of the opposing edges of the indentation that is less than half the depth D of the indentation, whereby a tight corner results. In other words, the edge-to-edge extent of the base of each indentation is substantial.

The process and roll set-up as described herein are thus carefully and controllably configured and operated so as to produce a rod with such precise configuration of the indentations.

It can also be seen in Figure 2 that a chord ‘e’ can be defined between edge 34 of indent 30 and edge 42 of indent 40 (i.e. the adjacent edges of adjacent indentations).

Similar such chords ‘e’ can also be defined between edge 44 of indent 40 and edge 22 of indent 20, as well as edge 24 of indent 20 and edge 32 of indent 30.

Again the cold-forming process and roll set-up as described herein are configured and operated such that the sum of each such chord (i.e. “Σe”), when moving one revolution around the centreline of the rod, is able to produce a value in the range 0.1 of the circumference C , and to a tolerance of ±0.1. This represents a significant reduction (i.e. of about or greater than one third) of the Σe when compared to values considered acceptable by Australian Standards [AS4672] as well as when compared to the Σe values of known steel prestressing materials. Further, it has not previously been thought possible to produce, nor has the significance been recognised of, such a low Σe value.

Where the cold-forming process and roll set-up are configured and operated to 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 produce such a low Σe value, a higher proportion of the circumference C of the rod 10 is indented. This increased amount of indentation has been observed to provide and allow for a greater extent/degree of bonding of the rod 10 with a surrounding material (e.g. concrete, cement, grout, adhesive, etc).

Referring now to Figure 3, a plan view of the circumferential (i.e. expanded) surface area of rod 10, illustrating a useful indent pattern, is shown (i.e. as if the circumference C of the rod 10 has been opened out into a 2-dimensional representation, to thereby show the indented 20, 30, 40 and unindented areas of the rod ).

Using the rod representation of Figure 3, it will be understood that the total circumferential surface area SA is equal to the circumference C multiplied by the tot u length L of the rod 10. Further, the indented surface area SA is determined as the combined surface areas of indents 20, 30 and 40 along the length L of the rod 10. The indented surface area SA represents that part of the total circumferential surface area SA which has been indented. As shown in Figure 3, the cold-forming process and roll set-up as described herein are able to be configured and operated such that the indented surface area SA is approximately equal to or greater than 50% of the total circumferential surface area SA of rod 10.

It can also be deduced from the rod representation of Figure 3 that the volume for a given indentation, for example indentation 20, can be determined to be the surface area SA multiplied by the depth D of the indentation. Again, the cold-forming i20 i20 process and roll set-up as described herein are able to be configured and operated such that, for the indentations 20, 30, 40, the total volume for all indentations for a given length of rod 10 is approximately greater than or equal to 5% of the volume of the rod 10, if it were unindented.

Experiments conducted by the applicant have also shown that a greater extent/degree of bonding of the tendon with a surrounding material can occur when the indented surface area SA is equal to or greater than 50% of the total circumferential surface area SA and/or when the total volume for all indentations for a given length of rod is approximately greater than or equal to 5% of the volume of the rod.

Reference is now made to Figure 4, which shows a side view of a rock bolt 50.

The rock bolt 50 has five tendons (only three of which can be seen in Figure 4), with each tendon being defined by a rod 10. The rods 10 of rock bolt 50 are generally as described above with reference to Figures 1 to 3 (i.e. having a plurality of indentations 20, 30, 40 around their circumferences and along their length). The rock bolt 50 is also shown with the rods 10 having ends 52 that are co-terminated by a head portion in the form of a boss 54. The boss 54 maintains a spacing, or gap, between rods 10 to allow 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 for grout, filler or adhesive to be pumped or to flow therebetween, and to thereby provide additional surface area for bonding with the grout, filler or adhesive. It is also possible to provide intermediary spacers along the length of the tendons to maintain, or to widen or narrow, the spacing/gaps therebetween.

While the rock bolt 50 in Figure 4 is shown having all five tendons in the form of rods 10, it should be appreciated by a person of ordinary skill in the art that the tendons may take another form, such as straight (unindented) rods, or rods with ribs (i.e. raised rather than indented), or with other indentation patterns. Similarly, the tendons may be a combination of rods some or parts of which have indentations/ribs, and some or parts of which do not. Similarly, while the rock bolt 50 is shown having five tendons, a person of ordinary skill in the art would appreciate that fewer or more tendons may be utilised, and depending on the use requirements of the rock bolt.

Reference is now made to Figures 5A to 5C, which show side and plan views, and a cross-sectional detail taken on the line C-C, of one (of a number of) toothed rolls suitable for implementing a cold-forming process as described herein to produce indented tendon as described with reference to Figures 1 to 4.

Each toothed roll 60 comprises a number of teeth 62 formed in and around a groove 64 that extends around the periphery 66 of the circular roll. In addition, a plurality of discrete, spaced and transversely extending but transversely angled mini grooves 68 are formed in the roll, across the peripheral groove. Adjacent grooves 68 define a respective tooth 62 therebetween.

As best shown in Figure 5C, each groove 68 is provided with opposing side walls 69 which extend out from a base of the groove at an incline. Whilst Figure 5C shows the incline as 40º, the inclination may vary. In addition, a chamfer is provided along an edge of each side wall, i.e. where it intersects with a respective tooth 62.

Again, whilst Figure 5C shows a 0.2 mm chamfer, the chamfer may be varied. It is this combination of transverse and angled extending of the grooves 68, together with a predetermined incline and chamfering, which enables the teeth 62 to impart the predetermined configuration to the indentations 20, 30 and 40 (i.e. as described above for Figures 1 to 3) of a given rod 10. In this regard, such indentations are imparted to an unindented metal (e.g. high carbon steel) rod that is fed and passed in and through opposing grooves 64 of a number of opposing such toothed rolls 60.

Examples Non-limiting Examples of a reinforcing element employing the rod 10 of Figures 1 to 3 will now be described to illustrate how the rods were utilised in, for example, a rock bolt such as that shown in Figure 4, or in concrete reinforcement. It 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 should, however, be appreciated that the rod 10 was able to be modified for use in other reinforcing applications and arrangements.

In each instance, a cold-drawn rod 10 was cold-rolled through a set of toothed rolls three times, to obtain the indentations 20, 30, 40 around the circumference and along the length thereof. Depth and chord ‘e’ measurements were taken to ensure that the rod 10 (and subsequent rods) were within the accepted specifications.

Example 1 A rod 10 for use in concrete railway sleepers was selected. In this application, five full length rods were required, with the sleepers being cut from a larger concrete slab.

Each rod was suitably spaced and positioned in a mould, and was tension applied longitudinally thereto. Concrete was then poured into the mould to surround and bond to the rods, and was allowed to cure for less than 24 hours. After this time, it was possible to release the tension from the rods and remove the concrete from the mould.

The concrete slab was then cut into predetermined size segments in a known manner to form the railway sleepers. The sleepers were left to finish curing for 28 days.

It was observed that the new indentation configurations allowed the tension to be released from the rods earlier than with known rods. This was equivalent to a time saving of about 15%.

Example 2 A rod 10 for use in a concrete slab was selected. In this application, sixteen half length rods were required, so eight rods were selected and cut in half. Each half-rod was suitably spaced and positioned in a grid formation within an area framed by formwork at the location where the slab was being poured. Longitudinal tension was then applied at the ends of each rod.

Concrete was then poured into the formwork to surround and bond to the rods, and was allowed to cure for three days. It was then possible to remove the tension from the rods and the concrete was left to finish curing for 28 days. In this example, it was observed that the use of the newly configured indented rods allowed a lower grade of concrete to be used, without a reduction in the overall strength of the concrete structure.

Example 3 A rod 10 for use in forming a rock bolt 50 was selected. The rock bolt 50 was fabricated with five tendons, such as a rock bolt as shown in Figure 4. Each tendon 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 comprised an indented rod 10. A single length of rod was cut into five varying lengths to form the five tendons, whereby each tendon comprised a plurality of indentations around its circumference and along its length. At one end of the to-be-formed rock bolt, an end of each tendon was aligned with an end of each other tendon, and the tendons were then co-terminated by moulding a head portion around the ends. In the resultant head portion the tendon ends were maintained spaced apart, to maintain a spacing between the tendons in the finished rock bolt. Discrete, intermediate spacers were also positioned at various distances along the length of the tendons to maintain the spacing.

The finished rock bolt 50 was part-way inserted into a pre-drilled bore hole.

Grout was pumped into the bore hole and was able to flow in to surround and extend between the tendons of the rock bolt. The grout was continued to be pumped as the rock bolt was inserted fully into the bore hole and the rock bolt was held in place until the grout set/cured.

Example 4 A rod 10 for use in forming a rock bolt was selected. The rock bolt was fabricated with seven tendons, having a combination of four indented rods 10 and three unindented rods. A single length of rod 10 was cut into four equal lengths to form the four indented tendons, whereby each indented tendon comprised a plurality of indentations around its circumference and along its length. A length of unindented rod was also cut into three lengths, equal to the lengths of the cut indented tendons, to form the three unindented tendons. The seven tendons were then arranged such that one of the indented tendons formed a core tendon and around which the other six tendons were arranged. The remaining three indented and three unindented tendons were arranged alternatingly (i.e. an unindented tendon had indented tendons located on either side thereof, and vice versa). At one end of the to-be-formed rock bolt, an end of each tendon was aligned with an end of each other tendon, and the tendons were then co- terminated by welding a head portion around the ends. Again, in the resultant head portion the tendon ends were maintained spaced apart, to maintain a spacing between the tendons in the finished rock bolt. Discrete, intermediate spacers were also positioned at various distances along the length of the tendons to maintain the spacing.

Again, the finished rock bolt was part-way inserted into a pre-drilled bore hole and grout was pumped thereinto, to flow in and to surround and extend between the tendons of the rock bolt. The grout was continued to be pumped as the rock bolt was fully inserted into the bore hole, and the rock bolt was held in place until the grout set/cured. 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14 It is noted that the controlled cold-rolling of indentations into especially a cold- drawn tendon such as wire, rod and bar as disclosed herein is able produce a tendon having a number of desirable characteristics for an end user of the tendon (e.g. a builder, a miner, or a manufacturer of concrete reinforced products). Such characteristics include high tensile resistance, low relaxation characteristic, indentations formed with a high and consistent tolerance, as well as consistently along the length of the tendon, with more precise control of the volume and shape of each indentation.

Such tendons can make the end uses in which the tendons are employed more efficient, and of increased composite strength and performance.

Whilst a number of specific tendons, rock bolts and cold-forming processes thereof have been described, it should be appreciated that the tendons, rock bolts and cold-forming processes can be embodied in many other forms.

In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the tendons, rock bolts and cold-forming processes thereof as disclosed herein. 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/12/14

Claims (6)

CLAIMS 1.:

1. A tendon comprising a plurality of indentations that have been cold-rolled into the tendon along the length and around the circumference thereof, each indentation 5 having opposing edges which generally extend longitudinally and in parallel to a longitudinal centreline of the tendon, wherein, when the tendon is viewed in transverse cross-section through the indentation from one edge to the other, and an axis is projected from the longitudinal centreline of the tendon to bisect a chord that extends between the edges, a base of each indentation is defined by a radius which extends from 10 a point on the axis which is near to but offset from the tendon centreline, with the radius being approximately equal to or less than a radius of the tendon at an unindented portion thereof.

2. A tendon as claimed in claim 1 wherein the base of each indentation which is 15 defined by the offset radius extends for a substantial proportion of the indentation base when the tendon is viewed in transverse cross-section.

3. A tendon as claimed in claim 2 wherein the extent of the base defined by the offset radius results in a corner radius at each of the opposing edges of the indentation 20 that is less than half the depth of the indentation.

4. A tendon as claimed in any one of the preceding claims wherein, when the tendon is viewed in transverse cross-section through the indentation from one edge to the other, a chord ‘e’ can be defined as the straight line distance between adjacent edges 25 of adjacent indentations, each edge being where each indentation commences, such that the sum of each such chord, when moving one revolution around the centreline of the tendon, produces a value in the range of 0.1 of the circumference of the unindented tendon. 30

5. A tendon as claimed in any one of the preceding claims wherein, for a given length of tendon, there is a total circumferential surface area SA which is equal to the circumference multiplied by the given length, and wherein there is an indented surface area SA which is that part of the total circumferential surface area SA which has been i tot indented, whereby the indented surface area SA is approximately equal to or greater 35 than 50% of the total circumferential surface area SA .

6. A tendon as claimed in any one of the preceding claims wherein a depth of a 6080607_1 (GHMatters) P89418.NZ SAMANTHA 24/