The present invention relates to prestressed concrete posts as well as to a method for manufacturing prestressed concrete posts.

Prestressed concrete posts have many applications, for example they may be used as fence posts or orchard posts. Typical fence posts are 2,20m high. Common orchard posts can be used for netting or trellis support, for example 3-4 m long posts can be used as a support for fruit trees in espalier orchard design, and 5 m long posts can be used for mounting anti-hail nets in such orchards.

The prestressed concrete posts are expected to have high reliability and durability. The prestressed concrete posts have higher, as compared to reinforced concrete posts, strength parameters at significantly improved elasticity, as well as they are characterised by high reliability.

In known prestressed concrete posts manufacturing techniques, a mould comprising parallel trays (formworks) is used, wherein prestressing tendons are stretched and which are then filled with concrete. After the concrete has solidified in the mould, the posts can be taken out of the mould and cut into posts having a required length. In this manner, posts of different lengths can be manufactured, even up to 120 meters.

There is a need to provide an alternative structure as well as an alternative method for manufacturing prestressed concrete posts, which would allow production of posts having a weight lower than typical prestressed concrete posts, in order to facilitate transportation as well as installation of the posts.

The object of the invention is a method for manufacturing prestressed concrete posts, the method comprising the steps of: providing a mould comprising a plurality of trays with prestressing tendons arranged lengthwise in the trays; and filling the trays with concrete and allowing the concrete to solidify within the tray; the method being characterised by: filling the trays with concrete using a concrete container mounted on a movable carriage over the trays, the container comprising mandrels arranged in correspondence with the trays such that the mandrels are submerged in the concrete output from the container when filling the trays; moving the carriage along the trays, thereby forming, in the concrete being poured into the trays, openings having a cross-section corresponding to the mandrels.

The container may have a concrete outlet having a width corresponding to the width of the mould such that during a single run of the carriage along the mould, all trays are filled with the concrete.

The container may have a plurality of outlets and during a single run of the carriage along the mould, a subset of the trays is filled with the concrete via one of the outlets, and wherein in a subsequent run of the carriage along the mould, a different subset of the trays is filled with the concrete via another of the outlets.

The container may have an outlet of a width smaller than the width of the mould and wherein during a single run of the carriage along the mould, a subset of the trays is filled with the concrete, and thereafter the carriage is moved perpendicularly to the mould and in a subsequent run of the carriage along the mould, a different subset of the trays is filled with the concrete.

The method may further comprise applying vibrations to the concrete in the tray in proximity to the mandrel when filling the tray.

The method may further comprise pressing the concrete in the tray in proximity to the mandrel when filling the tray.

The mandrels can be shorter than the tray.

Another object of the invention is a prestressed concrete post comprising prestressing tendons arranged along its length, characterised by comprising a through hole within the concrete along the length of the post between the prestressing tendons, the through hole being formed prior to solidification of the concrete.

The object of the invention is shown by means of exemplary embodiments on a drawing in which:

• Fig. 1 presents a manufacturing line for manufacturing prestressed concrete posts according to the invention;
• Fig. 2 shows a mould with trays and a movable carriage in a perspective view of a first embodiment of the invention;
• Fig. 3 shows a mould with trays and a movable carriage in a top view of a first embodiment of the invention;
• Fig. 4 shows a mould with trays and a movable carriage in a top view of a second embodiment of the invention;
• Fig. 5 presents a the trays during filling;
• Fig. 6 depicts a mould with trays and a movable carriage in a perspective view of a third embodiment of the invention;
• Fig. 7A-7E show prestressed concrete posts according to various embodiments of the invention.

Fig. 1 presents a manufacturing line for manufacturing prestressed concrete posts according to the invention.

A mixer 110 is used to prepare concrete of a class selected accordingly to the required durability of the post to be manufactured. A composition of the concrete mixture is selected according to known methods of concrete technology.

A mould 130 for manufacturing the posts comprises a plurality of long trays 131, having a length being a multiplicity of a length of a single post (for example, 40 meters or even up to 120 meters). The trays 131 have preferably rounded bottom internal edges, which after cleansing are lubricated with an anti-adhesive agent to facilitate later extraction of the post from the tray 131. A prestressing tendon 12 is arranged lengthwise in the tray 131 and stretched. A single mould 130 may comprise a few, a dozen or even a few dozen trays.

The trays 131 of the mould 130 are filled with concrete 11 prepared in the mixer 110. A first embodiment of the mould is shown in Figs. 2 and 3. The concrete 11 is poured to the mould from above from a movable carriage 132, propelled by an engine, on which a container 134 for concrete is mounted. The container 134 has a concrete discharging outlet 135 and mandrels 137 mounted below the outlet 135. The mandrels 137 may have a length of e.g. 1 m and a diameter of e.g. 2 cm. The mandrels 137 are submerged in the concrete 11 and move along with the carriage 132 in a direction parallel to the trays 131 along a full length of the element being formed, thereby forming through holes 13 in the concrete 11 that fills the trays 131.

The concrete 11 shall have a consistency such that the through holes 13 are not backfilled and stay as formed while the concrete 11 solidifies. For example, a concrete of a stiff - flowing consistency according to a Polish norm PN-88/B-06250:1988 or a concrete of a S1 class according to a norm EN 206:2014 and EN 12350-2:2011.

In a second embodiment, as shown in Fig. 4, the container 134 may comprise a plurality of outlets 135A, 135B, 135C, for simultaneous filling of some (e.g. a few or a dozen or so), but not all the trays 131, so that in a single run of the carriage 132 along the mould 130 only a subset of the trays 131 is filled.

In a third embodiment, as shown schematically in Fig. 6, the container 134A may have a width smaller than the width of the mould 130, i.e. a width of a few or a dozen or so, but not all the trays 131, so that in a single run of the carriage 132 along the mould 130 only a subset of the trays 131 is filled.

By filling only a subset of the trays 131 in a single run, as in the second and third embodiment, the amount of concrete required for a single run is limited, which allows for use of a relatively small container 134 and does not require much energy to move the carriage 132 along the mould 130 in order to form the through holes by the mandrels 137. Thereby, a relatively low power engine can be used to drive the carriage. In such a case, after filling a first subset of trays 131, i.e. after a first run of the carriage 132 along the full length of the mould 130, the mandrels 137 are lifted up above the trays 131 and the carriage returns to its initial position, i.e. to the front end of the trays 131. Thereafter, the concrete outlet 135 is opened over the trays 131 that have not been filled (according to the second embodiment) or the container 134 is moved over the unfilled trays (according to the third embodiment) and a subsequent run is executed, thereby filling subsequent trays and forming therein posts with the through holes. Fig. 5 presents a close up on the trays during the filling wherein a subset of trays 131A has been filled with concrete, thereby forming the posts 11 with the through holes 13 and wherein another subset of trays 131B is to be filled in a subsequent run.

In the first embodiment, all trays are filled in a single run, therefore the carriage does not need to return to the initial position after filling the trays.

In order to improve consolidation of the concrete poured into the trays 131, and to remove air bubbles, the carriage 132 may comprise a vibrating and/or a pressing device. The device shall act on a top surface of the poured concrete in proximity to the mandrel, preferably at a distance from a distal (free) end of the mandrel so that a shape of the formed through hole 13 which has been already formed and from which the mandrel has already been removed, is not affected. Therefore, the vibrating and/or pressing device shall act on the concrete 11 volume over the part of the through hole 13 being formed that still compromises the mandrel 137 therein.

After some time has elapsed, for example 2 hours from filling the mould with the concrete, the concrete can be heated (for example with steam) by means of a heating installation 140, in order to accelerate the consolidation of the concrete. The concrete may be heated for example to 60°C at a rate of 10°C per hour. After the concrete has reached the required durability, for example at least 50% of the final durability, the formed posts may be taken out of the trays 131 by releasing the stretch of the prestressing tendons 12 and lifting the posts up above the trays 131. Subsequently, the posts may be cut into the required lengths (for example 2,20m or 3,70m) using a circular saw on a cutting station 150. The finished posts can be labelled and stacked. The concrete achieves its durability after 28 days from solidification.

Figs. 7A - 7C show examples of prestressed concrete posts comprising prestressing tendons 12 in form of 3-wire strands made of steel.

Fig. 7A shows a prestressed concrete post for use in orchards with four tendons 12 and a circular through hole 13A.

Fig. 7B shows a prestressed concrete post for use in orchards with six tendons 12 and an oblong through hole 13B.

Fig. 7C shows a prestressed concrete post for use in orchards with six tendons 12 and an oblong through hole 13A having a central contraction.

The posts may have a trapezoidal cross-section as shown in Fig. 7A - 7C or other shapes, for example octagonal as shown in Fig. 7D or substantially oval as shown in Fig. 7E.

The trapezoidal form can be conveniently formed in a trapezoidal tray, with rounded internal edges, having a bottom which forms the shorter base of the trapezoid, which facilitates lifting up the formed posts from the trays. The side walls of the tray ma be inclined at an angle from 3 to 30 degrees.

A length of the post is determined by its application and typically ranges from 2,20 m to 5 m. A width and a height of a cross-section of the post, at the widest point, are determined by the required durability of the post and typically range from 3 cm to 30 cm. Preferably, the width is equal to the height and ranges from 7 to 9 cm.

In other embodiments, other types of the prestressing tendons 12 can be used, such as multi-wire strands (e.g. from 2 up to 7 wires) or a profiled wire. The prestressing tendon 12 can be made of steel or other material.

The shape of the through hole 13 may be selected depending on the geometry of the post and depends on the shape of the mandrel 137, which forms the through-hole in the concrete 11 volume before it has solidified. The container 134 may have different mandrels 137 attached to it, in order to form different through-holes in the trays 131.

Thus, the concrete post as described herein comprises a through hole 13A-13E within the concrete 11 along the length of the post between the prestressing tendons 12, the through hole 13A-13E being formed prior to solidification of the concrete 11. In other words, the through hole 13A - 13E is positioned on a line connecting, in the cross-section, at least two prestressing tendons 12. Preferably, a geometric centre of the through hole 13A - 13E is located at the geometric centre of the post.

The structure of the posts as described herein and the method for manufacturing the posts enable production of posts having a lower weight than standard prestressed concrete posts, which facilitates transport and installation of the posts. In addition, the lower amount of aggregates and cement used to manufacture a single post has a positive ecological aspect - posts can be more easily recycled.