NZ769929A - A shortenable void former for concrete structures - Google Patents

Abstract

A shortenable void former having an internal volume for excluding concrete from part of a structure, the shortenable void former comprising a truncated quadrilateral pyramid (100) having a top plane (106), a base plane, and a body with a closed top (107), closed side walls (108), a first closed end (101) and a second closed end (102). The base plane includes an open base surrounded by a skirt (109) to lie against a substrate. The first closed end (101) comprises a shaped end cap having an internal surface at a height substantially the same height above the base plane as the top plane of the shortenable void former body. In use, the end cap is capable of being separated from the shortenable void former, and then replaced so as to overlie and seal a shortened portion of the shortenable void former. The invention provides a void former that can be shortened to fit within a restricted space or against a pipe or an angled end, with the replaceable end cap acting to reseal the internal volume and preventing ingress of wet concrete.

Description

IT L E A SHORTENABLE VOID FORMER FOR CONCRETE STRUCTURES.

This invention relates to building uction; more particularly to the construction of concrete floors or other , and especially to the provision of void formers for use in the construction of concrete floors in order to balance the strength of concrete against the mass of concrete in such floors.

BACKGROUND It is nown to construct a concrete slab floor for such as a house out of concrete and to reinforce the floor with a matrix ofpre-assembled steel reinforcing bars to provide e strength. The floor of concrete a width, a length, and a depth and is a beam having stiffness conferred by the concrete and the mandatory reinforcing bars included. (Of course the invention is not restricted to use with te slab floors). During construction of a reinforced te ure there is a phase when the rk — the reinforced steel ) rods ties and links , are visible but not concealed by concrete. The bars will have been assembled upon a prepared substrate of grade, covered with a damp-course. The substrate and the formwork optionally includes piping for ng, cables, drains, and other utilities, and pile structures such as for supporting extra stories or to better anchor the floor to the substrate. A surround is built as boxing or shuttering, and then wet concrete is poured over the assembled bars and agitated enough to remove trapped air. The stiffness of such a floor, given a finite amount of concrete, can be increased ifthc depth of the slab is increased. This document relates to improvements in ways to optimize the strength by increasing the depth yet excluding concrete from parts ofthe slab floor that do not include reinforcing. The preferred exclusion method is to include sacrificial void formers at controlled positions.

For e the widely used "RlB-RAFT"® floor (trade mark of Fletcher Building Holdings Limited (NZ) ) embeds 3 number of polystyrene foam cubes as void formers within the concrete. They provide a thicker floor in cross-section, which will be stronger, without a proportional increase in concrete. Each cube is typically 1.0 — 1.1 metres square and has a height of perhaps 300 to 400 mm. Each cube is spaced apart from the adjoining cubes and the spacing may for example be maintained by wire stirrups that are also adapted to support reinforcing bars at a prescribed position, far from exposed surfaces, inside the concrete after pouring; alternatively by plastic spacers which lie in between the cubes upon the damp course, preferably at cube comers, and which e reinforcing bar supports.

Other kinds of spacer in a mesh of reinforcing rods over the surface of the void s, to be embedded in a sheet of te, so that all parts of the floor have a satisfactory load strength after the concrete has cured. Except at sites where piping or piles 40 penetrate the surface the slab floor has an upper surface including the mesh and an array of intersecting deep extensions that run in between the void formers and carry the steel rcing. The void formers provide the te floor with more height and hence strength to resist bending forces. It will be appreciated that the main contribution of the void formers is to keep the te, when poured wet, outside the defined volumes and 45 y save 75% or more of the total amount of concrete required. The voids have a temporary weight-bearing strength requirement at first — to survive being walked upon before the concrete has hardened. The ys force exerted by wet concrete, which is relatively dense, can tend to implode a weak void former.

PRIOR A 50 Void formers are usually manufactured. Formers that comprise empty boxes or shells include cardboard boxes (US 3,708,929), sheet steel boxes or shuttering perhaps using corrugated sides and ends to add strength (US 1,753,496) and wooden boxes (GB 1,179,430 for wood—chip, ribbed void formers). Cardboard boxes are one known alternative.

While the void former is needed to have strength temporarily, before the concrete sets, one 55 must remember that if the building is demolished it is inconvenient to find rusted or ise deteriorated void formers mixed in with concrete. An n product (EP 1263 843) uses the strength inherent in a dome—shaped sheet to provide formed sheet plastics void formers that have enough strength to be walked over before the concrete has set. US 20080035830 and US 20070214740 describe plastics-moulded void formers essentially 60 comprising a moulded plastics box with an open base and details within the formed surface such as corrugations and internal leg supports that confer extra th for the weight.

PROBLEM TO BE SOLVED One problem not ly solved by the prior art is how to conveniently close off the interior of the void former. In particular, from time to time the actual space available 65 happens to be smaller than the unit size of the former, which therefore must be reduced in size.

Providing the formwork constructors with a range of sizes of box or shell s to fit any space — gular or otherwise — is rendered ible by issues such as manufacturing costs and g stock. The cost of manufacture may include the significant cost of a 70 mould for each incremental size if the void former is made by ng.

A solid block of foam can be cut across using a hot wire cutter or a saw. lfa polystyrene or other solid plastics foam block used as a void former is sawn or cut in order to fit the block into a non-modular place, the foam and dust becomes an environmental hazard that has to be disposed of. It has to be picked up, bagged and taken to a dump where extra fees are 75 charged according to the nature of the foam plastics material. It will still be present when the building is demolished. Also, bits of foam that may break off during pouring tend to rise to the surface of the setting te where they leave defects in the surface. But when an empty box or shell serving as a void former is cut across, effective sealing means are required in order to prevent a slurry of wet cement flowing into the interior of the void 80 former.

DESIRABLE OUTCOMES A desirable outcome of the present application is to provide a suitable, efficient and preferably also economic alternative to the use of existing void formers within concrete uctions, or at least to provide the public with a useful choice. 85 In particular the present ation bypasses a need for supply of separate barrier strips.

More particularly, the moulded plastic formers should be elosablc even if the overall void size is restricted such that an entire void former will not fit into an existing space.

SUMMARY OF INVENTI In a first broad aspect the invention es a shortenable void former having an internal 90 volume for the purpose of excluding concrete from part of a structure to be comprised of reinforced concrete, the shortenable void former comprising a truncated quadrilateral pyramid having a top plane and a base plane and having a body with a closed top, closed sides, a first closed end and a second closed end, and an open base; wherein each shortenable void former has a shaped end cap comprising at least one closed end of the 95 shortenable void former; the end cap having an internal surface at a height at substantially the same height above the base plane as the external height or top plane of the shortenable void former body, so that when in use the end cap is capable of being separated from, and then ed over so as to overlie and seal a shortened portion of the shortenable void former. 100 ably both the first and the second closed ends are manufactured with removable end caps.

Preferably indicia or moulded s indicating a cut line are capable, when in use, of guiding a cutting means in order to separate the end cap from the body.

Optionally each nable void former is made in a bright colour selected from a range 105 including orange, so that, when in place in formwork, a person can readily see where each nable void former is d.

Preferably the shortenable void former is comprised of a substance selected from a range consisting ofa thermoplastics, an alloy of virgin and recycled thermoplastics, and a mixture of thermoplastics and a fibrous material selected from a range including glass fibre, rock 110 wool, wool, hair and synthetic fibres.

Preferably the former is shaped within a mould selected from a range including injection moulding, rotational moulding, drying of a wet pulp of fibrous material, and moulds adapted for a vacuum forming s.

In a second broad aspect the invention provides a method of using the shortenable void 115 former as previously described in this section in order to fit a void former into a space of reduced dimensions, wherein the method ses the steps of: a. ming a cutting operation along the cut line, across the shortenable void former in order to separate the end cap from the body ofthc shortenable void former, 120 b. optionally performing a second cutting operation along a selected line across the shortenable void former in order to shorten the void former, noting that use of the end cap leads to initial overlap of the parts of the shortenable void former, and c. replacing the end cap over the open end of the shortened void former body 125 where it serves as a barrier strip, thereby making a shortened and sealed void former capable of being installed within a restricted space within rk.

In a related aspect the invention provides a method of using the shortcnablc void former within an lar space, wherein the method comprises the further step of optionally cutting the skirt 109 and the top surface 303 of the separated end caps in order to tate 130 bending of the one or more separated end caps into a desired configuration and finally of placing the end cap over a deficiency in the wall of the shortenable void former.

Preferably the bending s is aided by localized g and softening of the thermoplastics.

E F E R R E D 135 P R EMBODIMENT The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention. In particular the dimensions shown in one illustration are purely illustrative.

The invention has been described in an illustrative manner, and it is to be understood that 140 the terminology which has been used is intended to be in the nature of words of description rather than oflimitation. (see US 6363671 O’Mara) hout this cation unless the text requires otherwise, the word "comprise" and variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other 145 r or step or group of integers or steps. Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference.

Reference to cited material or information cited in the text should not be understood as a concession that the material or ation was part of the common general knowledge or was known in New Zealand or in Australia or in any other country. 150 DRAWINGS Fig l: is an e isometric view of a cuboidal, shortenable void former from a corner.

Fig 2: is a longitudinal, dorsoventral cross—section (hereinafter simply "cross-section") of the shortenable void , part of which is a median cut h a rib that intersects an internal leg and part of which is offset and does not intersect a leg. 155 Fig 3: shows detail of the shortcnablc void former in cross-section showing the modified internal height (see also Fig 7a—d) Fig 4: is a plan view of the shortcnablc void former as seen from above Fig 5: is a plan view of the shortenable void former from the eath , the side to be placed upon a substrate. 160 Fig 6 is a schematic cross-section ofa typical prior-art former.

Fig 7 as Figs 7a-7d shows the s, as a series of four diagrams, of cutting the void former of the invention in order to simulate a barrier strip made from either of the moulded ends, within a shortened void former.

Fig 8 as Figs 8a-8e shows use of separated end caps to cover irregular cuts that may be 165 made into the interior space of shortenable void formers.

EXAMPLE 1 Please refer to the illustrations. Fig 6 shows a cross section of a tic prior-art void former in which a characteristic constant thickness, typical of the prior art, is shown.

Vertically directed wall corrugations, ribs over or under the entire top surface, and internal 170 support legs (all not shown) strengthen a relatively thin plastics object. The t application has been modified in order to facilitate conversion of (usually one of) the end caps 200, 406 into detachable barriers for the purpose of stopping ingress of concrete into the interion of a shortened void former, when in use.

Fig 1 is an oblique isometric view ofa al void former 100 from a corner. As is the 175 case in most of the prior art, each former is a "truncated quadrilateral pyramid"; a term including a reference to the tapered outline in the vertical axis , that is maintained within the d internal legs 201. The internal legs share a similar tapering to that of the sides 108, which is of use when moulding and during e and transport. The internal legs, as in the prior art, provide support for vertical loading when in use, including both before and 180 after the concrete has cured.

In Figs 1, 4 and 5 the quadrilateral is a square, as red. The present embodiment is typically about 1100 mm square and 300 mm high, gh dimensions will be varied ing to requirements such as prevailing modular sizes used in buildings such as l x 1.2 metres, or imperial sizes as used in the United States of America. Regardless of actual 185 size, the principles are consistent. Two end surfaces 101 and 102 are destined to be laid against a series oflike void formers, end to end. The other sides do not include the "end- cap modifications" ofthis invention. They may be used as sides, or, within a long array of void s, as ends, ng a square "footprint". The void former 100 is preferably moulded from a thermoplasties material and is intended to be effectively stiff and durable. 190 dge of the resultant material properties, along with suitable control over thickness and shape of moulded parts when d in (for example) ated planes allows the strength of a moulded void former to be ied. A cturing process is selected for principally economic reasons from a range including injection moulding, and a rotational moulding process. Vacuum forming is a possibility. The tapered shapes aid in parting the 195 finished void former from the mould. Selected plastics include, without limitation, virgin or recycled polyethylene (PE), high-density polyethylene (HDPE), polyethylene terephthalate (PET) or mixtures or eopolymers thereof, and the range includes plastics not yet in current use. A bright orange colour may be preferred, especially to help a worker safely navigate a construction area while assembling formwork especially under poor 200 lighting; alternatively any colour although preferably a light colour may be used. On the other hand, dark colours may be expedient for recycled plastics, serving as weather resistance before use. Another option is to make void formers from a paper—pulp process, in which a shaped wire gauze mould is dipped into a slurry of paper fibres and pulled out and dried. It may be impregnated with a wax or a fat. That has the advantage ofnot requiring 205 non-renewable resources from the petroleum industry.The surface of the former is not required to "key" into the concrete. The void former itself serves as a "concrete excluder" not a "strength member" and it may be useful if, at the time of demolition, the void s can be separated from residues of te and steel.

The void former is intended to be site—modifiable as with carpenters’ saws and drills in 210 order to best fit a foundation area with modular formers surrounded with sawn-across parts of formers, to fit around rising utility pipes and cables, and to fit around internal rcing such as between floors. Notably, the void former of this invention carries its own end caps to serve as barriers for exclusion of concrete in the event that an intact void former is too large — especially too long — to fit into an allocated space. 215 The near—vertical side walls are lly scalloped or corrugated to add strength to the walls, as is known in the prior art. As in the prior art, a skirt 109 (fig l) forms a complete surround of the wall of the void former. As shown in Fig 2, the sides 108 slope inward toward the top surface 106 of the body of the shortenable void former in accordance with the ated lateral pyramid" ption; enough to facilitate stacking, storage and 220 transport of the void formers. For that purpose small lugs (110 in Fig l) are provided at intervals along the lower edge of the walls, near the skirt 109 in order to support another former that is stacked above but to maintain a space in between so that adjoining tapered shapes do not lock together. The slant of the slope and the width of a flat base are together sufficiently wide to be used, by making edge contact between one void former and an 225 adjoining former, to define the width of a channel to hold reinforcing bars that is to be formed between adjacent void formers.

The flat top 401 of the void former, as shown in Fig 4, is preferably marked out with dimensional markings 402 such as in a 1 cm x 1 cm grid that may serve as a guide to placing bar stools for ting reinforcing mesh, or as a guide for installing utility piping or the 230 like, or when cutting a former to size. The marks may be d from ridges or grooves in a mould surface. or could be printed on or sprayed on through a mask. Unlike the prior art, Fig 4 includes two ic lines 404 and 405; one near each end, that comprise cutting guides for cutting off the end caps 406 and 407 in relation to an ble configuration within (namely the raised surface 302), although normally only one end would be detached. 235 See below and in relation to Figs 3 and 7a 2 7d for more details ofthc method. The external cutting lines 404, 405 are aligned near the al height step shown in Fig 3 so that a saw blade will separate the end cap accurately from the body of the void former.

As in some prior art, the top surface has an array of open apertures 403 leading to leg interiors best seen in section at 201 in Fig 2 which taper to a still effective diameter and are 240 closed at their bases, located in the plane of the base of the void . The number and spacing of the legs can be varied. It is convenient for a square void former that they are symmetrically placed for convenient stacking. Optimization of the preferred cs suggests a 3 x 3 array of legs for this example; providing either a leg or an edge spaced apart by 200 mm and resting on the floor. The concrete inside the legs when set comprises 245 a series of downwardly ed ressible shafts that helps to it downward forces from the surface of the floor above on to the substrate below. The rced beams created alongside each void former provide the majority of strength for the entire floor slab.

As shown in Fig 5, the underneath surface of the top of the former includes internal strengthening ribs 502 placed in a criss—cross array under the surface 501 and extended 250 downward from the underneath surface. Typically the ribs are 10 mm thick and 15 mm high and are spaced apart by 60 mm, but any sizes that suit the requirements will be acceptable.

The ribs could be laid out in a triangular, hexagonal or octagonal pattern rather than the preferred criss-eross rectangular layout. The ribs add to strength (as resistance to deflection) of the top surface when bearing weight and are intended to be sufficiently strong to bear the 255 weight of a worker walking over the surface or the weight of wet concrete plus mesh reinforcing that provides the floor surface.

Fig 2 is a cross section through a void former, from end to end though with a step in the plane of the cross section so that in the left half side of Fig 2 one (201) and a half tapered legs are cut , but in the right halfthe now offset section misses the legs and misses 260 the rib 202. Note the overall extent of the two end caps — shown in more detail in Fig 3. The projected outlines of corrugations on a far wall surface have been added to the sections.

Fig 3, a scale drawing is from a drawing for a mould, shows a cut surface through an end cap 200. Note that the eath or internal surface 302 of the end cap region 200 of the former is at or is significantly raised above the external height of the remainder of the 265 former 304. The underneath surface 302 is about the same height above the base plane as is the outer surface 304 of the body of the shortenable void former. The raised end cap interior is moulded in shape and position. The configuration allows every void former made according to the invention to provide its own end cap or caps as a variable-position barrier. Fig 3 also shows the internal ribs 301, 202 in section. As shown particularly in Fig 270 3, one or both ends of the void former are ed in order to e the foundation installer with an end cap sized, after being cut off, to fit over a ly shortened void former. The relative heights as ined at the time of mould design are a compromise between raised end cap heights and main body , given that an overly exaggerated rise will tend to distort placement of the reinforcing mesh as a later stage of foundation 275 assembly, but the mesh will be supported on bar stools or like supports in any case. Fig 3 also es a line, 404/405 which is a grooved line or an indicium that directs a person operating a saw to cut off the end cap 200 without including the thicker main top 300.

Fig 6 shows in schematic cross—section a typical art void former lacking the evident changes in internal height at the ends, intended to allow effective use of an end-cap if 280 removed and replaced Fig 7 is a series (a—d) based on a schematic version ofthe cross— section of the present invention shown in Figs 2 and 3 as shown in Fig 7 For the purpose of ting an end cap, Fig 7b shows, as a dashed line 701, one g line to be made along either line 404 or line 405 (see Fig 4) that will guide the saw accurately so that the removed end cap 200 has a higher internal e than that of the 285 top of the body 300 of the void former.

In Fig 7c the end cap shows another dashed line 702 to be cut through the void former body at a measured position which, when re-aligned under the end cap 200 as shown in Fig 7d, will produce a shorter void former that remains sealed.

Fig 7d shows the resulting shortened void former re-sealed by the end cap 200 as 290 separated previously. The other end cap 406 had not been modified. This diagram has produced a modified void former about 650 mm in length. All parts meet the plane ofthe base or surface of the substrate at about the same plane so that no significant leaks of wet slurry into the interior will occur.

A M PL E 295 E X 2 On occasion a void former will require to be cut to meet specific site requirements other than simple shortening of the void former . For example, only a corner may need to be taken out (see the void former 804 in Fig 8C), or an angled end is required (see the void former 805 in Fig 8d), or part ofa side needs to be taken out (see the void former 806 in 300 Fig 8c), such as to enclose a pipe. The symbol "X" denotes removed void former. Fig 8 c-e do not show the lower skiit. In all cases, one or more d end caps can be used on the side of the altered shortenable void former in order to maintain integrity. In some cases it may be necessary to join two end caps in order to create a longer barrier. Duct tape may be used to seal holes and to maintain the modified side walls in position. 305 The process for using a severed end cap taken from a shortenable void former is as follows: A severed end cap essentially comprises a length ofa "Z section" plastics material having a lower skirt 109, a side wall 108 and a top skirt 303 as shown diagrammatically in Fig 8a. Modifications usually e that the lower skirt and the top skirt ofthc severed end cap be cut such as with strong scissors or with tinsnips or a 310 w, as is commonplace in sheet metal work for example. In some cases the cut edges may p at corners as occurs at 802 in the skirt between Fig 8a and the bent version ofthe end cap as shown in Fig 8b; otherwise the cut edges are bent apart as occurs at 801 in the modified upper part of the cap between Fig 8a and Fig 8b.

Deformation of the severed end cap is caused by bending the wall 108 along a fold line at 315 a desired angle between the cuts 801, 802 in the skirt, normally by simple force or with the aid of a heat gun (hot-air gun) to soften the therrnoplasties. The heat gun will help in imating the bend around an imaginary vertical axis by stretching or pushing together the material at the bend, since the side wall 108 is at a slope relative to the power skirt and the top skirt.

RESULTS AND ADVANTAGES In a prototype made of fiberglass, a video camera placed inside the cavity showed no ingress of concrete slurry while the prototype was being buried in wet concrete in the usual way for concrete structures. 325 Advantages: only one size and shape of void former need be ctured thereby saving in mould costs, shipping, storage, and on—site inventory. No separate barrier strips are needed, since the formwork lers always obtain barrier strips from cut-down shortcnablc void formers when needed for sealing partial or incomplete void formers.

The invention overcomes foamed plastics restrictions imposed at building sites for 330 nmental reasons. Offeuts or scraps of foamed cs are a disposal problem.

Unlike domed versions of the prior art, the upper surfaces of the void formers are flat, allowing use ofa consistent minimum thickness ofconcrete that is ed in depth over an inter-pod channel.

The invention permits stacking of void formers into iently liftable stacks of 335 perhaps 10 formers; so that a typical floor for a dwelling can be made of stacks transported to the site perhaps With tens stacked on top of each other to make fewer piles and only part of a truck load.

Finally it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will iate that 340 various modifications, additions and substitutions are possible Without departing from the scope and spirit of the invention as set forth in the ing claims.

Claims (6)

WE CLAIM

1. A shortenable void former having an internal volume for the purpose of excluding concrete from part of a structure to be sed of reinforced te, the 345 shortenable void former comprising a truncated quadrilateral pyramid having a top plane and a base plane and having a body with a closed top, closed sides, a first closed end and a second closed end; the base plane including an open base to lie against a substrate; wherein each shortenable void former has a shaped end cap comprising a closed end; the end cap having an internal surface at a 350 height at substantially the same height above the base plane as the external height or top plane of the shortenable void former body, so that when in use the end cap is capable of being ted from, and then replaced so as to overlie and seal a shortened n of the shortenable void former.

2. The nable void former as claimed in claim 1, wherein removable end cap 355 configurations are included as both the first and the second closed ends.

3. The shortenable void former as claimed in claim 1, wherein indicia indicating a cut line are located on an external surface and are capable, when in use, of guiding a cutting means in order to te the end cap from the body.

4. The shortenable void former as claimed in claim 1, made in a bright colour 360 selected from a range including orange, so that, when in place in rk, a person can readily see where each shortenable void former is located.

5. A method of using the shortenable void former as claimed in claim 3 in order to fit a void former into a space of reduced dimensions, wherein the method comprises the steps of: 365 a. performing a cutting operation along the cut line across the shortenable void former in order to separate the end cap from the body of the shortenable void former, b. optionally performing a second cutting operation along a selected line across the shortenable void former in order to shorten the void former, 370 noting that use of the end cap as a separated part causes initial overlap of the parts of the nable void former, and c. placing the end cap over the open end of the ned void former body where it serves as a sealing barrier, thereby making a shortened and sealed void former capable of being installed within a restricted space 37 within rk.

6. A method as claimed in claim 5 of using the shortenable void former in order to fit a void former into an irregular space, wherein the method comprises the further step of optionally cutting the skirt 109 and the top surface 303 of a separated end cap in order to facilitate bending, and then bending the end cap 380 into a desired configuration and finally of placing the end cap over a deficiency in the wall.