AU6838894A - Improvements in concrete floor construction - Google Patents

Description

TITLE IMPROVEMENTS IN CONCRETE FLOOR CONSTRUCTION

FIELD OF THE INVENTION This invention is concerned with improvements in methods for constructing concrete floors or slab constructions and an apparatus for so doing.

BACKGROUND ART In the construction of large concrete slabs for floors and the like, it is customary to first cast a slab of a size capable of being worked by concrete finishers and then cast further slabs in abutment thereto.

After preparing the ground surface formwork defining the peripheral edges of the slab is erected and reinforcing mesh is positioned within the formwork surround and supported above the ground surface by spacers known as "bar chairs".

In order to maintain the upper surfaces of adjacent slabs in the same plane, steel reinforcing rods known as "dowel bars" are cast into the initial slab with a portion projecting from the side walls of that slab. When an adjacent slab is poured, the projecting portion of the dowel bar is encapsulated within the adjacent slab to resist relative movement in an upright plane between the edges of adjacent slabs. As some horizontal movement between adjacent slabs is inevitable due to thermal expansion and contraction, the free end of the dowel bar extending from the edge of a slab is coated with oil or grease to prevent adhesion in the subsequently poured adjacent slab. By allowing the dowel bar to slide within one slab during expansion or contraction, edge fractures are thereby avoided. Dowel bars for a floor slab construction typically comprise 300 mm to 600 mm lengths of 10 to 30 mm diameter round or square section steel bar arranged at about 600 mm intervals along the edge of a previously cast slab. The dowel bars extend into each adjacent slab from 150 mm to 300 mm.

Although the dowel bars are generally effective for their intended purpose, the method currently employed for positioning the bars in the initial slab edge is far from satisfactory in that not only is it extremely time consuming and therefore costly, it can lead to considerable frustration on the part of those engaged in slab construction.

At present, it is customary for specialised formwork erectors to erect a timber formwork surround for a slab to be cast and then to drill apertures for the dowel bars at approximately 300 mm to 600 mm intervals. The apertures are a neat fit to avoid leakage of concrete through these apertures when the slab is cast. Another team specialised in positioning the steel reinforcing mesh then takes over and sets up the necessary reinforcing structure including the steel dowel bars which protrude outwardly from the apertures in the formwork surrounds.

The main problem associated with this technique is that it is practically impossible to position the dowel bars perfectly parallel in both the upright and horizontal planes. Accordingly, after the slab has cured, extreme difficulty is incurred in removal of the formwork (usually a long timber plank) as a consequence of the non parallel array of protruding ends. To avoid loosening the dowel bars cast into the slab and also to avoid damage to the edge of the slab by attempting to lever the formwork away from the slab, it has become customary to cut the formwork between adjacent dowel bars and slide each segment over the protruding portion of the dowel bar. Apart from being a costly waste of time and materials, this procedure is frustrating and difficult in view of the fact that the formwork extends to the ground surface thus necessitating a hole to be dug into the ground to enable an electric saw to cut all the way through the formwork.

SUMMARY OF THE INVENTION It is an aim of the present invention to overcome or ameliorate the problems associated with construction of concrete floor slabs or the like and to provide an improved method and apparatus therefor.

According to one aspect of the invention there is provided a dowel bar socket for cast concrete slabs, said socket comprising:- a hollow tubular body, said body having an opening at one end and a closure at its opposite end; and, attachment means adjacent said opening for attaching, in use, said body to an inner surface of a formwork member.

Suitably said attachment means is formed integrally with said body.

Alternatively said attachment means is removably securable to said body.

Preferably said attachment means includes a securing flange for securing said body substantially perpendicular to a surface. Preferably said securing flange is adapted to be released from a surface to which said flange is secured by tension therebetween.

The dowel bar socket may be formed integrally with a plurality of hollow tubular bodies, each body being spaced from an adjacent body by spacer means.

If required a releasably securably spacer means may be employed in use to space adjacent hollow tubular bodies at predetermined intervals.

Suitably said socket includes retention means to prevent withdrawal from a body of concrete cast therearound. If required said hollow body may include longitudinal ribs extending inwardly of an inner wall of said body. Suitably said ribs are spaced about the periphery of the inner wall.

The ribs may be longitudinally tapered. Preferably the ribs taper convergently from adjacent said opening towards said closure.

Alternatively said socket is adapted to permit withdrawal from a body of concrete cast therearound.

According to another aspect of the invention there is provided a method for formation of cast concrete slabs said method comprising the steps of:- erecting at least one formwork barrier defining a peripheral edge of a concrete slab to be cast; securing at spaced intervals on an inner face of said at least one formwork barrier a plurality of dowel bar sockets, said sockets each comprising a hollow tubular body having a closure at an end remote from said inner face and an opening at an opposite end adjacent said inner face, said dowel bar sockets each being secured to said inner face by attachment means associated with said hollow tubular body; pouring a fluid concrete mix into said formwork barrier to form a concrete slab, finishing the surface of the slab and allowing the slab to at least partially cure; and, removing said at least one formwork barrier whereby a plurality of spaced, substantially parallel tubular apertures are formed in one or more upright edges of said concrete slab, said tubular apertures each being capable of slidably receiving to a predetermined penetration a dowel bar which protrudes from an upright edge of said slab for encapsulation in an adjacently cast concrete slab.

BRIEF DESCRIPTION OF DRAWINGS In order that the various aspects of the invention may be more fully understood, reference will now be made to preferred embodiments illustrated in the accompanying drawings in which:- FIG 1 illustrates a cross section of a dowel bar socket;

FIG 2 illustrates in cross section an alternative embodiment of a dowel bar socket; FIG 3 illustrates a cross sectional view of a joint between adjacently cast concrete slabs.

DETAILED DESCRIPTION FIG 1 shows a dowel bar socket 1 comprising a hollow tubular body member 2 with a closed end wall 3 and a mounting flange 4 adjacent an open end 5.

The socket 1 may be comprised of any suitable material such as metals or plastics but preferably comprises an inexpensive plastics material and such as regranulated polyethylene, polypropylene or polyvinyl chloride scrap. The socket 1 may be formed by injection moulding or blow moulding.

Mounting flange 4 is generally annular in shape and of a dimension sufficient to permit the socket to be mounted on the inner face of a timber boxing member by means of staples, small nails or the like. If required the mounting flange 4 may be formed with captive fasteners formed integrally with the flange during say an injection moulding process. Alternatively small staples or tacks may be inserted through the flange and held captive by frictional engagement with the flange.

In yet another embodiment, a fastening means may comprise an annular ring of sheet metal slidable over the body 2 and having integrally formed tapered projections extending from one face thereof.

In use, a ground site is prepared for casting a concrete slab and suitable timber formwork is erected to form a peripheral mould. After insertion of suitable reinforcing in the form of mesh or the like, dowel bar sockets according to the invention are secured to the inner surface of the formwork members at appropriate spacings, eg. 600 mm, by nailing or stapling through the flange 4.

The concrete slab is then poured and, after surface finishing, is allowed to cure for a predetermined time. The formwork members are then removed by pulling the members away from the edge of the slab. Depending upon the nature of the material employed in the socket flange and/or the fastening means the formwork is either pulled away from the flanges leaving the fastenings intact or the fastenings are pulled through the flanges.

By employing a relatively soft plastics material for the flanges, the fastenings are readily pulled therethrough. The flanges may be formed with regions of reduced thickness through which fastenings extend to facilitate easier demounting of the formwork.

After the formwork is removed, each socket defines a tubular aperture which extends a predetermined distance into the exposed edge of the concrete slab. Before casting an adjacent slab, dowel bars are inserted into the sockets with a portion produced therefrom. The exposed portion of dowel bar is thus cast into the adjacent slab and that portion extending into the socket is able to freely slide as a result of thermal expansion or contraction of the adjacent concrete slabs, thereby avoiding breakage of the slab edges.

To facilitate regular spacing of the sockets on the surface of a formwork member and to avoid a measuring step, the sockets may have associated therewith a spacer bar. The spacer bar may comprise an elongate member with resilient clips at each end which clip over the body portion of adjacent sockets. In this manner, not only is a regular predetermined spacing achieved but the spacer bars serve also to maintain the sockets substantially parallel relative to each other. FIG 2 illustrates an alternative embodiment of a socket comprising a hollow tubular body 6 closed at one end 7 and open at its other end 8. A separate mounting flange 9 is adapted to frictionally engage over tubular body 6 by means of a tapered central aperture 10. The generally annular flange 9 is reinforced by fillets 11.

Suitably the sockets of FIG 2 are formed from lengths of extruded plastics pipe sealed at one end by flattening and heat welding or gluing together the flattened end portions of pipe. The flange 9 is formed by injection moulding and may include an integrally formed spacer bar (not shown).

If required the central aperture of flange may be formed with a closure in the form of a thin, easily perforated membrane 12 (shown in phantom). The member 12 may be integrally formed in the moulding process or may comprise a plastics or metallic film secured to the face 13 of flange 9 by adhesive. Membrane 12 ensures that no concrete can enter the socket during the casting of a concrete slab.

Flange 9 may be releasably secured to body 6 by frictional engagement or it may be permanently secured by adhesives, friction welding etc. It will be clear to a skilled addressee that the dowel bar sockets according to the invention may be manufactured by any suitable inexpensive process. For example the hollow tubular body portion may be formed from a length of extruded tubing and a closed end may be formed by a plug or cap member.

By utilising inexpensive materials such as reclaimed plastics and inexpensive manufacturing methods, it is envisaged that the socket may be left encapsulated intact in a concrete slab. It is possible however to re-use part or all of the socket members according to the invention if required. For example, the body portion of the socket may be formed with a tapered wall converging towards the closed end. In this manner it would be possible to extract the entire socket member as an integrally formed unit or separately as body and flange members and then re-use the sockets.

Alternatively the body member may be adapted to be secured in the concrete slab by a tapered body portion converging towards the flange member or by means of protrusions extending outwardly from the outer body wall. In the case of a socket with an integrally formed flange or a permanently attached flange the entire socket member will remain embedded in the concrete slab when the formwork is removed.

Where the socket is formed with a frictionally engageable flange member, the flange member may be removed with the formwork member for subsequent re-use if required.

FIG 3 shows a cross sectional view of a joint between adjacent concrete slabs made in accordance with the method according to one aspect of the invention and utilising a socket according to another aspect of the invention.

The first slab 14 is cast in accordance with the method hereinabove described on a base 15 with spaced reinforcing mesh layers 16, 17. A socket 18 is cast within the body of slab 14 with flange 19 contiguous with an upright edge face 20 exposed upon removal of the formwork.

After inserting dowel bar 21 into socket 18 with a portion 21a extending therefrom adjacent slab 22 is cast to encapsulate the exposed portion 21a of dowel bar 21.

It will be readily apparent _ to a skilled addressee that the dowel bar socket and the concrete slab casting method according to the invention not only will serve to substantially alleviate the prior art problems addressed above but will substantially reduce labour costs. The relatively small additional cost of the sockets is far outweighed by the labour savings possible with the invention.

It will be equally apparent to a skilled addressee that many modifications and variations may be made to the various aspects of the invention without departing from the spirit and scope thereof.

For example, a plurality of spaced longitudinally extending ribs may be formed on the inner wall surface of the hollow tubular portion. These ribs may be resiliently defor able to enable easy insertion of a steel rod while allowing for variances in manufacturing tolerances but otherwise to firmly support the rod in the socket. For ease of removal from an injection moulding die assembly the tubular wall section may be tapered convergently towards the closure end of the body and/or the longitudinal ribs may be convergently tapered towards the closure end. In an alternative embodiment, the attachment means may comprise a releasably securable plug like member which is secured to an inner face of the formwork member. The socket, comprising a hollow tubular member with a closure at one end is releasably securable on the plug like member before casting the concrete slab.

After the slab is cured, the formwork, with the spaced plug like members secured thereto is removed from the end face of the slab, disengaging with the sockets which remain in the slab. The formwork planks, with plug like members still attached at spaced intervals can readily be reused.

The plug like member and socket member may include ribs or the like for secure engagement.

Claims (12)

1. A dowel bar socket for cast concrete slabs, said socket comprising:- a hollow tubular body, said body having an opening at one end and a closure at its opposite end; and, attachment means adjacent said opening for attaching, in use, said body to an inner surface of a formwork member.

2. A socket as claimed in claim 1 wherein said attachment means is formed integrally with said body.

3. A socket as claimed in claim 1 wherein said attachment means is removably securable to said body.

4. A socket as claimed in any one of claims 1 to 3 wherein said attachment means includes a securing flange for securing said body substantially perpendicular to a surface.

5. A socket as claimed in claim 3 wherein said attachment means comprises a plug like member releasably engagable with said opening, said plug like member being adapted for securing to said formwork member.

6. A socket as claimed in any preceding claim wherein said socket includes retention means to prevent withdrawal from a body of concrete cast therearound.

7. A socket as claimed in any preceding claim wherein said hollow body includes longitudinal ribs extending inwardly of an inner wall of said body.

8. A socket as claimed in claim 7 wherein said ribs are spaced about the periphery of the inner wall. The ribs may be longitudinally tapered.

9. A socket as claimed in claim 7 or claim 8 wherein the ribs taper convergently from adjacent said opening towards said closure.

10. A method for formation of cast concrete slabs said method comprising the steps of:- erecting at least one formwork barrier defining a peripheral end face of a concrete slab to be cast; securing at spaced intervals on an inner face of said at least one formwork barrier a plurality of dowel bar sockets, said sockets each comprising a hollow tubular body having a closure at an end remote from said inner face and an opening at an opposite end adjacent said inner face, said dowel bar sockets each being secured to said inner face by attachment means associated with said hollow tubular body; pouring a fluid concrete mix into a region behind said formwork barrier to form a concrete slab, finishing the surface of the slab and allowing the slab to at least partially cure; and, removing said at least one formwork barrier whereby a plurality of spaced, substantially parallel tubular apertures are formed in one or more upright edges of said concrete slab, said tubular apertures each being capable of slidably receiving to a predetermined penetration a dowel bar which protrudes from an upright end face of said slab for encapsulation in an adjacently cast concrete slab.

11. A socket assembly comprising a plurality of sockets as claimed in any one of claims 1 to 9, said sockets being connected by spacer means extending between adjacent tubular bodies.

12. A socket assembly comprising a plurality of sockets as claimed in claim 4, said sockets being connected by spacer means extending between respective securing flanges of adjacent sockets.