Apparatus for making concrete slabs

Adjustable forms for pouring precast concrete slabs and similar articles of manufacture. The forms may be used either on site to produce concrete slabs as needed, or at a central manufacturing location, for transport to the site where needed. Concrete slabs produced with the adjustable forms may be used in patios, sidewalks, storage room or pump house floors, driveways, mobile home landings, and the like. The slabs may be steel reinforced, with expandable interlocking design, of various sizes, patterns and colors. Similar construction materials or decorative articles, such as tile, wallboard, and the like may also be produced with the improved forms.

FIELD OF THE INVENTION 
This invention relates generally to adjustable forms for pouring precast 
concrete slabs and similar articles of manufacture. The forms may be used 
either on site to produce concrete slabs as needed, or at a central 
manufacturing location, for transport to the site where needed. Concrete 
slabs produced with the adjustable forms may be used in patios, sidewalks, 
storage room or pump house floors, driveways, mobile home landings, and 
the like. The slabs may be steel reinforced, with expandable interlocking 
design, of various sizes, patterns and colors. Similar construction 
materials or decorative articles, such as tile, wallboard, and the like 
may also be produced with the improved forms. 
BACKGROUND OF THE INVENTION 
Forms for the production of precast concrete slabs have traditionally made 
of wood, and while the wooden forms have the advantage that they can be 
cut and nailed to a desired form size, they have the known disadvantage of 
requiring considerable time, labor and expense in the assembling and 
lining for each dimensional job and also in the dismantling after the 
concrete has properly set. Further, the constant cutting, nailing and 
re-nailing limits the number of times the forms can be re-used. 
Forms made of other materials, such as steel, aluminum or other metals, 
have also been used. However, whereas the metal is more durable than the 
wood, the disadvantage is that the inability to cut the forms to size 
requires maintaining a large inventory of forms of varying size, or in the 
alternative developing telescoping and locking arrangements requiring 
multiple section sizes and movable parts for locking and anchoring. 
Efforts to avoid the use of wooden forms are disclosed for example in U.S. 
Pat. Nos. 2,722,045; 3,495,800; and 4,121,804. 
It is an object of the present invention to provide an adjustable form 
which substantially overcomes the several problems referred to above in 
connection with prior wooden and metal forms. 
It is another object of the invention to provide forms which may be 
adjusted to varying sizes but which are assembled from components all of 
which have identical size and configuration, so that stockpiling of 
multiple form components is unnecessary. 
It is a further object of the invention to provide forms which are 
versatile in the production of concrete slabs or other construction 
materials of varying sizes, patterns and colors, and with varying 
edge-interlocking configurations. 
It is a still further object to provide forms which are simple to assemble 
and disassemble, which are durable and can be reused indefinitely, and 
which avoid the wastage and inefficiency of the prior art forms. 
Other objects and advantages will become apparent as the specification 
proceeds. 
SUMMARY OF THE INVENTION 
The present invention relates to an adjustable form for producing concrete 
slabs comprising a plurality of like channel shaped sections similarly 
oriented in interlocking arrangement to define a form unit. Each section 
includes vertically spaced upper and lower arms with a vertical web 
connecting corresponding ends of said arms. Each section also includes a 
main body and a fork joint extension thereof on at least one end. The fork 
joint extension comprises upper and lower tines spaced apart at a distance 
substantially equal to the cross-sectional depth of said sections, so that 
an end of an adjoining section may be accepted between said tines. 
The upper and lower tines are each provided with opposing holes in vertical 
registration with each other, the holes being spaced apart from the end of 
said main section body for a distance substantially equal to the effective 
cross-sectional width of an adjoining section, so that the adjoining 
section may be accepted between the end of said main body and said holes. 
Pins are disposed through said opposing holes in the tines in each 
section, for retaining the adjoining section which is accepted between the 
tines. The interlocking arrangement of said plurality of sections is one 
in which the body of each section is inserted, at a predetermined point 
along its body, in a fork-jointed end of an adjoining section, to provide 
an enclosed geometric figure having predetermined dimensions. 
In a preferred embodiment of the invention, four of the sections are 
assembled to provide a rectangular geometric figure for the concrete slab. 
In a preferred version, the inner walls of the sections are provided with 
rabbet-forming shoulders, so that the resulting concrete slabs may be 
joined together in shiplapping fashion.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, one of the channel-shaped form sections used in 
the invention is illustrated in FIGS. 1 and 2. As indicated, the form 
section is channel-shaped in cross-section and comprises vertically spaced 
upper and lower arms, 11 and 12, connected by a vertical web 13. The 
section is composed of a main body portion 14 and a fork joint extension 
15, which extends beyond the end 20 of the main body portion 14. The fork 
joint extension comprises an upper tine 16 and a lower tine 17 which are 
welded or otherwise fastened to the upper arm 11 and lower arm 12 
respectively. Tines 16 and 17 are provided with opposing holes 18 and 19 
which are in vertical registration with each other. The drift pin 21 may 
be inserted through holes 18 and 19 to retain the main body portion of an 
adjoining section in the fork joint extension 15. 
As will be described hereinafter, all the sections used in an assembled 
form are identical to each other, and may be made of any suitable 
material, such as steel, aluminum or wood. Although wood has less enduring 
characteristics, it would be more durable in the present invention than 
the wood used in prior art forms, since in the present invention there is 
no need for cutting, nailing or renailing. The form sections may have any 
suitable dimensions. In a preferred embodiment, they are 12 feet long and 
have a depth of 4 inches, for the production of a 4 inch thick slab of 
concrete. 
The assembled form 10 of the invention is shown generally in FIG. 3. In 
this embodiment, the form 10 is assembled from four channel-shaped 
sections, identified as A, B, C and D. For clarity in description, the 
various parts of these forms sections will be identified with an A, B, C 
or D prefix, so that the manner in which they fit together can be 
understood. Thus, Section A includes parts A11 through A22, and so on. 
In the fork joint extensions of each of the Sections, the tines 16 and 17 
are spaced apart at a distance substantially equal to the cross-sectional 
depth of the Sections. Thus, in Section A, tines A16 and A17 are spaced 
apart substantially the same distance as the depth of Section B, so that 
the main body portion of Section B may be accepted between the tines, as 
shown in FIGS. 3 and 4. Setting the appropriate distance between tines A16 
and A17 may be most readily accomplished by welding or otherwise fastening 
a plate-like tine A16 on top of arm A11 and extending beyond the end A20 
of Section A, and by similarly welding a plate-like tine A17 on the bottom 
surface of arm A12 and extending beyond the end A20 of Section A, so that 
the distance between the inside surfaces of the two tines is substantially 
the same as the cross-sectional depth of Section A (and also Section B), 
so that Section B may be accepted between the tines with a frictional fit. 
In the preferred embodiment of the invention shown in FIGS. 1 through 9, 
rabbet-forming shoulders are welded or otherwise fastened along the length 
of the inwardly facing surface of web 13. "Inwardly facing" is intended to 
mean the surface which faces inwardly toward the geometric figure being 
formed, or in other words the surface which will be contacted by the 
cement when it is poured. Thus, Sections A and D have rabbet-forming 
shoulders or tubes A22 and D22, respectively, affixed along the top edges 
of webs A13 and D13, respectively, to provide top surfaces flush with the 
top surfaces of arms All and D11, respectively (see FIGS. 6 and 5), 
whereas Sections B and C have rabbet-forming shoulders B22 and C22 affixed 
along the bottom edges of webs B13 and C13 (see FIG. 4). This arrangement 
is useful in producing concrete slabs which may be interlocked through 
undercut and overcut edges in shiplapping fashion. 
In the fork joint extensions of each of the Sections, the holes 18 and 19 
are spaced apart from the end 20 of the body portion 14 for a distance 
substantially equal to the effective cross-sectional width of an adjoining 
Section, so that the adjoining Section may be accepted between the end 20 
of the main body portion 14 and the said holes 18 and 19 when the pin 21 
is inserted therein. Thus, in FIG. 4, the effective cross-sectional width 
of Section B is shown by the numeral 23, which represents the horizontal 
dimension of tube or shoulder B22 added to the horizontal dimension of arm 
B12. The numeral 23 likewise represents the distance between the end 20 of 
main body portion A14 and the holes A18 and A19. When pin A21 is inserted 
in holes A18 and A19, the main body portion of Section B is accepted 
between pin A21 and end A20 on a substantially friction-fit basis. In 
similar manner, the effective width of Section A is identified by the 
numeral 24 in FIG. 6. 
The effective cross-sectional width of an adjoining Section may be 
different if a concrete slab having a geometric figure other than a 
rectangle is being produced. For example, for a hexagonal figure, the 
angle at which the body of an adjoining Section is accepted by the fork 
joint extension will be greater, and a greater distance between the holes 
18 and 19 and the end 20 of the body portion will be required. If desired, 
multiple registering holes may be installed in the tine members 16 and 17 
at varying distances from the end 20, to accommodate the insertion of 
adjoining Section body members at different angles. 
It is a feature of the invention that all the Sections are identical to 
each other in size and configuration, thus eliminating the expense and 
inefficiency of inventorying and handling many different forms that have 
been tailored to the production of many different sizes and shapes of 
concrete slabs. Although it might appear (as in FIG.3) that Sections A and 
C are not identical, since in Section A the rabbet-forming shoulder A22 is 
at the top of web A13, and in Section C the shoulder C22 is at the bottom, 
it should be understood that Sections A and C are in fact identical, and 
that Section C has only been flip-flopped in position with respect to 
Section A. 
FIG. 7 illustrates a precast concrete slab 25 which may be produced by 
pouring cement into the form illustrated in FIG. 3 and allowing to set. 
Although the slab appears to have top and bottom sections, it is in 
reality a single piece of concrete having two undercut edges and two 
overcut edges, thereby providing rabbets useful in laying multiple slabs 
in interlocking arrangement, in a shiplapping fashion. FIG. 8 is a 
cross-sectional view of slab 25 taken along line 8--8 of FIG. 7, showing 
rabbets 26 and 27. FIG. 9 is a cross-sectional view of slab 25 taken 
along line 9--9 of FIG. 7, showing rabbets 28 and 29. According to the 
present invention, the slabs may be cast in any convenient length and 
width. Standard dimensions include 5'.times.5', 6'.times.6', 8'.times.10', 
9'.times.11', etc. 
The procedure for producing a precast concrete slab 25 as shown in FIG. 7, 
using the adjustable form arrangement shown in FIGS. 1 through 6, is 
described as follows. As the first step, a sand base is prepared and 
leveled. For a 9'.times.11' concrete slab, the standard procedure is to 
provide a sand base approximately 12'.times.14' in area. Four of the form 
Sections of the present invention are then assembled on top of the sand 
base. Each of the sections is 12' in length, and has a depth from top to 
bottom of 4 inches. The sections are assembled by inserting the body of 
Section B in the fork joint extension of Section A, the body of Section C 
in the fork joint extension of Section B, and so on. The fork joint of 
each Section is slipped along the body of the adjoining Section until the 
desired area dimension is achieved, and then drift pins 21 are driven 
through the registered holes 18 and 19 in the fork joints of each of the 
Sections to lock the form to the desired dimension. The resulting assembly 
is shown in FIG. 3. 
For most purposes, a large concrete slab, which can weigh as much as 3,000 
pounds, will require internal reinforcement, such as rebar, and also 
eyebolt inserts for use in lifting the slab after it has been formed. For 
these purposes, before pouring cement into the assembled form, standard 
tripod chairs, for holding the rebar, are placed upright on the sand, 
within the area bounded by the assembled form. The rebar is preferably 
installed criss-crossed, on 2 foot centers approximately 2 inches above 
the sand bed, for a 4 inch thick slab. 
Also, to provide anchored eyelet inserts for lifting the slab, a 
combination rebar and eyelet insert chair 30 may be placed adjacent the 
four corners of the slab, as best shown in FIGS. 10, 11 and 12. The chair 
30 comprises a vertical, internally threaded stem 31 having depending hook 
arms 32 and 33, which serve as a support for rebars 34 and 35. In the 
preferred arrangement, four chairs 30 are used for a slab, each chair 
being positioned within the form area equidistant from each corner of the 
form, spaced inwardly approximately 2 feet from the edge of the form. For 
a 4 inch thick concrete slab, the chairs 30 are designed so that the hook 
arms 32 and 33 hold the rebar 2 inches above the sand base. 
When the chairs and rebar have been installed, a suitable concrete mixture 
of desired color and texture is poured into the form, and the cement 
surface is floated and leveled. Prior to the pour, a protective bolt 36 is 
screwed into each of the threaded stems to prevent their filling with 
concrete. As shown in FIG. 10, the cement is floated and leveled so that 
the surface is flush with the top of the threaded stem 31. After the 
concrete has cured, the form sections are readily removed by disengaging 
the drift pins 21 and pulling the form sections from the hardened 
concrete. 
The resultant cement slab may be transported by removing the protective 
bolts 36 from each of the threaded inserts 31, which have now become 
securely anchored in the cement, and screwing an eyebolt 37 in its place, 
as shown in FIG. 11. A boom truck hoist may then be attached to the 
eyebolts 37, and used to transport the slab to a different location or to 
set the slab in place in the patio, driveway or other surface being 
prepared. When set in place, the eyebolts 37 may be removed and replaced 
by cosmetic bolts 38, as shown in FIG. 12. 
In another embodiment of the invention, illustrated in FIG. 13, the 
inwardly facing surface 13 of the form sections may be provided with a 
triangular groove-forming shoulder 38A. Also, as shown in FIG. 14, the 
face 13 of pairs of form sections may be provided with a tongue-forming 
recession 39 or a groove-forming shoulder 40, to produce concrete slabs 
which may be mated in the manner shown in FIG. 15. 
In a further embodiment of the invention, shown in FIG. 16, a flat mold 
form is laid on the sand base prior to assembly of the form sections. The 
mold form has pattern-forming raised shoulders 42 which create a desired 
pattern in the surface of the concrete slab poured into the mold. Numerous 
varied patterns can be produced in the surface of the concrete slab in 
this manner, see FIG. 17. Alternative means for creating a pattern in the 
top surface of the slab may be used, such as pattern forms which are 
placed on the top surface and pressed into the concrete after floating and 
leveling. 
The adjustable form apparatus of the present invention includes the 
following features which are significantly advantageous in terms of 
effectiveness and economy: 
1. Use of an adjustable form in which all the form components are identical 
in shape and size provides substantial savings in work and money, since 
the inventorying of multiple components is avoided. 
2. The form sections or components are simple and sturdy in construction, 
with no moving parts except a single drift pin. 
3. The form is easy to assemble, merely by sliding each component to a 
measured point on the adjoining component, which it is held in place by 
the friction of an inserted drift pin. When concrete is poured into the 
form, the outward pressure of the concrete against the form sections 
increases the friction which secures the sections together. 
4. The form sections are reusable indefinitely. Assembling and 
disassembling the form causes no damage or wastage. 
5. The form sections are easily portable, so that concrete slabs may be 
cast either at a central location or at a construction site. 
6. The form is readily adaptable for providing rabbeted mating edges, for 
use in shiplapping arrangement of adjoining slabs. The interlocking edges 
permit the slabs to be laid on any generally flat surface, without 
expensive compacting, cushioning, subflooring, or the use of adhesives or 
cements. 
7. The adjustable form is conveniently used for the production of heavy 
slabs, which may be rebar reinforced and equipped with hoisting eyelet 
inserts for use with boom trucks in the transport and placement of the 
slabs. 
8. The concrete slabs produced with the form are useful for patios, 
sidewalks, storage room or pump house floors, driveways, mobile home 
landings, and the like. 
9. The adjustable form is useful on a smaller scale in the production of 
other materials which are normally cast in forms, such as tile, ceiling 
tile, wallboard, and the like. 
10. Use of the form provides savings and flexibility for the consumer, 
since consumers with a budget can have patios or driveways constructed in 
stages as finances permit. When ready for the next stage, the adjustable 
forms permit the production of additional slabs having dimensions 
identical with those already installed. 
Although various preferred embodiments of the invention have been described 
herein in detail, it will be understood by those skilled in the art that 
variations may be made thereto without departing from the spirit of the 
invention.