Bubble relief form for concrete

A rigid, light-weight, thermoplastic bubble insulation form for cast in situ concrete slabs includes hemispherical void spaces for reduction of concrete volume and thermal insulation characteristics. An upper hemispheric surface provides an integral seating arrangement for wire mesh reinforcement. An under-surface of the form includes spacer nodules for facilitating drainage. The bubble relief form is water impervious for controlling curing of the concrete and further is supplied in modular units adapted for trimming and overlapping spliced connections.

TECHNICAL FIELD 
This invention relates generally to static structures, and especially to an 
improvement in cast-in-place concrete construction. 
In particular, the device of this invention concerns a bubble relief form 
adapted for incorporation into the finished concrete. 
BACKGROUND ART 
Concrete construction methods conventionally utilized forms for the 
placement, finishing and curing of concrete. The application of those 
forms to foundation structures, such as slabs, mats, footings and to 
pavements, usually required considerable preparation of the subgrade for 
providing a support surface for static and/or dynamic loading conditions. 
That frequently necessitated the compaction of the underlying soil and/or 
fill material, placement of successive layers of sand, crushed stone and 
gravel for distributing the superimposed loads and for drainage purposes. 
Also, the prepared base had to be moistened to reduce the absorption of 
water from the freshly poured concrete. Alternate steps included providing 
a vapor barrier which was usually in the form of a polyethylene sheet 
placed directly on the prepared base and the installation of side forms or 
"headers" to define the perimeter of the structure. That construction 
procedure further required the setting of reinforcing steel, usually in 
the form of wire mesh or wire fabric, to preserve aggregate interlock and 
prevent surface cracks. That reinforcement was placed upon chairs which 
were designed to support the reinforcement at a desired location below the 
finished grade of the concrete. The concrete, in a plastic state, was then 
deposited within that form arrangement and, after curing, the form had to 
be stripped. 
A problem with seating wire fabric, as described above, was that when the 
concrete was poured, the wire mesh tended to drape and, therefore, it was 
difficult to keep the reinforcement at a constant design depth below the 
finished grade. 
A further shortcoming of those construction methods was that the forms did 
not provide an optimum distribution of concrete but, rather, relied upon a 
uniform maximum thickness throughout even though not structurally required 
for withstanding compressive stresses under actual load conditions. Other 
attempts to modify concrete sections, so as to reduce the volume of 
concrete, appeared in structural members incorporated into floor systems, 
such as metal-pan, cellular and corrugated steel forms. 
Reference is also made to the above ground floor slabs illustrated in U.S. 
Pat. No. 3,334,458. The relief form of this invention in contrast is 
adapted primarily to accommodate the concrete on grade and conforming to 
the configuration of the form rather than to function as an integral 
structural member. 
Another disadvantage was that the multistep procedure of the prior art was 
not cost effective with regard to materials, time and labor. 
DISCLOSURE OF THE INVENTION 
Briefly, the nature of this invention involves a mold for receiving 
concrete in a plastic state. A base member is designed for substantially 
horizontal placement upon a subgrade and includes a relief matrix for 
minimizing the volume of concrete. The relief matrix is preferably formed 
as hemispherical convexities defining void spaces thereunder forming air 
insulation pockets when the under-surface of the base member is in 
confronting relationship with the subgrade. 
The base member of this exemplary embodiment is constructed of a rigid, 
light-weight, thermoplastic material which is impervious to water so as to 
obviate the need for an independent moisture barrier. The base member is 
intended to remain in place as an integral element in the completed 
concrete and is not stripped after curing. 
The upper surface of the convexities provides a support network for seating 
a wire mesh reinforcement at a constant depth within the concrete and 
includes tab members for snugably engaging the wire mesh reinforcement. 
The under-surface of the base member is provided with projections or spacer 
nodules arranged so as to provide a clearance between the base member and 
the subgrade thus facilitating drainage. These so formed passages 
eliminate the need for a graded gravel layer or under-drains as previously 
employed. 
A further aspect of this invention is that the dome-shaped void spaces and 
drainage passageways concomitantly provide areas for relieving hydrostatic 
pressure, localized frost heave and other uplift forces. 
Another feature of the invention is that the total volume of concrete is 
reduced and the resultant dead-weight of the concrete slab is decreased to 
thus alleviate the tendency of the support surface to settle as a result 
of consolidation from the overlying weight. 
In view of the foregoing, it should be apparent that the present invention 
overcomes many of the disadvantages of the prior art and provides an 
improved bubble relief form for concrete construction which is readily 
adapted to meet applications of practical use. 
Having thus summarized the invention, it will be seen that it is an object 
thereof to provide a bubble relief form for concrete construction of the 
general character described herein. 
Specifically, it is an object of the present invention to provide a bubble 
relief form which is integrated into the concrete structure and provides a 
stratum between the concrete and the supporting subgrade. 
Another object of this invention is to provide a bubble relief form which 
functions as a vapor barrier for preventing dissipation of moisture during 
curing of the concrete. 
Still another object of this invention is to provide a bubble relief form 
which incorporates a plurality of air pockets for providing insulation and 
reducing the volume of concrete required. 
Yet another object of this invention is to provide a bubble relief form for 
concrete construction with self-contained drainage provisions. 
A still further object of this invention is to provide a bubble relief form 
including a support system for facilitating the positioning and placement 
of reinforcement within the concrete. 
An additional object of this invention is to provide a bubble relief form 
for concrete construction which is simple in construction, low in cost and 
reliable in use. 
Other objects, features and advantages of the invention will in part be 
obvious and will in part be pointed out hereinafter. 
With these ends in view, the invention finds embodiment in certain 
combinations of elements and arrangements of parts by which the objects 
aforementioned and certain other objects are hereinafter attained, all as 
more fully described with reference to the accompanying drawings and a 
scope of which is more particularly pointed out in the appended claims.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now in detail to the drawings, the reference numeral 10 denotes 
generally a bubble relief form for concrete construction in accordance 
with this invention. 
The relief form 10, shown in FIG. 1, includes a substantially planar base 
12 having a plurality of uniformly spaced convexities 14 which, for the 
purpose of this invention, are typically shown as being hemispherical 
bubbles. It should be understood, however, that the relief areas of the 
base 12 can assume other shapes or configurations. The preferred 
curvature, as illustrated herein, provides a dome-shaped enclosure or void 
space 16. In addition, the under-surface 18 of the base 12 is provided 
with a pattern of spacer nodules 20. A pair of tabs 22 are provided on the 
convex relief surfaces 14 with each of the tabs 22 lying within a 
horizontal plane being substantially tangent to the convexities 14. 
Furthermore, the tabs 22 are preferably arranged in sets of four, as shown 
in FIG. 5, and are adapted for engaging a reinforcement wire mesh 24. 
It should be noted that the bubble relief form 10 is preferably constructed 
from a light-weight, rigid, thermoplastic material, which can be stamped, 
vacuum formed or otherwise molded in sheets providing the base member 12 
with typical dimensions of 4 ft. by 8 ft. (1.2 meters by 2.4 meters). 
Additionally, the base members 12 are adapted for nestable stacking for 
compact storage and shipment; the light-weight and size further permit 
convenient handling. Additionally, the base members 12 can be trimmed or 
spliced in an overlapping connection for special conditions. The splicing 
can be achieved without mechanical devices or solvents by utilizing the 
weight of the concrete for assuring the integrity of the splice. 
An application of the invention will be described in connection with a flat 
slab on grade having a typical 6 in. (15.2 cms.) depth. Initially, a 
subgrade 26 is dressed to provide a smooth, flat horizontal support 
surface. The perimeter of the slab is defined and conventional side forms 
28 are erected. The relief form 10 is then tailored for accommodation 
within the confines of the side forms 28. This may require cutting a 
typical 4 ft. by 8 ft. base sheet or trimming sections from an additional 
base sheet and placing same in an overlapping fashion, as shown in FIG. 6, 
so as to provide a continuance of coverage between the side forms 28. 
The reinforcing mesh 26 is typically a network of orthogonal steel rods and 
an individual rod can be snugly inserted between the tabs 22. In this 
regard, it should be noted that the center-to-center spacing between the 
convex surfaces 14 is preferably 12 in. (30.5 cms.) for compatibility with 
the standard wire mesh. The maximum diameter of the void spaces 16 in this 
embodiment is 8 in. (20.3 cms.). 
The spacer nodules 20 offset the under-surface 18 from the dressed subgrade 
26 and provide for drainage or water runoff. 
It should also be noted that the arrangement of the dome-shaped voids 14 
provide sufficient clearance therebetween to accommodate a worker's foot 
during installation of the reinforcement mesh 24 and pouring of a concrete 
mass 30. Furthermore, the reinforcement mesh 24 will be firmly positioned 
at the design depth below the concrete, preferably 1 in. (2.5 cms.). 
After the concrete 30 is poured, the bubble relief form becomes an integral 
element in the completed structure. The water impervious characteristics 
of the base member 12 advantageously prevents water seepage from the 
concrete 30 to the surrounding subgrade 26 and thus enhances the curing 
procedure. Additionally, air pockets within the void spaces 16, provide a 
thermal insulation system. 
Thus, it will be seen that there is provided a bubble relief form which 
achieves the various objects of the invention and which is well adapted to 
meet conditions of practical use. 
Since various possible embodiments might be made of the present invention 
or variant changes might be made in the exemplary embodiment set forth, it 
is to be understood that all materials shown and described in the 
accompanying drawings are to be illustrative and not in a limiting sense.