Two-part collapsible corrugated paper form void

A two-part collapsible form void for providing a space between a poured concrete structure and an underlying expansive soil is formed of a foldable outer section and a foldable inner section which, when erected, is longitudinally slidable into the erected outer section. The form void may be shipped in the separated and collapsed state, reducing shipping volume by up to 85 percent, and is easily erected by hand at the job site.

BACKGROUND OF THE INVENTION 
This invention relates generally to the construction of concrete walls, 
slabs or other structures adjacent to or inclusive of spaces. More 
particularly, this invention pertains to void forms for creating spaces 
beneath concrete structures to separate and protect the structures from 
underlying expansive soils. 
Expansive soils are prevalent in many areas of the United States, as well 
as in other countries. Such soils typically contain much clay, and expand 
and contract considerably as a result of cyclical changes in moisture 
content and/or as a result of natural freezing-thawing cycles. 
A common method of construction in such expansive soils uses spaced drilled 
piers or spread footings for supporting the walls and floors. In this 
method, the concrete walls or beams supported by the piers or footings 
must be provided with a substantial vertical spacing from the underlying 
expansive soils. Otherwise, upward expansion of the soil may contact and 
force the beams or walls upward, causing cracking and deformation of the 
concrete. Without the required spacing, the integrity of the concrete 
structure is eventually lost. 
Excavation of soil from beneath a concrete structure after it has "set" is 
a labor-intensive, very expensive method for resolving the problem with 
expansive soils. Where the structure has a lower edge below grade, a 
trench sufficiently wide to permit hand removal of soil below the 
structure must be provided. Furthermore, it is desirable to remove any 
forms of wood, metal or plastic used to form the lower surface of the 
structure. Such forms have a long life and should be removed after the 
concrete has set to provide further expansion space below the structure, 
and for re-use. 
The use of integral corrugated paper form voids is known. In one 
application, such form voids are placed at the bottom of wall forms and 
trenches to separate the subsequently poured concrete from the ground. The 
corrugated paper form voids have sufficient temporary strength to support 
the wet concrete at a distance above the ground, but gradually absorb 
water and deteriorate to a condition where they no longer provide support. 
However, by this time the concrete has set and needs no support other than 
that provided by the piers. During periods of upward expansion of the 
underlying soil, the soil occupies the space left by the deteriorated or 
weakened form voids. 
Form voids are available in various cross-sectional configurations. The 
generally rigid voids are prepared by forming the desired structural shape 
of panels of corrugated paper and joining the panels together with 
adhesive. An internal cellular grid structure may be used within the form 
void to increase the strength of the form void as required. The exterior 
surfaces of the paper form voids are typically treated with wax to provide 
temporary water resistance and thus an appropriate time delay in 
deterioration. 
Shipping charges are a major cost of using such form voids. Existing paper 
form voids are lightweight, their cross-sections being typically about 
70-90 percent space. Thus, the quantity of paper form voids which may be 
fitted into a truck is severely limited, and the weight of the truckload 
is only a small fraction of the available weight limit for the truck. 
It is an object of the invention to provide a form void which will occupy 
much less space in a truck without sacrificing void size. Thus, the 
shipping cost may be greatly reduced. 
BRIEF SUMMARY OF THE INVENTION 
An improved trapezoidal form void is fabricated from corrugated paper and 
has a two-part structure permitting complete separation of the two parts. 
An inner part is expanded and longitudinally inserted by sliding into an 
expanded outer part. Each of the parts may be separately folded and 
collapsed to a generally flat sheet of several panels thickness for 
shipping and storage. Each of the panels of the inner and outer parts is 
comprised of one or more plies of corrugated paper. The two-part form void 
may be formed in any convenient length appropriate to the end use, and is 
readily cut to length at the construction site with a saw or knife. 
The paper from which the form void is manufactured is like that from which 
paper cartons are typically formed, i.e. a corrugated paper structure 
sandwiched and cemented between two sheets of thin corrugated paper. The 
corrugated paper has greater strength in the direction of the corrugation 
ridges than across the ridges, hence a corrugation ridge direction is 
maintained parallel to the direction of applied compressive forces to 
increase the weight of wet concrete which may be supported. Though the 
two-part form void is easily assembled and disassembled, it maintains a 
high strength for temporary support of a high load of wet concrete. The 
corrugated paper as used in the manufacture of the form void described 
herein is readily obtainable from numerous sources. 
The form void is assembled and disassembled easily by hand, without 
machinery, and does not need on-site application of adhesive. In the 
disassembled or collapsed configuration, the two parts of the form void 
may be stacked or bundled to enable shipment at a much higher density. The 
shipping costs are substantially reduced when compared to the one-part 
non-collapsible form voids of the same size. 
These and other objects and advantages of the invention will be readily 
understood by perusal of the following description in conjunction with 
study of the accompanying figures of the drawings wherein like reference 
numerals have been applied to designate like elements throughout the 
several views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the drawings, and particularly to FIG. 1, a collapsible 
two-part corrugated paper form void 10 is shown as used in conjunction 
with vertical concrete forms 12 for making a concrete structure 14, e.g. a 
beam (see FIG. 2) to be supported by piers 36. The elongate form void 10 
has a generally rectangular cross-sectional shape whose outer part 52 
includes a base panel 16, upper panel 18 parallel to base panel 16, and 
parallel first and second side panels 20, 22, respectively. End caps 24 
may be used to seal the otherwise open ends 26 of the form void 10. The 
form void 10 may include a bottom flange 28 approximately co-planar with 
base panel 16, for more easily maintaining the position of the form void 
between the forms 12. Only small portions of the forms 12 are visible in 
FIG. 1, and a pier 36 is shown with reinforcing rods 44 for structurally 
tying the beam 14 to the pier. 
In the exemplary use illustrated, one or more units of the form void 10 are 
placed end to end on the ground 30 or other surface with the planar top 
surface(s) 32 of the upper panel(s) 18 at an elevation corresponding to 
the desired bottom surface elevation of the concrete beam 14. The form 
void 10 is shown as being placed between spaced drilled piers 36 which 
will ultimately support the hardened concrete beam 14. Any space 38 
between the form void 10 and the piers 36 is preferably filled with an 
appropriate disintegratable material such as a form void conformable to 
the piers. Such is not the subject of this application. 
In this discussion, the term "length" refers to the dimension corresponding 
to the long dimension of the assembled form void 10. Likewise, the term 
"width" refers to the dimension corresponding to the width of the 
assembled form void 10. 
The top surface 32 of the upper panel 18 of the form void 10 has a width 40 
generally equivalent to the desired width 42 of the beam 14 to be formed. 
The bottom flange or flanges 28 are approximately coplanar with base panel 
16 and each flange extends outwardly from a side panel 20 or 22 for 
stability on the ground 30. A form 12 may rest on a bottom flange 28, and 
in any case both forms 12 must be in sufficient contact with the first or 
second side panel 20, 22 to generally prevent passage of wet concrete 
between the form 12 and side panel. In FIG. 1, forms 12 are supportably 
placed against side panels 20, 22 of the form void 10, one of the forms 12 
resting on the single bottom flange 28 to hold the form void 10 in place. 
The height 46 of the form void 10 is the minimum upward distance available 
for soil expansion beneath the structure 14. 
The width 40 of the form void 10 does not have to be equal to the pier 
diameter 34. In many cases, the beam or wall 14 to be resting on piers 36 
has a width 42 less than the pier diameter 34. Alternatively, the beam 
width 42 may exceed the pier diameter 34. The form void 10 may be made in 
any useful width, or multiple units of form voids 10 may be placed side by 
side to equal the desired width. 
The form void 10 is manufactured with sufficient initial strength to 
support the wet concrete poured between the forms 12, and weakens and 
disintegrates in time upon passage of ground moisture and moisture from 
the wet concrete into the paper fibers. When the concrete has set and 
forms 12 removed, as shown in FIG. 2, the beam 14 or other structure so 
formed is supported entirely by the piers 36. The form voids 10 rapidly 
deteriorate and disintegrate to a non-supportive state. The ground 30 
(including expansive soils therein) underlying the beam 14 is spaced from 
the beam and may rise upwardly toward the beam without contacting it or 
exerting a high force thereon. Thus, the common destructive effects of 
expanding soils on concrete structures may be avoided. 
As shown in FIG. 3, the form void 10 is comprised of separate outer part 52 
and inner part 54, which are joined simply by unfolding of both parts and 
longitudinal sliding in direction 50 of the inner part into the outer 
part. It is preferred that the inner part 54 fit snugly into the outer 
part 52 without providing excessive resistance to sliding the parts 
together. 
Each of the outer part 52 and inner part 54 is formed by making 
longitudinal fold lines in corrugated paper sheets to produce panels 
therebetween, and joining some of the panels in specific areas with 
adhesive 60. Once formed, the two parts 52, 54 are easily erected and 
joined by hand, and no further application of adhesive 60 is required to 
complete the form void 10. The opposed base panel 16 and upper panel 18 
are of equal width, and the opposed side panels 20, 22 are of equal width. 
Together, these panels 16, 18, 20 and 22 form a rectanglar parallelogram 
in cross-section. When erected, the inner part 54 becomes an articulated 
structure generally extending to each "corner" of the outer part, i.e. 
proximate the fold lines defining the upper and base panels 18, 16, 
respectively. 
Looking now at FIGS. 3 and 4, we see the latter showing an outer part 52 in 
a folded or "knock-down" state conducive to shipping. The outer part 52 is 
formed of a single sheet of corrugated paper having length 56, although 
inclusion of an end cap 58 (having a fold-in tab 59 with fold line 61) at 
a first end 62 and/or the second end 64 of the outer part 52 will increase 
the overall unerected length for shipping. 
The corrugation ribs or ridges 78 of the outer part panels are preferably 
oriented as extending vertically or in direction 80 across the form void 
10, i.e. both at 90 degrees with the longitudinal direction, in order to 
provide the greatest strength in the direction of downwardly applied 
forces. 
The outer part 52 is formed by first folding the sheet along center fold 
line 66 and joining the first side edge 68 to the second side edge 70 with 
adhesive 60. The portions joined by adhesive 60 comprise a bottom flange 
28. Side panel 20 is formed by folding upward about flange fold line 72. 
Third fold line 74 is made to separate side panel 20 from upper panel 18. 
Likewise, fourth fold line 76 is made to separate side panel 22 from base 
panel 16. Base panel 16 is delineated by fold line 76 and a line 84 
congruent with flange fold line 72. Line 84 is not intended to be a fold 
juncture. Fold lines 66, 72, 74 and 76 are all parallel and extend 
longitudinally between first end 62 and second end 64. When erected, the 
interior 82 of the erected outer part 52 forms a rectangular 
parallelogram. Thus, the width 86 of base panel 16 and the width 88 of the 
opposed upper panel 18 are equivalent, and the width 90 of first side 
panel 20 is equivalent to the width 92 of the opposed second side panel 
22. 
The width 94 of bottom flange or flanges 28 is sufficient for a standard 
form 12 to hold the form void 10 in place. The form 12 may have a 
thickness 13 (FIG. 1) either greater than, equal to, or less than the 
width 94. 
In FIG. 5, an inner part 54 is shown in a non-erected condition, as 
manufactured. As shown in FIGS. 3 and 5, the inner part 54 is comprised of 
four panels formed from two or more sheets of corrugated paper. 
The corrugation ribs or ridges 78 of the inner part panels are preferably 
oriented as extending vertically or in direction 80 across the form void 
10, i.e. both at 90 degrees with the longitudinal direction, in order to 
provide the greatest strength in the direction of downwardly applied 
forces. 
The inner part 54 includes a top panel 96, a middle panel 98, and first and 
second strut panels 100, 102. The top panel 96 has a width 104 which is 
generally less than the width 88 of panel 18 by about two times the 
thickness 120 of the corrugated paper of panel 18. The middle panel 98 and 
two strut panels 100, 102 adjoined thereto are formed from one or more 
coextensive plies or layers of corrugated paper. FIG. 5 shows two layers 
116, 118 of width 122 which are joined together by adhesive 60 to form 
panels 98, 100 and 102 separated by fold lines 112 and 114. The overall 
strength, i.e. crush resistance of the assembled form void 10 may be 
varied by using multiple layers of corrugated paper in some or all panels. 
In addition, the use of corrugated paper with greater or lesser thickness 
120 will vary the strength of the form void 10. Thus, the form void 10 may 
be selectively produced in any particular strength over a wide range of 
useful strengths. 
Middle panel 98 is joined to the top panel 96 with adhesive 60. Strut 
panels 100, 102 may then be folded downward at fold lines 112, 114, 
respectively, and the inner part 54 longitudinally inserted into the 
erected outer part 52, as shown in FIG. 3. 
The panels joined by adhesive 60 in this form void 10 have the greatest 
strength when the layer of applied adhesive 60 is continuous between those 
panels so joined. However, non-continuous e.g. spot application of 
adhesive may optionally be done, resulting in a slight loss in strength. 
The adhesive 60 may be of any composition which will tightly bond the 
corrugated paper panels. Preferably, however, the adhesive 60 is 
biodegradable, as typified by adhesives with a starch base. 
For most uses of the form void 10, it is important that little or no wet 
concrete be permitted to flow past the upper panel 18 and into the form 
void 10 itself. Such would defeat the purpose of the form void 10. An end 
cap may be provided at one or both ends of the form void 10 and may be 
configured in several ways. First, as illustrated in FIG. 4. end cap 58 is 
an extension of upper panel 18 and has a height dimension 124 appropriate 
for tucking fold-in tab 59 into the lower portion of the outer part 52. 
In another embodiment illustrated in FIGS. 3 and 5, each end cap 126 is 
formed as an extension of top panel 96 of the inner part 54, and includes 
a fold-in tab 128 having fold line 130. 
In a third embodiment, not illustrated, a piece of paper stock such as 
corrugated paper is simply cut to the cross-sectional shape of the form 
void 10 and cemented to the end thereof. However, this method requires 
application of adhesive 60 at the job site. 
It should be noted that a more cohesive form void structure may be erected 
at a job site by joining adjacent outer parts 52 with a single inner part 
54. Thus, separate portions of the inner part 54 are inserted into each of 
several outer parts 52. In this way, adjacent outer parts 52 are joined 
end to end and the need for end caps is reduced. Where the form void 
immediately adjacent the pier 36 is configured to receive an inner part 
54, use of end caps may be avoided altogether. 
Looking now at FIG. 6, a cross-section of an erected form void 10 is shown 
having a rectangular parallelogram interior 82 within outer part 52, and 
an erected inner part 54 extending generally to each corner corresponding 
to one of the fold lines 66, 72, 74, and 76. The inner part 54 is shown as 
being symmetrical about central longitudinal vertical plane 132. 
Top panel 96 extends across the form void 10 below the upper panel 18 and 
is held rigidly between side panels 20 and 22. Strut panels 100 and 102 
comprise internal supports extending angularly from the top panel 96 to 
proximate opposing fold lines 72 and 76, respectively, at each side of 
base panel 16. Loads on the upper panel 18 are transmitted downwardly 
through panels 100, 102 to the corners 138 and 140 formed by fold lines 72 
and 76, respectively. The inner part 54 is thus held relatively immobile 
within the outer part 52. 
The angle 141 of internal strut panels 100 and 102 with the vertical is 
shown as about 35 degrees. The angle 141 is preferably less than about 60 
degrees, and more preferably less than about 45 degrees. 
As shown in FIG. 7, a form void 10 of enhanced strength uses additional 
side support panels 142, 144 as part of the inner part 54. The sheet of 
corrugated paper from which top panel 96 is formed is thus of greater 
width and is folded about fold lines 146 and 148 to form side support 
panels 142, 144, respectively. These support panels 142, 144 provide 
additional strength for supporting loads on the upper panel 18 near fold 
lines 66 and 74. 
As well known in the art, corrugated paper is constructed from an 
intermediate sheet of paper in which are formed multiple parallel reverse 
bends; the intermediate sheet is then cemented between parallel planar 
sheets of paper which form the opposing surfaces. 
The opposing surfaces of the corrugated paper may have different inherent 
strengths due to differences in paper thickness or type of paper. These 
differences may be used to vary the overall strength of the form void 10. 
Where more than one ply or layer of corrugated paper is used to form a 
panel, the greatest strength results when the panel is configured to have 
the stronger paper surfaces exposed, i.e. on the exterior of the panel. 
The size of the form void 10 will vary, depending upon the dimensions of 
the concrete structure 14 which is to be poured, and the desired spacing 
from the ground 30. Thus, for constructing a wall having a thickness of 6 
inches (15.25 cm) with 4 inches (10.16 cm) of ground clearance, the width 
88 of panel 18 will be about 6 inches and the width of panels 20 and 22 
about 4 inches. 
The length 56 of the completed form void 10 may vary, but the preferred 
length is such that an even number of voids will provide the desired 
distance between spaced-apart support piers 36. A form void length of 5 
feet has been found in practice to be one of the most useful lengths, but 
other lengths may also be provided to accommodate variations in structural 
designs. Of course, the form void 10 may be easily cut on-site to any 
desired length with a knife or saw. When form voids 10 are placed end to 
end, the abutting ends may be sealed with a covering such as tape or a 
piece of paper to prevent the entrance of wet concrete. As already 
discussed, staggering the ends 134, 136 of the inner part 54 (FIG. 5) 
relative to the ends 62, 64 of the outer part 52 (FIG. 4) effectively 
prevents leakage of wet concrete into the form voids 10 where they adjoin. 
Versatility may be gained by the manufacture of outer parts 52 in a series 
of standard lengths, and inner parts 54 in lengths appropriate for each 
length of outer part as well as for joining outer parts of different 
lengths. 
Although the form void 10 illustrated in FIGS. 1-7 has an inner part 54 
which is symmetrical about vertical plane 132, non-symmetrical inner parts 
may be used. The resulting load-bearing strength will be asymmetrical 
across the width of the upper panel 18, and may be computed using known 
methods of static and dynamic analysis. 
The exterior surfaces of the form void 10 are generally coated or 
impregnated with a water resistant material such as wax. As a result, an 
appropriate delay in disintegration and loss of strength of the form void 
10 is achieved. 
There are numerous ways to vary the strength of the form void 10. First, a 
corrugated paper panel of different thickness or design strength may be 
used. Secondly, one or more panels may be formed of more than a single ply 
of corrugated paper, the panel(s) thus being formed by cementing the plies 
or layers of corrugated paper material together with an adhesive 60. 
Third, interior side support panels 142, 144 may be added as adjoining top 
panel 96 to augment side panels 20 and 22. Fourth, as already mentioned, 
the adhesive may be applied in a continuous or non-continuous pattern. 
Fifth, the angle 141 of the strut panels 100, 102 may be varied. Sixth, an 
additional cellular structure of corrugated paper may be inserted within 
the form void 10 to enhance its strength, but such an addition generally 
negates the savings in shipping costs. 
In the unassembled, i.e. "knocked-down" state, the form void 10 comprises 
an inner part 54 and an outer part 52, both having a generally flat 
configuration. The parts 52, 54 may be stacked wherein the panels comprise 
about 94 percent of the total space. By comparison, the panels comprise 
about 15 percent of the total space, after the form void 10 is erected. 
The net saving of space is nearly 85 percent. The number of form voids 10 
which may be shipped in a given space is increased by a factor of about 6. 
Thus, the major object of the invention, i.e. a substantial savings in 
shipping costs, is realized. Where the form void 10 is reinforced through 
the use of additional plies of corrugated paper, or thicker paper, the 
shipping cost advantage may be slightly less. 
Generally, no adhesive 60 is required for assembling the collapsible form 
void 10 at the construction site. The form void 10 may be quickly and 
easily erected by hand, merely by inserting the unfolded inner part 54 
into the unfolded outer part 52 and sliding the inner part longitudinally 
therein. The form void 10 is easily cut to length with a saw or knife. Of 
course, there is no need to remove the form void 10 from its location 
below the poured concrete structure 14. The form void 10 disintegrates 
with time as it absorbs moisture and permits the underlying soil to expand 
without forcing the concrete structure 14 upward. 
While the use of the form void 10 is particularly described relative to the 
construction of a concrete beam formed with vertical forms 12, it is 
understood that the form void 10 may also be used for constructing other 
types of concrete structures with spacing from underlying soils, or to 
produce spaces within the structures themselves. 
It is anticipated that various changes and modifications may be made in the 
construction, arrangement, operation and method of construction of the 
two-part collapsible form void disclosed herein without departing from the 
spirit and scope of the invention as defined in the following claims.