Precast composite floor panel with integrated joist and method of manufacturing same

Abstract

A fiber reinforced floor panel usable in a building comprised of a joist and at least one boot whereby the boot is fixedly connected to an end of the steel joist; a planar section comprised of reinforcing members, whereby a deflection strength of the planar section is higher than a deflection strength of a planar section without the reinforcing members; and a reinforcing material covering whereby the at least one boot and the steel joist are not completely surrounded by the reinforcing material covering.

Description

FIELD OF TECHNOLOGY

This invention relates to precast concrete floor and roof systems and to methods for constructing precast concrete elements for floor and roof structures (referred to as “panels” in the remainder of the document). In particular, this invention relates to lightweight and, in some cases, fiber reinforced precast concrete floor and roof panels including a cementitious slab and an integrated structural steel joist.

BACKGROUND

Floors and roofs of residential, commercial, and public buildings are generally expected to cover as large an area as possible with as minimum a structural weight as possible. Also, floors and roofs are expected to possess proper load capacity, be economical with respect to the combination of construction labor and material costs and on-going maintenance costs, have deformation and deflection within acceptable limits under dead weight and live loads, and to be adapted for prefabrication and for use in mounted constructions.

Wood floors are lightweight, however, they are limited in strength and stiffness. Problems occur due to relatively large deflections and vibrations in panels making up the floor, poor fire rating, and poor thermal and acoustic properties. Traditional steel reinforced concrete floors provide higher strength and stiffness compared to wood floors; however, they are relatively heavy and labor intensive and often experience problems due to crack formation (sumperimposed loads, shrinkage and temperature deformations); they require steel reinforcement (rebar and wire mesh) with a relatively large minimum slab thickness for purposes of corrosion protection of the steel reinforcement.

Other types of floors are typically constructed by spanning joists of steel or other materials between structural supports and laying a metal pan or decking across the tops of such joists. The decking forms a surface onto which concrete can be poured. However, to form a floor with sufficient strength and stiffness, additional shrinkage and temperature reinforcement must be provided combined with a relatively large slab thickness (typically 4 in and more) resulting in a heavier floor. These floor structures are also labor intensive to construct.

To provide a floor with improved strength and deflection characteristics, composite materials have been used. However, to insure proper acoustic characteristics, composite floor systems often employed more concrete than would otherwise be necessary to insulate an area from sound vibrations. The thickness of the concrete slab in these composite floor systems is again governed by the need for shrinkage and temperature reinforcement as well as transverse reinforcement of the slabs for flexural loads in between the joists. This of course increases the dead weight of such floors, adds to construction labor and material costs, and requires increased shoring while the concrete is curing. Shoring adds yet further to floor construction cost and time. Excess concrete may also require that the building be built on stronger foundations and have a stronger superstructure. In some areas, ground or soil conditions may militate against such heavier buildings. Also, higher gage joists and stronger beams and columns are required to support the heavier floors. Accordingly, fewer floors can be built in a building of a given weight.

SUMMARY

The Applicant has invented a novel concrete floor panel that can be precast and can include a fiber-reinforced slab thereby reducing or eliminating the need for steel reinforcement in the slab and a steel joist. Generally, the cast floor panel is modular and, depending on size, includes one or a plurality of light-gage steel joists (or other types of joists) that are integrated with the fiber reinforced slab. Fibers are dispersed throughout the panel thereby providing the slab with increased strength and deflection capacity.

One possible embodiment of the present invention includes a panel comprised of a fiber reinforced slab, a plurality of light gage steel joists, and footings at the ends of the joists (referred to as “boots” in the remainder of the document). The panel is securely connected to the frame structure of the building through connectors embedded in the boots. The loading capacity of the panels can be adjusted by the thickness of the slab and the spacing between joists. The flexural strength of the slab in the transverse (short) direction is provided by the fiber reinforcement, while the flexural strength in the longitudinal (long) direction is provided by the slab and the steel joist. Specifically, the deflection strength of the slab is significantly higher than it would be if the reinforcing fibers were not used; likewise, the deflection strength of the slab is increased significantly with the use of the joists.

The joist can be made of steel and, in a first preferred embodiment, has a block C-shaped cross-section. In another embodiment of the invention, the steel joist has a web section, a first flange section, a second flange section, and a lip. The first flange section is comprised of a plurality of cutout sections. The web section is comprised of a plurality of cutout sections. The joist is light gage, which decreases the overall weight of the finished floor panel. Due to the C-shaped construction of the joist, it provides a stiffening aspect to the slab to provide further support and to reduce deflections.

The boot can be made of the same fiber reinforced material as the slab or it can be made of some other kind of material such as steel, wood, plastics, recycled materials, or composites. The boot has a heel portion and a toe portion. The heel portion and the toe portion extend into the slab thereby serving to couple the slab and the joist. Furthermore, the boot has a first side, a second side, a front end, and a back end. The front end can be shorter in height than the back end. The front end is located in the area of the toe portion and the back end is located in the area of the heel portion. The joist slindingly engages the boot between the first side and the second side.

The presently disclosed precast composite panel is relatively lightweight, strong in flexure, resists large deflections and vibrations, is rapidly constructed, does not require extraordinary skill to install, and possesses good acoustic and thermal properties.

The inventive panel is created by positioning a pair of boots having slots coaxially in a mold such that the slots face each other. A slender light gauge steel joist is placed in the slots to form a boot-joist assembly. The boot-joist assembly is held in a shallow mold in which fiber reinforced composite material will be poured. The joist cutout sections can have any shape and can be located anywhere along the first flange section and/or web section that so that when the cementitious material is poured into the mold, the cutout sections are embedded in the cementitious material. The cutout sections must be large enough so that the cementitious material can flow therethough such that the joist is rigidly anchored in the cementitious material after the cementitious material cures, yet small enough so as to not negatively impact the behavior of the joist under load.

The boot slots are generally rectangular and are positioned vertically in relation to the bottom of the mold. Once the boot-joist assembly is placed into the shallow mold, the fiber reinforced composite material in slurry form is poured into the shallow mold. Once the fiber reinforced composite material cures, a slab of fiber reinforced composite material is formed in the shallow mold. After the slab cures, the completed floor panel with integrated joists is removed from the shallow mold and the process can be repeated.

The boot-joist assembly is held in place by means of a heel protrusion and a toe protrusion, each of which extend from a bottom surface of the boot into the shallow mold. During forming of the slab, the fiber reinforced material is poured in slurry form into the mold and surrounds the heal protrusion and the toe protrusion. The slurry also flows into the cutout sections of the joist in order to further help anchor the joist to the slab. The fiber reinforced material then cures around the protrusions and in the cutout/anchoring sections, thereby permanently locking the boot-joist assembly in the slab.

These and other aspects of the invention will be better understood by those of skill in the art with reference to the following drawings wherein like numbers represent like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are perspective top and bottom views of the fiber reinforced floor panel.

FIGS. 2a-2c are left, back and right side views of a boot.

FIGS. 3a-3c are bottom, front and top views of a boot.

FIG. 4 is a perspective view of a boot with a receiving slot identified.

FIG. 5A is a perspective view of a light gage steel joist having a C-shaped cross-section.

FIG. 5B is a perspective view of a light gage steel joist having a T-shaped cross-section.

FIG. 5C is a perspective view of a light gage steel joist having an I-shaped cross-section.

FIG. 5D is a perspective view of a light gage steel joist having a L-shaped cross-section.

FIG. 5E is a perspective view of a light gage steel joist having a Z-shaped cross-section.

FIG. 5F is a perspective view of a light gage steel joist having a U-shaped cross-section.

FIG. 5G is a perspective view of a light gage steel joist having a rectangular-shaped cross-section.

FIG. 6 is a boot-joist assembly.

FIG. 7 is a second embodiment of the present invention.

FIG. 8 is a mold for forming a slab with a boot-joist assembly disposed therein.

FIG. 9 is a mold containing a cementitious slurry with a boot-joist assembly disposed therein.

FIGS. 10a-10c are steps for manufacturing the inventive fiber reinforced floor panel.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

Referring to FIGS. 1a-b, a diagramatic embodiment of the inventive floor panel is generally shown. In this embodiment, a fiber reinforced floor panel 10 includes a slab 20 shown in outline form, light-gage steel joists 30 and boots 40 (also shown in outline form) disposed on at least one end of the light-gage steel joists 30. The slab 20 is made of a fiber reinforced cementitious material that is formed from a slurry and, after curing, becomes a hardened material. The slurry contains fibers dispersed throughout the cementitious material to help strengthen it.

The inventive fiber reinforced floor panel can be constructed with or without the boots 40. In this first embodiment, the floor panel 10 is formed with boots 40. Boots 40 are depicted in detail in FIGS. 2a-c, 3a-c, and 4. Boot 40 has a left boot side 210 and a similarly shaped right boot side 230 parallel to each other in spaced apart relation. Both boot sides 210 and 230 are generally rectangular. Other geometric configurations such as triangular and trapezoidal are possible. In the preferred embodiment, upper edges 255 and 265 slope downward from a boot back 220 to a boot front 270, described in more detail below. As can be seen in each of the side views of the boot 40, a rectangular toe 240 and a rectangular heel 250 extend from a bottom side 260 of the boot 40. The boot back 220 is generally rectangular and joins the left and right boot sides 210 and 230. A right edge 223 of the boot back 220 joins with a back edge 233 of the right boot side 230 to form right boot corner 237. Similarly, a left edge 227 of the boot back 220 joins with a back edge 243 of the left boot side 210 to form left boot corner 247.

Opposite the boot back 220 is the boot front 270. Boot front 270 is generally rectangular. In the preferred embodiment, upper edges 255 and 265 of boot sides 210 and 230 slope downward from back to front, boot front 270 is shorter in height than boot back 220. Alternatively, upper edges 255 and 265 can be parallel to bottom side 260 in which case the boot front would be the same height as the boot back. A right front edge 222 of the boot front 270 joins with a front edge 232 of the right boot side 230 to form right front boot corner 238. Similarly, a left front edge 218 of the boot front 270 joins with a front edge 242 of the left boot side 210 to form left front boot corner 248.

A receiving slot 280 is formed as a result of the connection formed between the boot sides 210 and 230 with boot back 220 and boot front 270. A width 285 of the receiving slot is determined by the width of the boot back 220 and the boot front 270 and also of a thickness of the boot sides 210 and 230, e.g. keeping the outer measurements of the boot constant, the size of the slot can vary with a variance in the thickness of the sides 210 and 230; alternatively, keeping the size of the slot constant, the outer dimensions of the boot can vary depending on the thickness of the sides 210 and 230. To provide a connector in the boot 40, a rod 290 is inserted into a rear section 295 of boot 40 and extends from the bottom side 260 of the boot to a top side 262 of the boot.

A light-gage steel joist is depicted in FIGS. 5A-5G. As is shown in FIG. 5A, a particularly preferred embodiment of the steel joist 30 generally has C-shaped cross-section. However, as shown in FIGS. 5B-5G, the steel joist used in any of the embodiments of the present invention can also have various other cross-sections such as a T-shape, I-shape, L-shape, Z-shape, U-shape, or a rectangular cross-sectional shape. In the C-, T-, I-, L- and Z-shaped cross-section joists, a single web 420 serves as the main body of the joist and provides resistance to deflection of the fiber reinforced floor panel when assembled therein. In the U- and square-shaped cross-section joists, the joist has a second web 470.

A joist with any of the various cross-sections has a plurality of flow-through holes 410. When the fiber reinforced floor panel is formed, the flow-through holes 410 allow the cementitious slurry to pass therethrough. Once cured, the cementitious material secures the steel joist 30 in fixed relation to slab 20. Also, the toe 240 and heel 250 of the boot are surrounded by the cementitious material and locked therein.

In all of the cross-sections in any of the embodiments of the present invention, the joist includes an anchoring member 430 positioned orthogonal to the web 420. The anchoring member can be positioned as anchoring member 430 is shown in FIG. 5A with a longitudinal edge thereof being attached to a longitudinal edge of web 420. Or, a longitudinal edge of web 420 can be attached to a centerline of an anchoring member to form an I- or a T-beam such as shown in FIGS. 5B and 5C.

Steel joist 30 can have a lower member 440 extending from a lower edge 450 of the web 420. As with the anchoring member 430, the lower member 440 can be attached to the web 420 such that the steel joist 30 has a rectangular, a C-, or an I-cross section. Alternatively, lower member 440 can be positioned on an opposite side of web 420 so that the joist has a “Z” cross-section. If the lower member 440 is positioned such that the steel joist 30 has a C-, Z- or an I-cross-section, a lip 460 can be added to the lower member 440. If the lower member 440 is positioned such that a C-cross section is formed, the lip 460 will form the upper overhang section of the “C.” The lip 460 is beneficial for hanging suspended ceiling panels, conduit, plumbing, HVAC equipment and other components on a level of a building beneath the level on which the floor panel is being installed.

Included in the success of the present invention is the use of a unique cementitious material for the composition for the formation of the slab 20. This composition must be such as to be compatible with direct metal contact with joists 30 and while in the form of a slurry not be so viscous that it cannot flow through holes 410 such that once cured, the anchoring members 430 of the various joist components are enclosed and secured therein. It must also be substantially chemically inert, so that it does not actively attack, corrode, or oxidize the joist metal. The basic composition is described in the table below, with the various concentration ranges stated in parts by weight.

	TABLE
		Most
	Components	Preferred	Minimum	Preferred
	Cement	20%	10%	90%
	Fly Ash	40%	0%	70%
	Sand	25%	0%	50%
	Water	13.2%	10%	30%
	Superplasticizer	0.5%	0%	2%
	Fibers	1.3%	0.5%	20%

A particularly preferred composition for the cementitious composite in the slab is one comprising 20 parts of portland cement, 1.3 parts of inorganic fiber (PVA fiber), 40 parts of fly ash, 25.5 parts of sand and 13.2 parts of water. A course Aggregate can be added also.

The portland cement and gypsum useful herein may be any suitable grade of commercial portland cement and/or gypsum. Extensive descriptions of both will be found in numerous references, typical of which are Shreve et al. Chemical Process Industries (4th ed.: McGraw-Hill Book Co., 1977), chapter 10; Considine, ed., Scientific Encyclopedia (7th ed.: Van Nostrand Reinhold, 1989), pages 548-550 and 1392-1393; and Urquhart, ed., Civil Engineering Handbook (4th ed.: McGraw-Hill Book Co., 1959).

Similarly, various types of suitable inorganic reinforcing fibers are also widely described in the literature. See, for instance, Rubin, supra, chapters 59, 60 and 64 (the preferred glass fibers are discussed in chapter 60); and Feinberg, Modern Plastics Encyclopedia, 64 (10A), 185-186 (1987). Glass fibers are particularly preferred because of their well-established reinforcing, handling and mixing properties, ready commercial availability, lack of color and low cost, although other inorganic fibrous materials such as mineral fibers and carbon fibers may also be useful. Organic fibers are not usually chemically compatible with the portland cement matrix. Commonly, the fibers will be in the form of “chopped” short fibers, having fiber lengths of about 1 11/2 inch (25-37 mm). Equipment for chopping fiber to length while simultaneously spraying the fiber in the mold is commercially available and recommended for use in this invention; see Feinberg, supra. Virgin or recycled fiber may be used; use of recycled fiber is advantageous because it provides for beneficial utilization of materials that would otherwise require disposal as waste. PVA Fiber can also be used.

Those skilled in the art will be readily able to select the particular choice of each of the above materials best suited for practice of this invention under any specific circumstances from the variety of commercially available materials.

When the present embodiment of the fiber reinforced floor panel is assembled, a boot 40 is positioned on each end of the joist 30 such that the joist 30 matingly engages with the receiving slots 280 of the boot 40. The resulting structure is a boot-joist assembly 500 as shown in FIG. 6. The boot joist assembly 500 is embedded in the slab 20 such that the flow through holes 410 are filled with cementitious material and thereby locked therein upon curing of the cementitious material. Anchoring members 430 further help to secure the boot-joist assembly in the cementitious material. Toe 240 and heel 250 of each boot 40 extend into and are held in place by the slab 20 and serve as a final means of securing the boot-joist assembly in the cementitious material. As such, the boot-joist assembly is securely locked into the slab 20.

After the present embodiment of the fiber reinforced floor panel 10 is assembled, the assembled floor panel 10 can be installed in a building (not shown). If the floor panel 10 is used on a ground level floor, boots 40 can rest directly on a grade or sub-grade load-bearing member. Or, if the floor panel 10 is used on higher-level floors, the boots 40 can rest on projections or other load bearing structures (not shown) that extend from columns, beams or walls of the building.

A second embodiment of the present invention is similar to the first embodiment; however, in the second embodiment of the present invention, no boots will be used. FIG. 7 shows the second embodiment of the fiber reinforced floor panel 600 without any boots. Light-gage steel joists 630 will be secured in the cementitious material in a manner similar to the first embodiment; however, the second embodiment of the present invention will be installed such that the joists 630 rather than boots, rest on a floor or projections from columns.

The overall manufacturing process will be discussed in more detail with respect to the description of FIGS. 8-10. FIG. 8 illustrates a mold 800 (usually rectangular) that may be formed of plastic, fiberglass, metal, and wood or any other convenient material which will not be damaged by the cementitious slurry from which the floor panel slabs are to be formed and from that the finished panel/frame member can be readily unmolded upon completion of the fabrication procedure. The mold 800 is a flat shallow mold, whose interior length and breadth are equivalent to the desired breath and length of the slab 20 that is to be molded. The mold walls 810 rise above the base 820 to a height not less than the desired thickness of the slab 20. It is convenient for the mold 800 to be of sufficient strength to be able to support the weight of the formed panel 20, so that underlying supports are not needed. In addition, this will permit the molds to be mounted on wheels (not shown) and thus moved around a factory floor if necessary.

Prior to molding, the mold 800 is coated on the inside surfaces with a conventional mold release agent, to aid in the subsequent unmolding of the finished panel/frame member.

The overall production process is illustrated schematically in FIGS. 10a-c. Step 1 shows a mold 800. The mold 800 is built preferably with wheels (not shown). In step 2, boots 40 are placed into the mold at predetermined lateral and longitudinal springs. Steel joists 30 are placed in receiving slots (not shown in this figure) of the boots 40. Alternatively, the boot/joist assembly 500 can be formed before the boots are placed in the mold 800. Assembly 500 rests on top of the mold base 820 and is aligned with mold walls 810 of the form mold 800. A cementitious slurry 830 is then poured into the mold 800 (as shown in FIG. 9) with the cementitious material enclosing and incorporating the anchoring members 430 of the joists, the toe 240 and heel 250 of each boot 40 and is finally allowed to cure to a complete slab, as shown in step 3, to form slab 20.

Once the unitary panel has cured to a desired degree of hardness and strength, it can be removed from the mold 800 by conventional demolding techniques. Thereafter the completed floor panel is demolded and is now ready for installation in a building. Preferably the mold will have been constructed so that it can be reused for manufacture of subsequent panels. Alternatively, it may be formed as a one-time-use mold that is destroyed during the unmolding.

It will also be evident that the interior base of the mold 820 can be provided with any desired pattern (in negative form), which will be reproduced in positive form in the corresponding surface of the panel in order to provide a pleasing appearance. Typical patterns include simulation of the appearance of wood, brick, tile, stucco or the like.

Thermal and/or sound insulation and fire proofing materials may be installed onto the slab before, during or after assembly depending on whether the insulation is in the form of solid batts blocks or is blown or sprayed onto the surface of the slab 20.

It will be evident from the above that there are many other variations that, while not expressly described above, are clearly within the scope and spirit of the invention. The description above is therefore to be considered exemplary only, and the actual scope of the invention is to be limited only by the appended claims.

Claims

1. A panel usable as a floor or a roof in a building structure comprised of:

an elongate joist having a vertical web and a side orthogonal to said web; and

a cementitious material comprising a planar section;

whereby an edge of the joist is embedded in the cementitious material and the vertical web extends away therefrom;

the vertical web is comprised of a plurality of through openings through which said cementitious material extends.

2. The panel as recited in claim 1 wherein the cementitious material includes fibers dispersed therein.

3. The panel as recited in claim 1 wherein a horizontal plane is disposed on an edge of the joist opposite the embedded edge of the joist.

4. The panel as recited in claim 3, whereby a lip is disposed on an unattached edge of the horizontal plane and extends toward the cementitious material.

5. The panel as recited in claim 1, wherein the joist is comprised of steel.

6. The panel as recited in claim 2, wherein the fibers are glass fibers.

7. The panel as recited in claim 2, wherein the fiber reinforced cementitious is cast whereby the planar section is formed.

8. A fiber reinforced floor panel usable in a building structure comprised of:

a joist; and

a fiber reinforced cementitious material comprising a planar section;

wherein the joist is comprised of an elongate member having a vertical side and first and second horizontal sides such that the joist has a C-shaped cross-section and whereby a boot is fixedly connected to at least an end of the joist;

wherein the boot is comprised of a heel and a toe; and

whereby the heel and the toe fixedly engage the fiber reinforced cementitious material.

9. The fiber reinforced panel as recited in claim 8 wherein the boot has a first side and a second side, and a front and a back end, whereby the front end is shorter in height than the back end.

10. The fiber reinforced panel as recited in claim 9 wherein the first and second sides are disposed at a distance from each other that is at least as large as a largest width of the first and second horizontal sides of the joist and whereby a joist receiving slot is formed therebetween.

11. The fiber reinforced panel as recited in claim 9 wherein the boot is further comprised of a reinforcing rod.

12. The fiber reinforced panel as recited in claim 8 wherein the boot is further comprised of the cementitious material.

13. The reinforced panel as recited in claim 10 wherein the joist matingly engages the boot in the joist receiving slot.

14. The fiber reinforced floor panel as recited in claim 9 wherein the joist is held in fixed communication with the planar section by at least the boot.

15. The fiber reinforced floor panel as recited in claim 8, wherein the joist is comprised of steel.

16. The fiber reinforced floor panel as recited in claim 8, wherein the fibers are glass fibers.

17. The fiber reinforced floor panel as recited in claim 8, wherein the fiber reinforced cementitious is cast whereby the planar section is formed.

18. A method of manufacturing a panel comprised of the steps of:

placing a first boot and a second boot at a predetermined distance from each other; and

placing a first end of the light-gage steel joist in the first boot and a second end of the light-gage steel joist in the second boot to form a joist assembly;

positioning the joist assembly in a mold;

depositing a cementitious material in the mold so that at least a portion of the joist assembly is surrounded thereby;

curing the fiber reinforced cementitious material thereby fixedly securing the joist assembly therein.

19. The method as recited in claim 18 further comprising providing through-holes in the joist.

20. The method as recited in claim 19 further comprising causing the cementitious material to flow through the through holes in the joist before curing.

21. A lightweight structural panel, comprising:

an elongate joist having a vertical web and a side orthogonal to the vertical web,

said vertical web and side each having a plurality of through-holes disposed therein;

a fiber reinforced cementitious material cast in cooperative engagement around said side and a portion of said web and extended through ones of said through holes in each of said side and said web so as to fixedly look said joist in relation to said cementitious material.

22. A lightweight structural panel as recited in claim 21, said joist having a cross-section profile of one of a C-, L-, I-, T-, and a rectangle.

23. A lightweight structural panel as recited in claim 21, further comprising a boot disposed on each end of said joist.

24. A lightweight structural panel as recited in claim 23, each boot comprising:

a pocket having a pair of spaced apart walls, said joist being disposed therebetween;

a foot connected between corresponding edges of said spaced apart walls; and

a through hole in said foot and portions of said spaced apart walls.

25. A lightweight structural panel as recited in claim 24, each boot further comprising a column connected between said spaced apart walls, said column extended from said foot to a side of said walls opposite said foot.

26. A lightweight structural panel as recited in claim 25, said column further comprising a reinforcing member disposed therein extending from said foot to said side of said walls opposite said foot.

27. A method of making a lightweight structural panel comprising:

providing a mold in the shape of the structural panel;

placing a joist in said mold, said joist having a vertical web and a side orthogonal thereto; and

placing a cementitious slurry in said mold, said cementitious slurry incorporating therein said side and a portion of said vertical web of said joist.

28. A method of making a lightweight structural panel as recited in claim 27 further comprising:

providing a plurality of through holes in each of said side and said web of said joist.

29. A method of making a lightweight structural panel as recited in claim 28, further comprising placing said cementitious slurry through ones of said through holes.

30. A method of making a lightweight structural panel as recited in claim 27, further comprising curing said cementitious slurry.

31. A method of making a lightweight structural panel as recited in claim 27, further comprising placing a pair of boots in said mold and disposing ends of said joist in said boots.

32. A method of making a lightweight structural panel as recited in claim 31, further comprising providing said boots with through-holes.

33. A method of making a lightweight structural panel as recited in claim 32, further comprising placing said cementitious material through said through holes in said boots.