| United States Patent | 3,845,593 |
| Zen | November 5, 1974 |
LIGHTWEIGHT CONCRETE PANEL
Abstract
Lightweight concrete panel having perimeter of parallel side and end edges, reinforcing grid extending between edges. Border portions adjacent edges of panel define relatively stiff peripheral frame which surrounds inner portion, inner portion having corrugated lower surface. Corrugations and lower surfaces of border portions have acoustical coating of elastomeric material to provide integral resilient mounting of panel and reduce transmission of air-borne and impact-generated sound. Acoustical coating is expanded polymer sprayed onto lower surface or granulated expanded polymer bonded to lower surface.
| Inventors: | Zen; Giovanni (West Vancouver, British Columbia, CA) |
| Appl. No.: | 05/288,362 |
| Filed: | September 12, 1972 |
| Current U.S. Class: | 52/144 ; 52/403.1; 52/483.1; 52/601; 52/602 |
| Current International Class: | E04C 2/26 (20060101); E04C 2/04 (20060101); E04C 2/288 (20060101); E04b 001/86 () |
| Field of Search: | 52/336,144,145,393,396,403,445-454,588,605,625,319,600,602,608,674,604,618,622 |
| 1839404 | January 1932 | Mazer |
| 1930024 | October 1933 | Varden |
| 1971900 | August 1934 | Cerveny et al. |
| 2114048 | April 1938 | Davis |
| 2337525 | December 1943 | Peik |
| 3300912 | January 1967 | Shumaker |
| 3720027 | March 1973 | Christensen |
| 594,368 | Sep., 1925 | FR | |||
American Concrete Institute, Lightweight Concrete, April 1970, pp. 147-160.. |
Primary Examiner: Murtagh; John E.
Attorney, Agent or Firm:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. In a building having a structural framework with spaced frame members, a lightweight concrete structural panel comprising:
a. a reinforced rectangular panel of lightweight low-density concrete having a smooth planar upper surface and a peripheral frame,
b. a continuous metal reinforcing grid embedded in the concrete,
c. the lower surfaces of the peripheral frame being co-planar and the side edges thereof presenting a concrete surface which is shaped to interfit a matching surface of an adjoining panel,
d. the peripheral frame including an embedded and enlarged grid member disposed adjacent to the frame exterior surfaces and integral with the reinforcing grid so that rigidity and strength are imparted thereto,
e. the lower surface of the panel having successive, narrow, continuous and parallel longitudinally extending crests and troughs extending between the peripheral frame,
f. the troughs extending inwardly approximately one-half the thickness of the panel, and the crest surfaces being flat and coplanar with the lower surfaces of the frame,
g. the crests and troughs being approximately the same lateral dimension and having a width approximately equal to the thickness of the panel,
h. a thin continuous coating of acoustical composition which is applied to the lower surface of the panel, including troughs, crests, and frame, to provide an integral resilient, mounting therefor between the panel and the frame members, and
i. the low density concrete composition of the panel including hydraulic cementitious material including lightweight aggregate and sufficient density reducing means for enabling nails to readily pass therethrough.
2. In a building having a structural framework with spaced frame members, the lightweight concrete structural panel as set forth in claim 1, in which:
a. the lightweight aggregate includes expanded shale, and
b. the density reducing means includes a further light-weight aggregate selected from a group containing perlite, vermiculite, glass beads, expanded plastic beads, plastic beads and pumice.
3. In a building having a structural framework with spaced frame members, the lightweight concrete structural panel as set forth in claim 1, in which:
a. the concrete is made from a mix containing one part cementitious material by volume which includes 10 percent by volume of Pozzolan,
b. 1.65 parts by volume of expanded shale,
c. 1.25 parts by volume of expanded polystyrene beads, such composition producing a material which has approximately a 28 day strength of 1,800 pounds per inch squared, and a density of approximately 90 pounds per cubic foot.
4. In a building having a structural framework with spaced frame members, the lightweight concrete structural panel as set forth in claim 1, in which:
a. the aggregate is a lightweight expanded shale, and
b. the density reducing means includes an air entraining agent in such proportion as to produce from 5 to 25 percent air voids by volume.
5. In a building having a structural framework with spaced frame members, the lightweight concrete structural panel as set forth in claim 1, in which:
a. the edge faces on opposite sides of the frame have complimentary male and female V's to provide for interfitting of adjacent panels.
6. In a building having a structural framework with spaced frame members, the lightweight concrete structural panel as set forth in claim 1, in which:
a. the acoustical coating is an elastomeric material and is an expanded polymer coating which adheres to the lower surface.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to a lightweight structural concrete panel, particularly adapted for use with wooden frame buildings as floor and wall panels.
2. Prior Art
Three main types of conventional building methods account for a large proportion of structures in North America, namely wooden frame, pre-cast concrete and poured concrete. Wooden frame buildings, that is a building having a wooden structural frame work secured to load-bearing membranes, have been used for hundreds of years and have many advantages over other types of construction. The advantages include flexibility of design, ease of modification and repair, reasonable durability when protected from the elements, and when properly designed and constructed, frame buildings show good resistance to dynamic loads such as earth quakes and high winds. Well known disadvantages of wood frame construction include its combustibility, vulnerability to rot and insect attack and, particularly in relation to high density, multi-family dwellings, its relatively poor air-borne and contact-generated sound insulation qualities.
Conventional ways of reducing sound transmission in wooden frame construction include increasing mass of the membrane i.e. floor covering or wall sheeting, and also providing resilient connections between the membrane and the framework. A common way of increasing mass of the floor membrane is to use a layer of lightweight concrete over a sub-floor, the layer having a thickness of about one and a half to two inches. The concrete increases mass of the membrane thus reducing sound transmission through the floor, but provides essentially no additional strength and requires heavier frame construction to support the additional weight. The concrete is poured on site and thus quality control is difficult. Resilient connections provided between the membrane and frame are expensive and time consuming to install and, for a given outside building volume, reduces inside usable volume by increasing thickness of walls and floors.
Pre-cast, reinforced concrete building elements, such as beams and wall panels are generally used in buildings larger than the wooden frame buildings but the elements generally require mechanised handling equipment and thus are difficult and expensive to transport and erect. Also, precast concrete elements are generally used in steel frame buildings and difficulties can arise from the dissimilar characteristics of the materials. However such concrete and steel frame construction has advantages of being fire and rot resistant and, due to inherent mass of the concrete have relatively good sound insulation qualities, provided care is taken to reduce sonorous characteristics of the steel. Also quality control in factory-produced products is easier to maintain than in products produced on site.
Poured concrete construction is not discussed in detail as it is not related to the invention but this type of construction has inherent difficulties of quality control of concrete poured on site, together with high labour content.
SUMMARY OF THE INVENTION
The invention reduces difficulties of the prior art wooden frame building construction by providing a prefabricated lightweight concrete panel which, as a structural membrane, can be substituted for a plywood panel. The panel is adapted for factory production, thus facilitating quality control of the concrete. The panel also has relatively good sound insulating qualities resulting from mass of the panel, which qualities are further improved by providing integral resilient mounting of the panel, and by coating a surface of the panel with a sound insulating covering.
One embodiment of the invention is a lightweight concrete panel having a perimeter defined by a pair of spaced parallel side edges and a pair of spaced parallel end edges. An outer portion of the panel has border portions adjacent the edges defining a relatively stiff peripheral frame, and an inner portion of the panel is integral with and within the outer portion. The inner portion has a lower surface provided with a plurality of corrugations having crests and troughs, the corrugations extending to the border portions. A reinforcing grid extends between the edges of the panel and provides additional structural strength. A coating of elastomeric material is provided on the corrugations and lower surfaces of the border portions to increase sound insulation both for impact-generated and air-borne sounds. The elastomeric material can be an expanded polymer sprayed on to the lower surfaces, or granulated expanded polymer bonded to the surfaces.
The panel is made from a concrete mix containing a hydraulic cementitious material and a lightweight aggregate, a density reducing means being provided to reduce density of the final concrete to be between 50 - 90 lbs/ft.sup.3. The lightweight aggregate includes expanded shale and the density reducing means includes air voids. A second lightweight aggregate can be included being selected from a group containing perlite, vermiculite, glass beads, expanded plastic beads and pumice.
A detail description following, related to drawings, gives exemplification of apparatus according to the invention, which however, is capable of expression in means other than those particularly described and illustrated.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the panel according to the invention, some portions being removed,
FIG. 2 is a fragmented section on 2--2 of FIG. 1, showing in addition a portion of an adjacent panel,
FIG. 3 is a fragmented plan of a portion of a floor joist system,
FIG. 4 is a fragmented detail section similar to FIG. 2 showing portions of adjacent panels and a supporting joist at a join,
FIG. 5 is a fragmented detail section showing corrugations of the panel in contact with a supporting joist, as seen on 5--5 of FIG. 3.
DETAILED DISCLOSURE
Figs. 1 and 2
A lightweight concrete panel 10 according to the invention has spaced parallel side edges 12 and 13 and spaced parallel end edges 15 and 16 as shown. The side edges have a length 18 and the end edges have a length 20, ratio and size of the lengths being selected so as to permit convenient application of the panel to joist and stud systems as used in floors and walls respectively. Border portions 22, 23, 25, and 26 are adjacent the edges 12, 13, 15, and 16 respectively and form a relatively stiff peripheral frame, hereinafter outer portion 28.
The border portions surround an inner portion 30 having a generally planar upper surface 31 and a corrugated lower surface 33 having crests and troughs severally 34 and 35 respectively. The border portions 22 and 23 have similar lower surfaces 38 and 39 which surfaces are co-planar with the crests 34. The lower surface 38 has a width 41 which width is, at a maximum, equal to width of a panel supporting member, such as a joist or stud, as will be described. Thus a maximum measurement of the width 41 is about 1 1/2 inches for normal building sizes, although in some applications this could be reduced to about three-fourths of an inch. Separation between the upper surface 31 and the lower surfaces 38 and 39 equals separation between the upper surface 31 and the crests 34 and defines maximum thickness of the panel 42. Hereinafter the term "nominal thickness" of a panel refers to maximum thickness above, a minimum thickness 43 arising at a trough of the corrugation as shown. A ratio of the maximum to minimum thickness is, as a maximum about 2:1, although this ratio could be reduced. A nominal thickness of a panel for normal applications as a floor membrane is approximately 1 inch, the minimum thickness 43 therefore being one-half inch; however the thickness 43 could be increased to about three-fourths inch. The corrugations and crests are symmetrical and a typical width 45 across a crest, or a typical width 46 across a trough, is approximately one-half inch. The corrugations as illustrated have a section similar to an `Acme` thread having flat crests, however other sections could be used. A flat crest is of particular value for load bearing as will be explained.
The corrugations extend lengthwise of the panel, that is they are parallel to the side edges 12 and 13. This has particular application in fitting the panels over a standard joist system in which center-to-center distance between the joists is a multiple of the length 18. If required the corrugations could run transversely, that is parallel to the end edges 15 and 16, in which case center-to-center spacing between joists running parallel to the side edges 12 and 13 would be a multiple of the length 20.
As shown in FIG. 2, the edge 12 has a V-sectioned face 47, the V having an included angle 48, of about 150 degrees, hereinafter a female V. An edge face 49 of the edge 13 has a similar but complementary V, that is a male V, having an included angle 50 of about 150 degrees. A typical adjacent panel 52 has an edge face 54 having a female V similar to the edge face 47, which face is therefore also complementary to the edge face 49 of the edge 13. Complementary edge faces as above facilitate alignment of adjacent panels and improve sealing between adjacent panels.
Edge faces (not shown) of the end edges 15 and 16 also have complementary male and female V's similarly to the edge faces of the side edges, thus facilitating alignment of each edge of the panel, adjacent border portions having similar lower surfaces.
The panel is stiffened by a reinforcing grid 57 having an inner portion 59, surrounded by four outer portions, two outer portions being designated 61 and 62 in FIG. 2. The outer portions are closed box sections, welded or wired closed, and extend adjacent outer surfaces of the border portions 22 and 23. The inner portion 59 extends as a continuous panel between the outer portions of the grid. Similar outer portions (not shown) of the grid are provided in the border portions 25 and 27. The grid is a rectangular welded steel mesh, either galvanized or ungalvanized, having wire sizes ranging from 21 gauge to 10 gauge, and spacings ranging from 1/2 .times. 1/2 inch to 2 .times. 2 inch rectangular openings. This material meets the requirements of ASTM A82-70 and ASTM A185-70, extended as required to cover smaller sizes of wire.
The corrugations are covered with an acoustical coating 65 shown in broken line in FIG. 2. The coating is an elastomeric polymer foam sprayed in place, or a granulated elastomeric expanded polymer bonded to the concrete surface. The acoustical coating reduces transmission of contact-generated sound into the air, and reduces reflection of sound due to its sound absorptive surface. The coating extends, if necessary to a somewhat greater thickness, over the lower surfaces of the four border portions, serving as an integral resilient mounting for supporting the panel when the panel is supported on a joist. Suitable elastomeric polymer foam includes resilient or relatively rigid polyurethane, or polyethylene. If granulated foam is used, the granules pass a sieve having mesh sizes within a range of U.S. Standard Sieve No. 16 to U.S. Standard Sieve No. 100, that is the granules have sizes within a range of 0.15 mm to 1.2 mm. A suitable adhesive for bonding the granules has a polyvinyl acetate base and sells under a registered trademark "Bondfast" manufactured by Lepage's Ltd. of Ontario, Canada. A further suitable adhesive is sold by Wescon Products Ltd. of Vancouver, B.C., Canada under a name "Conbond."
Fig. 3
the panels 10 and 52 are shown supported on a plurality of joists, severally 71, so that the corrugations running lengthwise of the panels contact portions of the joists, to be described with reference to FIG. 5. Adjacent edges of the panels are secured to the joists at joins in manner to be described with reference to FIG. 4.
Fig. 4
a typical join 80 between adjacent edges of two panels 81 and 82 is supported on a joist 84. The panel 81 has a female V end face 86 which accepts a male end face 87 of the panel 82. A gap between the end faces 86 and 87 is sealed with an elastomeric sealant 85 such as a common gunapplied sealant used for caulking wallboard and floor joins. This provides flexibility at the join and tends to reduce transmission of impact-generated sound from one panel to adjacent panels. An alternative sealant is to provide an adhesive butyl tape secured to the edges. A further alternative would be to eliminate the sealant and secure the end edges substantially in contact with each other. Border portions (partially shown) of the panels 81 and 82 have acoustical coatings 88 and 89 which coatings separate the panels 81 and 82 from the joist 84. This results in a resilient mounting of the panel as aforesaid and if required the coating on the border portions can be thicker than the coating on the corrugations, increasing resilience of mounting to reduce sound transmission. Common wire nails 90 and 91, as commonly used to secure wood panels, pass through the border portions of the panels and are held in the joists 84, similarly to nailing a piece of plywood to a joist. In some applications, fewer nails (e.g., about 20 percent fewer) can be used than would be used in nailing a plywood panel. This reduces time required in nailing and, to some extent reduces sound transmission from the panel to the joist. In some applications if fewer nails are used diameter of the nails is increased from that of common nails to maintain desired strength. Width 93 of the joist, usually about 1 1/2 inches, is sufficiently wide to accept the two nails as shown, and is sufficiently wide to accommodate variations in sizes of the panel.
Fig. 5
a portion of the panel 10 is shown supported on a joist 71, the acoustical coating 65 on the crests 34 of the corrugations being in contact with the joist. The acoustical coating on the border portions 22 and 23 is also in contact with the joint as seen in FIG. 4. Because only the crests 34, and not the troughs, are in contact with the joists, area of panel actually in contact with the joists is considerably reduced from that of a panel having two flat sides. Such reduction in area of contact is believed to help in reducing in transmission of impact-generated sound from the panel to the joist and thus results in a quieter building. Transmission of sound from the panel to the joist is further reduced by the coating of the elastomeric expanded polymer that cover the corrugations, such coating resulting in a resilient mounting of the panel at all points of contact between the panel and the joist. The flat crests of the corrugations in contact with the joists produce lower bearing stresses than sharp or cylindrical crests and thus reduce surface compression of the joist.
Lightweight Concrete Composition
Many different mixes of lightweight concrete can be used to produce a panel within a central concept of the invention. Of particular importance is reduction of density of the concrete by use of a lightweight aggregate with air entrainment and/or the use of the lightweight aggregate with a second lightweight aggregate selected from a group containing perlite, vermiculite, glass beads, expanded closed-cell plastic beads, plastic beads and pumice, the second aggregate added in any proportion which would yield the desired physical properties, in particular to reduce density of the concrete and attain desired strength and workability of the finished panel. The second aggregate is preferably spherical, to reduce unnecessary stress increase from sharp corners, and has a diameter between about one thirty-second inch to about three-sixteenths inch (0.5 mm - 5.0 mm).
The concrete is made from hydraulic cementitious material such as Portland cement, Type I or Type III, and if desired, Pozzolan, a finely divided active silica can be used, the Pozzolan adding to the workability of the mix and increasing its cementitious content. The first lightweight aggregate contains from 50 - 100 percent by volume of expanded shale, and to this is added in proportion from 0 - 50 percent one or more of the second aggregates selected from the above group of essentially non-structural aggregate.
A water reducing admixture complying with the requirements of ASTM C494 is added in the proportion of 1 - 10 ounces of admixture per 100 pounds of cement. Air entraining and/or foaming mixtures are added in such proportion as to produce from 5 - 25 percent air voids by volume, depending on the proportion of lightweight material and expanded shale. If expanded shale is the only lightweight aggregate, air voids would be between 15 - 25 percent by volume to attain desired density. Mixing water added in the ratio of 0.25 to 0.70 pounds of water per pound of cement provides a working slump in the range of 0 - 6 inches. The ratio of cement to total aggregate by volume is in the range from 1:1 to 1:5. Concrete made from mixes above have a wet cured strength of from 200 - 4,000 pounds per square inch at 28 days (14 to 280 kg/cu.sup.2).
A suitable mix includes the following ingredients, by volume:
1 part Portland Cement, containing 10 percent Pozzolan,
1.65 parts of expanded shale,
1.25 parts of expanded polystyrene beads, A suitable material is a styrene polymer, sold as expanded polystyrene beads as "Styropor" (a Registered trademark of Badische Anilin-and Soda-Fabrik Aktiengesellschaft, Rhein, Germany)
and water to attain desired slump value.
This particular mix has a working slump of 4 inches, a 28 day strength of 1,800 pounds per square inch (126 kg/cm.sup.2), and when 1 inch thick and used with a steel wire mesh of 16 gauge having 1 .times. 1 inch openings, the panel has an ultimate bending moment of 6,300 in. lbs. per foot width (238 cm. kg/cm. width) and a weight of 7.05 lbs. per square foot (0.00344 kg/cm.sup.2). This results in an overall density of 90 pounds per cubic foot (1.44 kg/dm.sup.3).
Comparison of Lightweight Panel with Conventional Floor Systems
Conventional floor systems use 3/4 inch, seven-ply plywood, nailed to 2 .times. 8 inch, or 2 .times. 10 inch joists pitched at approximately 16 inches, depending on floor load requirements. The average weight of 3/4 inch plywood used in conventional floor systems is 2 1/2 pounds per square foot when no additional sound insulation is provided.
A lightweight concrete panel according to the invention of nominal thickness one inch weighs from about 3 - 8 pounds per square foot (0.15 - 0.4 kg/dm.sup.2) thus increasing dead weight of the panel by a factor of approximately 20 - 300 percent.
To obtain an equivalent floor strength using the lightweight concrete panel above, pitch of joists 15 decreased by about 2 percent. Increase in dead weight is compensated to some extent by an increase in allowable bending moment, the panel having an allowable bending moment of 2,100 inch pounds per foot width, (80 kg cms per cm width). This compares with 3/4 inch plywood which has an allowable bending moment of approximately 1,600 inch pounds per foot width (60 kg cm per cm width).
An important consideration in designing with the lightweight concrete panel is in improved quality control, which permits use of a lower factor of safety. A usual factor of safety for plywood panels used as floor membranes is generally of the order of 8. This large factor allows for wide variations in the strengths of a given set of plywood panels of nominal equal strengths. Thus plywood is heavily penalized as a result of quality control during manufacture. The lightweight concrete panel, made under stricter quality control which is possible on automatic concrete molding methods, permits use of a safety factor of the order of 3, and thus the panels can be used more effectively.
A major consideration in the comparison relates to properties commonly associated with concrete, that is, improved sound insulation, and also fire and rot resistance. These properties are usually outweighed by the disadvantages of working with concrete, that is for poured concrete work, preparing forms which involves high labour content, or for precast work handling precast concrete structural sections by mechanized equipment.
Panels according to the invention are designed to be an essentially direct substitute for structural plywood sheets, and as such have a weight that can be handled easily by two men, and can be nailed in place using conventional wire nails in most applications where structural plywood sheet is normally used. The concrete can be sawn to size with conventional power sawing equipment using carborundum blades, and when installed additional sound insulation is not required. This saves considerably on-site labour, together with additional costs of materials for the conventional sound insulation practice. As shown in the above comparison, flexural stiffness of the lightweight panel is of the same order of magnitude as 3/4 inch plywood and thus a joist or stud framework supporting a series of such panels results in a composite structural system in which the widely dissimilar chemical materials have compatible physical properties. Thus as the properties of the concrete panel closely follow the properties of plywood, the structural combination of the two relatively dissimilar materials combines the ease of construction of wood frame buildings with the desirable acoustical properties of concrete.
The example above is for a panel having a nominal thickness of 1 inch. For applications requiring high thermal or sound insulation, density of the panel can be reduced to approach 50 lbs./ft.sup.3 and the thickness of the panel can be increased to a maximum of about 4 inches, which results in a panel capable of being handled by two men. The panel has dimensions dependent on conventional joist or stud pitches and density and thickness of panel. A nominal 1 inch panel of 90 lbs/ft.sup.3 density and dimensions of 48 inches .times. 80 inches can be handled by two men.
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