US2721369A - Method of concrete floor construction - Google Patents

Description

Oct. 25, 1955 w. T. BURKE 2,721,369

METHOD OE CONCRETE FLOOR CONSTRUCTION Filed March 18, 1952 JNVE/vv-oe. wLLfA/v/ 7'. BURKE.

BKZ a i United States Patent Office 2,721,359 Patented Oct. 25, 1955 METHOD OF CONCRETE FLOOR CONSTRUCTION William T. Burke, Pittsburgh, Pa.

Application March 18, 1952, Serial No. 277,307

1 Claim. (Cl. 25-155) This invention relates to concrete structures, and more particularly to concrete oors and roofs, and has for one of its objects the provision of a concrete mixture of such composition that the resulting slab or the like will have greater strength for a given weight of material than various structures heretofore employed, whereby lighterweight steel framing and reinforcement may be employed in buildings into which concrete enters than is possible with various concrete compositions heretofore employed.

Another object of my invention is to provide an irnproved method of laying oors and the like, whereby concrete slabs and the finish coatings or layers of concrete thereon will be more firmly bonded together than heretofore.

Still another object of my invention is to provide a concrete mixture of such nature that conduits and metal reinforcements and structural members will be more intimately encompassed by the concrete, by reason of the better flowability of the concrete mixture, even though a smaller amount of cement is incorporated thereon than is sometimes employed.

In ordinary steel frame structures, it is customary to lay conduits for electric and telephone wires on top of the steel beams and over the top of the heavy concrete structural floor or roof slab, after which a light-weight concrete floor fill is disposed on top of the concrete structural slab and covering the conduits. Later, after the radiators are installed and the plastering done, a cement mortar floor finish is applied to the fioor fill.

I propose to make the structural fioor or roof slab and the fill from a light-weight concrete of similar compositions. I also am able, in many cases, to eliminate the floor fill operation, by incorporating the conduits in a structural light-weight concrete slab, and I also make the cement mortar oor finish an integral part of the structural slab and profit by the great compression value of the cement fioor finish.

In making the cement mortar floor finish, which is applied after the floor fill and the structural slab have hardened, I use, in the structural slab, and also in the fioor fill concrete, sharp-edged vesicular surfaced aggregates which are derived from crushing such materials as expanded slag, clay or shale, etc., and also coral, pumice or crushed air-cooled blast furnace slag. The surfaces of these aggregates are vesicular or pitted, and provide excellent anchorage for the bonding of other concrete bodies to them. By making the concrete from those aggregates and incorporating in the mix a relatively small amount of water-cooled granulated slag and making this concrete of a certain plasticity, I find when I screed the body that the sharp-edged aggregates tilt up and are left only partially buried in the mix, The upper ends of the aggregates so displaced project above the body of the concrete structural slab or fill. Furthermore, a void is left behind each of the displaced aggregates and the fiuid cement in this body does not fill the void, so that numerous voids are left on the screeded surface and form excellent keyways to permanently anchor the cement mortar finish, and the up-ended or displaced aggregates project into the cement mortar oor finish and the sharp-edged and the vesicular surfaces thereof assist in securely and permanently anchoring or bonding this floor finish to the slab or fill. These displaced aggregates, being firmly embedded in the supporting slab and into the floor finish, guarantees that the finish layer is strongly bonded to the concrete supporting slab and can be taken into account when designing the slab. Rounded aggregates like gravel do not tilt to a substantial degree when the mix is screeded.

It has been customary to use a concrete, that is expanded by aluminum powder, for this oor fill, but bonding permanently a cement mortar fioor finish to this type of fill is expensive, as the surface has to be cleaned and a coat of cement grout is brushed on the surface of the fill. Furthermore, expanded concrete is hard to handle in cold weather and in hot weather and only certain brands of Portland cement reacts properly to the aluminum powder expanding agent. Small gravel or grits are used in this expanded concrete, and as they have round surfaces, they cannot be tilted like sharp edge aggregates.

Cinders were once common and were used extensively as an aggregate in floor fill concrete, but the advent of powdered coal, gas and oil for heating purposes have made cinders too scarce.

To make the supporting structural heavy-weight concrete slab and the floor fill concrete from a common light-weight mixture would be an advantage, as the two bodies would better unite, so that the concrete fill instead of merely being a useless dead weight could go to work and help the support slab in shear and compression. By making these two bodies of one common material, I make more simple the mixing and supply situation, and I greatly reduce the dead weight. For example, an oice building steel beam supported concrete floor and fill by present practice have the following dead weights, based on approximately seven foot spans between supports. 51/2 inches heavy concrete structural supporting slab=66 lbs., 31/2 inches of expanded concrete=35 lbs., and l inch finish=l2 lbs., all making a total dead weight of 113 lbs. per square foot of fioor. The total thickness of the floor would be l0 inches. Using light weight concrete whose aggregates have sharp-edged and vesicular surfaces, I cast the structural slab and later integrally bond the concrete fill to it and later apply the cement mortar floor finish. Using a light-weight concrete of 108 lbs. per cubic foot weight and having 2000 lbs. per square inch in ultimate compression, I can reduce the dead load as follows. With the same thickness of slab, which is l0 inches, of which 9 inches is light-weight concrete, with a weight of 8l lbs. per square foot and allowing l2 lbs. per square foot for the weight of the finish, a total of 93 lbs. is obtained for the dead load. Thus, a saving of 20 lbs. per square foot is obtained. It may be possible to reduce somewhat the total thickness of this oor. This homogeneous body could act as a fiat arch restrained by the spaced steel beams and very little reinforcing steel would be required in the body.

Where the separate iioor fill operation can be avoided, then it is possible to omit the floor fill dead weight and make the supporting slab function also as a conduitcovering body. In this case, the workmen in laying the conduits can work on the temporary field forms which will support the floor slab, and after the laying of the conduits, the floor can be completed in one operation, except for the finish which has to be applied later; as experience has taught builders that it costs too much to protect the iioor finish from damage by other mechanics in the building, and it is better to wait until the ventilating, heating and plastering contractors are finished before finishing the oors. The saving in dead weight from making the structural slab function as the iill also is very great. For example, a total of only 6 inch thickness will be required for the slab, which at inches for the light-weight concrete would be 45 lbs. per square foot and l2 lbs. per square foot for the finish would be a total dead load of only 57 lbs. per square foot, which is almost half the dead load required by present practice.

In the drawing, which more fully describes my invention, Figure l is a fragmentary section of my concrete floor slab, including the lill; Fig. 2 is a fragmentary section of my floor, till, and finish; Fig. 3 is a fragmentary section of my combination floor slab and ll with finish, and Fig. 4 is a sectional view showing a conventional form of structure, for purpose of comparison with that of Figs. 2 and 3.

In Fig. l, I show an enlarged section of a concrete slab, wherein the base or body portion 2 has coarse aggregates 3 which will be tilted upright during screeding of the initial layer 2, so that not only will such aggregates frequently project slightly above the screeded surface, but whether or not they project above the screeded surface, there will be voids left at 4, assuming that the screeding is done from right to left in the example shown. Also, the surface at x is scarified somewhat by the rough screeding operation.

When the till layer 5 is applied, the material thereof will enter the voids at 4 and thereby become keyed in the voids. Also, mortar in the fill 5 will enter the vesicular or pitted surface of the aggregates 3, and there will be good adherence to the rough surface at x.

For convenience of comparison, l use Fig. 4 which shows a section through a present type of structure that has a iioor 6 and steel beams 7 that support a structural concrete slab 8 and conduits 9 that are embedded in expanded concrete 10 and cement mortar lioor finish 11. Reinforcement 12 is embedded in the slab S. The supporting slab 8 is made from heavy concrete Weighing perhaps 150 lbs. per cubic foot, and its plaster coat 13 is very diflicult to apply and make permanently bond to this dense heavy concrete. There is here no bond between the structural slab 8 and the lill 10, and poor bonding is obtained between the iill 10 and the iinish 11.

In Fig. 2, I show a structural arrangement similar to that shown in Fig. 4, except my structural slab 14, which is supported by a steel beam 15 and contains reinforcing steel 16, is made from a light-weight concrete mixture described above. In Fig. 2, a conduit 17 rests on a beam 15 and the slab 14 and is covered by my floor lill 18 which is made of the same material as used in the slab 14. Floor fill 18 is bonded to slab 14 in the same manner as shown in Fig. l, and the floor till 18 is bonded to floor finish 19 also in the same manner as shown in Fig. 1. A plaster coat 20 bonds iirmly to my concrete mix, due to the vesicular surfaces of the aggregates. The bonding together of the structural slab, till and finish makes a much stronger tioor membrane and provides better wind bracing for the building.

Fig. 3 shows my combination iioor and fill slab 21 supported by steel beams 22 and including reinforcing 23; the conduits 24 resting upon steel beams 22 and on blocks 25' which, in turn, rest on a temporary form 26. The slab 21 is bonded to floor finish 27 in the same fashion asdescribed in Fig. l. The mechanics who install the conduit can walk on the form 26 and, as soon as the conduits are laid, the slab material 21 can be applied. The great strength of the rich-in-cement floor finish helps to compensate for some of the loss of cross section in the slab, where the conduits are located, but the conduits are almost always at the neutral axis of the slab, and any reduction of area would not weaken the slab. Raceways with outlets are generally run at right angles to the spaced supporting beams and do not cut across the compression area of the salb. The narrow width of these raceways would have little adverse effect when positioned at right angles to the supporting beams.

A fuller description of the above described light weight concrete licor lill composition is outlined in my co-pending patent application, Ser. No. 277,306, tiled March 18, 1952.

As stated in said application, crushed air-cooled blast furnace slag is used in my light weight concrete composition, in combined sizes ranging from large sizes to small sizes, and l incorporate in the mix a relatively small amount of friable cellular granulated blast furnace slag, adding a less than usual amount of Portland cement and water, and mixing this composition to a certain plasticity.

l claim as my invention:

The method of making a concrete body that comprises screeding a plastic concrete slab that contains sharpcornered aggregates, while causing some of the aggregates to become tilted by the screeding tool, to effect protrusion thereof from the surface of the slab, the remainder of the mixture being of such plasticity that voids will remain behind the tilted aggregates, and thereafter applying a cementitous layer to the said surface of the slab, to ll the voids and imbed the protruding aggregates.

References Cited in the tile of this patent UNITED STATES PATENTS Re. 16,799 Burdge Nov. 29, 1927 829,293 Reilly Aug. 2l, 1906 1,573,896 Alton Feb. 23, 1926 1,707,055 Driscoll Mar. 26, 1929 1,740,336 Crittal et al. Dec. 17, 1929 2,268,311 Sheehan Dec. 30, 1941 OTHER REFERENCES Journal of the American Concrete Institute- April 1949, pages 582-583.

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