US 3637457 A
A high-impact resistant concrete-spun bonded fabric laminae including a layer of concrete and a planar fabric comprised of continuous nylon filaments arranged without apparent order within the plane of the fabric and being autogenously bonded together at a substantial number of touching filament crossover points, the fabric being at least partially embedded and under tension in said concrete.
Description (OCR text may contain errors)
United States Patent Gothard et al. 1451 Jan. 25, 1972  NYLON SPUN BONDED FABRIC- 3,509,010 4/1970 Metzger ..161/162 CONCRETE COMPOSITE 3,531,367 9/1970 Karsten l6l/l60  Inventors: Edwin S. Gothard, Cary; John D. Calfee, FOREIGNPATENTS R APPUCATlONS bmh 1,125,663 8/1968 Great Britain 161/151  Assignee: Monsanto Company, St. Louis, Mo.
OTHER PUBLICATIONS  Filed: June 8,1970
Fibrous Reinforcement for Portland Cement from Modern PP N04 44,492 Plastics, by S. Goldfein, April, 1965, pages 156- 158.
Primary Examiner-William A. Powell  U.S.Cl ..161/140,l6l/l50,l61/l5l,
, 161/157, 161/170, 264/71, 264/228, 264/333 stt;mey-(.il.NBolwnl,1 1l3lss,Jr., Russell E. Wemkauf, John D. 51 1111.01. ..B28b 23/04, B32b 13/02, B32b 13/14 P am ea  Field of Search ..l6l/57, 59,140, 146, I48,
161 150,151,157,159, 162, 168-l70,402;  ABSTRACT /7 52/309 A high-impact resistant concrete-spun bonded fabric laminae including a layer of concrete and a planar fabric comprised of References continuous nylon filaments arranged without apparent order within the plane of the fabric and being autogenously bonded UNITED STATES PATENTS together at a substantial number of touching filament cros- 1,379,s37 5/1921 Ruppel ..161/269 ux Sever Points, the fabric being 311938! Partially embedded and 2,332,703 10/1943 Elmendorf ..161/157 undertension in said Concrete- 2,473,528 6/1949 Hoover ..161/269 X 3,336,179 8/1967 Campbell et al ..l6 l/72 8 Drawmg F'gms PAIENTEU JINZSIIIYZ K IMPACT FORCE STATIC SUPPORT STATIC SUPPORT FIG. I.
PREPARE CONCRETE RECIPE PREPARE MOLD- WET SPUNBONDED NYLON FABRIC PLACE WETTED FABRIC IN BOTTOM OF MOLD COVER FABRIC WITH CONCRETE RECIPE CURE CONCRETE INVENTORS JOHN D. CALFEE EDWIN S. GOTHARD PIC-3.3.7
ATTORNEY NYLON SPUN BONDED FABRIC-CONCRETE COMPOSITE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a cement concrete composite having a greatly improved impact strength, the composite consisting of a layer of spunbonded fabric adhered to the concrete in the area in which the concrete is under tensile stresses.
2. Description of the Prior Art It has been recognized that the low tensile strength of concrete severely limits its applications. In the past, attempts to compensate for the lack of tensile strength in concrete has usually involved either unstressed reinforcing steel rods or prestressed reinforcing steel rods. However, neither of these procedures really overcomes the low tensile strength limitation but merely bypasses it for any concrete structure which has a region in tension is subject to have cracks form and propagate through that region in tension. Such cracks form at relatively low stresses and continue either until they reach a free surface or until they reach a region that is in compression. When concrete is subjected to blast forces producing shock and vibration, it will most likely be destroyed unless reinforced by an extensive steel complex. This reinforcement, however, does not prevent the concrete from shattering and causing extensive damage.
Furthermore, the tensile strength exhibited in conventional reinforced or plain concrete, as calculated by standard tests, cannot be relied upon for design purposes since small incipient cracks due to fatigue, thermal shocks or cavities cannot be detected. Such crack formations and the subsequent propagation thereof are not always present but the conditions favorable for their existence cannot always be predicted. Even the exercise of exceptional control procedures does not eliminate crack formation and growth. It has long been accepted that about one-half of the material in a normally reinforced concrete beam is useless to resist tensile loads. The detrimental effects of tension cracks in reinforced concrete beams are not limited solely to loss of load-resistant area. For example, it is apparent that tension cracking severely limits the effectiveness of concrete tanks for containing liquids. Likewise, the wrapping of pipelines with concrete results in the addition of little load-bearing value.
U.S. Pat. No. 3,429,094, to Romualdi teaches the incorporation of short links of straight steel wire in the concrete recipe. The steel wire provides the two-phase material with a crack-arrest mechanism that increases cracking strength and provides toughness to the degree alleged unattainable in conventional concrete. However, in the Romualdi patent, crack retardation is provided only by the high modulus wire counteracting the stresses ahead of the crack. While such is an advantage, the Rornualdi two-phase concrete is incapable of turning the cracked plane so that the crack both multiplies and takes a torturous path through the material which substantially increases the energy needed to propagate the crack. Further, steel wire basically does not readily adhere to the concrete and is easily pulled out upon preceding low impact energies. The surface characteristics of the wire can be altered to improve adhesion such as by providing flattened areas; however, the flattened areas reduce the volume fraction of wire in the concrete which can be achieved by using round, smooth, wire.
SUMMARY OF THE INVENTION This invention is a composite structure comprised of a spunbonded nonwoven fabric lamina and a concrete lamina which are adhered together at least along their contiguous surfaces by a fabric lamina being at least partially embedded in the concrete lamina. The nonwoven fabric lamina is comprised of continuous nylon filaments which are arranged in the plane of the fabric without apparent order. The nylon filaments do not have a lubricant coating or other type of finish so that the adhesion of the nylon to the cement is enhanced. The nylon filaments comprising the fabric lamina are autogenously bonded together at a substantial number of touching filament crossover points to provide multidirectional stability. The array of filaments is adaptable to alter the direction of travel of the crack plane through the material so as to divide and subdivide its path thus increasing the energy needed to propagate the crack. Autogenously bonded" means that the bonds between the filaments are formed in the absence of an externa binder for the reason that binders may not withstand the alkalinity of the concrete. For example, two filaments may be autogenously bonded together by the application of heat in that the fibers are fused at the crossover points. Autogenous bonding also includes the use of solvents since upon the removal of the solvent from the filament, the polymers comprising the filaments are mixed at the filament crossover points. However, the preferred method for autogenously bonding nylon filaments is by the use of a hydrogen halide gas, and more specifically, hydrogen chloride gas. The filaments absorb the hydrogen chloride gas along the surface areas which results in the breaking of the intermolecular hydrogen bond between adjacent amide groups. Upon desorbing the hydrogen chloride gas from the nylon filaments, the intermolecular hydrogen bond between amide groups of different fibers reform resulting in bonding at the interfilament crossover points. As a byproduct of hydrogen chloride gas bonding, the hydrogen chloride gas etches the surface of the nylon filaments so that the filament surface area is substantially increased. it is thought that the increased surface area aids in the mechanical bonding or the adherence of the nylon filaments to the concrete,
The concrete recipe is generally comprised of cement, sand, aggregate and water. However, the concrete recipe may include strength increasing material such as chicken wire, short steel wire and nylon staple fibers. While the spunbonded nylon fabric as described herein may cover more than one surface, it must be contiguous with the concrete lamina along the concrete laminas surface subjected to the maximum tensile stresses. While one or more spunbonded nylon fabric lamina may be embedded a distance from the surface having the maximum tensile stresses, it has been found that the fabric is most efficacious when it comprises the surface of the concrete lamina receiving the maximum tensile stresses.
While the filaments comprising the fabric may be completely undrawn, partially drawn, completely drawn, it has been found that partially drawn and undrawn nylon filaments are more effective in increasing the energy required for postcrack separation. The reason is thought to be that upon the development of a crack, the nylon filaments must be cold drawn to the completely drawn state before rupture of the filaments occurs, such drawing consuming tremendous amounts of energy.
In preparing the composite of this invention, the nylon spunbonded fabric must be applied to the cement recipe while the fabric is in a wetted and elongated state. Upon being exposed to water, nylon expands or grows from 1 to 6 percent. Thus, the total surface area of the spunbonded nylon fabric will also increase by a proportional amount, for example, from 2 to 12 percent. Upon drying, the fabric will try to return to its original area. If the fabric were associated with the concrete recipe prior to being expanded by water, the moisture in the concrete recipe would cause the fabric to expand, thus creating bulges and ripples along the surface. Therefore, by associating wetted nylon spunbonded fabric with the concrete recipe, the fabric will inherently tend to return to its original state upon the curing of the concrete and the drying of the fabric, but is prevented from completely doing so by the hardening of the concrete. By the failure of the fabric to return to its original at rest state, the fabric is maintained under a tension within the concrete which aids in the dissemination of the crack plane, when developed, throughout the composite. Also, the concrete adjacent or proximate to the fabric is under slight compression, the extent to which the fabric is under tension.
Therefore, an object of this invention is to provide a concrete article which is reinforced with nylon spunbonded fabric along the exterior surfaces of the concrete receiving the maximum tensile stress.
Another object of this invention is to provide a concrete spunbonded nylon fabric laminae which is exceptionally resistant to high impact forces.
Another object of this invention is to provide a concrete spunbonded fabric laminae in which the fabric is adhered to the concrete and in which the fabric is under tension.
These and other objects of this invention will become apparent when the detailed description is read in conjunction with the drawings.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a section taken through a typical concrete-nylon spunbonded fabric laminae showing the fabric lamina being adhered to the concrete lamina along the side being subjected to the tensile stresses;
FIG. 2 is a greatly enlarged schematic view of the spunbonded nylon fabric showing the fiber arrangement with the fabric and showing the filaments dividing the crack plane into a multiplicity of directions; and
FIG. 3 is a block diagram illustrating the process of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Substantially all polyamide fibers may be used to form the spunbonded fabrics of this invention. Nylon 6, nylon 4 and nylon 6,6 are especially adaptable due to their affinity for water. For simplicity, the nylon subsequently referred to is nylon 6,6 which is prepared by condensing hexamethylene adipamide and adipic acid. Spunbonded nonwoven fabrics may be made by many processes, one of which being set forth in US. Pat. No. 3,338,992. The melt extruder is used for spinning continuous nylon filaments. The formed filaments are then drawn downwardly away from the extruder by an aspirator which also deposits the filaments by means of moving air on a conveyor belt. The nylon filaments comprising the fabric are bonded together at a substantial number of filament crossover points by being passed through a chamber containing an activating gas, such as, hydrogen chloride. The nylon filaments absorb the hydrogen chloride which renders them bondable upon the removal of the gas. Thus, the filaments are permanently bonded together at their touching crossover points by desorbing the gas from the filaments by either being subjected to heat or by being passed through a water bath. While the web just described is comprised completely ofnylon filaments, other continuous filaments may be incorporated into the web which are not subject to attack from the cements alkalinity such as, for example, polypropylene and polyethylene. However, the incorporation of other filaments which do not have the affinity for water as compared to nylon, results in the fabric having a reduced contractive force upon being dried. To fully illustrate this invention, the spunbonded nonwoven fabric as herein described is comprised wholly of nylon filaments.
The concrete recipe is generally comprised of cement, sand, aggregate and water. Other strength-inducing materials may be added such as staple wire and the like. The order of mixing found most efficient includes the placing of the course aggregate in the mixer while it is in operation after which the sand, cement and then water are added in that order. The mixer is generally allowed to run at least 5 minutes after all ingredients have been added.
Both wooden and metal molds may be used to form the specimen. Generally, a Saran-(polyvinylidene chloride) type liner is placed in the mold and allowed to have sufficient overhang to permit complete enclosure of the specimen. The Saran insures moisture retention and acts as a mold-releasing agent. To insure a flat surface for receiving the nylon spunbonded fabric, a thin sheet of acetate may be placed on top of the Saran. With the mold being prepared to receive the nylon spunbonded fabric, the fabric is thoroughly wetted and placed smoothly in the mold on the acetate sheet. The mold may then be placed on a vibrating table which is operated during the filling cycle and until a smooth surface is formed on the concrete. Where opposed surfaces of the composite may be subjected to tensile stresses, as for an example in a highway median strip which is placed between oncoming lanes of traffic, a second lamina of nylon spunbonded fabric may be wetted and placed on the top surface and troweled until all air pockets are removed.
Curing is accomplished by leaving the mold containing the respective ingredients at room temperature at least for 24 hours after which the same is subjected to atmospheric pressure steam in a curing chamber. After remaining in the steam chamber for at least 24 hours, the mold is removed and is allowed to be cooled down to room temperature before testing.
In reference to FIGS. 1 and 2, composite 20 is comprised of concrete lamina 22 and nylon spunbonded fabric lamina 21 with fabric 21 being at least partially embedded in concrete 22 so that adequate bonding between the laminae is achieved. For purposes of illustration, composite 20 rests on the static supports and is provided with an impact force. At the moment of impact, moiety A of concrete lamina 22 is under a compressive stress while moiety B is under a tensile stress which places fabric 21 under the greatest tension since fabric 21 represents the point being furthest from line C" which is the neutral layer of unstressed material. Assuming that in fabric 10 a crack plane developed along filament 11 at its termination point, the crack plane would be propagated along that filament to filament junction 12 where it would be divided and propagated along the filaments comprising the junction. With the crack plane having been partially dispersed at junction 12, a remaining portion thereof is propagated along filament 11 to filament junction 13 where the crack plane is again divided and propagated along the filaments comprising that junction. This process is repeated until the crack plane is completely dissipated. By such crack dissipation, large fissures which would extend through the concrete to rupture the same are prevented from forming. For the system to be operative, the filaments must readily adhere to the concrete, must be continuous so that the crack plane will be endlessly propagated and must be bonded together at a substantial number of touching filament crossover points to provide fabric integrity.
EXAMPLE I This example serves as a control. The concrete recipe was comprised of the following:
96-inch aggregate l 2. l 8 pounds;
water 3.84 pounds.
The recipe was prepared at room temperature in a tumbletype 1.3-cubic foot capacity mixer. The order of mixing was as follows: place course aggregate in mixer while mixer was operating, add sand, then cement and then the water. The mixer was allowed to run for 7 minutes after all ingredients were deposited therein. A 6 by 6-inch metal mold was used to form the specimen. A Saran sheet was placed in the mold and was allowed to have sufficient overhang to permit complete enclosure of the specimen, insuring moisture retention. A smooth acetate sheet was then placed on top of the Saran to insure a fiat planar bottom surface.
The mold was placed in a laboratory-size vibrating table and was vibrated during the filling operation until a smooth surface was formed on the concrete recipe. The specimen remained in the mold at room temperature for 26 hours after which curing was completed by having the specimen remain in a steam chamber for 24 hours. The steam chamber contained saturated steam at a pressure of 5 p.s.i.g. After the curing period, the specimen was removed from the steam chamber and allowed to cool to room temperature before testing. The resulting specimen sample was 6 by 6 by 3!; inch thick.
The impact strength of the specimen was tested by dropping a 5.35 pound weight having a bullet-shaped nose from different heights so as to give the impact force in foot pounds at an increasing force until initial failure and, ultimately, total failure occurred. Initial failure is where a first crack is detected in the specimen and total failure, or complete destruction of the specimen, is considered to be a -inch bow in the specimen in the vertical direction. The total foot pounds of force necessary for initial or total failure is the sum of the drops to reach these points and the preferred order of progression is as follows: 3, 3, 4, 5, 5, l0 and foot pounds.
The specimen was supported in a frame having a 41-inch thick hard rubber gasket which eliminated surface irregularities. The unsupported area of the specimen was 20.25 square inches. The weight was dropped from an electrically triggered mechanism which is centered over the specimen.
The testing of this sample resulted in an initial failure of 3 foot pounds and a total failure of 3 foot pounds, the initial and total failure being identical since the cracked plane was propagated through the specimen.
EXAMPLE 2 The concrete recipe used in this example was the same as prepared in example 1. A Saran-type sheet was placed in the bottom of a 6 by 6 inch mold, upon which was placed an acetate sheet to insure a smooth bottom surface. The nylon spunbonded fabric which weighted 3.0 oz./yd. and made as previously described was immersed in water and allowed to remain 1 minute so that fabric expansion occurs whereupon it was placed while in a wetted condition on the acetate sheet. The mold was then placed in the vibrator and filling occurred to a depth of three-fourths inch. The composite was cured in accordance with example 1.
Testing of the composite after curing in accordance with example showed an initial failure of 6 foot pounds and a total failure of 40 foot pounds.
EXAMPLE 3 The procedure as set forth in example 2 was repeated with the exception that the nylon spunbonded fabric had a weight of 1.0 ounce per square yard. Testing of this composite sample showed that the initial failure was 6 foot pounds and total failure was 10 foot pounds.
Thus, when comparing example 3 with example 2, it is shown that higher fabric weights result in a substantially greater total failure strength due to the increased number of filaments available to disperse the cracked plane and dis tribute the load.
What is claimed is: v
1. A composite comprised of a spunbonded fabric lamina and a concrete lamina being bonded together along the concrete-fabric interface, said spunbonded fabric lamina at least being present on the exterior surface of said concrete lamina positioned to receive a tensile stress, said spunbonded lamina being comprised of continuous nylon filaments arranged within the plane of the fabric and being autogenously bonded together at a substantial number of touching crossover points. 7
2. The composite of claim 1 wherein said nylon filaments are arranged within the plane of said fabric without apparent order, said filaments being free of surface coatings.
3. The composite of claim 1 wherein said spunbonded fabric lamina is under tension.
4. The composite of claim 1 wherein said filaments are at least only partially drawn.
5. A process for forming a spunbonded fabric-concrete composite comprising the steps of:
a. preparing a spunbonded nylon fabric;
b. preparing a concrete recipe;
c. aqueously wetting said fabric;
d. associating said wetted fabric with said concrete recipe;
e. curing said concrete recipe.
6. The process of claim 5 wherein said fabric is under tension after said concrete recipe has cured.
7. The process of claim 5 wherein said wetted fabric is placed in a mold and said concrete recipe is deposited thereon.
8. The process of claim 5 wherein said nylon filaments are at last only partially drawn.