Patent Application
20130212974
1. Field of the Invention
This invention relates to interlocking reinforcement inclusions for ultra-high performance concrete (UHPC) and other inclusion-containing materials, and also for other applications such as soil erosion prevention and beach or shoreline stabilization and protection.
The invention also relates to an improved UHPC and other materials having inclusions, to structures made of the improved materials, and to a method of making concrete structures that utilizes vacuum curing.
2. Description of Related Art
Reinforcement inclusions are objects that are placed within another material to increase the strength or durability of the material. For example, the addition of sand and gravel to cement results in concrete, a material having a substantially higher durability, flexural strength, and compressive strength than plain cement. The durability of ordinary concrete is evidenced by the fact that many ancient Roman concrete structures have lasted for two millennia.
Although normal-strength concrete, which typically displays compressive strengths of between 3 and 5 ksi (thousands of pounds per square inch), there is a need for even stronger types of concrete continues, as engineers seek to employ smaller and more durable concrete in structures. Replacing normal-strength concrete in many applications is high-performance concrete (HPC), which uses embedded steel reinforcement and typically achieves compressive strengths of 10 to 12 ksi. However, concerns about HPC's relatively low strength-to-weight ratio, low ductility and tensile strength, and objectionable volume instability, leaves most concretes used today with much room for improvement.
Much of the problems with HPC have been solved with the advent of ultra-high performance concrete (UHPC, often referred to as Reactive Powder Concrete, or RPC), which differs from conventional concrete in the addition of fine quartz, simple steel fiber inclusions (e.g., 0.008 diameter×−0.5 inch length, and a superplasticizer. In addition or alternatively to steel fibers, UHPC inclusions may take the form of nanotubes, dove-tailed plastic fibers, and PVA or cellulose fibers, including fibers made of plastic waste materials. UHPC is capable of achieving compressive strengths greater than 150 MPa (21.7 ksi). In addition, UHPC is nearly impermeable, an advantage that confers resistance against many destructive processes that degrade NSC and HPC, including freeze-thaw, corrosion of embedded steel, and solvation by chemicals that penetrate into the concrete.
Most reinforcement inclusions are intended to provide an “anchoring” effect that holds the concrete together even when it has yielded and cracked. However, the material can also lend its own compressive-strength properties to the concrete. The anchoring effect may be achieved by 1) friction or traction between the surfaces of the inclusion and the concrete components, 2) enclosure of concrete components by surfaces of the inclusion; and 3) chemical bonding between the inclusion surfaces and the surrounding matrix. Anchorage failure of steel reinforcement inclusions can be classified into four categories: 1) pull through; 2) concrete breakout; 3) splitting; and 3) steel failure. By far, the most prevalently used inclusions are steel fibers of various compositions, dimensions, and geometries. Such fibers share an elongated wire-like shape, but can have a variety of different cross-sections, as well as bends, hooks, or twists.
Notwithstanding the proven advantages of UHPC, the process requirements tend to be considerably more expensive than those required for other types of concrete. One of the contributors to the high cost of current UHPC is the requirement of a thermal curing step, which is in addition to the mixing and casting steps of conventional concrete. A typical thermal treatment consists of 48 hr steaming at 194° F. and 100% relative humidity reached through a ramp-up period (e.g., 6 hrs). A ramp-down period of about the same duration of the ramp-up follows thermal treatment. Upon completion of the curing process the concrete is allowed to return to room temperature. Other thermal regimens, including delayed and doubly-delayed thermal treatment, are also known, but all add significantly to the cost of UHPC applications.
In addition to higher processing costs, the inclusions typically used in UHPC add substantially to the cost, and especially those made of metal, such as steel fibers. Moreover, use of steel or plastic fibers as reinforcement inclusions has a number of additional disadvantages. First, when the concrete is poured, the fibers align themselves with the direction of flow, resulting in differences in compressive and tensile strength properties along different axes. Second, whether steel or plastic the fibers tend to clump during pouring and mixing. Third, UHPC with fiber inclusions may explode during thermal treatment because steam cannot escape the concrete due to its relatively high density. Fourth, when used in structures that must be protected from bombs or artillery, an explosion will eject the fibers out of the concrete upon impact, causing failure of the concrete.
An additional problem occurs with both conventional concrete and UHPC, in which inclusions can cause back up at twists or turns in the hose through which the concrete is pumped, with the resulting back pressure causing a possible blow out, waste of material, and injury to the operator.
Some of these problems have been addressed by replacing the conventional wire inclusions with three dimensional structures. A number of different examples of such three-dimensional inclusion structures are disclosed in U.S. Patent Publication No. 2011/0101266, and also in U.S. Pat. Nos. 5,404,688, 3,913,295, and 3,616,589. The structures are formed of regular wires, or wires/fibers with irregular or non-circular cross-sections, into a variety of regular and irregular three-dimensional polyhedrons or other geometric shapes having edges defined by the wires, as well as loop structures, coils having ends bonded together, and even DNA-like double helixes. These open geometric shapes are said to provide an interlocking effect in that, when packed tightly together, portions of the structures will penetrate into openings adjacent structures, there providing a “skeletal network of reinforcement to improve composite toughness and help prevent cracking or crack propagation” (paragraph [0134]). However, these shapes are difficult to form in that they require bonding of individual wires to form the three dimensional structures or loops. In addition, the shapes lack sufficient structure to improve the compressive strength of the concrete material to which they are added.
Yet another example of spherical inclusions is described in the publication by Guomundur Bjornson entitled “BubbleDeck Two-Way Hollow Deck” (www.bubbledeck.com, September 2003), which involved placement of tightly pack hollow spheres or balls between two layers of concrete reinforcement mesh. While displacing concrete materials and thereby lowering cost, and also achieving a degree of isotropy, the hollow balls used in the bubble deck do not provide any added strength.
An alternative approach is taken in U.S. Pat. No. 5,145,285, which discloses molded high density polypropylene concrete or soil inclusions made of arms or spokes extending from a central hub, and formed with polyhedral structures at the ends of the arms. The overall shapes of the inclusions are similar to those of a children's “jacks” game. These complex shapes are difficult to manufacture, and lack the interlockability and compressibility of structures with a generally polyhedral shape.
The present invention also provides three-dimensional interlocking inclusions, but offers several advantages over the inclusions described in U.S. Patent Publication No. 2011/0101266 and U.S. Pat. Nos. 5,404,688, 5,145,285, 3,913,295, and 3,616,589. Like the inclusions of U.S. Pat. No. 5,145,285, and unlike those of the other cited publications, the inclusions may be made of an inexpensive plastic material and yet are adapted for simple molding procedures that do not require insertion rods or multiple molding steps. Second, even though the inclusions have generally polyhedral shapes and openings or voids that allow interlocking, as with U.S. Patent Publication No. 2011/0101266 and, for example, U.S. Pat. No. 3,913,295 (and that can enclose sections of the cement or other material poured around, and leave space for venting excess steam to prevent explosions during curing), they also include axial or internal structures that add rigidity, while still permitting a degree of compression, so as to increase the compressive strength of the resulting concrete. This can be especially useful in creating inexpensive earthquake or tornado-proof concrete structures. Third, the inclusions can be formed with additional structures such as hooks or knobs to enhance the interlocking effect, without substantially increasing cost. Fourth, in an alternative embodiment, the inclusions can be made of wire coils that, when subject to a pulling force, tighten to increase resistance to ejection from the concrete material when subject to an explosion or extremely high force.
Additional three-dimensional or fiber inclusions are disclosed in U.S. Patent Publication Nos. 2010/0065491; 2009/0169885; 2008/0145580; 2006/0106191; and 2004/0217505, and U.S. Pat. Nos. 7,749,352; 6,706,380; 6,054,086; 6,045,911; 5,981,650; 5,419,965; 5,145,285; 4,628,001; 4,610,926; 4,585,487; 3,913,295; 3,846,085; 3,616,589; 3,400,507; 2,677,955; 1,913,707; 1,976,832; 1,594,402; and 1,349,901. Of these, U.S. Pat. No. 2,677,955 is of particular interest for its disclosure of fiber inclusions that are formed into single loops. The present invention includes inclusions made of multiple loops.
Byway of further background, U.S. Pat. No. 5,556,229 discloses the use of spherical inclusion-like structures for shoreline erosion control, while U.S. Patent Publication discloses the use of interlocking structures for “rubble mound structures” such as breakwaters. The present invention also has applicability to shoreline erosion prevention and rubble mound like structures.
It is accordingly a first objective of the invention to solve one or more of the above-described problems and disadvantages of conventional UHPC and other inclusion-containing materials such as, by way of example and not limitation, conventional concrete and resin or fiberglass materials.
It is a second objective of the invention to provide a UHPC material having a reduced cost.
It is a third objective of the invention to provide an improved method of casting structures made of UHPC and other concrete materials.
It is a fourth objective of the invention to provide UHPC and concrete materials, as well as other inclusion-containing materials, having improved structural integrity.
It is a fifth objective of the invention to provide low cost inclusions for UHPC and other inclusion-containing materials, as well as for reducing soil or shoreline erosion and similar applications.
It is a sixth objective of the invention to provide inclusions that increase the strength of UHPC or other inclusion-containing materials, either isotropically or anisotropically.
It is a seventh objective of the invention to provide UHPC or concrete structures, or structures made of other inclusion-containing materials, having increased resistance to damage from impacts, explosions, earthquakes, tornados, and other external forces.
It is an eighth objective of the invention to provide a UHPC or other concrete material that offers improved safety during pouring and/or curing.
These objectives of the invention are achieved, according to a preferred embodiment of the invention, by providing a concrete casting method that replaces the conventional use of steam for thermal treatment with vacuum curing, for example by placing a bag over the poured concrete and applying a vacuum to the bag. The use of vacuum curing greatly simplifies casting processes that would otherwise require heat treatment, such as UHPC casting processes, by rapidly drawing moisture out of the concrete while minimizing the risk of explosion due to steam trapped in the concrete. When inclusions of the type described herein are used, the open structure of the inclusions allows moisture to pass, expediting the curing process and decreasing the risk of problems caused by pressure build-up from trapped steam, although the vacuum curing method of the invention may also advantageously be applied to UHPC and other concrete materials that utilize inclusions other than those specifically described herein.
According to the principles of various preferred embodiments of the invention, conventional fiber inclusions are replaced by inclusions in the form of three dimensional structures having a generally polyhedral shape formed by an annular or disc-shaped central structure that defines a parting plane for an injection mold, and various structures extending transversely to the central annular or disc-shaped structure to form the generally polyhedral shape. Alternatively, the inclusions may be formed by a hub and radial structures, from which extend circumferential structures that define the polyhedral shape. Other preferred inclusion structures take the form of wires or tubes with multiple coils. Preferably, the inclusions are designed to be molded in simple two part molds without the need for movable rods or pins to form, but the invention also encompasses inclusions that require use of rods or pins, or other additional forming steps.
In addition to the basic structures described above, the inclusions of the preferred embodiments may have one or more the following features or advantages:
In the embodiments where the generally polyhedral inclusions have an annular structure or central disc, the annular structure or central disc may include a plurality of cut-outs, with the transversely extending structures being in the form of one or more semicircular plates or walls. The transversely extending plates or walls may be parallel, perpendicular, or oriented at any angle therebetween, and may also include cutouts or openings to reduce materials costs and permit venting of steam or passage of cement material past the inclusions. The inclusions may optionally further include outwardly extending pins that improve interlocking of the inclusions when packed together, and/or notches or openings for aligning the inclusions with respect to a mesh or similar reinforcing structure.
In the embodiments where the generally polyhedral inclusions are made up of a plurality of radial extensions from a central hub or intersection of the extensions, and circumferential structures, the circumferential structures may be arranged to form claw or hook like features that are especially advantages in applications involving soil or sand, the claw or hook like features serving as anchors as well as to provide secure interlocking of the inclusions.
Alternatively, the inclusions may include multiple disc structures rather than just a central disc, as well as asymmetric rather than symmetric sets of cutouts, and numerous other variations. In addition, the inclusions may be combined with or replaced by the coiled wire inclusion structures, as well as with reinforcing mesh layers, insulating layers, and other structural features.
The inclusions of the preferred embodiments may be made of polypropylene or a similar relatively inexpensive easily molded plastic material, although the invention is not limited to a particular material and the inclusions may also be made of metal or even concrete. In addition, the sizes of the inclusions can range from nanoscale to several feet, depending on the application.
In the case of multiple loop inclusions, the wires formed into the multiple loops may be made of basalt fibers, and/or the wires may include a core around which the wires are wrapped. If the core is made of plastic, the plastic can be arranged to burn away during a fire, leaving voids into which steam can enter to prevent the concrete from spalling, and the plastic can be partially melted into the surrounding steel or basalt fibers to hold the loop shapes.
The inclusions of the preferred embodiments are especially advantageous when used to reinforce structures such as armor for military applications and earthquake or tornado proof structures. Because the inclusions are inexpensive to manufacture, the add little to the cost of the structures, yet can result in substantially increased structural integrity.
FIGS. 26 and 27A-27C are side views of inclusions made up of wires formed into multiple loops.
The present invention involves both an improved method of making ultra high performance concrete (UHPC) structures, and inclusions suitable for use in UHPC structures. Although disclosed in the specific context of UHPC, the method of the invention, which involves vacuum curing, is applicable to concrete structures other than those that utilize UHPC, while the inclusions of the preferred embodiments may be used in application other than those involving UHPC or concrete. In addition, the method of the invention may be applied to concrete structures that utilize inclusions other than those of the invention, while the preferred inclusions may be included in concrete structures formed and cured by conventional forming and curing methods. Initially, an especially preferred embodiment of an inclusion will be described, followed by a description of the concrete structure forming method of the invention, and descriptions of additional preferred inclusions and structures utilizing the preferred inclusions.
Extending from a first side of the central disc is a pair of parallel semicircular plates or walls 103,104 and a transversely extending semicircular plate or wall 105. Extending from a second side of the central disc 101 is a pair of parallel semicircular plates or walls 106,107 and a transversely extending semicircular plate or wall 108. The pair of walls 103,104 on one side of the central disc 101 are transverse to the pair of walls 106,107 on the opposite side of the central disc 101 and the single transverse wall 105 on the first side is transverse to the single transverse wall 108 on the second side. Because walls 103,104,106,107 extend along chords rather than across an entire diameter of the central disc 100, it will be appreciated that they have a smaller area than the corresponding walls 105,108, with the result that the profile of the inclusion is slightly asymmetric, as can best be seen in
The inclusions of
In applications involving UHPC or other concrete materials, the inclusions may be added while the concrete is in a concrete mixer, before pouring into the mold. However, it is especially advantageous to pour the balls into the mold first and then pour the concrete into the mold to fill up the voids between the balls and mold walls that seal the mold, after which a vacuum may be applied to the mold to remove air bubbles and rapid cure the concrete. Filling the balls into the mold first allows the balls to compress against each other forming a uniform three-dimensional matrix that strengthens its compression and torsion strengths when the concrete is added last. The weight of the poured or pumped concrete will add a compressive pre-load to the balls to force them to nest tighter against each other during the filling.
The use of a vacuum to cure the UHPC material and remove air from the mold has advantages apart from the advantages of the inclusions described herein, and may be applied to UHPC materials even when conventional inclusions, such as metal fibers, are used. There are a variety of ways of achieving the vacuum. For example, the mold can be provided with a seal and a check valve to maintain the vacuum, or a hermetically or gasket sealed bag with a check valve can be placed over the mold. In addition, use of the vacuum can be combined with conventional steam curing to reduce the amount of steam required, and the vacuum mold can be employed as part of a metal, wooden, fiberglass, or composite tooling. Still further, even if the concrete is cured by conventional steam curing, the use of the preferred inclusions has the advantage that, as the inclusions shrink under the applied heat, additional voids will be formed to accommodate excess steam, allow steam to exhaust pressure, and prevent heat exploding spalling concrete.
As with the inclusion structures of
Still further strength, suitable for heavy load and earthquake proofing applications, may be achieved by providing the inclusions with both cut-outs 66 for the wire mesh layers 50,51 and openings 67 for additional strengthening rebarb pins 68, as shown in
The inclusion of
The inclusion 1010′ of
Inclusions with claw-like structures such as inclusion 1, and to a degree inclusion 1023 of
In the inclusion 1 of
As with the inclusions of
When used in soil retention applications, the inclusions of
While the inclusion structures described above are especially preferred, numerous variations of the above structures are possible. For example,
Yet another alternative inclusion structure is illustrated in
In addition to the above-described three-dimensional inclusions, it is possible to include other types of inclusions in a UHPC or other concrete material. FIGS. 26 and 27A-27C show novel inclusions 200-203 made of wire formed into multiple loops. These inclusions may be used in connection with, or instead of, the three-dimensional inclusions of the above-described embodiments, and are not limited to use in UHPC or vacuum-cured concrete materials.
In the inclusion of
The wire inclusions 200-203 of FIGS. 26 and 27A-27C may be made of solid wires. However, additional advantages are obtained if the inclusions are made of tubes. In that case, the tubes serve to vent excess steam that can result when the concrete material is subject to heat, thereby relieving pressure that would otherwise result in cracking or explosion of the concrete material in which the inclusions are situated. In addition, as shown in
In additional to conventional metal wires, for example made from low carbon or stainless steel, the inclusions 200-203 of FIGS. 26 and 27A-27C may advantageously be made of basalt fibers. The basalt fibers may, in the configuration illustrated in
The example where layers 211 and 212 are UHPC layers and layer 213 is an insulating layer is especially useful for earthquake or tornado proof structures. Because of the greatly increased strength of the inclusion-containing UHPC or concrete layers, and the relatively low cost of the inclusions, the resulting structure can provide insulated, earthquake or tornado resistant housing structures that cost little more than conventional concrete housing structures. While such structures would be subject to cracking during an earthquake or tornado, the interlocking inclusions would prevent the structure from complete failure or collapse, and thus prevent the massive loss of like that occurred during, for example, the Haiti earthquake of 2010. As an alternative to the sandwiched-insulation layer structure of
On the other hand, the structure shown in
An alternative structure that utilizes the inclusions of the invention is shown in
Having thus described preferred embodiments of the invention in sufficient detail to enable those skilled in the art to make and use the invention, it will nevertheless be appreciated that numerous variations and modifications of the illustrated embodiment may be made without departing from the spirit of the invention. Accordingly, it is intended that the invention not be limited by the above description or accompanying drawings, but that it be defined solely in accordance with the appended claims.
