Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2001-06-26
2004-08-24
Colaianni, Michael (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S171230, C264S172150, C264S173190, C264S174100, C366S002000, C366S006000
Reexamination Certificate
active
06780367
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to plastic fibers for toughening concrete and the concrete containing the fibers.
BACKGROUND OF THE INVENTION
Generally, concrete is a brittle material with high compressive strength but low tensile strength. In the concrete industry, all concrete work is, typically, specified on the basis of the compressive strength. Any attempt to improve the crack strength (tensile strength) and toughness of the concrete almost always requires the introduction of reinforcing addition. For example, rebar (steel rods) is added which provide structural integrity but does not eliminate cracking. Metal mesh has also been added to reduce cracking but it cannot be used effectively to reinforce concrete of complex geometry.
Plastic fibers have also been used to improve the tensile strength and toughness (resistance to cracking). However, the addition of synthetic polymer fibers almost always causes a reduction in the compressive strength. In addition, when plastic fibers are used they tend to only improve either the tensile strength (strength before the first crack appears) or the toughness (resistance to cracking), but not both at the same time.
Examples of plastic fibers include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), aramids (e.g., KEVLAR) and polyvinyl alcohol fibers. However, all of these fibers suffer from one or more problems, such as high cost, low alkaline resistance, low tenacity or low interfacial bonding between the concrete and the fiber.
Polypropylene and polyethylene have been the most preferred fiber to date due to their high tenacity and low cost. Unfortunately, these fibers suffer from very low interfacial bonding. To remedy this problem, coatings have been formed on the surface of the fibers by applying a liquid, such as glycerol ether or glycol ether on the fiber surface, as described by WO 980766. Coatings have also been applied by vapor deposition, such as described by JP 60054950. Similarly, chemically modifying the surface has been done, such as described by JP 10236855 (treatment of the surface of a polyoxyalkylenephenyl ether phosphate and polyoxalkyl fatty acid ester). Unfortunately, these methods naturally lead to increased cost, complexity and potentially insufficient bonding of the coating to the fiber.
Another remedy has been the incorporation of inorganic particles in and on the fiber, such as described by JP 07002554. Unfortunately, the fiber process becomes much more difficult (e.g., fiber breakage) and increases the cost and, generally, decreases the tenacity of the fiber.
Further, it is known that larger fibers are preferable for improving the toughness of the concrete. Unfortunately, larger fibers further exacerbate the problem of bonding with the concrete matrix because of reduced surface area. In addition, none of these methods address another problem associated with plastic fibers in concrete, which is the tendency of larger fibers to clump together into balls that are difficult to break up when added to concrete resulting in reduced properties of the concrete.
U.S. Pat. No. 5,993,537 and WO 99/46214 describe uncontrolled fibrillation of large fibers in concrete. They describe the desirability of fibrillating large fibers into many smaller fibers and partially fibrillated fibers. They both describe that fibrillation desirably should be so great that the surface area of the fibers increase 50 fold or more. However, this extreme amount of fibrillation may lead to problems with workability, slumping, mixing and lessen desirable toughness enhancement of larger fibers.
Accordingly, it would be desirable to provide an improved fiber for improving the properties of concrete, for example, that solves one or more of the problems of the prior art, such as improving the toughness without increasing the cost of concrete when using inexpensive polypropylene fibers, while at the same time not create other problems, such as slumping and reduced workability.
SUMMARY OF THE INVENTION
We have now discovered a new polymeric fiber that has improved bonding with concrete that results in concrete that has improved properties, lower cost or both, compared to other reinforced concrete, which is achieved by a fiber that has controlled fibrillation.
A first aspect of the invention is a reinforcing fiber comprised of at least two filaments bonded together and the filaments being comprised of a polymeric core, at least partially enveloped by a polymeric sheath comprised of a fusing-fraying polymer that has a lower melting temperature than the polymer core, such that the reinforcing fiber, when mixed with inorganic particulates, frays predominately only at an end or ends of the fiber.
The reinforcing fiber is comprised of at least two filaments that are bonded together, such that upon mixing with inorganic particles, the filaments predominately fray at the ends of the fibers (i.e., frays or fibrillates at the ends) under typical mixing conditions, for example, of concrete. This controlled fraying of the fiber overcomes the problem of inadequate bonding of large diameter fibers by giving greater surface area to anchor to at the ends, while not causing a deleterious rise in viscosity when fibers completely fibrillate.
Herein, predominately fraying at the end or ends means that under typical mixing conditions encountered when making inorganic cured articles, such as concrete, a majority of the fibers present in the article after curing have not separated into two or more fibers. This is analagous to the fraying of a rope without the rope splitting into two smaller ropes.
A second aspect of the invention is a concrete article comprised of concrete having therein a reinforcing fiber where at least about 50 percent by number of the reinforcing fibers are frayed only at an end or ends of the reinforcing fibers.
A third aspect of the invention is a method of preparing concrete comprised of mixing concrete, water and a reinforcing fiber for a sufficient time to fray the ends of at least about 50 percent of the fibers and curing the mixture to form the concrete article. Generally, this amount of fraying results in an increase of surface area of at least about 2 times to generally at most about 10 times, preferably at most about 5 times and more preferably at most about 3 times of the surface area of the original fiber.
A fourth aspect is a reinforcing fiber comprised of a polypropylene core polymer at least partially enveloped by a sheath comprised of a fusing/fraying polymer that has a lower melting temperature than the polypropylene core and is selected from the group consisting of low density polyethylene, maleic anhydride grafted low density polyethylene, ethylene-styrene copolymer or polyethylene having a melt index from about 5 to about 35 and a density from about 0.9 gram per cc to about 0.965 gram per cc, ethylene acrylic acid copolymer and combinations thereof.
The reinforcing fiber may be used in any low temperature cured inorganic article, such as concrete, mortar, gypsum, wall board and the like. The concrete of this invention may be used in any application suitable for concrete, but it is especially well-suited for parking garages, bridge decks, white toppings, tunnels, mining, slope stabilization, architectural purposes, such as landscaping stones, skate boarding rinks, modern architecture, art sculptures, fast setting
on-slumping ceilings, swimming pools and for repairing and retrofitting existing structures.
DETAILED DESCRIPTION OF THE INVENTION
The Reinforcing Fiber
The reinforcing fiber is comprised of at least two fused filaments comprised of a core polymer at least partially enveloped by a sheath comprised of a fusing-fraying polymer, such that the fiber, when mixed with inorganic particulates, frays predominately only at an end or ends of the fiber.
Fraying at an end or ends is when the fiber splits into at least two distinct frayed fibrils, where one end of these fibrils is completely detached from the fiber and the other end is still attached to the fiber. To reiterate, this is similar to a rope
Allen Sharon M.
Morgan Ted A.
Pyzik Aleksander J.
Reddy Hari
Stewart, Jr. Kenneth B.
Colaianni Michael
Dow Global Technologies Inc.
Poe Michael I.
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