The field of the invention is discrete macrosynthetic fibers for use in reinforcing concrete.
The macrosynthetic fiber, the invention disclosed herein, comprises a blend of polypropylene and polyethylene resins, or can comprise one or the other of these materials. As used herein, “macrosynthetic fiber” is a fiber having a linear density equal to or greater than 580 deniers and a diameter equal to or greater than three millimeters (3 mm). In a preferred embodiment of the fiber, it is 1800 deniers with an approximate range of +/−30%. ASTM standard D7508 is hereby incorporated by reference. The fiber is flexible compared to other fibers, as can be demonstrated in testing of the individual fiber's modulus of elasticity. The flexibility of the fiber, along with its other properties and configuration, aid in the workability of the fiber into the concrete in a uniform manner, adding to the strength of the hardened concrete.
The present invention embodies a number of unique configurations to maximize surface area to enhance mechanical bonding of the fiber to hardened concrete. The cross-section of one embodiment of the invention comprises a “U-shape” as shown, for example, in
An embodiment of the invention as shown in
The invention shown, for example, in embodiments 1A-1C, 3, 5, 6, 7, 7A is a macrosynthetic fiber comprising a cross-section comprising a U-shape, wherein the walls 5, 6 extend only to one side of the central panel 2, said cross-section comprising a central panel 2 comprising two borders C, D (depicted in
The invention in another embodiment is a macrosynthetic fiber in cross-section comprising an H-shape as in
In Fiber Reinforced Concrete the present invention fills a void created by itself in the properly consolidated fresh/plastic concrete. When the concrete hardens, there is a mechanical bond created between the hardened concrete and the invention. If a fiber intercepts a crack, there is a stress applied to the fiber, and the fiber then can break or it can de-bond thereby losing its bond to the concrete. If de-bonding occurs, the fiber will stretch/decrease in cross-section and vacate the volume it occupies in the hardened concrete. The fiber pulls out of the concrete on one side of the crack while remaining anchored to some degree on the other side of the crack. Since there is typically an uneven length of the fiber on either side of the crack, the side with the longest “bond length” will control. Bond length is a percentage of the overall length of the fiber that occupies one side of the crack or the other. Thus, by way of example only, if there is a 1″ long fiber and ¾″ is on one side of the crack and ¼″ o the other, then the ¾″ long fiber with a bond length of ⅝″ would control.
The embodiment of the present invention fiber for which data is presented herein comprises a blend of polyethylene and polypropylene extruded in a single from a die opening. In the “U” shaped embodiment of the present invention comprising walls comprising cylinders, the overall width of the die opening from one side to another is approximately 0.200 inches (5.0 mm). In the die opening in one embodiment, the thickness of the die opening at the central panel (between planes B and E) is approximately 0.0200 inches (0.50 mm), the diameter of the die opening for the circles is approximately 0.0530 inches (1.235 mm), the radius of the die at the intersection of the central panel and the bottom plane of the central panel are approximately 0.0040 inches (0.1 mm). The distance between the centers of the circles in the die opening is 0.1470 (3.675 mm) in one embodiment. From the die opening with the dimensions listed above, after being drawn in a water bath and stretched in an oven, final dimensions for one embodiment of the fiber cross-section is approximately 0.040 inch (1.0 mm) wide from the farthest extending points on each circle and approximately 0.013 inches (0.325 mm) thick at the central panel. All of these values are exemplary and may be varied from embodiment to embodiment.
After extrusion from a die, the fiber cross-section dimensions are reduced from the dimensions of the die opening as the polymer is drawn into a water bath and also when it is stretched in an oven. After extrusion, the extruded fiber is cut into discrete fibers 1 whose preferred length in one embodiment is within a range of approximately 1.0-3.0 inches (25 mm-75 mm), and in one embodiment, approximately 1.5 inches (38 mm). A portion of a single fiber is depicted in
The fiber 1 in one embodiment shown in
In
As shown in the scoring tool 23, or texturizer, in
In another embodiment of the fiber, as shown in
As shown generally in
The invention has demonstrated unexpected results in testing to evaluate its performance at dosages of 3.00, 5.00, 7.00 & 10.0 pounds per cubic yard of concrete (hereinafter “PCY”) in a typical slab concrete mix with a compressive strength of 4,000-5,000 psi at an age of 7 days. The concrete was batched and mixed in accordance with ASTM C192-15 Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory, which standard is incorporated herein in its entirety. The fibers were added at the beginning of the batch sequence and mixed with the rock and sand for 1 minute prior to the addition of the cementitious material. The concrete was then mixed for 3 minutes, allowed to rest for 3 minutes, and mixed for 2 additional minutes. Plastic properties were then determined and recorded in accordance with the applicable standards. Three 6″×6″×20″ beams were cast for testing in accordance with ASTM C1609/C1609M-12 Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading), which standard is also incorporated herein in its entirety. Three 6″×12″ cylinders were also cast for compressive strength determination. Mix proportions, plastic, and hardened properties are reported in Table 1:
Concrete comprises a mixture of sand and larger crushed rock in various sizes. The concrete mix used to evaluate the performance of the present invention consisted of cement, coarse aggregate, natural sand and water without admixtures or additives. The coarse aggregate was a size #57 (max top size 1.5″) and the sand was a concrete sand (⅜″ to zero). The cement was a Portland cement Type I and the water was potable. The proportions of the mix and the cement content were typical for a 4,000 psi compressive strength target at 28 days. Additional details about the mix are set forth in Table 1. The present invention's improvement in performance of the mix identified, however, is not limited to the mix in Table 1, but it will perform in a similar fashion for other types of mix as well, including those containing admixtures and additives.
Casting of the beam specimens was performed by discharging the concrete directly from the wheel barrow into the mold and filling to a height of approximately 1-2 inches above the rim. The 6″×12″ cylinder molds were filled using a scoop to a height of approximately 1-2 inches above the rim of the mold. Both the beam and cylinder specimens were then consolidated by means of an external vibrating table at a frequency of 60 Hz. The consolidation was determined to be adequate once the mortar contacted all of the interior edges, as well as the corners of the mold, and no voids greater than ⅛″ diameter were observed. Care was taken to ensure that all specimens were vibrated for the same duration of time and in concurrent sets. The specimens were then finished with an aluminum trowel and moved to a level surface. Specimens were covered with wet burlap and plastic in a manner as to not disturb the surface finish and prevent moisture loss. After curing in the mold for 24 hours the hardened specimens were removed from the molds and placed in a saturated lime bath at 73±3.5° F. until the time of testing.
Three beams specimens were tested per ASTMC 1609 at an 18″ span length using roller supports meeting the requirements of ASTM C1812-15 Standard Practice for Design of Journal Bearing Supports to be Used in Fiber Reinforced Concrete Beam Tests, which standard is hereby incorporated herein in its entirety. The test machine used was a Satec-Model 5590-HVL closed-loop, dynamic servo-hydraulic, testing machine conforming to the requirements of ASTM E4-14 Standard Practices for Force Verification of Testing Machines, which standard is hereby incorporated herein in its entirety. Load and deflection data were collected electronically at a frequency of 5 Hertz. The load was applied perpendicular to the molded surfaces after the edges were ground with a rubbing stone. Net deflection values, for both data acquisition and rate control, were obtained at the mid-span and mid-height of the beams. The rate of loading was held constant at 0.002 in/min of average net deflection for the entire duration of each test.
The testing uses third point loading, the two rockers in contact with the top side of the beam apply the load. The crack will appear at the mid-span of the beam. In this test closed-loop loading was employed. Instead of loading the beam at a constant rate per time increment, the beam was loaded based on the deflection of the beam. The point of L/600 first was reached and then L/150 thereafter. Measurements of deflection were made from the harness at the mid height of the beam. The standard beam is 6″×6″×20″ and the clear span length (between the rockers in contact with the bottom of the beam) was 18″. Tests were conducted at 7 days after casting.
In testing there was an unexpected beneficial anomaly found in the ASTM C1609 data. The load carrying results at the L/150 deflection were higher than the results for the lower deflection data at L/600. In the part of the program where the invention was compared to prior art products at 5.0 pcy, only the invention showed an increase in load carrying capability at the higher deflection, L/150. A summary of test results for the present invention fiber at doses of 3.0, 5.0, 7.0 and 10.0 pounds per cubic yard (pcy) are set forth in Table 2:
Table 2 contains averages of results for each dose of the present invention fiber, and all the data for each dose is shown in Tables 3-6 below:
The fibers of the present invention continued to hold their original shape and did not de-bond from the hardened concrete. Thus, the unique configuration of the invention provides superior performance when compared to prior art products utilizing a consensus standard test method, ASTM C1609.
In the C1609 graphs presented and discussed herein for the present invention fibers, the peak load at the point of first crack of the beam was around 7,250 lbf. The load carried by the fibers after first crack was in the neighborhood of 1,750 lbf for 3 pcy and 2,250 lbs for 5 pcy. For the Re3 numbers in Table 2 the basic residual strength was 17.5% for 3.0 pcy and 30.1% for 5.0 pcy. These numbers show the quantity, in percentages the fibers are capable of supporting in respect to the first-crack load of the beam.
The dosage level of the macrosynthetic fibers has a direct bearing on the data generated. Round robin testing conducted by ASTM Subcommitee Co9.42 has determined that the accuracy of the test decreases as the quantity of fiber decreases. As the dosage rate decreases the standard deviation and CoV (Coefficient of Variation) increase. Thus the validity of the test is compromised when the dosage level of fiber in the beams is below 3 pcy. Thus 3 pcy is the borderline for obtaining accurate test data. As the dosage rate increases above 3 pcy the L/150 value of the present invention accelerates over the L/600 value. This measured increase is unexpected. As the load is continued to be applied the deflection of the beam increases.
Prior art fibers A-I have also been critiqued in tests similar to those described above for the present invention fibers. As a result of their unique configuration and properties, when the present invention fibers are mixed in concrete which is hardened, bonding of the fibers is increased, the modulus of elasticity is increased and the Poisson's Ratio is decreased compared to hardened concrete containing the prior art fibers. Support for this conclusion includes, without limitation, the data for ASTM standard C39 testing for compressive strength as shown in Table 7
With prior art fibers A-I, as the deflection of the beam increases more of the fibers become less effective by either de-bonding or breaking at the crack, as summarized in Tables 7 and 8, and as depicted in
Full test results for prior art fibers A-I (names and manufacturers recorded in the test report) are presented in Tables 9-17 below:
All industry standards referred to herein are incorporated by reference in their entireties.
This application is a continuation of International patent application number PCT/US2017/018968, filed Feb. 23, 2017 (pending). International patent application PCT/US2017/018968 claims priority to and the benefit of, U.S. provisional application No. 62/298,287 filed on Feb. 22, 2016 (expired). The foregoing applications are incorporated by reference in their entireties.
Number | Date | Country | |
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62298287 | Feb 2016 | US |
Number | Date | Country | |
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Parent | PCT/US17/18968 | Feb 2017 | US |
Child | 15684541 | US |