Pultruded GFRP Reinforcing Bars, Dowels and Profiles with Carbon Nanotubes

Abstract

A glass fiber reinforced polymer reinforcing structure comprised of glass fibers mixed with one or more polymers. Incorporated in the polymer are a hybrid mix of pristine multi-walled carbon nanotubes at 0.0-4.0 wt. % of the polymer and multi-walled carbon nanotubes functionalized with carboxylic group at 0.0-2.0 wt. % of the polymer. The above mixture is pultruded to produce GFRP reinforcing bars, dowels or structural profiles.

Claims

1. A broom resistant glass fiber reinforced polymer reinforcing structure comprising: an elongated structure; said structure comprised of glass fibers mixed with one or more polymers; a plurality of pristine multi-walled carbon nanotubes at 0.0-4.0 wt. % of said polymer are incorporated in said polymer; and multi-walled carbon nanotubes functionalized with carboxylic group at 0.0-2.0 wt. % of said polymer are incorporated in said polymer.

2. The broom resistant glass fiber reinforced polymer reinforcing structure of claim 1 wherein said polymer is an ester (vinyl ester, poly ester or other ester type of polymers).

3. The broom resistant glass fiber reinforced polymer reinforcing structure of claim 1 wherein said elongated structure is made by pultrusion.

4. The broom resistant glass fiber reinforced polymer reinforcing structure of claim 3 wherein said elongated structure is a reinforcing bar.

5. The broom resistant glass fiber reinforced polymer reinforcing structure of claim 3 wherein said elongated structure is a reinforcing dowel, plates, angles, and I-beams.

6. A broom resistant GFRP reinforcing bar for concrete structures comprising: glass fibers mixed with one or more polymers; a plurality of/hybrid mix of pristine multi-walled carbon nanotubes at 0.0-4.0 wt. % of said polymer are incorporated in said polymer; and multi-walled carbon nanotubes functionalized with carboxylic group at 0.0-2.0 wt. % of said polymer are incorporated in said polymer.

7. The broom resistant GFRP reinforcing bar of claim 6 wherein said polymer is vinyl ester, poly ester or other types of polymers.

8. A reinforced concrete structure comprising: a plurality of broom resistant GFRP reinforcing bars embedded in the concrete structure; and said broom resistant GFRP reinforcing bars, dowels or profiles comprising: glass fibers mixed with one or more polymers; a plurality of hybrid mix of pristine multi-walled carbon nanotubes at 0.0-4.0 wt. % of said polymer are incorporated in said polymer; and multi-walled carbon nanotubes functionalized with carboxylic group at 0.0-2.0 wt. % of said polymer are incorporated in said polymer.

9. The reinforced concrete structure of claim 8 wherein said polymer is vinyl ester, poly ester or other type polymers.

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Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] In the drawings, which are not necessarily drawn to scale, like numerals may describe substantially similar components throughout the several views. Like numerals having different letter suffixes may represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, a detailed description of certain embodiments discussed in the present document.

[0017] FIG. 1: Test setup; (1A) Direct tension; (1B) Shear test of GFRP bars incorporating MWCNTs.

[0018] FIG. 2: Stress-strain behavior of GFRP bars Neat and with MWCNTs under uniaxial tension.

[0019] FIGS. 3A, 3B and 3C: Tension failure modes for GFRP bars with MWCNTs.

[0020] FIG. 4: Short beam shear strength for GFRP bars incorporating MWCNTs.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed method, structure or system. Further, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention.

[0022] In one embodiment, the present invention concerns GFRP reinforcing structures including, but not limited to, elongated structures such as bars and dowels. In one preferred embodiment, the GFRP structures may be made from pultruded glass fiber spools.

[0023] An ester-based resin (vinyl ester or polyester) with Methyl Ethyl Ketone Peroxide may be used as the curing agent in the polymeric matrix in fabricating the GFRP pultruded structures. P-MWCNTs and/or COOH-MWCNTs or a mixture of them may also be used. The MWCNTs preferably have an inner diameter of 5-10 nm and outer diameter of 20-30 nm with bulk density of 0.21 gm/cm.sup.3 and 110 m.sup.2/g specific surface area. For dispersing MWCNTs in the ester resin, ultrasonication at 40 C. for 60 min followed by mechanical stirring at 800 rpm for 120 min at 80 C. may be used. After the MWCNTs-ester nanocomposite cools to room temperature, it may then be pultruded into GFRP reinforcing elongated structures such as dowels, bars or profiles.

[0024] For the pultrusion process of the embodiment concerning a GFRP bar, a circular die with hole(s) with heating plates may be used to maintain a constant temperature inside the die to cure the GFRP. Other diameters and or shapes (profiles) might be produced using pultrusion technology. A constant pull speed is used with a speed-controlled gear motor. Post-fabrication, the GFRP bars/dowels are cured at 130 C. for 2 hrs (or other temperatures and time periods) to ensure complete polymerization of the polymer matrix. GFRP bars with constant fiber volume fraction (about 55%) with three example hybrid MWCNTs concentrations were fabricated as example. The bars were mechanically tested for each type under uniaxial tension following ASTM D7205/D7205M and 5 bars for each type under longitudinal shear test using short beam bend test following ASTM D4475 [10,11]. FIG. 1(a) and FIG. 1(b) presents the experimental protocol for tensile and short beam shear test for bar 100. The data for the two tests was acquired at 10 Hz interval. Fiber volume fraction of the GFRP bars with and without MWCNTs was determined using ASTM-D3171. In other aspects, a plurality of pristine multi-walled carbon nanotubes at 0.0-4.0 wt. % of the polymer, and multi-walled carbon nanotubes functionalized with carboxylic group at 0.0-2.0 wt. % of the polymer may be used to create a matrix.

[0025] The fiber volume fractions of the GFRP for Neat, hybrid mix 1 MWCNTs and hybrid mix 2 MWCNTs GFRP bars were 61.2%, 59.3% and 60.4% respectively. The results of the direct tension tests are presented in Table. 1. The stress-strain behavior of GFRP with and without MWCNTs is shown in FIG. 2. Tension test results indicate that an improvement in tensile strength by 20% was achieved compared with neat GFRP bars when functionalized COOH-MWCNTs were used. This improvement was proven to be statically significant with 95% confidence level using student t-test.

TABLE-US-00001 TABLE 1 Test results Tensile Tensile Shear Sample Strength Modulus Strength description MPa GPa MPa NEAT GFRP 694 45.4 24.6 71 0.29 1.0 GFRP with 832 45.5 49.6 MWCNTs Hybrid 42 1.66 2.4 Mix 1 GFRP with 708 46.8 37.8 MWCNTs Hybrid 18 0.28 2.1 Mix 2

[0026] The stress-strain behavior of GFRP with MWCNTs showed a linear elastic behavior to failure with similar slopes for all the GFRP samples with and without MWCNTs. The strain at failure was higher for the samples with hybrid mix 1 MWCNTs as shown in FIG. 2. This increase in the strain at failure can be attributed to the improved interfacial bond between the silane sizing on the glass fibers and the COOH functionalization on the MWCNTs. However, GFRP incorporating hybrid mix 2 MWCNTs showed a negligible improvement in tensile strength and strain compared with neat GFRP. This negligible improvement might be attributed to the absence of functional groups in hybrid mix 2 to interfere with the polymerization and to improve the bond with glass fibers. Moreover, GFRP bars with hybrid mix 2 showed a similar stress-strain behavior to that of neat GFRP. More interestingly, the modes of failure in tension of GFRP bars incorporating MWCNTs are presented in FIG. 3. Unexpectedly, GFRP bar 350 with hybrid mix 1 MWCNTs showed almost no broom failure. This is the result of the ability of COOH-MWCNTs to improve the interfacial bond between glass fibers and ester matrix. This results in an increased tensile strength and prevents the typical broom effect that follows fibers debonding from the matrix. GFRP bar 310 incorporating hybrid mix 2 MWCNTs showed limited improvement in broom failure.

[0027] The short beam shear strength results are presented in Table 1. A significant improvement in shear strength by 111% and 53% was observed for GFRP incorporating hybrid mix 1 MWCNTs and hybrid mix 2 MWCNT respectively compared with neat GFRP. The results are summarized in a bar chart shown in FIG. 4. The shear strength improvements of GFRP bars with MWCNTs compared with neat GFRP were proved to be statistically significant with 95% confidence level using student t-test. As the shear strength of the GFRP is matrix dominant behavior, it is obvious that both P-MWCNTs and COOH-MWCNTs and their combinations can significantly improve the shear strength of GFRP bars, dowels and profiles. The improvement using COOH-MWCNTs can be explained by the chemical reaction of COOH-MWCNTs and the ester matrix.

[0028] The addition of P-MWCNTs improves the shear strength of GFRP bars. The high content of P-MWCNTs (0.0-4.0 wt. %) as part of the hybrid mix used in producing GFRP bars enables the P-MWCNTs to act as microscale reinforcement in the ester matrix and thus enables improved transfer of shear stresses within GFRP composite bar.

[0029] The above results indicate that using low concentration of COOH-MWCNTs as part of the hybrid mix well-dispersed in the ester matrix before pultrusion of GFRP bar 350, as opposed to a higher concentration, can produce the unexpected result of significantly improving the tensile strength by 20% and shear strength by 111%. This high improvement in shear strength of GFRP can have significant economic benefits in the design of GFRP bars and dowels widely used in bridge decks and slabs on grades. Economic analysis of the above addition showed the use of MWCNTs could result in increasing GFRP cost by 10-15%. This is a very limited cost increase compared to the significant improvement in shear strength above 100% of neat GFRP bars.

[0030] While the foregoing written description enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The disclosure should therefore not be limited by the above-described embodiments, methods, and examples, but by all embodiments and methods within the scope and spirit of the disclosure.