SYSTEMS AND METHODS FOR MAKING EMBEDDED FRP DETECTABLE BY NDT

Description

BACKGROUND

In recent decades, Fiber-reinforced polymers (FRP) composites have emerged as a promising solution in the field of civil engineering, thanks to their exceptional mechanical properties and chemical resistance. These composites have been adopted as an alternative to mitigate corrosion and to retrofit and strengthen deteriorated steel-reinforced concrete structures.

BRIEF SUMMARY

Embodiments of the subject invention provide novel and advantageous systems and methods for making fiber reinforced polymer (FRP) bars embedded in concrete detectable by conventional non-destructive testing (NDT) methods. A metallic and/or conductive presence can be introduced in FRP bars to make them detectible by NDT methods that use electromagnetic and stress waves for detection of steel bars. The FRP bars can be coated with a suspension of metal/conductive particles in a matrix (e.g., a resin), and this could be also combined with bond-enhancing coating of bars. Also, metal/conductive wire and/or metal/conductive strips can be wound over the FRP bars. The FRP bars having the metallic/conductive presence can then be embedded in concrete, and they are detectable with customary NDT methods and devices.

In an embodiment, an FRP bar configured to be embedded in concrete can comprise a metallic/conductive element that is disposed on the FRP bar, in the FRP bar, or both on and in the FRP bar. The metallic/conductive element can be present (on and/or in the FRP bar) in an amount sufficient such that the FRP bar is detectable by NDT (e.g., conventional NDT, such as ground penetrating radar (GPR), ultrasonic testing (UT) (including pulse array ultrasonic (PAU)), infrared thermography (IR), and impact echo (IE)) when the FRP bar is embedded in concrete. The metallic/conductive element can be a suspension of metal/conductive particles in a matrix (e.g., a resin) coated on the FRP bar. The FRP bar can further comprise a bond-enhancing coating in physical contact with the suspension and/or the FRP bar, the bond-enhancing coating being configured to strengthen a bond between the suspension and the FRP bar. The metal/conductive particles can comprise, for example, iron, galvanized steel, copper, and/or aluminum. For example, the metal/conductive particles can comprise iron or can be iron particles. The metallic/conductive element can comprise at least one metal/conductive wire wound around an outer surface of the FRP bar. Each metal/conductive wire can comprise, for example, iron, galvanized steel, copper, and/or aluminum. For example, each metal/conductive wire can comprise iron or be an iron wire. The FRP bar can be, for example, a glass FRP (GFRP) bar, a carbon FRP (CFRP) bar, or a basalt FRP (BFRP) bar.

In another embodiment, a support structure can comprise concrete and at least one FRP bar embedded in the concrete, where any or all of the FRP bars present in the concrete can be as described herein (e.g., having any of the features described in the previous paragraph). Each FRP bar can be, for example, a GFRP bar, a CFRP bar, or a BFRP bar.

In another embodiment, a method for making an FRP bar detectable by NDT (e.g., conventional NDT, such as GPR, UT (including PAU), IR, and IE) when the FRP bar is embedded in concrete can comprise: disposing a metallic/conductive element on the FRP bar, in the FRP bar, or both on and in the FRP bar. The metallic/conductive element can be disposed in an amount sufficient such that the FRP bar is detectable by the NDT when the FRP bar is embedded in concrete. The disposing of the metallic/conductive element can comprise coating the FRP bar with a suspension of metal/conductive particles in a matrix (e.g., a resin). The method can further comprise disposing a bond-enhancing coating on the FRP bar and in physical contact with the suspension and/or the FRP bar, the bond-enhancing coating being configured to strengthen a bond between the suspension and the FRP bar. The metal/conductive particles can comprise, for example, iron, galvanized steel, copper, and/or aluminum. For example, the metal/conductive particles can comprise iron or can be iron particles. The disposing of the metallic/conductive element can comprise winding at least one metal/conductive wire around an outer surface of the FRP bar. Each metal/conductive wire can comprise, for example, iron, galvanized steel, copper, and/or aluminum. For example, each metal/conductive wire can comprise iron or be an iron wire. The method can further comprise embedding the FRP bar in concrete after disposing the metallic/conductive element. The FRP bar can be, for example, a GFRP bar, a CFRP bar, or a BFRP bar.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a schematic image of an FRP bar.

FIG. 1B shows a schematic image of an FRP bar wound with metal/conductive wire.

FIG. 1C shows a schematic image of an FRP bar coated with metal/conductive particles.

FIG. 2A shows an image of an FRP bar.

FIG. 2B shows an image of the FRP bar modified with a coating of metal/conductive (iron) particles.

FIG. 2C shows an image of the FRP bar modified with a coating of metal/conductive (aluminum) particles.

FIG. 3A shows an image of an FRP bar.

FIG. 3B shows an image of the FRP bar modified with metal/conductive (iron) wire winding.

FIG. 3C shows an image of the FRP bar modified with metal/conductive (galvanized steel) wire winding.

FIG. 3D shows an image of the FRP bar modified with metal/conductive (copper) wire winding.

FIG. 3E shows an image of the FRP bar modified with metal/conductive (aluminum) wire winding.

FIG. 4A shows a cross-section view of bar embedded at shallow depth before modification.

FIG. 4B shows an image of phase array ultrasonic (PAU) test results for bar embedded at shallow depth before modification.

FIG. 4C shows a cross-section view of bar embedded at shallow depth with iron particle coating.

FIG. 4D shows an image of PAU test results for bar embedded at shallow depth with iron particle coating.

FIG. 4E shows a cross-section view of bar embedded at deeper depth before modification.

FIG. 4F shows an image of PAU test results for bar embedded at deeper depth before modification.

FIG. 4G shows a cross-section view of bar embedded at deeper depth with iron particle coating.

FIG. 4H shows an image of PAU test results for bar embedded at deeper depth with iron particle coating.

FIG. 5A shows a cross-section view of bar embedded at shallow depth before modification.

FIG. 5B shows an image of ground penetrating radar (GPR) test results for bar embedded at shallow depth before modification.

FIG. 5C shows a cross-section view of bar embedded at shallow depth with iron particle coating.

FIG. 5D shows an image of GPR test results for bar embedded at shallow depth with iron particle coating.

FIG. 5E shows a cross-section view of bar embedded at deeper depth before modification.

FIG. 5F shows an image of GPR test results for bar embedded at deeper depth before modification.

FIG. 5G shows a cross-section view of bar embedded at deeper depth with iron particle coating.

FIG. 5H shows an image of GPR test results for bar embedded at deeper depth with iron particle coating.

FIG. 6A shows a cross-section view of bar embedded at shallow depth before modification.

FIG. 6B shows an image of PAU test results for bar embedded at shallow depth before modification.

FIG. 6C shows a cross-section view of bar embedded at shallow depth with iron wire.

FIG. 6D shows an image of PAU test results for bar embedded at shallow depth with iron wire.

DETAILED DESCRIPTION

Embodiments of the subject invention provide novel and advantageous systems and methods for making fiber reinforced polymer (FRP) bars embedded in concrete detectable by conventional non-destructive testing (NDT) methods. A metallic/conductive presence can be introduced in FRP bars to make them detectible by NDT methods that use electromagnetic and stress waves for detection of steel bars. The FRP bars can be coated with a suspension of metal/conductive particles in a matrix (e.g., a resin), and this could be also combined with bond-enhancing coating of bars. Also, metal/conductive wire and/or metal/conductive strips can be wound over the FRP bars. The FRP bars having the metallic/conductive presence can then be embedded in concrete, and they are detectable with customary NDT methods and devices.

Embodiments of the subject invention include: 1) coating FRP bars with a suspension of metal/conductive particles in a matrix (e.g., resin) (could be also combined with bond-enhancing coating of bars); and/or 2) winding metal/conductive wire and/or strips over the FRP bars. This makes FRP bars detectable with customary NDT devices. These alterations can be introduced either on the commercially available FRP bars or through an extra step during the manufacturing process of the FRP bars. The bond for FRP bars is normally introduced at the fabrication stage by creating variations in the geometry of their cross section and surface, including but not limited to helically wrapped (HW), sand coated (SC), helically wrapped sand coated (HWSC), indented (In) or grooved, ribbed (Rb), and other FRP bars. Metal/conductive wire and/or strip winding can be done on any type of FRP bar during or after manufacturing, as they further increase the bonding of the FRP bars to concrete. Though, the metal/conductive particle coating should preferably be applied in such a manner so as not to compromise their existing bond enhancing measures. For example, metal/conductive particles can be mixed with a resin coating containing sand or any other bond enhancing particles during the manufacturing process. The metal/conductive particle coating can be prepared by mixing metal/conductive particles with resin (e.g., at a proportion by weight in a range of, for example, from 1:10 to 10:1, such as 1:1 or about 1:1). The metal/conductive wire winding can be done, for example, by following the pitch of the grooves present on the surface of the FRP bar. The metal/conductive can be any suitable metal, including but not limited to iron, steel (e.g., galvanized steel), copper, or aluminum.

Corrosion of steel reinforcement is a major issue in traditional concrete structures, which severely affects their safety and serviceability. The use of FRP reinforcing bars instead of conventional steel reinforcement is one of the most promising alternatives available to stop the process of corrosion within reinforced concrete as it is immune to corrosion. The use of FRP bars has been thus gaining momentum in beams, deck panels, columns/piers, pile/pier-caps, piles, and footing. Regardless of the many advantages provided by FRP, their long-term performance and service life is a concern. To address this, there is a great need for inspection methods for detecting the embedded FRP bars in concrete in the first place, and consequently being able to detect damages and defects. However, related art NDT methods have been developed for detecting steel reinforcements, and the detectability of FRP bars embedded in concrete is still a major issue that needs to be addressed in the FRP industry. This is primarily because FRP and concrete are both non-conductive and do not respond to electromagnetic fields in the same way as steel does. As a result, several NDT methods that rely on electromagnetic waves such as ground penetrating radar (GPR) become less effective, if not obsolete. Similarly, other NDT methods such as ultrasonic testing (UT) based on stress waves, while having some capability of detecting steel reinforcements, perform poorly in the detection of FRP bars. When conventional NDT methods are attempted for detection of FRP bars, results indicate a wide range of limitations in detectability of embedded FRP bars.

Embodiments of the subject invention can have major impact on and considerably promote the application of FRP reinforcements in concrete elements. With the pressing need for a solution to the issue of corrosion in conventional steel reinforced concrete elements, there is substantial potential for commercialization of FRP bars that can provide the same level of detectability as the steel rebars. Embodiments of the subject invention can boost the use of modified bars in the construction industry and provide methods for making embedded FRP detectable by NDT to ensure their inspectability.

No related art systems or methods exist for application of NDT methods for damage detection in FRP reinforced concrete. The ability to assess the condition of the relatively new and unique FRP reinforcements would increase the confidence of the construction industry in their use as a reliable substitute for steel reinforcements.

In order to improve the detectability of FRP bars embedded in concrete, embodiments of the subject invention can include addition of metal/conducive wire and metal/conductive particle coating, as shown in FIGS. 1B and 1C. That is, embodiments can include: 1) coating FRP bars with a suspension of metal/conductive particles in a matrix (e.g., resin) (see, e.g., FIGS. 2A-2C); and/or 2) winding metal/conductive wire or strips over the FRP bars (see, e.g., FIGS. 3A-3E). Metal/conductive wire can be wound on any type of FRP bar during or after manufacturing as they further increase the bonding of the FRP bars to concrete. In the case of metal/conductive particle coating, in order to provide both the bond strength and detectability, the particles can be mixed with sand or any other bond enhancing coating during the manufacturing process. The corrosion of the metallic/conductive particles or wire would not be an issue as the introduced metallic/conductive presence can be covered with resin. Additionally, non-corrosive metals or other conductive particles can be used.

Embodiments can provide a metallic/conductive presence in FRP bars. Several customary NDT methods such as GPR, UT, magnetic flux leakage (MFL) and others can be used to detect the modified FRP bars embedded in concrete. The tests results obtained using GPR and PAU applications for detecting FRP bars with metallic/conductive coating and metallic wire demonstrate the advantages of embodiments of the subject invention (see Examples).

Embodiments of the subject invention provide many advantages, including: a) being easy to implement, as the FRP surface modification can be performed during FRP bar fabrication or later using similar or same machinery to what is currently being used; b) requiring no modifications to the NDT devices readily available for customary reinforced concrete; c) requiring no special training for the inspectors; d) being durable and corrosion resistant as the metallic/conductive coating or wire can be impregnated within resin; e) an insignificant added cost; and f) ability to eliminate the uncertainty in the use of FRP that would otherwise be present due to the limitations on their inspection. Embodiments can have a major impact on and considerably promote the application of FRP reinforcements in concrete elements.

When ranges are used herein, combinations and subcombinations of ranges (including any value or subrange contained therein) are intended to be explicitly included. When the term “about” is used herein, in conjunction with a numerical value, it is understood that the value can be in a range of 95% of the value to 105% of the value, i.e. the value can be +/−5% of the stated value. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

A greater understanding of the embodiments of the subject invention and of their many advantages may be had from the following examples, given by way of illustration. The following examples are illustrative of some of the methods, applications, embodiments, and variants of the present invention. They are, of course, not to be considered as limiting the invention. Numerous changes and modifications can be made with respect to embodiments of the invention.

EXAMPLE 1

Detectability of FRP bars with Metal/Conductive Particle Coating with the Use of Phased Array Ultrasound (PAU)

At present, FRP bars embedded in concrete are not detectable with PAU testing methods as shown in FIGS. 4B and 4F. A method of an embodiment of the subject invention, with modified FRP bars with metal/conductive particle coating, makes embedded FRP bar detectable by PAU. For example, as shown in FIGS. 4D and 4H, FRP bars with metal/conductive particle coating (iron coating in this case) are clearly visible in both shallow and deeper embedment, with red color profile representing strong detection.

EXAMPLE 2

Detectability of FRP Bars with Metal/Conductive Particle Coating with the Use of GPR

At present, FRP bars embedded in concrete are only slightly detectable and only for shallow depths by the GPR testing method as shown in FIGS. 5B and 5F. A method of an embodiment of the subject invention, with modified FRP bars with metal/conductive particle coating, greatly improves the capability of GPR in detecting these bars embedded in concrete at shallow depth while also making their detection possible for deeper bars. For example, as shown in FIGS. 5D and 5H, FRP bars with metal/conductive particle coating (iron coating in this case) improved detectability for shallow bars and made detection possible even for deeper bars, with red color profile indicating strong detection.

EXAMPLE 3

Detectability of FRP Bars with Metal/Conductive Wire Winding with the Use of PAU

At present, FRP bars embedded in concrete are not detectable with PAU testing method as shown in FIG. 6B. A method of an embodiment of the subject invention, with modified FRP bars with metal/conductive wire winding, makes PAU capable of detecting these bars embedded in concrete. For example, as shown in FIG. 6D, FRP bars with metal/conductive wire winding (steel wire in this case) are clearly visible with yellow color profile representing strong detection.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

All patents, patent applications, provisional applications, and publications referred to or cited herein are incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.