A framework for field inspection and condition assessment of FRP-reinforced and FRP-strengthened concrete bridge elements

Abstract

The increasing use of Fiber-Reinforced Polymer (FRP) composites in bridge infrastructure presents both opportunities and challenges for structural inspection and asset management. Although FRP systems offer superior corrosion resistance and high strength-to-weight ratios, their distinct material behavior and deterioration mechanisms are not adequately addressed in existing bridge inspection standards. This study presents a comprehensive framework for the field inspection and condition assessment of in-service FRP-reinforced and FRP-strengthened concrete bridge elements, developed in a research project funded by the Federal Highway Administration (FHWA). The framework integrates findings from experimental evaluation, nondestructive testing (NDT), and literature synthesis to produce a standardized methodology compatible with the Specifications for the National Bridge Inventory (SNBI) and the AASHTO Manual for Bridge Element Inspection (MBEI). It introduces FRP-specific element identifiers, defect typologies, and condition-rating scales consistent with national bridge data structures, enabling quantitative evaluation and uniform reporting across transportation agencies. The framework represents a foundational step toward incorporating composite materials into the federally mandated bridge management systems established under 23 CFR 650.317, facilitating data-driven maintenance, lifecycle analysis, and policy development.

Keywords

Fiber-Reinforced Polymer (FRP)bridge inspection reinforced concrete concrete strengthening nondestructive testing SNBI MBEI

Introduction

The widespread implementation of Fiber-Reinforced Polymer (FRP) composites in bridge engineering has transformed construction industry.^1,2 FRP materials, typically composed of carbon, glass, or aramid fibers embedded in a polymeric matrix, offer superior tensile strength-to-weight ratios and exceptional resistance to environmental degradation compared with conventional steel reinforcement.^3–5 These advantages have led to their adoption in both internal reinforcement as FRP bars, grids, and prestressing tendons and external strengthening systems as bonded sheets, laminates, or near-surface mounted (NSM) reinforcements.^3,4,6 Additionally, application of FRP as fully composite bridge decks, girders, and stay-in-place forms demonstrate the growing role of FRP in primary load-bearing elements of modern infrastructure.²

Despite these advances, inspection and condition assessment of in-service FRP systems remain largely unstandardized.⁷ Existing guidelines such as the National Bridge Inspection Standards (NBIS),⁸ the Specifications for the National Bridge Inventory (SNBI),⁹ and the AASHTO Manual for Bridge Element Inspection (MBEI)¹⁰ were primarily developed for steel and concrete materials and thus lack material-specific defect categories, inspection protocols, and rating criteria for FRP. As a result, agencies face challenges in identifying and evaluating deterioration mechanisms unique to FRP composites, which include delamination between plies, resin matrix cracking, fiber exposure, discoloration, and debonding at adhesive interfaces.¹¹ These deficiencies hinder consistent data collection, national-level asset management, and lifecycle performance modeling of bridges incorporating FRP components.

To address this critical gap, this study develops a comprehensive framework for field inspection and condition assessment of FRP-reinforced and FRP-strengthened concrete bridge elements.^12,13 The framework aligns experimental findings and nondestructive testing (NDT) evaluations with the reporting formats of the SNBI⁹ and MBEI.¹⁰ It proposes standardized defect typologies, inspection procedures, condition-state classifications (CS1–CS4) for MBEI and condition rating protocols (on a scale of 0-9) for SNBI, specific to FRP systems. Moreover, it introduces new FRP material codes and bridge-element identifiers for integration within existing bridge management databases.

By embedding FRP-specific parameters into the established federal inspection framework, this research enables bridge owners and engineers to record, interpret, and manage the condition of FRP elements using a nationally uniform methodology. Such integration enhances data comparability across jurisdictions, facilitates long-term durability modeling, and supports decision-making for maintenance and rehabilitation strategies. Ultimately, the proposed framework that has already garnered significant support among stakeholders represents a foundational step toward the inclusion of composite materials within the national bridge inventory and asset-management systems.

Background

The increasing use of FRP composites in bridge infrastructure reflects an industry-wide transition toward materials that combine high mechanical efficiency with exceptional corrosion resistance.^14,15 FRP bars, strands, laminates, and fabrics have been deployed in concrete bridge elements to address the persistent durability limitations of steel reinforcement, particularly in coastal and deicing-salt environments.^3,4 Their application falls into three principal categories: (i) internal reinforcement or prestressing within concrete members, (ii) external strengthening and repair systems bonded to existing structures,¹⁶ and (iii) fully composite or hybrid structural components such as decks, girders, and stay-in-place forms as shown in Figure 1.

Figure 1.

Applications of FRP composites in bridge construction.

While the structural performance of FRP systems has been extensively validated through laboratory and field research, their inspection and long-term condition assessment remain underdeveloped.⁷ Conventional bridge inspection standards originally designed for steel and concrete do not capture the unique deterioration modes of FRP materials. These modes include resin matrix cracking, fiber-matrix debonding, interlaminar delamination, surface blistering, discoloration from ultraviolet exposure, and bond degradation at the FRP-concrete interface.^17,18 Unlike corrosion in steel reinforcement, such defects often evolve internally and are not readily visible,¹⁹ necessitating nondestructive testing (NDT) techniques for reliable detection.

Recent studies have evaluated multiple NDT methods such as ground-penetrating radar (GPR),^20,21 phased-array ultrasonic testing (PAU),^22–24 infrared thermography (IR),^{19,25,26,27–33,34–43,44} and tap testing (TT)⁴⁵ to determine their sensitivity to FRP-specific defects. However, there has been no unified guidance on method selection, inspection frequency, or integration of NDT data into bridge management databases. Consequently, agencies lack consistent criteria for rating FRP components, comparing their performance with traditional materials, or incorporating their data into the National Bridge Inventory (NBI).

The motivation for this research, therefore, arises from the need to standardize FRP inspection and condition evaluation within national bridge management frameworks. Building upon experimental work performed at Florida International University and collaborating institutions, this study proposes an inspection framework compatible with the SNBI⁹ and the AASHTO MBEI.¹⁰ By introducing new FRP-specific item codes, defect severity tables, and condition-state definitions, the framework provides bridge owners with a structured methodology for identifying, documenting, and rating deficiencies in FRP-reinforced or FRP-strengthened concrete elements.

This alignment ensures that FRP components can be inventoried and managed using the same hierarchical data systems already in place for steel and concrete, thereby enabling consistent lifecycle analysis and supporting the broader adoption of composite materials in the U.S. transportation infrastructure.

Methodology

The methodology adopted to develop the proposed framework for the inspection of FRP-reinforced and FRP-strengthened concrete bridge elements combined three major components: (i) a comprehensive literature review and synthesis of existing practices, (ii) experimental evaluation of nondestructive testing (NDT) methods for FRP systems, and (iii) formulation and validation of an inspection framework aligned with the SNBI⁹ and the AASHTO MBEI.¹⁰

Literature review and data synthesis

A systematic review of over 150 publications, technical specifications, and case studies was conducted to identify inspection practices applicable to FRP-reinforced or FRP-strengthened concrete elements.^46–48 Key references included prior FHWA and NCHRP reports, ASCE and ACI guidelines, and peer-reviewed research addressing the mechanical behavior, durability, and field performance of FRP composites.⁴⁹

The review revealed significant variability in terminology, defect classification, and NDT application, underscoring the absence of a standardized inspection protocol comparable to those used for steel or reinforced-concrete structures. From this synthesis, the authors of this study categorized defects associated with FRP reinforced/strengthened concrete (FRP-RSC) elements into following⁵⁰ which is also shown in Figure 2:

Figure 2.

Deficiencies in FRP-RSC members.

1. Defect categories related to external FRP application.

• FRP composite material defects

• Bond or interface defects

• Concrete Substrate defects

2. Defect categories related to internal FRP application.

• Concrete-related defects

• FRP-reinforcement-related defects

This taxonomy formed the foundation for the defect-severity tables and condition-state definitions introduced in the later sections.

Experimental evaluation of nondestructive testing methods

To evaluate the capability of different NDT techniques for detecting FRP-specific defects, a series of laboratory experiments were performed on both externally bonded and internally reinforced FRP-concrete specimens.^22–24 The specimens were designed to replicate realistic field conditions, incorporating controlled delaminations, voids, cracks, and debonded zones.

The following NDT methods were investigated:

Ground Penetrating Radar (GPR): assessed for detecting internal FRP bars, strands, and voids at the FRP–concrete interface and inside concrete.

Phased Array Ultrasonic Testing (PAU): evaluated for internal defects, or cross-sectional loss in embedded FRP reinforcement.

Infrared Thermography (IR): tested for surface and near-surface delamination, blistering, and bond anomalies in externally bonded FRP.

Tap Testing (TT) and Visual Inspection (VI): used as baseline, low-cost techniques for preliminary field evaluation.

In addition, the research explored innovative enhancements such as coating FRP bars with metallic particles and wire-winding to increase the electromagnetic reflectivity and improve NDT signal interpretation in embedded applications.⁵¹ Comparative analysis of these techniques demonstrated that IR and TT were most effective for external FRP, while GPR and PAU were best suited for internal FRP detection. These findings guided the method-selection hierarchy as shown in Figure 3, which provides a generalized framework showing the suggested NDT methods suitable for each major defect category in FRP-strengthened and FRP-reinforced bridge elements.

Figure 3.

Suggested methods suitable for each type of defect

Development of inspection framework and condition rating protocols

The experimental findings and literature synthesis were integrated to develop a comprehensive inspection framework for in-service FRP-reinforced and FRP-strengthened bridge elements. The framework was structured to include both procedural guidance and defect documentation tools. A decision-support flowchart as shown in Figure 3 was established to help inspectors select appropriate NDT methods based on defect type and FRP application. For each category of FRP application, the framework specified required visual and NDT procedures, and expected observable indicators as shown in Table 1 and Table 2. This structure ensured consistency with existing bridge-inspection protocols while expanding them to include FRP-specific phenomena.

Table 1.

Inspection procedures for FRP strengthened bridge elements (external application).

Inspection for	Visual inspection, tap testing	NDT if required
Surface anomalies and defects	• Signs of surface anomalies such as blisters or bubble-like formations, fiber exposure, scratches, and cracks	• Not needed
Surface anomalies and defects	• Regions of discoloration	• Not needed
Defects in FRP composite and bond issues	• Signs of debonding and delamination in externally applied FRP	• Areas suspected of having void can be further investigated using tap testing or IR
	• Potential signs of voids
	• Signs of moisture, water seepage, efflorescence, and water stains
		• If warranted, detailed investigation of debonding, delamination and voids can be conducted using NDT methods suggested in Figure 3
	• Use tap testing to identify location of debonding/delamination in addition to visual inspection
Defects in concrete substrate	• Signs of FRP tearing due to spalling of the concrete substrate	• NDT devices that can penetrate through the external FRP composite layer can be used at suspected areas
	• Signs of rust stains, discoloration, or other visible abnormalities
	• Signs of moisture, water seepage, efflorescence, and water stains

Table 2.

Inspection procedure for FRP reinforced concrete elements (internal application).

Inspection for	Visual inspection, tap testing	NDT if required
Internal FRP	• Signs of water seepage into the element	• The presence of damage, its location, type, and severity in internal application of FRP can be further verified by using NDT methods suggested in Figure 3
	• Cracks in the FRP reinforced concrete elements
	• Signs of distress such as fire damage with excessive spalling or burn marks
	• Excessive deflection
Concrete	• Follow general purpose bridge inspection manuals and guides such as AASHTO - The Manual for Bridge Evaluation, AASHTO - Manual for Bridge Element Inspection, FHWA - Bridge Inspector’s Reference Manual and others
Concrete	• Refer to Figure 3 for more details on the selection of inspection methods for concrete inspection

The inspection framework was explicitly formatted to align with the terminology, coding structure, and rating system of the SNBI⁹ and the AASHTO MBEI,¹⁰ both incorporated by reference in 23 CFR 650.317.⁸

MBEI provisions

New element identifiers such as Items 32, 33, 335, 171–178, 237, and 601–604 defined to represent FRP decks, girders, piles, railings, strengthening systems, and other structural elements were proposed to be included in the AASHTO MBEI¹⁰ to ensure compatibility with the National Bridge Inventory (NBI) database as shown in Table 3.

Table 3.

New Items Proposed to be Included in New Table 3.1.5A—FRP in the AASHTO MBEI.

Decks and slabs
32	FRP Deck	Classification	NBE	Unit of Measure	ft²
	Description:	All FRP bridge decks regardless of the wearing surface or protection systems used
	Quantity Calculation:	Area of the deck from edge to edge, including any median areas and accounting for any flares or ramps present
33	FRP Slab	Classification	NBE	Unit of Measure	ft²
	Description:	All FRP bridge slabs regardless of the wearing surface or protection systems used
	Quantity Calculation:	Area of the slab from edge to edge, including any median areas and accounting for any flares or ramps present
Railings
335	FRP Bridge Railing	Classification:	NBE	Unit of Measure	ft
	Description	All types and shapes of FRP bridge railing. All or some elements of the railing are FRP.
	Quantity Calculation	Number of rows of bridge rail (or FRP components) times the length of the bridge. The element quantity includes only the rail on the bridge
	Note:	This element does not include concrete rails reinforced with FRP bars
Superstructure
172	FRP Closed Web/Box Girder	Classification:	NBE	Unit of Measure:	ft
	Description:	All FRP box girders or closed web girders. For all box girders regardless of protective system
	Quantity Calculation:	Sum of all the length of each box girder section. This quantity can be determined by counting the visible web faces, dividing by two, and then multiplying by the appropriate length of the box section. Elements such as adjacent box girders are considered individual girders
171	FRP Open Girder/Beam	Classification:	NBE	Unit of Measure:	ft
	Description:	FRP open web girders regardless of protective system
	Quantity Calculation:	Sum of all of the lengths of each girder
173	FRP Stringer	Classification:	NBE	Unit of Measure:	ft
	Description:	FRP members that support the deck in a stringer floor beam system regardless of protective system
	Quantity Calculation:	Sum of all of the lengths of each stringer
174	FRP Truss	Classification:	NBE	Unit of Measure:	ft
	Description:	All FRP truss elements, including all tension and compression members for through and deck trusses. For all trusses regardless of protective system
	Quantity Calculation:	Sum of all of the lengths of each truss panel measured longitudinally along the travel way
175	FRP Arch	Classification:	NBE	Unit of Measure:	ft
	Description:	Arch made of FRP as main load bearing element or FRP individual arches used in assembly of elements
	Quantity Calculation:	Sum of all of the lengths of each arch panel measured longitudinally along the travel way
176	FRP Floor Beam	Classification:	NBE	Unit of Measure:	ft
	Description:	FRP floor beams that typically support stringers regardless of protective system
	Quantity Calculation:	Sum of all of the lengths of each floor beam
177	FRP Main Cables	Classification:	NBE	Unit of Measure:	ft
	Description:	All FRP suspension or cable stay cables for all cable groups regardless of protective systems
	Quantity Calculation:	Sum of all of the lengths of each main cable measured longitudinally along the travel way
	Note:	This element is intended for use on main cables in suspension bridges or main cable stays in cable stayed bridges. Suspender cables or other smaller cables shall be captured using Element 178 below
178	FRP Secondary Cables	Classification:	NBE	Unit of Measure:	ea
	Description:	All FRP suspended cables for all individual or cable groups regardless of protective systems
	Quantity Calculation:	Sum of the individual cable or cable groups carrying the load from the superstructure to the main cable/arch elements
	Note:	This element is intended for use on suspender cables, other smaller cables, or groups of cables in one location acting as a system to carry loads from the superstructure to the main cable/arch
		Suspension bridge main cables or cable stays shall be captured using Element 177 above
Substructure
237	FRP Pile	Classification:	NBE	Unit of Measure:	ea
	Description:	FRP piles that are visible for inspection, including piles exposed from erosion or scour and piles visible during an underwater inspection. For all FRP piles regardless of protective system
	Quantity Calculation:	Sum of the number of piles visible for inspection
FRP External Strengthening/repair/retrofit or Shell
601	FRP Sheets	Classification:	BME	Unit of Measure:	ft²
	Description:	Layered FRP sheets or wraps, usually a woven cloth, normally saturated and installed at site, for strengthening/repair/rehabilitation regardless of the type of substrate material
	Quantity Calculation:	Area of FRP sheet application
	Notes:	This can also include factory-made layup to create a shell which serves as stay-in-place form
602	FRP Pultruded Laminate	Classification:	BME	Unit of Measure:	ft²
	Description:	FRP pultruded laminates, such as plates or shells, prefabricated at shop and attached to an element for strengthening/repair/rehabilitation regardless of the type of substrate material
	Quantity Calculation:	Area of FRP laminate application
	Notes:	This can also include prefabricated shells to serve as stay-in-place forms
603	FRP Near Surface Mounted (NSM) Reinforcing Bars	Classification:	BME	Unit of Measure:	ft
	Description:	FRP reinforcing bars placed in grooves cut in the substrate material and covered by grout or resin for strengthening/repair/rehabilitation regardless of the type of substrate material
	Quantity Calculation:	Sum of all the lengths of reinforcing bars
604	FRP Post-Tensioning	Classification:	BME	Unit of Measure:	ft
	Description:	FRP post-tensioning bars, strands, or laminates for elements bonded to or separate from the substrate, regardless of the type of substrate material
	Quantity Calculation:	Sum of all the lengths of post-tensioning bars, strands, or laminates
	Notes:	Anchorage devices are not covered in this item

SNBI provisions

In addition to the uniform 0–9 condition-rating scale, the SNBI⁹ provides clarifying defect-severity tables in its Appendix C⁹ for conventional bridge materials such as concrete, steel, timber, and masonry. These tables define representative defect types, severity levels, and their corresponding implications for condition rating, enabling consistent interpretation of inspection findings across agencies. However, a framework for assigning FRP material–specific defects had not been available on a national scale until recently with the introduction of this study. Table 4 and Table 5 developed herein can fit within the existing SNBI structure as a supplement to Appendix C, providing clarifying defect-severity descriptions specifically for FRP applications.

Table 4.

Suggested defect severity for component condition ratings for FRP external application and FRP deck and slabs.

Defect	Minor	Moderate
Cracking, scratching, abrasion	Moderate-width or shallow cracks or scratches or abrasion mostly parallel to major stress or fiber directions	Wide or deep cracks or scratches or abrasion, especially if perpendicular to major stress or fiber directions but no through rupture or puncture
Discoloration, fire damage	Shallow discoloration due to UV exposure or fire damage and protective coating degradation of 6” or less in diameter	Discoloration or UV exposure and protective coating degradation greater than 6” diameter. Brittleness distress or cracking is visible
Blistering, voids, wrinkling	Blistering or voids 1” or less raised, or 6” or less in diameter	Blistering or voids more than 1” raised, or greater than 6” in diameter
Fiber exposure	Exposed at the surface, but not ruptured or debonded	Visibly exposed and debonded, but not ruptured
Delamination or debonding	Delamination 6” or less in diameter, away from connections or other sensitive details	Delamination greater than 6” in diameter or near connections or sensitive details

Table 5.

Suggested defect severity for component condition ratings specific to FRP deck and slabs.

Defect	Minor	Moderate
Panel-to-panel joint/panel-to-girder joint/approach joint	Evidence of joint degradation visible due to cracking in overlay or topping above panel joint locations. Gaps and cracks of up to 1/16 in.; no loss of bolts, clips, or other devices. Signs of water leakage through joints present	Gaps, misalignment, and cracks of up to ¼ in. Few clips or bolts loose or lost, elevation changes for adjacent panels evident, crack movement observed with passing traffic loads. Free flow of water leakage through joints present
Facesheet debonding	None	Evidence such as noncritical damage to surrounding structural elements, reflective cracking at wearing surface or local damage to joints resulting in detection of debonding

Bridge owners can correlate the defect-severity language in Table 4 and Table 5 with the component condition-rating framework available in SNBI to assign a uniform 0–9 SNBI condition rating for FRP components and systems. In this way, the proposed tables serve as the FRP counterpart to the existing SNBI Appendix C, ensuring that deterioration in FRP materials can be interpreted and reported using the same national condition-rating protocol applied to steel or concrete components.

Results

The development of the field-inspection framework for FRP-reinforced and FRP-strengthened concrete bridge elements yielded a set of interlinked deliverables: a decision-support flowchart for NDT method selection, detailed inspection procedures, standardized defect classification, and integrated condition-rating tools compatible with national bridge-management systems. Collectively, these results transform disparate research findings on FRP inspection into an operational methodology consistent with the NBIS,⁸ SNBI,⁹ and the AASHTO MBEI.¹⁰

Flowchart for NDT method selection

The first output of the study was a decision-support flowchart that guides inspectors through NDT method selection according to defect type and FRP application (internal vs external). The flowchart (Figure 3) distinguishes between surface-observable anomalies and subsurface or bond-related deficiencies. For externally bonded FRP, visual inspection (VI) and tap testing (TT) are prioritized for identifying surface blisters, discoloration, and delamination, while infrared thermography (IR) is recommended for deeper interfacial voids or moisture-induced debonding. For internally reinforced FRP, ground-penetrating radar (GPR) and phased-array ultrasonic testing (PAU) are the primary methods for detecting bar misalignment, debonding, and voids.

The hierarchy emphasizes a progressive inspection approach beginning with low-cost, widely accessible methods and escalating to specialized NDT only when preliminary findings warrant further investigation. This structure mirrors the inspection progression defined in NBIS (routine, in-depth, special) while incorporating the unique material responses of FRP composites.

Inspection procedures

Table 1 and Table 2 of this study detail the inspection procedures for external and internal FRP applications. Each table identifies observable conditions, NDT options, and documentation requirements for specific defect classes. For external systems, inspectors record surface anomalies (blistering, fiber exposure, cracks) and bond defects (delamination, voids, adhesive failure), followed by substrate evaluation when spalling, efflorescence, or moisture intrusion is present. For internal FRP reinforcement, procedures emphasize inspection for visible distress (cracks, spalls, discoloration), water ingress, and other indirect indicators of potential issues related to the internal FRP. In both cases, the framework prescribes guidelines specifying when standard visual inspection should be escalated to specialized nondestructive testing (NDT) to confirm the nature and extent of the observed deterioration. These standardized procedures enable consistent documentation and minimize subjectivity among inspectors with varying levels of FRP experience.

Defect classification and severity tables

The framework establishes a comprehensive defect-classification system that categorizes deficiencies as shown in Figure 2. Each defect type is paired with a quantitative severity definition and corresponding inspection methodology to support objective field evaluation. For example, using Table 4:

Cracking or scratching is rated minor when shallow and parallel to fiber orientation, but moderate when deep or perpendicular to load direction.

Blistering or voids are classified by geometric size (≤6 in. = minor; >6 in. = moderate).

Delamination or debonding is considered critical when occurring near structural connections, anchors or regions of concentrated stress transfer.

By defining these parameters, the framework converts what were previously qualitative, inspector-dependent observations into measurable and repeatable indicators compatible with data-driven asset-management systems. The resulting defect-severity tables (Table 4 and Table 5) translate field observations into standardized terminology and rating criteria, ensuring that FRP deterioration can be documented and compared consistently across bridge inventories and inspection cycles.

This structured classification directly supports the integration of FRP-specific defect data into the national condition-rating systems described in the following section, enabling seamless correlation between field-identified deficiencies and the uniform 0–9 and CS1–CS4 rating frameworks used in the SNBI and MBEI, respectively.

Condition-rating

The framework extends both the SNBI 0–9 rating scale⁹ and the MBEI condition-state (CS1–CS4)¹⁰ protocol to FRP systems, allowing bridge owners to record FRP element conditions within the same national databases that are also used for steel and concrete.

The framework adopts the SNBI’s uniform 0–9 condition rating scale, historically used for conventional bridge materials such as steel, concrete, timber, and masonry. Figures 4, 5, 6 & 7, illustrate how the condition-rating language of SNBI⁹ can be applied uniformly to different FRP component applications such as decks with internal FRP reinforcement (Figure 4), externally strengthened superstructures (Figure 5), FRP-wrapped columns and crash walls (Figure 6), and FRP decks (Figure 7). Similarly, Table 6 shows the defect listing and guidance on how to determine the condition state (CS) for each defect related to FRP elements or FRP strengthened elements using the four-level condition-state scale (CS1–CS4) prescribed in the MBEI.¹⁰ In addition, Figure 8 provides visual guide on determining the condition states of each defect type.

Figure 4.

Illustrative Example. B.C.01 Deck condition rating—FRP internal application.¹³

Figure 5.

Illustrative Example. B.C.02 Superstructure condition rating—FRP external strengthened application.¹³

Figure 6.

Illustrative Example. B.C.03 Substructure condition rating—FRP external application.¹³

Figure 7.

Illustrative Example. B.C.01 Deck condition rating—FRP standalone application.¹³

Table 6.

FRP-Specific Condition State definitions Proposed to be included in AASHTO MBEI.

Defects	Condition states
	CS 1	CS 2	CS 3	CS 4
	Good	Fair	Poor	Severe
Defects for FRP-strengthened elements and FRP deck and slabs
Cracking (1230)	None	Shallow cracks, scratches, or abrasion, limited to the polymer, with no fibers visible and parallel to the major stress direction	Wide or deep cracks or scratches or abrasion, especially if perpendicular to major stress or fiber directions but no through rupture or puncture	The condition warrants a structural review to determine the effect on strength or serviceability of the element or bridge; OR a structural review has been completed and the defects impact strength or serviceability of the element
Scratches (1240)
Abrasion (1290)
Wrinkling (1210)	None	Less than 1 inch raised or less than 6 inches in diameter or length	More than 1 inch raised or more than 6 inches in diameter or length
Voids (1270)
Blister (1260)
Discoloration (1250) and fire damage (1215)	None, or cosmetic stain or fire mark	Permanent shallow discoloration or UV exposure and protective coating degradation 6 inches in diameter or less	Permanent discoloration or UV exposure with cracking, brittleness, or distress, or more than 6 inches in diameter
Fiber exposure (1280)	None	Exposed but not ruptured, buckled, or debonded at the surface damage location	Fibers exposed and debonded (especially in cracks perpendicular to major stress or fiber directions) but not buckled or ruptured at the surface damage location
Delamination/debonding (interlaminar/from substrate) (1205)	None	Delamination smaller in every dimension than 6 inches but away from sensitive details (e.g., connections) to have structural effects	Delamination smaller in every dimension than 6 inches but near sensitive details (e.g., connections) to have structural effects
Defects applicable only to FRP deck and slab (adapted from NCHRP report 564)
Panel-to-panel joint (1225)	None	Evidence of joint degradation visible due to cracking in overlay or topping above panel joint locations. Gaps and cracks of up to 1/16 inch; no loss of bolts, clips, or other devices. Leakage may be minimal	Gaps, misalignment, and cracks of up to ¼ inch in overlay. Few clips or bolts loose or lost, minor elevation changes for adjacent panels evident. Leakage may be moderate, more than a drip and less than a free flow of water
Panel-to-girder joint (1235)
Approach joint (1245)
Facesheet debonding (1255)	None	Visible minor bulge or peeling on the top surface indicating initiation of debonding	Noncritical damage to surrounding structural elements, such as reflective cracking at wearing surface or local damage to joints resulting in detection of debonding
General
Settlement (4000)	None	Exists within tolerable limits or arrested with no observed structural distress	Exceeds tolerable limits but does not warrant structural review
Scour (6000)	None	Exists within tolerable limits or has been arrested with effective countermeasures	Exceeds tolerable limits but is less than the critical limits determined by scour evaluation and does not warrant structural review
Damage (7000)	Not applicable	The element has impact damage. The specific damage caused by the impact has been captured in CS 2 under the appropriate material defect entry	The element has impact damage. The specific damage caused by the impact has been captured in CS 3 under the appropriate material defect entry	The element has impact damage. The specific damage caused by the impact has been captured in Condition State 4 under the appropriate material defect entry

Figure 8.

Visual guide for determining condition states.^13,52–55

Furthermore, to ensure interoperability, the framework introduces FRP-specific item codes and measurement units for AASHTO MBEI. These additions allow bridge owners to inventory FRP components alongside traditional materials and to track their condition through lifecycle performance models. The result is a unified methodology that brings FRP materials into the same regulatory and analytical ecosystem as conventional bridge components, facilitating long-term performance tracking, reliability analysis, and maintenance planning.

Additionally, the research team conducted field inspections using this procedure on two bridges in Broward County, Florida, to show the applicability of the inspection framework. One bridge was a newly constructed concrete bridge reinforced entirely with GFRP bars⁵⁶ and the other a prestressed concrete girder bridge along Interstate 95 strengthened using CFRP sheets.

Discussion

This study represents a major advancement toward the standardized inspection and rating of FRP-reinforced and FRP-strengthened concrete bridge elements. Its alignment with federally recognized standards, specifically the SNBI⁹ and the AASHTO MBEI,¹⁰ positions it for direct adoption by transportation agencies operating under the NBIS and the regulatory structure of 23 CFR 650.317.⁸ It translates the qualitative understanding of FRP deterioration into measurable inspection parameters through standardized FRP item codes, unified 0–9 and CS1–CS4 rating schemes, and clear criteria for NDT application.

Integrating FRP components into federally mandated bridge data systems provides significant benefits for long-term asset management. Once FRP elements are coded within the SNBI database, agencies can quantify their distribution across bridge inventories, monitor deterioration trends, and develop material-specific deterioration models analogous to those used for steel and concrete. This supports predictive maintenance, lifecycle-cost analysis, and national performance targets established under the Moving Ahead for Progress in the 21st Century Act (MAP-21). The framework also enhances inspection consistency, and provides a uniform data structure that facilitates research, policy development, and cost-effectiveness evaluation of FRP retrofits. Bridge owners can evaluate whether FRP retrofits/reinforcement deliver the anticipated durability and cost-efficiency benefits compared with conventional repair methods.

Conclusions

This study developed a comprehensive inspection and condition-assessment framework for FRP-reinforced and FRP-strengthened concrete bridge elements. The framework addresses the long-standing absence of standardized national guidance for evaluating the performance of FRP systems within the existing bridge inspection infrastructure. It translates the complex behavior of FRP composites into an operational methodology compatible with the NBIS and MBEI. The summary of the major contributions of this study is given below:

1. Development of Framework Aligning with National Standards: The proposed framework is fully aligned with the SNBI⁹ and the AASHTO MBEI,¹⁰ the two manuals incorporated by reference under 23 CFR 650.317. It introduces FRP-specific element identifiers, unit definitions, and condition-rating scales (SNBI 0–9⁹ and MBEI CS1–CS4)¹⁰ that enable direct compatibility with federally recognized bridge-management systems.

2. Defect Classification: A comprehensive defect classification covering FRP composites, bond interfaces, adhesives, substrate concrete, and FRP reinforcement, was established with quantitative severity level. The framework converts subjective field observations into structured, reproducible data suitable for long-term asset tracking and performance modeling.

3. NDT Method Selection and Inspection Procedures: The inspection flowchart guides inspectors from routine visual inspection to advanced nondestructive testing (NDT) based on defect type and severity. This systematic approach enhances consistency, reduces ambiguity, and promotes efficient allocation of resources during field inspections.

4. Condition-Rating: The SNBI 0–9 scale, ranging from 9 (Excellent) to 0 (Failed), was developed for FRP-specific deterioration mechanisms. Similarly, MBEI CS1–CS4 condition states were defined to capture element-level performance.

Adoption of the proposed framework will enable transportation agencies to inventory FRP components using standardized SNBI item codes, assign and track condition ratings through federally compliant systems, develop material-specific deterioration models, and incorporate FRP performance data into maintenance and lifecycle-cost analyses. This alignment promotes national data uniformity and supports performance-based asset management under MAP-21, extending the reach of the NBIS to advanced composite materials. It is recommended that FHWA and selected state DOTs should conduct pilot inspections using the proposed framework on bridges using FRP components/elements to evaluate field usability, consistency, and data integration. It is however realized that the inspectors who have no or little experience with the FRP material may face challenges in identifying the defects and determining the most applicable methods for damage detection. Accordingly, it is only prudent that the interested inspection firms and state department of transportation hold training sessions for their inspectors by the authors of the framework on the new inspection procedures. In the long term, the framework will help agencies evaluate the true lifecycle performance of FRP technologies, promote uniformity in national bridge data reporting, and guide future updates to AASHTO and FHWA standards. Overall, the framework provides the technical foundation for consistent condition assessment of FRP systems, facilitating their integration into national bridge inventories and advancing the shift toward data-driven, sustainable, and resilient infrastructure. More importantly, the availability of the inspection framework can promote the adoption of durable FRP material in bridge construction by removing one of the obstacles in evaluation and maintenance of this material.

In the longer term, the proposed framework has the potential to evolve toward integration with remote and image-based inspection technologies. As inspectors gain greater familiarity and confidence with hands-on FRP inspection procedures, these experiences can inform the development of automated or semi-automated assessment tools utilizing field-acquired imagery and data. Techniques such as drone-based photography, LiDAR scanning, and thermal imaging could facilitate the remote evaluation of externally bonded FRP systems, while internal FRP applications may benefit from sensor-based or vibration monitoring approaches. Such advancements would not only improve inspection efficiency and safety by reducing the need for physical presence in the field but also promote more standardized and data-driven evaluation practices across different inspection environments.

Footnotes

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Disclaimer

The views expressed in this paper are those of the authors and do not necessarily reflect those of the sponsor. The authors are solely responsible for the accuracy of the information presented.

References

Frankhauser

Kahl

McMillan

, et al. NCHRP 20-68A, U.S. domestic scan 13-03: advances in fiber-reinforced polymer composites in transportation infrastructure. Natl Coop Highw Res Progr 2015, [Online]. Available: https://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP20-68A_13-03.pdf

Kim

. Use of fiber-reinforced polymers in highway infrastructure. Washington, DC: The National Academies Press, 2017. https://nap.nationalacademies.org/catalog/24888/use-of-fiber-reinforced-polymers-in-highway-infrastructure

ACI 440.1R-15 . Guide for the design and construction of structural concrete reinforced with Fiber-reinforced Polymer (FRP) bars (ACI 440.1R-15). American Concrete Institute, 2015.

ACI 440.2R-17 . Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures, 2017.

Kossakowski

Wciślik

. Fiber-reinforced polymer composites in the construction of bridges: opportunities, problems and challenges. Fibers 2022; 10(4): 37.

Tripathi

Bohara

Malla

, et al. Seismic retrofitting of non-ductile RC beam-column joint with externally bonded CFRP sheets. Int J Adv Eng Manag 2019; 4(2): 1–7.

Tang

. Maintenance and inspection of fiber-reinforced polymer (FRP) bridges: a review of methods. Mater (Basel, Switzerland) 2021; 14(24): 7826.

NBIS . National bridge Inspection Standards [NBIS], 2022, pp. 1–20.

FHWA , Specifications for the national bridge inventory, 2022.

10.

AASHTO . Manual for bridge element inspection. American Association of State Highway and Transportation Officials, 2019.

11.

Fowler

Kinra

Maslov

, et al. Research report: inspecting frp composite structures with nondestructive testing. Report 2001; 7(19): 148.

12.

Mehrabi

Khedmatgozar Dolati

Malla

, et al. A framework for field inspection of In-Service FRP reinforced/strengthened concrete bridge elements. 2024. [Online]. Available: https://rosap.ntl.bts.gov/view/dot/73333

13.

Mehrabi

Khedmatgozar Dolati

Malla

, et al. A framework for field inspection of In-service FRP reinforced/strengthened concrete bridge elements. Technical Summary, 2025. [Online]. Available: https://rosap.ntl.bts.gov/view/dot/85145

14.

Qureshi

. A review of fibre reinforced polymer bridges. Fibers 2023; 11(5): 40.

15.

Ali

Akrami

Fotouhi

, et al. Fiber reinforced polymer composites in bridge industry. Structures 2020; 30: 774–785.

16.

AASHTO . Guide specifications for design of bonded FRP systems for repair and strengthening of concrete bridge elements. American Association of State Highway and Transportation Officials, 2023.

17.

Azad

Jung

Elahi

, et al. Failure modes and non-destructive testing techniques for fiber-reinforced polymer composites. J Mater Res Technol 2024; 33: 9519–9537.

18.

Kang

THK

Howell

Kim

, et al. A state-of-the-art review on debonding failures of FRP laminates externally adhered to concrete. Int J Concr Struct Mater 2012; 6(2): 123–134.

19.

Wang

Zhong

Lee

T-L

, et al. Non-destructive testing and evaluation of composite materials/structures: a state-of-the-art review. Adv Mech Eng 2020; 12(4): 1687814020913761.

20.

Dutta

. Nondestructive evaluation of FRP wrapped concrete cylinders using infrared thermography and groud penetrating radar. West Virginia University, 2006.

21.

Hing

CLC

Halabe

. Nondestructive testing of GFRP bridge decks using ground penetrating radar and infrared thermography. J Bridge Eng 2010; 15(4): 391–398.

22.

Malla

Dolati

SSK

Ortiz

, et al. Damage detection in FRP reinforced concrete elements. Materials 2024; 17(5): 1171.

23.

Ortiz

Dolati

SSK

Malla

, et al. Nondestructive testing (NDT) for damage detection in concrete elements with externally bonded fiber-reinforced polymer. Buildings 2024; 14(1): 246.

24.

Malla

Khedmatgozar Dolati

Ortiz

, et al. Feasibility of conventional non-destructive testing methods in detecting embedded FRP reinforcements. Appl Sci 2023; 13(7): 4399.

25.

Tashan

Al-Mahaidi

. Bond defect detection using PTT IRT in concrete structures strengthened with different CFRP systems. Compos Struct 2014; 111(1): 13–19.

26.

Wen

Zhou

Zeng

, et al. Pulse-heating infrared thermography inspection of bonding defects on carbon fiber reinforced polymer composites. Sci Prog 2020; 103(3): 36850420950131.

27.

Cantini

Cucchi

Fava

, et al. Damage and defect detection through infrared thermography of fiber composites applications for strengthening of structural elements. In: RILEM Bookseries, 2012, vol 6, pp. 779–784.

28.

Caldeira

Padaratz

. Potentialities of infrared thermography to assess damage in bonding between concrete and GFRP. Rev IBRACON Estrut Mater 2015; 8(3): 296–322.

29.

Corvaglia

Largo

. IRT survey for the quality control of FRP reinforced r.c. Structures 2008. Proceedings of the QIRT.

30.

Banthia

Aidin

Demers

, et al. Durability of FRP-concrete bond in FRP-strengthened bridges. Concr Int 2010; 32(8): 45–51.

31.

Kylili

Fokaides

Christou

, et al. Infrared thermography (IRT) applications for building diagnostics: a review. Appl Energy 2014; 134: 531–549.

32.

Brown

Chittineni

. Comparison of lock-in and pulse-phase thermography for defect characterization in FRP composites applied to concrete. Thermosense Therm. Infrared Appl. XXXVII 2015; 9485: 94850B.

33.

Sim

, et al. Optimum NDT using infrared thermography for defected concrete. In: Bridge Maintenance, Safety, Management, Health Monitoring and Informatics—IABMAS ’08: Fourth International IABMAS Conference, 2008, pp. 1223–1230.

34.

Dumoulin

Ibarra-Castanedo

Quiertant

, et al. Evaluation of FRP gluing on concrete structures by active infrared thermography, 2010. Proceedings of the QIRT; 155–163.

35.

Milovanović

Banjad Pečur

. Review of active IR thermography for detection and characterization of defects in reinforced concrete. J Imaging 2016; 2(2): 11.

36.

Foudazi

Donnell

Ghasr

. Application of active microwave thermography to delamination detection. In: 2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2014, IEEE, pp. 1567–1571.

37.

Mtenga

Parzych

Limerick

. Quality assurance of FRP retrofit using infrared thermography. Struct - A Struct Eng Odyssey, Struct 2001 - Proc 2001 Struct Congr Expo 2004; 109: 1–8.

38.

Nokes

Hawkins

, Infrared inspection of composite-reinforced concrete structures, 2001.

39.

Galietti

Luprano

Nenna

, et al. Non-destructive defect characterization of concrete structures reinforced by means of FRP. Infrared Phys Technol 2007; 49(3): 218–223.

40.

Jackson

Islam

Alampalli

. Feasibility of evaluating the performance of fiber reinforced plastic (FRP) wrapped reinforced concrete columns using ground penetrating RADAR (GPR) and infrared (IR) thermography techniques. In: Structural Materials Technology IV-An NDT Conference, 2000, pp. 390–395.

41.

Yazdani

Beneberu

Riad

. Nondestructive evaluation of FRP-concrete interface bond due to surface defects. Adv Civ Eng 2019; 2019: 2563079.

42.

Luprano

Tundo

Angelo Tatì

, et al. Non destructive defect characterization in civil structures reinforced by means of FRP. Proceedings of ECNDT 2006. 2006.

43.

Kaiser

Karbhari

Sikorsky

. Non-destructive testing techniques for FRP rehabilitated concrete ± II: an assessment. International Journal of Materials and Product Technology. 2004; 21(5): 385–401.

44.

Sen

, Developments in the durability of FRP-concrete bond. Constr Build Mater 2015; 78: 112–125.

45.

Haque

Raju

. Sensitivity of the Acoustic impact technique in characterizing defects/damage in laminated composites. J Reinf Plast Compos 1995; 14(3): 280–296.

46.

Dolati

SSK

Malla

Ortiz

, et al. Identifying NDT methods for damage detection in concrete elements reinforced or strengthened with FRP. Eng Struct 2023; 287: 116155.

47.

Khedmatgozar Dolati

Malla

Ortiz

, et al. Non-destructive testing applications for in-service FRP reinforced/strengthened concrete bridge elements. In: Nondestructive characterization and monitoring of advanced materials, aerospace, civil infrastructure, and transportation XVI 2022; 12047: 59–74.

48.

Dolati

SSK

Malla

Polanco

, et al. Nondestructive testing applications for FRP reinforced or strengthened concrete elements. Structures Congress 2023; 12047: 217–229.

49.

Ortiz

Khedmatgozar Dolati

Malla

, et al. FRP-Reinforced/Strengthened concrete: state-of-the-art review on durability and mechanical effects. Materials 2023; 16(5): 1–30.

50.

Malla

Khedmatgozar Dolati

Ortiz

, et al. Damage and defects in fiber-reinforced polymer reinforced and strengthened concrete elements. J Compos Constr 2023; 27(4): 04023035.

51.

Malla

Dolati

SSK

Ortiz

, et al. Applicability of available NDT methods for damage detection in concrete elements reinforced or strengthened with FRP. Bridge Struct 2023; 19(4): 149–164.

52.

Telang

Dumlao

Mehrabi

, et al. NCHRP report 564: field inspection of In-Service FRP bridge decks. Transp Res Board 2006.

53.

Pevey

Rich

Williams

, et al.

Repair and strengthening of bridges in Indiana using fiber reinforced polymer systems: volume 1—Review of current FRP repair systems and application methodologies

2021.

54.

Karbhari

Kaiser

Navada

, et al. Methods for detecting defects in composite rehabilitated concrete structures, 2005.

55.

Baniya

Milev

Henry

, et al. Durability sssessment of externally bonded Fiber-Reinforced Polymer (FRP) composite repairs in bridges. 2022; (Center for Integrated Asset Management for Multimodal Transportation Systems (CIAMTIS) (UTC)).

56.

Kiani

Abedin

Steputat

, et al. Structural health monitoring of FRP-reinforced concrete bridges using vibration responses. Springer International Publishing, 2022.