Durability of Externally Bonded Fiber-Reinforced Polymer Composites in Concrete Structures: A Critical Review

Abstract

Externally bonded fiber-reinforced polymer composites have been in use in civil infrastructure for decades, but their long-term performance is still difficult to predict due to many knowledge gaps in the understanding of degradation mechanisms. This paper summarizes critical durability issues associated with the application of fiber-reinforced polymer (FRP) composites for rehabilitation of concrete structures. A variety of factors that affect the longevity of FRP composites are discussed: installation, quality control, material selection, and environmental conditions. Critical review of design approaches currently used in various international design guidelines is presented to identify potential opportunities for refinement of design guidance with respect to durability. Interdisciplinary approaches that combine materials science and structural engineering are recognized as having potential to develop composites with improved durability.

Keywords: FRP; civil infrastructure; composites; concrete; degradation; durability; repair; retrofit; strengthening.

Figure 1

Application of externally bonded (EB) fiber-reinforced polymer (FRP) strip on Ibach bridge near Lucerne in Switzerland in 1991, what is believed to be the first application of EB FRP in the world (reproduced from [4]).

Figure 2

Examples of bond-critical applications of EB FRP: (a) flexural strengthening of a concrete slab in a parking garage and (b) shear strengthening on the Sunshine Skyway bridge in Tampa, FL, USA.

Figure 3

Example of contact-critical application of EB FRP: FRP-confined column in a Bridge in Florida, USA (note: FRP wrap is painted).

Figure 4

(a–c) EB FRP installation (reprinted from [24]).

Figure 5

Pull-off test setup (reproduced, with permission from [31]).

Figure 6

Pull-off test possible failure modes (reproduced, with permission from [31]).

Figure 7

Schematic representation of a cross-section of FRP externally bonded to concrete.

Figure 8

Epoxy adhesive precursors: (a) Bisphenol A diglycidyl ether (DGEBA) (epoxide groups marked with a square) and (b) example amine-based hardener–Diethylenetriamine (DETA) (amine groups marked with a square).

Figure 9

Change in the conversion (a) and T_g (b) of Epon 826/Jeffamine D-230 epoxy system over 28 days under standard laboratory conditions (“Control”) and water immersion at elevated temperatures (30, 40, 50, and 60 °C) (reprinted from [83]).

Figure 10

Comparison of different FRP composites to typical grades of steel used in concrete structures.

Figure 11

A typical shift in EB FRP/concrete pull-of bond test failure mode following accelerated conditioning in moisture: (a) cohesive failure mode in “dry” conditions and (b) adhesive failure mode after accelerated conditioning by water immersion.

Figure 12

(a,b) Possible degradation mechanism of bonded joints (reprinted from [66] by permission from Elsevier).

Figure 13

Maximum and minimum allowed service temperatures for six epoxy adhesives (A through F) calculated from glass transition temperature (T_g) measurements based on ACI 440.2R and AASHTO FRPS-1 design guidelines; shaded region represents the typical maximum design temperature range per AASHTO 2017 (reprinted from [66] by permission from Elsevier).

Figure 14

Stereo microscope photographs of epoxy-cement paste interfacial region at different length scales (reprinted from [115] by permission from Elsevier).

Figure 15

Supposed structure of epoxy-rich region within interphase (reprinted from [115] by permission from Elsevier).

Figure 16

The principle of distributed sensing shown on a prestressed concrete beam section: (a) cross section and (b) elevation view. GFRP: glass fiber–reinforced polymers; CNT: carbon nanotube (reproduced from [129] with permission from SAGE Publications).

Figure 17

Proposed interactions at the interface between epoxy and cement paste/concrete: (a) hydrogen bonding and (b) covalent bonding via 3-glycidoxypropyltrimethoxysilane (GPTMS) coupling agent.

Figure 18

(a–e) Different types of bond test methods in the literature (reproduced from [143] by permission from American Society of Civil Engineers).

Figure 19

Typical test configuration (reproduced, with permission from [114], copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428).