NSERC Research Chair in Innovative FRP Composite Materials for Infrastructures

Project 5.17

Prepared by:

Brahim Benmokrane and Patrice Cousin

ISIS-Sherbrooke, Department of Civil Engineering, Faculty of Engineering University of Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1 Tel: (819) 821-7758 Fax: (819) 821-7974 E-mail: brahim.benmokrane@usherbrooke.ca

April 2005 © Benmokrane et al.

UNIVERSITY OF SHERBROOKE GFRP DURABILITY STUDY REPORT

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Table of content

1. Introduction …………………………………………………………………………... 1

2. Thermogravimetric Analysis

2.1. Introduction ……………………………………………………………….…..

2.2. Procedure ……………………………………………………………………..

2.3. Results …………………………………………………………………………

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6

6

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3. Optical Microscopy ……………………………………………………………………

3.1. Introduction …………………………………………………………………...

3.2. Method of Preparation ………………………………………………………...

3.3. Results ………………………………………………………………………...

3.4. Conclusions …………………………………………………………………...

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7

7

7

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3. Scanning Electronic Microscopy …..…………………………………………………

4.1. Introduction …………………………………………………………………...

4.2. Method of Preparation ………………………………………………………...

4.3. Results ………………………………………………………………………...

4.4. Conclusions …………………………………………………………………...

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13

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5. Differential Scanning Calorimetry …………………………………………………...

5.1. Introduction …………………………………………………………………...

5.2. Experimental Procedure .……………………………………………………...

5.3. Results ………………………………………………………………………...

5.4. Conclusions …………………………………………………………………...

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6. Fourier Transform Infrared Spectroscopy …………………………………………..

6.1. Introduction …………………………………………………………………...

6.2. Method of Preparation ………………………………………………………...

6.3. Results ………………………………………………………………………...

6.4. Conclusions …………………………………………………………………...

32

32

32

32

33

7. X Ray Diffraction ……………………………………………………………………...

7.1. Introduction …………………………………………………………………...

7.2. Method of Preparation ………………………………………………………...

7.3. Results ………………………………………………………………………...

7.3.1. Aggregates ………………………………………………………...

7.3.2. Presence of alkalis …………………………………………………

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35

35

35

35

36

8. Conclusions …………………………………………………………………………..… 40

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List of Tables

Table 2.1: Percentage of inorganic compounds in the different GFRP materials.………... 6

Table 5.1: Calorimetry Results for GFRP Materials: Glass Transition Temperatures (Tg) and

Enthalpy and Temperature of Polymerization.

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Table 6.1: Ratio of OH/CH for reference and core samples. 33

List of Figures

Figure 1.1: Core samples extracted from Joffre Bridge showing the two types of GFRP bars.. 3

Figure 1.2: Core samples extracted from Crowchild Bridge.…………………………………. 3

Figure 1.3: Core samples extracted from Hall’s Harbour Bridge………………….………….. 4

Figure 1.4: Core samples extracted from Waterloo Creek Bridge………………….…………. 4

Figure 1.5: Core samples extracted from Chatham Bridge………………….………………… 5

Figure 3.1: Cross section of FRP composite embedded in concrete (Joffre Bridge)………..… 8

Figure 3.2: Cross section of FRP composite embedded in concrete (Crowchild Bridge)…….. 9

Figure 3.3: Cross section of FRP composite embedded in concrete (Hall’s Harbour)……….. 10

Figure 3.4: Cross section of FRP composite embedded in concrete (Waterloo Creek)…..….. 11

Figure 3.5: Cross section of FRP composite embedded in concrete (Chatham Bridge)……… 12

Figure 4.1: Micrographs of cross sections of 9 mm GFRP bar extracted from Joffre Bridge… 16

Figure 4.1: Micrographs of cross sections of GFRP bar extracted from Joffre Bridge (cont.)... 17

Figure 4.2: Micrographs of cross sections of 16 mm GFRP bar extracted from Joffre Bridge.. 18

Figure 4.3: Micrographs of cross sections of GFRP bar extracted from Crowchild Bridge….. 19

Figure 4.4: Micrographs of cross sections of GFRP bar extracted from Hall’s Harbour Bridge 20

Figure 4.5: Micrographs of cross sections of GFRP bar extracted from Hall’s Harbour (cont.) 21

Figure 4.5: Micrographs of cross sections of GFRP bar extracted from Hall’s Harbour (cont.) 22

Figure 4.6: Micrographs of cross sections of GFRP grid extracted from Waterloo Creek……. 23

Figure 4.7: Micrographs of cross sections of GFRP grid extracted from Chatham Creek……. 24

Figure 5.1: DSC results for 16 mm GFRP bars from Joffre Bridge…………………………… 27

Figure 5.2: DSC results for 9 mm GFRP bars from Joffre Bridge…………………………….. 28

Figure 5.3 DSC results for GFRP bars from Crowchild Bridge……………………………….. 29

Figure 5.4: DSC results for GFRP bars from Hall’s Harbour Bridge……………………..…… 30

Figure 5.5: DSC results for GFRP grid from Waterloo Creek Bridge…………………………. 31

Figure 5.5: DSC results for GFRP grid from Chatham Bridge………………………………… 31

Figure 6.1: FTIR spectra of GFRP bars……………………………………………………… 34

Figure 7.1: X Ray Diffraction Diagram of Hall’s Harbour Concrete Samples………………… 37

Figure 7.2: X Ray Diffraction Diagram of Joffre Bridge Concrete Samples…………………... 37

Figure 7.3: X Ray Diffraction Diagram of Crowchild Bridge Concrete Samples……………... 38

Figure 7.4: X Ray Diffraction Diagram of Chatham Bridge Concrete Samples…………….…. 38

Figure 7.5: X Ray Diffraction Diagram of Waterloo Creek Concrete Samples…………….…. 39

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1. INTRODUCTION The expansive corrosion of steel reinforcing bars stands out as a significant factor limiting the life expectancy of reinforced concrete structures. In North America, significant temperature fluctuations and the use of de-icing salts exacerbate the phenomenon in parking garages and on bridge decks. Indeed, North America's freeze-thaw cycles and heavy salt applications subject roads and bridges to quite severe environmental conditions. Furthermore, the expansive corrosion of steel causes cracking and spalling of concrete bridge decks resulting in major rehabilitation costs and traffic disruption. Problems related to expansive corrosion could be resolved by protecting the steel reinforcing bars from corrosion-causing agents or by producing bars made of non-corrosive materials. One of the most interesting alternatives is the fibre reinforced polymers (FRP) materials because of their corrosion resistance to harsh chemical environments (alkaline or salted solutions), and electrical and magnetic neutrality. Fibre-reinforced polymer (FRP) composite reinforcement has been used successfully in many industrial applications and more recently has been used as concrete reinforcement in bridge decks and other structural elements. Since glass FRP composite bar is more economical than the available types (carbon and aramid) of FRP bars, it is more attractive for infrastructure applications and to the construction industry. However, to be acceptable to the construction industry on a large scale, the life-cycle cost of FRPs must be competitive. Durability is the most crucial element governing life-cycle cost. The research focusing on the durability of FRP materials is considered in an early stage especially due to the wide spectrum of durability issues and effects to be investigated. The objective of this work is to determine the effect of ageing in the field on several GFRP materials used as main reinforcement in five concrete structures in Canada. These structures are:

1. Joffre Bridge (Quebec) 2. Crowchild Bridge (Alberta) 3. Hall’s Harbour Bridge (Nova Scotia) 4. Waterloo Creek Bridge (British Columbia) 5. Chatham Bridge (Ontario)

More specifically, microscopic and physico-chemical analysis have been conducted on core samples (concrete cylinders including GFRP composite materials) extracted from these structures to investigate the degradation in the GFRP material, concrete, and the interface between the GFRP material and concrete, if any. The details of the extracted core samples are as follows (Figures 1.1-1.5):

− From Joffre Bridge (including two samples, GFRP ribbed-deformed C-BARTM rods; 9-mm diameter bent bars, and 16-mm diameter straight bars),

− From Crowchild Bridge (including one sample, GFRP ribbed-deformed C-BARTM), − From Hall’s Harbour Bridge (including one sample of sand-coated GFRP ISORODTM bars), − From Waterloo Creek Bridge (including one sample of GFRP NEFMACTM grids), − From the Chatham Bridge (including one sample of GFRP NEFMACTM grids).

In addition to core samples and for comparison purposes, GFRP reference samples (stored in normal environment at room temperature) were also provided for two bridges only: Joffre and Hall’s Harbour Bridges.

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The analyses performed on the available core and reference samples are: 1. Thermogravimetry analysis to measure the glass fibre contents of the different GFRP

materials. 2. Optical Microscopy to evaluate the adhesion at the interface concrete/reinforcement and

debonding. 3. Electronic Microscopy to study the structure and degradation (delamination, microcraking,

corrosion) of the GFRP materials (fibres, resin matrix, and interface glass fibre/resin). 4. Differential Scanning Calorimetry to evaluate the thermal properties of the polymeric resins

(glass transition temperature, post-curing, plasticization due to water). 5. Fourier Transform Infrared Spectroscopy to measure the chemical degradation of polymeric

resins (hydrolysis caused by the presence of alkalis). 6. X Ray Diffraction to determine the changes occurring in the concrete structure in contact

with the GFRP materials and which could be due to a chemical reaction with compounds migrating from the reinforcements.

For each technique, the method of preparation and/or analysis procedure is presented. Then the results and a short conclusion follow. All the presented studies and analyses were conducted at the Department of Civil Engineering, University of Sherbrooke, Sherbrooke (Quebec).

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Two types of ribbed-deformed GFRP bars (C-BARTM):

− 9.0 mm diameter bent bars − 15.9 mm diameter straight bars

Figure 1.1: Core samples extracted from Joffre Bridge (Quebec).

One type of ribbed-deformed GFRP bars (C-BARTM):

− 15.9 mm diameter straight bars The concrete (using a maximum aggregate size of 20 mm) contains synthetic fibres

Figure 1.2: Core samples extracted from Crowchild Bridge (Alberta)

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One type of sand-coated GFRP bars (ISORODTM):

− 15.9 mm diameter straight bars

Figure 1.3: Core samples extracted from Hall’s Harbour Bridge (Nova Scotia).

One type of GFRP grids (NEFMACTM):

Figure 1.4: Core samples extracted from Waterloo Creek Bridge (British Columbia).

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One type of GFRP grids (NEFMACTM):

Figure 1.5: Core samples extracted from Chatham Bridge (Ontario).

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2. THERMOGRAVIMETRIC (TGA) 2.1. Introduction The objective of thermogravimetric analysis is to determine the loss of weight with temperature under controlled conditions. In the present case, TGA has been used to evaluate the glass fibre content of the different composite materials used in Joffre, Crowchild and Hall’s Harbour Bridges. 2.2. Procedure Samples have been cut from the GFRP core samples to avoid contamination with the coatings, which could affect the measurement of glass fibre contents. The analysis has been conducted on a Setaram TGA, Setsys 24 model, in air up to 600°C at 10oC/min. The loss of weight at 600°C corresponds to the weight of organic compounds present in the materials and the remaining mass to the inorganic compound content. 2.3. Results Table 2.1 presents the content in inorganic compounds of the different composite materials. The inorganic phase is composed of glass fibres and, eventually, inorganic fillers/additives. Consequently, the glass fibre content is equal to or lower than the inorganic phase content. SEM analysis performed on Hall’s Harbour (ISORODTM), Crowchild Bridge (C-BARTM), and the two Joffre Bridge bar samples (C-BARTM) shows that the C-BARTM type samples contain significant amounts of fillers, while the ISORODTM sample does not contain any significant quantity of other inorganic compounds. Consequently, it may be assumed that the glass fibre content of Hall’s Harbour sample is equal or very close to the inorganic compounds content, i.e. 74.7 %. However, for samples from Joffre and Crowchild Bridges, the glass fibre content has a slightly lower percentage than those of the inorganic phase. Table 2.1: Percentage of inorganic compounds in the different GFRP materials.

Sample Inorganic phase (%) Joffre Bridge (9 mm diameter) 64.0 Joffre Bridge (16 mm diameter) 73.7 Crowchild Bridge 61.5 Hall’s Harbour Bridge 74.7

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3. OPTICAL MICROSCOPY 3.1. Introduction In reinforced concrete structures, the interface between the reinforcing bar and the concrete must properly transfer the stresses. The loads applied to the structure are transferred from the concrete to the reinforcement through bond stress at the surface between the reinforcing bars and the concrete, which can eventually lead to the formation of delaminated areas, i.e. free spaces between the concrete and the surface of the GFRP reinforcing bar/grid. An optical microscopy analysis has been performed on the surface of core samples to study the interface between the different FRP composite reinforcements (bar and grid) and the concrete. This section includes the Optical Microscopy analyses conducted on core samples extracted from the five bridges: Joffre, Crowchild, Hall's Harbour, Waterloo Creek, and Chatham Bridges. 3.2. Method of preparation The surface area of the cores, where the FRP reinforcement is embedded, was carefully sanded with #500 sand paper to get a smooth surface. The samples were then observed with a Leica MZ FLIII stereomicroscope. 3.3. Results: Two sets of micrographs from two different cores were taken for each of the five concrete structures (i.e., Joffre, Crowchild, Hall’s Harbour, Waterloo Creek, and Chatham Bridges). Each set contained three micrographs taken at three different magnifications: 8, 20, and 40X. Figure 3.1 shows the pictures of the cross section of two GFRP C-BARTM bars embedded in concrete (Joffre Bridge). As it may be clearly seen, the contact between the bars and the concrete is intimate since no free space is visible even for higher magnifications. It should be noted that Figure 3.1b shows that the rod core contains some bubbles. Figure 3.2 presents the pictures of the cross sections (A, C, and E) and longitudinal sections (B, D, and F) of GFRP C-BARTM reinforcing rods and surrounding concrete. As for Joffre Bridge, no void or any indication of delamination was detectable. Pictures in Figures 3.2b, 3.2d, and 3.2f show the ribs of this type of GFRP bars. The surrounding concrete goes around the curves of the rod in almost a perfect match. However, a small void is visible at the right of the rib cross section as shown in Figure 3.2d. The cross sections of GFRP ISORODTM bars embedded in Hall’s Harbour concrete bridge deck slab are shown in Figure 3. The GFRP ISORODTM bar has a rough sand-coated external surface (opposite to C-BARTM reinforcing bar which has a smooth external surface with the presence of ribs). From the photos illustrated in Figure 3.3, it can be concluded that the contact between the sanded coated GFRP ISORODTM bars and the surrounding concrete is excellent. Samples containing GFRP NEFMACTM grids have also been observed under the microscope. Figures 3.4 and 3.5 show the pictures obtained by examining the core samples from Waterloo Creek and Chatham Bridges, respectively. For both cases, the contact between the GFRP grids and concrete is excellent. 3.4. Conclusions The observation and examination of the interface between the GRRP reinforcing material and concrete, which were carried out on core samples extracted from the five concrete structures (mentioned above) using optical microscopy do not show any damage. The contact between the GFRP composite reinforcement (bars and grids) and the concrete is intimate and the bars and grids did not get loose with time.

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Core # JB3 Core # JB8

X8 a) b)

X20 c) d)

X40 e) f)

Figure 3.1. Cross section of FRP composite embedded in concrete (Joffre Bridge)

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Core # CB10 Core # CB4

X8 a) b)

X20 c) d)

X40 e) f)

Figure 3.2. Cross section of FRP composite embedded in concrete (Crowchild Bridge)

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Core # HH13 Core HH7

X8 a) b)

X20 c) d)

X40 e) f)

Figure 3.3. Cross section of FRP composite embedded in concrete (Hall’s Harbour Bridge)

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Core # WC5 Core # WC2

X8 a) b)

X20 c) d)

X40 e) f)

Figure 3.4. Cross section of FRP composite embedded in concrete (Waterloo Creek Bridge)

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Core # CHB-SE4 Core # CHB-SW1

X8 a) b)

X20 c) d)

X40 e) f)

Figure 3.5. Cross section of FRP composite embedded in concrete (Chatham Bridge)

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4. SCANNING ELECTRONIC MICROSCOPY (SEM) 4.1. Introduction In this section, the results of Scanning Electronic Microscopy (SEM) analysis that was conducted on core samples extracted from the five bridges are presented. Micrographs obtained at different magnifications, 50X to 5000X, have been compared to those obtained for reference samples, if available. It should be noted that for the bridges where there were no GFRP reference samples available (Crowchild, Waterloo Creek, and Chatham Bridges), the comparison to the extracted samples was not possible. 4.2. Method of preparation A 2.5 cm long GFRP grid sample was cut from each concrete core sample and vertically placed in a plastic mould. Epoxy resin was then cast into the mould and cured overnight at room temperature. The following day, the sample was removed and cut using an Isomet Buehler low speed saw equipped with a low concentration diamond wavering blade. The lubricant used during the cutting process was Ultramet Sonic Cleaning solution diluted in distilled water (1:20). The cross sections obtained were then polished using a Struers polishing machine (Model DAP-7, equipped with a Pedemin-2 arm). The polishing consumables consisted of three different water/oil soluble diamond pastes (15, 3, and 1 micron diamond size) and an oil soluble lubricant (purchased from Beta Diamond Products Inc.). Each paste was used with a separate Struers polishing cloth to avoid contamination. The sample was polished twice with each diamond paste at two different speeds (250 and 125 rpm) for 2 or 5 minutes depending on the size of the diamonds. Following each polishing process, the sample was immersed in methanol for at least 5 minutes before being sputtered with a gold/palladium alloy and analyzed on a Jeol SEM, Model JSM-840A at 15 kV. 4.3. Results Figure 4.1 presents the micrographs obtained for the 9-mm diameter C-BARTM sample extracted from Joffre Bridge (on the right). The micrographs that were taken at different magnifications are compared to those obtained for the reference sample (on the left). Micrograph 4.1a shows the outside part of the rod. The area containing the fibres is located on the left bottom side of the picture. A coating, with a thickness of approximately 0.8 mm, covers the fibres. Large bubbles are clearly visible. Micrograph 4.1b shows the same type of bar taken from Joffre Bridge at the same magnification. In this case, there is no coating and the fibres are in direct contact with the surface, showing that the coating is not uniform. Closer views of the fibres below the surface are presented in micrographs 4.1c to 4.1j. Filler particles are visible between the fibres. No change can be detected comparing the reference and field samples. The highest magnifications (micrographs 4.1i and 4.1j) clearly show that the interface between glass fibres and the resin is intimate and that no debonding (or delamination) occurred to date (for the in-service structure). Moreover, no matrix cracking or micro-cracking is detected. Figure 4.2 compares the micrographs obtained for the 16 mm diameter GFRP C-BARTM sample extracted from Joffre Bridge (on the right) with a reference sample (on the left). Similar to the previous figure, no significant changes are observed even with the most degradation sensitive fibres located just underneath the surface. A small delamination may be observed with certain fibres of the reference sample (micrograph 4.2e). This should not be attributed to the sample preparation but to an adhesion defect occurred during the manufacturing process. In fact, it is known that the first generations of GFRP reinforcing bars presented several defects. However, the

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bridge sample does not show any further delamination or debonding as illustrated on micrograph 4.2f. Crowchild Bridge sample micrographs are presented in Figure 4.3. Although, in this case, there is no reference sample, the same conclusions may be drawn. No signs of interfacial, matrix, or fibre degradation have been detected and the adhesion between the fibres and the matrix remains very good. The micrographs presented on the left correspond to the reference sample, whereas those on the right correspond to the GFRP rod taken from Hall’s Harbour core sample. Figures 4.4a and 4.4b show the outside part of the rods. Silica particles embedded in the coating are not strongly bonded to the resin in both cases because of the presence of a clearly visible space. Some of the fibres closed to the surface are also debonding, whereas those located more deeply present a better adhesion to the matrix. This observation is clearly confirmed in Figures 4.4c and 4.4d, where the fibres in contact with the coating at the left of the micrographs are debonded and fractured, whereas those further from the surface are not damaged. No significant difference may be observed between the two samples. The thickness of the reference sample coating was more than 200 microns all over the perimeter of the bar. However, the coating of Hall’s Harbour sample was not uniform and was very thin in some areas (less than 50-100 microns). Severe fractures or a stronger delamination between fibres and matrix were observed in the areas where the coating was very thin, whereas the fibres below the reference sample coating and Hall’s Harbour sample areas presenting a thick coating, were much less affected (Figures 4.4e-4.4f). The adhesion between fibres and resin is one of the most critical factors in GFRP composites since the strength and residual properties of the material highly depend on the this interface. The cohesion of the two components of the material is essential to provide good properties and phenomena such as debonding, delamination, and microcraking must be avoid. Figures 4.5a to 4.5f shows the state of fibre/matrix interface at high magnification just below the coating. A 0.2-0.3 micron space can be observed between the resin and the fibres. This debonding occurs on almost the whole perimeter of the fibres. Similar micrographs have been taken more deeply in the rods (Figures 4.5g and 4.5.h). At this level, the delamination phenomena is much less important and the adhesion of the fibres remains very good in both samples. Figure 4.6 presents typical micrographs, at different magnifications, of the cross section of the GFRP grid sample extracted from Waterloo Creek Bridge. Micrographs 4.6a and 4.6b, taken at low magnifications, show overall views of the material. It can be observed that the fibre distribution is not fairly uniform within the resin matrix. However, no defects or voids are observed. This shows that the glass fibres were properly wetted and the resin is mobile enough to fill all the gaps during the manufacturing processing. Micrographs 4.6c and 4.6d, taken at higher magnifications, show that the integrity of the resin is good since no cracking is observed. However, the micrographs taken at the highest magnifications (X2000 and X5000) reveals that the adhesion of the resin to the fibres is not as good as it should be since gaps do exist at the interface (Micrographs 4.6e and 4.6f). To investigate and consider these observations valid for the whole sample, several views were taken at different locations in the sample. It should be noted that no reference sample was available for comparison. Consequently, it is not possible to draw any conclusion about the causes of the debonding phenomena. This latter can stem from the manufacturing process, the field service, or the sample preparation process (cutting and polishing) for the SEM analysis. Figure 4.7 presents typical micrographs, at different magnifications, of the cross section of the GFRP grid sample extracted from Chatham Bridge. Micrographs 4.7a and 4.7b show overall views of the material. It is clear that the distribution of the fibres is not uniform within the resin matrix.

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However, no voids or air bubble are observed. This shows that the glass fibres were properly wetted and the resin is mobile enough to fill all the gaps during the manufacturing processing. Micrographs 4.7c and 4.7d, taken at higher magnifications, show that the integrity of the resin is excellent since no matrix cracking is detected. Finally, the micrograph taken at highest magnification reveals that the adhesion of the resin to the fibres is very good since no gaps are observed at the resin-fibre interface (Micrographs 4.7e and 4.7f). To investigate and consider these observations valid for the whole sample, several views were taken at different locations in the sample. It has to be noted that no reference sample was available for comparison. 4.4. Conclusions The SEM analysis of Joffre and Hall’s Harbour samples does not show any significant change as compared to the reference. In both cases, the different components of the composites (fibres, resin, and interface) present the same appearance: The resin does not present cracks or micro-cracks; the fibres are not fractured and properly adhere to the matrix. For Hall’s Harbour sample, the only part which is damaged is the very thin area located just below the coating. In this 100-200 microns thick area, fibres are debonding and microcrackings may occur, specially where the coating is very thin or inexistent. As compared to the diameter of the rods, the thickness of this area is infinitesimal. Moreover, the degradation of this zone can be due to the method of preparation since it is also observed with the reference sample. The service conditions have not affected the integrity or the structure of the GFRP materials in any way. For Crowchild and Chatham Bridges (no reference samples are available), the SEM micrographs show that the integrity of the GFRP composite is very good and that no cracking, microcraking, or debonding occurred in the samples during its service life. For Waterloo Creek Bridge (no reference samples are available), the SEM micrographs show that the integrity of the resin matrix of the GFRP composite grid is very good. However, a debonding phenomena has been observed within the sample. The cause of this delamination is unknown. Generally, the SEM analysis does not show any significant change in the core samples extracted from the five bridges and the state of the GFRP rods or grids seems to be unchanged as compared to the reference samples, when available. Other analysis have to be performed to confirm these results.

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Reference Extracted sample

X50 a) b)

X500 c) d)

X750 e) f) Figure 4.1. Micrographs of the cross sections of a 9-mm diameter GFRP bar extracted from Joffre

Bridge compared to the reference.

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Reference Extracted sample

X1000 g) h)

X5000 i) j)

Figure 4.1: Micrographs of the cross sections of a 9-mm diameter GFRP bar extracted from

Joffre Bridge compared to the reference (cont.).

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Reference Extracted sample

X750 a) b)

X1000 c) d)

X5000 e) f)

Figure 4.2. Micrographs of the cross section of a 16-mm diameter GFRP bar extracted from Joffre Bridge compared to the reference.

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X200 a) b)

X750 c) d)

X5000 e) f)

Figure 4.3. Micrographs of the cross section of a GFRP bar extracted from Crowchild Bridge

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Reference Extracted sample

200X a) Coating and fibres under the surface b) Coating and fibres under the surface

X500 c) Near the coating d) Near the coating

X750 e) Below a thick coating f) Below a thin coating

Figure 4.4: Micrographs of the cross sections of a GFRP (ISORODTM) bar extracted from Hall’s

Harbour Bridge compared to the reference (X200 to X750).

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X1000 a) Close to the surface (thick coating) b) Close to the surface (thin coating)

X1000 c) 200 ìm below the coating d) Close to the surface (thick coating)

X5000 e) 100 microns below the coating f) 100 microns below the coating

Figure 4.5: Micrographs of the cross sections of a GFRP (ISORODTM) bar extracted from Hall’s

Harbour Bridge compared to the reference (X1000 to X5000).

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X5000 g) 500 microns below the coating h) 500 microns below the coating

Figure 4.5: Micrographs of the cross sections of a GFRP (ISORODTM) bar extracted from Hall’s Harbour Bridge compared to the reference (X1000 to X5000) (cont.).

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a) X50 b) X200

c) X750 d) X1000

e) X2000 f) X5000

Figure 4.6: Micrographs of the cross sections of the GFRP grid extracted from Waterloo Creek Bridge

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a) X50 b) X200

c) X500 d) X750

e) X1000 f) X5000

Figure 4.7: Micrographs of the cross sections of the GFRP grid extracted from Chatham Bridge

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5. DIFFERENTIAL SCANNING CALORIMETRY (DSC) ANALYSIS 5.1. Introduction The mechanical properties of FRP composite materials are linked to their thermal properties. One of the most important thermal parameter is the glass transition temperature (Tg). Tg is related to the viscoelastic properties of the material and is defined as the temperature where a polymer in a vitreous state becomes viscoelastic. At this temperature, mechanical properties decrease because of the polymeric phase softening. The degradation of FRP composite materials may affect the fibres, the resin matrix, or the interface between them. In the case of GFRP composite materials embedded in concrete, polymer (resin matrix) degradation may decrease Tg if polymeric chains are ruptured, such as through an hydrolysis reaction occurring in the presence of alkalis. On the other hand, the presence of water may also decrease Tg since it may have a plasticizing effect. In this study, Tg has been measured by calorimetry (DSC). DSC also detects the post-curing (also called post-polymerisation/crosslinking) phenomenon, which occurs when a material has not been sufficiently cured during the manufacturing process. This section of the report includes the DSC analyses conducted on core samples extracted from the five bridges under consideration. 5.2. Experimental Procedure Small pieces (20-30 mg) of GFRP materials were cut from the GFRP reinforcing bars. The coating layer of the bars was discarded. The measurements were conducted under air on a TA DSC apparatus, model Q10 between 40 and 200°C at a heating rate of 10°C/min. Two scans were obtained for each sample for comparison purpose. 5.3. Results Table 5.1 presents the obtained results for the different FRP materials. The results for the available reference samples are also included. Figures 5.1a and 5.1b show the results obtained for the large diameter (15.9 mm) bars (both reference and field samples) from Joffre Bridge. No significant differences were observed between the two samples, which means that the service conditions did not affect the thermal properties of the material. However, it should be noted that the Tg of the material (108°C), even fully cured, was very low compared to other materials. Moreover, a small post-curing phenomena occurred at 180°C during the first heating scan. Nevertheless, the magnitude of this post-curing was too small to have any influence on Tg. The small diameter bar (9 mm) samples, extracted from Joffre Bridge, have not been affected by the service conditions since their Tg did not significantly change compared to the reference sample (123-128°C) as shown in Figures 5.2a and 5.2b. The FRP material was fully cured and the thermograms obtained for the field sample were similar to those obtained for the reference sample. It should be noted that there were no reference samples available for Crowchild, Waterloo Creek, and Chatham Bridges. Consequently, the effect of service conditions on these GFRP composites cannot really be evaluated since no comparison was possible. The first and second heating run conducted on FRP sample extracted from Crowchild Bridge composite did not present any change since their shape and Tg values are very close (Figures 5.3). Therefore, it can be concluded that the material was fully cured. The reference bar sample of Hall’s Harbour was not fully cured since the glass transition temperature was equal to 105°C and a large peak was observed at 160°C (Figures 5.4a). This peak was due to the post-polymerization of the resin. The enthalpy of polymerization was also calculated considering that the material contains 25.3% resin. The calculated value of the enthalpy was equal to 28 kJ/g of resin. Knowing that the enthalpy of polymerization for a full cured vinyl ester material is equal to 250 kJ/g (±15%), it can be concluded that the degree of polymerization of

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the material stored during several years was 85-90%. Following the first heating run, the resin was totally crosslinked and the Tg reached 125°C. However, the sample extracted from the bridge did not show any significant change between the first and second runs (Figure 5.4b). This means that the sample has been post-cured during the time it was embedded in the concrete structure. Consequently, the Tg was almost similar before and after the first heating run (123-125°C). Since this sample was located near to the surface, it seems that the summer temperatures have completed the crosslinking mechanism. The temperature at which the reference sample was kept (room temperature around 23°C) was too low to initiate the post-curing phenomenon. A similar defect to that of Crowchild affects the GFRP grid sample extracted from the Waterloo Creek Bridge since the Tg obtained during the first scan was 40°C lower than that obtained during the second run (78°C versus 117°C) (Figures 5.5). This low Tg is related to an important post-curing mechanism at 115°C. Processing defects have affected the polymerisation/crosslinking of the two GFRP grids studied in this work. In this case, the exposure to summer temperatures did not lead to a post-curing reaction. This is also the case, to a less extend, for the GFRP grid sample extracted from Chatham Bridge since the Tg obtained for the first and second runs were equal to 98 and 116°C, respectively (Figures 5.6). A small post-curing (polymerization) peak is also observed around 135°C. Table 5.1: Calorimetry Results for GFRP Materials: Glass Transition Temperatures (Tg) and

Enthalpy and Temperature of Polymerization.

Sample Tg (1st run) (°C)

Tg (2nd run)(°C)

Enthalpy of polymerization (post cure;

1st run) (J/g)

Temperature of polymerization (post cure; 1st run) (°C)

JBB (Ref.) (15 mm) 107 108 small 180 JBB (15 mm) 107 108 small 180

JBS (Ref.) (9 mm) 123 126 - - JBS (9 mm) 127 128 negligible -

CB 126 129 - - HH (Ref.) 105 125 28 160

HH 123 125 negligible negligible WC 78 117 14 115 CHB 98 116 small 135

5.4. Conclusion DSC measurements show that several GFRP composites (reinforcing bars and grids) used in the concrete structures were not fully cured. In the case of Hall’s Harbour, this processing (curing) defect has been “repaired” since a post-curing occurred during the service time. Large diameter bars (15.9 mm) extracted from Joffre Bridge present a low Tg because of the formulation/processing of the material. However, these Tgs are not affected by the service conditions. In fact, the three FRP bars which could be compared to reference samples (one from Hall’s Harbour and two from Joffre Bridge) did not show any thermal property “loss”. No sign of chemical or polymer structure degradation was detected. Also, no irreversible degradation phenomenon was observed since the Tgs measured during the second heating run reached the reference or the expected values.

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(a) Reference sample

(b) Field sample

Figure 5.1: DSC results for the large diameter (15.9 mm) GFRP bars from Joffre Bridge

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(a) Reference sample

(b) Field sample

Figure 5.2: DSC results for the small diameter (9.5 mm) GFRP bars from Joffre Bridge

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Figure 5.3: DSC results for the GFRP bar sample from Crowchild Bridge

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(a) Reference sample

(b) Field sample

Figure 5.4: DSC results for the GFRP bar sample from Hall’s Harbour Bridge

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Figure 5.5: DSC results for the GFRP bar sample from Waterloo Creek Bridge

Figure 5.6: DSC results for the GFRP bar sample from Chatham Bridge

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6. INFRARED ANALYSIS 6.1. Introduction The presence of alkaline ions may induce a degradation reaction of ester groups located on the backbone of the polymeric chain of the FRP composite resin. This chemical reaction, called hydrolysis, breaks the resin molecules, leading to the formation of hydroxyl groups such as alcohols or carboxylic acids. It affects the structure of the polymer and weakens the material, which will eventually be unable to play its role in the transfer of stresses between the fibres. One way to determine if a hydrolysis reaction occurs in the matrix is to measure the amount of hydroxyl groups present in the composite material by Fourier Transform Infrared Spectroscopy (FTIR). This is carried out through comparing the spectrum obtained with a material extracted from a core to a reference spectrum. This section of the report includes the FTIR analyses conducted on core samples extracted from two bridges: Joffre and Hall's Harbour Bridges. In this work, three different samples were analysed, two from Joffre Bridge (including GFRP ribbed-deformed C-BARTM rods; 9-mm diameter bent bars, and 16-mm diameter bars) and one from Hall’s Harbour Bridge (including GFRP sand-coated ISORODTM bar, 16-mm diameter bars). The core samples extracted from the other three bridges (Crowchild, Waterloo Creek, and Chatham Bridges) could not be analyzed since no reference samples were available. 6.2. Method of preparation The core samples were crushed into small pieces and then ground into powder. The obtained powder was placed in an oven at 105°C overnight to remove any trace of water that could affect the measurement. The powder was composed of short pieces of glass fibres, coarse material and fine powder. The finest part of the powder, which was rich in resin, has been mixed with dry FTIR grade potassium bromide powder and the mixture was then pressed to obtain KBr pellets. The analysis has been conducted on a Perkin Elmer 1000pc spectrophotometer taking a pure KBr spectrum as reference. 6.3. Results The measurement of the relative amount of hydroxyl groups in the sample was obtained by determining the ratio between the maximum of the band corresponding to the hydroxyl groups at 3430 cm-1 and those of the band corresponding to the carbon-hydrogen groups at 2900 cm-1. The hydroxyl peak was located at the left of the spectrum and the C-H peak at the right. The C-H content was considered as constant. Since the vinyl ester resins “naturally” contain hydroxyl groups, all the spectra present a strong absorbance band in the hydroxyl region. The different spectra are presented in Figure 6.1. These spectra were typical but small changes have been observed for the same samples because the studied powder was not homogenous. Consequently, the small amounts of powder, which were mixed to the KBr powder, may have different contents in matrix resin. A larger or smaller content in glass fibres and/or coating may affect the intensity and the shape of the absorbance bands. Table 6.1 presents the content ratio of OH / CH for the three samples under consideration. The measurements show that the intensity of the hydroxyl band has not been increased for the three samples, which means that there is no significant hydrolysis reaction in the samples extracted from the corresponding structures. However, it can be noted that the intensity of the shoulder at the left of the hydroxyl band at 3530 cm-1 for the 9-mm diameter bar core sample extracted from Joffre Bridge (Figure 6.1.A2) is stronger than that for the reference sample (Figure 6.1.A1). This increase may be due to the formation of hydroxyl groups through a hydrolysis reaction or to

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different proportions of matrix resin, glass fibres, and/or coating. Nevertheless, the magnitude of this change is rather small. 6.4. Conclusion The FTIR analysis has not shown any significant or important changes in the intensity of the main hydroxyl band for the three studied samples. A small change corresponding to a small increase of OH groups was detected for one of the samples (Joffre Bridge, 9-mm diameter bars – GFRP C-BARTM bent bars). The reaction of hydrolysis has not occurred significantly for at least two of the samples (Hall’s Harbour and Joffre Bridges, 16-mm diameter GFRP bars – C-BARTM and ISORODTM). For one of the sample, it is possible that a small degradation exists even if the observed change might be due to the sampling and not to a chemical reaction, such as hydrolysis. Table 6.1: Ratio of OH/CH for reference and core samples.

Structure Reference Core sample

Joffre Bridge, 9-mm diameter bar (GFRP, C-BARTM) 0.64 0.60 Joffre Bridge, 16-mm diameter bar (GFRP, C-BARTM) 0.50 0.46 Hall’s Harbour, 16-mm diameter bar (GFRP, ISORODTM) 0.97 0.91

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A1 A2

B1 B2

C1 C2 Figure 6.1. FTIR Spectra for GFRP bars: (A) Joffre Bridge, 9-mm diameter bar; (B) Joffre Bridge,

16-mm diameter bar; (C) Hall’s Harbour. Number 1 for Reference and number 2 for core samples.

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7. X RAY ANALYSIS OF CONCRETE SAMPLES 7.1. Introduction The degradation of composite materials may lead to the formation of low molecular weight products, which can diffuse out of the rods/grids. Therefore, the embedded GFRP materials could affect the concrete environment since small diffused molecules could react with concrete and modify its chemical composition or structure. X-ray diffraction measurements have been conducted to detect potential changes between the structure of the concrete samples located close to the GFRP materials and that of the reference samples located far from the GFRP reinforcement. This section of the report includes the X-Ray diffraction analyses conducted on core samples extracted from the five bridges under consideration. 7.2. Method of preparation Concrete samples have been extracted from core samples using a concrete saw. The samples called “close” refer to the material in contact with the GFRP materials, whereas the “far” samples (i.e. reference samples) were located at least 5 cm far from the composite surface. After having removed the coarse aggregates, the concrete samples were crushed with an electrical grinder. The final step consisted of a very fine manual grinding using an agate mortar to obtained sufficiently fine particles to avoid preferred orientations, which could affect the results. The measurements have been performed on a Panalytical X-Ray diffractometer, model X’Pert Pro implementing the following experimental parameters: Tension, 45 kV; Current, 40 mA; Goniometer, Theta/Theta; Soller Slit, 0.04 rad.; and Mask, 10 mm. The duration of each analysis was one hour. Generally, the intensity of the peaks is low (less than 500-1000 counts), which shows that the materials are highly amorphous. Consequently, it is more difficult to interpret the data and identify the different crystalline structures present in the samples. 7.3 Results Once hydrated, cement is mainly constituted of calcium hydroxide (Portlandite) and silicon oxide. Other metal oxides are present in lower ratios (aluminium, iron, magnesium, sodium, and potassium oxides). Cement also contains few amount of different salts such as calcite (calcium carbonate). All these compounds are generally combined in different ways to form more or less hydrated minerals such as ettringite (Ca/Al silicate). Concrete also contains aggregates. Fine aggregates are constituted of sand (silicon oxide/quartz), whereas coarse aggregates may be calcareous, quartzitic, or granitic. Calcite (calcium carbonate) and dolomite (calcium/magnesium carbonate) are calcareous aggregates, whereas amesite (Mg/Al silicate), muscovite (K/Al fluorosilicate), albite, and anorthite are present in granitic aggregates. It has to be noted that calcium carbonate can be also produced by the carbonation of calcium hydroxide/oxide. Consequently, the diffraction diagram of a concrete will show peaks related to cement paste and aggregates. Even if coarse aggregates have been removed before sample grinding, small amounts may still be present in the analysed sample. Therefore, the relative amount of aggregate may be different for two samples taken from the same concrete structure. 7.3.1. Aggregates The upper part of Figure 7.1 shows the diffraction diagrams of the two samples taken from Hall’s Harbour cores. HH close (in black) and HH far (in blue) are the samples close to and far from the GFRP material, respectively. The only large peaks correspond to quartz (20.85; 26.65; 67.7-68.3), whereas small peaks, characteristic of mica structure, correspond to amesite (12.59; 25.33) and muscovite (8.88; 34.93; 45.47) structures. However, no important peak related to calcite or

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dolomite are detected, which shows that the aggregate is not calcareous. Moreover, no feldspar family mineral is observed. Consequently, the coarse aggregates are constituted of quartz. Small amounts of granite may also be present in the concrete. Figure 7.2 shows the results obtained with Joffre Bridge samples. As for Hall’s Harbour samples, the largest peak observed is due to the presence of quartz (26.65). However, important peaks characteristic of calcite and dolomite (29.41; 30.94) show that the aggregate also contains calcareous aggregates. As the fine aggregate (the sand) is constituted of quartz, the coarse aggregates must be dolomitic lime, i.e. a mixture of calcite and dolomite. The aggregates used in Crowchild Bridge are of the same type than those present in Joffre Bridge since the same peaks are observed (Figure 7.3). However, the intensity of the peak related to dolomite is higher (30.94). Consequently, the coarse aggregate is a dolomitic lime containing a high dolomite content. For Chatham Bridge, the calcareous aggregate ratio is higher than for the two previous structures since the two largest peaks are due to dolomite and calcite (29.41; 30.94) (Figure 7.4). The amount of quartz is much lower than with the three previous concretes. This concrete contains less sand than the others and its coarse aggregate is dolomitic lime. Waterloo Creek samples are different since their diffraction diagrams show a strong peak at 28.02 (Figure 7.5). This peak can be related to a feldspar family mineral, such as albite. It could also be anorthite, which is a very similar mineral. Small amounts of mica family minerals, such as amesite and muscovite, are detected. However, the content of calcite and dolomite is very low. Strong peaks related to quartz are observed (20.85; 26.65). The simultaneous presence of quartz, mica, and feldspar minerals shows that the coarse aggregate is constituted of granite. 7.3.2. Presence of alkalis For every type of concrete, the superimposition of the two diffraction diagrams does not reveal any modification due to changes in the structure or formulation of the crystalline phase of the material since no peak appears or disappears. Only the intensities of some aggregate related peaks are observed. Consequently, it may be assumed that there is no evidence that the presence of GFRP materials has affected the concrete. It is well known that GFRP materials may be sensitive to the presence of alkalis. Therefore, the degree of alkalinity of the surrounding concrete may eventually affects the long-term chemical resistance of these materials. The relative amounts of calcium hydroxide in the crystalline phase of concretes can be evaluated from the intensity of the peaks related to Portlandite, a mineral constituted of calcium hydroxyde. These peaks are located at 18.01, 34.10, 47.12, and 59.81. Three concretes (Chatham Bridge, Joffre Bridge, and Hall’s Harbour) present low Portlandite contents (less than 300 counts for the largest peak at 34.10), whereas two concretes contain higher Portlandite quantities (Crowchild Bridge and Waterloo Creek; more than 500 counts). From these results, it can be concluded that the degree of alkalinity of Crowchild Bridge and Waterloo Creek concretes could be higher. It has to be noted that these assumptions are only made from the crystalline phase of the concrete and that X ray diffraction analysis does not take into account the main phase, i.e the amorphous phase.

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Figure 7.1: X Ray Diffraction Diagrams of Hall’s Harbour Concrete Samples.

Figure 7.2: X Ray Diffraction Diagrams of Joffre Bridge Concrete Samples.

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Figure 7.3: X Ray Diffraction Diagrams of Crowchild Bridge Concrete Samples.

Figure 7.4: X Ray Diffraction Diagrams of Chatham Bridge Concrete Samples.

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Figure 7.5: X Ray Diffraction Diagrams of Waterloo Creek Concrete Samples.

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8. CONCLUSIONS The objective of this work is to determine the effect of natural ageing (in the field) on several GFRP materials used as main reinforcement in five concrete bridges in Canada. These structures are: Joffre Bridge (Québec), Crowchild Bridge (Alberta), Hall’s Harbour Bridge (Nova Scotia), Waterloo Creek Bridge (British Columbia), and Chatham Bridge (Ontario). Microscopic and physico-chemical analysis have been conducted on core samples (concrete cylinders including GFRP composite materials) extracted from these concrete structures to investigate the degradation in the GFRP material, concrete, and the interface between the GFRP material and concrete, if any. In addition, for comparison purposes, GFRP reference samples (stored in normal environment at room temperature) were also provided for two bridges only; Joffre and Hall’s Harbour Bridges. Based on the results of this study, the following conclusions may be drawn:

1. The adhesion of concrete to the GFRP reinforcement has not been affected with time under field conditions as may be observed from optical microscopy pictures of core samples from the five concrete bridges under consideration. No significant free spaces or voids were detected at the concrete/GFRP material interface.

2. The various GFRP materials were examined by Scanning Electronic Microscopy and were

compared to reference samples when available. This was the case for the GFRP rods from Joffre Bridge (2 types of C-BARTM, bent and straight bars) and Hall’s Harbour (ISORODTM). The different components of the reinforcements (fibres, resin, and interface) did not show any significant changes. The resin and the glass fibres did not show any sign of deterioration, such as microcracking or corrosion. In addition, the contact at the glass fibres/resin interface remained intimate since no delamination or debonding was detected. No reference samples from Crowchild Bridge (GFRP rod) or Waterloo Creek and Chatham Bridge (GFRP grids) were available. However, the analysis of these materials extracted from the core samples showed that no degradation seems to have affected the Chatham and Crowchild Bridges reinforcements. However, a certain debonding has been observed at the GF/resin interface of Waterloo Creek GFRP grid. This debonding was maybe already exist in the GFRP material before installation in the field and can be due to a process defect.

3. The measurements of the glass transition temperature determined by Differential Scanning

Calorimetry did not show any non reversible degradation, which means that no important hydrolysis reaction occurred during the service. However, it has been observed that some GFRP samples (Hall’s Harbour, Waterloo Creek, and Chatham Bridges) had not been fully cured during the manufacturing process.

4. Fourier Transformed Infrared Spectra were obtained for the core samples extracted from

Joffre and the Hall’s Harbour Bridges and compared to reference samples. No changes were observed for the 16 mm-diameter GFRP bar samples. An insignificant increase of the number of hydroxyl groups, which may be related to an hydrolysis reaction, has been noted for Joffre Bridge 9 mm diameter GFRP sample. However, this low increasing can be due to the sampling or the material heterogeneity, and not to a chemical degradation.

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5. The X-Ray analysis has not shown any significant changes in the diffraction pattern of the concrete in contact with the GFRP materials. This shows that no reaction occurred because of the diffusion of compounds from the reinforcements through the crystalline phase of the concrete.

Consequently, the different analysis performed in this work have demonstrated that the GFRP materials have not been negatively affected by the service conditions. Moreover, it has not been shown that the small changes observed in some cases for a few samples is due to a degradation in the field because they could be caused by a processing defect, the inhomogeneity of the material or a sampling problem.

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