Durability of GFRP Pultruded Profiles Made of Vinylester Resin

7/24/2019 Durability of GFRP Pultruded Profiles Made of Vinylester Resin

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Durability of GFRP Pultruded Profiles made of Vinylester

Resin

Joo Pedro Giro Meireles de Sousa

M.Sc. Dissertation Extended Abstract

October 2011


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DURABILITY OF GFRP PULTRUDED PROFILES MADE OF

VINYLESTER RESIN

Joo Pedro Giro Meireles de Sousa

Summary: This paper presents new findings of an ongoing research project developed in

partnership byInstituto Superior Tcnico andLaboratrio Nacional de Engenharia Civil(IST-

LNEC). It essentially focuses on the deterioration of glass fiber reinforced polymer (GRFP)

made of vinylester resin and E-glass fibers, when exposed to different environmental agents.

Keywords:GFRP; E-Glass; Vinylester; Durability; Ageing environments; Experimental tests

1 INTRODUCTION

The need of higher construction speed in civil engineering applications, together with the

durability problems experienced by traditional materials, such as steel and reinforced concrete,

have been fostering the development of new structural solutions [1]. The structural use of glass

fiber reinforced polymer (GFRP) as pultruded profiles in civil engineering applications has

grown significantly in the last two decades. This is due to their several advantages when

compared to traditional materials, namely, high strength, lightness, good insulation properties

and resistance to corrosion [2]. Until recently, the effect of fluids on composites has often been

considered to be of secondary importance in glass-fiber reinforced polymers because, to date,

the detrimental effects have been overcome by significant overdesign [3,4]. However, the use of

inordinately high factors of safety on this account cannot be easily justified and there is a urgent

need to deepen the understanding of mechanisms leading to moisture-associated degradation,

especially as related to vinylester systems for which there is still a significant lack of data.

Together with this fact, the relatively low elasticity modulus, a brittle behaviour and material

costs (which are still not competitive for mainstream applications) are delaying the widespread

use of GFRP profiles [1,5].

This paper presents results of an ongoing experimental research on the physical, chemical,

aesthetical and mechanical changes suffered by GFRP pultruded profiles made of vinylester

resin and E-glass fibers, following accelerated exposure to moisture, water as well as natural

ageing. This study also aims to understand the influence of moderate temperature cured systems

(dried systems) in order to access reversibility effects, as well as coating of unprotected

specimen parts (isolated systems) into deterioration of the GFRP profiles, measured by the same

changes as described above.


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2 MATERIALS

The material under study was obtained from one commercial GFRP pultruded tubular profile

(50 mm x 50 mm, thickness of 5 mm, with common usage as part of ladders and handrails,

produced byALTO Perfis Pultrudidos Lda, Portugal). This material consists of alternate layers

of unidirectional E-glass fiber rovings and strand mats embedded in vinylester resin.

3 METHODS

3.1 Exposure environments

In order to study the potential degradation of the GFRP profiles in typical civil engineering

applications environments, test specimens were subjected to the exposure conditions described

in Table 1. The latter also indicates the batches of aged material already tested.

Table 1Exposure aging conditions.

Type of exposure Duration Conditions

Group I (represents the ongoing study related to prior researches)

Immersion in

demineralised water

(W-20)

3,6,9,

12,18,24 months (a)

Temperatures: 20 (2) C,

40 (1) C e 60 (1) C(W-40)

(W-60)

Immersion in salt-

water

(S-20) Composition: 35g/l NaCl

Temperatures 20 (2) C,

40 (1) C e 60 (1) C

(S-40)

(S-60)

Natural Environment (NE) 1, 2, 5, 10 years (b)

In the roof of the LNEC building,

where temperature, relative

humidity and UV radiation are

continuously monitored

Group II (represents the effects of isolated (I) and dried(D) systems)

Immersion in

demineralised water

(WI-20)

6, 12, 18 months (c)Temperatures: 20 (2) C,

40 (1) C

(WI-40)

(WD-20)

(WD-40)

Continuous

Condensation

(CCI-40)6, 12, 18 months (c)

Temperatures: 40 (2) C

Relative humidity: 100%(CCD-40)

Batches of aged material previously tested: (a) 3, 6 and 9 months [6,7].

Batches of aged material tested in this study: (a) 12, 18 and 24 months; (b) 1 and 2 years;

(c) 6 and 12 months

3.2 Experimental procedures

Before exposure, Group II batches were prepared using the following techniques:


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(i) Isolated systems: unprotected specimen parts (namely its side parts) derived from their

cut and preparation. Therefore, the epoxy resin Icosit K 101 N provided by Sika was

applied and cured one week at 50 C onto those unprotected parts.

(ii) Dried systems: test specimens were subjected to moderate temperature cure, until no

significant mass change was reported according to ASTM D 5229 standard [8].

After exposure to the different ageing conditions described in Table 1, the aged batches were

subjected to the following characterization techniques:

(i) Sorption behaviour:Mass changes for the control specimens (with similar geometry to

that of specimens used in dynamic mechanical analysis) were recorded using an

electronic scale, removing them periodically from immersion and continuous

condensation exposures. To complement this data, apparent diffusion coefficients were

calculated assumingFickiansorption behaviour.

(ii) Aesthetical characterization: Samples aged at Natural Environment conditions were

tested in comparison with unaged and QUV accelerated tested material:

Colour changes: specimens with similar geometry to that used in tensile

properties were tested in accordance with parts 1 and 2 of ISO 7724 standard

[9,10], using the colour system CIE 1976 [9]. Tests were carried out using a

Macbeth Coloreye 3000colorimeter.

Gloss: specimens with similar geometry to the one used in tensile properties weretested in accordance to ISO 2813 standard [11]. 20 , 60 and 85 incidence

angles were measured withNovo-Gloss Statistical Glossmeter.

(iii) Dynamic mechanical analysis (DMA): DMA technique has been used to analyse the

viscoelastic response of materials such as the GFRP, as well as to assess the glass

transition temperature (), in accordance with part 1 and 5 of ISO 6721 standard [12,13].

Three-point bending type clamp specimens with 5 x 15 x 60 mm were tested at a constant

frequency of 1 Hz and strain amplitude of 15 m, using a Q800model of TA Instruments.

The analyses were conducted from room temperature up to 200 C, at a rate of 2 C/min.

Three replicates were tested for each duration and ageing condition.

(iv) Mechanical behaviour: Five samples for each duration of ageing condition were

submitted to mechanical tests in the longitudinal direction:

Flexural properties: three-point bending flexural tests were performed according

to ISO 14125 standard [14] in rectangular test specimens with 5 x 15 x 150 mm

in a 100 mm span. Tests were carried out at a loading rate of about 2 mm/min,

using a system from Seidner Form Test, constituted by a hydraulic press with a

10 kN load capacity.


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Tensile properties: tensile tests were conducted according to parts 1 and 4 of ISO

527 standard [15,16] in rectangular test specimens with 5 x 25 x 300 mm, without

end tabs. Tests were carried out in an Instronuniversal testing machine with a

load capacity of 100 kN at a 2 mm/min loading rate.

Shear properties: interlaminar shear tests were carried out in accordance with

ASTM D2344 standard [18] in rectangular test specimens with 5 x 15 x 30 mm in

a 20 mm span. Tests were carried out at a loading rate of 1 mm/min, with the

Seidner Form Testsystem.

Excluding the study of the mass changes, after being removed from the different exposure

environments and prior to further testing, specimens were placed inside polyethylene bags.

These were hermetically closed, trying to maintain the moisture content of the material, and

then placed inside a room with temperature controlled at 20 (2) C. Prior to testing, specimens

were removed from the polyethylene bags and immediately tested without any further

conditioning.

4 RESULTS AND DISCUSSION

4.1 Initial characterization

To fully understand the ongoing changes in the properties of the GFRP pultruded profiles,

results of their initial physical and mechanical characterization are listed in Table 2.

Table 2 - Physical-chemical properties of GFRP profiles (un-aged) [1].

Property Method Results

Glass fiber

content (%)Calcination 68,7 0,4

Density Immersion (g/cm3) 2,03 0,052

(C) DMA

Einitial

tan

98,6 7,0

126,9 2,3

Mechanical

properties

Flexuretu(MPa)

Et (GPa)

393 51

38,9 4,1

Tensionfu(MPa)

Ef (GPa)

537 73

28,4 3,4

Interlaminar

shearu(MPa) 39,2 4,2

With regard to the mechanical behaviour, in all characterization tests (tension, flexure and

interlaminar shear) the GFRP profile exhibited a well-defined linear elastic behaviour up to

failure, which is one of the main features of this material.


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4.2 Sorption behaviour

Figure 1 illustrates the mass changes that occurred during the ageing exposure to immersions

(both in demineralised and salt water) for each temperature (20 C, 40 C and 60 C). Figure 2

shows the evolution of the same characteristic considering fully (FI) and partially coated (I)

specimens compared with unprotected ones, in demineralised water and continuous

condensation, for each temperature (20 C and 40 C) in order to evaluate coating sorption

effects.

Figure 1Mass changes for different hygrothermal ageing conditions.

Figure 2Mass changes for coated specimens at different hygrothermal ageing conditions.

The overall results, in terms of maximum percentage weight gains and apparent diffusion

coefficient (D) are listed in Table 3. It should be noted that mass changes showed, roughly, a

Fickian response, with rates of mass uptake increasing with temperature, especially at a short

time, which are concordant with Karbhari and Zhang [18]. After 8700 hours saturation point has

been already achieved, however some mass reduction is noted at higher temperatures suggesting

post-cure effects, which were also noted by Liao et al.[19] although at an earlier point in time.

Moreover, for similar temperatures, mass uptakes of specimens immersed in salt water were

always lower compared to specimens immersed in demineralised water. Although mass changes

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Massc

hange

(%)

Time (h)

W-20

W-40

W-60

S-20

S-40

S-60

0,00

0,20

0,40

0,60

0,80

1,00

1,20

0 2000 4000 6000 8000

Massc

hange

(%)

Time (h)

WD-20

WI-20

WFI-20

WD-40

WI-40

WFI-40

CCD-40

CCI-40

CCFI-40


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were not as low as expected in coated specimens, possibly due to some previous saturation of

unprotected specimens, diffusion coefficient results indicate decreasing values as the protection

degree increases and therefore showing sorption retention by the protective epoxy. All these test

results are consistent with mass changes from other batches having a 2% variation, which points

out to the system reliability.

Table 3Maximum percentage weight gain and apparent diffusion coefficient.

Group I Group II

Environment Mm(%) D(x10-7

mm2/s) Environment Mm(%) D(x10

-7mm

2/s)

W-20 0,77 1,69 WD-20 0,64 11,1

W-40 0,64 1,22 WI-20 0,68 3,52

W-60 0,77 2,26 WFI-20 0,74 3,22

S-20 0,34 1,47 WD-40 1,04 2,70

S-40 0,31 1,65 WI-40 0,96 2,46

S-60 0,45 6,14 WFI-40 0,64 2,30

CCFI-40 0,77 2,67 CCD-40 0,44 5,55

CCI-40 0,91 3,00

4.3 Aesthetical characterization

4.3.1 Colour changes

Two years old natural ageing specimens were subjected to testing for aesthetical

characterization. Table 4 lists the values of colour space system coordinates including their

colour variation E*.

Table 4Values of colour space system coordinates after natural ageing.

Specimens L*

a*

b*

L* a

*b

* E

*

Unaged 74,15 -0,88 1,13 - - - -

NE (2 years old) 72,31 -1,70 7,94 -1,85 -0,82 6,82 7,11

These results show that there is a loss of coloration mainly due to the UV radiation. The values

of L*, a* and b* have shown that the material becomes more yellow (roughly 7,5% increase),which corresponds to significant colour changes, easily identifiable. These results can correlate

to QUV accelerated ageing (measured by Carreiro [6]), differing 1,4% when compared to 2000h

of ageing and showing significant changes after 2 years of exposure (as described also by

Bogner and Borja [20]).

4.3.2 Gloss

Gloss testing was made on the same specimens at 20 , 60 and 85 light incidence angles. The

results obtained are listed in Table 5.


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Table 5Gloss values for profiles after natural ageing.

Specimens SurfaceLight incidence angle

20 60 85

Unaged - 4,3 27,7 27,4

NE (2 years old) Sun 0,9 2,0 1,4Shade 3,7 21,2 19,6

All light incidence angles show significant gloss loss, especially to sun oriented surfaces which

only retained 7% at 60 after being exposed for two years. Comparing again with QUV

accelerated ageing values are nearly the same as the ones obtained by Carreiro [6] at 3000h of

exposure. Significant gloss loss is attained when exposed to prolonged UV radiations.

4.4 Dynamic mechanical analysis

Figures 3 and 4 plot Tgvariation (mean value and standard deviation) against time, representing

all ageing environments of Groups I and II, respectively.

Figure 3variation of Group I ageing conditions.

Figure 4variation of Group II ageing conditions.

Attained results through DMA analysis show that higher Tgloss is initially observed in higher

temperature environments. In addition, it is also possible that this exposure accelerates post-cure

110

115

120

125

130

135

140

145

0 4 8 12 16 20 24

Tg

(C

)

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

110

115

120

125

130

135

140

145

0 4 8 12 16 20 24

Tg

(

C)

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40


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phenomena, which are the most accentuated at W-60 environment. This was also suggested by

Chin et al. [21]. After two years of exposure, Group I environments results show little

difference between them, consisting of 5-7 C when compared to initial values. Additionally,

results show that demineralised immersions and salt-water environments cause similar changes

in Tg parameter. Lowest Tgvalues were noted at 9 months of exposure never decreasing more

than 10%. Group II environments show that in most of them Tgis likely susceptible to higher

temperature and moisture content. It is also noted that both moderate temperature cured systems

and protective coatings translate into a positive factor, since they attenuate the degrading

process resulting even in Tgregains (more highlighted on the dried state). Consequently, it is

suggested that moderate temperature cured systems helps to reach the post-cure status in a faster

way. Protective coating specimens presented different individual results compared to the other

environments, due to the different Tgof the epoxy coating.

4.5 Mechanical behaviour

4.5.1 Flexural properties

Results obtained from flexural tests, namely the flexural strength and modulus as a function of

time for the different exposure environments, are presented in Figures 5 to 8.

Figure 5Flexural Strength of Group I ageing conditions.

Results show an overall tendency of flexural strength and modulus degradation over time.

However, there are signs of post-cure effects, resulting in property gain, consistent with

moisture sorption mass reductions. Salt immersed environments tend to accentuate post-cure

effects. All Group I environments show significant flexural strength loss after two years of

exposure (apart from natural ageing which caused negligible loss).

200

300

400

500

600

0 4 8 12 16 20 24

Flexura

lStrength

[MPa

]

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

NE


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Figure 6Flexural Strength of Group II ageing conditions.

Figure 7Flexural Modulus of Group I ageing conditions.

Figure 8Flexural Modulus of Group II ageing conditions.

These losses vary between 17,8 % (S-20) and 47,7% (W-60). Both higher temperatures and

moisture potentiate flexural strength decrease and salt water has less influence than

demineralised water. The latter have been also noted by Liao et al. [19]. Group I flexural

modulus show its greatest losses at 12 months of exposure, where W-60 dropped 45,4%,

experiencing a recovery process afterwards. Group II environments show that coated systems

200

300

400

500

600

0 4 8 12 16 20 24

Flexura

lS

trength

[MPa

]

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40

10

15

20

25

30

0 4 8 12 16 20 24

Flexura

lMo

du

lus

[GPa

]

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

NE

10

15

20

25

30

0 4 8 12 16 20 24

Flexura

lMo

du

lus

[GPa

]

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40


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experience greater flexural strength loss at 12 months than on cured systems and nearly the

same flexural modulus. Compared with Group I, only slight differences are found, presenting

slightly less mechanical deterioration.

4.5.2

Tensile properties

Results obtained from tensile tests, namely the tensile strength and modulus as a function of

time for different exposure environments, are presented in Figures 9 to 12.

Figure 9Tensile Strength of Group I ageing conditions.

Figure 10Tensile Strength of Group II ageing conditions.

As in flexural properties, results show an overall tendency of tensile strength and modulus

degradation over time. The same post-cure related gains are noticeable especially in Group I

lower temperature environments. The biggest tensile strength reductions are shown at higher

temperatures with a 38,1% loss in W-60 environment. Two years of exposure immersion in

demineralized water shows bigger deterioration effects when compared to salt water

environments.

200

250

300

350

400

450

0 4 8 12 16 20 24

Tensi

leStrngth

[MPa

]

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

NE

300

350

400

450

500

0 4 8 12 16 20 24

TensileStrngth

[MPa

]

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40


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Figure 11Tensile Modulus of Group I ageing conditions.

Figure 12Tensile Modulus of Group II ageing conditions.

Natural ageing specimens show only 3,3% loss of tensile strength after one year of exposure.

Tensile modulus show some initial oscillations, maintaining a decrease tendency until 12

months of exposure, subsequently stabilizing over time. The maximum reduction of this

property is 16,2% in S-60 environment after two years of exposure. Group II environments

show little change in tensile strength and a slow decreasing tensile modulus. The maximum

Group II tensile loss occurred in CCI-40 environment with a 8,13% decay after one year of

exposure, where higher temperatures and increased moisture are relevant to this deterioration.

However, both Group II systems helped slowing overall deterioration in test specimens.

Chu et al. [22] described that the same reversibility system on GFRP vinylester pultruded

profiles presented a 6,9-27,3% improvement in tensile strength, after 28 days of exposure in

23 C demineralised water.

4.5.3 Interlaminar shear strength

Figures 18 and 19 illustrate the variation of the interlaminar shear strength as a function time,

for different exposure environment conditions.

25

30

35

40

45

50

55

0 4 8 12 16 20 24

Tensi

leM

odu

lus

[GPa

]

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

NE

30

35

40

45

0 4 8 12 16 20 24

Tensi

leMo

du

lus

[GPa

]

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40


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Figure 13Interlaminar shear strength of Group I ageing conditions.

Figure 14Interlaminar shear strength of Group II ageing conditions.

Interlaminar shear strength results point to the same tendencies as the other mechanical tests. It

generally decreases over time and Group I environments show possible post-cure effects due to

strength gains after 9 months of exposure, which has also been noted by Karbhari [5]. However,

it is noticed the existence of a plateau until 18 months, followed by a slow downward deflection

in strength. Losses after two years of exposure, highlight high variations - from 52,3% at higher

temperatures and only 6,6 % at lower ones. This fact suggests that interlaminar shear strength

degradation is highly temperature dependant. Over time demineralized water seems to havemore deteriorative effects than salt water, however, final results present almost no differences

between these two types of environments. Natural ageing results point towards a slight gain of

interlaminar shear strength at 12 months of exposure. However, after two years, deteriorative

effects are noticed resulting in a 19,7% loss, when compared to the initial data. On the other

hand, group II environments present minor changes after 6 months of exposure and some

significant changes in continuous condensation and high temperature environments after 12

months, where CCI-40 decayed 35,2%. Nevertheless, Group II environments show less

deterioration when compared with the same Group I conditions at 6 month of exposure. Group

15

20

25

30

35

40

45

0 4 8 12 16 20 24

Interlaminarsh

earstength

[MPa

]

Time (months)

W-20

W-40

W-60

S-20

S-40

S-60

NE

20

25

30

35

40

45

0 4 8 12 16 20 24

Inetr

laminars

hearstrength

[MPa

]

Time (months)

WD-20

WD-40

CCD-40

WI-20

WI-40

CCI-40


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II environment do not show strength recovery, in spite of some cases where this phenomena

occurred for longer exposure times.

5 Conclusions

The main objective of this study was successfully achieved, leading to the determination of the

mechanical, physical and aesthetical variations suffered by GFRP pultruded profiles as result of

time and under different ageing conditions.

Regarding moisture sorption it was confirmed that water molecules incorporation is temperature

dependant, especially in the initial states. High initial sorption rates, slowing down to a plateau

over time indicates approximate Fickian behaviour. Higher temperatures environments showed

higher initial sorption rates. However, demineralised water immersions at 60 C highlighted

mass losses after 8000h of exposure. Mass loss at high temperature is strongly related to

hydrolysis. Group I environments presented 0,77% maximum mass change in two years and in

Group II the WD-40 environment absorbed higher amounts of water (1,04%). Apparent

diffusion coefficients of both groups present a decrease pattern with lower temperatures and

with the use of protective coating (lowest on fully protected ones). Moreover, the latter supports

the fact that temperature increases sorption rates and the protective coating decreases it and acts

as a sorption wall. All these test results are consistent with mass changes of other batches

having a 2% variation, which, in turn, confirms the system reliability.

Colour and gloss variation showed significant variations. Initially grey, two years old natural

aged specimens presented themselves 7,5% more yellow, which could be visually confirmed on

them and showed only 20% gloss retention at 20 , being these changes similar to accelerated

QUV tests.

DMA analysis revealed that the biggest variations occurred in environments where moisture and

temperature play an important role. Group I environments presented biggest T g changes at 9

months of age in both immersion types. However, Tg loss never surpassed 10%. It was noted

that demineralised water immersion and salt water caused, at different temperatures, identical Tg

variations taken from tan peak over time. Salt water presented the same tendency as

demineralised water but with fewer variations. Decreased Tg values over time indicate

plasticization phenomena, usually found when polymeric materials contact with water

molecules. However, Tg decrease seems to slow after a given exposure period and even

presenting some gains, especially at higher temperatures, which suggests post-cure effects on

the vinylester matrix. The applied coating helped in maintaining Tgvalue over time (slowing

deterioration effects) - protected specimens showed no significant loss during one year.

Moderate temperature cured system effects showed Tggains over time, which are subsequently

related to the material reversibility process.


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All mechanical tests showed linear elastic behaviour until rupture. Mechanical behaviour

revealed significant performance decrease especially in tensile (maximum 38,1% loss) and in

interlaminar shear strength (52,3% loss). Temperature and moisture content effects highly

influence the material deterioration degree. Different testing offer complementary data as tensile

properties are strongly correlated to fiber performance, and interlaminar shear strength is related

with matrix and its interface deterioration. The biggest interlaminar shear strength reductions

suggest performance loss not only due to fiber degradation but general composite deterioration.

All test showed, at some time, property gains implying a possible post-cure effect in the

vinylester matrix that can be related to incorrect cure state achieved during production. In a

global sense, moderate temperature cured and protective coated systems tests went as expected,

showing less overall deterioration over time when compared to other testing environments. This

can be a decisive factor to improve the real material performance when in service conditions,

which can even result in reconsideration of the safety coefficients related to material behaviour.

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Documents

Durability of GFRP Pultruded Profiles Made of Vinylester Resin