of 10, 11, 2019 issn 2229-5518 evaluating the long-term

International Journal of Scientific & Engineering Research, Volume 10, Issue 11, November‐2019 1 ISSN 2229-5518

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Evaluating the Long-Term Performance of Locally Produced GFRP Reinforcing Bars under

Sustained Load E. F. Sadek

Abstract—In recent years, Fiber Reinforced Plastics (FRP) have been used in different civil engineering applications because of their in-

herent properties, which include high resistance to loads and environmental conditions. These materials are available in variety of forms in-

cluding rebars, which have been already manufactured and used abroad in reinforcing of concrete elements in several projects. Unfortu-

nately, these rebars have not been yet widely produced in Egypt. This research is the second phase of a research began by producing FRP

rebars locally. In this first phase, short-term tensile properties of locally produced FRP rebars have been investigated. The aim of the current

research is to assess the creep behavior of the locally produced FRP rebars under sustained load and comparing this behavior with that of

the imported rebars in order to check the adequacy of the locally produced GFRP rebars for structural purposes. For this purpose, creep

tests have been conducted on both locally and imported rebars under four levels of sustained service load (nominally 15%, 30%, 45% and

60% of the average ultimate tensile strength) with a creep test duration of 10000 hours (417 days). At the end of the test duration, the sam-

ples were tested statically to investigate their residual tensile properties. It has been found out that the creep behavior of the locally pro-

duced rebars is comparable to those of the imported ones with the same diameter and approximately the same fiber volume fraction. Creep

rupture stress limit was found to be less than 60% of average ultimate tensile strength for the locally produced rebar. Locally produced re-

bars were found, however, to be satisfying the creep rupture stress limit state stated in ACI 440.1R-15. The Microstructural analysis indicat-

ed that there is no degradation in the matrix or the fiber-matrix interface within the GFRP bars after the lengthy duration under sustained

load up to 45% of the average ultimate tensile strength.

Index Terms—Glass fiber-reinforced polymers (GFRP), Reinforcing bars, Creep behavior, Serviceability, Sustained service load

—————————— ——————————

1 INTRODUCTION

IBER reinforced polymer (FRP) materials are gaining wider acceptance for use as primary reinforcement in concrete structures. Due to its high strength and non-corrosive na-

ture, FRP provides an alternative to steel reinforcement. The use of FRP as structural reinforcement, in turn, provides the poten-tial advantage of lowered maintenance costs and extended ser-vice life for several types of structures, including bridge deck slabs, abutments, walls and other structures exposed to corro-sive environments [1],[2]. In the past two decades, a plenty of researches have taken place on fiber reinforced polymer rein-forced concrete (FRP-RC) [3],[4],[5]. A better understanding is now available on paramount characteristics such as strength, stiffness, bending, and shear and FRP-concrete bond. Existing guidelines and specifications provide practitioners with the tools they need for the design and construction of FRP-RC structures [6],[7],[8]. Guidelines are periodically updated to re-flect advancements in the state-of-the-art and allow for more efficient design where possible.

Under sustained load, FRP bars suffer plastic (perma-nent) deformation, typically occurring under unfavorable envi-ronments over a long time. This phenomenon is what is com-

monly referred to as “Creep”. Creep typically increases the long term deflection of FRP reinforced concrete elements and may, under certain circumstances, cause catastrophic failure [9]. De-spite its higher tensile strength over conventional steel, FRP exhibits less tensile and shear stiffness. As a result of the rela-tively lower axial stiffness of the FRP bars, FRP reinforced con-crete members deform more than their steel reinforced counter-parts. Therefore, when FRP bars and tendons are used as rein-forcement bars and prestressed tendons, the long-term tensile behavior of these materials must be taken into account in addi-tion to their short-term behavior [10],[11]. Moreover, creep be-havior of GFRP is also affected with other adverse environmen-tal conditions yielding a more pronounced effect on GFRP rein-forced concrete [12]. Consequently the design of FRP reinforced concrete members is predominantly governed by serviceability requirements.

Based on the findings of researchers such as Yamaguchi et al. [13] and Seki et al. [14] and using the most conservative results available in literature, ACI 440.1R-15 [6] design guideline has assigned GFRP reinforcement the creep rupture stress limit of 20 % of the bar’s tensile strength. Nevertheless, several stud-ies [15] and [16] indicated that if the sustained stress is less than 60 % of the average ultimate tensile strength (fu,ave), creep rup-ture is less likely to occur. They have also suggested that creep rupture stress limits is varying between 45% and 60% (fu,ave).

F

————————————————

E. F. Sadek is currently Assistant Professor, Structural Engineering De-partment, Ain Shams University, Cairo, Egypt

E-mail: [email protected]

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D Bridge Desigrete [18] and,

ds, allowed foents [19].

The aim of the creep deformrent levels of aand comparingrebars targetinoduced GFRPle properties (a 10000 hour t

The first stes ago [20], wheufactured, at Paculty of Enginucing pultrudediameters 10,

of 60 % have be

It is importae tapers downned measurem(50 years). The

period that cap[13], [21], and

XPERIMENTAL

Materials and

Both locally ested in creep is made of mme) impregnaton has a 10 mmin diameter anthe bar’s volum

Prior to cree

rs are to be dettension test w

s according tocarried out on GFRP rebarson test. This pppropriate len of D7205 / Dample was fitt

poxy grout, as to the tension

of Scientific & En

vestigation intorement of the e20% to 30% oronmental knodopted in thegn Guide Spec along with a or a more effi

the current stumation of locaaxial sustainedg its creep beh

ng the evaluatioP rebars for str(modulus of etest-period (41

ps of the currere a pultrusioProperties and neering, Ain Sed FRP rebars.13, and 16 mmeen produced.

ant to considern greatly with

ments over thee 10000-hour pptures most of[22].

L PROGRAM d Sample Pre

manufactured in this study.

medium-strengtted in polyestem diameter. Thnd made of E-me, as supplie

ep test, tensile termined to bewas carried ouo ASTM D7205n three specims were first prpreparation begth (1000 mm

D7205M [24]. Eted into a 300 mshown in Figun test frame i

ngineering Resea

o available expexploitable cap

of the guarantock-down fact second editi

cifications for G rationalizationicient design o

udy is to provilly produced G

d load and in ahavior with thaon of the adeq

ructural purpoelasticity and 7 days), have

rent research hon machine wa Testing of Ma

Shams Univers. Indeed, GFRP

m and with a f.

r that the rate oh time when e service life of

period has gainf the resulting

eparation

d and the im The locally pth E-glass fibeer resin. The bahe imported ty-glass fibers thd by the manu

properties of e used later in ut on the GFR5 / D7205M [

mens of FRP rrepared to be

egins by cuttinm) guided by tEach one of themm-long steel ure (1). After atillustrated in F

rch, Volume 10,

htt

perimental resupacity under steed strength, or [17]. The nion of AASHGFRP-Reinforcn of the load of certain brid

ide essential dGFRP bars unambient tempeat of the imporquacy of the locoses. The resid

tensile strengbeen observed

has been initiaas developed aaterials Laborasity, to be usedP reinforcing bfiber volume fr

of creep-strainextrapolating f a concrete strned consensus

g creep strain

mported FRP bproduced bars ers (60 % fiberar’s circular crype (I-Bars) is

hat constitute 7ufacturer [23].

the tested GFcreep test. The

RP rebars of b[24]. Tension trebars from ea able to perfo

ng the rebars ithe recommene two ends of tube (grip) usttaching the spFigure (2), wh

Issue 11, Novem

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ults sus- re-new

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data nder era-rted cal-

dual gth), d as

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both test ach

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sign or guaranteed m

s per the ACI 440.1R‐1

MECHANICAL P

imate tensile

ess (MPa)

aranteed tensile

ess (MPa)

sign tensile stress a

Pa)

CI 440.1R‐15)

dulus of elastici‐

(GPa)

imate strain

)

aranteed strain

)

sign tensile strain

) (ACI 440.1R‐15)

Figure 1:

Figure 2: Tension

to carry out thble differentiathe bar at the c

The LVDT had

hanical propesile strength fue tensile strain D7205 / D7205were summariz

) is associated with no

modulus of elasticity E

5 guide [6].

TABLPROPERTIES OF

Nomenclature

fu,ave

f*fu

(f*fu = fu,ave ‐ 3σ

ffu = CE × f*fu ; CE

0.8

Ef = Ef,ave

εu,ave

ε*fu

(ε*fu = εu,ave ‐ 3σ

εfu = CE × ε*fu

Preparation of G

n Test Setup

he tension testal transducercenter of the te

d a gage length

erties of the prfu,ave, modulus εu,ave; have be

5M [24] prior tozed in Table (1)

on‐exposure to earth a

Ef equates the mean m

LE 1 GFRP REINFO

e I‐Bars

854 ± 34

σ) 752

E = 602

46.9 ± 1.2

18209 ± 767

σ) 15908

12726

GFRP bars specim

2

t on FRP rebarr (LVDT) waesting length ah of 200 mm.

repared rebarsof elasticity Ef

een determinedo creep testing).

and weather.

modulus of the samp

ORCING BARS

L‐Bars

760 ± 38

646

516

40.8 ± 1.4

7 18627 ± 835

16122

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of Scientific & En

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es (120 ohm hed –on oppoch specimen. Fgauges were pthe bar. Each

dicator when ng the specimfrom the cali

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bar-type and e, four levels

% fu,ave) were ging from arouo each sustainom each bar ty the surround long-term cre. The purpose

d the allowablehere the availawhen it comessed to earth a

amples 37 / D7337M [have been manrials Laborato

ersity. Schemare shown in Fhe loading frad location of have a constor extended ti

perfectly axialrs to the bar isying system (n) multiplies ercentage of

been prepared steel pipes us specimen in

e threaded on keep the sam

resistance andosite sides- at For gauge insproperly align

h gauge was c strain measuen in the loadibration proceights as illustr

Issue 11, Novem


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[25] nu-ory, atic Fig-ame the

tant ime l as s of (the the the

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Trecordesearch, days; evchange ment, inaveragesample.

Aspecimetested incentage

F

mber‐2019

The reinforcinoon as the GFRhen at followihours at least)

The frequencyed decreases w readings wervery day for t of creep straindicated on t

e of the two ba.

After the comens were unin tension. Res

e of the

Figure 3: Schema

Figure 4: Creep

ng bar elongatiRP bars are ining times for .

y at which with time. Forre taken everythe first weekin significantlthe graphs (Sack-to-back ga

mpletion of thinstalled fromsidual tensile p

average u

atic of bar sustai

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loading frame

ion measuremnstalled under the extended

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See Figure 5), auges installed

he 10000 hourm the test fra

properties, indultimate tens

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3

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d test duration

easurement ithe current re

or the first twohen the rate oEach measure is actually and onto the bar

r duration, almes and thendicated as persile strength

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IJSER

InternISSN 2

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3.1 C For amoniapplidisplserveure foCreepBars. volumof 60

a max% forcorre15 %,expecmagnlevel


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ESULTS AND D

Creep Tensile

any GFRP baitoring the chaied stress. Theayed in Figur

ed that for botor sustained lp rupture too It is worth nme fraction th % fu,ave for 100

The upper-bximum valuesr sets 15 %, 30

esponding valu, 30 % and 45 ctedly, no connitude of accu in the case of

Figure 5a:

of Scientific & En

rcentage of theed.

DISCUSSION

e Strain

ar, the creep ange in axial ste creep behavre 5 as well asth bar-types, toad levels upk place at 60 noting that I-B

hat allowed its00 hours with

bound creep-ss after 10000 h0 %, 45 %, anues for L-Bars% fu,ave, respec

nsistent relatioumulated cre I-Bars.

Strain evolution

ngineering Resea

e average You

characteristicstrain with timior of the test

s Table 2 to Tahere was no s to to 45 % fu,

% fu,ave after 1Bars bars hav sample to sus

hout creep rup

strain percentahours are 9.1,

nd 60 % fu,ave, rs are 2.5, 5.5 actively (See Taonship is evidep strain and

with time of I-Ba

rch, Volume 10,

htt

ng’s modulus

s are known me under const

ted GFRP barsable 4. It was sign of creep f

ave. Unlike I-Ba14.6 hours forve a higher fistain a load leture.

ages for I-Bars0.50, 4.1, and respectively. Tnd 9.4 % for s

able 2 and 3). Udent between d sustained lo

ars bars

Issue 11, Novem


(%

by tant s is ob-

fail-ars, r L-iber evel

s as 2.8 The sets Un-the

oad

Aficients curve imannerfor the t

where 𝜀riod t (1strain vdε(t)/dtcreep co44.8, 11spectivewere 9.7where tdetermithat theof appli

locally pof the iture at sThe occlevel lolower fpected drials or noticed mentionture strein ACI 4

mber‐2019

According to A can be deteinto strain ver, the curve betotal strain of

𝜀 𝑡 is the to10000 hours f

value and β ist. Using lineaoefficients of

16.0 and 149.7ely. Similarly,7, 68.2, and 27the creep coeined due to the coefficient βied stress.

Creep tensileproduced rebimported onesstress 60% of currence of creower than thefiber volume difference in e the manufact slight superioning, howeveress limits of F440.1R-15 [6] w

Figure 5b: St

ASTM D7337 ermined by lersus log timeecomes a lineathe commerci

otal strain in tfor this study)s the creep ratar regression I-Bars sample

7 for 15 %, 30 , the creep coe73.2 for 15 %, 3fficient at 60%he creep ruptuβ increases sig

e strain resultars possess sis, excluding thaverage tensileep rupture o

e case of I-Barfraction of L-either the quaturing processor creep behavr, that L-Bars sFRP reinforcemwhich is 20 % f

train evolution w

/ D7337M [25linearizing the. When plot

ar relationshipial bars can be

the material a), 𝜀 , is the te parameter t

for the obtaies were determ %, 45 %, andefficients for L30 %, 45 % fu,a

% fu,ave could nure occurrenc

gnificantly wit

ts indicated cmilar creep behe occurrencele strength in

of L-Bars unders could be a-Bars in additality of the cons itself leadingvior of the I-Bsatisfy clearly ment for GFRP fu,ave.

ith time of L-Bars

4

5], Creep coefhe creep-straintted in such p. The equation written as:

after a time peinitial (elastic

that is equal toined data, thmined as 28.7

d 60 % fu,ave, reL-Bars sampleave, respectivelynot have beene. It is evidenth the increas

clearly that thehavior to thae of creep rupcase of L-Barser sustain loadascribed to thtion to the exnstituent mateg finally to thars. It is worth the creep rupP that is stated

s bars

f-n a n

e-c) o e

7, e-s y n

nt e

e at p-s. d e

x-e-e h

p-d

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International Journal of Scientific & Engineering Research, Volume 10, Issue 11, November‐2019 5 ISSN 2229‐5518


TABLE 4L-BARS CREEP-TEST RESULTS (60 % fu,ave)

Nominal

Applied

Load

εfrp,0

εfrp,0 /εu,ave

ratio

( %)

εfrp,0 /ε*fu

ratio

( % )

Creep‐rupture

Time

(hour)

Creep Strain In‐

crease at Rupture

Time

(με)a

Creep

Strain/Initial

Strain at Rup‐

ture Time (%)

60%fu,ave 14030 75.3 87.0 14.6 332 2.4

a Creep strain readings were taken manually; the measurements taken are expected to be less than the actual value at rupture time.

TABLE 3L-BARS CREEP-TEST RESULTS (15 %, 30 %, AND 45 % fu,ave)

Nominal

Applied

Load

εfrp,0

εfrp,0 /εu,ave

ratio

( %)

εfrp,0 /ε*fu

ratio

( %)

Creep Strain (Strain In‐

crease)

(με) after

Creep Strain/Initial

Strain ratio (% of actual

initial strain) after

1000

hrs

3000

hrs

10000

hrs

1000

hrs

3000

hrs

10000

hrs

15%fu,ave 2105 11.3 13.1 35 34 53 1.7 1.5 2.5

30%fu,ave 5600 30.0 34.7 206 230 308 3.7 4.1 5.5

45%fu,ave 8977 48.2 55.7 633 757 843 7.1 8.4 9.4

TABLE 2I-BARS CREEP-TEST RESULTS (15 %, 30 %, 45 % AND 60 % fu,ave)

Nominal

Applied

Load

εfrp,0

εfrp,0 /εu,ave

ratio

( %)

εfrp,0 /ε*fu

ratio

( %)

Creep Strain (Strain In‐

crease)

(με) after

Creep Strain/Initial

Strain ratio (% of actual

initial strain) after

1000

hrs

3000

hrs

10000

hrs

1000

hrs

3000

hrs

10000

hrs

15%fu,ave 2631 14.4 16.5 155 145 239 5.9 5.5 9.1

30%fu,ave 5674 31.1 35.7 74 39 29 1.3 0.7 0.5

45%fu,ave 8195 45.0 51.5 192 179 339 2.3 2.2 4.1

60%fu,ave 10416 57.2 65.4 ‐101 179 292 ‐0.9 1.7 2.8

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InternISSN 2

3.2 RM

Afterwere tests For bburrisiduaThe maboutwas aelastithe oto be

3.3 MThe fat thenomeand/spectusingtest dhind

Figu


Residual TenModulus) r the elapse o dismantled were conduct

both I-Bars anng of the fibe

al strength wamaximum pert 4 % for 60 %almost 5 % foricity, the resid

original values 46.2 GPa 41.0

Microstructuformation of me interface ofena occurringor adverse en

t, Scan Electrog selected samduration to ha strength loss,

Figure 6:

ure 7: Residual te

of Scientific & En

nsile Properti

of the test dufrom their co

ted to obtain rnd L-Bars specers, as shown as barely affecrcentage loss i% fu,ave. The cor 45 % fu,ave (Fi

dual values shs. The average GPa for I-Bar

ral Analysis microcracks inf fibers/matrixg in a GFRP mnvironment [1on Microscopy

mples of the teave a better un if any.

Typical mode of

ensile strength fo

ngineering Resea

ies (Strength

uration (10000 omprising fraesidual mecha

cimens, the ruin Figure (6).

cted by creepin strength fororresponding gure 7). As fo

howed barely ae residual modrs and L-Bars,

n the resin anx are the mosmaterial unde15], [21], and y - SEM - ana

ested bars aftenderstanding

f failure of tested

or I-Bars bars an

rch, Volume 10,

htt

h and Young’

hours), all bames and tenanical propert

upture mode w The average tests (Figure r I-Bars bars wvalue for L-Br the modulusany change frdulus was fourespectively.

d the debondst common pr sustained lo [12]. In this alysis took pl

er the 10000 hoof the causes

rebars

d L-Bars bars

Issue 11, Novem


’s

bars sile

ties. was re- 7).

was Bars s of rom und

ing phe-oad re-

lace our be-

Mimages fu,ave afttypes hano indufu,ave) forI-Bars. Faround

Ttioned bthe coning as wafter 13

4 SUMM

Creep band imhours (nominatensile sfrom th

Figur

hours

mber‐2019

Micrographs, i of I-Bars andter creep test ad no signs of

uced microcrar L-Bars and uFor L-Bars, su the fibers (Fig

This noticed dbefore, the di

nstituents and well could jus.8 hours.

MARY AND Cbehavior tests

mported GFRP (417 days at ally (15 %, 30 strength fu,ave).

he current reseUnlike I-Barsimen at 60 %ticed in I-Barels, which inimported barresults show

re 8: Magnified s

of loading: (a) I-

in Figure 8, shd L-Bars subje

duration. Resf debonding b

acks under theunder sustain

ubjected to 60 gure 8c).

debonding inifference in qu the manufactustify the ruptu

CONCLUSION were conduct

P reinforcing bdifferent leve% 45 % and 6. The followin

earch study: s, creep ruptu

% fu,ave wherears specimens un turn reflectrs which is ex

wed clearly tha

(a)

(c)

samples’ cross se

-Bars at 60 % fu.

Bars at 60 % f

(b)

how magnifiedected to 45 % sults showed

between fiberse sustained lo

ned load level % fu,ave, thin v

tiation may reuality control uring process

ure of L-Bars t

ted on both locbars over a peels of axial su60 % of the avng conclusions

re took place ias no creep ruunder all sustas a slight hig

xpected. Howeat the locally

ection after exhib

ave; (b) L-Bars a

fu.ave

6

d cross-sectionfu,ave and 60 % that both ba

s and resin andoad level (45 %

(60 % fu,ave) fovoids appeared

eflect, as menon both level. This debondthat took plac

cally producederiod of 1000ustained load

verage ultimats can be drawn

in L-Bars specupture was noained load lev

gher quality oever, creep tes manufactured

biting 10000

t 45 %; (c) L-

n % ar d % or d

n-s

d-e

d 0

d, e n

c-o-v-of st d

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International Journal of Scientific & Engineering Research, Volume 10, Issue 11, November‐2019 7 ISSN 2229‐5518


GFRP bars rupture in creep at stress level lies clearly beyond the stress limits specified by ACI 440.1R-15.

No change was detected in residual tensile strength and modulus of elasticity for all samples that sur-vived the 10000 hour duration and all reinforcing bars have almost retained their initial full strength.

Microstructural analysis illustrated that no mi-crocracks were found in reinforcing bars of both types up to 45 % fu,ave. Under sustained load level of 60 % fu,ave, debonding has initiated in L-Bars, whilst, no cracks or deboning was noticed in case of I-Bars. Mi-crostructure analysis emphasized, as mentioned be-fore, the better quality of I-Bars compared with L-Bars.

Based on the investigations carried out in the current research, it has been emphasized that the creep stress limits imposed by ACI 440.1R-15 on GFRP reinforce-ment underestimate the stresses GFRP bars can actu-ally sustain.

Creep test results of the current study in addition to the results of first phase of this research carried out in 2005; refer to the adequacy of the locally produced GFRP reinforcing bars to be used as reinforcement for concrete structures.

As a recommendation for further research, it is rec-ommended to perform creep test under severe envi-ronmental conditions, such as alkalinity and high temperature, for test durations not less than 10000 hours to be able to propose new creep rupture stress limits which could be higher than those specified in ACI 440.1R-15.

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