journal of composite materials 2013 almusallam 393 407

JOURNAL OFC O M P O S I T EM AT E R I A L SArticle

Tensile properties degradation of glassfiber-reinforced polymer bars embeddedin concrete under severe laboratory andfield environmental conditions

Tarek H Almusallam, Yousef A Al-Salloum, Saleh H Alsayed,Sherif El-Gamal and Mohammed Aqel

Abstract

This paper presents the test results of an experimental study to investigate the durability of newly developed glass fiber-

reinforced polymer bars. The main objective of this study is to investigate any degradation in the tensile properties of the

glass fiber-reinforced polymer bars using accelerated aging methods. Glass fiber-reinforced polymer bars were embedded

in concrete prisms and exposed to several environmental conditions for 6, 12, and 18 months. The environments

included exposure to tap water and seawater at two temperatures (room temperature and 50�C), seawater dry/wet

cycles and alkaline solution at 50�C. In addition, two typical field conditions of the Kingdom of Saudi Arabia (Gulf area

and Riyadh area) were included. The performance of the glass fiber-reinforced polymer bars was evaluated by conducting

tensile tests on the bars extracted out from the concrete prisms after exposure to different conditions. In addition,

scanning electron microscope was used to investigate the degradation mechanism of the bars. After 18 months of

exposure, test results showed that both the tap water at 50�C and the alkaline solution at 50�C had the maximum

harmful effect on the tensile strength of glass fiber-reinforced polymer bars. The two field conditions showed almost no

degradation in the tensile properties of the tested bars.

Keywords

Durability, glass fiber-reinforced polymer bar, environmental degradation, tensile properties, concrete, scanning electron

microscope

Introduction

Conventional concrete structures reinforced with steelare initially protected against corrosion by the alkalin-ity of the concrete. For many structures subjected toaggressive environments, such as marine structures,bridges, and parking garages, combinations of mois-ture, temperature, and chlorides reduce the alkalinityof the concrete and result in the corrosion of the rein-forcing and prestressing steel.1 The costs of repairs andrestoration in USA, Canada, and in the majority of theEuropean countries constitute a high percentage oftheir total expenditure on infrastructure.2–4 This initi-ated the development of new technologies in order toreduce the corrosion of steel reinforcement. Varioustechniques such as epoxy-coated, galvanized steelbars, and cathodic protection were employed; however,

any of the above conventional or new protection tech-niques could not completely eliminate the corrosion.This failure directed the research toward the develop-ment of new corrosion-resistant materials for reinforce-ment such as fiber-reinforced polymers (FRP).5,6

Due to their corrosion resistance, light-weight, andhigh strength, FRPs have been widely used for civilinfrastructures throughout the world for the last 20years. Among different types of FRPs, glass FRP(GFRP) bars have drawn more attention in civil

Department of Civil Engineering, King Saud University, Riyadh, Saudi

Arabia

Corresponding author:

Yousef A Al-Salloum, Department of Civil Engineering, King Saud

University, P.O. Box 800, Riyadh 11421, Saudi Arabia.

Email: [email protected]

Journal of Composite Materials

47(4) 393–407

! The Author(s) 2012

Reprints and permissions:

sagepub.co.uk/journalsPermissions.nav

DOI: 10.1177/0021998312440473

jcm.sagepub.com

by guest on January 4, 2015jcm.sagepub.comDownloaded from

http://jcm.sagepub.com/

engineering applications due to their low cost comparedto other types of FRPs.7,8 Durability of GFRP bars,however, is not a straightforward subject; it tends to bemore complex than corrosion of steel reinforcementbecause the durability of FRPs is related not only tothe strength of its constitutive materials (fibers andmatrix) but also to the integrity of the interface betweenthese two components while aging. A deterioration ofthis interface reduces the transfer of the loads betweenfibers and thus weakens the composite material.6

During the last two decades, several studies7,9–24

have been carried out on the parameters affecting dura-bility and long-term behavior of FRP materials used incivil engineering applications. These studies concludedthat most common types of GFRP bars appeared tohave some deterioration problems when subjected toharsh environments and that moisture, alkalinity, andtemperature are the main parameters affecting thedurability of composite materials. The moistureabsorbed by the composites, combined with the tem-perature of exposure, induces stresses in the materialthat damage the fibers, the matrix, and their interface.This gradually decreases the strength of the compositematerial with time. The glass transition temperature(Tg) of the matrix is also a key parameter, since itmarks a point beyond which significant changes in theproperties of the matrix occur and considerable reduc-tion of the mechanical properties takes place.6 Hence,understanding the durability of GFRP bars as a func-tion of glass fibers and polymeric resin is essential todesign GFRP-reinforced concrete members and toguarantee the typical infrastructure service life(50–100 years) and safety. Therefore, accelerated test-ing and evaluation programs are needed to evaluate theexpected service performance of concrete membersreinforced with these bars. In addition, calibration ofthe accelerated test results with different naturalweathering data of in-service structures is needed toestablish safe service life of a structure.9

Several research studies were carried out to investi-gate the durability of GFRP bare bars under differentenvironmental conditions. Porter and Barnes25 con-ducted accelerated tests to determine the long-term ten-sile strength of three types of GFRP bars exposed to analkaline solution at a high temperature (60�C) for per-iods of 2–3 months. The tensile tests resulted in residualstrengths of 34%, 52%, and 71% compared to the orig-inal tensile strength. Chu and Karbhari26 and Chuet al.27 conducted a study on the characterization andmodeling of the effects of moisture and alkalis onE-glass/vinylester composite strips at different temper-atures (23, 40, 60, and 80�C). The degradation levels inthe tensile strength ranged between 35% and 62% ofthe initial strength. In a durability study conducted byGaona28 on GFRP bare bars, the test results showed

that tensile strength of the tested GFRP bars decreasedwith time when the bars were in direct contact withsolutions simulating the interstitial solution of the con-crete. Losses up to 24% were measured for bars condi-tioned in an alkaline solution with high pH value (12) ata temperature of 35�C for 50 weeks.

Wang29 conducted 330 accelerated aging tests on dif-ferent diameters of E-glass/vinylester reinforcing bars.The samples were conditioned in alkaline solution (pH12.6–12.8) and distilled water at 23, 40 and 60�C for150 and 300 days. For all 150-day-aged samples, nodefects were observed in the fiber, whereas matrixcracks were observed in 300-day-aged samples.

Al-Zahrani4 investigated the degradation in theresidual tensile strength of three types of GFRP barsin aggressive solutions. Bare bars were conditioned infour solutions (alkaline, alkalineþ seawater, alka-lineþ sabkha, and acidic) at three different tempera-tures for 3–12 months. The maximum reduction inthe tensile strength ranged between 27% and 71% inalkaline environment and sabkha at 60�C. For thermalvariation and out-door, the reduction ranged between5% and 21%.

Kim et al.24 conducted a short-term durability teston two types of commercially available GFRP barebars (E-glass/vinylester) under four different environ-mental conditions (moisture, chloride, alkali, andfreeze–thaw cycling) for up to 132 days. In additionto the room temperature (25�C), elevated temperaturesof 40 and 80�C were employed to accelerate the degra-dation of the GFRP bars. They concluded that, alka-line environmental condition had more influence on thedegradation of tensile strength of GFRP bars than theother influencing factors.

Few research studies investigated the durability ofGFRP bars embedded in concrete. Table 1 shows asummary of these studies and their test results.Al-Zahrani4 subjected small concrete prism specimens(10� 10� 100 cm) reinforced with single GFRP barembedded centrally to continuous wetting at 30�C inpotable water, seawater, sabkha solution, or out-doorfor 6–24 months. He observed that the reductions in thestrength were much lower than in the case of bare bars.This reduction ranged between 10% and 35% after24 months of exposure. The researcher concludedthat this behavior could be attributed to the limitedavailability of moisture around the bars and the lowertemperature of the condition solutions which was 30�Cfor the embedded bars compared to 60�C for bare bars.Another durability study on GFRP bars was carriedby Chen et al.30 Bare FRP bars and also bars embeddedin concrete were exposed to five different solutions.The results showed that significant strength lossresulted from the accelerated exposure of both bareand embedded GFRP bars especially for solutions

394 Journal of Composite Materials 47(4)



at 60�C. Continuous immersion resulted in greater deg-radation than exposure to wetting and drying cycles. Incontrast, freezing and thawing cycles combined withsolutions had little degradation effects on the GFRPbars.

A recent study on the durability of GFRP barsin moist concrete was conducted by Robert et al.31

Sand-coated GFRP bars with a nominal diameter of12.7mm were embedded in concrete and exposed totap water at 23, 40, and 50�C for periods of 60–240days. The tensile test results showed that at 40 and50�C, the decrease of the tensile strength was 10%and 16%, respectively, of the original tensile strengthafter 240 days of exposure. In a field study by Muftiet al.,32 concrete cores were taken from five in-serviceconcrete bridge structures of 6–8 years age across

Canada, reinforced with GFRP bars. On the basis onmicroscopic and chemical analysis, they concluded thatthe concerns about the durability of GFRP in alkalineconcrete, based on simulated laboratory studies in alka-line solutions, are unfounded.

The abovementioned studies showed wide and sig-nificant variations in the strength reduction due to envi-ronmental exposure. In addition, most of the studieshave been carried out in USA, Canada, Japan, andsome of the European countries. Unfortunately, the cli-mate in all those countries is relatively temperate anddoes not resemble the local environment of hot coun-tries such as Middle East in general and the ArabianGulf in particular where GFRP bars are extensivelyused. In addition, many of the previous studies havebeen carried out on the old generations of FRP bars.

Table 1. Previous test results of GFRP bars in concrete

Reference Glass material/matrix

Bar diameter

(mm)

Conditioning

solution

Temp

(�C)

Duration

(days)

Tensile

strength

loss

Al-Zahrani 20074 E-glass/modified vinylester 12 Water 30 720 10

Seawater 12

Sabkha solution 10

Outdoor Varied 14

E-glass/vinylester Water 30 720 33

Seawater 35

Sabkha solution 32

Outdoor Varied 12

E-glass/polyurethane

(thermoplastic)

Water 30 720 21

Seawater 21

Sabkha solution 20

Outdoor Varied 20

Alsayed et al. 20027 E-glass/urethane-modified

vinylester

9.5 Water (LACP) 50 180 9

Water (LACP) 65 34

Seawater (LACP) 50 3

Water (HACP) 50 11

Water (HACP) 65 39

Seawater (HACP) 50 12

Robert et al. 200931 E-glass/vinylester 12.7 Water 23 240 9

40 10

50 16

Chen et al. 200730 E-glass/vinylester (type 2) 9.5 Water 20 90 10

Alkaline solution

(pH¼ 12.7)

60 39

Almusallam and

Al-Salloum 200621E-glass/modified vinylester 10 Tap water 40 480 16

Seawater 40 480 20

Dejke 200115 E-glass/vinylester 9 Water 20 582 43

40 245 44

GFRP: glass fiber reinforced polymer; LACP¼ low alkali cement (Na2O equivalent¼ 0.2%) paste; HACP¼ high alkali cement (Na2O equivalent ¼ 1.0%)

paste.

Almusallam et al. 395



The manufacturers of GFRP are now claiming thatthey have produced new types of GFRP bars thathave greater resistance to alkaline and to other environ-mental conditions.22 Therefore, before prescribing thenew materials to practitioners, there is an essential needto evaluate the long-term performance of the newlydeveloped GFRP bars when subjected to different envi-ronmental and loading conditions.

This study aims to investigate the tensile propertiesof new generations of GFRP bars under acceleratedlaboratory environmental conditions as well as actualfield conditions. The laboratory environments includeexposure to ordinary tap water and seawater at twodifferent temperatures. They also included exposure toseawater dry/wet and alkaline solution at high temper-ature. The field conditions include the hot weather fieldconditions of the Middle East, the Arabian Gulf area inparticular. This is represented in this study by theCentral Province (hot-dry) and Eastern Province (hot-humid) of the Kingdom of Saudi Arabia.

Research significance

Although a number of durability studies on FRP barshave been reported by various researchers, no generalconclusions are possible as researchers used differenttesting procedures and conditions. In some cases,even conflicting results have been reported. This studyinvestigates the performance of newly developed GFRPbars when subjected to several accelerated aging tests inthe laboratory (simulating the highly aggressive envi-ronments). In addition, it investigates the performanceof the bars in two actual service (field) conditions. Inthis study, GFRP bars embedded in concrete are testedto simulate the real conditions of concrete structures.The results of this investigation will provide a certainconfidence level in using the new GFRP bars in con-crete structures taking into account the long-termbehavior of these bars in hot weather countries. Italso allows for a direct comparison between the perfor-mance in laboratory and the real-field conditions.

Experimental program

The experimental program of this study includes twophases. The first phase investigates the short-termmechanical properties of four types of GFRP barsavailable in the market to select the best type to beused in the second phase. The second phase investigatesthe durability of the selected type of the GFRP bars.

Phase-1: short-term mechanical properties

The properties of composite materials are dependenton the individual component properties, the

manufacturing technique, and the quality control ofthe production process. Any variations in the charac-teristics of these three items will produce compositematerials with variable short-term mechanical proper-ties. Durability study cannot be conducted using mate-rials with intolerable variations in short-termmechanical properties. Such variation will make theresults of the durability study meaningless. Therefore,before commencing the durability tests, tensile testswere carried out to identify the short-term mechanicalproperties of the available GFRP bars. Four differenttypes of E-glass/vinylester GFRP bars were procuredfrom three different suppliers.

All the GFRP bars were subjected to the screeningtest to determine their properties. GFRP bars thatscored the highest stable results were used for the dura-bility study. Tensile test was used to identify the suit-able bars. Information collected from this test includestensile strength, tensile modulus of elasticity, and strainat failure. Ten GFRP bar specimens of each type wereused in the screening tensile tests. The tensile tests werecarried out according to the ASTM D7205.33 All thespecimens were tested up to failure. The average stan-dard deviation (SD), and coefficient of variation (COV)of the tensile test results for all the tested specimens aregiven in Table 2. It is observed from Table 2 thatGFRP bars type I are the weakest with lowest tensilestrength and modulus of elasticity. The modulus ofelasticity of remaining three types is almost same butthe tensile strength of bars type II is the highest. Thefracture strain of type II bars is also high, which isprimarily due to its relatively higher tensile strength.The test results of type II bars also show minimumscatter in test results thus indicating their relativelypromising quality of manufacturing. It is due to thesereasons that the GFRP bars type II were selected to beused in the durability phase of this investigation. Theselected bars were 12mm diameter (area¼ 113mm2)with special surface profile of regular ribs (Figure 1)to enhance bond and force transfer between bars andconcrete. The bars were made of continuous longitudi-nal fibers impregnated in a thermosetting vinylesterresin with a fiber content of 83%.

Phase 2: durability of GFRP bars

This second phase of the study investigates the effect ofdifferent environmental conditions (control, labora-tory, and field) on the tensile properties of the selectedtype of GFRP bars. To be closer to real-field conditionswhere the bars are embedded in concrete, the GFRPbars used in this study were also embedded in concreteprisms before aging under different environmental con-ditions. For the test specimens, concrete was first cast




and cured under normal conditions then the specimenswere transferred to the different environmental condi-tions until the day of testing.

Test specimens. The durability study presented in thispaper focuses on the sole effect of different environmen-tal conditions on test specimens without applying anystress on the GFRP bars. Figure 2 shows a schematicdrawing and a photo of the test specimens. For thesespecimens, GFRP bars were centrally embedded incement mortar prisms (50� 50� 500mm). Thecement mortar was prepared using 1:3 mix proportionof ordinary Portland cement and regular coarse sand.Both ends of the GFRP bars were protected againstenvironmental conditions using a plastic tape. Theseends were used later for the anchorage of the barsbefore testing. The specimens were cast in woodenmolds. After demolding, specimens were cured usingwet burlaps for a period of 28 days.

Environmental conditions. The specimens were subjectedto nine environmental conditions for 6, 12, and 18months. The environments included exposure to ordi-nary tap water and seawater at two temperatures (roomand 50�C). They also included exposure to seawaterdry/wet and alkaline solution at 50�C. Seawater wasbrought from the Arabian Gulf-Eastern Provinceof Saudi Arabia. Alkaline solution was preparedusing calcium hydroxide, potassium hydroxide andsodium hydroxide (1.185 g of Ca(OH)2þ 9.0 g ofNaOHþ 42.0 g of KOH per 10 l of water). The envi-ronments also included two typical field conditions ofthe Kingdom of Saudi Arabia (Riyadh area and Gulfarea). Table 3 summarizes the test program of the dura-bility study. The test program was divided into threemain categories as follows:

Unconditioned specimens (control specimens).

Specimens of this group, LE, were exposed to controlledlaboratory environment (temperature 23� 2�C) as

Table 2. Screening tensile test results of different types of GFRP barsa

FRP samples

Peak stress

(MPa)

Fracture strain

(mm/mm)

Modulus of

elasticity (GPa)

Type I Average 432 0.0104 41.9

Standard deviation 59.2 0.0016 1.56

Coefficient of variation (%) 13.68 15.76 3.71

Type II Average 1478 0.0245 60.4



Type III Average 838 0.01 59.9



Type IV Average 611 0.0097 63.3



FRP: fiber reinforced polymer; GFRP: glass FRP.aValues indicating minimum scatter are shown in bold.

Figure 1. GFRP bars used in this study.

GFRP: glass fiber reinforced polymer.




shown in Figure 2. Similar to the specimens in otherconditions, after 6, 12, and 18 months of exposure,bars were extracted out of the specimens and tested intension. The great care was observed during the processof extraction of bar for making sure that the bar is notdamaged. A small hammer was used for gently removingthe cement mortar. Test results of this group were usedas reference results for specimens under all otherconditions.

Specimens under different environmental conditions:The specimens of this group were exposed to differentenvironmental conditions (at normal room temperatureor at 50�C) by either immersion into different types of

liquids or exposure to some specified conditions.Similar to the unconditioned specimens, the condi-tioned specimens were tested in tension after beingexposed to the different conditions for 6, 12, and 18months. The effects of each environmental conditionon the tensile strength of the bars were determined bycomparing the test results of this group with those ofthe counterpart control specimens, LE specimens. Theenvironmental conditions considered in this group oftesting were as follows:

. Immersion in tap water at ambient and 50�C (TWRand TW50 specimens).

Table 3. Program of the durability study (control, laboratory, and field)

Specimens Environment Temp. (�C) Nomenclature

No. of

specimens

Control Unconditioned lab room LE 5

Lab conditioned specimens Tap water (immersed) room TWR 5

50 TW50 5

Seawater (immersed) room SWR 5

50 SW50 5

Seawater (dry/wet) 50 SW50DW 5

Alkaline (immersed) 50 ALK50 5

Field specimens Gulf area (hot humid) Field GF 5

Riyadh area (hot dry) Field RF 5

Subtotal 45

No. of exposure periods (6, 12, 18 months) 3

Total no. of specimens 135

ALK50: alkaline solution at 50�C; LE: lab environment; SEM: scanning electron microscope; TWR: tap water at ambient; TW50: tap

water at 50�C.

250 mm 500 mm 250 mm

50

Figure 2. Specimens exposed to lab environment (LE).




. Immersion in seawater at ambient and 50�C (SWRand SW50 specimens).

. Wet/dry cycles in seawater at 50�C (SW50DWspecimens).

. Immersion in alkaline solution (pH 12.5–13) at 50�C(ALK50 specimens).

Specimens under field conditions: Two field condi-tions were considered. A set of specimens, RF, wasexposed to Riyadh hot-dry field conditions representinghot-dry arid land of the Middle East. A second set, JF,was exposed to the Eastern coast of the Kingdom ofSaudi Arabia (Jubail city), which represents the hot-humid environment of the Middle East. It should bementioned that the temperature are almost similar forboth field conditions. Monthly average temperatureranges between 9 and 45�C with annual average highand low temperatures of 33 and 19�C, respectively.However, the relative humidity is different. Theannual average relative humidity in Riyadh andJubail areas is about 26% and 52%, respectively.34

Tensile tests. All bars were tested in tension accordingto the ASTM D720533 and the ACI 440.3R-04 B2test method.35 Each specimen was instrumented witha Linear Variable Differential Transformer (LVDT)to capture the elongation during testing. The totallength of bar was 1.0m (Figure 2). After the extractionof bar from cement mortar prism, 300-mm-long gripsof pipes were made; thus the test length of the specimenbetween the grips was 400mm. The gauge length for themeasurement of strain was 50mm. The tests were car-ried out using an INSTRON testing machine and theload was increased until failure (Figure 3). For eachtensile test, the specimen was mounted on the presswith the steel pipe anchors gripped by the wedges ofthe upper and the lower jaw of the machine. The rate ofloading ranged between 250 and 300MPa/min. Theapplied load and bar elongation were recorded duringthe test using a data acquisition system monitored by acomputer.

Microstructural analysis. Scanning electron microscope(SEM) was used to investigate the phenomena of deg-radation occurring during aging. The outer surfaceand the cross-sections of the GFRP bars in ALK50and TW50 environments after 18 months of expo-sure were examined using the SEM technique and com-pared to those of the control specimens in the labenvironment.

Tensile tests results and discussion

The stress–strain curves for both unconditioned andconditioned specimens were almost linear up to failure.

All test specimens showed fiber rupture in the testlength region. Table 4 summarizes the tensile testresults of all tested bars. It can be noticed that thespecimens in the controled lab environment, LE, didnot show any degradation in the tensile strengths withage of exposure compared to the results obtained fromPhase I (Table 2). Therefore, the results reported inTable 2 were used as a reference for all other testspecimens.

Tensile strength

Figure 4 shows the tensile strength retention of the con-ditioned specimens as a function of exposure time andenvironmental conditions. In Figure 4, the tensilestrength of the conditioned specimen is divided bythat of the unconditioned specimen in the controlledlap environment, LE, and the corresponding value isdenoted as the retention ratio in percent.

For the TWR specimens, most of the reduction inthe tensile strength occurred after the first 6 months ofexposure. After 12 and 18 months of exposure, almostno additional reductions in the tensile strength wererecorded. The residual strengths were about 95%,94%, and 94% (reduction by 5.3%, 5.9%, and 6%)after 6, 12, and 18 months of exposure, respectively.Figure 5 shows a comparison between the tensilestrength retention of the TWR specimens compared

Figure 3. One GFRP specimen during tensile testing.





Table 4. Tensile test resultsa

Exposure period

Environment

Strength (MPa) Modulus of elasticity (GPa) Fracture strain (%)

Average SD CV (%) Average SD CV (%) Average SD CV (%)

6 months LE 1474 16.2 1.10 61.4 0.2 0.37 2.40 0.040 1.65

TWR 1397 11.4 0.82 60.2 0.1 0.16 2.30 0.046 1.99

TW50 1229 23.2 1.88 57.2 3.5 6.05 2.16 0.146 6.78

SWR 1393 72.6 5.21 58.4 1.3 2.22 2.38 0.080 3.36

SW50 1269 5.58 0.44 57.0 0.7 1.14 2.23 0.018 0.79

SW50DW 1371 22.2 1.62 59.6 1.7 2.81 2.30 0.114 4.96

ALK50 1296 22.3 1.72 59.3 2.3 3.80 2.29 0.049 2.15

RF 1464 21.6 1.47 60.2 1.4 2.24 2.41 0.061 2.51

JF 1454 65.6 4.51 57.7 0.4 0.62 2.56 0.097 3.78

12 months LE 1474 12.5 0.85 60.7 1.1 1.76 2.43 0.049 2.04

TWR 1388 26.3 1.89 57.5 3.2 5.52 2.41 0.130 5.37

TW50 1158 17.3 1.49 56.8 2.4 4.29 2.04 0.030 1.45

SWR 1349 4.36 0.32 57.5 3.1 5.34 2.35 0.164 6.98

SW50 1300 11.2 0.86 57.4 0.3 0.53 2.26 0.035 1.55

SW50DW 1370 22.3 1.63 57.9 1.5 2.57 2.37 0.058 2.46

ALK50 1211 29.3 2.42 56.4 0.3 0.51 2.15 0.213 6.90

RF 1459 33.2 2.27 57.8 2.1 3.62 2.53 0.085 3.37

JF 1450 21.6 1.49 59.8 2.5 4.14 2.43 0.194 8.00

18 months LE 1468 23.2 1.58 61.6 0.9 1.50 2.38 0.066 2.76

TWR 1379 49.3 3.58 61.0 2.0 3.20 2.23 0.046 2.05

TW50 1123 32.1 2.85 56.2 0.5 0.80 2.00 0.048 2.40

SWR 1267 25.5 2.01 55.3 1.6 3.00 2.29 0.023 0.98

SW50 1238 39.8 3.21 58.1 0.6 1.00 2.16 0.056 2.59

SW50DW 1331 18.8 1.41 61.6 0.8 1.30 2.15 0.060 2.78

ALK50 1149 49.2 4.28 55.9 1.5 2.70 2.02 0.084 4.16

RF 1450 8.80 0.61 60.5 1.6 2.70 2.40 0.078 3.25

JF 1443 28.0 1.94 57.1 1.3 2.30 2.53 0.040 1.58

ALK50: alkaline solution at 50�C; CV¼ coefficient of variation (%); LE: lab environment; SD: standard deviation; SEM: scanning electron microscope;

TWR: tap water at ambient; TW50: tap water at 50�C.aHighest value of CV for each property is written in bold.

95

83

94

86

93

88

99 99

94

79

92 88

93

82

99 98

94

76

86 84

91

78

99 98

0

20

40

60

80

100

120

TWR TW50 SWR SW50 SW50DW ALK50 RF JF

Res

idu

al T

ensi

le S

tren

gth

(%

)

Environment

6 Months 12 Months 18 Months

Figure 4. Residual tensile strength of tested bar after exposure.




to other GFRP bars in the literature exposed to a sim-ilar condition. It may be observed from Table 1 thatthere were two types of cement paste used by Alsayedet al.7 namely, low alkali cement (Na2O equiva-lent¼ 0.2%) and high alkali cement (Na2O equiva-lent¼ 1.0%) paste. The low alkali cement being theregular cement used in most of the studies includingthe current study, only the test results of low alkalicement paste of Alsayed et al.7 are considered for com-parison in Figure 5 and in subsequent comparisons. Itcan be noticed that the GFRP bars tested in this studyshow higher residual strengths compared to most of theGFRP bars in the literature, which are plotted inFigure 5. The test results of GFRP bars type 1 usedby Al-Zahrani4 show similar trend as observed in thepresent study but the results of type 2, which is the oneused in the present investigation show low residualstrength. One of the predominant factors that mayinfluence the test results is the procedure of extractionof bars from concrete, which was better controlled inthe present investigation. This is also evident from thelow values of SD and coefficient of variation in thepresent study. The concrete cover in the present studywas 19mm. The cover in one of the earlier studies7 wasslightly less at 15mm whereas in another study4 it wasas great as 44mm. Despite large cover in experiments ofAl-Zahrani,4 which provided more protection of bar,the loss of tensile strength was more than the presentstudy.

For the TW50 specimens, higher reductions in thetensile strength were recorded. After 6 months of expo-sure, the strength loss was about 16.7%. After 12 and18 months of exposure, this strength loss increased to21.4% and 23.5%, respectively. This indicates thatincreasing the temperature to 50�C increased the diffu-sion rate of water and harmful ions into the bars, whichresulted in a faster degradation in the resin and glass

fibers leading to the significant decrease in the tensilestrength with time, which is also confirmed by themicroscopic examination of bar discussed latter.A comparison between the TW50 specimens andother GFRP bars exposed to hot water (40–65�C) inthe literature is presented in Figure 6. It can be noticedthat the current results are comparable to most of theresults in the literature. As expected, the results in theliterature at 60 and 65�C showed higher reductions inthe tensile strength.7,30

For the specimens in seawater at room temperature,SWR, it can be noticed that the reduction in the tensilestrength increased gradually with time. It was about6%, 8%, and 14%, respectively, after 6, 12, and 18months of exposure, which is slightly higher than thereductions in the TWR environment. Increasing thetemperature to 50�C, SW50, resulted in additionalreduction in the tensile strength after 6 months of expo-sure. This reduction, however, did not increase withtime. After 6, 12, and 18 months, the strength losswas about 14.0,% 11.8%, and 15.7%, respectively.

Figure 7 shows a comparison between the tensilestrength retention of the SWR and SW50 specimensand other GFRP bars in the literature exposed to sea-water. Again, it can be seen that the GFRP bars con-sidered in this study have comparable or better residualtensile strengths compared to most of the GFRP barsreported in the literature, which is due to the reasonstated above.

For the specimens in dry/wet seawater at 50�C,SW50DW, the recorded tensile strengths were greaterthan those obtained in the SW50 specimens, which maybe due to the fact that SW50DW specimens wereexposed to wet condition for nearly 50% duration ascompared to SW50 specimens because of alternatedrying and wetting. This also indicates that the alter-nating dry/wet condition has no effect on the tensile

0

20

40

60

80

100

120

0 200 400 600 800

Res

idu

al T

ensi

le S

tren

gth

(%

)

Exposure Period (Days)

Water (room temperature) Al-Zahrani 2007 (25°C)(Type1)

Al-Zahrani 2007 (25°C)(Type2)

Al-Zahrani 2007 (25°C) (Type3)

Alsayed 2002 (23°C)

Dejke 2001 (20ºC)

Chen et al 2007 (20ºC)

Current Study (23°C)

Figure 5. Residual tensile strength of concrete-covered GFRP bars exposed to water at room temperature.





strength of the tested GFRP bars, which is in agree-ment with the results obtained by Chen et al.30

It can be also noticed, for both SW50 and SW50DWconditions, that the tensile strengths were almost stablewith time. The tensile strengths after 12 and 18 monthsof exposure were almost similar to those obtained after6 months. This may be attributed to the formation of avery thin layer of salt on the concrete surface, especiallyat higher temperature, which decreases the diffusionrate of the solution into the bars. This was not recordedin the TW50 specimens.

For the specimens in alkaline solution at 50�C,ALK50, a significant reduction in the tensile strengthwas recorded, which increased with the passage of time,which is primarily due to the damage to the resin asobserved in the microscopic examination. After 6, 12,and 18 months of exposure, the decrease was 12.1%,17.8%, and 21.7%, respectively. These reductions were

close to those obtained in the TW50 specimens. Thisindicates that, for the GFRP bars embedded in con-crete, the effect of tap water was almost similar to theeffect of alkaline environment. Thus, the alkaline envi-ronment as high as 12.5 pH has no effect on the tensilestrength of GFRP bars. This could be attributed to theconcrete around the GFRP bars. It is well known thatthe internal concrete environment is alkaline with pHbetween 10.5 and 13, depending on the design mixtureof the concrete and type of cement used. The alkalinityof concrete has been observed to have almost no effecton the tensile strength of GFRP bars, as observed fromthe test results of control specimen (Table 4), which isalso confirmed by earlier studies on bond behavior.36

As the alkalinity of concrete is not affecting the GFRPbars, thus the alkaline solution, ALK50, whose alkalin-ity is also in the range of that of concrete, is also notexpected to affect the GFRP bars.

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700

Exposure Period (Days)

Hot Water (40 to 65°C) Almusallam and Al-Salloum 2006 (40ºC)

Chen et al 2007 (60ºC)

Mathieu et al. 2009 (40ºC)

Mathieu et al. 2009 (50ºC)



Dejke 2001 (40ºC)

Current Study (50°C)Res

idu

al T

ensi

le S

tren

gth

(%

)

Figure 6. Residual tensile strength of concrete-covered GFRP bars exposed to hot water.


Figure 7. Residual tensile strength of concrete-covered GFRP bars exposed to seawater. GFRP: glass fiber reinforced polymer.




For the specimens in the two field conditions:Riyadh field condition, RF, and Gulf field condition(Jubail), JF, almost no reduction in the tensile strength(1%–2%) was recorded even after 18 months. The tem-perature conditions for the two fields being almostsame and the temperature seldom increasing beyond50�C, the humidity is the only factor that differentiatesone environment from the other. Thus, the humdity ofgulf region of Jubail has not affected the GFRP barsembedded in concrete. This indicates that the usedaccelerated laboratory environments were too harshcompared to the real-field conditions.

Young’s modulus

Figure 8 shows the retention of tensile modulus after 6,12, and 18 months in different exposures. It can benoticed that the environmental conditions did not

have significant influence on the elastic modulus ofGFRP rods. For all environments, a slight decreaserangeing between 0% and 10% was observed. Thismay be due to the fact that the modulus of elasticityis measured for low stress values and in this range ofstress, the fibers were intact in the resin, which had onlyslightly degraded under the exposure of some of theenvironmnts. Whereas the degradation of resin, how-ever small, had significant effect on the tensile strengthof GFRP bars because of the delamination occuringduring relatively early loading stage. These results arein agreement with the results reported by differentresearchers.4,6,24,31,35,37 Furthermore, Correia38 con-cluded that this behavior is due to the fact that tensilemodulus of GFRPs is only affected by temperaturesapproaching polymer glass transition temperature thatis well above 50�C – the temperature of exposure con-sidered in the present study.

100

98

93 95 93

97 97 98

94

100

95

93 95 95 95 93 95

98100

99

91 90

94

100

91

98

93

0

20

40

60

80

100

120

LE (control) TWR TW50 SWR SW50 SW50DW ALK50 RF JF

Environment


Res

idu

al T

ensi

le S

tren

gth

(%

)

Figure 8. Residual tensile modulus for different exposures.

96

90

99

93

96 95

100 10

7

99

84

97

93

98

89

104

100

93

84

96

90 90

85

101 10

6

0

20

40

60

80

100

120

TWR TW50 SWR SW50 SW50DW ALK50 RF JF

Environment


Res

idu

al T

ensi

le S

tren

gth

(%

)

Figure 9. Residual tensile strain at failure for different exposures.




Strain at failure

Figure 9 shows the retention of tensile strain at failureafter 6, 12, and 18 months in different exposures. It canbe noticed that the retention of tensile strains at failurepresents a similar pattern to that of the tensile strength.For the specimens in the tap water at room tempera-ture, Riyadh field condition, and Gulf field condition,almost no decrease in the strain at failure was recorded

after 18 months of exposure. After the 18 months ofexposure, the specimens in the seawater solution atroom temperature and at 50�C show a decrease ofabout 4% and 10%, respectively. The reduction wasabout 10% for the specimens in the wet and dry sea-water exposure at 50�C. After 18 months of exposures,the specimens in the TW50 and ALK50 environmentshow a loss of about 16% and 15%, respectively. Thefracture of GFRP bars occur after delamination of

Figure 10. SEM micrographs of the outer surface of the bars in LE, ALK50, and TW50 environments. (a)LE (b) ALK50 (c) TW50

ALK50: alkaline solution at 50�C; LE: lab environment; SEM: scanning electron microscope; TW50: tap water at 50�C.

Figure 11. SEM micrographs of the cross sections of the bars in LE, ALK50, and TW50 environments. (a)LE (b) ALK50 (c) TW50

ALK50: alkaline solution at 50�C; LE: lab environment; SEM: scanning electron microscope; TW50: tap water at 50�C.




fibers and thus the degradation of resin had almostinsignificant effect on the fracture strain.

Microstructural analysis results

Figures 10 and 11 show the SEM micrographs of theouter surface and the cross sections, respectively, of thebars in LE, ALK50, and TW50 environments at differ-ent magnifications. Figure 10 shows that the surface ofthe LE specimens was not affected. In contrast, theouter surface of the ALK50 and TW50 specimens wassignificantly deteriorated after 18 months of exposure.It can be noticed that the matrix layer at the surfacethat covers and protects the glass fibers was lost in someareas, which allows for fast diffusion of water and alkaliions into the bars.

In addition, Figure 11 shows that the matrix aroundthe glass fibers in both the ALK50 and TW50 speci-mens were deteriorated. Many gaps were observedbetween fibers and at fiber–resin interfaces, whichaffected the bond between glass fibers and vinylesterresin; consequently affected the tensile properties ofthe GFRP bars at failure. The damage to the resinleads to the non-uniform distribution of load amongfibers, which thus fail progressively leading to lowertensile strength. There were also few cracks in theglass fibers as shown in Figure 10(c) at 2000�. Atlower load levels, the glass fibers in the deterioratedarea withstood the applied load resulting in slightreductions in the tensile modulus of the GFRP barsas observed from the tensile test results (reductions ofonly 0%–10% in the tensile modulus). However, athigher load levels close to failure, these fibers werethe weak point in the GFRP bars and failed resultingin reductions in the tensile strength and fracture strainsas observed from the test results.

Conclusions

This study is a part of an ongoing durability researchprogram on FRP reinforcing bars for concrete struc-tures. From the test results presented in this paper, thefollowing specific conclusions can be drawn.

1. After 18 months of exposure, the specimens in thecontrolled lab environment and in the two harshfield conditions show almost no degradation in thetensile properties of the GFRP bars.

2. Increasing the temperature of the tap water solutionsignificantly increased the degradation rate in thetensile strength of the GFRP bars, which gotincreased from 6% at room temperature to 23.5%at 50�C after 18 months of exposure.

3. The exposure to seawater at room temperatureshowed a decrease in the tensile strength of 13.7%

after 18 months of exposure. Increasing the temper-ature to 50�C, caused 14% reduction after 6 monthsof exposures but almost no additional increasebeyond 6 months.

4. The alternate wet/dry cycles in seawater showed lessharmful effect on the tensile strength of GFRP bars,which could be related to the absence of humidityduring the dry stage that results in less diffusion ofthe solution into the bars.

5. For exposure to alkaline environment at 50�C, agradual decrease in the tensile strength was recordedwith time and a loss of 21.7% was observed after 18months of exposure.

6. For all tested specimens, the tensile modulus was notsignificantly affected even after 18 months in differ-ent exposures. These results are in agreement withthe results reported by several researchers.

7. The strains at failure, showed a similar pattern tothat of the tensile strength. The maximum decreasein the strain at failure was recorded in the alkalineand tap water environment at 50�C.

8. The SEM micrographs show that the matrix aroundthe glass fibers in both alkaline and tap water envi-ronment at 50�C were significantly deteriorated.However, there was almost no deterioration in theglass fibers. This explains the test results where sig-nificant losses were recorded in the tensile strength.

It is reasonable to assume that alkaline and tapwater environments at 50�C are too harsh comparedto the two real-field conditions that did not cause anydegradation in the tensile properties of the testedGFRP bars even after 1.5 years of exposure.

Funding

The authors would like to acknowledge the Center ofExcellence for Research in Engineering Materials(CEREM), College of Engineering, King Saud University,

for funding the project.

Acknowledgments

The authors would like to acknowledge the Specialty Unitsfor Safety and Preservation of Structures and MMB Chair for

Research and Studies in Strengthening and Rehabilitation ofStructures at the Civil Engineering Department, for their sup-port in conducting this research project.

Conflict of Interest

None declared.

References

1. ACI 440.1R-06. Guide for the design and construction of

concrete reinforced with FRP bars. Farmington Hills, MI:

American Concrete Institute, 2006.




2. Yunovich M and Thompson N. Corrosion of highway

bridges: economic impact and control methodologies.

Concr Inst 2003; 25: 52–57.3. Cusson D and Isgor B. Durability of concrete structures:

prevention, evaluation, inspection, repair and prediction.

Can J Civ Eng 2004; 21: 4–5, 19.

4. Al-Zahrani M. Tensile strength degradation of glass fiber

reinforced polymer bars in aggressive solutions both as

stand-alone and cast-in-concrete. In: Proceedings of the

eighth International Conference on FRP reinforcement for

concrete structures, Patras, Greece, July 16–18, 2007,

pp.1–10.5. El-Gamal SE, El-Salakawy EF and Benmokrane B.

Behavior of concrete bridge deck slabs reinforced with

FRP bars under concentrated loads. ACI Struct J 2005;

102: 727–735.6. Nkurunziza G, Debaiky A, Cousin P, et al. Durability of

GFRP bars: a critical review of the literature. Proc Struct

Eng Mater 2005; 7: 194–209.

7. Alsayed SH, Alhozaimy AM, Al-Salloum YA, et al.

Durability of the new generation of GFRP rebars under

severe environments. In: Proceedings of the Second

International Conference on Durability of Fiber

Reinforced Polymer (FRP) Composites for Construction

(CDCC 2002), Montreal, Quebec, Canada, May 29–31,

2002, pp.651–663.8. El-Gamal SE, El-Salakawy EF and Benmokrane B.

Influence of reinforcement on the behavior of concrete

bridge deck slabs reinforced with FRP bars. J Compos

Constr ASCE 2007; 11: 449–458.

9. Ceroni F, Cosenza E, Gaetano M, et al. Durability issues

of FRP rebars in reinforced concrete members. Cem

Concr Compos 2006; 28: 857–868.10. Alsayed S and Alhozaimy A. Effect of high temperature

and alkaline solutions on the durability of FRP bars. In:

Proceedings of the First International Conference on

Durability of Fiber Reinforced Polymer (FRP)

Composites for Construction (CDCC’98), Sherbrooke,

Canada, 5–7 August, 1998, pp.623–634.11. Chong K. Durability of composite materials and struc-

tures. In: First International Conference on Durability of

Fiber Reinforced Polymer for Construction (CDCC’98),

Sherbrooke, Quebec, Canada, 5–7 August, 1998, pp.1–12.12. Tannous E and Saadatmanesh H. Environmental effects

on the mechanical properties of E-glass FRP rebars. ACI

Mater J 1998; 95: 87–100.13. Swit G. Durability of stressed E-glass fibre in alkaline

medium. In: Cardon AH, Fukuda H, Reifsneider KL

and Verchery G (eds) Recent developments in durability

analysis of composite systems. Rotterdam, Netherlands:

Balkema, 2000, pp.473–476.

14. Valter T and Ralejs T. Durability and service life predic-

tion of GFRP for concrete reinforcement. In: Proceedings

of 4th International Conference on Fibre-Reinforced

Plastics for reinforced Concrete Structures, University of

Cambridge, Vol. 1, 2001, pp.505–514.15. Dejke V. Durability of FRP reinforcement in concrete.

Thesis for the degree of Licentiate of Engineering,

Chalmers University of Technology, Sweden, 2001.

16. Sen R, Mullins G and Salem T. Durability of E-glass/

vinylester reinforcement in alkaline solution. ACI Struct

J 2002; 99: 369–375.17. Almusallam T, Al-Salloum Y, Alsayed S, et al. Durability

of GFRP rebars in concrete beams under sustained loads

at severe environments. In: Proceedings of the 6th

International Symposium on FRP Reinforcement

for Concrete Structures, Singapore, 8–10 July 2003,

pp.823–832.18. Uomoto T. Durability design of GFRP rods for concrete

reinforcement. In: Proceedings of the sixth international

symposium on FRP reinforcement for concrete structures,

Singapore, July 8–10 2003, pp.37–50.

19. Nkurunziza G. Performance of glass FRP bars as rein-

forcement for concrete structures under the effect of sus-

tained loads and elevated temperature in humid and

alkaline environment. PhD thesis, Department of Civil

Engineering, University of Sherbrooke, Sherbrooke,

Quebec, Canada, 2004.20. Micelli F and Nanni A. Durability of FRP rods for con-

crete structures. Constr Build Mater 2004; 18: 491–503.21. Almusallam T and Al-Salloum Y. Durability of GFRP

rebars in concrete beams under sustained loads at severe

environments. J Compos Mater 2006; 40: 623–637.22. Al-Salloum Y and Almusallam T. Creep effect on the

behavior of concrete beams reinforced with GFRP bars

subjected to different environments. Constr Build Mater

2007; 21: 1510–1519.23. Demis S, Pilakoutas K and Byars E. Durability of fibre

reinforced polymers in concrete-procedures for reduced

alkalinity exposures. In: Proceedings of the eighth

International Conference on FRP reinforcement for con-

crete structures, Patras, Greece, July 16–18 2007.24. Kim H, Park Y, You Y, et al. Short-term durability test

for GFRP rods under various environmental conditions.

Compos Struct 2008; 83: 37–47.25. Porter M and Barnes B. Accelerated durability of FRP

reinforcement for concrete structures. In: Proceedings of

the 1st International Conference on Durability of Fiber

Reinforced Polymer for Construction, Sherbrooke,

Canada, 1998, pp.191–202.26. Chu W and Karbhari V. Characterization and moisture

and alkali effects on E-glass/vinylester composites. In:

Proceedings of 2nd International Conference on

Durability of Fibre Reinforced Polymer Composites

for Construction, Montreal, Quebec, Canada, 2002,

pp.359–369.27. Chu W, Wu L and Karbhari V. Durability evaluation of

moderate temperature cured E-glass/vinylester systems.

Compos Struct 2004; 66: 367–376.

28. Gaona F. Characterization of design parameters for com-

posite reinforced concrete systems. PhD thesis. Texas

A&M University, 2003.29. Wang P. Effect of moisture, temperature, and alkaline on

durability of E-glass/vinyl Ester reinforcing bars. PhD

thesis, University of Sherbrooke, Sherbrooke, Quebec,

Canada, 2005.

30. Chen Y, Davalos J, Ray I, et al. Accelerated aging tests

for evaluations of durability performance of FRP




reinforcing bars for concrete structures. Compos Struct2007; 78: 101–111.

31. Robert M, Cousin P and Benmokrane B. Durability of

GFRP reinforcing bars embedded in moist concrete.J Compos Constr 2009; 13: 66–73.

32. Mufti A, Onofrei M, Benmokrane B, et al. Durability ofGFRP reinforced concrete in field structures. ACI Spec

Publ 2005; 230: 1361–1378.33. ASTM D 7205. Standard test method for tensile proper-

ties of fiber reinforced polymer matrix composite bars,

2006.34. Syed S. Atmospheric corrosion of hot and cold rolled

carbon steel under field exposure in Saudi Arabia.

Corros Sci 2008; 50: 1779–1784.35. ACI 440.3R-04. Guide test methods for fiber reinforced

polymer (FRP) for reinforcing or strengthening concrete

structures. Farmington Hills, MI: American ConcreteInstitute, 2004.

36. Masmoudi R, Masmoudi A, Ouezdou MB, et al. Long-

term bond performance of GFRP bars in concrete undertemperature ranging from 20�C to 80�C. Constr BuildMater 2011; 25: 486–493.

37. Liao K, Schultheisz CR and Hunston DL. Effects of

environmental aging on the properties of pultrudedGFRP. Composites Part B 1999; 30: 485–493.

38. Correia J, Cabral-Fonseca S, Branco F, et al. Durability

of glass fibre reinforced polyester (GFRP) pultruded pro-files used in civil engineering applications. In: Proceedingsof the Third International Conference – Composites in

Construction, Lyon, France, July 11–13, 2005.




journal of composite materials 2013 almusallam 393 407

Documents