Construction and Building Materials 44 (2013) 458–463

Contents lists available at SciVerse ScienceDirect

Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Low-cost glass fiber composites with enhanced alkali resistance tailoredtowards concrete reinforcement

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.03.055

⇑ Corresponding author. Tel./fax: +1 517 485 9583.E-mail addresses: sayyarbi@msu.edu (M. Sayyar), soroushi@egr.msu.edu

(P. Soroushian), sadiqmuh@msu.edu (M.M. Sadiq), abmetnaco@gmail.com(A. Balachandra), jlmetnaco@gmail.com (J. Lu).

Mohammad Sayyar a, Parviz Soroushian a,⇑, Muhammad Maqbool Sadiq a, Anagi Balachandra b, Jue Lu b

a Department of Civil and Environmental Engineering, Michigan State University, E. Lansing, MI 48824, USAb Metna Co., 1926, Turner Street, Lansing, MI 48906, USA

h i g h l i g h t s

�Weak-acid cation exchangers were used as a coating for glass fiber reinforcements.� The practice requires no modification of the production process of composite bars.� The modification improved durability of the bars in alkaline environments.� The coating of composite bars did not decrease their mechanical performance.

a r t i c l e i n f o

Article history:Received 10 March 2009Received in revised form 15 March 2013Accepted 15 March 2013Available online 15 April 2013

Keywords:Glass fiber compositesConcrete reinforcementIon-exchangersAlkali resistancePultrusion

a b s t r a c t

Glass fiber reinforced polymer (GFRP) composites were modified through introduction of ion-exchangersin order to enhance their longevity in the alkaline environment of concrete. Glass fiber composites offer adesired balance of performance and cost for replacement of corrosion-prone steel reinforcement in con-crete; their rapid deterioration in the alkaline environment of concrete is, however, a major drawback.Ion exchangers are insoluble solids carrying cations (or anions) which can be exchanged with ions ofthe same sign. Cation exchangers of hydrogen form replace alkali metal cations (e.g., K+ in alkaline solu-tions diffusing into the polymer matrix) with H+. This exchange of cations neutralizes aggressive alkalinesolutions by converting K+ OH� (and Na+ OH�, etc.) into H2O. Fine weak-acid cation exchangers, whenintroduced as coating on glass fiber composite bars (applied immediately after pultrusion and before cur-ing of polymer matrix) proved to be compatible with the industrial-scale pultrusion process of compositebars without any need to modify the curing process. Thorough laboratory investigations and industrial-scale pultrusion efforts, were undertaken, which successfully demonstrated that introduction of selectedion exchangers into the polymer matrix (or a surface layer of matrix) does not interfere with the pultru-sion process, and yields significant gains in the alkali resistance of glass fiber composites. The durabilitycharacteristics of glass fiber composite bars modified with weak-acid cation exchanger coating wereinvestigated under two different accelerated aging conditions. The modified composite bars provideddesirable durability attributes under these two different accelerated aging effects, including exposureto the alkaline pore solution of concrete and salt solution. The mechanical characteristics of modifiedglass fiber composite bars (with weak-acid cation exchanger coating) were investigated by conductingcompression, flexure, and shear tests. The results indicated that the modification of pultruded bars didnot alter their mechanical performance.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Concrete is the most widely used material of construction, offer-ing major advantages in terms of moisture resistance, durability,versatility, cost, energy-efficiency and environmental impact [1].

Concrete provides a relatively high level of compressive strength;its tensile strength, however, is fairly low. Hence, efficient concretesystems generally incorporate reinforcing steel to resist tensilestresses under structural loads. While steel receives certain levelof protection against corrosion from the surrounding concrete, cor-rosion of reinforcing steel is still a predominant factor underminingthe longevity of the concrete-based infrastructure [1,2]. Epoxy coat-ing is commonly used to mitigate corrosion of steel reinforcement inaggressive environments. Susceptibility to corrosion, however, re-mains a problem in spite of epoxy coating [3,4]. The fact that total

Table 1Comparative cost and performance of different concrete reinforcement systems(12.5 mm diameter).

Reinforcement type Cost($/m)

Tensile strength(GPa)

Specific cost($/m/GPa)

Conventional steel 0.79 0.42 1.90Epoxy-coated steel 1.38 0.42 3.30Stainless steel 5.25 0.42 12.50Glass FRP 2.13 0.85 2.50Aramid FRP 9.19 1.60 5.70Carbon FRP 8.20 1.70 4.80

K+

K+

H+

H+

K OH+ -

H+

H+

H

H+

H+

H+

H

H+

H+

H+

H

H+

H+

H+

H

H+

+

+

++

Glass Fiber

Polymer Matrix

H+

H+

H

H+

+H+

H+

H

H+

+

H OH+ -(H O)2

Ionexchanger

Concrete

Moisture

Fig. 1. Conversion of diffusing KOH into H2O through ion exchange.

M. Sayyar et al. / Construction and Building Materials 44 (2013) 458–463 459

annual cost of metallic corrosion in the United States is estimated as$273 billion reflects on the tremendous economic implications ofcorrosion [5].

Several techniques have been used in order to mitigate the cor-rosion of concrete reinforcements. Stainless reinforcement hasbeen investigated as a solution to this problem [6,7]. Various devel-opment efforts have been concerned with the use of coatings suchas epoxy, to hinder corrosion of steel reinforcements in concrete[8–10].

Fiber reinforced polymer composites are, at the first glance,ideal replacements for steel in concrete. Glass fiber composites of-fer a particularly desirable balance of structural performance andcost; most importantly, fiber reinforced polymer composites arenot prone to the electrochemical processes of corrosion [11]. Table1 highlights the competitive structural performance and cost posi-tions of various composite bars against conventional, epoxy-coatedand stainless steel reinforcement in terms of tensile strength andspecific cost. These observations have naturally prompted tremen-dous research and commercial efforts towards broad use of com-posites as reinforcement in concrete [12].

While cost-competitive glass fiber composite reinforcementsystems are living up to expectations in terms of structural perfor-mance, and although they are not susceptible to electrochemicalcorrosion damage, serious doubts have been raised about theirlong-term durability in the alkaline environment of concrete[13–15]. Depending on its design, the internal concrete environ-ment is high alkaline with a pH between 10.5 and 13.5 [16,17],which is sufficient to break down the network structure of glass[18,19]. Early generations of glass fiber composite reinforcementfor concrete comprised polyester matrices with E-glass fibers andcalcium carbonate fillers, with polyester chosen as matrix largelybased on cost considerations [14]. Due to concerns with long-termstability of polyester in concrete, new matrix formulations usingvinylester/polyester blends and later vinylester alone (with fillerssuch as clay) were adopted [15]. Several studies have been con-ducted to protect glass fiber reinforced polymer rebars againstchemical attack. Gao et al. reported on the use of nanostructuredcoatings to protect of glass fibers in the alkaline environment ofconcrete [20,21]. Liu et al. proposed the use of nanoclay coatingson glass fibers in vinylester composites [22].

A novel approach was investigated in the work reported hereinfor effective control of alkali attack on glass fiber composites. Thisapproach essentially involves neutralization of the alkaline poresolution of concrete as it diffuses through the polymer matrix ofglass fiber composites [23]. Fine ion-exchange particles were em-ployed as coatings (or fillers) in order to accomplish this objective.Ion exchangers, by common definition, are insoluble solid materi-als which carry exchangeable cations (or anions) [24]. These ionscan be exchanged for a stoichiometrically equivalent amount ofother ions of the same sign. Fig. 1 presents the schematics of theapproach. The approach is quite versatile, and can tailor compos-ites to remain stable in diverse aggressive chemical environmentsencountered in different industrial applications.

2. Laboratory evaluation of ion exchanger interactions with polymer matrix

2.1. Experimental program

Preliminary tests were performed to select the most effective type of ionexchanger. Different percentages of ion exchangers (weak and strong acid) wereconsidered in order to select the optimum dosage that would enhance GFRP barsproperties without significant side effects or cost implications.

At early stages of the project, efforts were focused on blending of the ion ex-changer (as filler) with the polymer matrix of the glass fiber composites at differentdosages. Laboratory experiments did not reveal any retarding effects of ionexchangers on the curing of the vinylester resin at less than 1% ion exchanger/resinratio; some retarding effects were, however, observed for the specific materials andconditions used in industrial-scale pultrusion of glass fiber composite bars at 0.75%strong-acid ion exchanger content (by weight of resin). Therefore, it was decided tointroduce the ion exchanger as a coating rather than mixing it with the matrix.

The polymer matrix used in laboratory tests was produced by blending 50 gm ofHetron 922™ vinylester (Ashland Specialty Chemical Company, Columbus, Ohio,USA), with 0.075 gm of 6% Cobalt NAP-ALL™ (OM Group, Cleveland, Ohio, USA)and 0.0375 gm of N,N-Dimethylaniline (DMA). The ingredients were stirred manu-ally and with magnetic stirrer for 15 min and 24 h, respectively. After 24 h, 0.5 g ofMEK Peroxide was added to the mixture and manually stirred for 5 min. The weak-acid and strong-acid ion exchangers (Dowex Resins, Dow Chemical, Midland, MI,USA) at 1.47% of weight of resin and the silica sand at 8.2% by weight of resin weremixed together, half of the amount was spread on the bottom of the mold. The poly-mer mix was then poured into the mold, and the specimen was stored at 21 ± 3 �Cand 45 ± 5% relative humidity. After one hour, the second half of the ion exchanger/silica sand blend was spread on the top surface of specimens. The specimens werethen cured in oven at 65 �C for 3 h. Both strong- and weak-acid ion exchangers wereused in the experiment. Specimens coated with 100% silica sand were also tested ascontrol. Fig. 2a and b shows the uncoated and coated specimens, respectively.

Specimens were tested either in unaged condition or after different acceleratedaging effects; all specimens were conditioned at 50% relative humidity and 20 �Cprior to testing. The key accelerated aging condition considered involved immersionof specimens in an alkaline environment simulating the pore solution of concrete.This alkaline solution compromised 16.6 g/L Potassium Hydroxide (KOH), 2.36 g/Lof Sodium Hydroxide (NaOH), and 2.5 g/L of Calcium Hydroxide (Ca(OH)2); it washeated to 60 �C. The solution was selected to simulate the pore solution of concrete,and to provide a pH value of 13.5 ± 0.1; the pH values were measured daily in orderto assess any effects of cation exchangers on pH.

Flexure (ASTM D4476) tests (Fig. 3) were used to determine the quality of pul-truded composite bars prior to and after accelerated aging. Abrasion tests (ASTMC944) were used to assess any adverse interactions between the ion exchangercoating and the vinylester-based polymer matrix.

3. Test results and discussion

Fig. 4a presents the flexural strength test results, and Fig. 4bshows the abrasion weight loss of different specimens. Fig. 4a indi-cates that there is no significant difference between the flexuralstrength of specimens coated with sand or ion exchange resin.

(a) (b)

Fig. 2. Uncoated polymer specimens and those coated with ion exchanger/silica sand blend. (a) Uncoated specimens. (b) Coated specimens.

Fig. 3. Flexure test set-up.

460 M. Sayyar et al. / Construction and Building Materials 44 (2013) 458–463

The weak-acid ion exchange coating yielded a higher average flex-ural strength when compared with the strong-acid ion exchangecoating. Abrasion test results in Fig. 4b did not show any statisti-cally significant difference between the coated specimens withonly sand or with blends of sand and ion exchanger.

The measured values of pH over time are summarized in Table 2.The results clearly highlight the effectiveness of incorporating ionexchangers into composite coatings on lowering the pH of the alka-line solution into which the composite specimen is immersed.

Fig. 4. Flexural strength results and abrasion weight loss for different specimenswith vinylester (VE) resin.

4. Industrial-scale production and laboratory evaluation ofpultruded glass fiber reinforced composite bars

4.1. Production of glass fiber composite bars

The strong- and weak-acid ion exchangers were shipped to theproduction plant for use as coating during manufacturing of glassfiber reinforced composite bars. The ion exchangers were blendedwith silica sand (60% ion exchange and 40% silica sand by weight).This blend was spread onto the glass fiber composite bar surfacesafter pultrusion of the bars (in a continuous process).

The production process was successful, and the blend of ion ex-changer and silica sand could be applied onto glass fiber compositebars following the process commonly used for application of silicasand. The composite bars were successfully cured, and the generalappearance of the bars with ion exchanger coating was similar tothat of control bars (Fig. 5). The weak-acid ion exchanger particlesformed strong bonds to the surface of composite bars; this was not

the case with the strong-acid ion exchanger particles. Hence, theexperimental work on composite bars focused on those with ion-exchanger coating as well as control bars (with silica sand coating).Fig. 6 shows micrographs of glass fiber composite bars with differ-ent coatings.

4.2. Experimental program

An experimental program was conducted to assess the mechan-ical performance and durability characteristics of glass fiber com-

Table 2Effects of strong acid (SA) and weak acid (WA) ion exchanger coating on pH of thealkaline solution into which the composite specimen is immersed.

Day 0% WA SA

1 12.88 ± 0.14 12.88 ± 0.36 12.88 ± 0.373 13.03 ± 0.16 13.01 ± 0.33 12.97 ± 0.296 12.93 ± 0.21 12.97 ± 0.44 12.93 ± 0.417 12.96 ± 0.21 12.98 ± 0.41 12.93 ± 0.289 12.9 ± 0.2 12.91 ± 0.42 12.88 ± 0.26

13 12.9 ± 0.19 12.88 ± 0.31 12.85 ± 0.5114 12.8 ± 0.17 12.8 ± 0.36 12.8 ± 0.3623 12.81 ± 0.17 12.3 ± 0.4 12.1 ± 0.2727 12.85 ± 0.13 12 ± 0.46 12.1 ± 0.3234 12.67 ± 0.18 11 ± 0.23 10.77 ± 0.3340 12.65 ± 0.2 10.7 ± 0.28 10.37 ± 0.23

M. Sayyar et al. / Construction and Building Materials 44 (2013) 458–463 461

posite bars with ion exchanger (and silica sand) coatings. Themechanical properties evaluated in this investigation includedflexure, shear and compressive strengths of pultruded compositebars. Two different accelerated aging effects representing variousenvironmental effects on composite bars were considered. Theseaging conditions included exposure to the simulated alkaline poresolution of concrete and salt water. The primary reason for use ofion exchanger coating on glass fiber composite bars is to enhancethe alkali resistance of composites. The alkaline pore solutionwas prepared (as described earlier) with pH of 13.5 ± 0.1. The saltwater was prepared following ASTM G44-94 requirements with3.5% concentration of sodium chloride. The GFRP bars were im-mersed in the pore solution and salt water for three months.

The standard test method ASTM D4476-97 for flexural proper-ties of fiber-reinforced pultruded plastic rods was used to deter-mine the flexural strength of unmodified and modified glass fibercomposite bars prior to and after different accelerated aging ef-fects. Fig. 7 shows the set-up used for performance of flexure testson composite bars. Flexural strength was determined using thepeak load in flexural tests as follows: rf ¼ 8PL

pd3 where, rf is the ulti-mate flexural stress in the outer fibers at midpoint, P is the appliedload, L is the rod span, and d is the bar diameter.

A simple shear test method was developed for evaluation ofglass fiber composite bars. This test method does not produceany significant bending moments, and determines the strength ofcomposite bars in shear. As shown in Fig. 8, the shear test set-upconsists of two (upper and lower) components; the upper part con-tains a hole (with diameter to suit the test specimen) where the

Fig. 5. Glass fiber composite bars with different coatings (strong-acid ‘‘left’’, weak-acid ‘‘middle’’, and silica sand ‘‘right’’).

Fig. 6. Optic micrographs (100�) of glass fiber composite bars with differentcoatings: (a) silica sand coating; (b) strong-acid ion exchanger coating; and (c)weak-acid ion exchanger coating.

specimen is placed during the test. The two components are con-nected together by the specimen during the shear test.

The compressive strength of composite bars is relatively diffi-cult to determine, and a large degree of variability in compressiontest results is commonly experienced. A key challenge in compres-sion test lies in the need for subjecting the specimen to a uniformstate of stress and strain without buckling. Any slight variation inthe test specimen geometry can result in eccentricity that willcause premature failure. Examples of failure modes stemming fromgeometric instability in compression test are end crushing, longitu-dinal splitting of fibers, global specimen buckling; shear failure,and local fiber buckling. The choice of compression test setupand specimen geometry can reduce the possibility of such prema-ture failure modes. Material quality can also affect buckling;

Load Cell

End of Testing Specimen

Upper Part

Lower Part

Fig. 8. Shear test setup.

Hardened Block

Hardened Ball

Load Strut

Test Specimen

Hardened Block

Fig. 9. Compression test setup.

Fig. 7. Flexure test setup.

Table 3Flexural test results for unmodified and modified composite bars (average values).

Acceleratedaging condition

Unmodified GFRP bars Weak-acid modified GFRPbars

Flexuralstrength(MPa)

Strengthloss (%)

Flexuralstrength(MPa)

Strengthloss (%)

Unaged 173.71 ± 4.93 – 191.06 ± 5.94 –Pore solution 122.55 ± 5.53 29.45 145.87 ± 5.91 23.41Salt water 138.51 ± 5.44 20.26 169.86 ± 5.97 11.1

462 M. Sayyar et al. / Construction and Building Materials 44 (2013) 458–463

flawed areas within the material where the matrix is unable totransfer applied loads between fibers offer reduced compressivestrength; it is likely that buckling would overcome such weakerareas prior to material failure in compression. Fig. 9 presents thecompression test setup developed for testing glass fiber composite

bar specimens. The setup comprises two (upper and lower) hard-ened blocks and a ball to equally distribute the load on the speci-men. The specimen is stabilized during the test using a load strutthat can move freely only in the vertical direction (along the spec-imen length). Specimen length was selected to be two to threetimes its diameter in order to reduce the chance of prematurebuckling during the compression test.

5. Experimental results

Flexure, shear and compression tests were conducted onunmodified and modified (with weak-acid ion-exchanger parti-cles) glass fiber composite bars in unaged condition and afterexposure to pore solution and salt water. Modification with fine,weak-acid ion exchanger also generated gains in the flexuralstrengths of unaged glass fiber composite bars. Results of flexuretests (Table 3) indicated that the average flexural strength ofweak-acid modified GFRP bars at the unaged stage increasedfrom 173.7 MPa to 191.1 MPa. This gain can be attributed to ef-fect of modification on bonding between fibers and the polymermatrix. After extended exposure to pore solution and salt water,modified composites experienced less drop in flexural strengthwhen compare with unmodified ones. The drops in flexuralstrength of unmodified GFRP subjected to pore solution and saltwater were about 29% and 20%, respectively; the correspondingvalues for modified bars were about 23% and 11%, respectively.This finding validates the primary hypothesis of the approach,where ion-exchange phenomena are relied upon to reduce theaccess of aggressive ions to glass fibers.

The shear strength test results are summarized in Table 4.Gains in shear strength were also observed when glass fiber com-posite bars were modified through application of a blend of fine,weak-acid ion exchanger and silica sand coating, when comparedagainst control composite bars with silica sand coating. The aver-age unaged shear strength of modified GFRP was 166 MPa, whichdropped to 113 MPa and 115 MPa after accelerated aging underexposure to pore solution and salt water, respectively. Theunmodified GFRP bar provided 117 MPa shear strength in unagedcondition, which dropped to 77 MPa and 78 MPa after externalexposure to pore and salt solution, respectively. The drop in shearstrength of unmodified GFRP bars was 34.5% and 33.4% in poresolution and salt water, respectively; the corresponding dropsfor modified GFRP bars were decreased to 32.3% and 30.6%respectively.

Compression test results (Table 5) indicated that the averagecompressive strength in unaged stage for modified GFRP barswas is lower than that of unmodified GFRP bars. However, the for-mer bars, exhibited better durability under accelerated aging ef-fects when compared with the latter one. The drop in averagecompressive strength for unmodified glass fibers composite bars,in pore solution and salt water were 27.6% and 16.6%, respectively.Modification with weak-acid ion exchanger and silica sand reducedthe drops in pore solution and salt water to 16.4% and 11.3%,respectively.

Table 4Shear strength of unmodified and modified composite bars (average values).

Accelerated aging condition Unmodified GFRP bars Weak-acid modified GFRP bars

Shear strength (MPa) Strength loss (%) Shear strength (MPa) Strength loss (%)

Unaged 117 ± 3.54 – 166.41 ± 5.44 –Pore solution 76.65 ± 2.71 34.49 112.64 ± 4.41 32.31Salt water 77.94 ± 2.43 33.38 115.42 ± 3.8 30.64

Table 5Compressive strength of unmodified and modified composite bars (average values).

Accelerated aging condition Unmodified GFRP bars Weak-acid modified GFRP bars

Compressive strength (MPa) Strength loss (%) Compressive strength (MPa) Strength loss (%)

Unaged 109.61 ± 6.23 – 101.91 ± 6.97 –Pore solution 79.33 ± 5.06 27.60 85.19 ± 6.65 16.40Salt water 91.42 ± 5.09 16.59 90.45 ± 5.32 11.27

M. Sayyar et al. / Construction and Building Materials 44 (2013) 458–463 463

Modification with weak-acid ion-exchanger consistently im-proved the stability of GFRP bar flexural, shear, and compressivestrength under accelerated aging effects involving exposure to poresolution and salt water. In unaged and, for modified GFRP bars pro-vided higher flexural and shear strength when compared withunmodified ones.

6. Conclusions

Glass fiber composite bars were modified with week-acid ion-exchanger coating for enhanced durability in concrete environ-ment. An experimental study was conducted to assess the gainsin composite bar durability resulting from this modification. Thekey conclusions of this study are listed below:

(1) Fine weak-acid cation exchangers, when applied as a coatingimmediately after the pultrusion process, are compatiblewith the conventional industrial-scale pultrusion processof glass fiber reinforced vinylester matrix composite bars.This practice does not require any modification of the pro-duction process of the composite bars used as reinforcementin concrete.

(2) Modification of glass fiber composite bars with weak-acidcation exchanger does not alter (or, in some cases, improves)the physical and mechanical characteristics of bars.

(3) Glass fiber reinforced composite bars modified with weak-acid cation exchanger coating offer improved durabilitycharacteristics when compared with control bars underaccelerated aging effects involving immersion in the alkalinepore solution of concrete and in salt solution.

(4) Strong-acid ion exchanger particles (unlike the weak-acidion-exchanger particles) do not strongly bond to compositebars in the pultrusion process; this points at the potentiallyadverse interactions of strong-acid ion-exchanger with cur-ing of the vinylester resin used in this investigation.

Acknowledgment

This project was sponsored by the National Science FoundationAward # 0215179.

References

[1] Neville AM. Properties of concrete; 1995.[2] Shi X et al. Durability of steel reinforced concrete in chloride environments: an

overview. Constr Build Mater 2012;30:125–38.[3] Kumar V. Protection of steel reinforcement for concrete – a review. Corros Rev

2011;16(4):317–58.[4] Shackelford J, Muralidhara M. Materials science for engineers. New

Jersey: Prentice Hall; 2009.[5] Thompson NG, Yunovich M, Dunmire D. Cost of corrosion and corrosion

maintenance strategies. Corros Rev 2011;25(3–4):247–62.[6] García-Alonso M et al. Corrosion behaviour of new stainless steels reinforcing

bars embedded in concrete. Cem Concr Res 2007;37(10):1463–71.[7] Kim B, Boyd A, Lee J-Y. Effect of transport properties of fiber types on steel

reinforcement corrosion. J Compos Mater 2011;45(8):949–59.[8] Tang F et al. Corrosion resistance and mechanism of steel rebar coated with

three types of enamel. Corros Sci 2012.[9] Zhou Q et al. Effects of coating/electroplating on corrosion resistance of steel

bar in reinforced concrete. Adv Mater Res 2012;446:3176–9.[10] Dong S et al. Corrosion behavior of epoxy/zinc duplex coated rebar embedded

in concrete in ocean environment. Constr Build Mater 2012;28(1):72–8.[11] Gibson RF. Principles of composite material mechanics. CRC Press; 2011.[12] ACI Committee 440. Guide for the design and construction of concrete

reinforced with FRP bars. ACI 440.1R-06, A.C.I., Farmington Hills, MI, 44; 2006.[13] Prian L, Barkatt A. Degradation mechanism of fiber-reinforced plastics and its

implications to prediction of long-term behavior. J Mater Sci1999;34(16):3977–89.

[14] Bank LC, Puterman M, Katz A. The effect of material degradation on bondproperties of fiber reinforced plastic reinforcing bars in concrete. ACI Mater J –Am Concr Inst 1998;95(3):232–43.

[15] Soroushian PRS, Drzal LT. Non-metallic reinforcement of concrete bridgedecks. Report MSU ENGR-001-01. College of Engineering, Michigan StateUniversity; January 2001. p. 152.

[16] Diamond S. Effects of two danish flyashes on alkali contents of pore solutionsof cement-flyash pastes. Cem Concr Res 1981;11(3):383–94.

[17] Angus M, Glasser F. The chemical environment in cement matrices. In: MRSproceedings. 1985. Cambridge Univ Press.

[18] Chaallal O, Benmokrane B. Physical and mechanical performance of aninnovative glass–fiber-reinforced plastic rod for concrete and groutedanchorages. Can J Civ Eng 1993;20(2):254–68.

[19] Bank LC, Gentry TR, Barkatt A. Accelerated test methods to determine the long-term behavior of FRP composite structures: environmental effects. J Reinf PlastCompos 1995;14(6):559–87.

[20] Gao SL, Mader E, Plonka R. Nanostructured coatings of glass fibers:improvement of alkali resistance and mechanical properties. Acta Mater2007;55(3):1043–52.

[21] Gao SL, Mader E, Plonka R. Coatings for glass fibers in a cementitious matrix.Acta Mater 2004;52(16):4745–55.

[22] Liu M-Y et al. Glass fibers with clay nanocomposite coating: Improved barrierresistance in alkaline environment. Compos A Appl Sci Manuf2011;42(12):2051–9.

[23] Soroushian P et al. Effects of ion-exchange fillers on durability of the polymermatrix of composites. Polym Compos 2005;26(5):679–83.

[24] Helfferich F. Ion exchange. Dover Publications; 1995.