Tensile Properties of Carbon Fiber Textile Reinforced Mortar (TRM) Characterized by Different Anchorage Methods

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1 Kim et l. Int J Concr Struct Mter (218) 12:73 Interntionl Journl of Concrete Structures nd Mterils RESEARCH Open Access Tensile Properties of Cron Fier Textile Reinforced Mortr (TRM) Chrcterized y Different Anchorge Methods Hee Seung Kim, Gi Toi Truong, Sung Ho Prk nd Kyoung Kyu Choi * Astrct In the present study, tensile tests were crried out to investigte the tensile ehviors of textile reinforced mortr (TRM) composite specimens. The TRM specimens were composed of one lyer of cron fiers, s the reinforcement, nd luminum cement-sed mortr, s the mtrix. The primry prmeter of the test specimens ws the nchorge method, which ws newly developed to improve the tensile ehvior of the composite: spreding the ends of fier filments, reinforcing the ends of fier filments using glss fier reinforced polymer ts or steel rers, nd coting the ends of fier filments with luminum oxide powder. From the test results, it ws found tht most TRM specimens using developed nchorge methods exhiited ductile ehvior. Moreover, the use of the developed nchorge methods could increse the crcking strength nd pek strength of the composite specimens up to 66.1 nd 97.9%, respectively. The filure mode of the test specimens ws governed y prtil rupture of cron fiers, except for the BASE specimen nd specimen reinforced with steel rers. Finlly, the tensile stress strin reltionship of TRM specimens ws idelized s iliner stress strin response curves following the guidnce specified in ACI 549.4R-13. Keywords: tensile test, cron fiers, luminum cement, textile reinforced mortr, nchorge 1 Introduction Externlly onded composite mterils, such s fier reinforced polymers (FRPs), were widely used s retrofitting technique y engineers for repiring nd strengthening existing msonry nd concrete structures. The dvntges of FRP composites re; they re lightweight, hve corrosion resistnce cpcity, excellent curing nd strength development t room temperture, high tensile strength nd elstic modulus, nd they cn e rrnged in vrious shpes s required in n ppliction (Di et l. 211; Ry nd Rthore 215). However, the cost of orgnic mtrices, such s epoxy resin, is reltively high. The use of orgnic mtrices in FRP composites could result in reduction of tensile strength t high tempertures, diminish the vpor permeting cpcity nd low fire resistnce. In ddition, their *Correspondence: kkchoi@ssu.c.kr School of Architecture, Soongsil Univ., 369 Sngdo ro, Dongjk gu, Seoul, 6978, South Kore Journl informtion: ISSN / eissn comptiility with sustrte mterils should e crefully considered nd there is no reversiility of the instlltion, such s sustitutility nd removility (Wu et l. 214; Co et l. 212). Thus, from 198s, the use of inorgnic mtrices, e.g. cement-sed mortrs, s sustrtes of composite mterils, ws introduced to expectedly reduce the shortcomings s forementioned (Brmeshuer 26; Nnni 212). The development of cement-sed mortrs resulted in n lterntive solution etween FRP composites nd fier reinforced mortr (FRM) or textile reinforced mortr (TRM) composites for the structurl retrofitting. The TRM composite consisted of fiers in form of textiles nd inorgnic mtrices. The use of textiles s reinforcement fric could help to overcome the interfcil onding etween fiers nd mortr mtrix in TRM composites due to their good interlock performnce through textile mesh openings (Trintfillou nd Ppnicolou 25; Omres 215). However, for the further pplictions of TRM composites, numer of experimentl progrms hve een performed for etter understnding of the mechnicl properties, especilly tensile ehviors of TRM composites The Author(s) 218. This rticle is distriuted under the terms of the Cretive Commons Attriution 4. Interntionl License ( iveco mmons.org/licen ses/y/4./), which permits unrestricted use, distriution, nd reproduction in ny medium, provided you give pproprite credit to the originl uthor(s) nd the source, provide link to the Cretive Commons license, nd indicte if chnges were mde.

2 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 2 of 13 (Contmine et l. 211; Donnini et l. 216; Crozzi et l. 214; Lrring et l. 214). Cggegi et l. (217) investigted experimentlly the effects of different reinforcing textile rtios nd vrious kinds of mortr on the tensile ehvior of slt TRM composite specimens. From the test results, it ws found tht the use of more resistnt mortr resulted in closer crcks in the TRM specimens, which developed t the loction of the trnsversl roving. In ddition, using lower strengthening rtio of slt fiers showed higher tensile strengths. In the study y Donnini nd Corinldesi (217), the sme ehvior ws lso investigted when multiple fric plies were used in the TRM composites. Moreover, the tensile test results lso indicted tht the use of coted frics, including cron nd slt fiers, could improve the ultimte tensile strength nd modulus of elsticity in the crcked stge (Signorini et l. 218). The use of cementitious mortr slightly incresed the ultimte strength of FRCM composites in comprison to tht of lime-sed mortr. Besides, in the cse of the coted cron reinforcement fric, using cementitious mortr insted of lime-sed mortr might chnge the filure mode from fiers slippge within the mtrix to fiers rupture. D Antino nd Ppnicolou (218) compred the effect of two different tensile test setups including clmping-grip nd curved-flnge methods on mechnicl ehvior of inorgnic mtrix composites. The clmpinggrip method ws pplied to rectngulr prism specimens while the curved-flnge method ws pplied to dumell specimens. From the test results, it ws found tht using different test setups resulted in completely different tensile ehviors for the sme composite mteril. Thus, the tensile test results should e consistent with selected test setups. In ddition, Donnini nd Corinldesi (217), De Sntis nd de Felice (214), Lrring et l. (213) lso investigted tht the use of vrious clmping methods of the TRM specimens t the gripping res could significntly ffect the tensile ehviors of the composite specimens during the direct tensile test. In this study, experimentl studies on the tensile ehviors of TRM specimens were investigted through direct tensile tests ccording to ACI 549.4R-13 (213) nd AC434 (211). The specimen ws mnufctured y using one lyer of cron fier-textile reinforcement nd luminum cement-sed mortr. Different nchorge methods were developed in the gripping res to improve the tensile ehvior of the composite. Such methods included spreding the ends of fier filments, reinforcing the ends of fier filments using glss fier reinforced polymer (GFRP) ts or steel rers nd coting the ends of fier filments with luminum oxide powder. The test results were nlyzed in terms of initil stiffness, crcking strength nd strin, modulus of elsticity of crcked stge, nd pek strength nd correltive ultimte strin. Finlly, the test results were idelized s iliner tensile stress strin response curves sed on ACI 549.4R-13 (213) stndrd. 2 Experimentl Progrm 2.1 Mteril Properties In this study, the textile reinforced mortr (TRM) ws fricted using two primry elements of textile reinforcement nd mortr. The textile reinforcement ws mde from T7S cron fier yrns. Ech cron fier yrn hd n verge thickness of.21 mm nd consisted of 24k filments with filment dimeters of 7 μm (see Fig. 1). In ddition, s given y the mnufcturer, the tensile strength, elstic modulus nd ultimte tensile strin of the cron fier filments were 49, 23, MP, nd.15, respectively. Figure 1, c present the detils of cron fier yrn used s textile reinforcement in this study. It should e noted tht such textile reinforcement ws fricted in lortory y the uthors. In generl, for ech textile reinforcement in the longitudinl direction, four yrns of cron fier were used, nd the cron fiers in the longitudinl nd horizontl directions were glued together (Fig. 1). It should lso e noted tht the longitudinl yrns were composed of three cron fier lyers nd kept stright during the mking of the test specimens. Thus, the totl thickness of longitudinl yrns ws pproximtely.63 mm nd the numer of cron fier filments ws 72,. The horizontl yrns were composed of two lyers of cron fier nd were in rided shpe. Consequently, the horizontl fiers hve theoreticl thickness of.42 mm nd comprised of 42, cron fier filments. The textile reinforcement net ws intentionlly mde to e lnced with spcing of 2 mm, center to center (see Fig. 1c). The free spce etween yrns ws pproximtely 13.2 mm. In this study, n lumin cement-sed mortr ws used s the mtrix. Alumin cement hs excellent het resistnce nd fluidity. In the mortr proportion, grnulr snd with grnultion rtio of 2.6 ws used. The rtio etween wter nd grnulr snd ws 1:2, nd tht of grnulr snd nd fine ggregte ws 1:3. The verge compressive strength of mortr ws MP, which ws tested ccording to the test stndrd KS L 515 (217). 2.2 Test Specimens In this study, direct tensile test of TRM specimens ws crried out ccording to ACI 549.4R-13 (213) nd AC434 (211). Figure 2 shows the geometricl detils of the TRM test specimen. In the figure, the TRM test specimen hs prismtic shpe with rectngulr cross

3 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 3 of 13 Longitudinl fiers 6.8 mm 2 mm Horizontl fiers 2 mm Fig. 1 Detils of cron fier mesh used s textile reinforcement. filment provided y mnufcturer, mesh, c Geometricl dimensions. c 8 Gripping re (GFRP plte) Trns. zone Mesurement rnge of the LVDTs Trns. zone Gripping re (GFRP plte) Fig. 2 Typicl detils of test specimens Unit: mm section of 8 3 mm (width thickness). The overll length of the TRM test specimen ws 45 mm, including the gripping res, trnsition zones nd centrl re in which the strin of the specimen could e mesured. The length of the gripping re, trnsition zone nd centrl re ws 125, 1, nd 18 mm, respectively. At the gripping res (t two ends of the test specimen), glss fier reinforced polymer (GFRP) pltes were used s clmping grip mterils, nd the determintion of the gripping length ws sed on the studies y Donnini nd Corinldesi (217) nd Aroled et l. (216). The purpose ws to void slippge etween the test specimen nd grip of the testing mchine nd ny dmge within the gripping zones. In ddition, it ws lso to induce pressure to the specimen ends to prtilly enhnce the stress-trnsfer mechnism etween the reinforcement fric nd mtrix. It ws noted tht the stress in the trnsition zone ws influenced y the clmping pressure. In some cses the crck hd occurred in the trnsition zone. Therefore, in this study, the GFRP pltes in the gripping res were lengthened to the trnsition zones to void such crcks (see Fig. 2). It lso should e noted tht ll test specimens hd the sme geometricl properties nd clmping grip method. In ddition, s shown in Fig. 2, for ech test specimen, only one lyer of reinforcement fric ws emedded in the mortr mtrix. Five different nchorge methods were developed nd experimented in this study. The purpose of the vrious nchorge methods ws to improve the onding etween fiers nd mtrix to prevent slippge of fiers efore reching the ultimte lod-crrying cpcity (Crozzi nd Poggi 215; Ascione et l. 215; Leone et l. 217).

4 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 4 of 13 For ech nchorge method, two specimens were mde nd tested. The numer of test specimens ws reltively fewer thn the other studies (Donnini nd Corinldesi 217; De Sntis nd de Felice, 214; Crozzi et l. 217; D Antino nd Ppnicolou 217). Thus, in the further reserch, for selected nchorge methods, dditionl test specimens re necessry to improve the test results reliility. The detils of nchorge methods re presented in Fig. 3. In the figure, it cn e seen tht the nchorge ws pplied only in the gripping res. It should e noted tht to distinguish the TRM test specimens, the specimens were nmed following the nchorge methods. In Fig. 3, no nchorge method ws pplied to the TRM specimen, which ws considered s control specimen nd nmed BASE. Figure 3 descries the detils of the TRM specimen nmed SPREAD. In this test specimen, t the gripping res, cron fier filments of the textile reinforcement mesh were seprted nd expnded to enlrge the onding re etween cement mortr nd textile reinforcement mesh. In the cse of the specimen nmed TAB (see Fig. 3c), two glss fier reinforced polymer (GFRP) ts with dimensions of 6 6 mm were instlled inside the specimen to clmp textile reinforcement mesh t the gripping res. In ddition, with holes hving dimeter of 5 mm eqully rrnged on GFRP ts, it ws expected to improve the fixing performnce y the pressure etween the cement mortr nd GFRP ts. In Fig. 3d, t the end of the specimen nmed REBAR, two short pieces of D1 reinforcing rs, hving dimeters of 1 mm nd lengths of 8 mm, were wound nd fixed y longitudinl cron fier filments of the textile reinforcement mesh. In the cse of the specimen nmed L_COAT (Fig. 3e), cron fier filments of textile reinforcement mesh in the gripping res were prtilly impregnted with epoxy resin nd coted with luminum oxide powder tht hd dimeter of 25 μm (Bruer et l. 1967; Xie nd Sherwood 1994). The nchorge detils of the specimen nmed SL_COAT re presented in Fig. 3f. Similr to the L_COAT specimen, cron fiers in the gripping re of SL_COAT specimen were first impregnted with epoxy resin. Two cron fier sheets (6 12 mm) were then ttched to clmp such cron fier mesh y using epoxy resin. Finlly they were lso coted with luminum oxide powder. 2.3 Test Setup nd Mesurements Tensile tests were performed using universl testing mchine (UTM) with loding cpcity of 1 kn. The test setup of the tensile tests for TRM specimens is presented in Fig. 4. As shown in the figure, prior to testing, the gripping res of the TRM test specimens were clmped with couple of steel pltes nd then fstened y use six olts. The clmping force induced y the fstening force of these six olts ws considered to e the gripping pressure pplied to the test specimens. In this study, the clmping force pplied to the specimen surfce ws pproximtely 126 kn resulted in clmping stress of 12.6 MP. This clmping stress ws much lower thn the compressive strength of the mtrix (39.56 MP), thus the mortr crushing could e voided. In ddition, the slippge etween the GFRP nd steel pltes could lso e prevented. The lignment of the test specimen nd steel pltes ws very importnt to void ending moment tht could rise during the loding. The test specimens were then connected with testing mchine through steel r, which cn rotte freely (see Fig. 4). Finlly, the tests were crried out in displcement control mnner with test velocity of.5 mm/min. In this study, to mesure the tensile strin of the test specimens, two liner vrile displcement trnsformers (LVDT) were instlled within the centrl re (18 mm) long the verticl direction of the test specimens. In ddition, nother LVDT ws centrlly plced on the horizontl direction of the test specimen to mesure the rottion Sym. Unit: mm filments GFRP plte Steel rer (D1) Epoxy 12 sheet c d e f Fig. 3 Detils of nchorge methods. BASE, SPREAD, c TAB, d REBAR, e L_COAT, f SL_COAT.

5 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 5 of 13 F F Bonded length 125 Guge length 18 1 Steel plte GFRP plte LVDT (Axil Disp.) LVDT (Rottion) Bonded length F F Unit: mm Fig. 4 Tensile test setup. Scheme of test setup, Photo of test setup. of the specimen due to prtil stiffness reduction (see Fig. 4). Gripping re Tensile filure 3 Experimentl Results nd Discussions 3.1 Mode The tensile strength of TRM test specimen is minly governed y the strength of cron fiers nd interfcil onding strength etween the cron fiers nd mortr mtrix. Figure 5 shows three different types of filure modes tht were otined during tensile test of TRM specimens ccording to the studies y Loene et l. (217) nd Crozzi et l. (217). Figure 5 descries the filure mode A, of which tensile filure occurs in the trnsition zone ner the gripping re. This is due to the ixil stress in the trnsition zone induced y the comintion of compressive force of the gripping clmps nd pplied tensile force. mode B (Fig. 5) is cused y rupture of cron fiers fter crcking of the mortr mtrix long the length of the test specimen. Menwhile, in the cse of the filure mode C (Fig. 5c), mjor crcking of the mortr mtrix is lso oserved ut the finl filure is due Gripping re Slippge Cron textile Mtrix Cron textile Tensile filure Mtrix Gripping re Cron textile Mtrix c Fig. 5 mode of direct tensile test of TRM test specimens (Leone et l. 217; Crozzi et l. 217). mode A, mode B, c mode C. to the slippge of cron fiers within the mortr mtrix t the gripping re. Figure 6 presents crck ptterns of the test specimens in this study. In the cse of the BASE specimen (Fig. 6), the crcks occurred ner the gripping re. However,

6 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 6 of 13 Fig. 6 mode of TRM test specimens in this study. BASE, SPREAD, c TAB, d REBAR, e L_COAT, f SL_COAT. the finl filure is due to the fiers slippge within the mortr mtrix (filure mode C). The filure mode of the REBAR specimen ws lso denoted s C, with the susequent fiers slippge fter crcking of the mortr mtrix (see Fig. 6d). The slippge etween the fiers nd mortr could e explined tht due to the compressive ction of the clmping grip, minor crcks might occur t the interfce etween the mortr nd steel rers, which could result in the reduction of interfcil onding in the gripping re. Menwhile, in the cse of the SPREAD specimen, s shown in Fig. 6, t filure, the longitudinl cron fiers were ruptured fter the first crck of the mortr mtrix. However, the filure mode of the SPREAD specimen could e clssified into A or B ecuse such crcks occurred oth ner the gripping re nd in the centrl zone. The other test specimens- including TAB, L_COAT nd SL_COAT in Fig. 6c, e, f, respectively-exhiited lmost the sme filure modes s those of the SPREAD specimen. 3.2 Tensile Behviors of TRM Test Specimens In this study, the tensile ehviors of TRM test specimens were investigted in terms of initil stiffness (E) referred to s un-crcked stge of the specimens, crcking strength (f ft ), pek strength (f fu ) nd ultimte strin (ɛ fu ). The initil stiffness ws determined in the rnge of 4% of the crcking strength nd correltive strin. The strength ws clculted s the pplied lod divided y the totl cross section re of cron fier filments. The ultimte strin ws defined s the point from the test results. In the BASE specimen, ɛ fu ws defined in the descending rnch. However, in the other specimens, ɛ fu ws defined in the scending rnch. In ddition, coefficient of vritions of ech prmeter nd envelope of experimentl curves ws lso provided to estimte the vriility of the test results. The stress strin response curves of the TRM test specimens in this study re presented in Figs. 7, 8 nd Tle 1. In generl, ll the test specimens showed lod

7 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 7 of Minimum strin for flexurl memer Crcking of the mtrix Slip of fier reinforcement filments; tensile strength is MP Minimum strin for flexurl memer Crcking of the mtrix filments; tensile strength is MP Minimum strin for flexurl memer Crcking of the mtrix filments; tensile strength is MP Minimum strin for flexurl memer Crcking of the mtrix Slip of fier reinforcement filments; tensile strength is MP Crcking of the mtrix c filments; tensile strength is MP Minimum strin for flexurl memer e Crcking of the mtrix Fig. 7 Stress strin reltionship of test specimens. BASE, SPREAD, c TAB, d REBAR, e L_COAT, f SL_COAT. filments; tensile strength is MP Minimum strin for flexurl memer d f drop in the experimentl curves due to the crck development within the mortr mtrix. After tht, the finl filure of these test specimens ws governed y the rupture of cron fiers or fiers slippge. The contriution of mortr in the uncrcked stge is ctully pprent ecuse the initil stiffness is considerly higher thn tht of the cron fier filments. As shown in Fig. 7, the tensile stress strin curves were locted ove tht of cron fier filments except for the cses of the BASE nd REBAR specimens. This is due to the tension stiffening effect of the mortr mtrix (D Antino nd Ppnicolou 217). It should e noted tht the ultimte tensile strength nd strin of cron fier filments otined from the test results in this study ws MP nd.15, respectively. In the cse of the BASE specimen (Fig. 7), fter crcking, residul stress showed sudden drop due to the slippge of fiers within the mortr mtrix. As presented in Tle 1, the verge initil stiffness of the BASE specimen ws GP with coefficient of vritions (COV) of.29. The verge crcking strength ws MP with COV of.174. In ddition, the verge ultimte strin ws oserved s.44 with COV of.16. The pek strength of the BASE specimen could not e determined

8 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 8 of BASE SPREAD 2 16 BASE TAB BASE REBAR BASE L_COAT c BASE SL_COAT d e Fig. 8 Effect of nchorge methods on tensile ehviors of test specimens. Effect of SPREAD method, Effect of TAB method, c Effect of REBAR method, d Effect of L_COAT method, e Effect of SL_COAT method ecuse of the fiers slippge in one specimen. Thus, in this BASE specimen, the pek strength (846. MP) ws otined from only one test specimen. For ll tht, it cn e seen tht the pek strength ws lmost the sme s the crcking strength. Figure 7 presents the stress strin reltionships of the SPREAD specimens. As shown in the figure, during the crck development, the tensile stress ws smoothly trnsferred to the cron fiers, nd the slope of the stress strin curve ws lmost prllel to tht of the cron fier filments. As presented in Tle 1, the initil stiffness, crcking strength, pek strength, nd ultimte strin of the SPREAD specimen ws GP, 891.7, MP nd.59. According to ACI (214), for flexurl concrete memer, the minimum tensile strin tht is required is.4. Thus, the otined ultimte strin is greter thn tht specified in the ACI (214). From Fig. 7 nd Tle 1, it cn e seen

9 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 9 of 13 Tle 1 Tensile test results of TRM specimens in this study. Specimen Initil stiffness Crcking strength Crcking strin Elstic modulus of crcked stge Pek strength Ultimte strin f fu /f ft mode E (GP) COV f ft (MP) COV ε ft COV E f (GP) COV f fu (MP) COV ε fu COV BASE C SPREAD A or B TAB A or B REBAR C L_COAT A or B SL_COAT A or B Test results otined from only one test specimen. tht the ultimte strin of the two SPREAD specimens showed sctter with COV of.192. Menwhile, the initil stiffness, crcking strength nd pek strength of the two SPREAD specimens were lmost the sme. Figure 8 compred the tensile ehviors of the SPREAD specimen with those of the BASE specimen. It is cler tht y using spred nchorge method, the crcking strength incresed pproximtely 6.3%. In prticulr, the pek strength incresed significntly up to 86.8%. It ws ttriuted to the fct tht the spred of cron fiers in the gripping res incresed the interfcil onding re etween fiers nd mortr mtrix, nd thus cused considerle improvement of the onding strength of the fiers nd mtrix. The stress strin response curves nd mechnicl prmeters of the TAB specimen re presented in Fig. 7c nd Tle 1, respectively. In terms of the first crck, the verge crcking strength ws MP with COV of.153. The verge pek strength nd ultimte strin ws MP nd.55, respectively. The ultimte strin ws lso higher thn the required vlue (.4) specified in ACI (214). Clerly, similr to the SPREAD specimen, the use of GFRP ts s n nchorge method could significntly increse oth the crcking nd pek strengths. Figure 8 shows the comprison of test results of the TAB specimen with those of the BASE specimen. The increse of the TAB specimen in terms of the crcking nd pek strengths compred to those of the BASE specimen were pproximtely 16.4 nd 77.4%, respectively. The initil stiffness of the TAB specimen ws lso higher thn tht of the BASE specimen. However, it showed significnt sctter (COV = 1.51). Figure 7d shows the stress strin response curves of the REBAR specimen. As shown in the figure, the response curves of the REBAR specimen were similr to those of the BASE specimen. However, in comprison to the BASE specimen, the residul stress fter crcking of the REBAR specimen ws significntly greter, nd showed lmost flt trend until filure of the test specimen. The REBAR specimen showed ductile ehvior with the ultimte strin up to.1. Figure 7e presents the stress strin curve otined from the test results of the L_COAT specimen. It should e noted tht one of the L_COAT test specimens filed during mnufcturing. Thus, the test prmeters were otined from only one specimen. The crcking nd pek strengths of the L_COAT specimen were nd MP, respectively. It is evident tht the crcking nd pek strengths of the L_COAT specimen were greter thn those of the BASE specimen (see Fig. 8d nd Tle 1). In ddition, the initil stiffness of the L_COAT specimen lso incresed up to 46.9%. Menwhile, the ultimte strin of the L_COAT specimen showed reltively low with vlue of.21, which ws considerly less thn the minimum requirement of the flexurl strin of.4 (ACI ). The experimentl results of TRM specimens, using SL_ COAT s n nchorge method, re presented in Fig. 7f in terms of stress strin response curves. The mechnicl prmeters re presented in Tle 1. From Fig. 7f nd Tle 1, the verge crcking nd pek strengths of the SL_COAT specimen were nd MP, respectively (see Tle 1). Figure 8e presents the comprison etween the SL_COAT nd BASE specimens in terms of stress strin ehvior. Similr to the L_COAT specimen, the use of comintion of cron fier sheets nd coting cron fier filments, with epoxy nd luminum oxide powder, could significntly increse the crcking nd pek strengths of the SL_COAT specimen up to 66.1 nd 97.9%, respectively, compred to those of the BASE specimen. Menwhile, the otined ultimte strin ws in rnge of In generl, the SL_COAT specimen showed rittle filure with n verge ultimte strin of.35, which ws less thn

10 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 1 of 13 Crcking strength (MP) Pek strength (MP) BASE SPREAD C BASE SPREAD C TAB TAB REBAR C REBAR C L_COAT L_COAT SL_COAT SL_COAT the flexurl strin (.4) specified in ACI (214). Moreover, the initil stiffness ws lso less thn tht of the BASE specimen, pproximtely 49.9%. From the otined test results in this study, it could e found tht the most developed nchorge methods showed effectiveness on improving the mechnicl ehviors of the TRM specimens. Figure 9 presents the comprison of the test results otined from different nchorge methods in terms of the crcking nd pek strengths, nd ultimte strin. As shown in Fig. 9,, the coted specimens with luminum oxide powder (L_COAT nd SL_COAT) showed effectiveness in the increse of crcking strength. In ddition, except for the specimen reinforced with steel rer (REBAR), the remined nchorge methods showed effectiveness in the increse of the pek strength. In Fig. 9c, the coted specimens showed less ultimte strins compred to the other cses. In Tle 1, the rtio (f fu /f ft ) etween the pek strength nd crcking strength ws presented. As shown in the tle, the SPREAD nd TAB specimens showed high vlues of f fu /f ft ; 1.77 for SPREAD nd 1.54 for TAB specimens, respectively. This mens tht the pek strength ws significntly higher thn the crcking strength. 3.3 Idelized Stress Response Curves of TRM Test Specimens In this study, idelized tensile stress strin response curves of the TRM test specimens were proposed sed on the guidnce specified in the test stndrd ACI 549.4R-13 (213). The response curves were simply plotted s iliner curves with only one trnsition point (crcking point) etween the crcked nd uncrcked stges. Figure 1 illustrtes iliner stress strin curve Ultimte strin BASE SPREAD C TAB c REBAR C Minimum strin for flexurl memer L_COAT SL_COAT Fig. 9 Comprison of verge crcking strength, verge pek strength nd verge ultimte strin of TRM test specimens. Effect of nchorge methods on crcking strength, Effect of nchorge methods on pek strength, c Effect of nchorge methods on ultimte strin. Tensile stress f fu f fi f ft E CFRP Rupture TRM Crcking of mortr Textile slippge ft fi fu Fig. 1 Idelized stress strin curve of TRM test specimen ccording to ACI 549.4R-13 (213). E f

11 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 11 of 13 of TRM test specimen. In the figure, it cn e seen tht in the uncrcked stge, the stress strin curve is linerly chrcterized y the initil stiffness (E); wheres in the crcked stge, the stress strin curve is linerly chrcterized y the modulus of elsticity E f. The elstic modulus of crcked stge cn e clculted s shown in Eq. (1) elow; E f = f / ε = ( ) /(.9 f fu.6 f fu ε.9ffu ε.6ffu ). (1) Moreover, s shown in Fig. 1, to chrcterize the tensile ehvior of TRM specimen, dditionl mechnicl prmeters should e considered, including pek strength (f fu ), correltive ultimte strin (ɛ fu ), tensile strength (f ft ) nd correltive strin (ɛ ft ) t the trnsition point. From the experimentl results, such mechnicl prmeters could e determined nd the otined vlues re presented in Tle Experimentl curve Idelized curve Experimentl curve Idelized curve Experimentl curve Idelized curve Experimentl curve Idelized curve c 2 Experimentl curve 16 Idelized curve d 2 Experimentl curve 16 Idelized curve e Fig. 11 Idelized nd experimentl stress strin curves of TRM test specimens in this study. BASE, SPREAD, c TAB, d REBAR, e L_COAT, f SL_ COAT. f

12 Kim et l. Int J Concr Struct Mter (218) 12:73 Pge 12 of 13 Figure 11 presents the idelized tensile stress strin response curves of the TRM test specimens in this study. In generl, the method proposed y ACI 549.4R- 13 (213) could e effectively pplied to illustrte the stress strin curve of TRM specimens using different nchorge methods. In prticulr, in the first stge (uncrcked stge), the nlyticl stress strin curves showed good greement with the experimentl curves. In the second stge (crck stge), in the cses of specimens SPREAD (Fig. 11), TAB (Fig. 11c), nd SL_COAT (Fig. 11f), the nlyticl stress strin curves were slightly ove the experimentl results. It ws due to the fct tht the elstic modulus of crcked stge (E f ) ws slightly higher thn tht otined from the experimentl results. Note tht E f ws clculted sed on the mechnicl prmeters including pek strength (f fu ) nd correltive ultimte strin (ɛ fu ) [see Eq. (1)], which might e ffected y the nchorge methods used in this study. However, the numer of test dt ws very limited in this study. Thus, to get improved E f, ccumulted test results re needed considering the nchorge effect. 4 Conclusions Tensile tests hve een performed to investigte the tensile ehviors of TRM specimens, which were mde from cron fier-textile reinforcement nd luminum cement-sed mortr. Five different nchorge methods in the gripping res- including SPREAD, TAB, REBAR, L_COAT nd SL_COAT- were proposed to enhnce the mechnicl properties of TRM specimens. The primry findings re s follows: 1. Most filure mode of test specimens ws governed y prtil fiers rupture fter crcking occurred in the mortr. However, the REBAR specimen ws governed y fiers slippge within the mortr mtrix. 2. Due to the tension stiffening effect of mortr mtrix, except for the cse of REBAR specimen, the tensile stress strin response curves of other test specimens were locted ove tht of cron fier filments. 3. The crcking nd pek strengths of the TRM specimens, using nchorge methods, incresed significntly up to 66.1 nd 97.9%, respectively, compred to those of the BASE specimen. 4. The use of SPREAD nd TAB methods showed ductile ehvior with the ultimte strin up to.59 nd.55, respectively. The REBAR specimen lso exhiited gretly ductile ehvior with n ultimte strin of up to.1. Menwhile, the use of coting nd cron fier sheets s nchorge methods resulted in rittle ehviors of the L_COAT nd SL_ COAT specimens with ultimte strins lower thn the minimum strin for the flexurl memer (.4), s specified in ACI The tensile stress strin ehvior of the TRM specimens in this study could e simply idelized y iliner stress strin response curves sed on the test stndrd ACI 549.4R-13. The mechnicl prmeters for the idelized iliner stress strin curves were otined from the test results. Authors contriutions All of the uthors contriuted criticlly to the conception, experiment, nlyzing the test dt s well s drfting nd revision of the mnuscript. All uthors red nd pproved the finl mnuscript. Acknowledgements This reserch ws supported y Grnt (18CTAP-C ) from Infrstructure nd Trnsporttion Technology Promotion Reserch Progrm funded y Ministry of Lnd, Infrstructure nd Trnsport of Koren Government. Competing interests The uthors declre tht they hve no competing interests. Avilility of dt nd mterils The dt nd mterils hve een experimentlly performed nd investigted y the uthors. Consent for puliction Accepted. Ethics pprovl nd consent to prticipte Not pplicle. Funding Accepted with rticle-processing chrge (APC) policies. Pulisher s Note Springer Nture remins neutrl with regrd to jurisdictionl clims in pulished mps nd institutionl ffilitions. Received: 8 Mrch 218 Accepted: 4 July 218 References AC434. Acceptnce criteri for msonry nd concrete strengthening using fier-reinforced cementitious mtrix (FRCM) composite systems. A Susidiry of the Interntionl Code Council, Birminghm, UK; 211. ACI (214). Building code requirements for structure concrete (ACI ). Frmington Hills: Americn Concrete Institute. ACI 549.4R-13. (213). Guide to design nd construction of externlly onded fric-reinforced cementitious mtrix (FRCM) systems for repir nd strengthening concrete nd msonry structures. Frmington Hills: Americn Concrete Institute. Aroled, D., Crozzi, F. G., Nnni, A., & Poggi, C. (216). Testing procedures for the unixil tensile chrcteriztion of fric-reinforced cementitious mtrix composites. Journl of Composites for Construction, 2(3), Ascione, L., de Felice, G., & De Sntis, S. (215). A qulifiction method for externlly onded fire reinforced cementitious mtrix (FRCM) strengthening systems. Composites: Prt B, 78, Brmeshuer, W. (26) Stte-of-the-rt report of RILEM Technicl Committee 21-TRC: Textile reinforced concrete. RILEM Report 36. Bruer, G. M., McLughlin, R. P., Huget, E. F. (1967) Aluminum oxide s reinforcing gent for zinc oxide-eugenol-e cements. Ntionl Bureu of Stndrds Report.

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