A STUDY OF WARP-KNITTED FABRIC STRUCTURE PARAMETERS AFFECTING THE MECHANICAL PROPERTIES OF TEXTILE- REINFORCED CONCRETE

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1 20 th Interntionl Conference on Composite Mterils Copenhgen, th July 2015 A STUDY OF WARP-KNITTED FABRIC STRUCTURE PARAMETERS AFFECTING THE MECHANICAL PROPERTIES OF TEXTILE- REINFORCED CONCRETE Oleg Stolyrov 1, Till Qudflieg 2 nd Thoms Gries 2 1 Deprtment of Strength of Mterils, St. Petersurg Stte Polytechnicl University Polytechnichesky 29, St.Petersurg, Russi Emil: oleg.stolyrov@rmler.ru, we pge: 2 Institut fuer Textiltechnik of RWTH Achen University Otto-Blumenthl-Str. 1, D Achen, Germny Emil: it@it.rwth-chen.de, we pge: Keywords: Wrp-knitted frics, High-strength rovings, Textile-reinforced concrete, Stitching pttern, Mechnicl properties ABSTRACT In this work, twelve smples of wrp-knitted reinforced fric nd concrete from four different types of reinforced rovings (glss nd three cron rovings) were fricted. The results of investigtions on the three common types of wrp-knit stitches i.e., tricot, cord nd pillr re presented. The smples were tested for mechnicl properties to determine the sic chrcteristics for reinforced frics nd concrete. In ddition, the shpe of the roving cross section ws ssessed s function of the type of the stitch. The otined results indicte tht the stitch type exerts significnt effect on the mechnicl properties of the reinforced concrete nd the roving cross section shpe. For given type of roving, the mechnicl properties of concrete with tricot nd cord stitches re greter thn tht of concrete with the pillr stitch. The min fctor ffecting the properties of concrete ws found to e the cross-section shpe of the roving in the reinforced fric, which due to its flttening in the cse of frics with tricot nd cord stitches or compctness in the cse of the frics with the pillr stitch, ffected the trnsfer of mechnicl lod cross the roving cross-section. In ddition, the strength of the originl rovings used for the fric mking significntly ffected the retention of the strength of the reinforced fric nd concrete. 1 INTRODUCTION High-performnce textiles re widely used in structurl nd civil engineering pplictions s reinforcements in structurl composites. Vrious textile structures, such s short fiers, yrns, rovings nd frics, which differ in the mnufcturing process, re used s reinforcements in concrete prts. Textile reinforced concrete is chrcterized y its rod rnge in mechnicl properties, high hndling potentil nd production cpility [1-5]. High-strength yrns used for producing the reinforced frics re continuous filment yrns without twist, consisting usully of few hundreds or thousnds of individul filments. In the mnufcture of high-strength reinforcing mterils for concrete, minly yrns such s lkli resistnt (AR) glss nd cron re used. These types of fires hve very high mechnicl chrcteristics (tensile strength, modulus, etc.) nd disply high potentil s concrete reinforcements ecuse of their dequte mechnicl performnce nd durility in lkli environments. One of the most importnt prmeters ffecting the properties of cementitious composites is the geometricl chrcteristics of reinforcing structure. The given geometry my improve the onding t the reinforcement-mtrix interfce. The onding of stright yrns with cement systems is reltive poor [6]. It my e enhnced y using the specil yrn or fric structures nd increse the efficiency of reinforcement. The fctors tht determine the properties of yrn nd frics, nd the cementitious composites re determined y the structure in yrn cross section nd long the yrn length or fric pttern. Peled et l. [7] found tht the flexurl strength of cement-sed composites depend the fric

2 Oleg Stolyrov, Till Qudflieg nd Thoms Gries structure. They studied the effect of the geometry of woven plin weve frics with vried fills density on the ond etween monofilment polyethylene yrns nd cement mtrix. It ws found tht the yrn nd woven fric structures hve significnt influence on incresing the ond etween the woven fric nd the cementitious mtrix [8]. The fier mtrix microstructure ws lso nlyzed y opticl microscopy in [9]. Microstructurl fetures for the different fier type were chrcterized nd correlted with their mechnicl properties. The microscopy oservtions on specimen cross-sections showed tht distriution nd compct of filment undles hs n effect on ond strength nd cement penetrility etween the filments. More open undle leds to etter chrcteristics. The filments distriutions in undles were qulified y simple terms like more compct nd more open. However, the results of such nlysis depend lrgely on the sujective opinion of the person doing the testing. Textile fric reinforcements come in the forms of woven, non-woven, nd knitted structures, which differ in their mnufcturing process. Knitting is one of the most verstile technologies of production for textile frics. Wrp-knitted frics with the directly inserting yrn oriented specificlly long the direction t which forces rise re suitle s concrete reinforcements. In the mnufcturing of wrp-knitted frics, directly oriented high-strength yrns re inserted in the mchine in longitudinl (wrp) nd trnsverse (weft) directions [10, 11]. The reinforced yrns re then comined y knitting yrn. The structure nd properties of the inly yrns re influenced y loop length, knitting yrn tension, nd the stitching pttern [5, 12, 13]. The stitching pttern in the wrp-knitted frics determines the geometry of the cell of the fric structure. Typiclly two groups of knitting stitches, nmely pillr nd tricot stitches re used in the wrp-knitting process for mnufcturing of technicl frics. In the pillr stitch, the sme guide lwys overlps the sme needle [14]. In the tricot stitch, the underlps connect oth the courses nd the wles. In the simplest of this group, one yrn crosses etween the djcent wles in tricot stitch (1 1 lp). Two yrns cross etween the wles in cord stitch (2 1 lp). In the pillr stitch, the sme guide lwys overlps the sme needle. The chins of loops connected together y the underlps in unconnected wles re produced [14]. Geometriclly, the difference etween the tricot stitch nd cord stitch is expressed in the ngle of the underlp with respect to verticl xis, which in the cord stitch is greter thn tht in the tricot stitch, s shown in Fig. 1 nd 1, respectively. In the pillr stitch, ll underlps re oriented long the verticl xis, s shown in the Fig. 1c. c Figure 1: Wrp-knitted frics of glss rovings with tricot (), cord () nd pillr stitches (c) s reinforcements in concrete. Jnetzko et l. [13] showed tht the yrns in wrp-knitted frics with tricot stitch hve flt rion shped cross section tht provides the increse in the contct length etween the filments nd the concrete. According to Roy et l., [15] wrp-knitted frics with tricot pttern show higher lodering cpcity thn specimens reinforced with pillr stitch. Zhou et l. [16] showed tht the sic stitches of multixil wrp-knitted structure re importnt fctors tht cn influence the mechnicl properties of the structure. This work ims to develop frics with common stitch types nd investigte their mechnicl chrcteristics ecuse the resulting strength of the textiles is importnt for designing textile reinforced concrete prts.

3 20 th Interntionl Conference on Composite Mterils Copenhgen, th July EXPERIMENTAL 2.1 Mterils For the experiment, lkli resistnt (AR) glss roving nd 3 different types of cron rovings were chosen. To investigte the influence of the rw mteril different in precursor mterils, polycrylonitrile sed fiers (PAN) nd pitch sed cron fiers were used. Tle 1 lists n overview of the properties of reinforcing rovings considered in this study. Polyester multifilment yrn (16.7 Tex) ws used s the knitting yrn. Smple designtion Roving Filment count, type Liner density, Tex GR Glss roving Alkli-resistnt 2400 CR-1 Cron roving (1) 24K, PAN-sed 1600 CR-2 Cron roving (2) 24K, PAN-sed 810 CR-3 Cron roving (3) 12K, Pitch-sed 1560 Tle 1: Roving specifictions. 2.2 Frics For the experiments, twelve types of wrp-knitted frics were produced on 6 gge wrpknitting mchine (MALIMO/c/P2-2S, Krl Myer Textilmschinenfrik GmH) t the Institute fuer Textiltechnik (ITA) of the RWTH Achen University with different specifictions in terms of the mterils nd the stitching pttern used. AR-glss nd cron rovings were used s the wrp inly yrns, while the weft yrns were glss rovings only. The smples contin three rovings per inch of fric width. The wrp-knitted frics nmes re comined s follows: GR (glss roving) or (CR) cron roving used roving mteril; 1/2/3 roving type; T (tricot)/c (cord)/p (pillr) knitting pttern. 2.3 Composite preprtion The wrp-knitted frics were integrted t the top nd ottom fces of concrete smples (5 mm from ech side). The preprtion of the concrete ws done in the mold (30 mm thick). In order to chieve good penetrtion of concrete with reinforced frics the fine grin concrete ws chosen. The mix proportion of fine grin concrete is given in the Tle 2. The specimens were demolded fter 1 dy nd tested t the ge of 28 dys. Portlnd cement Fly sh Snd ( mm) Snd ( mm) Plsticizer Silic fume Wter Tensile testing of the roving nd fric smples Tle 2: The constitutes of fine grined concrete (kg/m 3 ) The tensile properties of the rovings were investigted using Zwick universl testing mchine (model Z100). The roving smples were prepred ccording to the test method developed t the Institute fur Textiltechnik. The free ends of the specimen were clmped in ruer mold nd ligned with mild tension. The emedding of the roving ends ws ensured y pplying epoxy resin into the mold. The specimens were left undistured until testing, which ws crried out on the following dy. The rovings were tested to filure with test speed of 10 mm/min nd gge length of 125 mm. The tensile properties of the wrp-knitted frics were determined y stndrd method termed s strip test. The free ends of the fric specimens were fixed with pieces of crton pper nd emedded with epoxy resin to void the dmging of rittle rovings. The stress-strin digrms were otined with 100 mm smple se nd clmp movement of 10 mm/min. Tensile stress ws determined s the

4 Oleg Stolyrov, Till Qudflieg nd Thoms Gries mximum pplied force divided y the initil cross sectionl re of the specimen using the following eqution. F (1) Tn n is numer of rovings in the cross sectionl re of the specimen. 2.5 Flexurl testing of the concrete smples The flexurl properties of the composite specimens were determined y four point ending test. The specimens with dimensions of mm were cut. The flexurl tests were crried out in Zwick Z100 testing mchine t cler spn of 60 mm. Crosshed rte ws 1 mm/min. 2.6 Anlysis of the roving cross section The smples of the roving cross sections were exmined y opticl microscopy. The specimens were cut nd polished to chieve high ccurcy of recognition. The microgrphs were cptured using n opticl microscope (Leic type DM 4000 M) equipped with digitl cmer nd the filments in roving cross section were recognized using co-ordinte system. An opticl microgrph nd the coordinte ssignment of the cross section of the cron roving re shown in Fig. 2 nd 2 respectively. Figure 2: Opticl microgrph of cross section of glss roving () nd its coordinte ssignment (). 3 RESULTS AND DISCUSSION 3.1 Tensile properties of the fric smples The tensile strength nd Young s modulus vlues were plotted s histogrms nd re shown in Fig. 3 nd 3 for glss nd cron frics. As cn e seen from the dt otined, the type of the stitch significntly ffects the tensile properties of the wrp-knitted frics. The tensile strengths of the wrp-knitted structures of glss roving (GR) with the tricot stitch nd the pillr stitch re slightly higher (y out 14%) thn the glss fric with the cord stitch (Fig. 3). The plot of the Young s modulus for glss frics showed similr chrcter (Fig. 3) reching mximum vlue for the smple with the tricot stitch which ws out 11% greter thn the fric with the cord stitch. Smples of wrp-knitted structures of cron rovings CR1 nd CR3 demonstrte similr ehvior depending on the stitch pttern. The smples with the tricot stitch showed the mximum tensile strength for ll three cron rovings (Fig. 3). Smples with cord stitch showed lower tensile strength thn tht with the tricot stitch. In the cse of smple CR1-C, the tensile strength decresed y 8% nd the tensile strength ws lower thn 14% for smple CR2-C in comprison to tht of the smple with the tricot stitch. The reduction in the tensile strength of the smple CR3-C ws insignificnt. The

5 20 th Interntionl Conference on Composite Mterils Copenhgen, th July 2015 smples of the frics with pillr stitch showed even lower tensile strengths (vlues of CR1-P, CR2-P nd CR3-P were lower y 21%, 7% nd 14.4%, respectively, in comprison to the vlues shown y CR1-T, CR2-T nd CR3-T). Smple CR2-P ws the only exception, which exhiited higher strength thn the fric with the cord stitch. As shown in Fig. 3, the stitch type did not ffect the modulus of the smple CR1. The dependence of the Young s modulus of the stitch type in the cse of smples CR2 nd CR3 is similr to grdtion noticed for tensile strength. The mximum Young s modulus ws chieved for the smple CR2. Moreover, the Young s modulus for the frics with the tricot nd pillr stitches for smple CR2 were out 14% higher in comprison to the corresponding smple with the cord stitch. In the cse of the smple CR3, the difference etween the Young s moduli of the frics with tricot nd pillr stitches ws 25%. Figure 3: Effect of the stitch pttern on the tensile properties of wrp-knitted frics. By nlyzing the results, it cn e concluded tht for frics with the cord nd pillr stitches, the underlps re longer in comprison to the fric with tricot stitch in which the ngle of the underlp is midwy etween the ngles tken y pillr nd cord stitches. This leds to more rpid tightening of the knitting yrn nd prevents further stretching for frics. For fric with tricot stitch, the midwy position of the underlp ngle llows for the higher deformtion of the rovings. 3.2 Flexurl chrcteristics of the concrete smples The flexurl strength vlues for glss nd cron frics reinforced concrete were plotted s histogrms nd re shown in Fig. 4. As cn e seen from the dt otined, the type of the stitch ffects the flexurl strength of the concrete smples. The flexurl strengths of the concrete smple of the glss fric with the tricot stitch GR-T re higher (y out 14%) thn with the cord stitch nd (y out 19%) thn the pillr stitch. The smples of cron rovings CR1 with the tricot stitch showed the mximum flexurl strength. Smples with cord stitch showed lower flexurl strength thn tht with the tricot stitch. In the cse of smple CR1-C, the flexurl strength decresed y 6.5% nd the tensile strength ws lower thn 25% for smple CR1-P in comprison to tht of the smple with the tricot stitch. Concrete smple of roving CR2 demonstrte similr ehvior depending on the stitch pttern. The smples with cord nd pillr stitched showed even lower tensile strengths, vlues of CR2-C nd CR2-P were lower y 6.3% nd 36%, respectively, in comprison to the vlues shown y CR2-T. Concrete smple of roving CR3 ws the only exception, which exhiited higher strength with the cord stitch. The reduction in the tensile strength of the smple CR3 ws insignificnt. 3.3 Cross-section oservtions The shpe of the inly roving in the fric is minly formed during knitting nd is determined y the stitch type. Anlysis of the roving cross section in the fric nd in the concrete smples reveled significnt differences in their shpes. The coordinte ssigned model of the cross sections oserved in

6 Oleg Stolyrov, Till Qudflieg nd Thoms Gries ech type of the stitch in the cse of GR nd CR1 rovings re shown in Fig. 5. As seen from the models of the rovings, in frics with tricot (Fig. 5) nd cord stitches (Fig. 5), the cross section is flttened. The limited length of the underlp in the tricot stitch (1 1 lp) leds to higher degree of tightening of the yrn. The cross section of the cord stitch tkes hemi-ellipticl symmetricl shpe ecuse of the longer underlp (2 1 lp) thn tht in the tricot stitch. The cross section of the pillr stitch (Fig. 5c) cquires n ellipticl, lmost circulr shpe on ccount of the orienttion of the knitting yrn in the direction of pplied force nd ecuse of the tightening round the reinforced yrn. Figure 4: Effect of the stitch pttern on the flexurl strength wrp-knitted fric reinforced concrete. The results of the roving cross sectionl shpes provide cues to explin the differences in the results seen in the mechnicl tests. In most cses, the mximum strength ws chieved in smples with tricot stitch, which my e ttriuted minly to the flttened shpe of the cross sections, its uniform expnsion nd, s consequence, etter force trnsmission etween the filments of the roving during strining. An lmost circulr shpe ttined in smples with the pillr stitch provides lower trnsfer of mechnicl lod through the undle of filments ecuse of their uneven working in tension nd friction etween filments. () () (c) Figure 5: Coordinte ssigned models of the cross sections of glss roving (left) nd cron roving (right) with tricot stitch (), cord stitch () nd0 pillr stitch (c).

7 20 th Interntionl Conference on Composite Mterils Copenhgen, th July Effect of the roving nd stitch type The efficiency of textile reinforcement depends on the use of the properties of the originl rovings with vrious chrcteristics. One of the min chrcteristics determining the suitility of the use of fric for reinforcement my e strength retention fctors. This indictes the use of the roving properties in the fric depending on the effect of the stitching pttern. The ltter fctor hs significnt influence on the retention properties in the light of dmge of rittle yrns during textile processing. The reltionship etween the tensile strength of the reinforcing rovings nd the corresponding fric nd concrete properties re shown in Fig. 6 nd 6, respectively. In these plots, the tensile strength of the rovings is on the xes of the scisss, nd on the xis of the ordinte, the tensile strength of the frics nd the flexurl strength of concrete mde of these rovings re plotted. The sloping dshed line drwn t n ngle of 45 indictes complete trnsltion of the roving properties in the frics (Fig. 6). Idelly, ll points should e locted s close s possile to this line. As seen from the dt for the strength retention, the glss roving shows highest retention of strength in smples with ll types of stitches (85-98% of the originl roving strength). All cron smples lie elow this line. With increse in the strength of the cron roving, the trnsltion of strength from the roving to the fric reduces. Hence, the glss roving demonstrtes the highest level of property retention. For cron rovings, the highest tensile retention vlues were oserved in smple CR-1, 87.6%, 80.9% nd 69.1% for frics with the tricot, cord, nd pillr stitch, respectively. The lowest strength retention (only 65-76%) ws oserved for smple CR2. This could e ttriuted to the fct tht CR2 shows the highest stiffness mong the cron rovings, leding to high rittleness nd low properties fter textile processing. Figure 6: Roving utiliztion properties in the frics () nd concrete (). A similr dependence ws oserved for the roving strength properties in concrete (Fig. 6). As seen from the results, the tensile strength of the originl rovings is not lwys key fctor for selecting reinforcing rovings. The glss roving demonstrtes very good level of property utiliztion in the concrete. The utiliztion of the strength in the cron rovings worsened nd decresed with increse in the tensile strength of the constituting originl rovings. For exmple, roving with lower tensile strength (smple CR3) shows highest flexurl strength in concrete, providing lmost the sme flexurl strength in concrete s smple CR2 on ccount of lower losses in textile processing. The lower extent of trnsltion of properties cn e explined y the high rittleness of the cron rovings nd with increse in the strength nd stiffness of rovings, prtil destruction of the filment occurs during strining, exerting significnt influence on their tensile properties. It cn e seen tht the reinforcement efficiency depends on the tensile properties of the constituting originl rovings nd knitting pttern. We conclude tht it is possile to reduce the cost of the rw mterils y using originl rovings constituting the frics with lower tensile chrcteristics ut with higher retention properties in the fric.

8 Oleg Stolyrov, Till Qudflieg nd Thoms Gries 4 CONCLUSIONS One of the most importnt prmeters ffecting the properties of cementitious composites is the geometricl chrcteristics of reinforcing structure. In this work, we present the results of our investigtions on the three common types of wrp-knit stitches i.e., tricot, cord nd pillr. For the experiment, lkli resistnt (AR) glss roving nd 3 different types of cron rovings were chosen. Twelve smples of wrp-knitted fric nd concrete smples were produced. The wrp-knitted frics were integrted t the top nd ottom fces of concrete smples. In order to chieve good penetrtion of concrete with reinforced frics the fine grin concrete ws chosen. The tensile properties of the rovings nd the wrp-knitted frics were determined. The flexurl properties of the composite specimens were determined y four point ending test. The smples of the roving cross sections depending on stitch type were exmined y opticl microscopy. The results reveled tht the stitch type exerted significnt effect on the tensile properties of the frics, the roving cross section shpe, nd the composites. The min fctor ffecting the properties is the cross section shpe of the roving of in the fric, which due to its flttening in the cse of frics with tricot nd cord stitches or compctness in the cse of the frics with the pillr stitch, ffects the trnsfer of mechnicl lod cross the roving cross section. On the sis of otined results, the recommendtion on the optiml ppliction of the developed frics s concrete reinforcement nd the possiility of reducing the cost of the rw mterils y mking reinforcing frics with using originl rovings of lower tensile chrcteristics, which result in higher retention properties in the concrete, re provided. ACKNOWLEDGEMENTS This work ws supported y the Ministry of Eduction nd Science of Russin Federtion (Mikhil Lomonosov Progrm) nd Germn Acdemic Exchnge Service (DAAD) [grnt numer ]. REFERENCES [1] M. Tsesrsky, A. Ktz, A. Peled, nd O. Sdot, Textile Reinforced Concrete (TRC) Shells for Strengthening nd Retrofitting of Concrete Elements: Influence of Admixtures, Mterils nd Structures, 48, 2015, pp (doi: /s z). [2] A. Shms, M. Horstmnn, nd J. Hegger, Experimentl investigtions on Textile-Reinforced Concrete (TRC) sndwich sections, Composite Structures, 118, 2014, pp (doi: /j.compstruct ). [3] I. G. Colomo, A. Mgri, G. Zni, M. Colomo, nd M. di Prisco, Textile Reinforced Concrete: experimentl investigtion on design prmeters, Mterils nd Structures, 46, 2013, pp (doi: /s ). [4] A. Roye nd T. Gries, 3-D Textiles for Advnced Cement Bsed Mtrix Reinforcement, Journl of Industril Textiles, 37, 2007, pp (doi: / ). [5] A. Peled, Z. Cohen, Y. Psder, A. Roye nd T. Gries, Influences of textile chrcteristics on the tensile properties of wrp knitted cement sed composites, Cement nd Concrete Composites, 30, 2008, pp (doi: /j.cemconcomp ). [6] A. Peled, S. Sueki nd B. Mosher, Bonding in Fric cement Systems: Effects of Friction Methods, Cement nd Concrete Reserch, 36, 2006, pp (doi: /j.cemconres ). [7] A. Peled, A. Bentur nd D. Ynkelevsky, Flexurl Performnce of Cementitious Composites Reinforced with Woven Frics, Journl of Mterils in Civil Engineering, 11, 1999, pp (doi: /(ASCE) (1999)11:4(325)). [8] A. Peled, A. Bentur nd D. Ynkelevsky, Effects of Woven Fric Geometry on the Bonding Performnce of Cementitious Composites, Advnced Cement Bsed Mterils 7, 1998, pp (doi: /S (97) ).

9 20 th Interntionl Conference on Composite Mterils Copenhgen, th July 2015 [9] A. Peled, E. Zguri nd Gd Mrom, Bonding Chrcteristics of Multifilment Polymer Yrns nd Cement Mtrices, Composites Prt A: Applied Science nd Mnufcturing, 39, 2008, pp (doi: /j.composites ). [10] N.V. Pdki, R. Algirusmy nd B. Sugun, Knitted Preforms for Composite Applictions. Journl of Industril Textiles, 35, 2006, pp (doi: / ). [11] N. Gokrneshn, B. Vrdrjn, C.B. Sentil kumr, et l. Engineering knits for verstile technicl pplictions: Some insights on recent reserches, Journl of Industril Textiles, 42, 2012, pp (doi: / ). [12] V. Hnisch, A. Kolkmnn, A. Roye nd T. Gries, Influence of mchine settings on mechnicl performnce of yrns nd textile structures, Proceedings of the Interntionl RILEM Conference on Mteril Science - 1nd ICTRC - Textile Reinforced Concrete (Ed. W. Brmeshuer), Achen, Germny, 6-8 Septemer 2006, RILEM Pulictions, 2006, pp [13] S. Jnetzko, P. Krvev, T. Gries, et l., Textile reinforcement with spred nd commingled yrn structures, Proceedings of the Interntionl RILEM Conference on Mteril Science - 2nd ICTRC - Textile Reinforced Concrete (Ed. W. Brmeshuer), Achen, Germny, 6-8 Septemer 2010, RILEM Pulictions, 2010, pp [14] D.J. Spencer, Knitting technology, A comprehensive hndook nd prcticl guide, 3rd edn, Woodhedpulishing, Cmridge, [15] A. Roye, Hochleistungsdoppelrschelprozess für Textiletonnwendungen, PhD Thesis, RWTH Achen University, Schker, Achen, [16] R. Zhou, H. Hu, N. Chen nd X. Feng, An improved MWK structure for composite reinforcement. Textile Reserch Journl, 2005, pp (doi: / ).