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1 Construction nd Building Mterils 27 (2012) Contents lists vilble t SciVerse ScienceDirect Construction nd Building Mterils journl homepge: Effect of crylic fibres geometry on physicl, mechnicl nd durbility properties of cement mortrs Luiz A. Pereir-de-Oliveir, João P. Cstro-Gomes, Miguel C.S. Nepomuceno Centre of Mterils nd Building Technologies (C-MADE), University of Beir Interior, Clçd Fonte do Lmeiro, Covilhã, Portugl rticle info bstrct Article history: Received 31 December 2010 Received in revised form 27 July 2011 Accepted 28 July 2011 Avilble online 23 August 2011 Keywords: Acrylic fibre Aspect rtio Cement mortr Plstic shrinkge This pper presents the results of n experimentl investigtion to verify the fesibility of using crylic textile fibre to improve cement bsed mortrs properties. The ssessment of crylic fibres influence on mortrs properties ws performed compring the physicl, mechnicl nd durbility behviour with mortrs produced using glss nd polypropylene fibres. The influence of the mixing procedures ws lso investigted. Effects of crylic fibre spect rtio (l/d) nd volume frction (V f ) on mortr bulk density, compressive strength, flexurl strength, wter bsorption nd plstic shrinkge were investigted. For this purpose, crylic fibres hving six different l/d rtios 93, 148, 222, 278, 444 nd 833 were used nd the volume percentge of fibres were dded to mortr mixes ws of 0.2%, 0.5% nd 1.0%. The mortr plstic shrinkge ws lso studied on slbs csted with 0.5%, 0.2%, 0.1% nd 5% crylic fibres volume. It ws found tht crylic fibre reinforced mortrs hve physicl, mechnicl nd durbility relted properties similr to the mortr reinforced with glss or polypropylene fibres. These results indicte tht there is potentil technicl fesibility of using this type of fibres in cementitious composites. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Plstic shrinkge nd plstic shrinkge crcking if not controlled properly, my compromise the durbility of structure by llowing vrious fluids contining ggressive ions to penetrte the concrete [1]. These plstic shrinkge crcks will ffect not only the ppernce of concrete but lso its mechnicl nd physicl properties [2]. The plstic shrinkge cn occur in the first few hours fter csting nd cn be incresed by the effect of environmentl conditions more specificlly the temperture, the ir moisture nd the wind conditions. To control plstic shrinkge crcking of mortr, the most widely ccepted current method is to incorporte rndomly distributed smll quntity of fine synthetic fibres [2,3]. The fibres volume frctions commonly used is round 5 0.5% [1]. The most used synthetic fibres in concrete re, since the lte 1960s, the polypropylene fibres. Concerning the polypropylene fibres s mortr reinforcing, n extensive reserch work hs been crried out bout plstic shrinkge crcks [4,5] nd bout the fibre prmeters influence on mortr mechnicl behviour [6 8]. In fct, mong the polymer fibres, the polypropylene fibres re the most populr in the domin of concrete follow by the nylon nd glss fibres tht shows rising cceptnce [9]. Other synthetic fibres s the crylic fibres used in the textile industry re not so much pplied s technicl fibres in construction products. Corresponding uthor. Tel.: ; fx: E-mil ddress: luiz.oliveir@ubi.pt (L.A. Pereir-de-Oliveir). Regrding fibres production nd consumption in Europe, the Eurostt [10] report to 79.1 thousnd enterprises cross the EU-27 for which the mnufcture of textiles ws their min ctivity in They generted n estimted EUR 3 billion of vlue dded in Portugl, Bulgri nd Itly were reltively specilized in the mnufcture of textiles, s this sector contributed bout 1.5% of the totl vlue dded in their respective non-finncil business economies in 2006, between two nd hlf nd three times the EU-27 verge. According CIRFS [11], in 2007 the Europen fibres consumption ws 5.6 million tonnes where round 10% is crylic fibres. On the other hnd, imports of fbrics nd pprel from Asi re cusing decline in yrn demnd in Western Europe, it ws 35% down in 8 yers. The use of technicl textiles in construction products is recently discussed s n importnt tool for fibres Europen industry innovtion [12]. Besides high tensile strength, crylic fibres exhibit very good resistnce to cids nd lklis nd re low in cost. Theoreticl nd pplied reserch hve indicted tht, even with low modulus fibres, considerble improvements cn be obtined with respect to the strin cpcity, toughness, impct resistnce nd crck control of the fibre-reinforced concrete composites. In mny pplictions, the enhncement of these properties is of much greter significnce thn modest increse in tensile (flexurl) strength [13]. In fct, t n mount of l 3% by volume, the ddition of crylic fibre cn led to considerble increse in flexurl strength which is /$ - see front mtter Ó 2011 Elsevier Ltd. All rights reserved. doi: /j.conbuildmt

2 190 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) prcticlly independent of the mtrix w/c rtio nd is effective in enhncing toughness [14]. Hhne et l. [15] hs been reported tht the inclusion of 2.5% crylic fibre in reinforced concrete is effective in reducing shrinkge crcking induced during setting nd hrdening, s evluted by the ring test. The min objective of this reserch is therefore to study the behviour of cement mortr specimens reinforced with crylic fibres. The fibres used were trnsformed from the textile ppliction to technicl ppliction by ntionl Portuguese textile fibre industry nd compring it with the most used polypropylene nd glss fibres. In this reserch, the effect of spect rtio (l/d) nd volume fction (V f ) of crylic fibres on compressive nd flexurl strength nd s well plstic shrinkge, were ssessed. For this purpose, crylic fibres with six different l/d rtios 93, 148, 222, 278, 444 nd 833 were used nd three different fibres volumes were dded to mortr mixes t 0.2%, 0.5% nd 1.0%. 2. Mterils nd methods The experimentl study to ssessing the bility of crylic fibre reinforcement ws developed with typicl cement mortr 1:3 volume proportion of cement nd nturl snd. The wter cement rtio of 0.90 ws constnt for ll mortrs tested. Using this mortr mix proportion s reference, other fibres reinforced mortrs with different types nd volumes of fibres were produced. The glss nd polypropylene fibres were used s bsis for compring the performnce of crylic fibres Mterils The mterils used for the control mix of plin mortr consisted of Portlnd cement type CEM II/BL 32.5N conforming to Europen Stndrds EN [16], nd nturl snd hving mximum prticle size of 4.76 mm, density of 2450 kg/m 3 nd fineness modulus of To the plin mortr, the glss, polypropylene nd crylic fibres were dded t the volume concentrtion of 0.2%, 0.5% nd 1.0%. Tble 1 present the chrcteristic of fibres used in this study, to produce mortrs of different fibres incorported Methods Specimen preprtion, curing nd testing The mixing procedure nd specimen preprtion ws performed ccording to EN [17] nd the fresh mortr consistence ws determined using the flow-- tble test ccording to EN [18]. For ech mortr mixture, six specimens of mm size were produced, cst nd cured for 7 nd 28 dys. Both compressive nd flexurl strength were evluted t ges of 7 nd 28 dys in conformity with EN [19]. The mortr bulk density ws determined t the ge of 28 dys ccording to EN [20] nd the wter bsorption coefficient due to cpillry ction of hrdened mortr ws determined ccording to EN [21] t ges 7 nd 28 dys. The plstic shrinkge developed during the first hours of cementitious mteril hydrtion led to the formtion of micro- nd mcro-crcks tht cn ffect the mortr durbility. Thus durbility ccelerte test ws crried out to evlute the effect of the temperture, humidity nd wind in mortr shrinkge. For this purpose, mortrs slbs of 4.0 cm high by 25.0 cm wide nd 32.0 cm long were produced nd subjected to ir temperture of 40 C nd 40% reltive humidity in wind tunnel with constnt wind speed of 12 km/h during 24 h. The slbs were csting with mortrs reinforced with crylic fibres of dimeter 14.4 lm nd lengths 4, 6 nd 12 mm. To observe the minimum fibre volume ble to void the mortr plstic shrinkge, two supplementry mixtures with 0.1% nd 5% fibres volume were lso tested. As shown in Fig. 1, the mortrs slbs were reinforced with steel mesh of 6.0 mm dimeter spced of 10 cm, in order to mplify the plstic shrinkge effect in the first curing hours Mixture procedures From prcticl viewpoint, the mixbility of fibre nd mortr is very importnt. For exmple, it is necessry for the fibre to be uniformly dispersed in the mortr without forming fibre blling. Thus, the mixbility ws investigted by both mechnicl mixing nd hnd dry mixing. The mechnicl-mixing procedure ccording to EN [22] ws conducted for the mixture shown in Tble 2, identified s Wet. First, wter hs been introduced into the mixer followed by cementitious mterils. Afterwrds, fine ggregtes nd fibres were dded. The mixed mortr ws crefully observed. It ws found concentrtion of fibres in formt of smll blls, nd tht the fluidity of mortr ws influenced during the mould csting. Bsed on the bove observtion, the mixbility of the reinforcing fibres nd mortr only by mechnicl mixing ws considered not stisfctory to obtin the uniform fibres dispersion. Thus, hnd dry-mixing before the wet mechnicl mixing ws conducted for the mixture shown in Tble 2, identified s Dry. In this dry mixing process, the fibres were mixed with snd nd cement before being plced in the mixer. After weighing, the mteril is grdully introduced in continer. The fibres re mnully entered the continer nd lwys mixed first with the finer mteril (cement). The dry mixing is crried out by three steps: Step 1: The continer is shken in the verticl nd horizontl direction for bout 1 min. Step 2: The mixture is performed mechniclly for bout 2 min. Step 3: The continer is shken gin, long the verticl nd horizontl xis for bout 1 min. The process is repeted for the remining mteril. After the dry mixing the dry mortr is mixed by the procedure ccording the EN [22]. The mixed stte ws crefully observed, nd neither fibre blling nor ny bnormlities were observed. 3. Results nd discussion 3.1. Fresh nd physicl properties Regrding the mortr consistency the results re shown in Tble 3. It is observed tht for the sme dimeter nd fibre volume, the consistency index decreses with the incresing of fibres length. By contrst, the consistency index increses when the fibre dimeter is lso incresed for constnt length nd fibre volume. This result is explined by the chnge in fibres surfce re. Thus, for given fibres volume, the quntity of wter necessry to dsorb in the fibres surfces is incresed or reduced when the length or dimeter of the fibres is chnged. It mens tht there is consistency index decresing tendency for higher vlues of l/d rtio s is shown in Fig 2. This influence is quite significnt when the fibres volume increse from 0.2% to 1%. However, it is norml for ll types of fibres tht consistency is lso reduced with the spect rtio incresing. According to the bulk density results presented in Tble 3, it is possible to conclude tht the fibres ddition in mortr mixtures decreses the density, s ws expected, since these hve lower density thn the mtrix. However, this decrese is not very significnt for low levels of fibre (0.2% nd 0.5%). In these cses, the density reduction ws between 1% nd 12%. This effect ws more pronounced, with the highest density reduction vlue of 18%, when the fibre volume is rised to 1%. It is lso known tht the fibres incorporte ir during the mortr mixing nd this occurrence becomes more significnt in the cse of using high percentges of fibres [23]. This hs led to further reduction of the density Mechnicl properties The results presented in Tble 4 point out tht in generl, the 28 dys flexurl strength of mortrs produced with fibres of sme Tble 1 Mechnicl nd chemicl properties of fibres. Type Dimeter (lm) Length (mm) Density. (kg/m 3 ) Tensile strength (N/mm 2 ) Elongtion (%) Alkli resistnce Acrylic ; Good 27 4; 6; Good 43 4; Good Glss AR Fir Polypropylene Good

3 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) Fig. 1. Slb formwork with the steel mesh reinforcement (), slb of plin mortr before (b) nd fter (c) shrinkge test. Tble 2 Mortr mixtures chrcteristics. Mix no. Mixture method Type of Fibre dimensions Fibre fibre Length, l Dimeter, d volume (%) (mm) (lm) 1 Dry N 2 Wet A Wet A Wet A Wet A Wet G Wet P Wet A Wet A Wet A Wet A Dry A Dry A Dry A Dry P Dry A Dry A Dry A Dry A N Plin mortr; A Acrylic; P Polypropylene; G Glss. length nd the sme dimeter vlues, decreses due to the increse (l/d) V f (fibre fctor). It mens tht the flexurl strength is reduced by the fibres volume increment. Rther, when the fibre volume nd fibre length re constnt nd the dimeter increses, the vlues of flexurl strength lso increses. This is due to l/d (spect rtio) reduction. Consistency index (%) Vf=0.2% Vf=0.5% Vf=1.0% Aspect rtio l/d Fig. 2. Influence of spect rtio in the mortr consistency. Gthering in Fig 3 ll the results obtined for flexurl strength it is possible, even with wek correltion, to disply trend towrd lower vlues of flexurl strength with fibre fctor incresing. However, it ws observed tht the fibre fctor is not influent on flexurl strength t 7 dys, but slightly decrese of flexurl strength is pronounced t 28 dys. It ws lso observed tht for higher vlues of fibre volume there is minor discrepncy between the vlues of flexurl strength obtined t 7 nd 28 dys. Tble 3 Results of consistency of fresh mortr nd bulk density of hrdened mortr. Mix no. Mixture method Fibre chrcteristics Consistency Bulk density Type of fibre l (mm) d (mm) Volume (%) Averge flow dimeter (mm) Stndrd devition (mm) Consistency index (%) Averge density (kg/m 3 ) 1 Dry N Wet A Wet A Wet A Wet A Wet G Wet P Wet A Wet A Wet A Wet A Dry A Dry A Dry A Dry P Dry A Dry A Dry A Dry A N Plin mortr; A Acrylic; P Polypropylene; G Glss. Stndrd devition (kg/m 3 )

4 192 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) Tble 4 Mortr flexurl strength. Mix no. Mixture method Type of fibre Fibre chrcteristics 7 dys 28 dys l (mm) d (mm) V f (%) Averge (MP) Stndrd devition (MP) Averge (MP) Stndrd devition (MP) 1 Dry N Wet A Wet A Wet A Wet A Wet G Wet P Wet A Wet A Wet A Wet A Dry A Dry A Dry A Dry P Dry A Dry A Dry A Dry A N Plin mortr; A Acrylic; P Polypropylene; G Glss. Flexurl strength (MP) dys 28 dys Fibre fctor (Vf*l/d) Fig. 3. Flexurl strength of crylic fibres reinforced mortr versus fibre fctor. Flexurl Strength (MP) Wet A Vf=0,2% Dry A Vf=0,2% Plin mortr 7 28 Age (dys) Flexurl Strength (MP) dys 28 dys G P A A (d=43) Type of Fibres Fig. 4. Flexurl strength of mortrs with different type of fibres. The whiskers plots used in Fig. 3 show the mximum coefficient of vrition obtined for 7 nd 28 dys, tht is respectively 3.8% nd 3.0%. As seen in Fig. 4, compring the results obtined with mortrs produced with three types of fibres (glss, polypropylene nd crylic fibres), equl length nd incorporting 0.5% of fibres volume, it ws obtined higher flexurl strength vlues t 28 dys for mortrs with crylic fibres. The crylic fibre dimeter increse A(d = 43) Fig. 5. Flexurl strength of crylic fibres reinforced mortr. did not chnge significntly the flexurl strength t 28 dys, lthough decresing ws observed t 7 dys. Compring the two types of mixing procedures with mixtures produced with the sme crylic fibre volume nd spect rtio, the results presented in Fig 5 show tht better dispersion of fibres obtined by dry pre-mixing improves the flexurl strength. Moreover, this mixture composed with 0.2% of fibre volume nd l/ d = 278, reched the highest vlue of flexurl strength obtined in this study. Tking into ccount the mximum stndrd devition vlues for ech ge nd fibres volume, the results presented in Fig 6 show tht incresing fibres volume within groups of sme l/d cuses slight reduction of flexurl strength, especilly t 28 dys tht is more distinguishble t 1.0% fibres volume. Although the strength reduction hs been observed, this becomes unimportnt in the cse of higher l/d for 7 nd 28 dys. According to the results presented in Tble 5, in generl, it is observed tht, when the fibre dimeter is mintined constnt the compressive strength decreses with the fibre volume or the fibre length incresing. Fig 7 shows the compressive strength results obtined, t 7 nd 28 dys, for mortrs reinforced with fibres of sme spect rtio,

5 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) Vf0,2_7d Vf0,2_28d Vf0,5_7d Vf0,5_28d Vf1,0_7d Vf1,0_28d Flexurl Strength (MP) Aspect rtio l/d Fig. 6. Flexurl strength of crylic fibres reinforced mortr versus spect rtio. Tble 5 Mortrs compressive strengths. Mix no. Mixture method Type of fibre Fibre chrcteristics 7 dys 28 dys l (mm) d (lm) V f (%) Averge (MP) Stndrd devition (MP) Averge (MP) Stndrd devition (MP) 1 Dry N Wet A Wet A Wet A Wet A Wet G Wet P Wet A Wet A Wet A Wet A Dry A Dry A Dry A Dry P Dry A Dry A Dry A Dry A N Plin mortr; A Acrylic; P Polypropylene; G Glss. Fig. 7. Compressive strength of reinforced mortrs with different type of fibres. sme fibres volume nd sme mixing procedure. Tking into ccount the stndrd devition vlues presented in Tble 5, it is conclude tht the type of fibres does not significntly influence the Fig. 8. Compressive strength of reinforced mortrs with different mixing procedures. compressive strength of mortrs. These results re consistent with the expected behviour.

6 194 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) Compressive strength (MP) dys 28 dys Fibre fctor (Vf*l/d) Fig. 9. Compressive strength of mortrs s function of fibre fctor. According to the results of compressive strength shown in Fig. 8 nd their respective stndrd devitions vlues, which re presented in Tble 5, it ppers tht the mixing procedures does not significntly ffect the results of compressive strength. These results seem to be due to the fct tht the fibres volume incorported to the mortrs is reltively low nd in this cse does not cuse significnt hrdened mortr structure disturbnce sufficient to ffect the compressive strength. Finlly, tking into ccount ll compressive strength results, presented in Fig. 9, it is possible to observe compressive strength reduction tendency t the ge of 7 dys when the fibres fctor is incresed. This tendency is not present t the ge of 28 dys when the structure of hrdened mortr seems to be better defined nd compct, thereby nullifying the effect seen in erlier ge. Although the literture reports few studies with the ppliction of crylic fibres, this study confirm once gin tht, by the point of view of the mechnicl behviour, the interest of incorporting short synthetic fibres with high spect rtio is relted to the effects on cementitious composites resulting from tensile stress. Therefore, the crylic fibres, independently of their dimensions give to mortrs similr performnce s those offered by trditionl synthetic fibres (glss nd polypropylene) Wter bsorption by cpillrity The results of wter bsorption by cpillrity t the ge of 7 nd 28 dys were obtined ccording to EN [23] nd the coefficient ws clculted between the period of 10 min nd 90 min. In generl, the vlues presented in Tble 6 re reltively low compred to mortr commonly used in cotings, normlly between 1.0 nd 1.5 kg/m 2 min 0,5. These low vlues re due to the fct tht the mortrs here studied re rich in cement content nd hve reltive low wter/cement rtio (W/C = 0.90). It ws observed t 7 dys tht the wter bsorption by cpillrity of fibres reinforced mortrs re higher thn plin mortr, wht is nturl, becuse the fibres contribute to the ir incorportion nd in this erly ge the mortr mtrix structure is in the crystlliztion process, which tht is less compct. However, some vlues s for mixture nos. 8, 9, 10, 11 nd 19 did not follow this generl ssumption, nd revel more complex behviour. It seems tht the mortr porosity structure in the cse of mortrs nos. 8, 9, 10 nd 11 is ffected by the fibre dimeter tht define the number of fibres present in the mortr This misconception needs further study to clrify the effect of mixing procedures nd fibres vribles interctions t 7 dys wter bsorption by cpillrity. Anlyzing the vlues of wter bsorption cpillrity of fibres reinforced mortrs t 28 dys, shown in Figs. 10 nd 11, it is concluded, overll, tht the insertion of fibres is responsible by slightly wter bsorption cpillrity reduction. This behviour corresponds to the formtion of pores contining ir tht ct s brriers preventing the rise of wter through the mtrix, prtilly reducing the cpillry pressure inside the pores. The cpillry reduction is lso due to the progressive formtion of microstructure of mortr mtrix tht increses the non cpillries pores. Fig. 10 shows the cpillrity coefficient results for reinforced mortrs with 0.5% of crylic, polypropylene nd glss fibres volume. The fibres types influence ppers to be more slightly significnt t 7 dys. This influence ppers to be more due to the fibres dimensionl chrcteristics thn to the fibres type. Tble 6 Mortr wter cpillrity bsorption. Mix no. Mixture method Type of Fibre chrcteristics 7 dys 28 dys fibre l d V f Averge kg/ Stndrd Devition kg/ Averge kg/ (mm) (lm) (%) (m 2 min 0.5 ) (m 2 min 0.5 ) (m 2 min 0.5 ) 1 Dry N E E 02 2 Wet A E E 02 3 Wet A E E 02 4 Wet A E E 02 5 Wet A E E 02 6 Wet G E E 02 7 Wet P E E 02 8 Wet A E E 02 9 Wet A E E Wet A E E Wet A E E Dry A E E Dry A E E Dry A E E Dry P E E Dry A E E Dry A E E Dry A E E Dry A E E 02 N plin mortr; A Acrylic; P Polypropylene; G Glss. Stndrd Devition kg/ (m 2 min 0.5 )

7 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) Type of fibre Acrylic Acrylic Acrylic Length (mm) Dimeter ( Fibre content (kg/m 3 ) Fig. 10. Wter cpillrity coefficient of mortrs reinforced with different type of fibres Cpillrity coefficient [Kg/(m 2 *min 0,5 )] Tking into ccount the stndrd devitions results, presented in Tble 6, it is possible to conclude, in Fig.10, tht the sme fibres volume incorportion does not significntly modify the mortrs coefficient of cpillrity t the ge of 28 dys. On the other hnd, Fig. 11 shows tht the incresing of fibre spect rtio l/d is, in generl, responsible by wter bsorption cpillry rising. This tendency is little more significnt for the wter bsorption cpillry results obtined t 7 dys. However, the most importnt observtion is tht disturbnce cused in the porous structure t 7 dys is prcticlly nnulled t 28 dys, resulting in coefficients of cpillry below or ner the plin mortr vlue Shrinkge 7 dys 28 dys Aspect rtio l/d Fig. 11. Mortr cpillrity coefficient s function of fibres spect rtio. The shrinkge test in the wind tunnel ws designed to evlute the fibres effect on the mortr erly ge shrinkge. After cst, the smll slbs were inserted into the tunnel inside climtic chmber under conditions described previously. At the end of wind tunnel shrinkge test visul inspection of the specimens ws crried out nd photos were recorded, in order to observe the crcking ppernce nd distribution on slbs surfces. Observing the slbs surfces, shown in Fig 12, it ppers tht the fibres ddition in mortr llows reduction nd redistribution of crcks or even void them if more lrge fibres volume is incorported t the mortr mixtures. Regrdless the crylic fibres spect rtio, it ws observed for dosges greter thn or equl to 1.17 kg/m 3 (wht is equivlent to 0.1% fibre volume) tht there is no crcking. For doses equl to 0.59 kg/m 3 (5% fibres volume) crcking occurred, lthough more distributed nd not s loclized thn s in the cse of the mortr without fibres, since the crcks were hving much smller openings. 4. Conclusion Fig. 12. Crcking mp fter the wind tunnel shrinkge test. From this study conducted to evlute fesibility of using crylic fibre type to improve the cementitious mortrs properties, compring with others synthetic fibres, the following conclusions cn be drwn: () The consistency index is modified by the fibres surfces re; it mens tht there is consistency index decresing tendency for higher vlues of the spect rtio l/d. For the sme spect rtio, the consistency index is lso reduced by the fibres volume incresing, wht mens with the incresing of fibre fctor. (b) Addition of fibres cused slightly mortr density decresing, s ws expected, since this effect ws more pronounced, with the highest density reduction vlue of 18%, when the fibre volume is rised to 1%. (c) In generl, it ws observed on the present reserch tht the 28 dys flexurl strength of mortrs decreses due to the increse of fibre fctor [(l/d) V f ]. However, when this fibre fctor remins constnt, the increse of fibres volume is responsible by the flexurl strength reduction. By other hnd, when the fibre spect rtio is reduced, the vlues of flexurl strength increse. (d) A better dispersion of fibres obtined by dry pre-mixing improves the flexurl strength.

8 196 L.A. Pereir-de-Oliveir et l. / Construction nd Building Mterils 27 (2012) (e) In generl, s ws expected due the reltively low fibre volume incorported, it ws observed tht the type of fibres nd the mixing procedures does not significntly influence the compressive strength of mortrs t the ge of 28 dys. (f) It ws observed t 7 dys tht the wter bsorption by cpillrity of fibres reinforced mortrs is higher thn the plin mortr, but slightly wter bsorption cpillrity reduction ws observed t 28 dys. This influence more slightly significnt t 7 dys ppers to be due more to the fibres dimensionl chrcteristics thn to the fibres type. The most importnt observtion is tht disturbnce cused in the porous structure t 7 dys is prcticlly nnulled t 28 dys, resulting in coefficients of cpillry below or ner the plin mortr. (g) Regrdless the crylic fibres spect rtio, it ws observed for dosges greter thn or equl to 1.17 kg/m 3 (wht is equivlent to 0.1% fibre volume) tht there is no crcking. For doses equl to 0.59 kg/m 3 (5% fibres volume) crcking occurred, lthough more distributed nd not s loclized thn s in the cse of the plin mortr. (h) Although the literture contins few studies with the ppliction of crylic fibres, this study confirm tht, by the point of view of the physicl, mechnicl nd durbility behviour, the crylic fibres independently their dimensions give to mortrs similr performnce s those offered by trditionl synthetic fibres (glss nd polypropylene). References [1] Aly T, Snjvn JG, Collins F. Effect of polypropylene fibers on shrinkge nd crcking of concretes. Mter Struct 2008;41: [2] My TM, Wu K. Effect of different geometric polypropylene fibers on plstic shrinkge crcking of cement mortrs. Mter Struct 2002;35:165 9 [April]. [3] Brnch J, Rwling A, Hnnnt DJ, Mulheron M. The effects of fibres on the plstic shrinkge crcking of high strength concrete. Mter Struct 2002;35: [April]. [4] Qi C, Weiss WJ, Olek J. Chrcteriztion of plstic shrinkge crcking in fiberreinforced concrete using semi-utomted imge nlysis. Concr Sci Eng 2003;36(260): [5] Mesbh HA, Buyle-Bodin F. Efficiency of polypropylene nd metllic fibres on control of shrinkge nd crcking or recycled ggregte mortrs. Constr Build Mter 1999;13: [6] Tnyildizi H. Sttisticl nlysis for mechnicl properties of polypropylene fiber reinforced lightweight concrete contining silic fume exposed to high temperture. Mter Des 2009;30: [7] Sun Z, Xu Q. Microscopic, physicl nd mechnicl nlysis of polypropylene fiber reinforced concrete. Mter Sci Eng, A 2009;527: [8] Liu X, Ye G, De Schutter G, Yun Y, Terwe L. On the mechnism of polypropylene fibres in preventing fire splling in self-compcting nd highperformnce cement pste. Cem Concr Res 2008;38: [9] Sonj PS, Hwng S, Sheu BC. Strength properties of nylon nd polypropylene fiber reinforced concretes. Cem Concr Res 2005;35: [10] Europen Commission. Europen business fcts nd figures 2009 edition, Eurostt Collection: Sttisticl books, ISBN: DOI: / 23246, 547pp. [11] Purvis C. The Europen Mrket for Polyester fibres. IV Moscow Interntionl Conference PET 2008, < 20Polyester%20Fibres%20in%20the%20Europen.pdf> [ccessed 26.10]. [12] Schultes PM. Fiber requirements from civil engineering. In: Proc. 47th mnmde fibre congress, Dornbirn, Austri, September 2008, Osterreichisches Chemiefser-Institut; [13] Bentur A, Mindess S. Fibre reinforced cementitious composites. London: Elsevier Applied Science; [14] Dniel JI, Anderson ED. In: Swmy RN, Wgstffe RL, Okley DR, editors. Developments in fibre reinforced cement nd concrete. Sheffield: RILEM; [15] Hhne H, Konig G, Womer JD. In: Swmy RN, Brr B, editors. Fibre reinforced cements nd concretes: recent developments. London: Elsevier Applied Science; [16] Europen Committee for Stndrdiztion. Cement. Composition, specifictions nd conformity criteri for common cements EN 197-1; [17] Europen Committee for Stndrdiztion. Methods of test mortr for msonry Prt 2: Bulk smpling of mortrs nd preprtion of test mortrs. EN ; [18] Europen Committee for Stndrdiztion. Methods of test mortr for msonry Prt 3: Determintion of consistence of fresh mortr (by flow tble) EN ; [19] Europen Committee for Stndrdiztion. Methods of test mortr for msonry Prt 11: Determintion of flexurl nd compressive strength of hrdened mortr EN ; [20] Europen Committee for Stndrdiztion. Methods of test mortr for msonry Prt 10: Determintion of dry bulk density of hrdened mortr. EN ; [21] Europen Committee for Stndrdiztion. Methods of test mortr for msonry Prt 18: Determintion of wter bsorption coefficient due to cpillry ction of hrdened mortr EN ; [22] Europen Committee for Stndrdiztion. Methods of testing cement Prt 1: Determintion of strength. EN 196-1; [23] Silv RP. Mortrs with polypropylene fibres ddition study of rheologicl nd mechnicl behviour (in Portuguese), Civil Engineering Mster s Thesis, University of São Pulo, Brzil; p.