INFLUENCE OF RECYCLED VEGETABLE FIBRES ON THE FRESH PROPERTIES OF PASTES FORMULATED FROM SELF COMPACTING CONCRETE

Transcription

1 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium INFLUENCE OF RECYCLED VEGETABLE FIBRES ON THE FRESH PROPERTIES OF PASTES FORMULATED FROM SELF COMPACTING CONCRETE A. El Hilali (1), E. Ghorbel (1) and P. Gonnon (2) (1) LM2GC-University of Cergy Pontoise, 5 Mail Guy-Lussac, Neuville Sur Oise, Cergy Pontoise Cedex, France (2) OMYA SAS 5 Rue de l Aiguillon, ZI Lyon-Nord, Genay, France Abstract This aer deals with the influence of vegetable fibres on the rheological roerties of astes used in the formulation of self comacting concrete. Emirical tests such as sread and Marsh cone tests are used to characterise the effect of short recycled fibres on the water and suerlasticizer demand. Five tyes of fibres are investigated differing in their geometrical roerties and in their content of cellulose. The aste is comosed by cement and calcareous fillers (BETOCARB P2). All formulations are made by imosing a water aste ratio by mass W P 0.4. The results show that the water owder ratio by volume is linearly related to the relative slum. By introducing vegetable fibres a saturation of the relative slum is noticed. The quantity of cellulose influences significantly the quantity of water required to fill the voids in the owders system while the geometrical arameters does not lay a notable role comared to the cellulose content. However, the length of the fibres affects the suerlasticizer demand. The determination of the SP dosage is indeendent of the testing rocedure. Finally, it has been established that increasing the cellulose content and decreasing the fibre length rovide a aste with the best fluidity and flow ability. Keywords: Self-comacting Concrete, calcareous Filler, vegetable Fibres, Rheological roerties. 1. INTRODUCTION The self comacting concrete is characterised by their high fluidity so that they can be imlemented without vibration. The effects of the fibres on their behaviour in both the fresh and the hardened states are of great significance for a broader use of these materials. The urose of fibre reinforcement is to imrove the roerties of a building material, basically the mechanical ones, which would be otherwise unsuitable for ractical alications. 907

2 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium Several investigations have shown that short vegetable fibres imrove the deformation behaviour, the durability, the shrinkage and the cracking toughness of cement-based mortars [1, 2, 3]. However, few researches have been ublished on the behaviour of self comacting concrete reinforced with vegetable fibres. On the other hand it is well known that the fluidity of the binder aste controls that of the SCC and its viscosity lays an imortant role the stability and on the segregation of SCC. Hence, the objective of this work is to study the effect of cellulose fibres on the flow behaviour and the fluidity of astes reinforced with short recycled vegetable fibres. Five tyes of fibres are investigated differing in their geometrical roerties and in their content of cellulose. To manufacture the aste calcareous filler (BETOCARB P2) is used. The astes are investigated using Marsh cone and mini cone. The objective of using such emirical tests is to characterise the effects of vegetable fibres on the fluidity and the yield shear of the binder astes. The SP dosage has been determined using both tests while the water demand retained by the owder is obtained throughout mini cone tests. 2. MATERIALS Portland cement (CPA CEM I 52.5 according to EN 196-3) rovided by CALCIA is used. It has a secific gravity of 3.11 and a Blaine surface equal to 395 m²/kg. The fillers contain rimarily carbonate of natural calcium manufactured by OMYA SAS Grou using crushingmicronisation technique of natural rocks (marbles). The secific gravity of filler is 2.7, the bulk density is 0,720 Kg/m 3 and the Blaine surface is equal to 552 m²/kg. The suerlasticizer used is Cimfluid 2002 roduced by Axim Italcementi grou with solid contents of 35. It s a new generation roduct based on chains of modified olycarboxylate, esecially conceived for SCC and secifically for recast alication. Five tyes of fibres are investigated differing in their geometrical roerties and in their content of cellulose (Table1). All the fibres are obtained from the recycling of aers. Table1: Proerties of the Fibres Fibre Cellulose content Average fibre length Average fibre thickness FbA FbB FbC FbD TESTING METHODS To study the influence of fibres on the flow of the binder or owders (cement and filler) flow sread and Marsh cone tests are used. Such tests have been already utilised to investigate the rheological behaviour of fresh cement astes formulated for SCC and high erformance concrete [4, 5, 6] It has been shown that the flow time can reflect the lastic viscosity and the yield shear in the case of Bingham fluids [5] as well as in the case of Herschel-Bulkley ones 908

3 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium [7]. For urely viscous fluid the flow time is roortional to the viscosity. The flow sread tests allow to obtain indications on the retained water ratio and the sensitivity of the owder to increasing water content. The relative flow area is linearly related to the yield shear stress. 3.1 Marsh cone tests If the geometry f the cone varies from one country to another, the rincile of the test is usually the same. It consists to record the time, t v, needed for a given volume of aste (here 1 L) to flow trough the nozzle (diameter: 8mm and height: 6mm). The initial aste volume oured into the cone is 2 L. The flow time is linked with the fluidity of the aste. The longer the flow time, the lower is the fluidity. 3.2 Flow sread tests The aaratus consists on a mini cone (diameters: 10 and 7 cm, height: 6cm). The cone is laced on a steel late filled with binder and lifted. The slum, D( mm, ) of the fresh aste is the average of the sread diameters measured in two erendicular directions. The relative slum, Γ, is calculated as given in Eq. (1). D Γ= where D = D D (1) 2 4. EXPERIMENTAL RESULTS The considered aste is comosed of cement and calcareous filler formulated from a Self Comacting Concrete. According to NF EN 2061 the minimum amount of cement to be used for roducing normal concrete subjected to a class of exosure of the tye XF1 with D<12,5 3 mm is Cmin = 308 kg/ m. Moreover if the concrete contains calcareous fillers, the amount of F fillers F is calculated by imosing 0.25 F + C = and the total amount of binder to be used is B = C F. As this investigation deals with SCC, the following quantities are imosed 3 with regard to revious works [8]: C = 350 kg/ m, the amount of mixing fillers F required 3 in SCC is consequently equal to: F =116 kg/ m. The content of added fibres into the aste is in ercent by weight of cement. The water owder ratio by volume,( Vw V ), must not exceed the value of 1.2 which corresonds to water/owder ratio by mass, W P 0.4 which is considered as a imum for the realisation of SCC [8]. 4.1 Flow sread test on single owders and owder combinations The relative slum is set out against the water/owder ratio by mass, W P, or by volume, Vw V. Some authors have shown that for astes made with any articular owder or combination of owders, the water owder ratio by volume is linearly related to the relative slum according to Eq. 2. V / V = β +Γ. E (2) W P P P 909

4 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium Where β gives an indication on water content that can be retained by the binder and E is the deformation coefficient which measures the sensitivity of the fluidity characteristics of the owder to increasing water content. For the owders utilised in this study the same trend is observed. However, by introducing vegetable fibres in the binder, this tendency is not checked any more (Figure 1). A saturation V V. This of the relative slum, Γ c, is noticed at a critical water/owder ratio by volume ( ) w c means that the water in surlus of V β has reached a critical value from which it does not affect any more the lubrication of both the articles and the fibres, the flow ability and the slum of the fibre reinforced owders. This reort is observed in mini cone exeriments V V does not exceed conducted on binder reinforced with 2 and 3 fibre content when ( w ) the value of 1.2 which corresonds to water/owder ratio by mass, W P 0.4 that is considered as a imum for the realisation of SCC [8]. Below ( Vw V ) the fitted aste c lines of the reinforced owders (cement and filler) are of the form of Eq. (2). The values of the fitted coefficients β and E are listed in Table 2. Table2 : Fitted coefficients of Equation (2). Fibre content () Coefficient β E β E β E β E FbA 0,332 0,119 0,349 0,130 0,356 0,158 FbB 0,295 0,099 0,299 0,131 0,343 0,141 FbC 0,71 0,055 0,229 0,102 0,287 0,110 0,358 0,123 FbD 0,181 0,103 0,298 0,094 0,367 0,108 0,201 0,092 0,228 0,094 0,293 0,107 Powder combination used for the develoment of SCC is also tested, as listed in Table 2. It aears that the aste flows when W P f 0.2. By introducing the recycled vegetable fibres the quantity of water required for flow decreases while the sensitivity to increasing water decreases ( E increases). Hence, by introducing vegetable fibres, the void fraction of the binder decreases and consequently the amount of water that can be retained to fill the voids of the owder is reduced. Moreover, as the content of the fibres increases E and β values increase indicating the lower sensitivity of the astes to increasing water content and the higher quantity of the water to ensuring the binder flow. The quantity of cellulose influences significantly the quantity of water required to fill the voids in the owders system. The lowest values of β are obtained when the added fibres contain the highest value of cellulose. The geometrical arameters of the fibres does not lay a notable role comared to the cellulose content. 910

5 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium 1,20 1,10 1,00 FbD FbC FbB FbA Vw/V 0,90 0,80 0,70 0, Γ=(D/100)²-1 Figure 1: Flow sread test results for aste fibres combinations (2). 4.2 Marsh cone test on single owder and reinforced owder The marsh cone test are conducted on ure astes and reinforced ones to have indication on the otimal water/owder ratio by mass, W P, to be introduced in SCC. Table 3: Values of the otimum water owder ratio by mass obtained using Marsh cone tests Fibre content () Coefficient ( W P ) min ( W P ) o ( W P ) o ( W P ) o FbA 0, FbB 0, FbC ,286 0,301 FbD 0,294 0,330 0,296 0,341 Results obtained from sread flow tests show that aste will flow when Γ f 0 and consequently when V V f β. β can be considered as the water/owder ratio by volume w below which no slum takes lace and hence estimates the minimal value of V w V. Marsh cone tests conducted on astes differing in the water content show that a saturation oint exists,( W P, which corresonds to an otimum water content beyond which the flow time ) o decreases drastically and consequently the lastic viscosity, μ, of the astes. Hence increasing the water content induces an increase in the fluidity of the aste. The introduction of vegetable fibres induces a reduction of the otimum water content beyond which the fluidity of the astes increases significantly. It can be observed that ( W P increases by ) o 911

6 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium increasing the fibre content. The higher the cellulose content, the greater is ( W P increasing both the fibres content and the amount of cellulose contained into the fibres, ( W P) o increases and exceeds the value obtained for not reinforced aste (Table 3). Sread tests and Marsh cone ones allow to fix the range of water roortioning which can be alied for the SCC formulation. The astes have to be viscous to suort the aggregates and fluid to ensure the fluidity of the self comacting concrete itself. 4.3 Influence of suerlasticizer In this study sread tests as well as march cone tests are conducted on astes differing in the fibres content and characterised by a fixed water/owder ratio by mass 0.35 W P =. Table 4: SP saturation oints obtained from flow sread tests fibre S S S SP ( ) SP ( ) D ( mm ) SP ( ) D ( mm ) i FbA FbB , FbC 1, , FbD 1, , From flow sread tests, the saturation value, i 1, , S SP ) o. By, is determined as the oint from which no increase of the slum flow is observed. The introduction of the fibres causes an increase of the SP dosage (Table 4). The quantity of cellulose as well as the geometrical roerties of the fibres affect the suerlasticizer demand. For fibres with the same length and diameter, the SP dosage increases by increasing the cellulose content while the slum flow decreases. If the cellulose content is constant, the longer the fibre, the greater is the SP dosage. The lowest SP dosage with the better flow ability are obtained for the shorter fibres containing the highest cellulose amount. Results obtained from Marsh cone tests reveal that by increasing the SP dosage the flow M time increases and reach a saturation value, SP from which it remains constant and equal to t v (Table 5). The saturation values of SP dosage obtained by erforming Marsh cone tests are very close to those obtained using mini cone tests. The introduction of the recycled vegetable fibres in the formulation of SCC generates on the one hand an increase in the SP dosage for a given water/owder ratio by mass and an augmentation of the aste viscosity exect for short fibres containing the highest cellulose amount on the other hand The lowest SP dosage with the best flow ability and the highest fluidity of the aste are obtained for the shortest fibres containing the highest cellulose amount. 912

7 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium Table 5: SP saturation oints obtained from Marsh cone tests. fibre M M M SP ( ) t ( s ) SP ( ) t ( s ) SP ( ) t ( s ) v v FbA 1,87 24,84 2,32 22,87 FbB 1,91 26,70 2,38 24,32 FbC 1, ,80 22,86 2,28 21,56 FbD 1,74 20,58 2,22 20,46 1,70 19,22 2,14 19,14 v 5. CONCLUSIONS Marsh cone tests and mini cone tests are erformed on astes formulated for Self Comacting Concrete and reinforced with recycled vegetables fibres differing by the cellulose content and the geometrical characteristics. The objective is to determine the range of water roortioning and SP dosage which can be alied for the SCC formulation. The results show that the water owder ratio by volume is linearly related to the relative slum according to Eq.( 2). By introducing vegetable fibres in the binder, this tendency is not checked any more and a saturation of the relative slum is noticed at a critical water/owder ratio. Moreover, the void fraction of the binder decreases by introducing vegetable fibres and consequently the amount of water that can be retained to fill the voids of the owder is reduced. In addition, the higher the fibres content the lower is sensitivity of the astes to increasing water content and the higher is quantity of the water to ensuring the binder flow. The quantity of cellulose influences significantly the quantity of water required to fill the voids in the owders system while the geometrical arameters of the fibres does not lay a notable role comared to the cellulose content. The lowest values are obtained when the added fibres contain the highest value of cellulose. However the length of the fibres affects the suerlasticizer demand. The determination of the SP dosage is indeendent of the testing rocedure. Finally by increasing the cellulose content and decreasing the fibre length the formulated aste has the best fluidity and flow ability. REFERENCES [1] V.Agoyan, H.Savastano Jr., V.M. Jhon, M.A.Cincotto, Develoments on vegetable fibre- cement based materials in Sao Paulo, Brazil:An overview, cement and concrete comosites (27) (2005) [2] A.Grimaldi, R. Luciano, Tensile stiffness and strength of fiber reinforced concrete, Journal of the Mechanics and Physics of Solids (48) (2000)

8 5th International RILEM Symosium on Self-Comacting Concrete 3-5 Setember 2007, Ghent, Belgium [3] P.J. Kim, H.C. Wu, Z.Lin, V.C.Li, B. delhoneux, S.A.S. Akers, Micromechanics based durability study of cellulose cement in flexure, cement and concrete research (29) (1999) [4] P. Domone and C. His-Wen, Testing of binders for high erformance concrete, cement and concrete research (1997) [5] N. Roussel, R. Le Roy, The Marsh cone: a test or a rheological aaratus? Cement and Concrete Research 35 (2005) [6] H.J.H. Brouwers, H.J. Radix, Self comacting concrete: Theoretical and Exerimental Study, cement and concrete research (2005) [7] V. H. Nguyen, S. Rémond, J. L. Gallias,.P. Bigas, P. Muller, Flow of Herschel-Bulkley fluids through the Marsh cone J. of Non Newtonian Fluid Mechanics, 139 (2006), [8] P. L. Domone, A review of the hardened mechanical roerties of self comacting concrete Cement &Concrete Comosites 29 (2007)