Particle packing: An important concept for mix design of better compacted interfacial transition zone in cementitious composite systems

Transcription

1 Partcle packng: An mportant concept for mx esgn of better compacte nterfacal transton zone n cementtous composte systems Y. Gao (1), G. D. Schutter (1), G. Ye (1,2), Z. J. Tan (1) (1) Magnel Laboratory for Concrete Research, Ghent Unversty, Belgum (2) Mcrolab, Delft Unversty, The Netherlans Abstract It s well known that the nterfacal transton zone (ITZ) of concrete between aggregate an bulk paste often acts as a negatve effect wth respect to overall propertes lke strength an urablty. To reuce the negatve nfluence of ITZ, t was usually consere to a varous pozzolan or mneral atons nto concrete, such as granulate blast furnace slag (GBFS). These atons coul ncur both physcal packng an affect the chemcal hyraton reacton. In ths paper, the physcal packng effect n ternary blene cementtous system was stue n more etal. The maxmum packng ensty can be calculate by employng lnear packng moel (LPM), base on the scretzaton of partcle sze strbuton (PSD). Wth varous mx proportons of raw materals, the overall strbuton of packng ensty was splaye. In orer to show how the ntal ITZ property was nfluence by packng ensty, numercal moelng by means of ranom sequental aton (RSA) has also been conucte. 1. INTRODUCTION As well known, Portlan cement base concrete has been one of the most mportant constructon materals n present nustral realtes. Vast usage of concrete has le to the occurrence of many extraornary bulngs all over the worl. However, the proucton of raw materals makng concrete coul brng many resource an envronment problems, for nstance, CO 2 emsson urng proucton of Portlan cement [1]. Fortunately, after ecaes of research, varous kns of pozzolanc materals as partal replacement of cement have been successfully employe n practce, such as granulate blast furnace slag [2, 3], fly ash [4], an slca fume [5]. On the other han, wth the help of superplastczer, t became possble to esgn mxtures contanng hgh volumes of pozzolans. Those were the reasons for numerous applcatons of blene cements n engneerng proects. Many researchers beleve that a specal nterfacal transton zone characterze by hgher porosty exste aroun aggregates, an t playe an mportant role n the overall property [6].

2 More specfcally, the bonng strength of ITZ can nfluence concrete strength. Furthermore, the exstence of hgher porosty wthn ITZ an ncrease overall pore connectvty woul ecrease urablty of concrete when expose to aggressve envronments [7]. Therefore, many efforts have been ecate to relate research, an results showe that ITZ coul be nfluence by many factors, such as water bner rato, curng age, aggregate property an so on [8-10]. Though some research work ha been conucte on the nfluence of partcle sze strbuton of Portlan cement [11], the packng ensty was not often consere as a relevant parameter. Therefore, ths paper s tryng to make some contrbuton concernng ths topc, startng from analytcal precton of maxmum packng ensty of blene cement systems base on lnear packng moel. In orer to fferentate from other hyraton factors, the ITZ s stue n ntal state wthout any hyraton. Hereafter, ITZ s referrng to the ntal ITZ. The paper outlne s arrange lke ths: the lnear packng moel enablng an analytcal precton of packng ensty s ntrouce n secton 2; calculaton results are gven n secton 3; ITZ structure moelng s processe n secton 4, nclung a scusson of the nfluence of packng ensty; fnally, some conclung remarks are gven n secton METHODOLOGY In ths secton, a bref ntroucton of LPM an PSD of cementtous materals nclung Portlan cement, GBFS, an lmestone fller are presente. Due to the fact that extremely complcate nteractons exst n a multsze mxture consstng of very small partcles (for nstance n cementtous systems: electrostatc, Van er Waals an all other cohesve or repulsve forces), a comprehensve an nclusve theory of packng of multsze partcles oes not exst [12]. Therefore, t woul be helpful to fn some approxmaton methos to estmate packng ensty. Among them, the lnear packng moel ha receve much attenton for the sake of ts smplcty an effectveness [12-14]. The LPM was base on two smplfe assumptons: noneformable partcles an lnear nteractons. The frst assumpton requre no overlap between two partcles, an the secon assumpton mple that complex nteracton among partcles can be approxmate lnearly. Conser a mxture compose of n szes (=1 n) of smlarly shape grans orere from largest to smallest or vce versa, wth a known nepenent monosze packng ensty for each component. Here, for the purpose of smplcty, only the fnal equaton for calculatng packng ensty s gven whle the eucton process s omtte. More etals can be foun n lterature [12-14]. mn{ } (1) 1 n 1 (1 ) g(, f (, 1 1 Where,, are monosze packng ensty an volume fracton of th component n mxture, respectvely; functons g(,, f(, represent the lnear nteracton contrbute by smaller an larger partcles, orgnatng from the fllng an loosenng effects n partcle packng; the symbol mn means the mnmum value. Compare wth the contaner, partcle szes of cementtous materal are very small, so the bounary effect of packng can be gnore, whch means that the monosze packng enstes are the same. Interacton functons can be measure by experment. In current research, g(,, f(, are followng expressons as suggeste n reference [14].

3 g(, (1 ) 0.4 (1 ) ; f (, (1 ) 2.8 (1 ) ; In orer to estmate the packng ensty of multsze components, t s necessary to etermne the partcle sze strbuton of the system. In the present applcaton, the cementtous composte system was compose of Portlan cement, GBFS an lmestone fller, an ther respectve enstes were 3120 kg/m 3, 2896 kg/m 3, 2650 kg/m 3. The PSD of each composton was obtane by means of laser ffracton measurement as shown n Fgure 1. Beses, a kn of fne lmestone fller was employe n calculaton an the PSD ata can be foun n reference [15]. (2) (3) Fgure 1: Partcle sze strbuton of cementtous materals from laser ffracton measurement As suggeste, the Rosn-Rammler functon coul be use to escrbe PSD of sngle cementtous composton [16]. Nevertheless, the mxture was ternary blene n current stuy, so t woul be ffcult to ft n unque Rosn-Rammler functon nclung all components. Even f t was possble, the calculaton of packng ensty n terms of mx proporton woul stll be unavalable. So, the frst necessary treatment was to obtan screte sze classes of each composton an sort them n overall mxture. Equaton 4 an equaton 5 were employe to acqure equvalent screte szes an relate volume fracton. upp 3 3 ( low upp ( ) low upp [ ) ( )] (4) low (5) Where,, are lower an upper lmt relatng to certan screte sze, respectvely. low upp

4 3. RESULT In current stuy, four an eght classes for each composton were use. Specfcally, the former was base on the orer of general length menson whle the latter took avantage of preset characterstc szes. Packng enstes versus mx proporton of raw materals n terms of mass percentage are shown n Fgures 2 to 5. It s foun that packng ensty ncreases monotonously wth ncreasng lmestone fller content (see Fgure 2 an Fgure 3), however t was fferent for fne lmestone fller (see Fgures 4 an 5), now showng some obvous peaks. By comparson, fne lmestone fller s able to ncrease packng ensty, for nstance from 76% to 83% usng four classes (see Fgure 2 an Fgure 4). Beses, the screte classes also show an nfluence on the fnal result. Wth more sze classes, the largest packng ensty among the whole oman s hgher (see Fgures 2 an 3, an Fgures 4 an 5 for fne lmestone fller). For fne lmestone fller, the nfluence s larger, as compare between Fgures 4 an 5. The overall graent of packng ensty ecreases whle usng eght classes. Ths ncates that t s necessary to employ more classes to characterze fne lmestone fller. After all, no matter how many classes were consere, the mx proportons for obtanng the largest packng ensty are stll the same. Fgure 2: Packng ensty usng four szes Fgure 3: Packng ensty usng eght szes

5 Fgure 4: Packng ensty wth fne lmestone fller usng four szes Fgure 5: Packng ensty wth fne lmestone fller usng eght szes 4. MODELING As acknowlege by many authors, the wall effect was the man reason to form ITZ aroun aggregate, an ue to ffcultes encountere n rect expermental nvestgaton, numercal smulaton turne out to be a goo opton [10, 17]. So, n orer to stuy the nfluence of packng ensty, the numercal metho by means of ranom sequental aton was use to moel the partcle packng process. Base on CEMHYD3D moel [10], two rg bounary walls were set at top an bottom surfaces mposng vrtual aggregates, an the remanng faces were assume to be peroc as shown n Fgure 8 (note that the color ID was same as n Fgure 6 an Fgure 7, specfcally, water: 0; cement: 1-5; slag: 10; CaCO 3 : 26). The moel sze was 100 um n each menson an water bner rato was 0.4. Detals about moelng are specfe n Table 1, an t shoul be note that such mx proportons are only for numercal mplementaton. Table 1: Mx proportons use n moelng n terms of mass percentage Sample Fne Lmestone fller Lmestone fller Portlan cement GBFS Packng ensty Mx1 / 10% 85% 5% Mx2 10% / 85% 5% Mx3 60% / 5% 35% Dsplayng of moele ntal state shows that closer to aggregates, small partcles appear more often than larger ones, whch s a rect nterpretaton of the wall effect (see Fgure 6 an Fgure 7). Comparson among the three mx proportons s shown n Fgure 9. Frst, the ITZ wth oes not vary much aroun 10 mcrons for Mx1 an Mx2, whch s n agreement wth the meum sze of packng partcles. Then, for Mx1 an Mx2 wth close packng ensty, the consequence s that ther respectve porosty an wth of ITZ show very small screpancy. Whle for Mx3, t splays obvous lower porosty an narrower transton zone. The results

6 suggest that there s no rect relatonshp between fller type an ITZ property. The packng ensty however seems to be an mportant parameter. The most ntutve explanaton s that, wth larger packng ensty, partcles ten to pack more compact n a general way, nclung n the ITZ. Fgure 6: Image of 2D slce (1 um from top surface) from Mx2 Fgure 7: Image of 2D slce (15 um from top surface) from Mx2 50um Fgure 8: Moele partcle packng (Mx2) Fgure 9: Porosty varaton wth stance 5. CONCLUSION

7 (1) The lnear packng moel s a goo canate to estmate packng ensty of cementtous composte systems ue to ts easy mplementaton an flexblty. (2) Packng ensty vares wth varyng mx proportons. The scretzaton methos have an nfluence on the absolute packng ensty values an ts strbuton, however, the mx proporton achevng the largest value oes not change as the number of screte classes change. (3) Ranom sequental aton metho expose to rg bounary can smulate the wall effect very well. A rect relaton between packng ensty an ITZ property was foun from the moelng results. 6. REFERENCES [1] Worrell, E., Prce, L., Martn, N., Henrks, C. an Mea, L.O., 'Carbon oxe emssons from the global cement nustry', Annual Revew of Energy an the Envronment 26 (2001) [2] Schutter, G.D. an Taerwe, L., 'General hyraton moel for Portlan cement an blast furnace slag cement', Cement an Concrete Research 25 (3) (1995) [3] Chen, W., Brouwers, H.J.H. an Shu, Z.H., 'Three-mensonal computer moelng of slag cement hyraton', Journal of Materals Scence 42 (23) (2007) [4] Chnaprasrt, P., Jaturaptakkul, C. an Snsr, T., 'Effect of fly ash fneness on mcrostructure of blene cement paste', Constructon an Bulng Materals 21 (2007) [5] Bentz, D.P. an Stutzman, P.E., 'Evoluton of porosty an calcum hyroxe n laboratory concretes contanng slca fume', Cement an Concrete Research 24 (1994) [6] Maso, J.C., 'Interfacal transton zone n concrete', (RILEM REPORT 11, 1996). [7] Ollver, J.P., Maso, J.C. an Bourette, B., 'Interfacal transton zone n concrete', Avance Cement Base Materal 2 (1995) [8] Scrvener, K.L., Crumbe, A.K. an Laugesen, P., 'The Interfacal Transton Zone (ITZ) Between Cement Paste an Aggregate n Concrete', Interface Scence 12 (2004) [9] Scrvener, K.L. an Nemat, K.M., 'The percolaton of pore space n the cement paste/aggregate nterfacal zone of concrete', Cement an Concrete Research 26 (1) (1996) [10] Bentz, D.P., Schlangen, E. an Garbocz, E.J., 'Computer smulaton of nterfacal zone mcrostructure an ts effect on the propertes of cement-base compostes', n 'Materals Scence of Concrete IV', The Amercan Ceramc Socety, 1995 (Westervlle, OH) [11] Bentz, D.P., Garbocz, E.J., Haecker, C.J. an Jensen, O.M., 'Effects of cement partcle sze strbuton on performance propertes of Portlan cement-base materals', Cement an Concrete Research 29 (1999) [12] Stovall, T., Larrar, F.D. an Bull, M., 'Lnear Packng Densty Moel of Gran Mxtures', Power Technology 48 (1986) [13] Yu, A.B. an Stansh, N., 'Estmaton of the Porosty of Partcle Mxtures by a Lnear-Mxture Packng Moel', In. Eng. Chem. Res. 30 (1991) [14] Yu, A.B., Zou, R.P. an Stansh, N., 'Mofyng the Lnear Packng Moel for Prectng the Porosty of Nonsphercal Partcle Mxtures', In. Eng. Chem. Res. 35 (1996) [15] Poppe, A.-M., Influence of fllers on hyraton an propertes of self-compactng concrete, Doctoral thess, Magnel Laboratory for Concrete Research, Ghent Unversty, Belgum, [16] Breugel, V.K., 'Numercal smulaton of hyraton an mcrostructural evelopment n harenngcement base materals (I) theory', Cement an Concrete Research 25 (2) (1995) [17] Stroeven, P. an Stroeven, M., 'Assessment of packng characterstcs by computer smulaton', Cement an Concrete Research 29 (1999)