Dominique Petit

Houria Chemmi

Jean-Pierre Korb

Pierre Levitz

Comptes Rendus Chimie

Full paper/MémoireNMR control of aging and durability of hardened cement pastesC. R. Chimie 13 (2010) 405–408Contents lists available at ScienceDirectComptes Rendus Chimiewww.sciencedi rec t .comHouria Chemmi *, Dominique Petit, Pierre Levitz, Jean-Pierre KorbPhysique de la matière condensée, école polytechnique (CNRS), 91128 Palaiseau, FranceA R T I C L E I N F OArticle history:Received 1 July 2009Accepted after revision 7 September 2009Available online 4 December 2009Keywords:DurabilityCementMoisture transportConfinementNuclear relaxationMots clés :DurabilitéCimentTransport hydriqueConfinementRelaxation nucléaireA B S T R A C TWe report on proton NMR relaxation of hardened and aged grey and white CEM I pastewith several controlled degree of relative humidity. A proton NMR relaxation study ofthese two CEM I cement pastes shows very different pore size hierarchies for these twomaterials. The good sensitivity of the proposed method for analysing the evolution of thepore size dependencies under drying and wetting history of the material could be veryuseful for studying the durability of building material under severe conditions of use. 2009 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.R É S U M ÉNous présentons la relaxation RMN du proton dans des pâtes de ciments de type CEM I griset blanc durcies et vieillies sous différents taux d’humidité. L’étude de la relaxation RMNdu proton de ces deux pâtes de ciments CEM I montre que ces deux matériaux présententune hiérarchie très différente de la taille des pores. La bonne sensibilité de la méthodeproposée pour analyser l’évolution de la dépendance de la distribution de taille de pore enfonction du séchage ou de l’humidification du matériau peut être très utile pour suivre ladurabilité des matériaux de constructions sous des conditions d’utilisation extrêmes. 2009 Académie des sciences. Publié par Elsevier Masson SAS. Tous droits réservés.1. IntroductionHow the texture of white and grey cement-basedmaterials behaves over long times and how to follow theaging of these building materials? Answering thesequestions is particularly important for improving thesustainability and mechanical performance of thesebuilding materials and for limiting the necessary CO2emission required for their production. Moreover, a realand noninvasive multiscale experimental approach mustbe used to answer these questions. For instance, long-termdurability is closely related to unsaturated moisturetransport on different length scales of these materials.Among the different techniques, nuclear magnetic relaxa-tion is probably one of the most appropriate experimental* Corresponding author.E-mail address: houria.chemmi@polytechnique.edu (H. Chemmi).1631-0748/$ – see front matter  2009 Académie des sciences. Published by Edoi:10.1016/j.crci.2009.09.003approaches to study continuously the evolution of themicrostructure of these highly disordered materials.Several attempts have already addressed the question,but only in the early aged of the materials [1]. In this casethere is always enough liquid species in the intricateporosity of the material to achieve a good NMR signal.However, to follow the characteristic features of aging ofthe material over a long period of time, a sufficientlysensitive NMR technique should be used.It is well known that hardened cement pastes exhibit athreefold hierarchy pore structure: intra-CSH (hydraulicbinder) microscale (below 2 nm), mesopore structure at ascale ranging from 2 to 50 nm and capillary (macro) porenetwork above 50 nm [2]. To study this material, we arecurrently studying the moisture transport at differentwater filling, controlled by temperature and relativehumidity ratio, by using a proton NMR multiscaleapproach including PFG diffusometry, field cycling relaxo-metry and spectroscopy correlated with T1, T2 and T1rmeasurements. Here, we report two particular studies.lsevier Masson SAS. All rights reserved.H. Chemmi et al. / C. R. Chimie 13 (2010) 405–408406First, we present a proton NMR relaxation study ofhardened grey and white CEM I Portland cement pastesthat shows different pore size hierarchies for these twomaterials. Second, we focus on the grey cement to showthe effects of different degrees of humidity on the transportof moisture during the aging.2. Materials and experimentsCement pastes are prepared at 20 8C by mixinganhydrous grey or white CEM I powder and distilledwater with a water-to-cement mass ratio w/c = 0.5. After24 h, the material is kept in a saturated limewater solutionFig. 1. Different steps of the ‘‘curve-peeling’’ method are used to extract successiv1.1 and 1.2) and shown on semi-logarithmic plots. Then the exponential componfive extracted weight factors Ai vs. the five relaxation times T1i shown on curve 1.8hydrated 5 days with w/c = 0.5 at 20 8C.to prevent the autodesiccation of the pores. Then, long-itudinal relaxation NMR experiments by inversion recov-ery are performed at a proton Larmor frequency of360 MHz on these materials in different conditions.Evolutions of longitudinal proton magnetizations areanalysed by a ‘‘curve-peeling’’ method as illustrated onFig. 1. First, one extracts an exponential at long times onthe raw data (curve a on Fig. 1.1). Then, we iterativelycontinue this extraction of exponentials at long times aftersubtraction of the previous exponential until we reach amono-exponential behavior (curves b, c, d, e on Figs. 1.1and 1.2). Finally, we verify the accuracy of the curvepeeling procedure by reintroducing all the exponentialely five exponential components from the magnetization raw data (curvesents are summed step by step (curves 1.3 to 1.7). Logarithmic plots of theexemplify a proton population distribution (1H-P.D.) of a grey CEM I pasteH. Chemmi et al. / C. R. Chimie 13 (2010) 405–408 407components to compare with the raw data of longitudinalmagnetization decay (Figs. 1.3 to 1.7). This ‘‘curve-peeling’’analysis leads to a proton population distribution (1H-P.D.)expressed through the weighting factors Ai vs. the long-itudinal relaxation times T1i (Fig. 1.8).3. Results and discussion3.1. Comparison of data obtained from grey and whitecement pastesWe present on Fig. 2 logarithmic plots of 1H-P.D. vs. therelaxation times T2i, T1ri and T1i (2.a._, 2.b._, 2.c._,respectively) obtained for 50 days-aged grey (2._.1) and75 days-aged white (2._.2) CEM I pastes. In these cementpastes, the nuclear relaxation process is mainly controlledby paramagnetic ferric ions [3] and well understood usinga biphasic fast exchange model [4] leading to a propor-tionality relation between Tl with l 2 {1, 2, 1r} and thevolume to surface ratio of pores V/S which defines anaverage NMR pore radius<R>NMR a Tl. Halperin et al. havedemonstrated the validity of the biphasic fast exchangemodel for cement pastes, showing the linear relationbetween the relaxation times and the volume-to-surfaceratio of the pores or average pore size [5]. These resultsconfirm the discrete distributions of pore sizes previouslyfound for similar materials but at the early-aged period [1].Here, the originality results in the possibility to obtain suchstructural information well after the complete hydration ofthe materials. These data have been obtained by pulsesequence operating at different frequencies showingunambiguously the following features:Fig. 2. Fig. 2 reports logarithmic plots of 1H-P.D. vs. the relaxation times T2i, T1ri anand 75 days-aged white (2._.2) CEM I pastes. odne observes power laws with different exponents forthe 1H-P.D. obtained from the T2i data (Fig. 2.a._) for bothmaterials but in different time scales. For the greycement, the exponent of 0.6 is similar to the onespreviously found from the T1i in C3S paste [6]. For thewhite cement, one notes a net enhancement of theexponent with a value of 1. Such a difference reveals amore hierarchical drying process in white than in greycement. Often, a power law for a pore size distributionindicates a scale invariance of the data or equivalently ahierarchy of pore sizes. These differences of exponentsand time scales indicate clearly distinct drying behaviorat large scales for the grey and white cement; the 1H-P.D. found from T1i data (Fig. 2.c._) confirms thedifferent behaviours obtained for both materials. Thevery long T1 = 10 s is characteristic of portlandite crystalsand should not be considered as giving any pore sizeinformation. However, the macroscopic and microscopicscales do not follow the same distribution laws for thetwo materials evidencing again distinct drying behaviourat large scales for the grey and white cement; T1ri is limited due the higher power involved in themeasurement which limits the dynamics needed tofollow a large hierarchical behaviour.3.2. Effect of aging of grey CEM I cement pasteWe present on Fig. 3 the proton T1i distribution for greyCEM I cement in different conditions of drying and aging. Incondition 1 (Fig. 3.1), the material is used after a 5 dayssetting delay. In condition 2 (Fig. 3.2), the material is driedduring 3 days under vacuum in a oven after an aging periodT1i (2.a._, 2.b._, 2.c._, respectively) obtained for 50 days-aged grey (2._.1)Fig. 3. Fig. 3 reports successively 1H-P.D. vs. T1 of a 5 days setting grey CEM I (Fig. 3.1), then of the same material dried 2 months later (Fig. 3.2), and finally ofthe same dried material hydrated at R.H. = 90% during one month (Fig. 3.3). The dotted lines underline the power law behavior of the proton distributions.H. Chemmi et al. / C. R. Chimie 13 (2010) 405–408408of 2 months at 25 8C and R.H. = 50%. Finally, in condition 3(Fig. 3.3), the same material is hydrated again during onemonth at 25 8C and R.H. = 90% using a saturated watersolution by BaCl2 salt. These data reveal the followingpoints: at five days, the observed data follow two power lawswith a negative and positive exponents at small andlarge scales, respectively. This is not a surprising resultfor a material that does not achieve a completehydration; after 50 days of aging and 3 days drying process, oneobserves a 1H-P.D. that follows a unique power law overa large range of relaxation time scale, without countingthe longest T1 of 10 s coming from portlandite crystals.Here the microstructure is not modified by the dryingprocess which impacts mainly on the macrostructurerange; after 90 days and 30 days of hydration at R.H. = 90%, werestore the distribution corresponding to the macro porerange. The drying processes following these three stepsshow that only the macro pore populations are involvedin the overall drying process. The net change in the signof the exponent at 5 and 90 days for small and largelength scales can be formally understood by either asurface proton distribution S(R) =<R>2-Df in the region ofsmall length scales or a volume proton distributionV(R) =<R>3-Df in large length scales where Df is a fractaldimension between 2 and 3 [7]. The overall behavior ofthese distributions thus shows the very good sensitivityof our method of analysing the drying history of thematerial.4. ConclusionsThe main results of this study are twofold. (i) A protonNMR relaxation study of hardened grey and white CEM IPortland cement pastes shows very different pore sizehierarchies for these two materials. (ii) We prove the goodsensitivity of our method for analysing the evolution of thepore size dependencies under drying and wetting historyof the material. We believe that the proposed methodcould be very useful for studying the durability of buildingmaterial under conditions of extreme use.AcknowledgementsThis work has been supported by a grant from a CPRcontrat pour la recherche between CNRS and Associationtechnique de l’industrie des liants hydrauliques (ATILH).References[1] (a) S. Philippot, J.-P. Korb, D. Petit, H. Zanni, Magn. Reson. Imaging 16(1998) 515 ;(b) A. Plassais, J.-P. Korb, D. Petit, N. Lequeux, M.-P. Pomies, P. Boch,Magn. Reson. Imaging 21 (2003) 369.[2] T.C. Powers, J. Am. Ceram. Soc. 41 (1958) 1–6.[3] F. Barberon, J.-P. Korb, D. Petit, V. Morin, E. Bermejo, Phys. Rev. Lett 90(2003) 116103.[4] K.R. Brownstein, C.E. Tarr, Phys. Rev. A 19 (1979) 2446.[5] (a) W.P. Halperin, J.-Y. Jehng, Y.-Q. Song, Magn. Reson. Imaging 12(1994) 169 ;(b) J.-Y. Jehng, D.T. Sprague, W.P. Halperin, Magn. Res. Imaging 14(1996) 785.[6] A. Plassais, M.-P. Pomiès, N. Lequeux, J.-P. Korb, D. Petit, F. Barberon, B.Bresson, Phys. Rev. E 72 (2005) 041401.[7] C. Porteneuve, J.-P. Korb, D. Petit, H. Zanni, Cem. Concr. Res. 32 (2002) 97.

NMR control of aging and durability of hardened cement pastes

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NMR control of aging and durability of hardened cement pastes

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