Characterization of the Bonds Developed between Calcium Silicate

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Characterization of the bonds developed between calcium silicate hydrate and polycarboxylate-based superplasticizers with silyl functionalities Carlos A. Orozco, Byong-Wa Zen Chun, Guoqing Geng, Abdul-Hamid Emwas, and Paulo J.M. Monteiro Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b04368 • Publication Date (Web): 22 Mar 2017 Downloaded from http://pubs.acs.org on March 25, 2017

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Characterization of the bonds developed between calcium silicate hydrate and polycarboxylate-based superplasticizers with silyl functionalities Carlos A. Orozcoa,b*, Byong W. Chunc, Guoqing Genga, Abdul H. Emwasd, Paulo J.M. Monteiroa a

Department of Civil Engineering, University of California Berkeley, United States Research and Development Center, R&D, Cementos Argos S.A, Medellin, Colombia c W.R. Grace & Co, Grace Construction Products, Massachusetts, United States d NMR Core Lab, King Abdullah University of Science and Technology, Saudi Arabia b

Corresponding author: Paulo J.M. Monteiro, email [email protected] Abstract: Major developments in concrete technology have been achieved with the use of polycarboxylate-based superplasticizers (PCEs) to improve the concrete rheology without increasing the mix water content. Currently, it is possible to control the fluidity of the fresh concrete and obtain stronger and more durable structures. Therefore, there is a strong incentive to understand the interactions between PCEs and cement hydrates at the atomic scale to design new customized functional PCEs according to the ever-increasing requirements of the concrete industry. Here, the bonding types generated between a PCE with silyl functionalities (PCE-Sil) and a synthetic calcium silicate hydrate (C-S-H) are analyzed using XRD, 29Si NMR and synchrotron-based techniques, such as NEXAFS and EXAFS. The results indicated that the carboxylic groups present in PCE-Sil interact by a ligand-type bond with calcium, which modified not only the symmetry and coordination number of the calcium located at the surface of C-S-H but also the neighboring silicon atoms of the C-S-H. In addition, the silyl functionalities of the PCE-Sil generated covalent bonds through siloxane bridges between the silanol groups of PCE-Sil and the non-bonding oxygen located at the dimeric sites in C-S-H, forming new bridging silicon sites and subsequently increasing the silicate polymerization.

Keywords: Calcium silicate hydrate (C-S-H), PCE, Bonding, NEXAFS, EXAFS, 29Si NMR.

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1. Introduction: Polycarboxylate-based superplasticizers (PCEs) have been one of the most outstanding developments in concrete technology over the past few decades; they are added to concrete mixes to improve the rheology and other important properties, such as strength and durability 1,2. PCEs are copolymers conformed by a negative charged central backbone of polyacrylic (PAA) or methacrylic acid (MAA), which contains carboxylic groups, and by pendant chains composed of polyethylene oxide (PEO) that are grafted to the backbone to form comb-branch structures. The anionic part of PCE is adsorbed onto specific cement particles and cement hydration products once they are formed, while the pendant PEO chains point out to pore solution in different configurations from the hydrated surface (i.e., the surface of cement hydration products) and cause the dispersion of particles by steric repulsion, which is the main dispersion mechanism 2,3. Furthermore, it has been determined that the carboxylic groups (COO-) contained in PCE structure interact by chemical bonds with calcium species in solution and with those located at the surfaces of solids. This PCE adsorption mechanism is controlled in part by the PCE molecule conformation and the calcium content 4,5,6. The calcium binding from the pore solution and the adsorption of PCE onto the hydrate surface are affected, among other PCE structural parameters, by the length and density of the pendant chains because they alter the amount of free carboxylic groups that are available for adsorption 5,6,7,10. Moreover, the entropic contribution of the counter ions and water molecules present onto the mineral surface that are released to pore solution by the PCE adsorption, as well as the PCE architecture contribute to the Free energy of the system, driving the PCE adsorption process as well 8. PCE adsorption is also affected by the presence of specific ions in solutions, such as sulfates, which results in the competitive adsorption and/or desorption of PCE and consequently affects the expected rheology improvements 9,10. To overcome these issues, several modifications of the PCE structure have been proposed to enhance the adsorption of PCE onto the hydrate surface, some of them are the increment of the effective backbone charge using dicarboxylate structures in the backbone and the inclusion of phosphate groups in the PCE structure 11. Novel PCE designs have been proposed to enhance the PCE interaction with the hydrate surface by including silanol


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groups in the PCE structure to increase the affinity with silicate surfaces 12,13,14,15. These novel PCEs with silyl functionalities exhibited stronger adsorption performances, even in the presence of sulfate ions in the solution, and enhanced resistance of PCE against competitive adsorption and/or desorption from the hydrate surface. One of the mechanisms proposed for the interaction of PCE with silyl functionalities and hydrate surfaces is the formation of strong covalent bonds between the silanol contained in the PCE and the silicon located at the hydrate surfaces, mainly from calcium silicate hydrates (C-S-Hs) 13,15. Calcium silicate hydrates are one of most important hydrate phases in concrete; they act as binders and are responsible for strength development and other important features, such as shrinkage and creep. They are formed during the hydration of the tricalcium silicate and dicalcium silicate minerals present in Portland cement. C-S-Hs are described as imperfect semicrystalline structures related to the natural minerals Tobermorite or Jennite, which are mainly differentiated based on their crystalline structure and calcium/silicon ratio. For cement, the hydration products called C-S-H(I) and C-S-H(II) are described as poorly crystalline phases with imperfect Tobermorite-like and Jennite-like structures, respectively. C-S-Hs exhibit layered structures that are conformed by a distorted central Ca-O layer, which is flanked on both sides by silicate chains; the same layered structure is repeated but separated by a basal space that includes calcium ions and water molecules, which neutralize charges 16,17. The type of C-S-H produced at early ages of cement hydration is as dimeric structure (i.e., silicate chain conformed by two silicon tetrahedral sharing one oxygen) 17,18, which exhibits a considerable amount of reactive sites (non-bonded oxygen) that are available to form chemical bonds with other species.

The use of PCE with silyl functionalities in Portland cement may exhibit different performance than regular PCE. Indeed, the enhanced affinity for silicate surfaces along their natural attraction by positive charge surface contained in Portland cement and hydrates, they can generate longer delays in cement hydration. Fortunately, this can be countered by changing the incorporation level of the silane groups in the PCE structure 13. Additionally, the enhanced adsorption property of silyl PCEs increases their initial dispersion capabilities of cement particles, but reduces the concrete workability


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retention15. In concrete, workability is a property required in concrete application to transport and place the concrete mix on construction site.

The purpose of this paper is to give a detailed characterization of the bonds generated between the carboxylic and silanol groups contained in PCE-Sil and the calcium and silicon species present at the surface of the C-S-H. Thus, to determine if the interaction between calcium and carboxylic groups occurs through the ligand-bond type and/or through possible changes in the symmetry and coordination number of calcium, techniques such as Ca L-edge NEXAFS and Ca K-edge EXAFS are performed. Moreover, the possible covalent bonds formed between the silicon contained in the silanol groups of PCE-Sil and in C-S-H are analyzed with Si K-edge NEXAFS measurements, as a complement to the 29Si NMR results reported in 12,13,15. Si K-edge NEXAFS measurements enable the determination of changes in the chemical environment of silicon produced by either new neighboring atoms and/or an increment in silicon polymerization. Therefore, it is possible to confirm if covalent bonds are established between PCE-Sil and C-S-H, which increases the adsorption stability of the PCE-Sil onto the hydrate surface. As a result, a better understanding of the types of interactions between PCEs with silyl functionalities and cement hydrate phases can enable the improvement and new designs of PCE molecules with tailored adsorption functionalities. Additionally, the results reported here can be useful inputs for computational simulation studies, where detailed features related to the polymer interaction with cement hydrates can be introduced into these models.

2. Materials and methods:

2.1 Polycarboxylate-based superplasticizer with silyl functionality (PCE-Sil).


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PCE with silyl functionalities (PCE-Sil) was prepared via the thermal grafting of polyether monoamine (NPEO) followed by chemical condensation of aminopropyltriethoxysilane (APTES) to the backbone that is composed of polyacrylic acid (PAA) with a nominal molecular weight of 5,000. The procedure is as follows: A prescribed amount of NPEO was charged to the reactor, and then agitation was started. The reaction mixture was heated incrementally under nitrogen environment until 150°C for one hour to remove water via a Dean-Stark trap. After, the reaction was held at 150°C for one hour and then cooled until 50°C, ethanolic solution of APTES (100 mL) was added to the reaction product to achieve a 5% substitution of carboxylic groups by silanol groups, as the conservative amount needed to improve the PCE interaction, thus reducing the impact on rheology and cement hydration 12,13. The reaction mix was heated to 80°C to remove the ethanol and then cooled to room temperature, then ethanolic solution (150mL) of N,N-dicyclohexylcarbodiimide (DCC) was slowly charged to the reactor and held for one hour at room temperature; then, 300 grams of ethanol were added to the mix to facilitate the filtration of DCC by products precipitate. Once the solution was filtered, the excess ethanol was removed by evaporation at 80°C. The final neat product was cooled and packed for later use. For its use, a portion of the highly viscous solution is dissolved in water that contains sodium hydroxide to neutralize the carboxylic acid and partially hydrolyze the silanol groups. Figure 1 shows the PCE-Sil structure.

Figure 1. Schematic structure of PCE-Sil. a, b and c: Moles of carboxylate, PEO lateral chains and silanol lateral groups, respectively. To characterize the PCE-Sil produced, its weight-average molar masses (Mw, Mn) were measured in a gel permeation chromatography (Waters GPC), equipped with a refractive


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index detector and column set of ultra hydrogel guard, ultra hydrogel 1000, 250 and 120. The test temperature was set to 35˚C with a 1% of Potassium Nitrate in water as mobile phase, an injection volume of 315 µl and a flow rate of 0.6 ml/min. Polyethylene glycol and polyethylene oxide with narrow molecular weight distribution were used as calibration standards. The charge density of the PCE-Sil polymer was measured by acidbase titration test and it is reported in Appendix B of the supplementary information. 1H NMR test was conducted on a Varian INOVA 400 MHz spectrometer running VNMRj version 2.2b using the S2PUL pulse sequence under temperature set at 40 °C. The FID was processed using Mestrelab Research MNova version 8.1.4. For the test, approximately 40 mg of the PCE Si1 sample was dissolved in D2O using TMSP as a chemical shift reference. The NMR result is in good agreement with the calculated a:b:c ratio from the PCE-Sil components reported in Appendix A and C. The structural parameters of the PCE-Sil polymer are included in Table 1.

2.2 Calcium silicate hydrate C-S-H. Synthetic C-S-H was produced by the reaction between calcium oxide (CaO) and fumed silica; the materials were mixed in stoichiometric proportions to obtain a Ca/Si ratio equal to 1.3. This Ca/Si ratio produces a C-S-H with mostly dimeric structures that allows the incorporation of most of the calcium without the presence of distinguishable Ca(OH)2 phases 19. The CaO is produced by calcination of pure CaCO3 at 900°Cfor 24 hours, and the synthetic fumed silica is referred to as Cabosil-5000. The materials were mixed with decarbonated and deionized water in a solid/liquid ratio of 1/40 in polypropylene containers to prevent any silica dissolution from glass. To prevent carbonation of the samples, nitrogen gas was fluxed inside the bottles once the materials were mixed. After 60 days of the reaction under continuous gentle agitation, the samples were centrifuged under nitrogen environment and washed out twice. The pH of the centrifuged liquors were measured around 12.3 as reported in Appendix D of the supplementary information. Similar results have been reported in 20 for C-S-H with similar composition. The drying process was carried out in an oven at 45˚C for 72 hours under a mild vacuum pressure.


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Finally, the C-S-H samples were stored in containers fluxed with nitrogen until they were used for the analysis. Synthetic C-S-H/PCE-Sil and C-S-H/PAA were obtained by following the steps described before, but PCE-Sil and polyacrylic acid PAA were pre-added to the mix water in a polymer/C-S-H proportion of 1/20, as used in previous studies 20. This polymer proportion was selected to simulate the high polymer to C-S-H ratio exciting during the early cement hydration when the polymer adsorption and dispersion effects are relevant. Calcium hydroxide Ca(OH)2 is obtained by the hydration of calcium oxide CaO in an excess of water and dried following the same procedure done for the C-S-H synthesis.

2.3 X-ray diffraction XRD. The equipment used for XRD measurements was a PANalytical X’Pert Pro diffractometer, operating at 40KeV and 40 mA with a cobalt anode. The 2-theta scanning range was between 5° to 60° degrees, with a step width of 0.0084° and a collection time of 0.475 second per step. The HighScore (Plus) software was used to identify the peak positions related to the referenced structure. The XRD results allowed us to determine the type of C-S-H structure formed, the presence of other phases, such as carbonates and Ca(OH)2, and any structural change produced by the effect of the PCE-Sil with respect to the C-S-H reference.

2.4 Scanning transmission X-ray microscopy (STXM). STXM measurements were carried out at beam lines 5.3.2 and 5.3.2.1 for the calcium and silicon edge, respectively, at the Advanced Light Source facility in Lawrence Berkeley National Laboratory. Ca L-edge spectra were recorded with a photon energy between [340 – 360] eV, and Si K-edge spectra were recorded at a photon energy range of [1830 – 1880] eV. STXM enables the analysis of materials by combining transmission images and chemical speciation based on near-edge X-ray spectra NEXAFS, which is considered within a range of 30 eV below and above the absorption energy edge, with a spectral resolution as high as 0.1 eV and a high spatial resolution of up to 30 nm. From the spectra, symmetries, oxidation states, coordination numbers and other chemical characteristics of the specific atoms analyzed can be obtained from the STXM results. A


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detailed description of the sample preparation and optical geometries of the beam line, as well as the data processing and applications for cementitious materials are well described in 21,22,23.

2.5 Extended X-ray absorption fine structure (EXAFS), Ca k-edge. Ca K-edge EXAFS spectra were collected at the Brazilian Synchrotron Light Laboratory in the beamline XAFS2 using TEY detection. The synchrotron radiation from a 1.3 GeV storage ring uses a Silicon (111) monochromator and a Mo material for energy calibration. For beam collimation, slits with an aperture of 0.8 mm and 0.5 mm in the horizontal and vertical directions were set. The EXAFS in the X-ray absorption spectrum represents the normalized oscillatory part of the absorption coefficient above the absorption energy edge for approximately 1000 eV. The EXAFS spectra enable the determination of important information related to the chemical and structural environment of the adsorbed atom, such as the coordination number, bond length and neighboring atom types. The analysis of the EXAFS spectra was conducted as follows: pre- and post-edge spectra normalization and conversion to wave vector k-space with the energy reference E0 = 4040 eV was conducted using the Athena software 24. The Fourier transform of the EXAFS k3-weighted spectra was conducted with the Arthemis software 24

with a range of k = [3.0 – 12.1 A-1] using a Kaiser-Bessel window and by setting most

of the variables, as reported in 25. Finally, from the Fourier transformation, the modulus represents the radial distribution function (RDF), which shows a series of peaks that represents the distance R [Å] from the central atom. FEFF simulation was run in the same Arthemis software using the crystal structure of a dimeric C-S-H labeled T2_ac, as reported in 26.

2.6 29Si NMR: Experiments were performed at the NMR Core lab of King Abdullah University of Science and Technology in a Bruker UltraShield 900 MHz spectrometer operated at 178.5 MHz for 29Si equipped with a magic-angle spinning (MAS) probe at 54.734


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degrees. The samples were packed in a 3.2 mm zirconia rotor spun at 20 Hz. Data acquisition was performed using a single pulse width of 6.5 micro-seconds with a flip angle of 30˚, 4000 acquisitions and a relaxation delay d1 = 30 seconds. As a reference, TMS was used for the chemical shifts with respect to its downfield resonance at -9.8 ppm. For data processing, the Fourier transform was performed using the 1-D NMR processor software, and the Origin software was used for deconvolution of the peaks. 29

Si NMR allows one to determine the chemical condition of the silicon contained in the

C-S-H structure. Following the conventional nomenclature, Qn is the term used to describe the silicate structure, where Q is the silicon tetrahedrally coordinated to oxygen, and n indicates the number of tetrahedral silicates bonded to the specific unit. Thus, Q0 describes the silicate monomer found in the chemical shift range [-68 to -76], Q1 represents the end-group and describes the dimeric structure where two silicon tetrahedra share one oxygen, which is found at [-76 to -82 ppm], and Q2 represents the middle groups related to silicon tetrahedra that connect two dimeric structures, which is found between [-82 to -88 ppm]. Structures Q3 and Q4 are related to chain branching and the three-dimensional cross-linked framework found in the ranges [-88 to -104 ppm] and [104 to -120], respectively 27,28. Once the intensities of the peaks related to Qn are calculated, the main chain length MCL is computed using the expression MCL = 2*(Q1+Q2)/Q1 given in 19; this value is an indication of the polymerization degree of the silicon chains contained in C-S-H.

3. Results.

3.1 XRD The spectra obtained for the C-S-H samples are shown in Figure 2. They confirm that the structure formed is a C-S-H (I), according to the main peaks obtained that are associated to the (hkl) planes reported in 16. These results confirm that despite the presence of the polymer from the beginning of the reaction, the C-S-H formation in the C-S-H/PCE-Sil sample was not affected. Moreover, the peaks related to crystalline carbonates were not detected, at least for the detection level of this technique.


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Figure 2. XRD spectra of the samples showing a C-S-H type 1 structure.

The only difference between the two XRD spectra is the relatively small shift in the position of the basal peak d00l for the C-S-H/PCE-Sil sample, which represents an apparent increase in the d-spacing value of approximately 0.4 Angstroms with respect to the reference. This is shown at the upper left side of Figure 2. The reason for the change in the basal d00l peak cannot be related to the PCE-Sil intercalation due to the relatively large size of the PCE molecules, as indicated in

20

.

However, changes in the stacking order of the C-S-H layers and the induced strains due to the polymer interaction during C-S-H formation can produce this apparent basal expansion

29

. Moreover, another possible reason for the basal expansion is the

complexation of Ca2+ from the solution by COO- present in the PCE-Sil 5,6. Complexation can generate a reduction in the Ca2+ ions available within the basal spacing of C-S-H and a subsequent incorporation of more water molecules. As a result, weaker cohesive forces are generated due to the lower Ca2+ content present in the basal space, contributing to the expansion detected in the XRD measurements 30.


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3.2 STXM-NEXAFS, Ca L-edge NEXAFS spectra for the Ca L3,2 edge of the C-S-H_Ref and C-S-H/PCE-Sil samples have been analyzed together with the Ca(OH)2 and C-S-H/PAA samples used as comparative spectra. The results reported are the average of several measurements taken on different sample edge sites to generate more representative results. The NEXAFS spectra obtained for the Ca L-edge shown in Figure 3 exhibit two-pair characteristic major and minor peaks, labeled a2, b2 and a1, b1, respectively. The major peaks, a2 and b2 are related to the excited electron transition from the 2p63d0 to 2p53d1 orbitals and are a consequence of the spin-orbital degeneracy of the 2p orbitals, i.e., 2p3/2 and 2p1/2, respectively. The two minor peaks a1 and b1 appear as a consequence of additional breaking of the degeneracy of states due to the electrostatic interaction between the Ca2+ atom and the surrounding oxygen atoms in the first coordination shell. This electrostatic effect is explained using the Crystal Field Theory (CFT), which is applied to interpret the chemistry of coordination compounds 31,32. Thus, the relative intensities and energy differences between the minor and major peaks in the Ca L-edge NEXAFS spectrum provide valuable information related to the symmetry and indirect information on the coordination number of the Ca-O system contained in C-S-H.

Figure 3. NEXAFS of the Ca L-edge of different C-S-H samples.


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Moreover, the values of the energy peak difference (EPD) between the major and minor peaks i.e., [a2 - a1] and [b2 – b1] in Figure 3, are related to the type of central cation as well as the type and symmetry of the ligands around the central atom. CFT makes a connection between the EPD and the symmetry of ligands through the intensity of the crystal field splitting value (∆ ), as shown in Table 2; therefore, for a higher symmetry order of ligands, the ∆ and EPD values in the Ca L-edge spectra must be larger 31,32,33. Thus, a higher order symmetry, such as the octahedral configuration (Oh), shows a strong ∆ and a larger EPD, as is exhibited by Ca(OH)2 22,23. Consequently, as long as the ligands symmetry is disrupted, the EPD in the spectra is smaller, which produces a lower ∆ value based on the weak crystal field 23,31,33, as shown in Table 2. Indeed, the crystal field splitting obtained for the Ca(OH)2 and C-S-H_Ref samples is in agreement with the results reported in 22,23, where the octahedral symmetry of the surrounding six oxygen atoms of the Ca(OH)2 produce the largest EPD in Table 3. On the other hand, the C-S-H_Ref sample exhibits a small EPD and then a weak crystal field splitting due to the irregular oxygen symmetry around Ca2+ and a higher coordination number, as observed for the synthetic C-S-H in 22,23. Interestingly, increases in the EPD, higher than that of the C-S-H_Ref sample, were found for the C-S-H/PCE-Sil and C-SH/PAA samples, which indicates additional effects from the polymer interaction that result in an apparent higher symmetry order than the reference, as shown in Table 3.

A possible reason for the changes in EPD shown in Table 3 is the ligand-type interaction that occurs between free COO- groups contained in PCE-Sil and the Ca2+ located at the surface of C-S-H. This specific interaction produces changes in the calcium symmetry, depending on if the interaction is monodentate or bidentate 34,35. Furthermore, the effect becomes stronger when there is a greater availability of free COO- groups to interact with calcium, and therefore, the effect is more evident in the C-S-H/PCE-Sil and C-S-H/PAA samples, in which the content of free COO- increases.


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3.3 EXAFS, Ca k-edge. To obtain the information about the coordination number and bond length of calcium contained in the C-S-H structure, the quick first shell (QFS) method in the Arthemis software is used. This method only uses the spectra and simulation information of the first shell atoms (the closest oxygen atoms) around calcium and gives accurate results for only the first shell features 24. Thus, the R range used for the QFS analysis was between [1 – 2.35 Å], where the peak related to the Ca-O interaction is located in the radial distribution function (RDF) plot. Moreover, to determine which oxygen atoms are contained within the first shell, their radial distance difference with respect to the central atom must not be higher than 0.3 [Å] 36. The RDF of the samples and the simulated spectra obtained are shown in Figure 4. The limited region within the vertical dashed lines was used for the QFS analysis. The best simulation results and their structural parameters are shown in table 4 with R-factor values of 0.0297 and 0.0309 for the CSH_Ref and CSH/PCE-Sil samples, respectively.

Figure 4. RDF of Ca k-edge EXAFS.

The simulated parameters obtained are in agreement with those reported in 25,36, and they indicate differences in the coordination number (CN) and the corresponding bond length (R) (without shift corrections) connected with the symmetry of the ligands around the


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calcium atoms. Therefore, the shorter bond length of the C-S-H/PCE-Sil sample is expected due to the lower CN and the stronger attraction of the surrounding oxygen to the central calcium atom. Moreover, the specific interaction between COO- and calcium in the crystal structures that produce a CN of 6 in an octahedral symmetry is given by the monodentate-type ligand 34. This type of interaction can occur in solution between Ca2+ and PCE if the density of lateral chains is relatively low 35, which would allow enough access for calcium interaction. Therefore, considering the density of the side chains and the a : b : c ratio given in Table 1 for the PCE-Sil structure, it can be said that a similar monodentate-ligand type interaction may occurs between the COO- groups of PCE-Sil and the calcium located at the surface of C-S-H. This specific monodentate-ligand interaction produces a higher-order symmetry arrangement of surface calcium in the C-SH/PCE-Sil sample with respect to the ones in C-S-H_Ref, which is in agreement with the symmetry results obtained from the Ca L-edge NEXAFS and reported above. 3.4 Si29 NMR. The results shown in Figure 5a and 5b indicate that the C-S-H obtained by the two samples mostly exhibits a dimeric structure with two main peaks related to Q1 around -79 ppm, as the most abundant structure, and Q2 sites detected around -84 ppm. Similar C-SH structures obtained by other authors have been reported for synthetic C-S-H with a roughly similar Ca/Si = 1.3 as the sample used in this study 19,27. From the deconvoluted spectra, some important features can be highlighted in these results. The first one is that considering the total amount of Q1 and Q2 sites for each sample, there is an increment in the total Q2 bridging sites in C-S-H/PCE-Sil with respect to the reference C-S-H_Ref, as shown in Table 5. The second feature is related to a new chemical shift signal detected at -49 ppm in C-S-H/PCE-Sil, which is labeled T1; in addition, this signal can provide evidence related to the interaction between the PCE-Sil and the C-S-H 12,13,15. Interestingly, displacements to higher chemical shift values occurred in all the peaks, mostly in the Q1 site of the C-S-H/PCE-Sil sample, with respect to the reference. This can indicate possible changes in the shielding effect of the new atoms that surround the silicon sites. Finally, each of the Q1 and Q2 peaks was deconvoluted into two peaks due to the asymmetry in the local structure of the silicon sites 19,27,28. The Q1 signal was


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deconvoluted into Q1-Ca and Q1-H as a consequence of the shielding produced by the presence of Ca2+ or H+ as charge balancing ions in the dimeric structures 28. For the Q2 signal, it was deconvoluted into Q2BT and Q2PT as bridging and paired tetrahedral sites, respectively 19,27.

Figure 5a. NMR Si29 of CSH_Ref.

Figure 5b. NMR Si29 of CSH_PCE-Sil.


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The appearance of the new signal T1 can be a consequence of the siloxane-type bonds formed between the silanol groups contained in the PCE-Sil and the silicon present in CS-H, as was stated in a previous work 12,13,15; however, a signal with a similar chemical shift related to the condensation of the silanol groups present in the polymer, which reduce the silanol available for interaction with other species, is highlighted in 13. Thus, it would be useful to find additional results that enable the determination of whether these covalent bonds are formed and the C-S-H locations where they occur. Moreover, the peak shift with respect to the reference found in the silicon sites Q1 and Q2 in the C-S-H/PCE-Sil sample can give valuable information related to the change in the chemical environment of silicon sites in C-S-H. Indeed, this can be connected with either changes in the types of ions (i.e., Ca2+ and H+) that maintain charge neutrality in the dimeric structures 27,37,38 or modifications in the chemical environment of these ions. Thus, when the symmetry and/or coordination number of Ca2+ changes, more Ca2+ attached to C-S-H surface or hydrogen bonds formed between the polymer and the proton counter-ion of the dimeric structure can contribute to these peak shifts. The slight increment in the MCL of C-S-H/PCE-Sil can be related to the increase in silicon polymerization due to the reduction in the initial Ca/Si ratio 27, which is a result of the calcium complexation produced by COO-. Another possible reason is an extra silicon source from silanol groups detached from their original polymer structure, which become additional Q2 sites; however, this last condition is less probable due to the stability of the polymer structure.

3.5 STXM, Si K-edge The Si K-edge NEXAFS spectra are shown in Figure 6 and exhibit two characteristic peaks. The first one (X) is the absorption energy edge related to the excitation of the electron from the 1s to 3p orbital, and the second broader peak (Y) at a higher adsorption energy edge is related to the multi-scattering effect produced by the atoms located further than the second shell from the excited nucleus atom 39. Several types of C-S-H structures have been analyzed using this technique; it connects the shift of the main adsorption peak X to higher absorption energies and the increase in the energy difference between the two


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peaks (Y-X), which demonstrates a higher silicon polymerization produced by conditions, such as the initial Ca/Si ratio and reaction time 22,23. For the samples analyzed, the C-S-H/PCE-Sil presents a shift of the main adsorption peak X of 0.9 eV with respect to C-S-H_Ref, as shown in Table 6. Compared with other results, the shift in the peak X obtained in 22 due to the increase in silicon polymerization of C-S-H by the reduction of the Ca/Si ratio was lower than the peak shift obtained in this study; therefore, the silicon polymerization in C-S-H/PCE-Sil is conducted by incorporating a new silicon source from a different structure than only Q2, which generates a different chemical environment that contribute to a stronger shift of peak X. This new interaction can be attributed to the bonds formed by the silanol groups present in the PCE-Sil structure and the reactive non-bonded oxygen located at the dimeric structures of the CS-H surface; thus, these new interactions allow the formation of new silicon bridging sites on C-S-H. Therefore, the incorporation of a new silicon source contributes to C-S-H silicon polymerization by the generation of these new bridging sites that are conformed by T1 structures. This result is a good complement that proves that the signal detected in this work, which is labeled T1 in 29Si NMR and reported in 12,15, is related to an effective linkage between the organic and inorganic structures, which specifically form new bridging silicon sites on the C-S-H surface.

Figure 6. Si k-edge STXM of C-S-H samples.


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Finally, another possible contribution to the peak X shift in the Si K-edge spectrum is the binding of Ca2+ in the solution by COO- groups. This restrains the number of calcium ions available for incorporation into the C-S-H structure, which can be subsequently located on the surface of the formed C-S-H to balance the charges at the non-bonding oxygen of the dimeric structures. Therefore, it can produce changes in the chemical environment of silicon atoms since the charge balancing is now performed by complexed calcium at the C-S-H/PCE-Sil surface

39

. This is a similar process, but it occurs in the

opposite direction as that described in 18, where to produce pentamers from dimeric C-SH structures, the calcium displaced from the surface by the new Q2 sites are relocated at the basal spacing to maintain charge neutrality.

Schematic representations of the predominantly dimeric structures exhibited by the C-SH_Ref and C-S-H/PCE-Sil samples are shown in Figures 7a and 7b, according to the findings described before. The ionic species located within the basal spacing and the lateral NPEO chains of PCE-Sil are not shown in the figures. For the C-S-H_Ref sample presented in Figure 7a, the surface charge balancing is performed by protons and calcium with low symmetry and a CN of 7, which specifically occurs at the non-bonded oxygen of the dimeric structures. In Figure 7b, the interactions between the COO- and silanol groups contained in PCE-Sil with the surface calcium and dimeric structures of C-S-H are presented. For the COO- and surface calcium, the monodentate ligand-type interaction is illustrated with the respective increase in the calcium symmetry. Furthermore, the formation of new bridging sites, referred to as T1 sites, by the interaction between the silanol groups and dimeric structures through covalent bonds is outlined.


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Figure 7. Schematic representation of a) C-S-H_Ref. and b) C-S-H/PCE-Sil.

5. Conclusions.

In this study, the bonds formed between calcium silicate hydrate and polycarboxylatebased superplasticizers with silyl functionalities were evaluated, with the following results.

It was proven that the interactions between C-S-H and PCE with silyl functionalities occur mainly at the C-S-H surface, with no evidence of PCE-Sil intercalation within the C-S-H basal space. The free carboxylic groups in PCE-Sil form bonds with the surface calcium of C-S-H through ligand-type interactions, which produce changes in the calcium symmetry (higher order) and reduce the coordination number from seven to six,


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according to the NEXAFS and EXAFS results. Moreover, the complexation of Ca2+ in solution by COO- seems to generate changes in the ions that maintain charge neutrality at the basal spacing and the surface of C-S-H; as a result, the complexed Ca2+ are relocated at the C-S-H surface, and more water molecules can be introduced in the basal spacing. Consequently, the chemical environment of the C-S-H silicon sites is modified by the change of the atoms located at the surface and basal spacing of C-S-H, according to the Si K-edge NEXAFS and 29Si NMR results.

Finally, covalent bonds are formed through the siloxane interaction between the silanol groups contained in the PCE-Sil and the non-bonded oxygen of the dimeric structures contained in the C-S-H. This interaction increases the silicon polymerization by the formation of new bridging sites at C-S-H surfaces, labeled T1, which was determined by the Si K-edge NEXAFS results; this confirms the results obtained here from 29Si NMR and those in other works 12,15 about the significance of the T1 signal.

Supporting information. Characterization of the PCE-Sil by gel permeation chromatography (GPC), charge density by acid-base titration and 1H NMR are reported in Appendix A, B and C respectively. In appendix D, the pH measurements of the centrifuge liquor of the samples C-S-H_Ref and C-S-H/PCE-Sil are reported.

Acknowledgements Research done at the Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This research was funded by the Republic of Singapore’s National Research Foundation through a grant to the Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore-Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Program. BEARS has been established by the University of California, Berkeley as a center for intellectual excellence in research and education in Singapore. We thank Erich D. Rodríguez (CNPq BJT Grant number 406684/2013-8), Marlon Longhi (UFRGS) and Flavio C. Vicentin


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(Brazilian Synchrotron Light Laboratory, LNLS) for performing Ca K-edge XAS experiments at LNLS (Brazilian Synchrotron Light Laboratory) funded by Grant number SXS-17805 and SXS-18902. Carlos A. Orozco thanks the Colciencias-Fulbright Fellowship for the financial support for graduate studies at UC Berkeley. Finally, we want to thank Dr. Lynne Batchelder of GRACE & Co. for the 1H NMR data analysis.

References (1) Mehta, P. K.; Monteiro, P. J. M. Concrete microstructure, properties and materials, 4th ed. Mc Graw Hill, 2012. (2) Ramachandran, V. S.; Malhotra, V. M.; Jolicoeur , C.; Spiratos, N. Superplastizicers: Properties and applications in concrete. CANMET Publishing, Canada, 2003. (3) Flatt, R.; Schober, I. Understanding the rheology of concrete, Ch 7. Woodhead Publishing, Oxford, 2012. (4) Fantinel, F.; Rieger, J.; Molnar, F.; Hubler, P. Complexation of polyacrylates by Ca2+ ions. Time-resolved studies using attenuated total reflectance fourier transform infrared dialysis spectroscopy. Langmuir, 2004, 20, 2539-2542. (5) Sowoidnich, T.; Rachowski, T.; Rößler, C.; Völkel, A.; Ludwiga, H. M. Calcium complexation and cluster formation as principal modes of action of polymers used as superplasticizer in cement systems. Cem. Concr. Res. 2015, 73, 42–50. (6) Marchon, D.;.; Flatt, R. Science and technology of concrete admixtures, Ch 12. Woodhead Publishing, Oxford 2012. (7) Winnefeld, F,; Becker, S.; Pakusch, J.; Gotz, T. Effects of the molecular architecture of comb-shaped superplasticizers on their performance in cementitious systems. Cem. Concr. Compos. 2007, 29, 251-262. (8) Plank, J.; Sachsenhauser, B.; de Reese, J. Experimental determination of the thermodynamic parameters affecting the adsorption behavior and dispersion effectiveness of PCE superplasticizers. Cem. Concr. Res. 2010, 40, 699-709. (9) Yamada, K.; Ogawa, S.; Hanehara, S. Controlling the adsorption and dispersing force of polycarboxylate-type superplasticizer by sulfate ion concentration in aqueous phase. Cem. Concr. Res. 2001, 31, 375–383. (10) Marchon, D.; Sulser, U.; Eberhardt, A.; Flatt, R. J. Molecular design of comb-shaped polycarboxylate dispersants for environmentally friendly concrete. Soft Matter. 2013, 9, 1071910728.


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(11) Dalas, F.; Nonat, A.; Pourchet, S.; Mosquet, M.; Rinaldi, D.; Sabio, S. Tailoring the anionic function and the side chains of comb-like superplasticizers to improve their adsorption. Cem. Concr. Res. 2015, 67, 21-30. (12) Franceschini, A.; Abramson, S.; Bresson, B.; Abramson, S.; Mancini, V.; Chassenieux, C,; H. Lequeux, New covalent bonded polymer-calcium silicate hydrate composites. J. Mater. Chem. 2007, 17, 913-922. (13) Fan W.; Stoffelbach, F.; Rieger, J.; Regnaud, L.; Vichot A.; Bresson, B.; Lequeux, N. A new class of organosilane-modified polycarboxylate superplasticizers with low sulfate sensitivity, Cem. Concr. Res. 2012, 42, 166–172. (14) Witt, J.; Plank, J. A novel type of PCE possessing silyl functionalities, 10th CANMET/ACI, Prague, 2012, 57-70. (15) Plank, J.; Yang, F.; Storcheva, O. Study of the interaction between cement phases and polycarboxylate superplasticizers possessing silyl functionalities, J. of Sustainable Cem-Based Mater. 2014, 3, 77-87. (16) Taylor, H. F. W. Cement Chemistry, 2nd ed; Thomas Telford Publishing: London, 1997. (17) Taylor, H. F. W. Proposed Structure for Calcium Silicate Hydrate Gel, J. Am. Ceram. Soc. 1986, 69, 464-467. (18) Richardson, I. G. Tobermorite/jennite- and tobermorite/calcium hydroxide-based models for the structure of C-S-H: applicability to hardened pastes of tricalcium silicate, B-dicalcium silicate, Portland cement, and blends of Portland cement with blast-furnace slag, metakaolin, or silica fume. Cem. Concr. Res. 2004, 34, 1733-1777. (19) Rodriguez, E. T.; Richardson, I. G.; Black, L.; Courjault, E. B.; Nonat, A.; Skibsted, J. Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesized by silica-lime reaction and by controlled hydration of tricalcium silicate (C3S), Adv. in App. Cer. 2015, 114, 362-371. (20) Pova, A.; Geoffroy, G.; Renou, M. F.; Faucon, P.; Gartner, E. Interactions between Polymeric Dispersants and Calcium Silicate Hydrates, J. Am. Ceram. Soc. 2000, 83, 2556–2560. (21) Chae, S. R.; Moon, J.; Yoon, S.; Bae, S.; Levitz, P.; Winarski, R.; Monteiro, P. J. M. Advanced Nanoscale Characterization of Cement Based Materials Using X-Ray Synchrotron Radiation: A Review. Int. J. Concr. Struct. Mater. 2013, 7, 95-110. (22) Bae, S.; Taylor, R.; Hernandez, D.; Yoon, S.; Kylcone, D.; Monteiro, P. J. M. Soft X-ray Spectromicroscopic Investigation of Synthetic C-S-H and C3S Hydration Products J. Am. Ceram. Soc. 2015, 1-7. (23) Geng, G.; Taylor, R.; Bae, S.; Hernandez, D.; Kilcoyne, D.; Emwas, A.; Monteiro, P. J. M. Atomic and nano-scale characterization of a 50 year old hydrated paste. Cem. Concr. Res. 2015, 77, 36-46. (24) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537–541.


Page 22 of 26

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(25) Grangeon, S.; Claret, F.; Lerouge C.; at all. On the nature of structural disorder in calcium silicate hydrate with calcium/silicon ratio similar to tobermorite. Cem. Concr. Res. 2013, 52, 3137. (26) Richardson, I.G. Model structures for C-(A)-S-H(I). Acta. Cryst. 2014, B70, 903-923. (27) He, Y.; Lu, L.; Struble, L. J.; Rapp, J. L.; Mondal, P.; Hu, S. Effect of calcium–silicon ratio on microstructure and nanostructure of calcium silicate hydrate synthesized by reaction of fumed silica and calcium oxide at room temperature. Mater. Struct. 2014, 47, 311-322. (28) Colombet, P.; Grimmer, A. R.; Zanni, H.; Sozzani, P. Nulclear magnetic resonance spectroscopy of cement-based materials. Springer, Berlin,1998. (29) Roosz, C.; Gaboreau, S.;Grangeon, S.; Pret, D.; Montouillout, V.; Maubec, N.; Ory, S.; Blanc, P.; Vieillard, P.; Henocq, P. Distribution of water in synthetic calcium silicate hydrates. Langmuir. 2016, 32, 6794-6805. (30) Van Damme, H.; Pellenq, R. J.; Ulm, F. J. Handbook of clay science, Second edition. Elsevier, 2013, Vol. 5. (33) Naftel, S. J.; Sham, T.; Yiu, Y.; Yates, B. Calcium L-edge XANES study of some calcium compounds. J. Synchrotron Rad. 2001, 8, 255-257. (32) Lee, J. D. Concise Inorganic Chemistry, fifth edition. Chapman Hall, London, 2008. (33) Fleet, M.; Liu, X. Calcium L3,2-edge XANES of carbonates, carbonate apatite and oldhamite. Am. Mineral. 2009, 94 1235-1241. (34) Kaufman, A.; Glusker, J.; Beebe S.; Bock, C. Calcium ion coordination: A comparison with that of Beryllium, Magnesium and Zinc, J. Am. Chem. Soc. 1996, 118, 5752-5763. (35) Plank, J.; Sachsenhauser, B. Experimental determination of the effective anionic charge density of polycarboxylate superplasticizers in cement pore solution. Cem. Concr. Res. 2009, 39, 1-5. (36) Lequeux, N.; Morau, A.; Philippot, S.; Boch, P. Extendend X-ray Absorption Fine Structure Investigation of Calcium Silicate Hydrates. J. Am. Ceram. Soc. 1999, 82, 1299-306. (37) Hopital, E. L.; Lothenbach, B.; Kulik, D.; Scrivener, K. Influence of calcium to silica ratio on aluminium uptake in calcium silicate hydrate. Cem. Concr. Res. 2016, 85, 111-121. (38) Rejmak, P.; Dolado, J.; Stott, M.; Ayuela, A. 29Si NMR in Cement: A Theoretical Study on Calcium Silicate Hydrates. J. Phys, Chem. 2012, 116, 9755-9761. (39) Li, D.; Bancroft, G. M.; Fleet, M. F.; Feng, X. H. Silicon K-edge XANES spectra of silicate minerals. Phys. Chem. Miner. 1995, 22, 115-122.


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For table of contents only

Table 1. Structural parameters of PCE-Sil. Polymer

Length PEO [moles]

PCE-Sil

45

a

Density of side chains 1:3.7

b

c

Charge density [meq/g]

AA : p(EO/PO) : Silane

Mn [g/mol]

Mw [g/mol]

PDI

1.41

7:1:0.5

12.117

26.715

2.2

a

Calculated from the moles a, b and c in PCE-Sil. Determined by acid-base titration test reported in Appendix B. c Determined by 1H NMR reported in Appendix C. Mn: Number-average molecular weight determined by GPC reported in appendix A. Mw: Mass-average molecular weight determined by GPC reported in appendix A PDI: Polydispersity index (Mw/Mn). b


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Table 2. Symmetry of Ca-O and crystal field splitting. Sample C.N.

Ca(OH)2

6

∆o

Symmetry

Crytsal field splitting

Strong (high value) Octahedral

C-S-H

7

Weak (low value) Non-defined

Table 3. Energy peak difference EPD for Ca L-edge NEXAFS.

Sample

[a2 – a1] eV

[b2 – b1] eV

Symmetry

Ca(OH)2

1.39

1.34

Octahedral

C-S-H_Ref

1.07

1.07

Low symmetry

C-S-H/PCESil

1.24

1.19

C-S-H/PAA

1.23

1.23

Higher-order symmetry Higher-order symmetry

Table 4. Structural parameters from EXAFS structure simulation. Sample

C.N.

R [Å]

∆ [eV]

CSH_Ref

7

2.35232

-3.7802

0.00078

CSH/PCE-Sil

6

2.34046

-2.5531

0.002858


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Table 5. 29Si NMR of Silicon tetrahedral sites in C-S-H. T1

Q1-Ca

Q1-H

Q2BT

Q2PT

Sample [ppm]

[%]

[ppm]

[%]

[ppm]

[%]

[ppm]

[%]

[ppm]

[%]

C-S-H_Ref

-

-

-77.0

19.37

-78.95

63.03

-82.91

5.28

-84.5

12.32

C-S-H/PCESil

-49.9

3.64

-77.7

18.18

-79.3

54.54

-82.6

7.27

-84.6

16.36

MCLC-S-H_Ref = 2.43, MCLC-S-H/PCESil = 2.65

Table 6. Si k-edge STXM of C-S-H samples. Sample

X [eV]

Y [eV]

C-S-H_Ref

1848.7

1865.0

C-S-H/PCESil

1849.6

1866.0


Characterization of the Bonds Developed between Calcium Silicate

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