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A new process for the manufacture of a novel hydraulic binder (Celitement) with a high potential for saving energy and reducing carbon dioxide emissions was developed at the Karlsruhe Institute of Technology. To obtain the ideal process conditions and to monitor the optimal product quality of the binder, it was necessary to develop a measurement system for the online determination of certain quality parameters. A method for the direct calculation of different quality parameters of both precursor and final product from online measured near-infrared (NIR) spectra is presented in this article. A successful transformation between calibration models gained with laboratory and online NIR is also demonstrated. This enables optimisation of the calibration models on a laboratory scale and a seamless transfer to industrial scale due to changes in composition of the raw materials, formulation or processing parameters.

Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS) that possesses a potential for minimizing the ratio C/S from above 3 in OPC down to 1, which significantly reduces the amount of CO$_2$ released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)$_2$ the concentration of the dissolved species c(Ca$^{2+}$) and c(SiO$_4^{4-}$) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation the mechanical properties of two different types of hardened pastes made out of Celitement (C/S=1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS., Comment: 32 pages, 8 figures

A single crystal of α-Ca2[HSiO4](OH) (α-C2SH) was repeatedly imaged at room temperature with synchrotron mid-infrared microscopy after heating to 310°C, 340°C, 370°C, and 400°C respectively. The mechanisms of the observed phase transformations are discussed on the basis of a modular concept of the crystal structures. All images show domains of dellaite, Ca6[Si2O7][SiO4](OH)2, which are predominantly formed in the core of the crystal. In the crystal rim area α-C2SH persists in higher abundance. The mechanism of the phase transformation of α-C2SH into dellaite includes the following: (1) Partial formation of killalaite (Ca3[HSi2O7](OH)) as nuclei according to the isochemical reaction 2Ca2[HSiO4](OH) → Ca3[HSi2O7](OH) + Ca(OH)2 probably induced by anisotropic thermal expansion, local chemical fluctuations, structural (proton) disorder, and different bond strengths of the OH groups in the α-C2SH structure. (2) Further dehydration of killalaite and α-C2SH domains results in the formation of dellaite according to Ca3[HSi2O7](OH) + Ca(OH)2 + Ca2[HSiO4](OH) – 2H2O → Ca6[Si2O7][SiO4](OH)2. The results suggest that the polymerization of two isolated [HSiO4] tetrahedra takes place without dehydration according to reaction (1) rather than through condensation with simultaneous H2O release: 2[HSiO4] → [Si2O7] + H2O. We suggest that reaction (1) cannot be completed at ambient pressure. Thus in the regions close to the rim of the crystals we expect the formation of x-C2S, which starts along the crystal edges according to Ca2[HSiO4](OH) → Ca2SiO4 + H2O. Based on a modular concept, a structural relationship between α-C2SH, killalaite, dellaite, and x-C2S has been established. Similarities and differences in the thermal behavior of α-C2SH and afwillite have been highlighted.

New cementitious materials based on calcium hydrosilicate hydrates were recently developed as potential substitutes for ordinary portland cement, but with a reduced CO2 footprint. The materials are produced by hydrothermal processing of SiO2 and Ca(OH)2, giving rise to calcium silicate hydrates, followed by mechanical activation of the latter via cogrinding with various siliceous materials. Thus, the chemical composition in terms of C/S ratio could be adjusted over a broad range (1–3). In this study the synthesis of a previously unknown cementitious material produced via the combination of mechanical activation in a laboratory mill and thermal treatment of a mixture of quartz and hydrothermally synthesized calcium silicate hydrates: α-Ca2[HSiO4](OH) (α-C2SH) and Ca6[Si2O7](OH)6 (jaffeite) are reported. It forms independently of the type of mill used (eccentric vibrating mill, vibration grinding mill) after thermal treatment of the ground materials at 360°C–420°C. The new material is X-ray amorphous and possesses a CaO/SiO2 ratio of 2. A characteristic feature in regards to the silicate anionic structure is the increased silicate polymerization (up to 27% Si2O7 dimers) as revealed by the trimethylsilylation method. Infrared (IR) spectra show a very broad absorption band centered at about 935 cm−1. Another characteristic feature is the presence of ~2.5 wt% H2O as shown by thermogravimetry (TG) coupled with IR spectroscopy. As this water is bound mostly as hydroxyl to Ca, we refer to this new cementitious material as calcium-oxide–hydroxide–silicate (C–CH–S). Calorimetric measurements point to a very high hydraulic reactivity which is beyond that for typical C2S materials. The influence of the type of grinding on the thermal behavior of α-C2SH upon its transformation into water-free Ca2SiO4 modifications is discussed.

Synchrotron-based X-ray diffraction has been used to analyze a series of mechanochemically prepared calcium silicate hydrate (C–S–H) phases with aimed Ca/Si ratios from 1/5 to 3/2. Fumed silica and CaO were used as starting materials. All samples contain 3-dimensionally ordered C–S–H phases. Pure C–S–H phases are present in samples with Ca/Si ratios from 2/3 to 6/5. The samples with C/S ratios 1/5 and 1/2 contain unreacted silica, while those with C/S ratios 4/3 and 3/2 contain portlandite as minor component. A new approach has been used to follow structural changes with C/S ratio, involving assignment of an orthorhombic space group (I2mm) to the C–S–H phase followed by refinement of the unit cell parameters by the whole powder pattern decomposition (WPPD) method. The results reveal a discontinuity in the c parameter at C/S 5/6–1/1, indicating that at least two different structural types separated by a miscibility gap are needed to describe C–S–H, there being two ordered end members with C/S ratios of 2/3 and 5/4, respectively. Nevertheless the structure of C–S–H phases within this interval may be well described by the defect-tobermorite model. At C/S 2/3 it consists of tobermorite slabs linked via H-bonds without interlayer Ca. At this C/S ratio, the layer thickness is 13.2 A˚ . Increasing the C/S ratio leads to little change in the layer thickness, but increased disorder due to competitive omission of bridging tetrahedra and incorporation of Ca in the interlayer in samples with 2/3

X-ray diffraction and thermogravimetry have been used to analyze the limits of incorporation of Ca in a series of mechanochemically synthesized, nanocrystalline calcium silicate hydrate (C–S–H) phases. Results based on bulk weight loss and Rietveld refinements show higher C/S ratios than those corrected additionally for X-ray-silent CaCO3 and Ca(OH)2. A pure C–S–H phase exists over the C/S range 2/3–5/4, with two ordered end members. The structure of C–S–H phases within the interval 2/3–5/4 may well be described by the so-called defect-tobermorite model. At C/S=2/3, the C–S–H consists of 14 A tobermorite slabs linked via H-bonds without interlayer Ca, resulting in the formula Ca4[H2Si3O9]2·xH2O, where x=4. After heating up to 1000°C, X-ray diffraction has shown that even samples with a low Ca content (Ca/Si

Thermal treatment transforms α-Ca 2 [SiO 3 (OH)](OH) (α-C 2 SH) into hydraulic Ca 2 SiO 4 polymorphs, which is a process of considerable interest to the cement chemistry community. The thermal behavior of differently synthesized samples of α-C 2 SH in air at ambient pressure has been investigated in detail by high-temperature powder X-ray diffraction (XRD), synchrotron-based infrared (IR) microspectroscopy of single crystals, trimethylsilylation method (TMSM), and thermal analysis. Powder XRD data on α-C 2 SH samples heated to different temperatures between 300° and 500°C suggest coexistance of α-C 2 SH and dellaite, Ca 6 [Si 2 O 7 ][SiO 4 ](OH) 2 . IR absorption bands typical for the initial α-C 2 SH phase diminish over the course of thermal treatment, accompanied by the appearance of bands characteristic for dellaite. The partial polymerization of the isolated SiO 3 (OH) tetrahedra present in α-C 2 SH to [Si 2 O 7 ] dimers, as expected for dellaite, was proven by the presence of an IR band at 1050 cm -1 and by TMSM. For the first time, dellaite, along with x-Ca 2 SiO 4 , was observed as an intermediate product of the dehydration of α-C 2 SH. Until now, dellaite was believed to be only a high-pressure phase. Dellaite coexists with x-Ca 2 SiΟ 4 up to 560°-620°C and decomposes to x-Ca 2 SiΟ 4 at higher temperatures. Upon further heating, the latter phase transforms into α'L-Ca 2 SiO 4 , and finally gives β-Ca 2 SiΟ 4 after cooling to room temperature. The thermal decomposition of α-C 2 SH is a much more complicated process than reported previously. Different factors, such as the source of Ca and the presence of NaOH during synthesis, seem to control the mechanism of its dehydration. The presence of dellaite is shown to lower the temperature of formation of β-Ca 2 SiO 4 .

The effects of carbonation of mechanochemically prepared C-S-H samples under ambient conditions for upto 6 months have been investigated by Raman spectroscopy and X-ray diffraction. The type and extent of carbonation are strongly dependent on the initial CaO/SiO2 (C/S) ratio of the samples. Amorphous calcium carbonate hydrate is formed within minutes upon exposure to air. It crystallizes, over time, to give primarily vaterite at C/S >= 0.67 and aragonite at C/S

Online measurement of the product quality is a challenging task in cement production, especially in the production of Celitement, a novel environmentally friendly hydraulic binder. The mineralogy and chemical composition of clinker in ordinary Portland cement production is measured by X-ray diffraction (XRD) and X-ray fluorescence (XRF), where only crystalline constituents can be detected. But only a small part of the Celitement components can be measured via XRD, because most constituents have an amorphous structure. This paper describes the development of algorithms suitable for an on-line monitoring of the final processing step of Celitement based on NIR-data. For calibration intermediate products were dried at different temperatures and ground for variable durations. The products were analyzed using XRD and thermogravimetric analyses together with NIR-spectroscopy to investigate the dependency between the drying and the milling processes on one and the NIR-signal on the other side. As a result, different characteristic parameters have been defined. A short overview of the Celitement process and the challenging tasks of the online measurement and evaluation of the product quality will be presented. Subsequently, methods for systematic development of near-infrared calibration models and the determination of the final calibration model will be introduced. The application of the model on experimental data illustrates that NIR-spectroscopy allows for a quick and sufficiently exact determination of crucial process parameters., {"references":["J. GJ. Olivier, \"Trends in global CO2 emissions: 2014 Report,\" Hague:\nPBL Netherlands Environmental Assessment Agency, 2014.","Celitement GmbH, http://www.Celitement.de/en/, (retrieved 20th of July\n2015).","P. Stemmermann, U. Schweike, K. Garbev and G. Beuchle, \"Celitement\n– a sustainable prospect for the cement,\" Cement International, pp. 52-\n66, 2010.","G. Beuchle, P. Stemmermann, U. Schweike, K. Garbev, \"Single-phase\nhydraulic binder, methods for the production thereof and building\nmaterial produced therewith,\" Grant, 2008.","Forschungsvereinigung Verein Deutscher Zementwerke e.V.: AiF\nForschungsvorhaben Nr.:1 7397N - Anwendung der quantitativen\nRöntgenbeugungsanalyse in der Qualitätskontrolle von Zementen.\nFebruar 2012 - Oktober 2014.","Bruker Corporation, http://www.bruker.com/, (retrieved 25th of\nSeptember 2014).","D.A. Burns, and E.W. Ciurczak, \"Handbook of near-infrared analysis,\"\nMarcel Dekker, New York, 1992.","Bruker Optik GmbH, \"OPUS Spectroscopy Software - User Manual\nQuant,\" Bruker Optik GmbH, Ettlingen, 2006.","R.J. Barnes, M.S. Dhanoa, and S.J. Lister, \"Standard Normal Variate\nTransformation and De-trending of Near-Infrared Diffuse Reflectance\nSpectra,\" Applied Spectroscopy, 5, Vol. 43, 1989.\n[10] C. Lutz, J. Matthes, P. Waibel, U. Precht, U. Schweike, G. Beuchle, K.\nGarbev, P. Stemmermann and H. B. Keller, \"Near-infrared spectroscopy\nfor prediction of auxiliary quantities to characterize the product quality\nof a novel cementitious material,\" Materials Characterisation VII, 90,\npp.183-194, 2015.\n[11] H. Martens, and T. Naes, \"Multivariate calibration,\" Chichester: Wiley,\n1989.\n[12] D. D. Ruscio, \"A weighted view on the partial least-squares algorithm,\"\nAutomatica, Vol. 36, 6, 2000.\n[13] DIN EN 12390-2: 2009-08–Prüfung von Festbeton–Teil 2: Herstellung\nund Lagerung von Probekörpern für Festigkeitsprüfungen. Dtsch. Fass.\nEN (2009): 12390-2."]}

The production of cement is one of the most energy and CO2 intensive industries. At the Karlsruhe Institute of Technology a new “green” process for the production of cementitious materials was developed with a high potential for saving energy and CO2-emissions. In a two-stage process a new hydraulic binder (Celitement) comparable to Portland cement is produced from limestone and sand. Until now, the product was only analysed with complex analytical methods. In the future it is necessary to have a robust measurement system, which is able to determine the product quality online during its manufacture. In this paper, the development of a method for the prediction of auxiliary quantities for characterization of the product quality based on an online near-infraredspectroscopy (NIR) is presented. Initial methods with data pre-processing and partial-least-squares-regression for systematic development of near-infrared calibration models and their application to new data sets are presented. In addition, a new method for data pre-processing by adapting the target vector to the working point in comparison to the calculation of calibration models with absolute values is shown.

X-ray photoelectron spectroscopy (XPS) has been used to analyse a series of mechanochemically synthesised, nanocrystalline calcium silicate hydrates (C-S-H). The samples, with Ca/Si ratios of 0.2 to 1.5, showed structural features of C-S-H(I). XPS analysis revealed changes in the extent of silicate polymerisation. Si 2p, Ca 2p and O 1s spectra showed that, unlike for the crystalline calcium silicate hydrate phases studied previously, there was no evidence of silicate sheets (Q{sup 3}) at low Ca/Si ratios. Si 2p and O 1s spectra indicated silicate depolymerisation, expressed by decreasing silicate chain length, with increasing C/S. In all spectra, peak narrowing was observed with increasing Ca/Si, indicating increased structural ordering. The rapid changes of the slope of FWHM of Si 2p, {delta} {sub Ca-Si} and {delta} {sub NBO-BO} as function of C/S ratio indicated a possible miscibility gap in the C-S-H-solid solution series between C/S 5/6 and 1. The modified Auger parameter ({alpha}') of nanocrystalline C-S-H decreased with increasing silicate polymerisation, a trend already observed studying crystalline C-S-H. Absolute values of {alpha}' were shifted about - 0.7 eV with respect to crystalline phases of equal C/S ratio, due to reduced crystallinity.

We have investigated the incorporation of zinc into both nanocrystalline and crystalline calcium silicate hydrates with starting C/S ratios of 2/3 (0.66). Zinc was added replacing calcium in the starting mixtures [Zn/(Zn+Ca)=0–1/4; 0–10 wt.% Zn], and the resultant phases were characterised using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential thermal analysis–thermogravimetry (DTA–TG) and environmental scanning electron microscopy (ESEM). In both groups of samples, increasing zinc content led to gradual structural changes, until eventually a second phase was formed. Zinc was incorporated to similar limits in both sets of samples. The thermal stability of the structures increased to a certain zinc content, beyond which there was structural destabilisation. Zinc incorporation is possible up to ∼6 wt.%. Our observations strongly indicate similar zinc incorporation mechanisms in both sample series, namely incorporation of zinc into the interlayer of C-S-H(I) and the X-sheet of gyrolite for nanocrystalline and crystalline samples, respectively.

We have synthesised 11-A tobermorite hydrothermally, both pure and with increasing isomorphic substitution of aluminium for silicon. The samples were analysed by X-ray photoelectron spectroscopy (XPS). Aluminium was found, on the basis of its Al 2p binding energies, to be tetrahedrally coordinated. We observed no changes in Ca/(Si+Al) ratio upon aluminium substitution, implying that charge balancing does not occur via the incorporation of additional calcium into the tobermorite structure. Aluminium substitution into the silicate structure led to a decrease in Si 2p binding energies. This implies one of two alternatives. Firstly, that charge balancing occurs via substitution of OH− for O2− in the tobermorite structure. Secondly, the presence of aluminium in the tobermorite structure may negatively influence the degree of silicate polymerisation. Further work is required to determine which of these possibilities is the case.

We have used X-ray photoelectron spectroscopy (XPS) to investigate both tricalcium silicate (Ca3SiO5, C3S) and β-dicalcium silicate (Ca2SiO4, β-C2S), the principal components of cement clinkers. In addition to showing how the two phases may be characterised and differentiated, we show how the sensitivity of these phases to atmospheric carbon dioxide and moisture may, as a result of improper sample preparation, lead to erroneous results. The observed alteration processes of the clinker minerals shed light upon the aging process of cement clinker during storage.

We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium–silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and α-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium–silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO) and nonbridging oxygen (NBO) moieties. Finally, the modified Auger parameter has proved particularly useful in determining the extent of silicate anion polymerisation. Of note also are the apparently unusual spectra for 11 A tobermorite. The silicon and oxygen photoelectron spectra indicate a phase with a lower degree of silicate polymerisation than predicted from its composition. The main contributing factor is the intrinsic disorder within the tobermorite structure. This study has shown how XPS may be used to obtain valuable structural information from C-S-H phases, and our analysis of the crystalline phases is the first step towards the analysis of real C-S-H-based cement systems.

We recorded the photoelectron spectra of various crystalline calcium silicate hydrates (C–S–Hs) and have examined their O 1 s photoelectron spectra. The spectra are asymmetric, with contributions assigned primarily to bridging and non-bridging oxygen species. There is an increased contribution due to the presence of non-bonding oxygen atoms with increasing calcium:silicon ratio. Additionally, there are slight changes in theO 1s-binding energies with changes in calcium:silicon ratio. These changes are explained in terms of bonding and silicate structure.

Nano-crystalline calcium silicate hydrates (C-S-H gels) are formed upon hydration of Ca3SiO5 and β-Ca2SiO4, and are therefore the primary hydration products of Portland cements. Raman and IR spectra of a series of mechanochemically prepared C-S-H samples of type C-S-H(1) with Ca/Si ratios ranging from 0.4 to 1.5 reveal changes in structure dependent upon Ca/Si ratio. Finite silicate chains (Q) dominate the structures of the samples at Ca/Si ratios 0.4-1.0, the spectra showing characteristic symmetrical stretching bands between 1010 and 1020cm (R) and asymmetrical stretching around 965cm (IR), with Q units present at Ca/Si 1.00, dimers (Q) are the main building unit of the silicate anionic structure (Raman bands at 890cm, IR band at 945cm). In these samples portlandite is also observed. The similarity of the silicate contribution to the spectra (R and IR) of the samples with Ca/Si = 1.33 and 1.50, and their differing portlandite contents, suggests a similar limit of incorporation of Ca into the C-S-H(I) structure in both phases, which lies under Ca/Si=1.33. In these phases we observe increased ordering of Ca-bonded OH groups. The same trend of increased ordering of the Ca environment is also seen in the development of the intensity and FWHM of the Ca-O band at 332cm (R), 255cm (IR) which is consistent with observations in the Ca2p XPS spectra [2].

Cement is an inorganic hydraulic binder widely used in civil engineering. By the reaction of cement with water calcium-silicate-hydrate (C-S-H) gel is the principal hydration product [1]. For example, buildingmaterials based on Portland cement could contain up to 70 wt% C-S-H gel. Therefore, the structure of the C-S-H gel is responsible for the mechanical properties of the hardened cement paste. The chemical compostion of C-S-H gel varies between the molar CaO/SiO2 (C/S) ratio of 0.5 in older and partly carbonated hardend cement paste and 2.2 in fresh ones. Reaction products (alkali containing C-S-H gels) of the deteriorative alkali-silica-reaction (ASR) show an even lower Ca content. Additionally, these gels have a significant amount of alkalis. Their formation processes and the reaction mechanism of ASR are still unknown and a subject of investigation. To get insights into the structure and formation processes of alkali-C-S-H gels, samples with differerent chemical compositions have been synthesized with the agate-ball milling technique. A part of the gels was converted into their crystalline analogues by hydrothermal treatment. Due to their low crystallinity the gels were investigated with complementary spectroscopic and diffraction methods. Synchrotron based measurements at the diffraction-, XAFSand IR-beamlines at ANKA (Angstromquelle Karlsruhe) were performed. By comparison of the gels and crystalline alkali-C-S-H with XAFS measurements at the Ca absorption edge, it turned out that the Ca environment is stronger affected upon hydrothermal treatment in Ca poor samples than in samples with a higher C/S ratio. Similar results for theK environment were achieved fromXAFS measurements at the K absorption edge. Data from IR spectroscopy show distinct changes in the region of Ca polyhedra vibrations around 240 cm [2]. This result is in good agreement with the XAFS measurements. To point out the role of water in the gels structure the dehydration of C-S-H and alkali-C-S-H was followed in situ with IR-microscopy and the total water loss was analyzed with DTA/TG. The IR data reveal a structural reorganization of the gel. Especially the bands in the Si-O-Si stretching region show distinct changes during the drying process whereas bands attributet to Ca polyhedra vibrations remain largely unchanged.