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The synthesis of low-temperature belite (C2S) clinker from wastes of autoclaved aerated concrete and limestone was studied in the presence of CaCl2 as a mineralizing agent. Synthetic chlorellestadite (SCE; Ca10(SiO4)3(SO4)3Cl2) forms in experiments at temperatures between 700 and 1200 °C. Samples were investigated by X-ray diffraction and Raman spectroscopy. In general, the amount of SCE depends mainly on the sulfate content and to a lesser extent on the synthesis temperature. At lower temperatures of formation, a non-stoichiometric SCE seems to crystallize in a monoclinic symmetry similar to hydroxylellestadite. Rietveld refinements revealed the presence of chlorine and calcium vacancies. Raman spectroscopy proved the partial substitution of sulfate by CO32− groups in ellestadites formed at 800 °C and 900 °C in air. Incorporation of CO3 results in a shorter unit cell parameters and smaller cell volume similar to CO3−apatite. At low temperatures, SCE coexists with spurrite intermixed on a very fine nm scale. At temperatures above 900 °C in air, ellestadite is carbonate-free and above 1000 °C chlorine loss starts in all samples.

Tobermorite is the model for calcium aluminosilicate hydrate (C-(A-)S-H), the glue in concrete, and is also the binding phase in cement-based materials under geological conditions and in ancient Roman concrete. Correlating the mechanical properties of tobermorite with atomic structures substantially improves the understanding of C-(A-)S-H. We study this correlation for tobermorite with various Al contents using Raman, nuclear magnetic resonance spectroscopy, and high-pressure X-ray diffraction. Al incorporation shortens the cross-linked tobermorite chains, leading to more charge-balancing Ca and strong H-bonding, and enhancing the incompressibility of the basal-layer of Al-tobermorite. Non-cross-linked tobermorite exhibits high incompressibility of the basal layer but low incompressibility of the interlayer due to lack of cross-linking. The substitution of stronger Si O with Al O shows no negative influence on the mechanical properties of tobermorite. The results provide fundamental information on how atomic structure influences the intrinsic properties of C-(A-)S-H and have implications in validating computational methods and 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

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 .

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.

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.

The effect of long-term stagnation on copper corrosion by-product release and corrosion rates was studied in pipe-rigs according to the German standard DIN 50931, Part 1. The analysis of the water phase was supplemented by surface analysis of corrosion scales. Copper concentration during stagnation did not follow a solubility process. The characteristic curves obtained can be explained by subsequent copper release and copper refixation processes. Oxygen consumption can be described by the first-order kinetic rate law. The corrosion scales consisted of cuprite (Cu 2 O) and malachite (CuCO 3 ·Cu(OH) 2 ). Malachite grew in well-defined crystals during stagnation, served as sink for dissolved copper and did not protect the pipe against corrosion attack. Copper concentrations measured after long-term stagnation (up to 122 h) correspond to the solubility of malachite in the testwater.

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.