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Lothenbach B.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Nied D.,HeidelbergCement Technology Center GmbH | L'Hopital E.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Achiedo G.,Institute for Radiological Protection and Nuclear Safety | Dauzeres A.,Institute for Radiological Protection and Nuclear Safety
Cement and Concrete Research | Year: 2015

The structure and chemistry of magnesium silicate hydrates (M-S-H) is significantly different from calcium silicate hydrates (C-S-H), although both phases are poorly crystalline and have a variable chemical composition. The molar Ca/Si ratio in synthetic C-S-H varies from approximately 0.7 to 1.5 and the Mg/Si ratio in M-S-H from 0.7 to 1.3. In M-S-H silica sheets are present, while the silica in C-S-H is organized in single chains. In addition, M-S-H contains more chemically bound water than C-S-H. Analyses of synthetic samples containing both magnesium and calcium with a total (Mg + Ca)/Si of 0.8 indicate the formation of separate M-S-H and C-S-H gels with no or very little uptake of magnesium in C-S-H or calcium in M-S-H. The clear difference in the silica structure and the difference in ionic radius of Ca2 + and Mg2 + make the formation of an extended solid solution between M-S-H and C-S-H gel improbable. © 2015 Elsevier Ltd. All rights reserved.


Dauzeres A.,Institute for Radiological Protection and Nuclear Safety | Achiedo G.,Institute for Radiological Protection and Nuclear Safety | Nied D.,HeidelbergCement Technology Center GmbH | Bernard E.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 2 more authors.
Cement and Concrete Research | Year: 2016

In the framework of the CI project, the interaction of two different low-pH cements (ESDRED and LAC) with Opalinus Clay (OPA) at Mont-Terri rock laboratory was studied. SEM-EDS analyses showed after 2.5 and 5 years of interaction a Mg-enriched zone associated with a decalcification of the C-S-H near the OPA contact zone of both cements. TGA and XRD investigations indicate that hydrotalcite and brucite predict classically in modeling are not formed. 29Si NMR and FTIR analyses showing a high polymerization degree of the Si-network typical of a sheet-like structure as observed for M-S-H. TEM/EDS investigations of the Mg enriched zone of both concretes indicate that the formed Mg phase exhibits a gel-like structure. New reactive transport modeling with the HYTEC code corroborates the formation of M-S-H at the interface. © 2015 Elsevier Ltd.


Wadso L.,Lund University | Arndt M.,HeidelbergCement Technology Center GmbH
Cement and Concrete Research | Year: 2016

The results of a round robin test on isothermal (heat conduction) calorimetry are presented. A total of 18 participants using three types of instruments conducted 3-day measurements of the hydration of one rapidly hardening Portland cement and one slag-containing cement. The results confirm that isothermal calorimetry is a suitable method for the determination of heat of hydration. As a part of the study, two laboratories also conducted measurements with the standardized heat of solution method. For the Portland cement, these results were in good agreement with the isothermal measurements, but for the slag-containing cement the results differed, both between the two laboratories and between their results and the result of isothermal calorimetry. However, this method performance study clearly shows that the heat of hydration determination of cement by heat conduction calorimetry is more precise than the traditional heat of solution method described in EN 196-8, if state-of-the-art calorimeters are used. © 2015 Elsevier Ltd.


Nied D.,HeidelbergCement Technology Center GmbH | Nied D.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Enemark-Rasmussen K.,University of Aarhus | L'Hopital E.,Empa - Swiss Federal Laboratories for Materials Science and Technology | And 2 more authors.
Cement and Concrete Research | Year: 2016

Investigations of synthetic magnesium silicate hydrate (M-S-H) samples have shown that M-S-H aged for 1 year can exhibit variable compositions with molar Mg/Si ratios in the range 0.7 ≤ Mg/Si ≤ 1.5. At lower Mg/Si ratio, additional silica is present whereas brucite is observed for Mg/Si ≥ 1.3. FT-IR and 29Si NMR data reveal a high degree of silicate polymerisation, indicating the formation of silicate sheets. TGA shows the presence of bound water and of hydroxyl groups bound to Mg and as silanol groups in the M-S-H, in accord with 29Si{1H}CP/MAS and high-speed 1H NMR measurements. Raman and XRD data suggest that the M-S-H structure is related to a disordered talc precursor at low Mg/Si and to a serpentine precursor at high Mg/Si ratio. Solubility products for M-S-H phases were calculated on basis of the compositions of the aqueous solutions and a solid solution model was suggested. © 2015 Elsevier Ltd.


Federhen S.,HeidelbergCement Technology Center GmbH
Cement International | Year: 2010

At HeidelbergCement many (chlorine) gas bypass systems have been installed in the recent years. The first solutions simply aimed at dedusting. Later, via adding hydrated lime, SOx was treated. Further steps were undertaken by adding raw meal to ease the dust handling. However, cost analysis showed that the most economic approach is SOx treatment by recycling the gas within the kiln system and reducing bypass dust disposal by homogenisation and pre-separation. The initial additional investment for the equipment was swiftly recovered due to reduced operational costs. Though the operation is challenging - it is manageable. Looking forward, the gas recycle back to the cooler and integral dust homogenisation are the dominant choice for the future.

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