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In this paper, we present a combined study of the length-change and tensile strength evolution of highand low-C3A Portland cements. This approach has proven useful to provide an assessment on the performance under severe and moderate sulfate attack. While higher expansion rates are observed in high-C3A samples, tensile strength evolution of both cement types is essentially identical. The simultaneous increase of expansion rate and decrease in tensile strength is strongly suggestive that both processes are related. This is attributed to the formation and development of microcracks that favor the ingress of the sulfate solution in the specimens. These results provide further insights into the commonly accepted idea that standard (accelerated) tests aiming to evaluate the expansion behavior do not provide reliable information on the expected performance (sulfate resistance) and damage potential of Portland cements.

Yalamanchili K.,Linkoping University | Yalamanchili K.,Center for Research in Nanoengineering | Jimenez-Pique E.,Center for Research in Nanoengineering | Pelcastre L.,Lulea University of Technology | And 7 more authors.
Surface and Coatings Technology | Year: 2016

Varying the Si-content in Zr-Si-N coatings from 0.2 to 6.3 at.% causes microstructural changes from columnar to nanocomposite structure and a hardness drop from 37 to 26 GPa. The softer nanocomposite also displays lower fracture resistance. The tribological response of these coatings is investigated under different contact conditions, both at room and elevated temperatures. At room temperature tribooxidation is found to be the dominant wear mechanism, where the nanocomposite coatings display the lowest wear rate of 0.64 × 10− 5 mm3/Nm, by forming an oxide diffusion barrier layer consisting of Zr, W, and Si. A transition in the dominant wear mechanism from tribooxidation to microploughing is observed upon increasing the test temperature and contact stress. Here, all coatings exhibit significantly higher coefficient of friction of 1.4 and the hardest coatings with columnar structure display the lowest wear rate of 10.5 × 10− 5 mm3/Nm. In a microscopic wear test under the influence of contact-induced dominant elastic stress field, the coatings display wedge formation and pileup due to accumulation of the dislocation-induced plastic deformation. In these tests, the nanocomposite coatings display the lowest wear rate of 0.56 × 10− 10 mm3/Nm, by constraining the dislocation motion. © 2016

Yalamanchili K.,Linkoping University | Forsen R.,Linkoping University | Jimenez-Pique E.,Polytechnic University of Catalonia | Jimenez-Pique E.,Center for Research in Nanoengineering | And 6 more authors.
Surface and Coatings Technology | Year: 2014

Zr-Si-N films with varying Si contents were grown on WC-Co substrates by reactive cathodic arc deposition technique. The resulting microstructures of the films correlate to dominant variation in mechanical properties and deformation mechanisms. Si forms a substitutional solid solution in the cubic ZrN lattice up to 1.8at.% exhibiting a fine columnar microstructure. Further Si additions result in precipitation of an amorphous (a)-SiNx phase and evolution of a nanocomposite microstructure (nc ZrN/a-SiNx) which completely suppresses the columnar microstructure at 6.3at.% Si. The rotation-induced artificial layering during film growth is used as a marker to visualize the deformation of the film. A dislocation-based homogeneous plastic deformation mechanism dominates the columnar microstructure, while grain boundary sliding is the active mechanism mediating heterogeneous plastic deformation in the nanocomposite microstructure. Film hardness increases with increasing Si content in the columnar microstructure due to an effective solid solution strengthening. The deformation mechanism of localized grain boundary sliding in the nanocomposite microstructure results in a lower hardness. When cracking is induced by indentation, the fine columnar microstructure exhibits pronounced crack deflection that results in a higher fracture resistance compared to the nanocomposite films. © 2014 Elsevier B.V.

Drozd-Rzoska A.,Polish Academy of Sciences | Rzoska S.J.,Polish Academy of Sciences | Rzoska S.J.,University of Silesia | Pawlus S.,University of Silesia | And 4 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

Glass transition constitutes one of main problems of condensed matter physics and material engineering that remains unsolved. The common acceptance of the Vogel-Fulcher-Tammann (VFT) equation for portraying the primary relaxation time or shear viscosity indicated a possible phase transition, hidden below the glass transition temperature (Tg). Recently Hecksher [Nat. Phys. 4, 737 (2008)]10.1038/nphys1033 delivered strong empirical arguments that VFT description lacks a direct experimental basis and thus theories not predicting a dynamic divergence should be focused on. We present clear evidence for a superiority of critical-like divergent equation τ (T) = τ0 ( T- TC ) - and TC < Tg for liquid crystalline (LC) glass formers and orientationally disordered crystals (ODIC). Such dependence was already known for spin-glasslike systems and the dynamical scaling model, although the latter was hardly explored so far. The pressure-related behavior is also discussed. Results obtained support arguments for the suggested direct link between critical phenomena and vitrification. LCs and ODICs may be considered as simple experimental model systems for the structural glass formers group. © 2010 The American Physical Society.

Rheinheimer V.,Center for Research in Nanoengineering | Casanova I.,Center for Research in Nanoengineering
Cement and Concrete Research | Year: 2012

Thin films of C 3S of a few tens of nanometers were produced by electron beam evaporation. After verification that the chemical composition of the bulk material remained unchanged, the samples were hydrated with water vapor in a reaction chamber under saturated pressure and temperature conditions, and were kept isolated from atmospheric exposure throughout the whole duration of the experiment. Analyses by X-ray photoelectron spectroscopy at different stages of hydration evidence a shift of the Si peaks to higher energies and a subsequent decrease of the Ca-Si binding energy distance, indicating silicate polymerization expected upon formation of C-S-H. The measured molar Ca/Si ratio evolves from that of a jennite-like material, of about 1.55, at the beginning of the experiment (attributed to pre-hydration of the thin films), to a tobermorite-like ratio of 0.85 after 3 h of hydration. © 2012 Elsevier Ltd.

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