Applying Tools from Glass Science to Study Calcium-Silicate- Hydrates

To explain the similarities between a glass and amorphous C-S-H, a C-S-H molecular structure with stoichiometry of (CaO)1.7(SIO 2)1(H2O)1.9 is produced using a mixed reactive-nonreactive force field modeling. As the consequence of reactive modeling using REAXFF potential, part of water molecules in the interlayer spacing dissociate into hydroxyl groups and proton, which produces Ca-OH bonds. In addition, it is shown that monomers condensate to produce dimmers. This reduces the monomer content and increases the mean silicate chain length. Comprehensive topological analysis is performed to identify the local environment of each atom, which is indicative of short range order in C-S-H. Specially, the topological analysis is shown to be essential to distinguish between oxygen atoms in water, hydroxyl groups, silica chain and calcium oxide sheets. The medium range order in C-S-H is shown to exist using first sharp diffraction pattern derived from structure factor calculations. © 2013 American Society of Civil Engineers

Closed-Form Solution of Road Roughness-Induced Vehicle Energy Dissipation

Copyright © 2019 by ASME. A major contributor to rolling resistance is road roughness-induced energy dissipation in vehicle suspension systems. We identify the parameters driving this dissipation via a combination of dimensional analysis and asymptotic analysis. We begin with a mechanistic model and basic random vibration theory to relate the statistics of road roughness profile and the dynamic properties of the vehicle to dissipated energy. Asymptotic analysis is then used to unravel the dependence of the dissipation on key vehicle and road characteristics. Finally, closed form expressions and scaling relations are developed that permit a straightforward application of the proposed road-vehicle interaction model for evaluating network-level environmental footprint associated with roughness-induced energy dissipation

The nano-mechanical properties of ultra high performance fibre reinforced concrete

Recent progress in nanoscience and technology makes it possible to assess the mechanical properties of cement based materials at the nanoscale and to identify the universal material properties. In this paper, we apply for the first time a novel statistical nanoindentation technique to identify the nano-mechanical properties of a class of ultra high performance concretes. A deconvolution analysis of the data allows to statistically determinate the invariant properties (elastic stiffness and hardness) of each single mechanical phase and the volume proportions of the low and high density calcium silicate hydrates. The results provide strong evidence that the macroscopic performance of UHPC materials is determined, at a nanoscale, by the pre-dominance of HD C-S-H among the cement hydration products ; and at a microscale by the absence of a weak transition zone between the fibers. Those two phenomena are intimately related since the higher density of the C-S-H entails and improved transition zone, which ultimately translates into the macroscopic performance

Is cement a glassy material?

The nature of Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains a controversial question. In particular, contrary to the former crystalline model, it was recently proposed that its nanoscale structure was actually amorphous. To elucidate this issue, we analyzed the structure of a realistic simulation of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue to cement, and to an artificial ideal glass. Results clearly support that C-S-H is amorphous. However, its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that its amorphous state mainly arises from its hydration. © 2014 Taylor & Francis Group

Applying tools from glass science to study calcium-Silicate- Hydrates

To explain the similarities between a glass and amorphous C-S-H, a C-S-H molecular structure with stoichiometry of (CaO) 1.7 (SIO 2 ) 1 (H 2 O) 1.9 is produced using a mixed reactive-nonreactive force field modeling. As the consequence of reactive modeling using REAXFF potential, part of water molecules in the interlayer spacing dissociate into hydroxyl groups and proton, which produces Ca-OH bonds. In addition, it is shown that monomers condensate to produce dimmers. This reduces the monomer content and increases the mean silicate chain length. Comprehensive topological analysis is performed to identify the local environment of each atom, which is indicative of short range order in C-S-H. Specially, the topological analysis is shown to be essential to distinguish between oxygen atoms in water, hydroxyl groups, silica chain and calcium oxide sheets. The medium range order in C-S-H is shown to exist using first sharp diffraction pattern derived from structure factor calculations. © 2013 American Society of Civil Engineers