The time-dependent response of structural materials dominates our aging infrastructure’s life expectancy and has important resilience implications. For calcium-silicate-hydrates, the glue of cement, nanoscale mechanisms underlying time-dependent phenomena are complex and remain poorly understood. This complexity originates in part from the inherent difficulty in studying nanoscale longtime phenomena in atomistic simulations. Herein, we propose a three-staged incremental stress-marching technique to overcome such limitations. The first stage unravels a stretched exponential relaxation, which is ubiquitous in glassy systems. When fully relaxed, the material behaves viscoelastically upon further loading, which is described by the standard solid model. By progressively increasing the interlayer water, the time-dependent response of calcium-silicate-hydrates exhibits a transition from viscoelastic to logarithmic creep. These findings bridge the gap between atomistic simulations and nanomechanical experimental measurements and pave the way for the design of reduced aging construction materials and other disordered systems such as metallic and oxide glasses.

Whether it is glass, ceramics, cement, or concrete, minimizing thermal conduction through disordered materials is a determining factor when it comes to reducing the energy consumption of cities. In this work, we explore underlying physical processes involved in thermal conduction through the disordered glue of cement, calcium-silicate-hydrates (CSH). We find that at 300 K, phonon-like propagating modes in accordance with the Boltzmann transport theory, propagons, account for more than 30% of the total thermal conductivity, while diffusons, described via the Allen-Feldman theory, contribute to the remainder. The cumulative thermal conductivity proves to be close to both equilibrium molecular dynamics calculations and experimental values. These findings help us establish different strategies, such as localization schemes (to weaken diffusons) and scattering mechanisms (to constrain propagons), for reduction of thermal conductivity of CSH without sacrificing its mechanical properties.

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The mechanical and thermal properties of the gigatonnes of concrete produced annually are strongly affected by the anharmonicity of the chemical bonds in its main binding phase, nanocrystalline calcium−(alumino−)silicate−hydrate (C−(A−)S−H). Improvements in C−(A−)S−H design increasingly depend on simulations utilizing a set of effective interatomic forces known as "CSH-FF", yet these assumptions have never been directly examined at the chemical bond level, and there is no guidance for their improvement. In this work, we use high-pressure Raman spectroscopy to directly measure bond anharmonicity in a representative series of C−(A−)S−H samples with varying composition and two natural model minerals, 14 Å tobermorite and xonotlite. We find that structural water molecules effectively scatter thermal energy, providing a heuristic for improving the thermal resistance of concrete. A comparison of experimental and calculated bond anharmonicities shows that a stiffer Si−O interaction would improve the transferability of CSH-FF to the thermal properties of C−(A−)S−H. High-pressure Raman spectroscopy is suggested to improve the calculations of C−S−H and to characterize other complex, nanocrystalline materials.