Nanoscale origins of creep in calcium silicate hydrates

Abstract

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.

Mechanical behavior and phase change of alkali-silica reaction products under hydrostatic compression

“…Similar phenomena have also been reported for calcium chain-silicate structures, e.g. C-S-H (Morshedifard et al, 2018;Masoumi et al, 2017). When high temperature (e.g.…”

Nanoparticle simulations of logarithmic creep and microprestress relaxation in concrete and other disordered solids

“…In turn, this relaxation reduces the local tensile stress at other sites, decreasing the rate of subsequent slips, and thus the creep rate. All these assumptions align with traditional [4] and modern understanding of shear slips in C-S-H at the molecular scale [5][6][7], and led to models that can fit the experimental results.…”

“…In the recent literature, logarithmic creep of C-S-H has been predicted both by molecular simulations of interlayer water [7,11,12] (in spaces where water features glassy structure and kinetics [33]) and by nanoparticle simulations like in the present work [10,13]. This raises the question of whether the decay of strain rate during creep stems from processes at the subnano scale or at the nano-to-micro mesoscale.…”

“…The result has been interpreted as viscous compaction of a nanogranular solid, using the framework of free volume theory [9]. Molecular and nanoparticle simulations have predicted logarithmic creep to emerge from plastic deformations in disordered structures [7,[10][11][12][13]. However, stress heterogeneities have not been analysed in those simulations, nor they can be accessed in nanoindentation experiments.…”

Deformation mechanism of hardened cement paste under high stress and application of flow law

“…The time-dependent response of C-S-H has been studied using various approaches, and recently, atomistic simulation has appeared as a powerful tool for its investigation. Morshedifard et al [40] carried out a molecular dynamics simulation to study the time-dependent response of C-S-H, and they reported a behavior often seen in glassy systems. In addition, these authors reported that the amount of interlayer water changes the time-dependent response of C-S-H.…”