UC Irvine

Calcium silicate hydrates (C-S-H), the main product of cement hydration, account for the majority of observed behavior in concrete. Cement production has a devastating environmental footprint and any improvement in its performance through innovative material design can have significant global impact. In this thesis, we first focus on understanding nanoscopic mechanisms underlying time-dependent mechanical response (e.g. creep) in cementitious materials. A viscoelastic behavior is observed at the scale of single C-S-H globules. However, we demonstrate a gradual transition from exponential viscoelastic behavior to logarithmic creep as we morph from intraglobular to interglobular regime. We also propose a phenomenological model for capturing the combined exponential-logarithmic creep of C-S-H. Next, we focus our attention on understanding thermal conduction in hybrid organic-inorganic calcium silicate hydrates. For a prototypical model, we show that incorporating organic chain in interlayer galleries of C-S-H can signficantly reduce thermal conductivity of the material. The vibrational modes are investigated to better understand the origins of this reduction. We find that although contribution of propagating modes is more or less intact, there is a reduction in mode diffusivities which can be attributed to phonon scattering due to organic-inorganic interfaces which ultimately result in the reduced thermal conductivity. As the last part of the thesis, we study a hybrid organic-inorganic C-S-H that our collaborators have been able to synthesize in the laboratory. Interpretation of X-ray data shows that the precipitated solid has the structure of portlandite with a cross-linked interlayer space. After the structure is resolved, we focus on developing a force field capable of modeling such hybrid systems. Cell parameters and elastic constants computed based on density functional theory (DFT) are used as observables in our fitting process. The computed properties using the developed force field compare well with DFT and experimental results. Finally we demonstrate applicability of the developed force field by calculating thermal conductivity and creep for the hybrid system. The developed force field paves the way for further investigations into properties of novel hybrid materials such as the one considered in this study.