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Hydration and ageing of cement: crossing timescales via transition state theory and nanoparticle simulations

The hydration of cement is largely determined by nucleation and growth of calcium-silicate-hydrate (C—S—H) at the nanoscale. Macroscopic creep is also a manifestation of nanoscale deformations in the C—S—H. Nanoscale simulations have the potential to shed some light onto the fundamental mechanisms that control hydration and creep. However, advances in this direction have been limited by the fact that the timescales of cement hydration (days) and creep (years) are enormous compared to the timescales of dynamical processes at the nanoscale (<microseconds).

Here we propose to overcome some timescale-related limitations by switching from the concept of dynamics to that of kinetics. Within the framework of kinetic theory, we use Transition State Theory (TST) to relate the free energy of model nanoparticle systems representing C—S—H, with the timescale of its chemo-mechanical evolution. TST requires a map of possible transitions, viz. transformations of the system from one state to a set of possible others. We combine information from molecular and nanoparticle simulations to generate phenomenon-specific transitions that are relevant to C—S—H precipitation and creep. This differs from other approaches to perform an extended sampling of all possible transitions.

Our results address some important features, including the effect of solution supersaturation on C—S—H nucleation, the difference between homogeneous and heterogeneous nucleation, and the progressive slowdown of deformation that characterizes long-term logarithmic creep. Furthermore the detailed information coming from the nanoscale simulations enables a new level of discussion on the underlying microscopic mechanisms that are often invoked by macroscale continuum models of hydration and creep, e.g. the concepts of nucleation and growth, solidification, and microprestress.

This work is in collaboration with MIT, Georgetown University, EHU (Spain), and ENPC (France).

Author(s):

Sophie-Anne Frith    
Newcastle University
United Kingdom

Igor Shvab    
Newcastle University
United Kingdom

Enrico Masoero    
Newcastle University
United Kingdom