From Ion Correlations to Macroscopic Rigidity: Multiscale Mechanics of Reactive Colloidal Gels

Cementitious materials are the most consumed substance on Earth, yet they represent a unique class of disordered matter: they are charged, amorphous, porous solids that form far from equilibrium. While often treated as engineering commodities, these binders are fundamentally reactive colloidal gels whose mechanical properties emerge from a complex interplay of physical forces across scales.

In this seminar, I will present a statistical mechanics framework that bridges the gap between nanoscale chemical interactions and mesoscale texture formation.

First, I will discuss the origin of cohesion between charged nano-grains. By computing Potentials of Mean Force, we show that standard DLVO theory breaks down in these highly confined electrolytes. Instead, cohesion is driven by ion-ion correlations and hydration forces, which we can tune to control the effective inter-particle attraction.

Second, I will address the non-equilibrium formation history of the gel. Using a hybrid Grand Canonical Monte Carlo / Molecular Dynamics approach,
we model the competition between particle precipitation rates and structural relaxation times. We demonstrate that the material’s hardening is effectively a transition from a colloidal suspension to a
kinetically arrested state, where the final density and rigidity are selected by the formation pathway.

Finally, I will examine the mechanical consequences of this frozen structural disorder. By analyzing the system’s inhomogeneity, we establish a direct quantitative link between local packing fractions and local stress fields.
We demonstrate that macroscopic rigidity is not uniform but emerges from the disordered granular network, where stress concentrations localize according to nanoscale density fluctuations.
This framework provides a granular-mechanics perspective on the elasticity and failure of cohesive amorphous solids.