Plenary Speaker Roland Pellenq

Professor Roland Pellenq

Professor Roland Pellenq

Massachusetts Institute of Technology

Cement: A Multi-scale Porous Material Under the Nanoscope

Setting up the stage, one can list important engineering problems such as hydrogen docking for transportation applications, electric energy storage in batteries, CO2 sequestration in used coal mines, gas-shale production, durability of nuclear fuels, stability of soils and concrete in the context of sustainability. These are basically the challenging engineering problems of the coming century that address energy and environment.

Behind all those problems are complex multi-scale porous materials that have a confined fluid in their pore void: water in the case cement and clays, electrolytes in the case of batteries and super-capacitors, weakly interacting molecular fluids in the case of hydrogen storage devices (H2), gas-shale (CH4) and nuclear fuel bars (Xe). All these examples come down to understanding chemo-poro-mechanics at different scales staring from the nanometer.

So what do we mean by “under the nanoscope” ? The nanoscope does not exist as a single experimental technique able of assessing the 3D texture of complex multiscale material. Obviously techniques such as TEM are part of the answer but are not the “nanoscope” in itself. In our idea, the “nanoscope” is more than a technique producing images. It is rather a concept that links a suite of modeling techniques coupled with experiments (electron and X-rays microscopies, tomography, nanoindentation, nanoscratching...). If properly defined, the nanoscope should allow accessing material texture, chemistry, mechanical behavior, and adsorption/condensation behavior at all scales starting from the nanoscale upwards in a bottom-up fashion. The toolbox of the simulation aspect of the "nanoscope" is akin to a statistical physics description of material texture and properties including the thermodynamics and dynamics of the fluids confined to their pore voids as a means to linking atomic scale properties to macroscopic properties and behaviors. The “Art of simulation” includes the description of realistic multiscale porous materials samples starting at the atomic scale, the set up and the validity checking of transferable interatomic/intermolecular/interparticle potentials, Grand canonical Monte Carlo and Molecular Dynamics simulation techniques with the goal of  probing mechanical (elasticity, strength, fracture energy), adsorption (fluid condensation/evaporation/docking) and transport properties (permeablility, etc...).

Ideally, the “dream” would be to have a unified  engineering/ physical approach consistent from the scale of atoms to the scale of continuum theories, to tackle the challenging problems evoked here above. In this talk, I will specifically address the case of cement hydrate (CSH), the glue that gives concrete its remarkable mechanics properties by putting "CSH under the nanoscope".