Emmanuela Del Gado

The physics of cement cohesion

Concrete and cement are the foundation of our global infrastructure and have a key role in the growth which is required to support a world population projected to surge past 9 billion by mid-century, with more than 70% of it living in urban areas. More than 20 billion tons of concrete are produced every year, more than any other material on Earth, such that concrete production is responsible for nearly 10% of the whole anthropogenic production of CO2. Reducing CO2 emissions for concrete production, designing and optimizing material performances, resilience and durability is hence crucial to sustainable growth and to meet Greet House Emissions reduction goals. Strength and other mechanical properties of concrete rely on cement (its main binding agent) and the formation/gelation of calcium-silicate-hydrates (C-S-H). While even a slight reduction of its carbon footprint will dramatically reduce global anthropogenic CO2 emissions, meeting emission-reduction targets for new constructions calls for a deeper scientific understanding of cement properties and performance. In recent years electron microscopy imaging, nano-indentation tests, X-rays and neutron scattering, NMR analysis, and atomistic simulations have elucidated several structural and mechanical features concentrated within a few nanometers. A potential breakthrough has been combining such experimental insights with the novel fundamental understanding gained through modeling and numerical simulations, which use statistical and condensed matter physics approaches to tackle the structural and mechanical complexity of the material over critical length scales. We are now able to link the surface charge and chemistry of cement hydrates to the emerging nanoscale cohesion, the gelation process, and the final material properties, opening new paths for science and technologies of construction materials.