From electrons to concrete infrastructures: A paradigm shift in turning a traditional material to an advanced composite.

A pulling computational experiment along the interlayer direction in a C-S-H model. The weakest planes lies in the water layers where the rupture occurs

Concrete is the world’s dominating manufacturing material, and as such it contributes to 5-8% of the total anthropogenic CO2 emissions worldwide and 2-3% of the primary global energy use. On the other hand, there is no other bulk material on the horizon that could replace concrete as the backbone for our increasing infrastructures demand imposed by mega-urbanization. Despite this global concern and decades of research on concrete, the interplay between structure, morphology and chemical composition of its smallest building block, Calcium-Silicate-Hydrate (C-S-H), is essentially unexplored. Together these characteristics of this "liquid stone" gel define cement hydrate and enable modulation of its physical and mechanical properties with the ultimate goal of reducing concrete environmental footprint. Here, we are interested in a bottom-up multi-scale approach to unravel the hierarchical structure of C-S-H, which is the principal source of strength and durability in all Portland cement concretes. The use of combinatorial chemistry in conjunction with statistical physics in extremely useful to decode several C-S-H polymorphs across a wide range of Ca to Si ratios. In deed, some of the stoichimetries and morphologies manifest a ductile or brittle behavior at the molecular level, thus opening up opportunities for tuning the mechanical response. By applying strain-controlled tension different directions to the decoded C-S-H polymorphs, we can identify the weakest strength planes that encapsulate the C-S-H core. This mechanistic approach allows realizing representative C-S-H particle sizes, which upon aggregation constitute the C-S-H microtexture. The latter can be modeled and equilibrated using meso-scale Monte-Carlo simulations with inter-particle interactions based on parameters directly obtained from partial atomic charges computed by ab-initio calculations. This bottom-up approach, motivated by a unique combination of combinatorial chemistry and statistical physics introduces innovative paradigms to revolutionize the cement chemistry at the molecular level to answer the global needs for greening construction materials.