It has recently been demonstrated that the addition of zinc can enhance the mechanical strength of tricalcium silicates (C 3 S) upon hydration, but the structure of the main hydration product of cement, calcium silicate hydrate (C-S-H), in zincmodified formulations remains unresolved. Here, we combine 29 Si DNP-enhanced solid-state nuclear magnetic resonance (NMR), density functional theory (DFT)-based chemical shift computations, and molecular dynamics (MD) modeling to determine the atomic-level structure of zinc-modified C-S-H. The structure contains two main new silicon species (Q (1,Zn) and Q (2p,Zn) ) where zinc substitutes Q (1) silicon species in dimers and bridging Q (2b) silicon sites, respectively. Structures determined as a function of zinc content show that zinc promotes an increase in the dreierketten mean chain lengths.

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Developing new sustainable concrete technology has become an urgent need, requiring faster and deeper insights into the fundamental mechanisms driving the cement hydration reactions. Molecular simulations have the potential to provide such understanding since the hydration reaction and the cement chemistry are particularly dominated by mechanisms at the atomic scale. In this letter, we review the application of two major approaches namely classical (including reactive) molecular dynamics simulations and density function theory calculations of cementitious materials. We give an overview of molecular simulations involving the major mineral and hydrate phases.