Atomic-Level Structure of Zinc-Modified Cementitious Calcium Silicate Hydrate.

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 zinc-modified 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.