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 (C3S) 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 29Si 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.