It has recently been demonstrated that the addition of zinc can enhance the mechanical strength of tri-calcium 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) modelling 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. The uploaded folder contains the pertinent CIF files, DFT files, raw NMR data files, raw XRD data files, and LAMMPS input files.