Protonated portlandite precursor unlocks enhanced nucleation and growth for cement hydration.

Calcium silicate hydrate (C-S-H) and calcium hydroxide (CH, portlandite) are the dominant hydration products of Portland cement. However, the anisotropic layered CH and uncoordinated nucleation of C-S-H and CH severely restrict the macroscopic performance of cementitious materials. Here, we report a hydrogen-bond-regulated proton transfer strategy to mechanochemically synthesize a positively charged, isotropic disordered CH precursor (CHP_H+). This precursor serves as a growth-accelerating nucleus to trigger dual heterogeneous nucleation of CH and C-S-H, in situ forming a CH@C-S-H composite. Free energy calculations reveal that hydroxyl vacancies on CH surfaces drive spontaneous water adsorption to generate ≡Ca-OH2+ sites, which stabilize silicate clusters and promote composite growth. The resulting cementitious material shows accelerated hydration kinetics, higher hydration heat release, and greatly improved elastic modulus and compressive strength, delivering a 5.4-fold improvement in 12 h strength over the control. This work provides an atomic-scale design principle for advanced cementitious materials by reprogramming the nucleation and growth pathways of hydration products via protonation regulation.