Endowing strength to calcium silicate hydrate (C-S-H) powder by high pressure mechanical compaction

The strength origin of C-S-H matrix is a key question in cement and concrete research, which remains largely unclear despite a century of study. Here we present a novel approach to endow strength integrity to C-S-H powders via mechanical compaction at room temperature. The unprecedented 2000 MPa compaction load results in a bulk C-S-H with tensile strength (~24 MPa) one order of magnitude higher than C-S-H matrix from hydration. This practice enables observations on how Ca/Si ratio (C/S) and initial moisture conditions affect their overall mechanical properties (hardness and strength), which are correlated with the micro-structures studied by 1H NMR and electronic microscope. We conclude that the bond between closely-contacted C-S-H particle, rather than the total porosity, is key to the bulk strength. The bond is clearly weakened when excessive water exists between C-S-H particles. This work provides novel insight to the strength origin of C-S-H.