Influence of decalcification on structural and mechanical properties of synthetic calcium silicate hydrate (C-S-H)

Decalcification causes critical degradation of calcium silicate hydrate (C-S-H) - the principal binder in concrete. Contrary to structural change, the decalcification-induced change of C-S-H mechanical properties has not been sufficiently investigated. To fill this gap, here C-S-H was synthesized and decalcified using NH4NO3 solutions. It was then subjected to chemical analysis and high pressure X-ray diffraction study. Our results indicate that C-S-H decalcifies only in the interlayer which reduces its stiffness along the c-axis. The incompressibility and the transverse isotropy remain unchanged for the calcium silicate main layer, despite the vast change of silicate chain linkage. The intralayer Ca does not leach as long as C-S-H maintains the tobermorite-like structure. A similar to 30% reduction of bulk modulus is estimated for decalcified C-S-H. Our results add fundamental knowledge to the structure-property correlation of C-S-H subjected to decalcification.