Experimental determination of bulk modulus of 14 Å tobermorite using high pressure synchrotron X-ray diffraction

Using a diamond anvil cell, 14 Å tobermorite, a structural analogue of calcium silicate hydrates (C–S–H), was examined by high-pressure synchrotron X-ray diffraction up to 4.8 GPa under hydrostatic conditions. The bulk modulus of 14 Å tobermorite was calculated, Ko = 47 GPa. Comparison of the current results with previous high pressure studies on C–S–H(I) indicates that: (1) the compression behavior of the lattice parameters a and b of 14 Å tobermorite and C–S–H(I) are very similar, implying that both materials may have very similar Ca–O layers, and also implying that an introduction of structural defects into the Ca–O layers may not substantially change in-plane incompressibility of the ab plane of 14 Å tobermorite; and (2) the bulk modulus values of 14 Å tobermorite and C–S–H(I) are dominated by the incompressibility of the lattice parameter c, which is directly related to the interlayer spacing composed of dreierketten silicate chains, interlayer Ca, and water molecules.