Does the Al substitution in C–S–H(I) change its mechanical property?

This study examines the influence of Al substitution for Si on the bulk modulus of calcium silicate hydrate I [C–S–H(I)], a structural analogue of C–S–H, by performing high-pressure synchrotron X-ray diffraction experiments in two C–S–H(I) samples: one a hydration product of alkali-activated slag and the other a synthetic C–S–H(I). The test result shows that not only the bulk modulus but also the incompressibility of the lattice parameters a, b, and c of two C–S–H(I) samples are very similar to each other, regardless of the Al substitution. This result may be due to the four-coordinated configuration of the substituted Al, which makes the dreierketten silicate chains maintain the same arrangement after the substitution.