Influences of cross-linking and Al incorporation on the intrinsic mechanical properties of tobermorite

Abstract

Tobermorite is the model for calcium aluminosilicate hydrate (C-(A-)S-H), the glue in concrete, and is also the binding phase in cement-based materials under geological conditions and in ancient Roman concrete. Correlating the mechanical properties of tobermorite with atomic structures substantially improves the understanding of C-(A-)S-H. We study this correlation for tobermorite with various Al contents using Raman, nuclear magnetic resonance spectroscopy, and high-pressure X-ray diffraction. Al incorporation shortens the cross-linked tobermorite chains, leading to more charge-balancing Ca and strong H-bonding, and enhancing the incompressibility of the basal-layer of Al-tobermorite. Non-cross-linked tobermorite exhibits high incompressibility of the basal layer but low incompressibility of the interlayer due to lack of cross-linking. The substitution of stronger SiO with AlO shows no negative influence on the mechanical properties of tobermorite. The results provide fundamental information on how atomic structure influences the intrinsic properties of C-(A-)S-H and have implications in validating computational methods and parameters.