Effect of Ca/Si and Al/Si on micromechanical properties of C(-A)-S-H

Calcium silicate aluminate hydrate (C(-A)-S-H) is the main hydration product used in cement-based materials. It plays a specific role in both the mechanical properties and volumetric deformation of the cement matrix. This study aims to clarify the effect of porosity and chemical composition of C(-A)-S-H on its micromechanical properties using nanoindentation. The results showed that porosity significantly affected the indentation, elastic, and creep moduli of the porous C(-A)-S-H compacts. Micromechanical properties of the “pure” C(-A)-S-H were improved by decreasing the Ca/Si ratio. The incorporation of Al slightly altered the creep modulus by affecting the volume of the large gel pores, basal spacing, and mean chain length (if no cross-linking occurred in C(-A)-S-H). Finally, the nanoindentation results of the mixed C(-A)-S-H and Al(OH)3 confirmed the distinct contribution of the individual component characteristics to the overall properties of porous mixtures.