Fumed Silica Modulation of 3D-Printed Cement Paste: (2026-03)¶

The rheological properties, particularly the thixotropy, of three-dimensional (3D) printed cement-based materials critically influence their pumpability and buildability. Traditional admixtures often face issues such as non-uniform dispersion, interference with the hydration process, or detrimental effects on mechanical properties when regulating thixotropy. This study systematically investigated the effects of an efficient nano-rheology modifier, fumed silica (FS), on the rheological behavior, microstructure, and printing performance of 3D-printed cement paste. The results indicate the existence of a critical FS dosage threshold (0.3%). At this dosage, the paste achieved an optimal rheological balance between high yield stress and moderate thixotropic recovery, while simultaneously exhibiting the maximum rate of heat release during hydration, thereby ensuring excellent printing shape fidelity. Exceeding this threshold led to the paste exhibiting a "strong yet brittle" rheological behavior. Although the structural strength increased, it easily resulted in greater extrusion resistance and weakened inter-layer bonding. This study confirms the significant potential of FS as a high-performance admixture for synergistically optimizing the rheological properties and promoting early-age microstructure formation in 3D-printed cement-based materials, providing a theoretical foundation and key process parameters for its engineering application.