Fibrillar calcium silicate hydrate seeds from hydrated tricalcium silicate lower cement demand

Abstract

Debates remain on the influencing factor and long-term performance of C-S-H-seeded paste. In this study, phase-pure seeds were prepared from diluted Ca3SiO5 hydration. The seed structures were determined using synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. Nano-foils and similar Ca and O environments were present in seeds of different Ca/Si; nanofibers were present in high-Ca seeds only which showed lower silicate polymerization. Calorimetry and setting results showed a greater hydration acceleration with high-Ca seeds; seed shape dominated the acceleration. 0.5 wt% high-Ca seeds increased 1- and 28-days paste strength by 300% and 20%, respectively. Life-cycle assessment showed negligible (<1%) influence of seeds on energy demand and CO2 emissions of the paste production. The CO2-intensity normalized by strength of seeded pastes decreases by ~25% at 28 days. This study sheds light on the use of C-S-H seeds from waste concrete and wash water, as a means of lowering cement demand.