<b>ABSTRACT</b></br>

The last generation of cement hydration accelerators relies on the seeding effect induced by amorphous calcium silicate hydrate particles. However, little is known about the effect of variables, such as the degree of crystallinity and morphology, on their performance. In this work, particles with a Ca/(Si+Al) molar ratio of 0.83 and different proportions of aluminum substitution for silicon were synthesized under hydrothermal conditions. X-ray diffractograms, nuclear magnetic resonance spectra, and scanning electron microscopy images showed that this altered the degree of crystallinity, structure, and morphology of the particles. Nevertheless, the addition of the synthesis products to cement pastes and their subsequent study by isothermal calorimetry and mechanical tests showed that the variables with the largest impact on cement hydration are the dosage and the proper dispersion of the particles. In fact, the use of a dispersing agent is highly recommended while drying of the particles should be avoided to prevent irreversible agglomeration processes from taking place.

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<b>ACKNOWLEDGEMENTS</b></br>

This study was carried out under the umbrella of the BASKRETE

initiative and the Laboratory for Transborder Cooperation

“Aquitaine-Euskadi Network in Green Concrete and Cement-based

Materials” (LTC-Green Concrete). Economic support was provided

by the Basque Government under the ELKARTEK Program

[project NEOMAT (KK-2021/00059)]. In addition, Marta Diez-

Garcia is grateful to the University of the Basque Country (UPV/

EHU) and the University of Bordeaux for her pre-doctoral fellow-

ship, within the framework of the Cross-Border Euroregional

Campus of International Excellence IDEX Bordeaux–Euskampus. Francisco B. Aguirre acknowledges the funding received from

Tecnalia to carry out his Ph.D. in cotutelle between the University

of the Basque Country (UPV-EHU) and University of Bordeaux

within the framework of the Cross-Border Euroregional Campus

of International Excellence IDEX Bordeaux–Euskampus. The

authors wish also to express their gratitude to the <b>SAREN</b> Re-

search Group (IT-1619-22, Basque Government) and MCIN/AEI/

10.13039/501100011033/ FEDER, UE (PID2021-124203OB-I00)