Investigation of aluminum nitrate as a set retarder of magnesium potassium phosphate cement: Mechanisms involved in diluted suspension

Céline Cau Dit Coumes (1) , Angélique Rousselet (2) , Biwan Xu (1) , Cyrille Albert Mercier (3) , sandrine Gauffinet (2)

1 LDPV - Laboratoire de Développement des Procédés de Vitrification
2 ICB - Laboratoire Interdisciplinaire Carnot de Bourgogne
3 CERAMATHS - Laboratoire de Matériaux Céramiques et de Mathématiques

In this study, the influence of aluminum nitrate on the hydration process of magnesium potassium phosphate (MKP) cement was investigated experimentally and through thermodynamic modelling using diluted systems with Mg/PO$_4$ molar ratio and water-to-cement ratio of 1 and 100 respectively. Three processes contributed to retard cement hydration: the acidic nature of aluminum nitrate which reduced the initial pH of the solution by two units, the early precipitation of a taranakite-like amorphous potassium aluminophosphate, which reduced the aqueous phosphate and potassium concentrations, and a salt effect due to the presence of soluble nitrate. Precipitation of potassium-containing magnesium phosphate hydrates, like Mg$_2$KH(PO$_4$)$_2$ ⋅15H$_2$O and K-struvite, was prohibited, whereas precipitation of newberyite and cattiite was delayed. Furthermore, the modelled phase development with ongoing cement hydration agreed rather well with the experimental findings.

Mots clés: Magnesium potassium phosphate cement; Aluminum nitrate; Hydration; Thermodynamic modelling

Domaines: Chimie

Céline Cau Dit Coumes, Angélique Rousselet, Biwan Xu, Cyrille Albert Mercier, sandrine Gauffinet. Investigation of aluminum nitrate as a set retarder of magnesium potassium phosphate cement: Mechanisms involved in diluted suspension. Cement and Concrete Research, 2021, 150, pp.106608. ⟨10.1016/j.cemconres.2021.106608⟩. ⟨hal-04280341⟩