Title: Leaching of Magnesium Phosphate Cement Pastes: Influence of the Mg/P Molar Ratio

Author(s): Laura Diaz Caselles, Ganaël Bon, Céline Cau Dit Coumes, Pascal Antonucci, Angélique Rousselet, Adel Mesbah, Valérie Montouillout

Publication: Symposium Paper

Volume: 362

Issue:

Appears on pages(s): 594-609

Keywords: cattiite, compressive strength, durability, K-struvite, leaching, magnesium phosphate cement, mineralogy

DOI: 10.14359/51741014

Date: 6/14/2024

Abstract:
This paper investigates the leaching behavior of magnesium phosphate cement-based materials (MPC) prepared using hard-burnt magnesia (MgO) and monopotassium phosphate (KH₂PO₄). Three different formulations of variable Mg/P molar ratios (1, 2, and 3) were tested. Upon hydration, K-struvite was the main hydrate formed in all cases. After 28 days of curing, mechanical properties were assessed on MPC mortars. Semi-dynamic leaching tests were performed on MPC paste monoliths for 28 days under well-controlled conditions and using demineralized water with a pH maintained at 7. Leaching solutions were frequently renewed. Solids were characterized before and after leaching using XRD and SEM/EDS. The cumulative element release, plotted against the square root of time, indicated that leaching was mainly controlled by diffusion in all samples. Examination of the solids revealed a zonation process involving K-struvite dissolution and cattiite precipitation. Analyses of leachates showed that fluxes of leached species increased with decreasing Mg/P molar ratios. This parameter was thus a key factor, influencing the pore network and the resistance of MPC-based materials to leaching.