Understanding the behaviour of magnesium potassium phosphate cements under alkaline environment - CEA - Commissariat à l’énergie atomique et aux énergies alternatives
Communication Dans Un Congrès Année : 2024

Understanding the behaviour of magnesium potassium phosphate cements under alkaline environment

Résumé

Magnesium potassium phosphate cements (MKPCs) are clinker-free acid-base binders that form through the reaction between magnesium oxide (MgO) and potassium dihydrogen phosphate (KH2PO4). In contact with water, dissolution and precipitation take place, mainly yielding K-struvite (MgKPO4.6H2O). MKPCs are of interest for patch repair work thanks to their fast setting and good adherence to old Portland cement (PC)-based concrete, but are also investigated for bioengineering, 3D printing and solidification / stabilization of hazardous waste. However, the understanding of their long-term evolution is still limited. Hence, this work aims at investigating the degradation mechanisms of MKPC paste under alkaline environment by considering two configurations: MKPC paste (i) in close contact with PC paste, or (ii) leached by an alkaline solution mimicking the pore solution of the PC paste. MKPC (Mg/P molar ratio = 1) and PC pastes were prepared at a water-to-cement ratio of 0.51 and 0.4, respectively, and cured under endogenous conditions at 20°C for 28 d or 180 d. For the MKPC/PC paste interface study (i), two cylindrical samples were initially resaturated with their own synthetic pore solutions and maintained confined in a Hoek cell for 3 or 8 months. For the leaching study (ii), semi-dynamic leaching tests were carried out for 14 d and 170 d on MKPC monoliths using an alkaline solution which was periodically renewed to avoid accumulation of dissolved species. Leachates were analysed by ICP-AES. In both kinds of experiments, post-mortem characterization of the solids was performed using XRD, SEM/EDS and 31P MAS-NMR. Leaching induced a decrease in the content of crystalline K-struvite, as well as the precipitation of Ca-deficient hydroxyapatite (CDHA), brucite and possibly magnesium silicate hydrates. A thin layer of CDHA was also evidenced at the MKPC/PC paste interface and could explain the good bonding between these two materials.

Domaines

Chimie Matériaux
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Dates et versions

cea-04665173 , version 1 (31-07-2024)

Identifiants

  • HAL Id : cea-04665173 , version 1

Citer

Celine Cau Dit Coumes, Laura Diaz Caselles, Gabriel Poras, Angélique Rousselet, Adel Mesbah, et al.. Understanding the behaviour of magnesium potassium phosphate cements under alkaline environment. 2nd International Conference on Innovation in Low-Carbon Cement & Concrete Technology, Jul 2024, Londres, United Kingdom. ⟨cea-04665173⟩
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