Thermodynamic data for magnesium (potassium) phosphates

Lothenbach, Barbara; Xu, Biwan; Winnefeld, Frank

doi:10.1016/j.apgeochem.2019.104450

Cited by 79 publications

(43 citation statements)

References 81 publications

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“…The longer time for MP2.7-S to reach its stable state confirms the slower heat development observed for the sample with the lower Mg/PO4 molar ratio. Formation of magnesium phosphate hydrates and their phase transformations are highly pH dependent [48]. Therefore, the much lower pH of MP2.7-S before 400 min could indicate a different hydration path than for MP8-S.…”

Section: Electrical Conductivity and Phmentioning

confidence: 99%

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Influence of magnesium-to-phosphate ratio and water-to-cement ratio on hydration and properties of magnesium potassium phosphate cements

Winnefeld

Kaufmann

et al. 2019

Cement and Concrete Research

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134

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Magnesium-to-phosphate (Mg/PO4) and water-to-cement (w/c) ratios are important 9 factors controlling hydration and properties of magnesium potassium phosphate (MKP) cements.This study investigated the influence of Mg/PO4 molar ratios (2.7, 4 and 8) and w/c (0.25 and 5) on cement hydration, compressive strength and volume stability. Low w/c ratio slowed down cement hydration at lower Mg/PO4 beyond 1 day, and prevented the precipitation of intermediate hydrates at higher Mg/PO4. At lower Mg/PO4 expansion and strength loss were observed with time due to the continuing hydration within the already hardened cement. Higher Mg/PO4 resulted in faster hydration, higher strength, and in the precipitation of traces of brucite, which had no significant influence on the long-term volume stability and strength. Therefore, moderate Mg/PO4 molar ratios between 4 and 8 depending on w/c ratio used are recommended for the production of MKP cements with robust performance.

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Section: Electrical Conductivity and Phmentioning

confidence: 99%

“…These XRD results illustrate the transformations between the different hydrates. Phosphorrösslerite is very unstable [12,48] and can be easily transformed to the thermodynamically more stable newberyite according to the following equation (Eq. ( 6)):…”

Section: Solid Phases In Suspension Experimentsmentioning

confidence: 99%

Influence of magnesium-to-phosphate ratio and water-to-cement ratio on hydration and properties of magnesium potassium phosphate cements

Winnefeld

Kaufmann

et al. 2019

Cement and Concrete Research

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134

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“…The GEM method and codes are described in more detail in Supplementary Material, Part A. The chemical system is set up using the PSI/Nagra [21] chemical TDB extended with the Cemdata18 [11], the zeolite2020 [12,13] and the phosphate [14][15][16] TDBs. These TDBs are expected to get updated or merged along with the progress of research, with their GEMS variants updated and exported into CemGEMS accordingly.…”

Section: Background Of Cemgemsmentioning

confidence: 99%

“…These thermodynamic data, valid for a wide range of geochemical and chemical engineering systems, are compiled in different chemical thermodynamic databases (TDB), such as e.g. the Cemdata18 [11] TDB, the zeolite2020 [12,13] and phosphate [14][15][16] TDBs that have been developed specifically for modelling hydrated Portland, calcium aluminate, calcium sulfoaluminate, phosphate and blended cements, as well as alkali-activated materials. Available from https://www.empa.ch/cemdata, these popular TDBs contain standard thermodynamic data for cement hydrates such as C-S-H, AFm and AFt phases, hydrogarnet, hydrotalcite, phosphates, zeolites, and M-S-H, valid for temperature range from 0 to 100 °C.…”

Section: Introductionmentioning

confidence: 99%

CemGEMS – an easy-to-use web application for thermodynamic modeling of cementitious materials

Kulik¹,

Winnefeld²,

Кулик³

et al. 2021

RILEM Tech Lett

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Thermodynamic equilibrium calculations for cementitious materials enable predictions of stable phases and solution composition. In the last two decades, thermodynamic modelling has been increasingly used to understand the impact of factors such as cement composition, hydration, leaching, or temperature on the phases and properties of a hydrated cementitious system. General thermodynamic modelling codes such as GEM-Selektor have versatile but complex user interfaces requiring a considerable learning and training time. Hence there is a need for a dedicated tool, easy to learn and to use, with little to no maintenance efforts. CemGEMS (https://cemgems.app) is a free-to-use web app developed to meet this need, i.e. to assist cement chemists, students and industrial engineers in easily performing and visualizing thermodynamic simulations of hydration of cementitious materials at temperatures 0-99 °C and pressures 1-100 bar. At the server side, CemGEMS runs the GEMS code (https://gems.web.psi.ch) using the PSI/Nagra and Cemdata18 chemical thermodynamic data-bases (https://www.empa.ch/cemdata). The present paper summarizes the concepts of CemGEMS and its template data, highlights unique features of value for cement chemists that are not available in other tools, presents several calculated examples related to hydration and durability of cementitious materials, and compares the results with thermodynamic modelling using the desktop GEM-Selektor code.

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“…An appropriate reaction temperature increase is conducive to improving the early strength of the MPC in severe cold environments. Increasing the specific surface area (SSA) of M, adding highly active magnesia, and reducing the B/M ratio or W/C ratio are beneficial for improving the reaction temperature increase and early strength of MPC in severe cold environments [33,34].…”

Section: Strength Improvement Of Mpc In Severe Cold Environmentmentioning

confidence: 99%

Preparation and Application of Self-Curing Magnesium Phosphate Cement Concrete with High Early Strength in Severe Cold Environments

et al. 2020

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The early strength of magnesium phosphate cement (MPC) decreases sharply in severe cold environments ≤−10 °C, with the 2 h compressive strength falling to 3.5 MPa at−20 °C. Therefore, it cannot be used as a repair material for emergency repair construction in such environments. In this study, MPC is adapted for use in such cold environments by replacing part of the dead-burned magnesia (M) in the mixture with a small amount of light-burned magnesia (LBM) and introducing dilute phosphoric acid (PA) solution as the mixing water. The heat released by the highly active acid–base reaction of PA and LBM stimulates an MPC reaction. Moreover, the early strength of the MPC significantly improves with the increase in the Mg2+ concentration and the initial reaction temperature of the MPC paste, which enables MPC hardening in severe cold environments. Although the morphology of the reaction products of the MPC is poor and the grain plumpness and size of the struvite crystals are remarkably reduced, the early strength of MPC prepared in the severe cold environment is close to that of MPC prepared under normal temperature. Furthermore, the increases in the early reaction temperature and early strength of magnesium phosphate cement concrete (MPCC) are significantly improved when the PA concentration in the mixing water and the LBM/M ratio are 10% and 4–6% at −10 °C and 20% and 6–8% at −20 °C, respectively. Moreover, self-curing of MPCC can be realized even at −20 °C, at which temperature the 2 h and 24 h compressive strength of MPCC reach 36 MPa and 45 MPa, respectively.

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Thermodynamic data for magnesium (potassium) phosphates

Cited by 79 publications

References 81 publications

Influence of magnesium-to-phosphate ratio and water-to-cement ratio on hydration and properties of magnesium potassium phosphate cements

Influence of magnesium-to-phosphate ratio and water-to-cement ratio on hydration and properties of magnesium potassium phosphate cements

CemGEMS – an easy-to-use web application for thermodynamic modeling of cementitious materials

Preparation and Application of Self-Curing Magnesium Phosphate Cement Concrete with High Early Strength in Severe Cold Environments

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