Optimization of Magnesium Potassium Phosphate Cements Using Ultrafine Fly Ash and Fly Ash

Area of Science:

• Materials Science
• Civil Engineering
• Geochemistry

Background:

• Magnesium potassium phosphate cement (MKPC) is a rapid-setting cement with diverse applications.
• Investigating supplementary cementitious materials like fly ash is crucial for enhancing cement properties and sustainability.
• Understanding the impact of ultrafine fly ash (UFA) and conventional fly ash (FA) on MKPC is essential for optimizing its performance.

Purpose of the Study:

• To investigate the effects of UFA and FA on the physical properties, phase composition, and microstructure of MKPC.
• To determine the optimal blend of UFA and FA for improved MKPC performance.
• To elucidate the role of UFA and FA in the hydration and reaction mechanisms of MKPC.

Main Methods:

• Calorimetry to monitor hydration heat and reaction kinetics.
• X-ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), Thermogravimetric Analysis (TGA), and Nuclear Magnetic Resonance (NMR) spectroscopy (including 31P MAS and 1H-31P CP MAS) for phase analysis and microstructural investigation.
• Compressive strength and fluidity tests to evaluate physical properties.

Main Results:

• UFA addition did not alter the initial hydration peak but potentially increased reaction duration.
• UFA:FA blends delayed hydration and setting times, improving workability.
• MgKPO4·6H2O was the primary phase; Mg2KH(PO4)2·15H2O was observed at low UFA levels (<30 wt%).
• SEM/EDS and NMR confirmed UFA and UFA:FA acted mainly as fillers/diluents.
• An optimized formulation (U10F30: 10 wt% UFA, 30 wt% FA) yielded the highest compressive strength and fluidity with a dense microstructure.

Conclusions:

• UFA and FA can be effectively utilized as supplementary cementitious materials in MKPC.
• The optimized U10F30 formulation offers enhanced mechanical properties and workability.
• The findings provide valuable insights for developing high-performance MKPC binders using fly ash components.