Influence of curing conditions on mechanical properties and microstructure of magnesium potassium phosphate cement

Abstract

This study investigated the effects of curing conditions such as dry air curing, moist air curing, water curing, and water-bath curing (30 °C, 50 °C) on hydration performance and mechanical properties of magnesium potassium phosphate cement (MKPC). The hydration temperature, compressive strength, and volume stability were investigated. Furthermore, microstructural analyses, including X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TG/DTG), and mercury intrusion porosimetry (MIP) were adopted. Experimental results showed that the compressive strength and volume stability of MKPC paste improved under early moist air curing and 30 °C water-bath curing, whereas they worsened under water immersion and 50 °C water-bath curing. The XRD and SEM examinations also indicated the instability and partial dissolution of K-struvite in water, with the formation of new precipitates. Early moist air curing and elevating-temperature curing below 50 ℃ both produced faster early strength development and good volume stability for the MKPC paste. However, further increase in humidity and curing temperature resulted in porous structures, with detrimental effects on the dimensional stability and strength.

Keywords

• Magnesium–potassium phosphate cement
• Curing conditions
• Compressive strength
• Volume stability
• Microstructure