Effects of recycled mortar powder on the properties and microstructure of magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) has become a popular research topic owing to its rapid hardening and high early strength. However, its high carbon emissions and cost limit its large-scale applications. To reduce MKPC's carbon emissions and preparation costs and to improve the resource reutilization of construction waste, we investigated the effects of the particle size and dosage of recycled mortar powder (RMP) on the setting time, mechanical properties, physical phase, and microstructure of MKPC. The results indicated that when the particle size of RMP increased from 30 to 66 & mu;m, the setting time of MKPC increased from 10.5 to 13.1 min, and the compressive strength (at 28 d) decreased from 52.4 to 38.0 MPa. Therefore, increasing the RMP particle size can prolong the setting of MKPC and reduce its compressive strength. Additionally, increasing the dosage of RMP reduced the setting time of MKPC and promoted the development of compressive strength in later stages. When the RMP dosage increased from 0% to 40%, the setting time of MKPC decreased by 26.1%, and the compressive strength increased by 50.2%. According to the results of pore structure and microstructural analysis, the incorporation of RMP improves the microstructure of MKPC, significantly enhancing its mechanical performance. Therefore, RMP can be used as an economical and ecofriendly cement blending material to reduce the preparation cost of MKPC and the carbon emissions of the construction industry and improve the resource reutilization of construction waste.