Abstract: In the research field of traditional cementitious composites,fibers enhance the strength,toughness,ductility and crack resistance of the materials. In order to improve the early strength of phosphogypsum cements,polypropylene fibers were doped as reinforcing agent,and fiber-doped phosphogypsum cements preparation test and uniaxial compressive strength test were carried out to analyze the effect of fibers on the damage law of phosphogypsum cements,and the toughening mechanism of fibers on phosphogypsum cements was investigated by SEM. The results show that:the uniaxial compressive strength of phosphogypsum cementum increased with the fiber dosage,the uniaxial compressive strength of phosphogypsum cementum showed a tendency to increase and then decrease,and the optimal dosage of fibers is 1%;the phosphogypsum cementum doped with fibers can delay the time of reaching the peak compressive strength and the peak stress is greater in destruction;the phosphogypsum cementum without doped fibers is rapidly destabilized after the load exceeded the peak stress,and the phosphogypsum cementum with doped polypropylene fibers showed a slow decrease in the trend;with the fiber dosage,the phosphogypsum cementum is slowly stabilized and the peak stress is reduced. With the incorporation of fibers,the number of cracks in the phosphogypsum cement gradually decreases,and the cracks are continuous,and the ductile deformation of the phosphogypsum cement is obvious;under the microscopic surface of polypropylene fibers,there are flocculated hydration products attached to the surface of the polypropylene fibers,and in the process of slurry solidification to form the mesh structure with mutual adhesive connection. The research results of this paper can provide certain reference for the application of phosphogypsum-based composites in solid waste cementation and filling site.

Key words: polypropylene fiber,phosphogypsum based composite cement,early mechanical properties,crack evolution