Abstract: In order to improve the utilization rate of solid waste and reduce the amount of cement,this study selected ordinary slag and ultra-fine slag for rheological characteristics tests,revealed the influence mechanism of particle size,dosage and cement hydration on the early rheology,and combined the microstructure of hardened paste and the compressive strength of mortar to analyze the micro-macro action mechanism of ultra-fine slag. The results showed that ordinary slag can improve the fluidity of the slurry at low dosage,while ultrafine slag significantly reduces the fluidity of the slurry,and the dosage of waterreducing agent needs to be increased at a low water-binder ratio. Ultrafine slag can accelerate the hydration of cement and enhance the stability of the flocculation structure. Thus,the thixotropic ring area and shear stress value are increased compared with those of ordinary slag slurry,and the shear stress of the ordinary slag slurry is the greatest at 30 minutes. Ultrafine slag causes the yield stress and plastic viscosity of the slurry to increase with the dosage. However,the plastic viscosity and yield stress of ordinary slag system do not change much with the dosage. Common slag with content of less than 20% can enhance the later strength and microscopic compactness of the mortar,but it is unfavorable for the early strength. The ultrafine slag simultaneously enhances the early and later strengths and forms a low-pore structure,with the greatest later strength at dosage of 20%. Ultrafine slag maintains excellent strength at a large dosage,but severely deteriorates rheological properties. 

Key words: ultra-fine slag,fluidity,rheology,microscopic,strength