Study On The Cement-based Cementitious Properties And Concrete Properties With Steel Slag And Micro Fines

At present,the research on hot-sealed and magnetic separation steel slag is relatively poor,and the low limit of micro fines content in the mechanism sand has obstacled the promotion and application of the mechanism sand.This article takes micro fines and hot-sealed and magnetic separation steel slag as objects to study its cementitious properties in cement base and its concrete properties.The strength of cement mortar and the mechanical properties and durability（electric flux）of concrete are studied from macro perspective by using steel slag and micro fines to replace part of cement,its microscopic morphology,hydration products and pore size distribution are studied from microscopic perspective by XRD,SEM,EDS and pore size analyzer.The main research conclusions are as follows:（1）The anti-fracture and compressive strength of cement mortar has a negative linear relationship with the amount of micro fines.The mineral composition of the micro fines-cement hardened paste mainly consists of CH phase（Ca（OH）₂）,calcium silicate hydrate（C-S-H）and calcium silicate（CS）,compared with the blank group,the mineral composition does not change qualitatively,but only changes in the phase proportion.Fibrous C-S-H is found in the 28d hardened slurry with the greater the amount of micro fines,which the more such fibrous cementite particles were found.Micro fines will increase the number of pores in the hardened slurry with micro fines and increase the number of pores larger than100nm,which can reduce the density of the hardened slurry structure with the more the amount of stone powder.（2）The anti-fracture and compressive strength of cement mortar has a negative linear relationship with the amount of steel slag.By XRD determination,compared with the mineral phase composition of steel slag powder treated by traditional process,it was found that there were Ca（OH）₂,C-S-H and Si O₂ in hot-sealed and magnetic separation steel slag.The RO phase with particle size less than 6um and high magnesium content may have hydration activity and can fill the pores of the hardened slurry,but the RO phase with smooth surface and large particle size is not firmly bonded to the surrounding hydration products.When the amount of steel slag is 30%,it can increase the pores of the hardened cement paste and the number of harmful pores larger than 100nm,reducing the compactness of the hardened paste structure.（3）Steel slag and micro fines are mixed in different proportions,the anti-fracture and compressive strength of cement mortar will become stronger with the increase of the proportion of steel slag.Compared with steel slag or micro fines mixed in cement mortar alone,steel slag and micro fines replace 20%of the cement at a ratio of 3:1 and mix them with cement mortar,its anti-fracture and compressive strength are stronger,its microscopic morphology of the hardened slurry structure is more compact,which increases the number of less harmful pores smaller than 50nm in the hardened slurry and reduces the number of harmful pores larger than100nm.Steel slag and a small amount of micro fines replace part of the cement and mixed in the cement mortar,which can refine the pore size distribution of the mortar,and has a certain coupling effect.（4）The mixed content of steel slag and micro fines is less than 30%,which can produce concrete with various working performance requirements.Within a certain range,the content of steel slag and micro fines has a linear negative correlation with the compressive strength of concrete at 28d.The mixed content of steel slag and micro fines is less than 30%,the content of steel slag and micro fines has little influence on the electric flux of concrete,far less than that influence of water-cement ratio and sand ratio,which can be neglected.