Research On The Cementitious Properties Of Superfine Steel Slag And The Utilization In Concrete

China is a country with huge production of steel, as well as a country with large amount of steel slag. Large amounts of steel slag not only pollute the environment but also occupy a large area of land. Compared with other industrial residue like blast furnace slag and fly ash, the utilization ratio of steel slag is low. New technology should be explored and the properties of steel slag should be studied and analyzed in order to improve the utilization ratio of steel slag.Superfine steel slag with different particle sizes were produced by superheated steam powered jet mill, which is designed by ourselves. And the raw steel slag is from Shanghai Baosteel. Laser particle analyzer, X-ray fluorescence spectrometer, X-ray diffractometer, scanning electron microscope, and building materials radioactivity detector were used to analyze the basic performance of superfine steel slag. And it was compared with that of ordinary steel slag powder. Based on the above analysis, superfine steel slag was used in cement, and the cementitious properties of blended cement were studied, then the hydration reaction mechanism of the blended cement was explored. Finally, the superfine steel slag was used as mineral admixture in concrete. Mechanical properties and working performance of the concrete were studied.The results show that, many chemical and mineral compositions of steel slag are similar to that of P·I425 cement, The content of f-CaO is decreased with the particle size of steel slag decrease. The radioactivity of ordinary steel slag and superfine steel slag all remain within the requirement of the national standard. With the particle size of steel slag decrease, the activity index is gradually increased, and the mortar strength of blended cement is also increased. The superfine steel slag (D50≤8.11μm) can satisfy the requirement of first grade steel slag powder in China. When the replacement ratio of superfine steel slag (D50=5.10μm) is 10%, the compressive strength of blended cement mortar is higher than that of P·I425 cement. When the replacement ratio is above 10%, the mortar strength of the blended cement is gradually decreased. When the superfine steel slag is combined with superfine blast furnace slag or superfine fly ash, the strength of blended cement mortar is increased significantly. The main hydration products of steel slag blended cement are Ca(OH)2, C-S-H and ettringite, et al. The hydration products of superfine steel slag blended cement is much more than that of ordinary steel slag blended cement.When the superfine steel slag was used in concrete, the compressive strength of the concrete is increased with the particle size of steel slag decreases, and the slumps are decreased. The strength of concrete with superfine steel slag (D50=2.52μm) can satisfy the strength requirement of C50. When the superfine steel slag is combined with superfine blast furnace slag or superfine fly ash, compressive strength of the concrete at middle and later ages is increased significantly. When the mass ratio of superfine steel slag and superfine blast furnace slag (or the superfine fly ash) is 1:1, the property of the concrete is at its best with a comprehensive consideration.