Performance And Application Of Restructed Steel Slag

Steel slag is a by-product of steelmaking process, its emission is about 15%-20% of steel output. By 2009, the amount of steel slag was 0.3 billion ton in our country. The accumulation of a large number of steel slag will pollute the environment and takes up a lot of land. As well as it causes tremendous damage to the ecological environment and a waste of resources, further more it hinders the sustainable development. So it is one important issue of iron and steel industry and building material industry in China that it realizes slag reduction, resource utilization and high added value research to make turning waste into treasure. In one word it realizes efficient recycling of steel slag.The composition of steel slag is very complex. By the chemical analysis, it shows that the steel slag contains minerals which are similar to Portland cement clinker, such as the gelling minerals of C₃S, C₂S and C₄AF. But the quantity of them is very a little which leads to a low activity. And the unsoundness of steel slag is caused by f-CaO and f-MgO. According to existing research we can find that the low activity and unsoundness of the steel slag are the two fundamental reasons for restriction of use in cement and concrete. Therefore, a design method of reconstructed steel slag is put forward in this paper. By adding industry calibration materials (clay, limestone), the properties of reconstructed steel slag were improved. After forming process, samples were put in high-temperature furnaces to reconstruct. Two kinds of experimental method were designed, one for corrected materials single-added, and the other for corrected materials compound-added. It is researched that corrected materials and reconstructed factors effected on the performance of reconstructed steel slag. At last, the optimal temperature, holding time and cooled system were determined. Prepare reconstructed steel slag in the best reconstructed system, and then the application of reconstructed steel slag in the fields of cement and concrete was studied. Through the study of reconstructed steel slag performance, the dosage was determined to meet the requirement of cement and concrete. The conclusions reached are as follows.(1) The process conditions had important influence on the performance of slag when the reconstructed steel slag was prepared. The results show that the properties of reconstructed steel slag become better with temperature increased and holding time prolonged. The optimal process system as follows: temperature was 1280℃, holding time was 60min, and cooling style was air cooling.(2) With the corrected quantity increased, the mechanical properties of reconstructed steel slag became elevated first, and then decreased. That exists an optimum value, makes reconstructed steel slag with more C₄AF, the activity and soundness of reconstructed steel slag were improved. The research shows that the best content of clay was 6% and slag was 94% and the best content of limestone was 15%, and slag was 85%. (3) The best ratio for corrected materials was 5% clay, 15% limestone and 80% steel slag. Compared with the reconstructed steel slag doped with single corrected material, the performance and volume stability of reconstructed steel slag doped with mixed corrected materials were both improved greatly. So mixed corrected materials were chosen for the use of cement and concrete. Meanwhile, the effect of fineness on the performance of steel slag was studied. The results showed that the greater the surface area of corrected materials, the better performance of reconstructed steel slag. The activity was increased and the soundness was also improved.(4) Compared with incorporation of equivalent steel slag, The compressive strength of ordinary Portland cement could be improved as incorporation of reconstructed steel slag, the water consumption of cement for normal consistency was reduced, the initial and final setting time of cement was shorten. When the amount of reconstructed steel slag is <50%, the soundness of cement was qualified. So it can meet the basic requirements of cement need.(5) Researches were carried out on the application of reconstructed steel slag on concrete. As the replacement mass fraction of reconstructed steel slag≤20%, the concrete curing compressive strength of all ages didn't significantly lower. Reconstructed steel slag grinded played a role of filling, which improved the pore structure and impermeability of concrete.