The purpose of the present study is to increase the utilization and added value of ladle furnace slag(henceforth referred to as LFS), which has a low level of utilization among steel slag by-products that have resulted from the growth of the steel industry. The research results which aimed at develo...
The purpose of the present study is to increase the utilization and added value of ladle furnace slag(henceforth referred to as LFS), which has a low level of utilization among steel slag by-products that have resulted from the growth of the steel industry. The research results which aimed at developing rapid hardening cement manufacturing technology to be used for up-cycling brought about the following conclusions.
1) The composition and property of the LFS differed depending on the steel company and the type of product process. Hence, the study collected the reduction slag that occurred in the various processes and analyzed the oxide, and the results were input into a modified Bogue equation to predict the minerals that occurred. The results show that the LFS that occurs in the manufacturing process of high grade steel products, the process of which makes use of high-priced ‘AI’ as the deoxidizer, contains a large amount of CA(Calcium Aluminate) based minerals, which have a high level of activity, making them suitable as a rapid hardening binder.
2) The results of the experiment for selecting a cooling method for calcium aluminate based LFS (henceforth referred to as CA based LFS) reveal that the application of rapid cooling by air to the reduction slag was capable of manufacturing rapidly cooled LFS, which has a high vitrification rate of over 90% within a short period of time, and the high reactivity of this method makes it the most efficient cooling method for producing a rapidly hardening binder. Furthermore, rapid cooling by air is an alternative capable of resolving various environmental issues including huge open-air hards for aging, dust, and leachate.
3) The study conducted an assessment on the physical and chemical properties and harmfulness of CA based LFS beads, which went through rapid cooling by air. The results show that the beads are spherical particles with a dry density of 2.87 and a particle size similar to fine aggregate. Vitrification was higher with a faster cooling rate as a result of a smaller particle size, and this consequently confirms a higher reactivity. The main composition minerals of rapidly cooled CA based LFS includes large amounts of rapidly hardening C12A7 and long-term strength developing β-C2S. The material satisfied the free CaO and heavy metal release test and the radiation leak test, indicating it to be environmentally harmless.
4) The results of assessing the hydration properties of rapidly cooled ladle furnace slag(henceforth referred to as RCLFS) as a reactive binder by grinding it show that it develops rapid setting and high initial strength. However, it also displays high shrinkage due to high hydration heat, low long-term strength development, and the production and rapid binding of CAH hydrates, which require subsequent improvement measures.
5) The problem of CAH production during the hydration of the afore explained RCLFS powder is tackled by inducing the production of ettringite by mixing gypsum as an alternative, with the manufacturing of CA slag based rapidly hardening cement in mind. The improving the high initial hydration heat and early-long term strength development and producing expansive ettringite by mixing gypsum enable the improvement of problems like volume stability as a result of shrinkage compensation.
6) The results of the experiment depending on gypsum type and dilution rates of the LFS show that the optimum gypsum for producing CA based rapidly hardening cement by using RCLFS powder is hemihydrate gypsum which has a high solubility, and depending on the dilution rate, using less than 30% is stable for cracks resulting from expansion.
The study developed a validly utilized technique for creating rapidly hardening cement by inducing a reaction that creates ettringite by mixing gypsum and by applying rapid cooling by air to CA based LFS, based on the result above.
The present technique adds value to reduction slag, which has been buried without any utilization, and the production of cement through this technique is expected to have various effects including the decreased use of natural resources, an improved recycling rate of waste, and improvements in environmental pollution.
However, over 2 million tons of reduction slag is slowly cooled and buried domestically each year, and the use of rapidly cooled CA based reduction slag is limited due to the perception that it is waste. Therefore, additional studies on the stability and durability of rapidly hardening binders based on rapidly cooled steel reduction slag are necessary. Furthermore, an expanded study on its various uses, by improving its perception as a stable material, is scheduled for implementation.
The purpose of the present study is to increase the utilization and added value of ladle furnace slag(henceforth referred to as LFS), which has a low level of utilization among steel slag by-products that have resulted from the growth of the steel industry. The research results which aimed at developing rapid hardening cement manufacturing technology to be used for up-cycling brought about the following conclusions.
1) The composition and property of the LFS differed depending on the steel company and the type of product process. Hence, the study collected the reduction slag that occurred in the various processes and analyzed the oxide, and the results were input into a modified Bogue equation to predict the minerals that occurred. The results show that the LFS that occurs in the manufacturing process of high grade steel products, the process of which makes use of high-priced ‘AI’ as the deoxidizer, contains a large amount of CA(Calcium Aluminate) based minerals, which have a high level of activity, making them suitable as a rapid hardening binder.
2) The results of the experiment for selecting a cooling method for calcium aluminate based LFS (henceforth referred to as CA based LFS) reveal that the application of rapid cooling by air to the reduction slag was capable of manufacturing rapidly cooled LFS, which has a high vitrification rate of over 90% within a short period of time, and the high reactivity of this method makes it the most efficient cooling method for producing a rapidly hardening binder. Furthermore, rapid cooling by air is an alternative capable of resolving various environmental issues including huge open-air hards for aging, dust, and leachate.
3) The study conducted an assessment on the physical and chemical properties and harmfulness of CA based LFS beads, which went through rapid cooling by air. The results show that the beads are spherical particles with a dry density of 2.87 and a particle size similar to fine aggregate. Vitrification was higher with a faster cooling rate as a result of a smaller particle size, and this consequently confirms a higher reactivity. The main composition minerals of rapidly cooled CA based LFS includes large amounts of rapidly hardening C12A7 and long-term strength developing β-C2S. The material satisfied the free CaO and heavy metal release test and the radiation leak test, indicating it to be environmentally harmless.
4) The results of assessing the hydration properties of rapidly cooled ladle furnace slag(henceforth referred to as RCLFS) as a reactive binder by grinding it show that it develops rapid setting and high initial strength. However, it also displays high shrinkage due to high hydration heat, low long-term strength development, and the production and rapid binding of CAH hydrates, which require subsequent improvement measures.
5) The problem of CAH production during the hydration of the afore explained RCLFS powder is tackled by inducing the production of ettringite by mixing gypsum as an alternative, with the manufacturing of CA slag based rapidly hardening cement in mind. The improving the high initial hydration heat and early-long term strength development and producing expansive ettringite by mixing gypsum enable the improvement of problems like volume stability as a result of shrinkage compensation.
6) The results of the experiment depending on gypsum type and dilution rates of the LFS show that the optimum gypsum for producing CA based rapidly hardening cement by using RCLFS powder is hemihydrate gypsum which has a high solubility, and depending on the dilution rate, using less than 30% is stable for cracks resulting from expansion.
The study developed a validly utilized technique for creating rapidly hardening cement by inducing a reaction that creates ettringite by mixing gypsum and by applying rapid cooling by air to CA based LFS, based on the result above.
The present technique adds value to reduction slag, which has been buried without any utilization, and the production of cement through this technique is expected to have various effects including the decreased use of natural resources, an improved recycling rate of waste, and improvements in environmental pollution.
However, over 2 million tons of reduction slag is slowly cooled and buried domestically each year, and the use of rapidly cooled CA based reduction slag is limited due to the perception that it is waste. Therefore, additional studies on the stability and durability of rapidly hardening binders based on rapidly cooled steel reduction slag are necessary. Furthermore, an expanded study on its various uses, by improving its perception as a stable material, is scheduled for implementation.
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