Solidification Conditions to Reduce Porosity of Air-cooled Blast Furnace Slag for Coarse Aggregate

Abstract

The solidification conditions to reduce the porosity of air-cooled blast furnace slag were investigated. From cross-sectinal observation of solidified slag, growth of gas bubble generated in molten slag was estimated to be cause of high porosity. With low thermal conductivity slag, increasing the cooling rate by thin slag casting was effective for reducing the porosity of air-cooled blast furnace slag.As a method of reducing the porosity of air-cooled blast furnace slag, a process was developed in which the slag is solidified to a plate thickness of 20-30 mm in about 2 minutes by pouring the molten slag in a cast steel mold. When porosity reduced, the abrasion resistance of the slag improved. The possibility of using low porosity slag as aggregate for drainage pavement was confirmed in an experiment with test pavement.

Behavior of Crack Generation of Slag in Continuous Solidification Process of Blast Furnace Slag

“…Yasutaka TA, 1) * Takeru HOSHINO, 1) Hiroyuki TOBO, 2) Keiji WATANABE 3) and Katsunori TAKAHASHI 4) 1) Steel Research Laboratory, JFE Steel Corporation, 1, Kawasaki-cho, Chuo-ku, Chiba, 260-0835 Japan.…”

“…It is possible to calculate thermal stress by measuring the physical property values shown above and carrying out a FEM analysis using those results in combination with the results of the heat transfer analysis in the previous report. 3) The reason why cracks do not occur in the crystal slag and the timing of crack generation in the slag with a glass layer can be clarified from the calculated values of thermal stress and the high temperature tensile strength and compressive strength measurements of the blast furnace slag. The calculation model used in the analysis of the continuous solidification process of the slag is the same as in the previous report 3) and is shown in Fig.…”

“…11. For the specific heat capacity and thermal conductivity, which are necessary in the heat transfer analysis, the measured values reported by the authors 3) were used in the range up to 1 373 K, and the measured value of the heat capacity of blast furnace slag reported by Ogino and Nishikawa 17) and the measured values of heat transfer reported by Kang and Morita 18) were used for the range from 1 473 to 1 773 K. For density, the measured values in the previous report 1,2) were used with a linear approximation up to 1 773 K. Two calculation conditions were examined, a) slag surface on the piled slags and b) slag inside the piled slag in the slag pit. Condition a) was defined as the condition in which the surface of the solidified slag that had been in contact with the mold surface is at the outer surface of the piled slags.…”

“…In previous research, [1][2][3][4][5][6] we demonstrated that plateshaped solidified slags with few pores and low water absorption suitable for use as coarse aggregate for concrete can be obtained in a continuous process by pouring molten blast furnace slag into steel molds to a thickness of approximately 25 mm. These desirable properties can be achieved because pore formation and growth are suppressed by rapidly solidifying molten slag.…”

Effect of Solidification and Cooling Methods on the Efficacy of Slag as a Feedstock for CO₂ Mineralization

“…Rapid solidification methods involving water tend to result in very high ϕ slags regardless of the process details, 42) whereas the ϕ in air cooled slags is sensitive to the equipment. 43) The porosity, ϕ, is dictated by the exclusion of gas from the solid phase upon phase transition from liquid to solid, followed by nucleation of gas pores, Ostwald ripening of the pores, and growth along grain boundaries when present. In general, longer solidification times lead to larger ϕ D , longer pore networks, and lower pore network tortuosity.…”