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

Abstract

A continuous solidification process of blast furnace slag was developed to promote the use of air-cooled slag coarse aggregate for concrete. In this process, the molten slag can solidify in only 120 s and the slag thickness is about 25 mm. This process suppresses gas generation and greatly reduces water absorption. Most of the slag is crystalline, and part of the slag has a glass layer on its surface. Slag with a glass layer is brittle because it contains several cracks. Therefore, microscopic observation and thermal stress analysis of the solidified slag were carried out to clarify the mechanism of crack generation in the plate-like slag. In the microscopic observation, several cracks with a length of about 8 mm were found in the slag with the glass layer. From the analysis, in the cooling pattern of the slag on the piled slag a temperature difference of about 200 K exists between the center and the mold side in the slag pit, and keeping this difference results in tensile stress of more than 50 MPa. However, in the cooling pattern of the crystalline slag in the piled slag, the temperature gradient in the slag in the slag pit was very small because the slag was retained in the piled slag, and as a result, the thermal stress was almost 0 MPa.