Dry and wet granulation of blast furnace slag and their influence on its reactivity; part 1

摘要

The transformation of liquid blast furnace slag into granulated blast furnace slag usually takes place via wet granulation, i.e. the fragmentation and abrupt cooling of the liquid slag by means of a high excess of water. This ensures a generally very high glass content, which is the prerequisite for the latent hydraulic behaviour of the blast furnace slag. The disadvantage of this is that granulated blast furnace slag has about 10 mass % residual moisture and, in particular, that the high heat content of the liquid slag cannot be utilised. For about ten years, therefore, more and more work has been done on plants that are intended to achieve dry cooling of the liquid blast furnace slag to a glassy material. In the years 2009 to 2019, the FEhS Institute was involved in several such projects. It was found several times that dry-produced blast furnace slag was less reactive than conventionally produced slag despite a comparably high glass content. The explanation for this behaviour could be found in a research project worked on with the Clausthal University of Technology to determine the fictive temperature, i.e. the real "freezing temperature" of the liquid blast furnace slag to glass, as well as the subsequent calculation of the cooling rate previously realised under practical conditions. It could be demonstrated that blast furnace slag particles of comparable size have a higher cooling rate, a higher fictive temperature and a higher enthalpy content when produced wet. Furthermore, parallel investigations on conventionally produced granulated blast furnace slags were able to demonstrate for the first time a concrete correlation between the fictive temperature as a measure of the enthalpy content of the granulated blast furnace slag and its reactivity in a cementitious system.