Estimation of the Environmental Impact for Recycling Blast Furnace Slag with a Hydrothermal Reaction Based on Life Cycle Inventory Data

Abstract

Blast furnace (BF) slag has been recycled in the construction industry mainly as cement and concrete. However, in the past few years, recycling conditions have changed and other recycled materials have become dominant; thus, new applications for BF slag need to be considered. In this study, we first reviewed applications in which BF slag was treated by hydrothermal reactions. Under hydrothermal conditions, tobermorite (Ca₅Si₆O₁₆(OH)₂·4H₂O) was formed from BF slag. This tobermorite, which was produced in a CaO–SiO₂–H₂O system, was used as the main binding mineral in autoclaved lightweight concrete (ALC), and the corresponding ALC exhibited excellent properties in terms of heat insulation and lightness.

Next, in the present study, the utilization of BF slag in the ALC manufacturing process as an alternative raw material was evaluated based on the environmental impacts associated with its use. Specifically, the environmental impact was evaluated with life cycle inventory (LCI) data for the resulting CO₂ emissions. The LCI data for ALC prepared with BF slag were compared with LCA data for other conventional production processes, and the results showed that the ALC prepared with recycled BF slag had lower levels of CO₂ emissions than the other processes that were evaluated.