Environmental applicability of converter steelmaking slag (Geotizer) in river embankment restoration: Effect of curing on pH stabilization

The potential application of converter steelmaking slag (Geotizer™, Nippon Steel Corporation) to river flood control structures, such as levees and revetments, was investigated from both theoretical and experimental perspectives. Although Geotizer™ has been utilized extensively in ground improvement, its use in river engineering has been limited due to environmental concerns over the leaching of alkaline components. Laboratory-scale column experiments were conducted, where a Geotizer-silica sand mixture was placed at the bottom of a 20-L polyethylene container, and water (ion-exchange or tap water) was flowed through at a constant rate. Without curing, the effluent pH rose to 10.7–11.8 under deionized water, but significantly decreased to 8.3–9.6 with tap water (bicarbonate concentration: 65 mg/L). After two weeks of curing, the pH of effluent stabilized at 7.2–7.8, close to that of tap water (∼7.3), regardless of weather tap water or river water from different sources was used. These results indicate that pre-curing of Geotizer™ effectively suppresses hydroxide ion elution. Furthermore, natural river water typically contains over 10–20 mg/L of bicarbonate, suggesting that the environmental impact of Geotizer™ can be minimized when proper curing and site-specific water quality assessments are conducted. This study demonstrates the feasibility of converting industrial by-products into environmentally safe, functional materials for sustainable river engineering applications. • Steel slag (Geotizer™) was evaluated for use in river levee and revetment structures. • Continuous flow tests revealed high pH leaching from uncured slag materials. • Bicarbonate-rich water significantly reduced pH to environmentally safe levels. • Pre-curing for two weeks stabilized effluent pH between 7.2 and 7.8. • Geotizer can be safely reused in rivers when water chemistry is properly assessed.