Greening effect of slag cement-based concrete: Environmental and ecotoxicological impact

Abstract

Materials containing ground granulated blast furnace slag (GGBFS) display a transient green–bluecolor after demolding. This greening effect has been investigated for leaching behavior and ecotoxicological impact. Color of concretes and pure pastes containing GGBFS was assessed with a portable spectrophotometer, and samples were then submitted to a tank monolith leaching test. Ecotoxicological tests were conducted on reference sample and a green concrete sample at both natural and adjusted pH of 8.1. Main results support that the temporary greening effect of GGBFS-containing materials has no particular impact neither on the chemistry of leachates, nor ecotoxicity. Additionally, alkaline leachates are the main issue of leached cement or GGBFS based materials with pH around 11.5–12.5. Alkaline pH is a preponderant factor of ecotoxicity to sensitive organisms such as Daphnia magna , immobilization assay (48 h) resulting in 5.10 Toxic Units (TU) for reference sample at pH 12.50 against 1.38 TU at pH 8.10. Furthermore, sulfides are a specific issue of GGBFS materials concentrated up to 0.94 mmol m −2 in leachates, having an ecotoxic impact on living organisms at all trophic levels. At pH 8.10, green concrete leachates have 4.85 TU for Raphidocelis subcapitata growth assay (sulfides concentration of 0.63 mmol m −2 ) against 3.0 TU for green concrete sample. However, sulfides are easily removed from natural solution by oxidation or evaporation. • Greening effect is not associated with hazardous leachates or ecotoxic effects. • Alkaline pH (> 11) is the main issue with cement or slag-based materials. • The algae R. subcapitata is not affected by high pH unlike the crustacean D. magna . • GBFS contain sulfides up to 1 wt.% release in eluates of concretes and pastes. • Sulfides are quickly neutralized in natural environment.