Environmental Impacts of Asphalt Mixes with Electric Arc Furnace Steel Slag

Abstract

Electric arc furnace (EAF) steel slag can be used as an alternative high-quality material in road construction. Although asphalts with slag aggregates have been recognized as environmentally acceptable, there is a lack of data concerning the potential leaching of toxic Cr(VI) due to the highly alkaline media of EAF slag. Leaching of selected water extractable metals from slag indicated elevated concentrations of total chromium and Cr(VI). To estimate the environmental impacts of asphalt mixes with slag, leachability tests based on diffusion were performed using pure water and salt water as leaching agents. Compact and ground asphalt composites with natural aggregates, and asphalt composites in which the natural aggregates were completely replaced by slag were prepared. The concentrations of total chromium and Cr(VI) were determined in leachates over a time period of 6 mo. After 1 and 6 mo, the concentrations of some other metals were also determined in the leachates. The results indicated that chromium in leachates from asphalt composites with the addition of slag was present almost solely in its hexavalent form. However, the concentrations were very low (below 25 μg L) and did not represent an environmental burden. The leaching of other metals from asphalt composites with the addition of slag was negligible. Therefore, the investigated EAF slag can be considered as environmentally safe substitute for natural aggregates in asphalt mixes.

Effect of FeO/MgO Ratio on Dissolution and Leaching of Magnesiowüstite

“…Logically, only minerals that can contain Cr can leach Cr. There are four major ferrous EAF slag minerals that usually contain Cr: spinels (AB 2 O 4 ), merwinite (Ca 3 MgSi 2 O 8 ), brownmillerite (Ca 2 (Al,Fe) 2 O 5 ), and magnesiowüstite (MeO) . Depending on which elements the spinels consist of they can either stable or unstable Spinels become more soluble as the calcium content increases .…”

“…Magnesiowüstite is mainly found in EAF slags, but can be found in other slags like BOS slags . Magnesiowüstite in steel slag primarily consists of FeO, MgO, MnO, and CrO x .…”

Recycling of ladle slag in cement composites: Environmental impacts

“…In order to estimate the long-term environmental impacts, leaching tests based on diffusion were proposed in the Dutch NEN 7345 (1995) standard and applied to concretes (Hohberg et al, 2000). Similar protocol was used also to assess the environmental impacts of asphalt mixes with the addition of electric arc furnace (EAF) dust (Vahčič et al, 2008) or EAF steel slag (Milačič et al, 2011) and cement composites with addition of EAF dust (Šturm et al, 2009).…”

Performance-Based Characterization of Bituminous Mortars Prepared With Ladle Furnace Steel Slag

“…The European steel industry continues to dump large proportions of LFS and to stockpile it, in some cases, while awaiting the approval of the relevant industrial standards.One use of this co-product is as filler material in bituminous mixtures, due to its appropriate particle size and slightly cementitious properties. Its encapsulation in bitumen also prevents the potential expansion of its components (mainly the hydration and carbonation of free lime and magnesia) [17], as well as possible contamination due to leaching, as bitumen will efficiently immobilizes metals found in asphalt mixes with slags [18].In early research on asphalt mixtures with ladle furnace slag, Skaf et al [19] reported the results of binder drainage tests that verified the good adhesion of the LFS filler with the bitumen and demonstrated the water-resistant quality of the mastic in moisture susceptibility tests. They also noted that LFS had higher bitumen absorption than the standard materials.Bocci [20] affirmed that the reuse of LFS in hot bituminous mixtures was feasible, in terms of mechanical behavior, water sensitivity and fatigue life.…”

“…One use of this co-product is as filler material in bituminous mixtures, due to its appropriate particle size and slightly cementitious properties. Its encapsulation in bitumen also prevents the potential expansion of its components (mainly the hydration and carbonation of free lime and magnesia) [17], as well as possible contamination due to leaching, as bitumen will efficiently immobilizes metals found in asphalt mixes with slags [18].…”