Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1 (2013)

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26 Ferrous slag Byproducts Background Ferrous slags are the byproducts of the iron, produced by the first furnace and steel, produced with a second furnace process. Iron is obtained by combining iron ore, iron scrap, and fluxes (limestone and/or dolomite) in the first blast furnace. The prod- uct from this furnace is pig iron, which can be used to fabri- cate products (e.g., cast iron) or as input for steel making. The byproduct from the this furnace is blast furnace slag (BFS), which is defined by ASTM as the nonmetallic product, con- sisting essentially of silicates and aluminosilicates of calcium and other alkaline materials that are developed in a molten condition simultaneously with iron in a blast furnace. Different cooling processes of the slag result in different BFS byproducts. Air-cooled BFS (ACBFS) is obtained when the BFS is poured into beds and slowly cooled under ambient conditions. A crystalline structure is formed and a hard, lump slag is the result. Cooling is accelerated by adding controlled amounts of water, air, or steam, which produces a byproduct with increased cellular structure. This byproduct is expanded or foamed BFS and is lightweight with high porosity. BFS cooled and solidified with water and air quenched in a spin- ning drum produces a pelletized BFS byproduct. Adjustments of the cooling process are used to increase or decrease the crystalline structure or to alter the glassy (vitrified) charac- teristics. Crystalline structures are desirable for use of the slag as an aggregate replacement; more vitrification (more glass content; amorphous) is needed for reactive cementi- tious applications. BFS that is cooled and solidified rapidly in water has little or no crystalline structure and has sand- sized particles. This byproduct is then crushed or milled into fine, cement-sized particles to produce granulated ground BFS (GGBFS). A second furnace is needed to produce steel (Figure 10). This furnace uses the liquid blast furnace metal, scrap, and fluxes (lime, dolomitic lime) and high-pressure oxygen injec- tion to produce a wide range of steel products. Steel furnace slag (SFS) can be obtained from any one of three types of furnaces: basic oxygen furnace (BOF), electric arc furnace (EAF), or open hearth (OH) furnace. Figure 10 indicates the different points in the process where steel slag is produced. As with iron manufacturing, the steel making byproduct charac- teristics will depend on the type of technologies and the com- position of the raw materials. The most common types of steel slag byproducts are BOF slag, EAF slag, and ladle slag. Addi- tional information can be found at the following websites: • National Slag Association: www.nationalslag.org • Slag Cement Association: www.slagcement.org • Recycled Materials Resource Center: www.rmrc.unh. edu/ • Turner–Fairbank Highway Research Center: http://www. fhwa.dot.gov/research/tfhrc/ literature review summary The list of the most commonly researched and used iron slag byproducts included BFS, GGBFS, and ACBFS. Other iron slag byproducts expand the list to include expanded or foamed BFS, pelletized BFS, and vitrified BFS; however, little was found in the literature for research or use of these byproducts. Steel slag byproducts were used much less frequently than iron slag byproducts. As with the iron slag byproducts, steel slag byproduct material properties depend strongly on the type of furnace and point in the process from which the byproduct was obtained. The steel slag byproducts identified in the lit- erature included steel furnace slag, EAF slag, BOF slag, OH furnace, and ladle slag. The generic term, steel slag, was used in a number of the articles found in the literature review. When the specific type of steel slag was determined, the EAF byproduct was the most frequently identified followed by the BOF slag. The following recommendations were identified for han- dling and stockpiling slag byproducts: • Slags had better material properties after weathering in a stockpile. • Using freshly produced BFS should be avoided to mini- mize the reactivity of slags. • A method statement for storing, handling, and measures for protecting water quality was needed. • Using BFS in wet, poorly drained soils or in areas below the water table should be avoided to limit the potential for ground-water contamination. • Good compaction was needed and ponded water should be avoided in unbound applications in the construction of heavily trafficked areas. chapter six slags

27 improved cost savings. The high specific gravity of steel slag made it more costly to haul because more tonnage was needed to produce the same volume. Higher water absorption capacities of some slags increased the demand for cements (portland or asphalt) and therefore the cost of the applica- tion products. The variability in the byproducts required additional preconstruction and construction quality control testing to design and monitor the uniformity of the project. The additional testing increased both the design and con- struction costs. One application for producing synthetic aggregates was found using GGBFS treated with carbon dioxide at ambi- ent temperatures and pressures to manufacture lightweight aggregates with aggregate impact values of between 14% and 17% loss after impact. Three methods of treatments for marginal steel slag materi- als were found. One method used wet grinding of EAF and argon oxygen decarbonization steel slags to reduce problems with harmful expansive reactions when used with alumi- num or galvanized metals. A second approach improved the strength-related reactivity of EAF slag by re-melting and rapidly cooling the steel slag to increase the glass content. This process showed potential for increasing the slag reac- tivity. The third method combined BOF steel slag with gyp- sum waste and cement bypass dust to form a binder without the use of cement. agency survey results for Ferrous slag Byproducts The most commonly used iron slag byproduct was GGBFS in PCC applications (Table 8). Steel slag was used primarily in HMA applications and pavement surface treatments. ACBFS was used in bound applications by some states in HMA, surface treatment, and PCC applications. Unbound usage of ACBFS The following plant adjustments need to be considered: • Increased silo storage at plants to handle additional materials. • Plant adjustments (e.g., air flow) to account for the dif- ferent specific gravities and dust contents. • Changes to the order of addition or rate of addition of individual components. Volumetric mix designs for either HMA or PCC need to consider the different specific gravities of the slag byproducts. In the case of HMA applications, the mat thickness is com- monly specified in units of pounds per square yard. When mixes contained byproducts with high specific gravities, the resulting mat thickness was reduced because the unit weights for the project were not initially adjusted to account for the change in unit weights. Standard QC/QA programs were used, although in some cases limits on the amount of byproduct in an application were occasionally necessary. One agency required a pre- construction trial mix program. A second agency imple- mented a requirement for a contractor to develop a self-test program. Skid resistance was improved with steel slags in the HMA surface course, but decreased when some non-ferrous slags were used. Contradictory skid resistance experiences were found in both the literature and agency responses. When permitting was based on environmental issues, using GGBFS in particular resulted in significant CO2 reduction credits. From the financial standpoint, byproducts situated close to the project location minimized the haul distance and Primary Steel Making Furnace Transfer Ladle Furnace Slag Synthetic Flux Addition Raker Slag Ladle Slag Clean Out or Pit Slag Ladle Waste & Dumped Residue Slag for Disposal Metals Recovery Metals Recovery Nonmetallic Steel Slag for Potential Aggregate Use Feedstock FIGURE 10 Slag production from steel making plant (after RMRC 2008).

28 included embankment and drainage applications. A number of states indicated a generic use of blast furnace slags in a range of applications, with embankments being the most common. Table 9 and Figure 11 show the states using the iron and steel byproducts. NoN-Ferrous slag Byproducts Background Non-ferrous slags are produced during the recovery and pro- cessing of non-ferrous metals from natural ores (RMRC 2008). As with steel slag, non-ferrous slag byproduct ends up as either a rock-like or granular material. Three groups of non- ferrous byproducts were listed on the RMRC (2008) website: (1) copper and nickel slags, (2) lead/zinc slags, and (3) phos- phorous slags. There are three basic steps in copper, nickel, and lead/zinc processing: • Roasting, which is heating below the melting point; • Smelting, which melts the roasted material; and • Converting, where the metal from the process is separated from impurities. Phosphorous, copper, nickel, and zinc slags can be air- cooled or granulated (RMRC 2008; TFHRC 2009). Often, molten slag is dumped into a pit and allowed to cool. When the slag is cooled rapidly by quenching with water, a vitrified frit- like granulated slag is obtained. The result is a more uniformly shaped small particle that is more reactive than air-cooled. Air quenching results in the solidification of larger masses. Copper slag produced by smelting the copper concentrates in a rever- beratory furnace is referred to as reverberatory copper slag. The cooling rate strongly influences the internal grain struc- ture of the slags and mineralogy that, in turn, influences the physical properties. literature review summary Research and pilot projects that indicated some non-ferrous slags, when used in asphalt concrete pavements, showed improved friction resistance, while others had poor friction properties. Both zinc and phosphorous slags were reported to improve friction properties but were limited in their use by Byproducts Number of States Using Byproduct in a Given Highway Application Asphalt Cements or Emulsions Crack Sealants Drainage Materials Embank. Flowable Fill HMA Pavement Surface Treatment (non- structural) PCC Soil Stability Blast Furnace Slag 0 1 1 6 1 5 3 3 2 ACBFS 0 0 3 4 0 6 6 4 0 GGBFS 0 1 1 1 6 2 0 30 2 Expanded BFS 0 0 0 0 0 0 0 1 0 Vitrified, Pelletized BFS 0 0 0 0 0 0 0 0 0 Steel Slag 0 1 0 3 0 13 4 2 0 Unknown Type 1 1 1 1 1 2 2 1 1 Embank. = embankment. TABlE 8 RESUlTS FOR AGENCy SURVEy FOR IRON AND STEEl SlAG ByPRODUCTS USED IN HIGHWAy APPlICATIONS No. of Applications States BFS (General) ACBFS GGBFS Expanded BFS Steel Slag Unknown Type of Slag 6 — — — — — — 5 WV IL, IN — — — ID 4 UT, VA OH — — — — 3 — — AL, PA — IN — 2 KY, WI KY, PA, VA KS, KY, MS, NJ, OH, TX, WA — MO, OH, SC, WI AK 1 AL, MD, NJ, NY, VT FL, MO, NJ AR, CT, DC, DE, FL, ID, IL, IA, LA, ME, MN, MO, NC, NE, NH, NY, OK, OR, SC, VA, VT, WI, WV IL AL, CO, CT, DC, IL, IA, KY, MN, OR, PA, VA, WV DC, FL, MA TABlE 9 STATES USING IRON AND STEEl ByPRODUCTS IN HIGHWAy APPlICATIONS IN 2009

29 Slag Byproducts 2009 Blast Furnace Slag (BFS) 4 2 5 VT-1 4 1 1 2 1 NJ-1 MD-1 2009 Air Cooled Blast Furnace Slag (ACBFS) 2 2 4 1 2 5 5 1 NJ-1 1 1 2 2 2 2 DE - 1 2 2 1 1 3 1 1 1 1 NJ - 2 1 CT - 11 1 1 1 1 1 3 1 1 DC - 1 2009 Granulated Ground Blast Furnace Slag (GGBFS) 1 VT-1 NH-1 2009 Steel Slag 2 CT-1 DC-1 3 2 2 1 1 1 1 1 2 1 1 1 1 1 FIGURE 11 Agency survey results for iron and steel slag byproducts (numbers indicate the number of applications that use the byproduct). Byproduct Number of States Using Byproduct in a Given Highway Application Asphalt Cements or Emulsions Crack Sealants Drainage Materials Embank. Flowable Fill HMA Pavement Surface Treatment (non- structural) PCC Soil Stability Copper and Nickel None Reported Lead, Lead-Zinc, and Zinc None Reported Phosphorous 0 0 0 0 0 1 (KY) 0 0 0 Embank. = embankment. TABlE 10 RESUlTS FOR AGENCy SURVEy FOR NON-FERROUS SlAG ByPRODUCTS USED IN HIGHWAy APPlICATIONS

30 agency survey results for Non-Ferrous slag Byproducts The agency survey question for non-ferrous slag usage in highway applications and agency responses are shown in Table 10. Only Kentucky indicated having used phospho- rous slag in HMA applications. the lack of availability, whereas nickel slags were reported to have poor friction characteristics as aggregates in pavement surface mixes. Some asphalt concrete mixes with non-ferrous slags were reported to exhibit moisture sensitivity, which could be addressed with lime treatment of the surface. These slags when used as an aggregate are likely to have poor friction properties.