Use of Steel Slag in Subgrade Applications

Abstract

Steel slag is a by-product of steelmaking and refining processes. In 2006, 10-15 million metric ton of steel slag was generated in the U.S. Out of the total steel slag produced in the U.S. every year, about 50-70% is used as aggregate for road and pavement construction and approximately 15-40% is stockpiled in steel plants and eventually landfilled at slag disposal sites. Since current levels of steel slag stockpiling and landfilling are not sustainable, alternative geotechnical engineering applications for steel slag are being explored to alleviate the slag disposal problem and to help save dwindling natural resources. The main objectives of this research were to determine the geotechnical engineering properties of two types of steel slag generated from different steelmaking operations and to assess their potential use in subgrade stabilization and embankment construction. Samples of fresh and aged basic-oxygen-furnace (BOF) slag and of fresh electric-arc-furnace-ladle (EAF(L)) slag were characterized through a series of laboratory tests (specific gravity, grain-size analysis, X-ray diffraction, compaction, maximum and minimum density, large-scale direct shear, consolidated drained triaxial and swelling tests). The effects of gradation on the engineering properties of both fresh and aged steel slag samples were also investigated. Various mixtures of steel slag [BOF and EAF(L)] and Class-C fly ash were also investigated. The mixtures were prepared by adding 5 and 10% Class-C fly ash (by weight) to aged BOF slag and 5, 10 and 20% Class-C fly ash (by weight) to fresh EAF(L) slag. Unconfined compression tests were performed after various curing times to evaluate the strength gain characteristics of the mixtures. Long-term swelling tests were performed for compacted mixtures of both fresh and aged BOF slag and 10% Class-C fly ash (by weight) and for compacted mixtures of fresh EAF(L) slag and 5, 10 and 20% Class-C fly ash (by weight). The effect of adding 10% ground rubber (by weight) to fresh and aged BOF slag on the long-term swelling behavior of the mixtures was also investigated. The optimum moisture content and maximum dry unit weight of BOF slag were in the ranges of 4-8% and 19.5-21.8 kN/m 3 , respectively. The critical-state friction angle of fresh and aged BOF slags was in the 45.3°-48.1° range according to large-scale direct shear test results. Based on isotropically consolidated drained triaxial test (CIDTX) results, the peak friction angles of aged BOF slag (with minus 9.5 mm gradation) samples prepared at 90% relative compaction were equal to 47.3°, 45.2° and 43.5° at effective confining stresses of 50, 110 and 200 kPa, respectively. The optimum moisture content and maximum dry unit weight of EAF(L) slag were in the ranges of 10-13% and 16.8-20.0 kN/m 3 , respectively. The critical-state friction angle of fresh EAF(L) slag was equal to approximately 40.6° according to large-scale direct shear tests results. Compacted mixtures of both Class-C fly ash and BOF slag and of Class-C fly ash and EAF(L) slag sho...

Electric arc furnace slag and its use in hydraulic concrete

“…Since the pioneering papers of Motz, Geiseler and Koros [1][2][3], almost all kinds of iron and steelmaking (as well as other metal) slags have been proposed for use in construction and civil engineering. Researchers now face the task of finding the most efficient and appropriate techniques for their reuse [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Several investigations on the re-use of steelmaking slags have been published over the last decades; some of them concerning mortar and concrete (rigid-stiff matrices) , and mixtures with granular soils (compliant-flexible and porous matrices) [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58].…”

A Feasibility Study on the Application of Basic Oxygen Furnace (BOF) Steel Slag for Railway Ballast Material

“…It is noted that free lime (CaO) in the steel slag is from two different sources: (1) residual free lime originally contained in the raw materials, and (2) precipitated lime from the molten slag. The remaining free lime (CaO) is known to react with water, transferring into Portlandite [Ca(OH) 2 ] [14][15][16][17]. This transformation induces 98% volumetric expansion of BOF slag [18].…”

“…Steel slag generally consists of free-CaO, free-MgO (periclase), various types of crystalline phases such as olivine, merwinite, γ-2CaO·SiO 2 , 2CaO·Fe 2 O 3 , and RO phases (CaO-MgO-SiO 2 -FeO solid solution) [14]. Depending on the steel manufacturing process (i.e., BOF and EAF) or cooling methods (i.e., natural drying and rapid cooling), it is proved that the chemical, physical and mineralogical properties are various.…”

Utilization of Steel Slag As Road Base And Subbase Material

“…Büyük ölçekli kesme kutusu deney sonuçlarına göre kritik içsel sürtünme açısı ve pik sürtünme açısı 43°'nin üstündedir. Elektrik ark fırın (EAF) cürufu kritik sürtünme açısı ise 40°'nin üstündedir [11]. Çelikhane cürufunun önemli bir bölümü inşaat mühendisliği alanında kullanılmaktadır.…”

“…Çelikhane cürufunun önemli bir bölümü inşaat mühendisliği alanında kullanılmaktadır. İnşaat mühendisliği alanındaki çelikhane cürufu kullanımını çimento ve beton sanayi, yol uygulamaları ile geoteknik uygulamalar olmak üzere üç başlığa ayrılabilir [11]. Çelikhane cürufunun yol yapımında kullanılması 1979 yılından beri Japon Endüstri Standardında yer almakta ve bu tarihten beri nakliye maliyetleri açısından ekonomik olan yerlerde yol temel ve sıcak asfalt karışımlarında kullanılmaktadır [4,12].…”