**Carbon Steel Slag as Cementitious Material for Self-Consolidating Concrete**

#### Yu-Chu Peng

*Graduate Institute of Construction Engineering, National Taiwan University of Science and Technology, Depart of Leisure Management, Taiwan Hospitality & Tourism College, China,Taiwan* 

#### **1. Introduction**

322 Material Recycling – Trends and Perspectives

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In Taiwan, self-consolidating concrete (SCC) exhibiting high-flow behaviour is a widely used concrete material to prevent conventional concrete problems such as honeycomb structures that occur as a result of poor practice. SCC is also used as the material of choice for heavily reinforced concrete structures located in seismic zones [Paczkowski Piotr,Kaszynska Maria,2007.]. Pozzolanic materials are important ingredients for making SCC [Mihashi H, Yan X,1995.]. For many years, pozzolanic admixtures, such as blast furnace slag (BFS), pulverized coal ash (fly ash), silica fumes, and copper slag have been recycled to partially replace Portland cement in concrete mixtures. The main advantages of using pozzolanic materials are improvements in performance and significant reduction in the life-cycle costs of concrete structures; the latter, in particular, continues as a significant problem for engineers [Khalifa AJ, Ramzi T,2002. Li G, Zhao X.,2003. Zhang MH, Bilodeau A, Malhotra VM, Kim KS, Kim JC,1999.]. Materials such as steel slag, normally considered as waste, have promising applications as partial Portland cement replacements in concrete mixtures. Considerable research and development has been conducted to develop new concrete technologies such as SCC. Further, the construction of durable concrete has also been pursued. Initially, pozzolanic admixtures were solid waste and it was extremely costly to treat and dump them into a final storage area. Today, however, in the concrete industries in Taiwan and elsewhere, these admixtures are important materials for the production of low-cost durable concrete, and an example of environmental protection and resource conservation.

In Taiwan, carbon steel slag (CSS) is a by-product of the reduction during the production of refining carbon steel in an arc furnace, and is seldom recycled. On average, the production of one ton of carbon steel yields 10 kg of CSS waste, and hence, in Taiwan, more than 56,000 tons of CSS is produced each year. Due to the relatively small amounts of CSS relative to blast furnace slag (BFS), environmental protection agency (EPA) regulations had previously permitted the dumping of CSS. Today, the dumping of such waste is not permitted, and the proper disposal of CSS has become a huge problem. Since lime, coke and silicon iron are added to promote the reducing process during high-temperature-refinery scrap steel procedures, the CSS contains large amounts of CaO, SiO2 and Al2O3. This waste composition, however, is similar to BFS or Portland cement [Chiang CC, Chenn YY, Lin TY,

Carbon Steel Slag as Cementitious Material for Self-Consolidating Concrete 325

Table 1. Physical properties and chemical composition of OPC and CSS.

Fig. 1. Comparison of compositions of CSS, BFS and Portland cement.

Physical properties

Chemical compositions (%)

Item OPC CSS

Specific gravity 3.14 2.67 Specific surface area (cm2/g) 3622 2504 pH - 11.50 Absorption capacity (%) - 7.60 Fineness modulus (FM) - 1.76 Dry loose density (kg/m3) - 1266

SiO2 21.46 26.52 Al2O3 4.84 5.95 Fe2O3 3.12 3.78 CaO 62.34 46.45 MgO 2.87 13.27 SO3 2.06 0.65 f-CaO 0.88 2.11 Na2O 0.22 0.26 K2O 0.70 0.11 CaO/SiO2 2.91 1.75

Hwang CL,2004.Yu-Chu Peng,2009.]. Hence, CSS can be considered for use as a pozzolanic admixture to partially replace Portland cement in a concrete mixture.

Rather than use CSS for backfill soil or as material to be retained in the plant, steel slag can be regarded as a low-quality clinker and can be used to partially substitute the clinker of composite Portland cement [Wu X, Zhu H, Hou X, Li H,1999.Sakuraya T,1999.]. In Japan and other industrialized countries, steel slag has already been applied for use in civil engineering applications such as road base construction and soil stabilization [Geiser J.,1999. Roy DM, Idorn GM.,1982.]. In Germany, anbout 17.1% of steel slag is used for highway construction, 5.4% is recycled, and 40.5% is used in agricultural fertilizer production [Luxán MP, Sotolongo R, Dorrego F, Herrero E.2000. Monshi A, Asgarani MK,1999. Mihashi H, Yan X, Arikawa S.,1995. Hogan FJ, Meusel JW.,1981. ACI Committee 211.,1993.]. The mineralogical composition of steel slag is as follows: anhydrous calcium silicates and silicoaluminates; gehlenite, larnite and bredigite; magnetite and magnesioferrite and manganese oxides [Esfahani M. Reza,Kianoush M. Reza,2005. Hwang Soo-Duck,2008. Koehler Eric P. ,Fowler David W.,2008.]. Thus, some researchers have tested the effects of mixed iron slag (36%~45%), steel slag (6%~22%) and limestone (40%~64%) on the setting time of cement paste and the compressive strength at 3, 7 and 28 days [Schindler Anton K.,Barnes Robert W.,Roberts James B.,2007. Whitcomb Brent L., Kiousis Panos D.,2008.]. Nevertheless, other than documenting the chemical composition of CSS, there are few studies on the pozzolanic reactions after the addition of CSS.
