Review
Characteristics of steel slags and their use in cement and concrete—A review

https://doi.org/10.1016/j.resconrec.2018.04.023Get rights and content

Abstract

Steel slags are industrial by-products of steel manufacturing, characterized as highly calcareous, siliceous and ferrous. They can be categorized into basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, and ladle furnace (LF) slag. They are found to be useful in many fields, such as road construction, asphalt concrete, agricultural fertilizer, and soil improvement. However, better utilization for value-added purposes in cement and concrete products can be achieved. In this paper, an overview of the recent achievements and challenges of using steel slags (BOF, EAF and LF slag) as cement replacement (usually ground into powder form with the size of 400–500 m2/kg) and aggregate in cement concrete is presented. The results suggest that the cementitious ability of all steel slags in concrete is low and requires activation. For the incorporation of steel slags as aggregate in concrete, special attention needs to be paid due to the potential volumetric instability associated with the hydration of free CaO and/or MgO in the slags. Studies have indicated that adequate aging/weathering and treatments can enhance the hydrolyses of free-CaO and -MgO to mitigate the instability. Considering the environmental and economic aspects, steel slags are also considered to have a potential use as the raw meal in cement clinker production.

Introduction

Recently, the green supply chain (e.g., waste-to-resources) has been aggressively established in industrial parks around the world to realize a circular economy (Li et al., 2015). Steel slags, industrial by-products of steel manufacturing, are annually produced in a huge quantity, which should be considered as a green resource. Modern steels can be broadly categorized into four types, i.e., carbon, alloy, stainless and tool steels. Carbon steel is produced either in a basic oxygen furnace (BOF) or an electric arc furnace (EAF), and then refined in a ladle furnace (LF) to achieve a better quality. As for stainless steel, it can be produced in an EAF, an LF, or an argon oxygen decarburization (AOD) furnace (Iacobescu et al., 2016; Kriskova et al., 2012; Zhang and Xin, 2011). During the manufacturing of carbon and stainless steels, a significant amount of by-product steel-slag is produced, accounting for about 15–20 wt.% of the total steel output (Han et al., 2015; Shi, 2004). The compositions of the generated steel slags are highly variable and basically, they can be classified into BOF slag, EAF slag and LF slag.

The annual production of steel slags is about 14 million tons in Japan (NSA, 2017), 21 million tons in Europe (Euroslag, 2012) and over a hundred million tons in China (Zhang et al., 2011). Compared with the widespread use of blast furnace slag, steel slags undergo less upgrading since they usually encounter several technological barriers to valorization such as volume instability (Pan et al., 2016). More than 400 million tons of steel slags have been deposited in China, with an annual accumulation rate of 100 million tons, leading to occupation of lands and potential pollution of water and soil due to the alkaline leachates from steel slags (Mayes et al., 2008; Shi and Qian, 2000; Zhang et al., 2011). Currently, steel slags can be recycled for internal metallurgical purposes (Yi et al., 2012) or used in road construction (Pasetto and Baldo, 2010a,b, 2015, 2016), cement and concrete (Carvalho et al., 2017; Yi et al., 2012), bituminous mixes (Skaf et al., 2017), fertilizer (Yi et al., 2012) and soil improvement (Poh et al., 2006). Several studies have also evaluated the feasibility of steel slags for CO2 mineralization (Pan et al., 2017; Yu and Wang, 2011) and water pollution control (Drizo et al., 2006). In the US, about 60.3% of the total steel slag production is directly used as road base, while the remainder is used for asphaltic concrete (10.9%), fill (10.8%) and cement clinker production (5.0%) (Ilyushechkin et al., 2012). In China, the utilization ratio of steel slags is less than 30%, found in cement production, chemical admixture for concrete, brick and block manufacturing (NDRC, 2014; Yi et al., 2012).

Due to the high demand for cement and concrete production worldwide, the cement and concrete industries have an increasing interest in finding alternative materials to replace the use of natural resources. Thus, extensive studies have been carried out to explore the possibility of utilizing steel slags as cement and concrete materials. Alternatively, they are involved in cement clinker production, which in turn reduces CO2 emissions and the total cost of the materials used (Reddy et al., 2006). This paper provides a critical review of the valorization of steel slags in cement, concrete and clinker production. The challenges and opportunities of using BOF, EAF and LF slags as supplementary cementitious materials and/or aggregates in cement and concrete are illustrated. The use of steel slags for cement clinker production is also discussed.

Section snippets

Generation processes

In China, BOF slag accounts for about 70% of the annual steel slag production (Cheng and Yang, 2010). In the BOF process (Fig. 1), minor steel scrap and a large amount of molten iron from ironmaking as well as fluxes (lime/dolomite) are added into the furnace, and a 99% pure oxygen flow is applied at supersonic speed through a lance to initiate intense oxidation reactions at a temperature of 1600–1650 °C. Once the desired chemical composition is achieved, the oxygen supply is stopped and the

Generation processes

EAF slag is the steel-making slag generated from the EAF. It is reported that the EAF process is dominating the steel industry of the US with a 55% share of the total steel output in 2006. An EAF is different from a BOF, for example, in the way of energy supply where the former uses high-power electric arcs instead of gaseous fuels (as shown in Fig. 9). Also, steel scrap has become the major feed material in the EAF process together with limited iron scrap, pig iron and direct reduced iron

Generation processes

After primary steelmaking, the refining operations of both carbon and stainless steel can be performed in an LF (Fig. 9), producing the LF slag. The LF process is based on the principles of deoxidation and alloying, temperature and composition homogenization, desulfurization, steel cleanliness improvement, inclusion flotation and the shape control of sulfide and oxide (Pretorius, 2015; Yang et al., 2007). Due to the uses of fluxes (e.g., calcium aluminate or CaF2) in the LF process, the

Environmental benefits from steel slag valorization

Improper disposal of steel slags can have a deleterious impact on surface- and ground-water through the release of trace elements and hyperalkaline drainage (Piatak et al., 2015). This may greatly threaten the safety of humans and the environment, especially stainless steel slag which contains different heavy metals (Pellegrino and Gaddo, 2009; Xiang et al., 2016; Zhang and Xin, 2011). Salman et al. (2014b, 2015) studied the heavy metals and metalloids leaching from alkali-activated and

Conclusions

The valorization of BOF, EAF and LF slags is an important strategy on industrial waste management toward a circular economy. One of the valorization pathways with great potential is for cement and concrete production. BOF slag is more alkaline and reactive than EAF and LF slags, which could be used as supplementary cementitious materials at a substitution ratio of 10–20 wt.% with satisfactory performance. The rock-like appearance of BOF slag also allows for its use as aggregates in concrete.

Acknowledgments

The research funding from Hunan Provincial Science and Technology Department (Hunan Province Key Research Project, 2017WK2090) and the National Natural Science Foundation of China (NSFC International (Regional) Cooperation and Exchange Program, 51750110506) are gratefully acknowledged.

References (114)

  • Y.C. Ding et al.

    Study on the treatment of BOF slag to replace fine aggregate in concrete

    Constr. Build. Mater.

    (2017)
  • A. Drizo et al.

    Phosphorus removal by electric arc furnace steel slag and serpentinite

    Water Res.

    (2006)
  • J. Geiseler

    Use of steelworks slag in Europe

    Waste Manage.

    (1996)
  • F. Han et al.

    Hydration heat evolution and kinetics of blended cement containing steel slag at different temperatures

    Thermochim. Acta

    (2015)
  • E.E. Hekal et al.

    Hydration characteristics of Portland cement – electric arc furnace slag blends

    HBRC J.

    (2013)
  • X. Huang et al.

    On the use of blast furnace slag and steel slag in the preparation of green artificial reef concrete

    Constr. Build. Mater.

    (2016)
  • R.I. Iacobescu et al.

    Ladle metallurgy stainless steel slag as a raw material in ordinary Portland cement production: a possibility for industrial symbiosis

    J. Clean. Prod.

    (2016)
  • R.I. Iacobescu et al.

    Valorisation of electric arc furnace steel slag as raw material for low energy belite cements

    J. Hazard. Mater.

    (2011)
  • R.I. Iacobescu et al.

    Synthesis, characterization and properties of calcium ferroaluminate belite cements produced with electric arc furnace steel slag as raw material

    Cem. Concr. Compos.

    (2013)
  • J.M. Kim et al.

    Improving the mechanical properties of rapid air cooled ladle furnace slag powder by gypsum

    Constr. Build. Mater.

    (2016)
  • L. Kriskova et al.

    Effect of mechanical activation on the hydraulic properties of stainless steel slags

    Cem. Concr. Res.

    (2012)
  • J. Li et al.

    Structural characteristics and hydration kinetics of modified steel slag

    Cem. Concr. Res.

    (2011)
  • J. Li et al.

    Building green supply chains in eco-industrial parks towards a green economy: barriers and strategies

    J. Environ. Manage.

    (2015)
  • Z. Li et al.

    Cementitious property modification of basic oxygen furnace steel slag

    Constr. Build. Mater.

    (2013)
  • Q. Liu et al.

    Effects of temperature and carbonation curing on the mechanical properties of steel slag-cement binding materials

    Constr. Build. Mater.

    (2016)
  • J.M. Manso et al.

    Durability of concrete made with EAF slag as aggregate

    Cem. Concr. Compos.

    (2006)
  • M. Maslehuddin et al.

    Comparison of properties of steel slag and crushed limestone aggregate concretes

    Constr. Build. Mater.

    (2003)
  • D. Mombelli et al.

    The effect of chemical composition on the leaching behaviour of electric arc furnace (EAF) carbon steel slag during a standard leaching test

    J. Environ. Chem. Eng.

    (2016)
  • A. Monshi et al.

    Producing Portland cement from iron and steel slags and limestone

    Cem. Concr. Res.

    (1999)
  • L. Muhmood et al.

    Cementitious and pozzolanic behavior of electric arc furnace steel slags

    Cem. Concr. Res.

    (2009)
  • N. Palankar et al.

    Durability studies on eco-friendly concrete mixes incorporating steel slag as coarse aggregates

    J. Clean. Prod.

    (2016)
  • S.Y. Pan et al.

    Integrated and innovative steel slag utilization for iron reclamation, green material production and CO2, fixation via accelerated carbonation

    J. Clean. Prod.

    (2016)
  • B. Pang et al.

    ITZ properties of concrete with carbonated steel slag aggregate in salty freeze-thaw environment

    Constr. Build. Mater.

    (2016)
  • B. Pang et al.

    Autogenous and engineered healing mechanisms of carbonated steel slag aggregate in concrete

    Constr. Build. Mater.

    (2016)
  • B. Pang et al.

    Utilization of carbonated and granulated steel slag aggregate in concrete

    Constr. Build. Mater.

    (2015)
  • M. Pasetto et al.

    Experimental evaluation of high performance base course and road base asphalt concrete with electric arc furnace steel slags

    J. Hazard. Mater.

    (2010)
  • M. Pasetto et al.

    Recycling of waste aggregate in cement bound mixtures for road pavement bases and sub-bases

    Constr. Build. Mater.

    (2016)
  • C. Pellegrino et al.

    Properties of concretes with black/oxidizing electric arc furnace slag aggregate

    Cem. Concr. Compos.

    (2013)
  • C. Pellegrino et al.

    Mechanical and durability characteristics of concrete containing EAF slag as aggregate

    Cem. Concr. Compos.

    (2009)
  • N.M. Piatak et al.

    Characteristics and environmental aspects of slag: a review

    Appl. Geochem.

    (2015)
  • H. Qasrawi

    The use of steel slag aggregate to enhance the mechanical properties of recycled aggregate concrete and retain the environment

    Constr. Build. Mater.

    (2014)
  • A.S. Reddy et al.

    Utilization of basic oxygen furnace (BOF) slag in the production of a hydraulic cement binder

    Int. J. Miner. Process.

    (2006)
  • N.H. Roslan et al.

    Performance of steel slag and steel sludge in concrete

    Constr. Build. Mater.

    (2016)
  • M. Salman et al.

    Effect of accelerated carbonation on AOD stainless steel slag for its valorisation as a CO2-sequestering construction material

    Chem. Eng. J.

    (2014)
  • M. Salman et al.

    Effect of curing temperatures on the alkali activation of crystalline continuous casting stainless steel slag

    Constr. Build. Mater.

    (2014)
  • M. Salman et al.

    Effect of accelerated carbonation on AOD stainless steel slag for its valorisation as a CO2-sequestering construction material

    Chem. Eng. J.

    (2014)
  • M. Salman et al.

    Cementitious binders from activated stainless steel refining slag and the effect of alkali solutions

    J. Hazard. Mater.

    (2015)
  • J.T. San-José et al.

    The performance of steel-making slag concretes in the hardened state

    Mater. Des.

    (2014)
  • A. Santamaría et al.

    The use of steelmaking slags and fly ash in structural mortars

    Constr. Build. Mater.

    (2016)
  • Y.N. Sheen et al.

    Innovative usages of stainless steel slags in developing self-compacting concrete

    Constr. Build. Mater.

    (2015)
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