Use of Iron and Steel Slags in Concrete: State of the Art and Future Perspectives

Abstract

In the two last decades, world production of pig iron and steel has undergone a significant increase. In 2018, 1252.87 and 1806.46 million tons of pig iron and steel, respectively, were produced as compared to the 575.78 and 809.94 million tons of 2000. Consequently, the amount of the different types of slags deriving from these production processes has also increased considerably. In relation to the principles of sustainability and circular economy, the available literature suggests several possible reuses for these slags (bituminous conglomerates, hydraulic engineering, metallurgy, fertilizers, etc.). This paper aims to provide an overview of the iron and steel slags production and their reuse in concrete (for example as replacement of cement, fine or coarse aggregates). The characteristics of slags are analyzed in terms of chemical, physical, and mechanical properties. Mechanical and durability tests (both from material and structures point of view) carried out in the different studies and research are shown as well. Particular attention was devoted to electric arc furnace slags (EAF) since they are the most produced in Italy. Based on this deep literature review, the gaps that still require further studies have been identified and discussed.

Exploring the Potential for Steel Slags Valorisation in an Industrial Symbiosis Perspective at Meso-scale Level

“…However, by consulting the MUD alone, there is the risk of obtaining a representation that is not the exact representation of the real situation of the steel industry, due to some weaknesses in the database layout, that, unfortunately, contribute to providing useful but incomplete data: The database contains information only related to steel slags classified as “waste”; there is no information on slags classified as “by-products” (which, on further investigation, represent, on average, about 30–40% of the annual steel slags production); Although the database allows searches to be carried out using the EWC code of interest, it is not possible to distinguish between slag from electric arc furnace (EAF) and slag from ladle furnace (LFS). This is due to the fact that the two types of slag are classified under the same EWC code by most of the steel mills operating in the area, despite the fact that they differ greatly in terms of chemical, physical and mineralogical properties, performance characteristics and fields of application and reuse [ 4 ]; By analysing sections BD and BE of the database, only partial information can be obtained on the disposal and recovery of slag classified as “waste”. In fact, disposal and recovery are only identifiable by the codes in Legislative Decree 152/2006, Annexes B and C of Part IV, from D1 to D15 for disposal and from R1 to R13 for recovery, respectively [ 55 ].…”

“…The BFS is then tapped from the blast furnace, in a range of approximately 250–300 kg per tonne of pig iron produced. Depending on the cooling process, the BFS can be divided in three main types [ 3 , 4 ]: GBS (“ Granulated Blast furnace Slag ”), produced after a quick cooling process with water to produce vitrified granulates, which can be used, after appropriate grinding treatments, in addition to concrete to partially replace the cement binder [ 5 – 9 ] or added to clinker for the production of Portland cement [ 10 ]; ABS (“ Air-cooled Blast furnace Slag ”), produced after a slow cooling process with air to produce crystalline material. This type of BFS slag will then be ground, sieved and graded to produce aggregates for road construction and concrete [ 11 – 13 ]; PBS (“ Pelletized Blast furnace Slag ”), produced after a quick cooling process with air to produce glassy or crystalline pellets.…”

“…The electric cycle is the main alternative to the integral cycle for steel production: it consists of a single step in the electric arc furnace starting from raw materials such as steel scrap (appropriately divided and selected), pig iron in small percentages and other minor additions [ 4 ]. Within the furnace, different reactions take place, which result in the formation of the primary material (molten steel) and the so-called “ Electric Arc Furnace slag ” (or “ EAF ”), in a range of approximately 150–180 kg per tonne of steel produced.…”

“…2 Summary of the two steps of the electric cycle and the secondary metallurgy process in the ladle furnace. Image modified and adapted from [ 4 ] …”

Bituminous base courses for flexible pavements with steel slags

“…Among the multiple uses of steel slag, the most widespread are: its reincorporation into the steel production process (Li et al, 2020;Varanasi et al, 2019) and its use in the construction sector, mainly as a substitute for natural aggregates and binders in the manufacture of concrete and cementitious composites (Brand and Fanijo, 2020;Piemonti et al, 2021) or bituminous mixtures (Li et al, 2018;Pasetto et al, 2017). One of the applications with the greatest potential is the incorporation of these materials in road pavements, replacing natural aggregates (Dondi et al, 2021;Maharaj et al, 2017).…”