**1. Introduction**

Due to its versatility and low cost, reinforced concrete is the most frequently used structural material in the field of building and engineering; it reaches annual volumes of 10 km3/year and causes major environmental problems. The manufacture of Portland cement produces between 5% and 8% of global CO2 emissions due to human activity [1–3].

The regulations [4–7] specify the importance of durability in reinforced concrete and take as a determining factor the corrosion of embedded reinforcement steel.

Corrosion of embedded steel reinforcement may occur through carbonation of the concrete cover, the presence of chlorides, or the combination of both. These are the factors which trigger the corrosion process and transfer the reinforcement from the passive state, in which the corrosion rates are barely significant, to the active state, in which corrosion affects the durability of concrete structures.

Besides these triggering factors, the continuous presence of oxygen and humidity is necessary as these are the controlling factors for the rate of the corrosion process. In practice, the presence of chlorides in concrete is a determining factor in the onset of reinforcement corrosion. In general, a threshold level of 0.4% of chloride ions by weight of cement is considered, as proposed by RILEM Committee 60-CSC [8].

Moreover, the particular feature of steel as an indefinitely recyclable material has meant that the use of scrap iron has become increasingly widespread in steel production at a global level. World crude steel production reached 1689.4 million tons (Mt) for the year 2017 [9]. Steel production in Spain has been increasing over the years, reaching 14.5 million tons in 2017 [10]. This provides major environmental benefits as a ton of steel manufactured in electric arc furnaces (EAF) consumes only 9–12 GJ/tcs, with a consequent reduction in CO2 emissions, though the continuous increase

in steel production has been the cause of a significant increase in environmental problems over the years [11,12].

EAF steel production generates approximately 120 to 180 kg of black slag and 20 to 30 kg of white slag for each ton of steel produced [13]. The volume of ladle furnace slag (LFS) generated in the European Union was 2.0 million tons in 2016 [14], while in Spain, with 70.5% of the steel produced by EAF, the volume of white slags was between 0.20 and 0.31 million tons in 2017 [10].

Among the most immediate applications of the LFS are the manufacture of clinker, the partial substitution of aggregates and/or cement in mortars and concretes, and the stabilization of soils and pavements [15,16]. The characteristics of the slag that can be used in concrete depend on the different treatments they have received [17].

There is some research on the characterization of ladle furnace slags and their hydration properties. These studies show that the LFSs are a dusty material and are composed mainly of calcium oxide (50%), silicon (15%), aluminum (12%), and magnesium (9%). Its density is of the order of 2.7 g/cm<sup>3</sup> and associated important volumetric expansions are due to the high proportion of free lime. If this expansion is controlled, it does not imply any inconvenience for its use in construction materials [18–20]. There has also been some research that studied the behavior of mortars or concretes in which the aggregate and/or the cement was partially replaced by LFS and that indicate that its application is viable, improving the properties of mortars and sustainability both in traditional concretes and in self-compacting concretes [21–27].

Taking into account the previous premises, it is observed that although the corrosion process of steel bars embedded in concrete has been studied in various research projects [28–30], no studies have analyzed this process when ladle furnace slag is introduced into the concrete instead of some of its components. In this work, corrosion behavior was tested using electrochemical techniques in order to evaluate the corrosion rate and the effects produced in the reinforcements of the specimens with and without LFS. These specimens were initially subjected to a natural corrosion process and then to accelerated corrosion; this allowed us to determine the influence range of the LFS slag.
