*Article* **Utilization of Industrial Ferronickel Slags as Recycled Concrete Aggregates**

**Petros Petrounias 1,2,\*, Aikaterini Rogkala 1, Panagiota P. Giannakopoulou 1, Angeliki Christogerou 3, Paraskevi Lampropoulou 1, Spyridon Liogris 4, Petros Koutsovitis <sup>1</sup> and Nikolaos Koukouzas <sup>2</sup>**


**Abstract:** The scope of this study focuses on the use of two different types of industrial byproducts such as slags (FeNi and Electric Arc Furnace slag) combined with natural sand as concrete aggregates as well as the evaluation of their suitability on the final physicomechanical behavior of the produced concrete specimens. For this reason, twelve concrete specimens were prepared using variable concentrations of these slags which were compared to concrete specimens made by natural rocks as aggregates (limestones). The mineralogical, petrographic, chemical and morphological characteristics of these raw materials were related to the physicomechanical characteristics of the produced concrete specimens. Those concrete specimens containing aggregates of higher amount of Electric Arc Furnace slags seems to present better mechanical strength both in 7 and in 28 days of curing regarding the other mixtures and regarding the specimens made by natural rocks as aggregates (limestones). This is due to the mineralogical, textural and morphological characteristics of the tested slags, which lead to a better bonding between them and the cement paste making them at the same time a promising alternative in the production of green concrete for construction applications. The compact texture of slags is responsible for the stronger bonding with the aggregates in relation to the unevenly distributed porosity of the natural aggregates. Wüstite presents negative effect on the final mechanical strength of concrete specimens which is documented both by the microscope images and by the three-dimensional study of the produced concretes.

**Keywords:** industrial by products; slags; recycled concrete; recycled aggregates
