Mix design and preliminary validation of sustainable asphalt concrete manufactured with electric arc and ladle furnace steel slags

In the manufacture of carbon steel in Spain and Italy, there is a prevalent process known as “the electric cycle”, which involves melting scrap in an Electric Arc Furnace (EAF) and then refining the steel in a Ladle Furnace (LF). In this process, the main residues generated are two types of slag: the EAF Slag and the LF Slag. The excellent properties of EAF slag are well known and guarantee its successful use as a coarse aggregate in the manufacture of bituminous mixtures. On the other hand, research and application concerning the use of LF slag in asphalt mixtures are still at an early stage notwithstanding such slag has appropriate particle size and promising chemical features to be used as fine aggregate and/or filler. In this research, a rational approach to manufacturing dense graded asphalt concrete exclusively with steel slag aggregates is developed, not using any natural aggregate and thus providing sustainable (and high-performance) asphalt mixes. The design of this mix involves using EAF slag as coarse aggregate and LF slag as fine aggregate and filler. A laboratory test program was organized to accomplish this objective based on the evaluation of different bituminous mixtures incorporating these slags. Such mixtures were designed according to the Marshall procedure and then compared with a reference material (manufactured with conventional aggregates). In particular, natural filler, fine aggregate and coarse aggregate of the reference mixture were progressively replaced by the corresponding slag in order to highlight the contribution of the different fractions. The laboratory study was carried out by performing different tests analysing mechanical behaviour, durability and moisture susceptibility. The results arising from this preliminary research show that, although some refining may be done in the mix design, a sustainable asphalt concrete manufactured entirely with steel slag aggregates can be successfully achieved