Marta Skaf

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.

Fiber Reinforced Concrete Manufactured with Electric Arc Furnace Slag

The use of electric arc furnace slag (EAFS), a by-product of the steelmaking industry, as an aggregate in concrete has been demonstrated to be a good practice in its manufacture. Furthermore, the incorporation of fibers in concrete provides a more ductile behavior, increasing their tenacity and load capacity, improving the flexotraction strength and controlling shrinkage cracking. The purpose of this research was to study the performance improvement by reinforcing steel-slag concrete with metallic or synthetic fibers added in different amounts. Some of the properties evaluated were: consistency of freshly mixed concrete by Abrams cone, compressive strength, flexotraction strength and indirect tensile strength. The results show a substantial improvement of the performance of the steel-slag concrete when it is reinforced with fibers. It also fulfils the requirements of “depth of water penetration under pressure” test, even in the worst environmental exposure case.

Porous Asphalt Mixtures with 100% Siderurgic Aggregates

In this research, the possibility of making a porous asphalt mixture manufactured completely with recycled aggregates from carbon steel production was explored. Electric arc furnace slag (EAFS) was used as coarse aggregate and ladle furnace slag (LFS) as fine aggregate and filler. Initially, the properties of both slags and their suitability to be used in the manufacture of porous mixtures were analyzed. Then, a series of asphalt mixtures were developed incorporating these slags and they were compared with a reference mixture, made with conventional components. A series of tests were performed, including concepts such as mechanical behavior, durability, moisture susceptibility, rutting resistance, permeability or skid resistance. The results show that it is possible to make a suitable porous asphalt mixture with 100% of steel slag aggregates, complying with the standard requirements and obtaining a durable and environmentally sustainable mixture.

Performance of Hydraulic Mixes Manufactured with Electric Arc Furnace Slag Aggregates

Electric arc furnace slag (EAFS) has for many years simply been dumped in landfill sites; over the past few decades many researchers have investigated its reuse in cement mortar and concrete. By doing so, a waste product may be converted into a useful material with added value as a substitute for natural resources, the consumption of which is also minimized. Hydraulic mixes manufactured with EAFS normally have similar or even better hardened properties than mixes manufactured with natural aggregates. One disadvantage in the use of EAFS has been the poorer workability of the mixes, due to its higher density, porosity and water absorption levels. In this research, different EAFS mixes are manufactured and their properties in the fresh and the hardened state are closely analyzed; the results were very promising. The aim of this research is to demonstrate that EAFS concrete can achieve an acceptable workability at the correct dosages.