This paper presents results of mineralogical and chemical research connected with the polymorphic transformations of dicalcium silicates in aggregate based on open-hearth slag and also slags from the current production of EAF (electric arc furnaces), and LF (ladle furnaces). Particular attention was paid to the transformation of the polymorph β-Ca2[SiO4] into the variant γ-Ca2[SiO4], which is undesirable from the perspective of using steel slags in road construction. A full mineralogical characterization of the tested metallurgical slags enabled the verification of the effectiveness of detecting the decomposition of dicalcium silicate in observations in UV light in line with the PN-EN 1744- 1+A1:2013-05 standard. On the basis of the conducted research, it was found that in the aggregate based on open-hearth slags and in the EAF furnace slag, dicalcium silicates are mainly represented by the β-Ca2[SiO4] polymorph, accompanied by α’-Ca2[SiO4]. The slag from the LF furnace was characterized by a different composition, with a strong advantage (57%) of the α’-Ca2[SiO4] variety, with a 1% share of the β-Ca2[SiO4] and 15% of the γ-Ca2[SiO4].
It was found that the transformation of β-Ca2[SiO4] into γ-Ca2[SiO4] can take place only under certain conditions in the metallurgical process, but the process is not influenced by hyperergenic factors, as evidenced by the fact that after more than 100 years of storage of open-hearth slag, on the basis of which the aggregate was produced, it was primarily marked with all the variants of β-Ca2[SiO4], without the polymorph γ-Ca2[SiO4].
The comprehensive characterization of the slag phase composition requires use of an appropriately selected research methodology; this is of key importance prior to the secondary use of this material, especially in the presence of the γ-Ca2[SiO4] polymorph. It has been determined that the most accurate test results are obtained using the XRD technique. The method of determining the decomposition of dicalcium silicate according to the PN-EN 1744-1+A1:2013-05 standard proved to be unreliable. It seems that in the situation of using LF slag as an artificial aggregate, taking the test results according to the method described in the PN-EN 1744-1+A1:2013-05 standard as being decisive is very risky, especially on a large scale (e.g. in communication construction).

With the rapid development of industry, abundant industrial waste has resulted in escalating environmental issue. Steel slag is the by-product of steel-making and can be used as cementitious materials in construction. However, the low activity of steel slag limits its utilization. Much investigation has been conducted on steel slag, while only a fraction of the investigation focuses on the effect of steel slag particle size on the properties of mortar. The aim of this study is to investigate the effect of steel slag particle size as cement replacement on properties of steel slag mortar activated by sodium sulphate (Na2SO4º. In this study, two types of steel slag, classified as fine steel slag (FSS) with particle sizes of 0.075mm and coarse steel slag (CSS) with particle sizes of 0.150 mm, were used for making alkali activated steel slag (AASS) mortar. Flow table test, compressive strength test, flexural strength test and UPV test were carried out by designing and producing AASS mortar cubes of (50 x 50 x 50) mm at 0, 10%, 20% and 30% replacement ratio and at 0.85% addition of Na2SO4. The results show that the AASS mortar with FSS possess a relatively good strength in AASS mortar. AASS mortar with FSS which is relatively finer shows a higher compressive strength than CSS up to 38.0% with replacement ratio from 10% to 30%. This study provided the further investigation on the combined influence of replacement ratio and particle size of SS in the properties of fresh and hardened AASS.

Steel slag stone can be used as a substitute for coarse aggregate in concrete. In this study, the performance of steel slag concrete (SSC) in the wall brick structure was analyzed. The specimens with a steel slag replacement rate of 0%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% were designed, and the slump, stability, and carbonation resistance were tested. The results showed that the slump decreased with the increase of the replacement rate of steel slag stone. At the 60th min, the slump of SSC50 was 74 mm, which was 25.25% smaller than SSC00. When the replacement rate was more than 30%, cracks or fractures appeared, and the stability was destroyed. Twenty-eight days after the carbonation experiment, with the increase of the replacement rate, the carbonation resistance of the specimen decreased, and the performance was best when the replacement rate was 25%. The experimental results show that the performance of SSC is the best when the replacement rate of steel slag stone is 25%, which can be further promoted and applied in practice.

This study was carried out to evaluate the effect of steel slag (SS) as a by-product as an additive on the geotechnical properties of expansive soil. A series of laboratory tests were conducted on natural and stabilized soils. Steel slag (SS) was added at a rate of 0, 5, 10, 15, 20, and 25% to the soil. The conducted tests are consistency limits, specific gravity, grain size analysis, modified Proctor compaction, free swell, unconfined compression strength, and California Bearing Ratio. The Atterberg limit test result shows that the liquid limit decreases from 90.8 to 65.2%, the plastic limit decreases from 60.3 to 42.5%, and the plasticity index decreases from 30.5 to 22.7% as the steel slag of 25% was added to expansive soil. With 25% steel slag content, specific gravity increases from 2.67 to 3.05. The free swell value decreased from 104.6 to 58.2%. From the Standard Proctor compaction test, maximum dry density increases from 1.504 to 1.69 g/cm3 and optimum moisture content decreases from 19.77 to 12.01 %. Unconfined compressive strength tests reveal that the addition of steel slag of 25% to expansive soil increases the unconfined compressive strength of the soil from 94.3 to 260.6 kPa. The California Bearing Ratio test also shows that the addition of steel slag by 25% increases the California Bearing ratio value from 3.64 to 6.82%. Hence, steel slag was found to be successfully improving the geotechnical properties of expansive soil.

This paper presents the results of tests of selected physical and mechanical properties as well as the chemical composition of two types of natural aggregates: porphyry and diabase, as well as artificial aggregate based on steel slags. Based on the conducted tests, it was established that the physical and mechanical properties of the artificial aggregate exhibit slightly lower parameters as compared to the results obtained for porphyry and diabase aggregates. However, this does not limit the possibility of using the aggregate based on steel slags, as according to the applicable WT-4 and WT-5 standards, it can be used in mixtures unbound to the improved subsoil and layers of the road foundation as well as road mixtures with hydraulic binders for each category of traffic load. The chemical composition of the aggregate based on steel slags differs from the chemical composition of the tested natural aggregates. The slags contain lower amounts of SiO2 and Al2O3, while the concentration of CaO and Fe2O3 is greater. Additionally, heavy metals have also been exhibited in the slags. However, it was established that the alkaline nature of the slags, which is affected by low sulphur content and a significant proportion of CaO, as well as the way the metals occur limit the possibility of heavy metals release and migration from slags. The tested steel slags may constitute a prospective material used in road construction.

The present study addresses the utilization of induction furnace steel slag which is an anthropogenic waste, for enhancing the mechanical properties of a commercial aluminium alloy A356. Different weight percentage (3wt%, 6wt%, 9wt%, and 12wt%) of steel slag particles in 1 to 10 μm size range were used as reinforcing particles in aluminium alloy A356 matrix. The composites were prepared through stir casting technique. The results revealed an improvement in mechanical properties (i.e. microhardness and tensile strength) and wear resistance with an increase in weight percentage of the steel slag particles. This research work shows promising results for the utilization of the steel slag for enhancing the properties of aluminium alloy A356 at no additional cost while assisting at same time in alleviating land pollution.