# Utilization of Industrial Ferronickel Slags as Recycled Concrete Aggregates
## 3 Results
### Results of Concrete Specimens  
Regarding the physical properties of investigated concrete specimens such as density, concrete specimens produced by natural aggregates (limestones) show density from 2621 to 2709 kg/m\({}^{3}\) (Figure 8a, Table 6). As for the specimens made from various percentages of two different slags (FeNi and ELECTRIC ARC FURNACE SLAG), samples of SA group present values of density range from 3093 to 3125 kg/m\({}^{3}\), samples of SB group values from 3095 to 3181 kg/m\({}^{3}\) and these of SC group from 3060 to 3169 kg/m\({}^{3}\) (Figure 8a). Samples of SA group display water absorption, which ranges from 0.68 to 1.08%, samples of SB group from 1.01 to 1.59% and these of SC group from 1.09 to 1.48% (Figure 8b, Table 6). Furthermore, the uniaxial compressive strength (UCS) of the produced concrete specimens was measured. The compressive strength of the standard concrete specimens (produced by natural aggregates) ranges from 36.00 to 38.00 MPa in 7 days and from 47.00 to 48.50 MPa in 28 days (Figure 8c). In 7 days, the UCS of SA group ranges from 62.24 to 66.35 MPa, while in 28 days ranges from 75.80 to 83.42 MPa simultaneously indicating these samples as those presenting the highest concrete strength (Figure 8c,d, Table 6). As for the SB group, the UCS in 7 days it ranges from 50.02 to 56.91 MPa and from 57.12 to 61.74 MPa in 28 days (Figure 8c,d). The UCS of SC group in 7 days ranges from 45.53 to 55.18 MPa and in 28 days from 52.84 to 66.85 MPa (Figure 8c,d, Table 6). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **Specific Gravity (T/m\({}^{3}\)) of FeNi** &
\begin{tabular}{c} **Specific Gravity (T/m\({}^{3}\)) of** \\ **Electric Arc Furnace Slag** \\ \end{tabular} \\ \hline S01 & 2.70 (limestone) & \\ S02 & 2.70 (limestone) & \\ S03 & 2.70 (limestone) & \\ SA1 & 4.51 & 3.61 \\ SA2 & 4.51 & 3.61 \\ SA3 & 4.61 & 3.59 \\ SA4 & 4.51 & 3.61 \\ SA5 & 4.51 & 3.61 \\ SA6 & 4.61 & 3.59 \\ SB1 & 4.59 & 3.52 \\ SB2 & 4.54 & 3.70 \\ SB3 & 4.56 & 3.60 \\ SB4 & 4.59 & 3.52 \\ SB5 & 4.54 & 3.70 \\ SB6 & 4.56 & 3.60 \\ SC1 & 4.59 & 3.45 \\ SC2 & 4.62 & 3.51 \\ SC3 & 4.70 & 3.56 \\ SC4 & 4.72 & 3.61 \\ SC5 & 4.71 & 3.70 \\ SC6 & 4.69 & 3.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of the specific gravity test of the tested slags. As for the concrete specimens made by slags, the presence of fractures between the slags and the cement paste is partially observed (Figure 8). Moreover, samples SA1-SA6 and SC1-SC6 are characterized by satisfactory bonding with the cement paste (Figure 9a-d,f,h). On the contrary, samples SB1-SB6 presents lower microroughness and unsatisfactory bonding with the cement paste, which indicated from the zone around twisting grains which acts as detachment zone during the load (Figure 9e,g). During the petrographic study of the concrete specimens, a large number of twisting and spinel crystals were found to have been detached from the cement paste on a large scale after loading, while in none of the studied slags crystalline microcracks were found penetrating their mass. The general microroughness of the mineral components of the slags does not show any increase which is likely to work adversely within the concrete.