# Effect of Micro-Silica Addition into Electric Arc Furnace Steel Slag Eco-Efficient Concrete
## 3 Results and Discussion
### Hardened Properties
#### 3.2.1 Compressive Strength  
The result is obtained by dividing this force by the cross section of the sample. Compressive strength increased with age of the samples. In the mixing schemes of this study, the ratio of water to cement is the same. Therefore, the effect of this factor is the same in all concretes, and the variable factor in this study is the different percentage of EAFS as aggregates and cement have been consumed. Fracture speed in samples with 100% coarse EAFS aggregates was faster than in samples with 100% fine EAFS aggregates. Due to the fact that all the factors in the mixing design and processing steps are the same in all samples, as well as using the same speed and pressure to crack the samples, this can only be due to the type and size of aggregates used. Figure 8 shows an example of breaking different designs under constant pressure and velocity. Figure 9 shows consumable cement, due to high softness, has a significant effect on concrete compressive strength, so that compressive strength in 10 days has gained more than 50% compressive strength in 28 days. Figure 5: Slump of concrete containing different percentages of micro-silica (**left**) and slump of concrete optimal each of the previous parts (**right**). Figure 6: Density of concrete containing different percentages of EAFS (**left**) and density of concrete containing 25% of slag (**right**). In all designs, with increasing replacement of EAFS aggregates in the samples, we see an increase in compressive strength to control concrete. By replacing EAFS as aggregates (coarse and fine) from zero to 100%, we see an increase in compressive strength. As can be seen in Figure 10 samples with coarse-aggregates, EAFS show higher compressive strength than samples with EAFS fine-aggregates replacement, but this amount is not very high; as expected, the highest amount of resistance is related to the replacement of 100% of natural aggregate with EAFS. It is observed that the replacement strengths of 75% and 100% of coarse aggregates have the same and close behaviour, which is also observed in 50% and 75% of fine grains. By replacing the top of the consumed aggregates with natural aggregates, the strength of the samples increases sharply, but this increase in resistance is also accompanied by a large increase in the density of the samples. After 90 days, it is observed that the strength of 25, 50 and 75% EAFS fine-aggregates samples is equal to the strength of samples with 25 and 50% EAFS coarse-aggregates. To control the specific gravity of the samples, which do not become too heavy during the next steps, 25% coarse and fine aggregates replacement with 90-day resistance with 100% fine-aggregates replacement strength and 50 and 75% coarse-aggregates replacement are close and imperceptible. Considering the sustainability of EAFS and its lack of reactivity with other materials, the behaviour and reaction between cement and EAFS is only a physical reaction, and no chemical reaction occurs. Figure 10 shows that in the same sizes of aggregates, EAFS have better performance than natural aggregates in compressive strength, so that by replacing 50% aggregates, compressive strength of about 10 MPa increases compared to control concrete (A\({}_{3}\)). The particle size used by micro-silica used in this study has had a great impact on the process of acquiring concrete strength. This led the activity between cement and micro-silica, and concrete reached the ultimate resistance earlier than normal, also increasing compressive strength in concrete, with an increase of 10 MPa to the substance, the final resistance being about 71 MPa. EAFS aggregates have a higher density than natural aggregates, but as shown in Figure 11, EAFS aggregates have a good dispersion on the concrete surface, and this may indicate that despite the heavier weight of this aggregate, it can be used without worrying about settling in the concrete due to the transport time or vibration of the concrete.