## 4 Results
### Mineral Filler Application of BOF Slags  
The testing of AC samples made of stockpiled BOF filler and MP1 (limestone) filler in the proportions of 100-0%, 75-25%, 50-50%, 25-75%, and 25-75% with 0.4% DAD-KT additive produced the following results of the tensile strength at break up (crack), as shown in Figure 19.  
According to ST RK 1225, the crack resistance of AC mixes must meet the criteria of 3.5-6.5 MPa, which indicates that none of the mixtures corresponded to this range. From these values, it seems that the mixture with a 50-50 proportion of BOF filler and MP1 filler had the highest tensile strength at break (3.18), indicating better crack resistance compared to the other mixtures. However, it did not meet the crack resistance criteria currently outlined in the standard. Thus, in order to enhance the crack resistance of the asphalt concrete mixtures, considerations may need to be given to adjusting the mixture proportions, exploring alternative additives, or utilizing different types of fillers. Potential achievement of the crack resistance values specified within the range mentioned in ST RK 1225 could result from modifications to the mixture design. The compressive strength values of 5 AC mixes are given in Figure 20, which shows that the mixture with 25% BOF slag filler and the other mixture of 25% BOF plus 0.4% added DAD-KT correspond to the criteria of compressive strength of more than 1.3 MPa, as indicated in ST RK 1225 (Figure 20). The mixture's strength is influenced by factors such as the particle size distribution, reactivity, adhesion properties, and overall compatibility. Figure 19: Crack resistance results of 5 AC mixtures. Moreover, it was found that the residual porosity values of the five mixes were 11.63%, 10.35%, 8.59%, 7.11%, and 5.0%, respectively, for 100-0%, 75-25%, 50-50%, 25-75%, and 25-75% with 0.4% of DAD-KT additive mixtures. The residual porosity was established by the test method that determines the level of pores in a compacted asphalt mixture and is calculated based on the average density (\(\rho\_\)avg) and the true density (\(\rho\_\)true). Only the last mixture (25% BOF filler with 0.4% DAD-KT additive) provided a barely suitable result of 5.0%, as the limits for this criteria are 2.5 to 5.0%, as stated in ST RK 1225. Also, poor cohesion was demonstrated for the mixes of 100-0% and 75-25% (BOF-MP1 filler), as they had cohesion of less than 0.38, whereas the standard dictates this value to be more than 0.38. A cohesion value below the prescribed threshold implies that the particles within the mixtures lack effective bonding, potentially leading to compromised pavement integrity and performance. Poor cohesion in mixtures with BOF slag filler (100-0% and 75-25%) could be due to the irregular shapes and angular nature of BOF slag particles. This can hinder effective interlocking and bonding between particles, resulting in weak cohesion. However, other standard physical and mechanical properties of five AC mixes fully correspond to the criteria set in ST RK 1225. For example, in Figure 21 the compressive strength at 20 \({}^{\circ}\)C is given and all five mixtures have values of CS more than 2.5 MPa. Also, all five AC mixes have adequate values of water saturation (1.5-4.0 MPa), compressive strength at 0 \({}^{\circ}\)C (less than 13 MPa), internal friction coefficient (tg\({}_{\varphi}\)), which is not less than 0.83, water resistance (not less than 0.85%). This implies that:  
* Water saturation within the specified range indicates that these mixtures are resilient to moisture-related issues, which is crucial for the long-term durability of pavement structures;
* Compressive strength values below 13 MPa at 0 \({}^{\circ}\)C suggest that these mixtures can perform well under cold temperature conditions.