## 3 Test Results and Discussions
### Marshall Test Value  
The Marshall Test variable values for the three asphalt mixture gradients containing different BOF slag contents are shown in Table 6. In Table 6, the stability of dense, SMA, and PA-graded asphalt mixtures will be increased with the increasing BOF slag substitution ratio. The apparent specific gravity of the BOF slag is greater than the traditional aggregate and has a better load-bearing capacity; the asphalt film attached to the aggregate surface is also thicker. The stability of SMA and PA-graded asphalt mixtures is greater than that of the dense-graded ones. The stability of dense, SMA, and PA-graded mixtures were between 16.4 to 20 kN; 16.5 to 20.2 kN; and, 16.4 to 20.4 kN, respectively. The stability of all the asphalt mixtures complies with the minimum requirement value of 80 kN. The flow value of asphalt mixture decreases with the increase in the BOF slag substitution ratio; furthermore, if the flow value is too high, it means that permanent deformation may easily result for the pavement, possibly causing the phenomenon of plastic flow. However, the flow value of SMA and PA mixtures is much higher than that of the dense-graded mixture, which might indicate that the porosity of SMA and PA gradation lack the fine aggregate filled void among the aggregate. As well, the optimum amount of asphalt cement is high; thus, relative skidding may easily occur among aggregates, increasing the flow value. The unit weight of the asphalt mixture will increase with the increased BOF slag substitution ratio. BOF aggregate contains CaO, and its apparent specific gravity is greater than that of natural aggregate. Design coarse aggregate ratios of SMA and PA mixtures are more than that of the dense-graded  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Gradient**} & \multirow{2}{*}{**BOF (\%)**} & \multirow{2}{*}{**Optimum Asphal**} & \multirow{2}{*}{**Unit**} & \multirow{2}{*}{**Air Voids (\%)**} & \multirow{2}{*}{**VMA**} & \multirow{2}{*}{**VFA**} & **Flow** & **Stability** \\  & & & **Content (\%)** & & & & **(0.25 mm)** & **(0.8N)** \\ \hline \multirow{4}{*}{Dense} & 0 & 5.25 & 2.362 & 3.6 & 14.6 & 72.2 & 8.75 & 16.43 \\  & 20 & 5.20 & 2.420 & 3.5 & 17.7 & 72.9 & 8.25 & 17.  
mixture, and BOF slag was used to substitute for coarse aggregate; therefore, the unit weight of the asphalt mixture is obviously higher than that of the dense-graded one. The void ratio is the ratio that is occupied by the void after mixing aggregate with an asphalt binder, and the specification is set at 3-5%. The results showed that the void ratio of asphalt mixture decreased with the increased BOF slag substitution ratio. Since SMA and PA mixtures lack fine aggregate to fill the voids among aggregate particles, mixtures need more asphalt binder to achieve void replacement so as to comply with the specification set at 3-5% for the asphalt mixture void ratio. Nevertheless, since the apparent specific gravity between BOF slag and natural aggregate differs from each other, the compaction energy would cause aggregate fracture in the rolling process, making the gap-aggregate for gradation. As a result, the aggregate particles of dense-graded asphalt mixture might be rearranged, leading to the plastic flow or causing an increased void ratio for the asphalt mixture. VMA is the occupation percentage of void in compacted aggregates without adding asphalt, and the standard specification is set at 13-14% as the minimum value. Rutting permanent may result if the value is less than the minimum value. The results showed that the asphalt mixture VMA value decreased with the increased BOF slag substitution ratio. The VMA value of the SMA-graded mixture is greater than that of the dense and PA-graded ones. BOF slag has porous properties, and asphalt cement can easily be permeated into the aggregate.