## 4 Results  
### Effect of Different Additives on WMA Behaviour  
Figure 1 shows the curves of densification (reduction in air void content) of the asphalt mixtures manufactured at 145 \({}^{\circ}\)C (Figure 1a) and 120 \({}^{\circ}\)C (Figure 1b) with 0.5% of various additives, as well as the curve measured for the conventional HMA. From the results, it is clear that the use of additives during the manufacturing of mixtures at 145 \({}^{\circ}\)C allows for workability that is comparable to that obtained for the conventional HMA, since quite similar air void content (near 4.5-5.5%) was recorded, highlighting the case of the additive A2. In addition, the workability study showed that the use of these chemical additives to reduce the manufacturing temperature to around 20 \({}^{\circ}\)C allows for values of density higher than 98%, in reference to the conventional HMA (2.44 Mg/m\({}^{3}\)), which indicates its suitability for application in pavements for roads, avoiding the problems often associated with the low level of compaction for this material [26]. For the mixtures manufactured at a lower temperature (around 120 \({}^{\circ}\)C), the results revealed that in this case the effectiveness of the additives is slightly lower than in the previous case (manufactured at 145 \({}^{\circ}\)C), since higher values of air void content were recorded, indicating lower compaction of the asphalt mixture associated with lower workability due to the increase in bitumen viscosity when the temperature is reduced. Nonetheless, the additives A1 and A2 led to decrease in densification in reference to that presented by the HMA, which allows for density values close to 98%, which was measured for the conventional hot mix asphalt. This shows that the use of these two additives could be appropriate for manufacturing WMA at 120 \({}^{\circ}\)C whilst adequate workability and compaction characteristics are obtained in reference to traditional HMA, which is in accord with other studies examining the use of additives for WMA [27; 28]. Therefore, these results suggest that the use of these two additives reduces susceptibility to manufacturing temperature with respect to the additive A3, which led to a significant decrease in density when the temperature was reduced from 145 \({}^{\circ}\)C to 120 \({}^{\circ}\)C.  
Figure 1: densification curves of the mixtures with various additives and different manufacturing temperatures. (**a**) 145 \({}^{\circ}\)C vs. 165\({}^{\circ}\)C; (**b**) 120\({}^{\circ}\)C vs. 165\({}^{\circ}\)C.  
In order to obtain a more in-depth study of the influence of the different additives, Figure 2 displays the values of Indirect Tensile Strength (ITS measured in kPa) measured for the specimens from the workability study (with gyratory compactor) for the different mixtures at low temperatures with the additives A1, A2 and A3, as well as the results obtained for the HMA. In addition, the Indirect Tensile Strength Ratio (ITSR) values obtained in the water sensitivity test [22] are shown in order to evaluate the moisture susceptibility of the various mixtures analysed. According to the results, it appears that the use of the different additives to manufacture WMA at 145 \({}^{\circ}\)C leads to quite similar values of ITS to those measured for the HMA, thereby avoiding the failure of the mixture associated with the reduction in adhesion and cohesion due to the decrease in manufacturing temperature, which could in turn lead to coating problems. Similarly, application of the additives generally improved the ITSR values, which reflects an important reduction in water sensitivity for the WMA manufactured at 145 \({}^{\circ}\)C when using the additives analysed. These findings are also in agreement with other studies that employed chemical additives to act as anti-stripping agents [29; 30].