# Methodology for Efficient Bitumen Storage with Reduced Energy Consumption
## 3 Results and Discussion
### Penetration Index and Temperature Susceptibility  
The penetration index is a quantitative measure of the response of bitumen to a given temperature. It represents the temperature susceptibility of bitumen, which is how fast the binder changes its consistency as temperature changes. The lower the penetration index,  
Figure 6: Ageing index for penetration at 25 \({}^{\circ}\)C.  
Figure 7: Ageing index for the softening point R&B. the faster the binder changes its consistency as the temperature changes (which shows greater temperature susceptibility). This index, conceived by [PERSON] and [PERSON] [28], is calculated from the penetration and softening point values (Equation (10)). It provides a criterion for measuring the susceptibility of bituminous materials to temperature changes. It also helps in predicting their rheological behavior. Most of the bitumens used in road construction have penetration index values between \(-1\) and \(+1\). In this range, bitumens have intermediate characteristics between elasticity and viscous behavior [29]. \[\text{PI}=\frac{1952-500\,\log\,\text{pen}-20\,\text{softening point}}{50\,\log\, \text{pen}-\text{softening point}-120} \tag{10}\]  
The value of the temperature susceptibility varied from 0.0015 and 0.06, and we calculated it using Equation (11). [PERSON] and [PERSON] developed this equation assuming a temperature susceptibility value of about zero for road bitumen [30]. \[50\text{S}=\frac{20-\text{PI}}{10+\text{PI}} \tag{11}\]  
We calculated the penetration index for our three samples according to Equation (10), and the results are shown in Table 3. Then, we calculated the temperature susceptibility using Equation (11) and represented the results in Figure 8. We can see from Table 2 that the PI values of BP and BP + RT are the same, whereas it decreased a little for BP + TC. Observing Figure 8, the temperature susceptibility values of BP and BP + RT are the same (0.045), whereas that of BP + TC (0.046) has increased by 0.001, which we can consider negligible. Thus, these results confirm the previous results, showing that the control sample and the room-temperature-stored sample are the same, which means that bitumen storage at 25 \({}^{\circ}\)C for 90 days does not affect its physical properties. Although the thermally cycled sample exhibits a small change, we can store bitumen in a dynamic temperature-heating regime, between 140 and 160 \({}^{\circ}\)C, for three months or less. The difference in physical properties was imperceptible for three months of storage and will be more negligible or nonexistent if the storage duration is shorter. We observe from Figure 9 that the BP at its unaged state shows no carbonyl peak, whereas the Sulfoxide peak at 1036 cm\({}^{-1}\) is present. After short-term ageing, the sulfoxide peak is wider, which indicates an increase in sulfoxide group formation, and we can see a weak, broad carbonyl peak at 1739 cm\({}^{-1}\) (aldehydes). After long-term ageing, we can see that the sulfoxide peak is larger, and we observe the appearance of a broad peak of carbonyl at 1700 cm\({}^{-1}\) (ketones). Both the sulfoxide group and the carbonyl group changed significantly after ageing; thus, they can reflect the ageing degree of bitumen to a certain extent. The appearance of the absorption peak of the carbonyl group (C=O) is probably due to the oxidation reaction of carbon and corresponds to the long-term ageing. From Figure 10, it is clear that BP + TC has the same behavior as BP. At the unaged state, it shows no carbonyl peak and a sharp sulfoxide peak at 1032 cm\({}^{-1}\). After short-term ageing, a carbonyl peak appears at 1730 cm\({}^{-1}\) (aldehydes), and the sulfoxide peak becomes larger. After long-term ageing, we observe a broad carbonyl peak at 1700 cm\({}^{-1}\) (ketones), and the sulfoxide peak is even larger.