# Potential of Waste Oyster Shells as a Novel Biofiller for Hot-Mix Asphalt
## 3 Results
### Dynamic Shear Rheometer (DSR) Test  
#### 3.7.1 Putting Performance (G*/sin \(\delta\))  
The high temperature performance grade of each bitumen sample was determined using DSR (i.e., dynamic shear rheometer) test results (G*/sin \(\delta\)) and the Superpave (i.e., Superior Performance Asphalt Pavement) binder specification. Based on the specification to minimize rutting, G*/sin \(\delta\) at 10 rad s\({}^{-1}\) must have a minimum of 1 kPa for unaged bitumen sample and 2.2 kPa for rolling thin-film oven (RTFO)-aged bitumen sample [38]. The Superpave rutting parameter G*/sin \(\delta\) is inversely proportional to the dissipated energy, and thus higher G*/sin \(\delta\) will have lesser dissipated energy, and thus higher rut resistant. Figure 8 shows the DSR results, at various temperatures (e.g., 52, 58, 64, and 70 \({}^{\circ}\)C), for the unaged base asphalt (i.e., AP-5 OSP 0 wt %) and unaged asphalt containing different fractions of OSP (e.g., 5, 10, 15 wt %). The performance grade of neat asphalt (i.e., AP-5 OSP 0 wt %) was 64 \({}^{\circ}\)C prior to failure at 70 \({}^{\circ}\)C. Whereas, the 5 and 10 wt % OSP-filled asphalt samples can resist rutting until 70 \({}^{\circ}\)C. Their rutting parameters (G*/sin \(\delta\)) were higher than those of the neat asphalt sample. The G*/sin \(\delta\) values recorded at 70 \({}^{\circ}\)C for 5, 10, and 15 wt % OSP, were 1175, 1484, and 832 Pa, respectively. The most outstanding value of rutting resistance was observed with 10 wt % OSP. High rutting parameter was observed from 52 \({}^{\circ}\)C to 70 \({}^{\circ}\)C. The rutting resistance increased as the OSP content increased up to 10 wt % OSP, followed by a decrease with 15 wt % OSP. This may be due to the agglomeration among the OSP particles with further increment of additive in asphalt cement blends. Generally, this finding showed that the OSP increased the stiffness of the virgin bitumen. The mineral particles (i.e., CaCO\({}_{3}\)) seemingly reinforced the bitumen matrix by increasing the bond strength between the filler and binder combinations, improving thereby the cohesion of the bitumen. Consequently, the bitumen properties were enhanced by increasing the stiffness and improving rutting performance. The RTFO-asphaltic samples shown in Figure 9 demonstrate clearly that both the unfilled and 15 wt % OSP-filled asphalt samples resisted rutting until 64 \({}^{\circ}\)C before failing at 70 \({}^{\circ}\)C. After short-term aging, all the samples obviously became markedly stiff, thereby increasing the rutting resistance. The asphalt mixtures containing 5 and 10 wt % OSP showed higher performance compared to the neat asphalt and asphalt treated with 15 wt % OSP at all the tested temperatures practically. These results are in tune with those obtained from unaged OSP-asphalt mastic samples. The rutting resistance values of the asphalt filled with 10 wt % OSP at 52 \({}^{\circ}\)C were 17,250 Pa and 2794 Pa at 70 \({}^{\circ}\)C, which were the highest of all aged asphalt samples. Furthermore, rutting performance showed significant differences between the OSP contents. The 15 wt % OSP obtained the lowest rutting parameters at 64 \({}^{\circ}\)C and 70 \({}^{\circ}\)C with G*/sin \(\delta\) of 2960 and 1886 Pa, respectively. This asphalt exhibited a lower stiffness than the OSP-filled asphalt samples during short-term aging. The large surface area of the OSP absorbs and distributes the heat rapidly relative to the unfilled asphalt, which stands alone at distributing the heat in the slow rate and causing the bitumen to age swiftly. Therefore, 10 wt % OSP was the optimum dose that could retard the aging of the bitumen at higher temperature compared with other OSP fractions (e.g., 5 and 15 wt %). The results of penetration and softening point tests shown in Table 4 confirm the positive impact of OSP on high temperature of filled bitumens.