# Potential of Waste Oyster Shells as a Novel Biofiller for Hot-Mix Asphalt
## 3 Results
### Dynamic Shear Rheometer (DSR) Test
#### 3.7.2 Fatigue Cracking Performance (G*.sin \(\delta\))  
G*.sin \(\delta\) is the fatigue cracking factor in the Superpave (i.e., Superior Performance Asphalt Pavement) binder Specification. Requirement to address fatigue cracking in Superpave binder specification is that G*.sin \(\delta\) at 10 rad s\({}^{-1}\) shall not exceed 5000 kPa [38]. Thus, low values of G* and \(\delta\) are considered desirable attributes from the standpoint of resistance to fatigue cracking. The higher G*.sin \(\delta\) value, the more fatigue cracking is susceptible the bitumen. Figure 10 displays the fatigue cracking performance of the base asphalt (i.e., AP5 OSP 0 wt %) and asphalts treated with different concentrations of OSP (e.g., 5, 10, and 15 wt %) under the PAV (i.e., pressure aging vessel) condition.  
Figure 8: Effect of temperature on the rutting parameter of unfilled and OSP-filled asphalts under unaged condition.  
Figure 9: Effect of temperature on the rutting parameter of unfilled and OSP-filled asphalts under short-term aging condition (RTFO: rolling thin-film oven).  
The increasing trend of the master curve highlighted that the treated samples resist fatigue cracking from intermediate to lower temperatures (e.g., 31, 28, 25, 22, and 19 \({}^{\circ}\)C). The failure temperature was reached when the fatigue cracking parameter (G\({}^{*}\).sin \(\delta\)) exceeded 5000 kPa. From the foregoing data it is obvious that 15 wt % OSP exhibited G\({}^{*}\).sin \(\delta\) value of 5325 kPa, which failed at temperature of 19 \({}^{\circ}\)C. Also, the failure temperature of the base asphalt sample was attained at 19 \({}^{\circ}\)C, with G*.sin \(\delta\) value of 5225 kPa. Similarly, failure temperature was observed on 5 wt % OSP-filled asphalt with a recorded G\({}^{*}\).sin \(\delta\) value of 5125 kPa. The optimum was reached only with 10 wt % OSP-filled asphalt sample, because it showed lower G*.sin \(\delta\) value than the base asphalt and met the Superpave minimum requirement at 19 \({}^{\circ}\)C (G\({}^{*}\).sin \(\delta\) = 4925 kPa). It becomes clear that 10 wt % OSP exhibits higher resistance to fatigue cracking as compared with other OSP contents.  
The higher geometric irregularity of the OSP yields higher adsorption intensity. This effect will result in a strengthening of the filler-binder bonds and a relative increase in the fixed binder amount, while the mastic will get higher consistency and strength (i.e., stiffness) than the control specimen. However, during the service life of the road pavement, bitumen tends to stiffen due to oxidation phenomenon, leading to fatigue cracking. In this investigation, the absorbed heat in the OSP-filled asphalts during high temperatures was stored longer than that in the neat asphalt. Thus, during the decrement of test temperature, the OSP slowly released the heat and the heat loss under equilibrium condition, which helped to maintain the viscoelasticity of the bitumen instead of rapidly releasing the heat and stiffening its matrix. Overall, an intermediate dose of OSP (i.e., 10 wt %) can retard the aging process effectively as compared with 5 and 15 wt % OSP-asphalt mastic samples. The large surface area of the OSP particles delayed the heat loss, especially, when more appropriate amounts were added. With the viscoelasticity of the bitumen and its capacity to resist rutting and cracking under consideration, 10 wt % OSP was considered as the optimum filler dose for bitumen because of its superior performance compared to that of the control binder.