# Potential of Waste Oyster Shells as a Novel Biofiller for Hot-Mix Asphalt
## 3 Results
### Thermogravimetric Analysis (TGA/DTGA)  
Response of the bio-composite specimens to thermal loads was assessed using TGA/DTGA (i.e., thermogravimetric and derivative thermogravimetric). The percentage of weight loss (i.e., degradation, wt %) versus temperature increase is displayed in Figure 13. TGA analysis was performed under an inert atmosphere of nitrogen (i.e., N\({}_{2}\)) and from 25 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C. This temperature range was chosen, not only to simulate the temperature at which the HMA (i.e., hot mix asphalt) is produced (150-190 \({}^{\circ}\)C) but also to gain some insight into the material stability when it is subjected to higher temperatures. The TGA/DTGA curves of OSP, and unfilled and OSP-filled asphalts, are depicted in Figures 13 and 14, respectively. Table 5 lists the different events that occurred during the experiment. As shown in Figure 13, it is apparent that there are three typical decomposition stages for neat asphalt (i.e., AP-5 OSP 0 wt %): (1) The first phase of mass loss happened in the temperature up to around 362.23 \({}^{\circ}\)C, corresponding to release of oil content from the asphaltic samples (i.e., mainly saturates and aromatics). (2) Afterwards, there was a minor variation in weight, and then substantial weight loss occurred again in the second stage from approximately 362.23 \({}^{\circ}\)C to 457.56 \({}^{\circ}\)C, which was primarily caused by the thermal degradation of hydrocarbonaceous materials (i.e., resins and some portion of asphaltene fraction). (3) The last stage occurred, corresponding to the combustion of the remaining asphaltenes and the formation of char residues (ca. 14.29 wt %) [57]. TGA was conducted also to determine the calcination characteristics of the oyster shell powder. The TGA profile of OSP is shown in Figure 13. It is evident that in the first stage, the humidity was removed from OSP (i.e., CaCO\({}_{3}\)), i.e., only 1.33 wt %. According to European Standards UNE-EN 13043 [58], the moisture content of filler for bituminous mixtures should be below 1 wt %. However, OSP was found to contain 1.33 wt % of humidity, which may cause stripping in HMA (i.e., hot mix asphalt) pavements and ultimately result in premature failure. Accordingly, the water should be removed to ensure proper adhesion between bitumen and the aggregate surface, thus providing the mixture with adequate resistance to moisture, the most deleterious factor affecting road pavement quality [59]. On the other hand, like many other additives (e.g., natural and synthetic zeolites) [60; 61; 62], the water-containing OSP could be used in the production of WMA (i.e., warm mix asphalt). The most common WMA technology utilizes asphalt foaming by adding a small amount of water into the hot binder or directly to the aggregate and asphalt mixer [60]. This process allows the asphalt mixture to have good workability during laying and compaction, and durability during traffic exposure [63]. At the second stage from 641.31 \({}^{\circ}\)C to 710.76 \({}^{\circ}\)C, the total weight loss referred to loss of carbon dioxide (CO\({}_{2}\)) as 42.78 wt %. Theoretical weight loss is known to be 44 wt %. In the third stage at 710.76-999.98 \({}^{\circ}\)C, the total weight loss was 45.09 wt %. There was a considerable change in the weight of the oyster shell powder as the temperature was raised from 25.21 \({}^{\circ}\)C to 999.98 \({}^{\circ}\)C due to calcination reactions, which commenced at 641.31 \({}^{\circ}\)C; however, the complete calcination of OSP resulting in a phase-change of the sample was only achieved at 999.98 \({}^{\circ}\)C. A major component of the oyster shell powder was identified as pure CaCO\({}_{3}\) at the temperature of 641.31 \({}^{\circ}\)C. The moisture and organic content removal was achieved below 641.31 \({}^{\circ}\)C. When temperature was raised from 641.31 \({}^{\circ}\)C to 710.76 \({}^{\circ}\)C, CaCO\({}_{3}\) (i.e., calcite, calcium carbonate) and CaO (i.e., lime, calcium oxide) were identified as the main components of the OSP.