Study of Thermal Aging of Model Compounds Present in Asphalt Cement by GC/MS, ESI-MS, NMR, and FTIR

The study of petroleum asphalt cement (AC) aging is essential for the production of good quality pavements with high durability. Because of the complexity of this material, one of the biggest challenges is understanding the chemical variations that occur in the molecules present in the AC during the aging processes. This work proposes to study 15 standards of model compounds present in the AC composition, representing the fractions of saturated compounds (5-α-cholestane and hexatriacontane), aromatics (hexamethylbenzene, coronene, and benzo­[a]­anthracene), nitrogenous compounds (acridine, carbazole, indole, and N,N′-Bis­(3-pentyl)­perylene-3,4,9,10-bis­(dicarboximide)), sulfur compounds (2-naphthalenethiol, 4,6-diethyldibenzothiophene, and naphtho­[1,2-b:6,5-b′]­dithiophene­(NDT)), and naphthenic acids (stearic (SA), pentadecanoic (PA), and sinapinic acids (ASN)), which were thermally aged by two methods: (i) they were subjected to a constant temperature of 80 °C, varying the time of analysis over 5, 10, 15, 30, and 60 days; and (ii) temperatures ranging from 80, 100, 120, to 140 °C for 15 days. The analyses of these compounds were performed by GC/MS, 1H and 13C NMR, ESI(−)­MS (FT-ICR and LTQ), and FTIR. The results obtained showed that at 80 °C, from 15 days, only the indole standard compound showed the presence of thermal products, i.e., compounds detected from thermal aging of the standard model compounds. When the degradation temperature was increased from 100 to 140 °C, we observed the formation of thermal products at 100 °C in 6 out of 15 model compounds. However, at 140 °C, 12 of the 15 model compounds presented some type of degradation. Reactions of oxidation, polymerization, thermal aging, volatilization, and formation of double bonds were observed.