Bitumen microstructure by modulated differential scanning calorimetry

Abstract

/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://dx.doi.org/10.1016/S0040-6031(01) Thermochimica Acta, 374, 2, pp. 105-114, 2001-07-10 Bitumen microstructure by modulated differential scanning calorimetry Masson, J-F.; Polomark, G. M. Bitumen microstructure by modulated differential scanning calorimetry Masson, J-F. ; Polomark, G. M.A version of this paper is published in / Une version de ce document se trouve dans : Thermochimica Acta, pp. 105-114, v. 374, no. 2, 2001 www.nrc.ca/irc/ircpubs assigned to the maltenes, the other at 70°C to the asphaltenes. The heat capacity of these transitions was found to depend on thermal history. From the total heat capacity, it was calculated that the relative size of the bitumen repeat unit is between 36 and 91 g mol -1 , which given an average molecular weight of 300-1000 g mol -1 for bitumen, translates into a "degree of polymerisation" of ~10. After cooling from the melt and annealing at 22°C, bitumen microstructure was found to develop in three stages. Most rapid is an ordering process that occurs when bitumen is quenched from the melt. It is postulated that this first stage arises from the partial ordering of simple aromatic structures into micro-and nano-phases; a second stage, which ends within ~3h of annealing, relates to the ordering of somewhat larger aromatic structures; and a third stage, which ends in ~16h, is thought to arise from the ordering of the largest bitumen structures, the resins and the asphaltenes. The development of bitumen microstructure and the calculations of the entropy and enthalpy of transitions suggest that bitumen is a multi-phase system with a small crystalline phase, and a large mesophase, i.e, a structured amorphous phase. NRCC-44278

Steric Hardening and the Ordering of Asphaltenes in Bitumen

“…With bitumen, the two phases are the maltenes and the asphaltenes, and what the MDSC non-reversing heat flow effectively shows (Figure 2) is the rate at which the asphaltenes segregate out of the maltenic phase to form the asphaltenic mesophase. 6 Given the isotropization of the mesophase at 40-50°C and the steric hardening below 60°C, 3 a UCST is likely close to 60°C. It would be below this UCST that asphaltenes would order into a mesophase, possibly due to nucleation and growth, 11 and that steric hardening would arise.…”

“…6,7 The segregation being time dependent, it was suggested that the formation of the mesophase was responsible for the steric hardening of bitumen. This communication provides evidence of this relationship.…”

Enhancing the viscoelastic properties of bituminous binders via thiourea-modification

“…Hence, above the frozen state defined by T > Tg, molecular mobility increases and those saturates segments order into crystalline domains [22,23,25]. Table 2, which displays second event temperatures (T2nd) confirms a decrease after addition of 9 wt.% Th and 60 days of curing, as the frozen state threshold was shifted to lower temperatures.…”

“…8B presents two welldefined peaks (with peak maximum, Tg1 and Tg2, located at -30.5 and 3.0 ºC, respectively) which, according to Masson et al [22,23], derive from two overlapped glass transitions corresponding to saturates and aromatics. Tg2 values were also determined for the modified binders studied, and compare with neat bitumen's.…”

“…Figures 8A and 8B show the non-reversing thermograms and derivate heat capacity (dCp/dT), respectively, for neat bitumen and its corresponding 9 wt.% Th-binders at different curing times. According to Masson and co-workers [22,23] non-reversing heat flow curves for a neat bitumen presents four clearly marked thermal events: i) a broad endothermic background which approximately extends from -40 up to 80 ºC; ii) and iii) two exotherms located at about -9 and 40 ºC; iv) an endothermic peak, at around 50 ºC, being related to the diffusion of relatively large structures, as those typically found in asphaltenic micelles. Enthalpy associated to this fourth event can be ascertained by mere integration of the corresponding peaks (see Fig.…”