Study of Vacuum Residues and Their Transformation to Asphalts for the Pavement Industry by Nuclear Magnetic Resonance and Chemometric Methods

Abstract

This paper reports the findings of a one-year long study, that every week measured the physicochemical properties (P: penetration; A: softening; Ip: penetration index; V: rotational viscosity, R: mass loss), and the spectroscopic and the relaxometry properties via nuclear magnetic resonance, of the vacuum residues (VR) produced in a refinery and those modified into asphalts to fabricate pavements with penetration grade 60/70. The evolution of the structural changes, along the time of study, was measured via high-field and low-field 1H NMR and analyzed through multivariate statistical methods. The attained results with high-field 1H NMR showed that when the VR are oxidized, the proportion of protons associated with the high-molecular-weight polyaromatic increases. On the other hand, the low-field 1H NMR results, through a greater number of unimodal distribution plots of T2 relaxation time, showed the homogenization of the aggregation as well as of the dynamic properties of the molecules, thus indicating that the aging of asphalts cannot be prevented despite the treatment. After analysis of the physicochemical properties, it was found that some refinery VR samples do not meet the quality specifications of penetration grade 60/70, dictated by the National Roads Institute of Colombia (INVIAS), to be employed as raw material in the manufacturing of pavements, but only after being processed and modified.