Fulfilling the dual functionality for asphalt rejuvenator formulation: An experimental and computational exploration

Recycle and reuse of waste asphalt materials is a key strategy for pavement sustainability and carbon reduction. Studies on the recycling agents or rejuvenators have produced fruitful findings but there is still an imperative need for a general principle/guideline on the compositional design of competent rejuvenators. Given the fact that the percentage and aggregation degree of asphaltenes are both increased upon aging, and considering that in theory rejuvenation should reverse such impacts, it is advocated in this study that rejuvenators ought to fulfill the dual functionality of diluting and dispersing asphaltenes . It is then proposed that rejuvenators should be formulated as a small proportion of asphaltene dispersants carried and distributed by a matrix of asphaltene diluents (or the so-called softeners), so as to diffuse into and soften the aged asphalt while in the meantime restoring the microstructural homogeneity by improving the colloidal dispersion. Preliminary verification of this concept was based on three rejuvenation schemes involving three selected additives representative of aromatic softeners as well as phenolic and ionic dispersants . Experimental investigations included rheological evaluations, and analytical characterizations consisting of infrared spectrum and gel permeation chromatography (GPC) analyses. Quantum chemical computations were conducted to probe the mechanisms underlying the different rejuvenating/dispersing performances by means of molecular descriptors in the framework of conceptual density functional theory (CDFT) and by inspecting the molecular interactions. The results suggested that by optimizing the respective dosages, the three rejuvenation schemes would all effectively restore the rheological performance in the full temperature range of interest. All the chemicals considered were physically blending with the aged asphalt without discernible signs of chemical reactions. Incorporation of either dispersant was able to reduce a significant proportion of the softener required while providing similar rejuvenating effectiveness as compared to using the softener alone, which was attributed to the improved asphaltene dispersion. Ranking of the dispersing capability among the three additives was in consistency with the strength of their interactions with the asphaltene. The cation-π and CH-anion interactions were identified as major contributors in the case of the ionic dispersant, and hydrogen bonding and π-π interactions for the phenolic dispersant. The great prospect demonstrated by the ionic additive in terms of high rejuvenating efficiency and significant environmental benefits warrants further investigation into this type of dispersants. It is anticipated that the findings would contribute to the scientific formulation of rejuvenators for improved pavement sustainability.