Laboratory Study of the Effects of the Addition of Softwood Kraft Lignin by the Dry Process on the Compactability, Moisture Sensitivity, Rutting and Low-Temperature Cracking Resistance of an HMA

In this experimental laboratory study, a 0–10 mm bituminous surface mix (ESG-10) was developed with a softer and unmodified bitumen PG58S‒28 for standard traffics and cold regions and, with 0, 5 and 20% softwood Kraft lignin that was added by the dry process i.e., directly in the hot mix asphalt (HMA). The study encompassed the evaluation of compactability, moisture sensitivity, rutting resistance, and thermal cracking resistance. The mix design resulted in a single gradation, maintaining a constant binder (bitumen and lignin) content of 5.29% by the total weight for all mix variations. In particular, lignin was considered a binder in its own right, and the results revealed shifts in properties related to binder density, compaction ability, and moisture resistance of HMA, suggesting that the addition of lignin impacts the mix characteristics, especially at higher lignin concentrations. The study also explored rutting resistance and thermal cracking resistance, with results indicating some interactions between lignin, bitumen, and mix properties. Overall, this research provides valuable insights into the intricate relationship between lignin and bitumen in bituminous mixes, offering information about their suitability and effects on the performance of asphalt.