Use of softwood bark charcoal as a modifier for road bitumen

Abstract

Bitumen produced in refineries does not have the performance required for road pavement applications. As a consequence, producers are testing various additives to improve the bitumen performance. These additives include various polymers, carbonaceous materials, fine minerals, oils from different origins, etc. In the present work, charcoal obtained during the vacuum pyrolysis of softwood bark residues was tested as an additive. A commercial carbon black (CBc) sample was used for a comparison purpose. Both carbonaceous materials were incorporated at different concentrations into two different reference petroleum bitumens. The samples prepared were subjected to classical and rheological tests in order to obtain the optimal blend. The latter was blended with aggregates for mechanical testing. The wood-derived charcoal (WCp) was found to improve the viscoelastic properties of the straight binders, particularly at high temperatures. The thermal susceptibility of the WCp-modified bitumens was lower than that of the bitumens modified with CBc. Rutting resistance was also increased by the addition of WCp in the matrix bitumens. It was determined that for both commercial bitumens tested, the addition of 5–15% of wood charcoal resulted in blends with lower susceptibility to crack propagation and conferred a high performance to the binders. Both the commercial carbon black and the pyrolytic wood charcoal additives have low resistance against settling during long hot storage period.