Modification of asphalt by dispersing waste polyethylene and carbon fibers in it

Recycled waste packaging polyethylene (WPE) and chopped polyacrylonitrile-based carbon fibers (PAN-CFs) were dispersed in molten asphalt at 170 °C with a shearing machine at 3 800 r/min for 60 min to modify its properties to meet the demands of motorway paving. WPE and PAN-CFs were mixed by three methods before the dispersion: (a) simple blending, (b) first dissolving WPE in xylene, then mixing and evaporating and (c) blending and extrusion to rods of 1mm diameter at 170 °C which were fed directly into the hot asphalt. The PAN-CF content was varied in the range 0 to 0.12 wt% while the WPE content was constant (4 wt%). Results indicate that WPE and PAN-CFs are dispersed in asphalt to form a network structure by the xylene-assisted mixing or blending-extrusion methods. The softening points, penetration degree and ductility are improved with increasing content of PAN-CFs up to 0.1 wt%. Aggregation of the two modifiers occurs beyond 0.12 wt% of PAN-CFs, which degrades the properties of the modified asphalts. A fiber length of 5 mm is optimum for their best dispersion in the asphalt. Segregation of the modifiers from the modified asphalts can be prevented by increasing the content of PAN-CFs. The blending-extrusion method is best to form a fine network structure, which achieves a best performance. A model is proposed to explain the observed dispersion behavior in asphalt.