Performance evaluation of bauxite residue modified asphalt concrete mixes

This study attempts to recycle bauxite residue (red mud) as an alternative to conventional stone dust filler in asphalt concrete mix. For this, relevant physical, chemical and morphological properties of both fillers were determined. Subsequently, asphalt concrete mixes incorporating both fillers were prepared using Marshall mix design procedures, and their performances against primary aspects (strength, rutting resistance, cracking resistance, moisture susceptibility, ravelling resistance, long-term ageing, active and passive adhesion) were investigated. Although red mud mixes had higher optimum asphalt content than conventional mixes, they also delivered higher Marshall stability, rutting resistance and cracking resistance. This was majorly attributed to fineness and porosity of red mud which facilitates uniform distribution of filler and higher absorption of asphalt binder. Red mud was highly alkaline and hydrophobic in nature and had the presence of adhesion promoters like calcite in its composition. Hence, red mud mixes displayed satisfactory resistance against moisture permeation and had good active-passive adhesions. Although red mud mixes had marginally lower resistance against ravelling and long-term ageing than the conventional mix, red mud could effectively be utilised as a filler in asphalt concrete mixes.