Investigating the effects of carbon black on asphalt binder and moisture damage resistance of porous and stone mastic asphalt using free surface energy parameters

Abstract: Moisture damage is one of the major distresses of asphalt pavements, which occurs due to de-bonding aggregate and asphalt binder at their interface due to moisture. One of the existing solutions for enhancing the resistance against moisture damage is using additives, known as anti-stripping additives. In this study, the effects of adding carbon black to an asphalt cement and porous asphalt and stone mastic asphalt (SMA) made by the modified binder have been investigated. 0, 4, 8, 12 and 16% (by the weight of asphalt) of carbon black has been added to the asphalt binder and the samples were subjected to penetration grade, softening point, ductility and Sessile drop test for determining the surface free energy components. The indirect tensile strength (ITS) in dry and wet condition of the mixtures were also measured and compared with the parameters determined from free surface energy method. Results show that penetration grade and ductility decreases up to 8% of carbon black and beyond that the trend reverses. Softening point increases up to 8% of carbon black and beyond that decreases with increase of carbon black content. Free surface energy components of asphalt show that the total surface free energy increases up to 8% and decreases beyond that level. The wet and dry indirect tensile strength of the porous asphalt and the wet indirect tensile strength of SMA mixture increases with increasing carbon black content up to 8%, and beyond that the trend reverses. The ratio of dry to wet ITS, known as tensile strength ratio (TSR), increase with increasing carbon black up to 8% and decreases after that. The effect of carbon black on porous asphalt is more significant than that on the SMA. Good correlation is found between the TSR results and the parameters obtained by surface free energy.