Evaluating the effects of styrene-butadiene rubber (SBR) and polyphosphoric acid (PPA) on asphalt adhesion performance

The styrene-butadiene rubber (SBR) latex and polyphosphoric acid (PPA) are extensively utilized alone or together to optimize the properties of base asphalt to tackle the booming traffic loads and volumes. In this paper, the influences of SBR, PPA, and SBR&PPA on the adhesion performance of base asphalt were evaluated by atomic force microscopy (AFM), surface free energy (SFE), binder bond strength (BBS), and split tensile strength tests from multiple scales under dry or moisture conditions. Finally, the one-way analysis of variance (ANOVA) was conducted. According to the results, both SBR and PPA dosages show significant influence on the adhesion performance of the asphalt binder and its mixture. Specifically, at the nanoscale, the PPA and SBR modifiers are beneficial to improving the adhesion force of base asphalt from 17nN to 21-30nN. At the asphalt scale, both PPA and SBR modifiers enhance the SFE of base asphalt. However, only asphalts modified with 1% PPA, 1.5% PPA, 3% SBR, and 1.5% SBR&2% PPA are less prone to ravel. At the asphalt-aggregate and mixture scales, the SBR modifier enhances the pull-off strength of base asphalt significantly from 1.83 MPa to about 4 MPa, as well as the dry tensile strength (TSD). However, after the freeze-thaw condition, the PPA&SBR modified asphalt demonstrates the most satisfying freeze-thaw tensile strength (TSFT) and the tensile strength ratio (TSR). Considering the unfavorable moisture damage resistance of asphalt and its mixture when being modified with a single modifier, the asphalt modified with 1.5% SBR&2% PPA is recommended and could improve the adhesion performance between asphalt and aggregate even under moisture conditions.