Moisture damage mechanism and material selection of HMA with amine antistripping agent

Abstract

This study investigates the moisture damage mechanism and material selection of hot-mix asphalt (HMA) with amine-based antistripping agent (ASA). The surface free energy (SFE) of virgin and ASA modified asphalts and five aggregates with different acidities were measured, yielding the compatibility of each asphalt-aggregate combination. The corresponding compacted mixtures were evaluated by tensile strength ratio (TSR) considering the freeze–thaw and MIST conditioning. The use of amine ASA changed the thermodynamic properties of asphalt by decreasing the nonpolar components and increasing the polar components, which enhanced the work of adhesion between asphalt and aggregate and reduced the free energy released at the presence of water. The wettability of asphalt over aggregate was also increased due to the ASA, suggesting a better coating quality of asphalt mixtures was achieved. All those changes led to the increased energy ratio (ER), indicating the improved moisture resistance and compatibility of materials. At the molecular level, it might be because the amino groups from ASA adsorbed the silanol groups at the aggregate surface, leading to a stronger bond between asphalt and aggregate. The asphalt mixtures with acidic aggregate exhibited more serious moisture damage, which could be attributed to the lower dry adhesion energy and the larger free energy released with moisture. To enhance the moisture resistance, the selection of compatible asphalt-aggregate combinations seemed more effective than the use of amine ASA. The ERs of all the asphalt-aggregate combinations correlated well with the TSR results, and the SFE-based criteria for material selection of HMA were tentatively proposed.