Interfacial compatibility and fusion mechanism between modified emulsified asphalt and aged asphalt in cold recycled mixture

The interfacial compatibility and fusion behaviors of emulsified asphalt and aged asphalt on reclaimed asphalt pavement (RAP) aggregates greatly affects cold recycled mixture’s properties. To evaluate the compatibility and reveal fusion mechanism between shape-memory hydrogenated epoxy modified emulsified asphalt (SHEA) and aged asphalt on RAP aggregates, fused asphalt specimens were prepared. The dynamic evolution changes in molecular weight, surficial morphology, micromechanical characteristics, chemical composition and phase structure of asphalt specimens during the fusion progress were investigated. Results indicate that a concentration gradient occurs between SHEA and aged asphalt, where high-molecular-weight components from aged asphalt diffuse into SHEA, promoting molecular-level compatibility. This compatibility exhibits a more uniform molecular distribution, enrichment of long-chain structures, reduced asphaltenes content, and improved overall performance. Also, long-chain SMHE molecules in SHEA form complex aggregations with aged asphalt. Three-dimensional SMHE network permeates into asphalt matrix, filling voids and contributing to reduced surface roughness, decreased hardness, and improved viscoelasticity. The surficial undulation of fused specimen is small, and its viscoelasticity is restored. The presence of –C–O– and sulfoxide absorption peaks indicates that chemical reaction between SHEA and aged asphalt occurs, resulting in uniform fusion at a molecular level. Next, X-ray diffraction reveals significant changes in interplanar spacing and crystallite size. Crystalline structures resembling MoS₂ and sodium silver chloride are identified in fused asphalt, further supporting molecular-level interaction between the above components. These findings offer a theoretical basis for performance enhancement of SHEA cold recycled mixture.