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Cold-mixed epoxy asphalt (CEA) has attracted extensive attention in overloaded and steel bridge pavement and maintenance engineering because of its room temperature construction and low energy consumption. However, the compatibility of epoxy resin and asphalt in CEA is still a challenge, limiting its application to some extent. This study aims to enhance the compatibility of CEA with low amounts of plant oil-based compatibilizers and suggest appropriate methods for assessing the compatibility of CEA. GO-grafted epoxidized soybean oil (GOESO) and GO-grafted soybean oil (GOSO) were synthesized and used to modify CEA. The GO and ESO (or SO) solutions were prepared at concentrations of 0.5 mg/mL and 5 mg/mL, respectively. The pH of the solution was adjusted to 5∼6 before heating. The results showed that 0.2 wt% of GO-modified oil-based compatibilizers had similar effects as 30 wt% of oil-based compatibilizers and did not significantly alter the crystal and chemical structures of the CEAs. GOESO is the preferred recommended GO-modified compatibilizer because of the enhanced compatibilizing ability of the epoxy groups in ESO. The compatibilization mechanism involved the effects of the oils on the chemical structures, curing reaction rate, and microstructures of CEAs. The proportion of asphalt particles larger than 20 μm and the reaction rate had strong correlations with the mechanical properties of the cured CEAs. Molecular dynamics simulations revealed that GOSO reduced the solubility parameter (δ) and Flory-Huggins parameter (χ) difference between components A and B by 39.4% and 65.8%, respectively, while GOESO increased the δ and χ difference between components A and B by 10.4% and 15.8%, respectively. • 0.2 wt% graphene oxide modified oil compatibilizers achieved comparable effects to 30 wt% oil-based compatibilizers. • GOESO and GOSO enhance compatibility by changing the curing reaction rate and the microstructures. • The oil with epoxy groups possibly had a strong capability of compatibility enhancement. [ABSTRACT FROM AUTHOR]

The compatibility of cold-mixed epoxy asphalt (CEA) significantly influences its mechanical properties, primarily mediated by the epoxy group content within CEA. However, the feasibility and mechanisms for regulating the external epoxy group content to achieve optimal performance have yet to be explored thoroughly. Herein, soybean oil, epoxidized soybean oil, and epoxy-terminated hyperbranched epoxy resin (EHER) were used to construct CEA with different external epoxy group contents, and their effects and mechanisms on the compatibility and mechanical properties of CEA were investigated based on experiments and molecular dynamics simulation. Our findings suggest that maintaining an external epoxy group content between 8.4%∼11.4% in the CEA blend and below 12.17% in the cured CEA is crucial. These criteria can be met by adding no more than 5 wt% EHER. CEA with 3 wt% EHER exhibited the most balanced compatibility and mechanical properties, characterized by a pot life of 91 min, a tensile strength of 5.02 MPa, an elongation at break of 61.3%, and a tensile toughness of 1.58 MJ/m3. The presence of external epoxy groups increased the cohesive energy density and the solubility parameter difference between epoxy resin and asphalt prior to curing, forming a "sea-island" structure with varying particle sizes, primarily comprising small-sized particles. This structure was preserved post-curing, establishing a stable system with minor energy alterations. Simultaneously, EHER enhanced the molecular rigidity and uniformity of CEA, thereby improving its mechanical properties. It is recommended to relate epoxy group content in CEA blends with indicators of compatibility and mechanical properties, enabling better prediction. • Desirable performance is exhibited by CEA with no more than 5 wt% EHER. • ER provides strength and asphalt acts as a toughener in CEA. • The "sea-island" structure is preserved post-curing with minor energy variations. • Epoxy group content in blends has a high grey correlation with performance. [ABSTRACT FROM AUTHOR]