## 4 Conclusions  
In this study, the water-boiling method was used to observe the peeling area of asphalt film from the surface of aggregates and to obtain the adhesion grade. The surface free energy method was used to calculate the adhesion work and exfoliation work of COBA. Meanwhile, the moisture damage resistance of COBA was analyzed using the contact angle moisture susceptibly test. Finally, the quantitative evaluation of the aging of COBA was performed via FTIR, and the correlation between the aging of COBA and COBA-aggregate adhesion was analyzed. The following conclusions were drawn:  
(1) Since COBA has a strong adsorption effect on phenosafranine, and steel slag has almost no absorption, photoelectric colorimetry is not suitable to evaluate the adhesion between steel slag and COBA.  
(2) The cohesion in COBA increased by 23.1% on average due to the addition of bio-oil, and the adhesion between COBA and aggregates increased by 5% due to acidic compounds that formed in the process of the interaction with Si inside the aggregates.  
(3) Under short-term aging, the work of adhesion between COBA and aggregates increased within a 10% dosage of bio-oil due to the increase in colloidal and polar substances in COBA. As the content of bio-oil and thermal oxidation degree continued to increase, the heavy component of COBA increased, and the excessive C=O content was converted to carboxylic acid and other substances that made asphalt brittle. At the same time, the microcracking of COBA during the aging process also increased the risk of moisture damage.  
Figure 9: Correlation between \(I_{\text{C=O}}\) and adhesion work and pull-out strength.  
(4) Regarding the effect of aggregate types on COBA adhesion, the adhesion grades of COBA-limestone and COBA-steel slag were always consistent during the boiling process. Under dry conditions, steel slag formed acidic compounds and higher roughness; its work of adhesion with COBA was 7% and 9% higher than that of COBA-limestone before and after short-term thermal oxygen aging. However, under the influence of water, the acidic compounds that formed at the aggregate interface are easily hydrolyzed, and with the high hygroscopicity of steel slag and hydration reaction, the exfoliation work of COBA-slag is still higher than that of COBA-limestone.  
(5) The change of oxygen-sensitive groups of COBA correlated well with the change of the adhesion of COBA-aggregate before and after thermal oxidation. And the adhesion performance of COBA-aggregate under thermal oxidation could be evaluated by calibrating the internal C=O content of COBA with the adhesion performance of COBA-aggregate.  
R.Z.: Methodology, writing--original draft, funding acquisition. Q.S.: Data curation, writing--original draft. P.H.: Data curation. J.J.: Conceptualization, methodology. L.W.: Conceptualization. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by National Key R&D Program of China (2022 YFB2601900), the National Natural Science Foundation of China (52208412), Research Project of Beijing Municipal Commission of Education (KM202210016009, KM202110016011), Open Fund of Key Laboratory of Road Structure and Material of Ministry of Transport (Changsha University of Science & Technology) (kfj210302), the Project of Construction and Support for High-Level Innovative Teams of Beijing Municipal Institutions (BPHR20220109).  
Not applicable.  
All data, models, and codes generated or used in this study are included in the submitted manuscript.  
Thanks to [PERSON] for her significant assistance in conducting the experiments.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.