A novel method for enhancing coating performance of emulsified asphalt mortar to RAP in cold recycled mixture

Emulsified asphalt mortar (EAM) is prone to agglomeration and has poor adhesion to reclaimed asphalt pavement material (RAP) with residual-aged asphalt, which can deteriorate the durability of emulsified asphalt cold recycled mixture (EA-CRM). In this work, silane coupling agent (SCA, 3.75 wt% and 6.25 wt% by weight of emulsified asphalt) and polycarboxylate superplasticizer (PCS, 3.75 wt%, 7.5 wt%, and 11.25 wt%) were used to modify the EAM in order to improve the coating performance of EAM on RAP. Seven kinds of samples with different modifier dosages were prepared. Modification mechanism, micro-morphological changes, workability, rheological property, and coating degree of EAM on RAP were investigated. Furthermore, action mechanism of the SCA/PCS composite modifier (SPCM) in EAM/RAP and the cost-benefit were analyzed. Results show that EAM is physically modified by SPCM. Carboxylic group and polyethylene glycol side chain in PCS possess excellent improvement on the workability of EAM, while silanol group generated by hydrolysis of SCA plays a major role in improving coating performance. An appropriate dosage of SPCM can improve the workability of EAM, and enhance its shear deformation resistance and elastic properties. Meanwhile, SPCM can improve the coating degree of EAM on RAP, but SPCM with a PCS dosage exceeding 7.50 wt% can cause EAM to slightly detach from RAP surface. Therefore, 6.25 wt% of SCA and 7.50 wt% of PCS were proposed to modify EAM to obtain the best overall performance. The application of SPCM had a good cost performance and additional environmental benefits based on the optimal dosage. This work provides a novel method to enhance the coating performance of EA-CRM while facilitating the expansion of RAP applications.