Preparation, shape memory performance and microstructures of emulsified asphalt modified by multi-walled carbon nanotubes

•MWCNTs modified EA with better shape memory effect is prepared at a proposed content.•A new convenient method is developed to evaluate shape memory property of EA samples.•MWCNTs further improve shape memory effect of EA due to reinforced network structures.•MWCNTs, SBS and asphalt form intercalation structures to increase mutual interactions.•Shape memory mechanism of modified emulsified asphalt materials is further understood. To develop styrene-butadiene-styrene/multi-walled carbon nanotubes (SBS/MWCNTs) compositely modified emulsified asphalt (SM/EA) with shape memory performance, and reveal its shape memory mechanism, SM/EA samples were first prepared. Then basic properties and shape memory performance of SM/EA were characterized, and the microstructures were discussed to reveal its shape memory mechanism. Results indicate that basic properties of SM/EA samples meet the requirements of technical specifications. SBS and asphalt phases serve as elastic and switching domains, respectively, endowing EA better shape memory performance. MWCNTs further improve shape memory effect of EA due to reinforced interpenetrating network structures at the proposed content of 0.03 wt%. Further, MWCNTs increase the swelling degree of SBS, and cause SBS molecular chains to become more densified and oriented. When the MWCNT content reaches 0.03 wt%, SBS can still be uniformly dispersed in asphalt matrix with a highest swelling degree. MWCNTs become the junctions between SBS and asphalt to closely connect the formed interpenetrating networks at the proposed MWCNT content, improving the shape memory performance of SM/EA. Also, MWCNTs increase the disorder of carbonaceous structures and density of C=C bonds in SM/EA as MWCNTs are excessive, lowering shape memory effect of EA. Additionally, as the MWCNT content is increased, MWCNTs, SBS and asphalt phases enter into each other's structural layers to form intercalation structures, increasing the space between aromatic layer of asphalt and graphite atomic layer of MWCNTs so that the interaction between asphalt phase and MWCNTs is enhanced. The increase in interlayer spacing is the greatest at the MWCNT content of 0.03%. Finally, MWCNTs play a reinforcing role, and increase mechanical anchorages among MWCNTs, SBS and asphalt phases. Shape recovery rate and speed of SM/EA are also improved. These findings provide a basis for the crack self-healing of EA maintenance materials on asphalt pavement.