Moisture migration characterization of bitumen emulsion-based cold in-place recycling mixture over curing

Bitumen Emulsion-based Cold In-place Recycling (BE-CIR) pavement has been widely used all around the world due to its superior environmental benefits. BE-CIR pavement presents a unique moisture migration behavior after compaction because of the breaking of bitumen emulsion, contributing to the strength formation of the mixture. However, previous studies have mainly evaluated water diffusion by mass loss and ignored its effect in the depth direction. In this study, a one-way evaporation method was developed to simulate the field moisture migration of the BE-CIR mixture specimens. An image processing method was proposed to extract the moisture distribution of the BE-CIR mixtures by images from Multiple X-ray Computed Tomography (XCT) scanning tests at different curing times. The effects of curing temperature were investigated as well. According to the detailed description of the micro-morphology variation of moisture instead of only mass loss, a gradient feature in the depth direction which was more significant near the surface in contact with air could be found. Among different curing stages, the gradient characteristic could be observed only at the curing ages of 3 to 7d, and moisture was more likely to migrate from the edges and have a more irregular thickness at the curing of 0 to 3d. Curing temperature would significantly influence the range of gradients and the variation of water content in the depth direction. The outcomes of this study can enhance the understanding of the dynamic moisture migration characteristics of the BE-CIR pavement over curing.