Moisture migration of bitumen emulsion-based cold in-place recycling pavement after compaction: Real-time field measurement and laboratory investigation

Abstract

Bitumen emulsion-based cold in-place recycling (BE-CIR) has gained in popularity due to its cost-effectiveness, energy saving and environmental friendliness. Unlike hot mix asphalt (HMA), BE-CIR is manufactured at room temperature and requires a longer curing time to allow for water evaporation. However, little attention has been given to the water migration process in BE-CIR pavement. Given the difficulty of simulating field curing conditions in laboratory, a series of on-site sensors were used to continually monitor the temperature and moisture gradient inside BE-CIR pavement at different depths after compaction. After one month of curing, field cores were drilled from the experimental road, and the volumetric properties and semi-circular bending strength of both top and bottom halves were studied. The obtained humidity index (HI) was used to quantify the relative moisture content in BE-CIR mixture. Testing results show that the moisture migration over time can be divided into two stages, with the first exhibiting a quick fall and the second exhibiting a minor downward tendency. During the curing phase, a unique gradient characteristic can be identified for the initial moisture distribution and moisture movement of the BE-CIR layer in the field. Both the temperature gradient and depth location can affect the water migration process significantly. Furthermore, the final moisture content, air void content and the semi-circular bending strength of field cores also present clear gradient characteristics, indicating the importance of the moisture gradient migration process on the long-term performance of the BE-CIR pavement.