Use of DIC and AE for investigating fracture behaviors of cold recycled asphalt emulsion mixtures with 100% RAP

Cracking damage have great influence on the service life of cold recycled asphalt emulsion mixtures (CRAEM). As non-destructive methods, digital image correlation (DIC) and acoustic emission (AE) techniques can diagnose and visualize various distresses efficiently. The objective of this research was to explore and characterize the fracture behaviors of CRAEM with DIC and AE. Firstly, the semi-circular bending (SCB) tests, accompanied with DIC and AE monitoring were conducted on CRAEM with different cement contents. Secondly, the fracture energy examined by DIC as well as the tracked cracking path were analyzed to correlate with the fracture characteristics of CRAEM. Then, the variation of AE parameters (i.e., AE energy, AE amplitude) were investigated to identify the damage stages of SCB specimens. Finally, the box-counting dimension and the AE b-value were established based on cumulative AE energy and AE amplitude separately to quantitatively assess the transition of damage state. The results indicate that the cement content would significantly affect the cracking resistance performance of CRAEM, and CRAEM with a moderate content could have the benefits of more alternative energy release paths in the process of crack initiation and propagation. The fracture failure process of CRAEM could be divided into four stages through the simultaneous mutations of cumulative AE energy and AE amplitude. The difference of fracture surface morphologies of CRAEM with different cement contents obtained by the digital microscope could provide a reliable explanation for the fracture behaviors of the whole damage evolution process of CRAEM. The transition of the value of box-counting dimension from the maximum to the minimum could reflect the formation of macrocracks of CRAEM. The inflection point of the AE b-value curve arriving at the minimum value could be regarded as a precursor information to predict the complete fracture of CRAEM.