Measuring moisture susceptibility of Cold Mix Asphalt with a modified boiling test based on digital imaging

Cold Mix Asphalt (CMA) is a promising alternative material for a wide range of paving applications from preventive maintenance and repair, to new pavement construction. However, the reported higher moisture susceptibility of CMA relative to traditional Hot Mix Asphalt (HMA) presents a challenge that limits the more widespread usage of CMA in the field up to date. To identify the potential of moisture susceptibility for CMA, a simple and effective test procedure based on modifications to the Boiling Test specified in ASTM D3625 is proposed in this paper. The modified boiling test can provide a quick measurement of moisture susceptibility for CMA in the material selection stage of the mix design. Digital imaging is used to quantify the coating of CMA mixture samples before and after the boiling test instead of subjective visual assessment. The “Coating Ratio” parameter is proposed as an index to evaluate the coating quality of CMA, and as a means to ensure adequate bonding between asphalt and aggregate. The results from the modified boiling test were verified by AASHTO TP-91 Binder Bond Strength (BBS) test and the AASHTO T-283 Tensile Strength Ratio (TSR) test of the compacted mixture. It is found that the results from modified boiling test correlated very well with those from BBS test and TSR test, indicating that the modified boiling test can be used as an effective tool to evaluate the moisture damage potential of CMA.