Moisture susceptibility evaluation of asphalt mixes based on image analysis

• By applying an image analysis technique, visual rating in boiling water test is converted to a more objective evaluation.
• The stripping results of boiling test show significant linear relationship with TSR and ESR values.
• There is not a significant correlation between RMS values and the boiling test results.

Moisture damage in hot mix asphalt (HMA) is one of the major concerns in durability of flexible pavements. Numerous methods have been developed to evaluate moisture susceptibility of HMA in last decades. Some of these methods are simpler and less costly (qualitative tests) and some of them are more reliable.In this research, a digital image analysis approach was utilized to convert boiling water test (ASTM D3625) from visual rating to objective evaluation. Some laboratory tests were conducted on specimens to compare the stripping percentages obtained from image analysis of the boiling water test and modified Lottman test (AASHTO T283) results. In AASHTO T283 test, in addition to Indirect tensile test, the dynamic modulus |E*| test and the Marshall stability test were performed. Therefore, three criteria; tensile strength ratio (TSR), |E*| stiffness ratio (ESR) and Retained Marshall stability (RMS) were used to compare the results of the two methods. The dynamic modulus test was conducted in indirect tension mode; and a linear viscoelastic solution was used for calculation of |E*|.Findings showed that the results of boiling water test have significant relationship with TSR and ESR. Good correlation was found between three tests; however, the results of boiling test did not show significant relationship with RMS.