An ultrasonic technique for the measurement of adhesion of asphalt to aggregate

An ultrasonic technique was developed to measure the adhesion of asphalt to aggregate. Eight different asphalts were tested in combination with two aggregates. Very reproducible values of the adhesion forces were obtained (95% confidence limits within 10% of the mean for most asphalts). No significant differences in the measured adhesion forces were observed for the various asphalts on each aggregate, but statistically significant differences (>95% confidence based on the Student's t-test) were observed between the two aggregates for each asphalt. This observation is in general agreement with trends in measured heats of bonding of asphalts with aggregates, which show a significant variation with aggregate for a given asphalt but not much variation with asphalt for a given aggregate. The measured adhesion forces (based on the apparent planar area of the test sample) were of the order of 107 N m-2. The ability of the technique to distinguish between different materials is very encouraging and suggests that it may be more broadly applicable.