Nanomechanical Characterization Effect of Mica and Aging on Asphalt Binder

Asphalt concrete (AC) consists of approximately 95% aggregate, by weight. Of this 95%, about 6% is smaller than 0.075 mm in size (passing the #200 sieve and called filler). The fillers often contain mica, which is a formation of silicate minerals having perfect basal cleavage. Mica has been shown to reduce the strength of AC. This study evaluates the effects of mica on asphalt materials subjected to aging. Mica is combined with asphalt binders to make mastics. Mastics are aged at four different levels and tested by nanoindentation to determine modulus and hardness values. It is shown that mastic with no mica becomes much harder after long-term aging. Aged mastic with no mica is shown to be harder than the aged mastics with low concentrations of mica. Mastic with less than 5% mica in the fillers behaves similarly to binder. However, with a mica content of 7.5%, the modulus decreases after long-term aging. A mastic sample containing 5% mica is shown to have the highest modulus value. Therefore, low-concentration mica reduces hardness but increases modulus value of aged mastic. Therefore, mica can be used to control long-term aging behavior of asphalt concrete.