Bitumen adheres well to all normal types of road
aggregates provided they are dry and free from dust. In the absence of water
there is practically no adhesion problem of bituminous construction. Adhesion
problem occurs when the aggregate is wet and cold. This problem can be dealt
with by removing moisture from the aggregate by drying and increasing the
mixing temperature. Further, the presence of water causes stripping of binder
from the coated aggregates. This problems occur when bitumen mixture is
permeable to water. Several laboratory tests are conducted to arbitrarily
determine the adhesion of bitumen binder to an aggregate in the presence of
water. Static immersion test is one specified by IRC and is quite simple. The
principle of the test is by immersing aggregate fully coated with binder in
water maintained at 400C temperature for 24 hours.
specified maximum stripping value of aggregates should not exceed 5%.