Abstract:
Moisture damage has been one of the major concerns for hot mix asphalt (HMA)
pavements. In an asphalt mixture moisture damage can be defined as the loss of strength,
durability and stiffness due to presence of moisture leading to adhesive failure at the binderaggregate
interface and/or cohesive failure within the binder-filler mastic. In this research efforts
were made to evaluate the moisture susceptibility of a dense-graded surface HMA mixture using
simple performance test (SPT) and Superpave indirect tensile test (IDT).
The nature and extent of fines (passing no 200 sieve) can have a major effect on the
moisture damage potential of the hot mix. Coating of fines (dust) on the aggregate can prevent
the asphalt binder from bonding directly to the surface of the aggregate. Therefore SPT and IDT
tests have been performed by varying the proportion of fines from (3%, 6% and 9%) in the mix.
For each proportion of fines optimum asphalt content has been determined and was used for
further preparation of test specimens.
The addition of hydrated lime [Ca(OH)2] to asphalt mixtures improved the adhesive bond
between aggregate and bitumen, also reduces the occurrence of stripping. In addition when
aggregates are coated with clays, hydrated lime react pozzolanically to remove those deleterious
materials that would otherwise damage the mixture. Therefore hydrated lime has been used as
antistripping agent in this research. The amount of antistripping agent incorporated was 1.5% by
weight of dry aggregate.
Pen Grade 60-70 bitumen and NHA class B aggregate gradation were evaluated in this
study. Standard Marshall Mix design procedure was employed to design the asphalt mixtures.
For all the tests cylindrical samples were compacted using Superpave Gyratory Compactor
(SGC). A freeze-thaw cycle was given to condition the specimens according to ASTM D 4867.
Laboratory test results and statistical analysis performed using Minitad-15 software suggests that
hydrated lime is an effective antistripping additive and improves the stability of asphalt concrete
mixtures.
