A Test Method For Identifying Moisture Susceptible Asphalt Concrete Mixes
Under Strategic Highway Research Program (SHRP) the Environmental
Conditioning System was recently developed. A comprehensive study
of the test setup showed that it is a promising concept that needs
further modification and evaluation. In this study several modifications
to the original Environmental Conditioning System are proposed.
The major aspects of the ECS identified for modifications are
the conditioning procedure and the resilient modulus measurement
setup.
A new test setup was developed which can measure resilient modulus
of asphalt concrete specimens more precisely. The developed
setup was evaluated to further minimize the problems. To increase
the precision of resilient modulus test, static load of 450 N,
no Teflon disks in between the end platens and specimen, and a
gauge length of 38 mm are suggested.
The effects of conditioning parameters were studied to implement
a predictive criteria based on resilient modulus. A rate of water
flow during conditioning period of 9 cc/min is suggested. The
unconditioned resilient modulus should be measured 1 hour after
flowing water through the specimen at 9 cc/min for 1 hour. One
continuous conditioning cycle of 18 hours (instead of three 6
hours conditioning and 3 hours of cooling cycles) is suggested.
The conditioned modulus should be measured 24 hours after the
completion of the conditioning period. If the circumferential
deformation after 6 hours of conditioning is more than 2 percent
of the initial circumference, the mix will be considered as moisture
susceptible. If the resilient modulus ratio is less than 0.8,
the mix will be considered as marginal material, and if the resilient
modulus ratio is greater than 08, the mix will be considered as
well performing mix. This suggested test procedure and predictive
criteria were found effective to identify two moisture susceptible,
two marginal, and one well performing mixture.