Abstract:
Premature failure of pavements due to distresses like fatigue cracking and permanent deformation
are generally attributed to high temperature conditions and uncontrolled axle loads. These distresses
attract additional costs in the form of hastened Maintenance and Rehabilitation (M&R) activities.
Numerous research studies propose additives to enhance the mechanical properties that enhances
pavement longevity by decreasing the rate of permanent deformation in conventional asphalt
mixtures e.g., the temperature susceptibility of the binder can be reduced with addition of crumb
rubber – a polymer derived from waste tyre. This study utilizes six percentages of crumb rubber
(CR) modified bitumen (0, 4%, 6%, 8%, 10%, & 12%) for producing NHA Class B gradation
specimens, tested for Dynamic modulus in Asphalt Mixture Performance Tester (AMPT) using four
temperature and six different frequency sweeps that were used to construct stress-dependent master
curves for each mixture. The experimental finding suggested that an increase (75.53% on average)
in dynamic modulus values reported at 8% CR modified mixture – better performance at all
combinations of temperature and frequency. Statistical analysis was conducted using Two level
factorial design for dynamic modulus and phase angle. Sensitivity analysis showed that dynamic
modulus is sensitive to temperature and frequency, as an increase in temperature from (21.1 to 37.8°C) reduces dynamic modulus (73.24% at average) and a decrease in frequency (25 to 0.1Hz)
reduces the dynamic modulus (52.7% at average). The Artificial Neural Network (ANN) technique
was also employed to predict the dynamic modulus of CR modified mixtures which captured 99%
of the variance in the tested data – a significant improvement as compared to non-linear regression
model. The proposed model has the capability to capture the non-linearity associated with crumb
rubber modified bitumen mixtures and can be used by transport agencies and practitioners as a
surrogate to tedious laboratory testing.
