Experimental Investigation of Crumb Rubber Modified Asphalt Mixtures Using Dynamic Modulus Test

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.