Abstract:
Stone mastic asphalt (SMA) due to its stone-to-stone aggregate skeleton, can resists heavy loading and reduces deformation. Additives are proposed to improve the mechanical properties that will improve the performance of the pavement over the design life. This study comprises of Styrene Butadiene Styrene (SBS) modification of SMA wearing course and dynamic complex modulus calculations using Simple Performance Tester (SPT). The experimental design include preparation of SMA 19 specimens with 6 different percentages of SBS (0%, 3%, 4%, 5%, 6%, and 7%) mixed in bitumen. Dynamic response of neat and SBS modified SMA mixtures under the compressive sinusoidal loading was determined. The dynamic modulus (|E*|) tests at four temperatures (4.4, 21.1, 37.8 and 54.4 °C) depicting the cold and hot conditions in the field, and six loading frequencies of (0.1 to 25 Hz) were led using SPT in accordance with AASHTO TP62-07. Addition of SBS to the mix translated in an increase in the stiffness of the mix, as 70% increase in dynamic modulus (at average) was reported at 5% SBS as compared to neat mixture. Optimum SBS percentage was evaluated using master curve comparison of all six SBS percentages, at 21°C reference temperature, using NCHRP 9-29 Master Curve Excel Solver. Master curves were compared on a single graph which showed 5% SBS modifier giving highest dynamic modulus values. Statistical analysis by Two-Level factorial was employed to evaluate the significance of factors affecting the modified SMA mixture in terms of dynamic modulus. Sensitivity analysis concluded that an increase in temperature from 21.1 to 37.8° C translated in a 63% decrease in |E*| (at average) and an increase in frequency from 25 to 0.1 Hz dictated a 70% decrease in |E*| (at average). Furthermore, a comparison is made between the proposed ANN model and non-linear regression model, and the ANN model outperforms the latter. The developed ANN model can be used as a substitute to laboratory testing and utilized by highway departments and pavement analysts to assess the dynamic modulus and phase angle behavior of SMA mixtures.
