Performance Evaluation of Styrene-butadiene-Styrene (SBS) Modified Asphalt Using Simple Performance Testing Test (SPT)

Abstract

Roads are the dominant mode of inland transportation as it facilitates 96% of freight operation and 91% commuter traffic in Pakistan. Heavy loading, extreme weather, poor subgrade conditions and binders of inadequate performance grade are causing premature failure in pavements. Additives are proposed to improve the mechanical properties that will extend pavement service life. This study comprises of Styrene Butadiene Styrene(SBS) Modification of HMA wearing course and dynamic complex modulus calculations using SPT. Four percentages of SBS were involved and their results were compared to access the optimum modifier content. Literature Review of past researchers on SBS show that SBS Modified Asphalt has better Adhesive properties and is less sensitive to temperature changes. This Study explored the dynamic response of plain and modified HMA mixtures under the compressive sinusoidal loading. Procured Aggregate was tested for ASTM standards. National Highway Authority Class A gradations was used in this project. Plain and SBS modified binder was compared using Consistency Tests. The softening point values of SBS 2%,4% and 6% samples increased by 5.7%,9.6% and 15.3% respectively. 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 frequencies of (0.1 to 25 Hz) were led using Simple Performance Tester (SPT) in accordance with AASHTO TP62-07. The sensitivity of temperature and loading frequency on determination of dynamic modulus values was observed by typical isothermal and isochronal curves. Optimum SBS percentage was evaluated using Master Curve comparison of all four 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 4% SBS giving highest dynamic modulus values. Statistical Analysis by Two-Level factorial was employed to evaluate the significance of factors affecting the Asphalt mixtures in terms of dynamic modulus. Relative effect of Temperature, Frequency and SBS percentages and their combined effect displayed using Main plots, Standard interactions plot, Analysis of Variance and Pareto Chart in Minitab Software showed a direct relation of Frequency, SBS% till optimum value, with Dynamic Modulus values. Whereas temperature and phase had an inverse relation. High temperature had the most inverse effect on Dynamic Modulus amongst all factors. The results conformed with SBS 4% being Optimum with an increase of 39.4% Dynamic Modulus value at 21.1°C. Hence we concluded that addition of 4% SBS modifier can became a recipe to make our pavement Rut resistant and fatigue resistant in Pakistan.