Introduction of Polymer Nanocomposites to Bitumen to Enhance its Thermomechanical Properties

Abstract

This paper examined the merits of using a polymer nanocomposite containing styrene-ethylene/propylene-styrene (SEPS) and montmorillonite (MMT) clay to enhance bitumen thermomechanical properties. To investigate the effects of hybrid usage of SEPS and MMT on bitumen properties, a series of physiochemical and rheological characterization was performed, including frequency sweep tests, multiple stress creep and recovery (MSCR) tests, bending beam rheometer (BBR) tests, and linear amplitude sweep (LAS) tests. Three different dosages (2%, 4%, and 6%) of SEPS and 5% nanoclay were used to modify the original bitumen. The study results showed that the addition of SEPS increased the high-temperature performance of bitumen based on the increase of complex modulus and recoverable strain ($R$ ). As the percentage of SEPS increased from 2% to 6%, the high-temperature grade of bitumen increased from 64°C to 82°C, and the low-temperature grade decreased from $-22°\mathrm{C}$ to $-16°\mathrm{C}$ . Nanoclay had an additional stiffening effect while enhancing the storage stability of bitumen. The hybrid use of SEPS and MMT also improved the aging resistance of bitumen as evidenced by a lesser increase in carbonyl functional groups when exposed to oxidation, as measured by Fourier transform infrared spectroscopy (FTIR). The latter improvement was attributed to SEPS and MMT’s compatibility, leading to polymer intercalation into clay intercalary spacing, promoting clay exfoliation. Exfoliated silica platelets of clay can act as a barrier to oxygen diffusion into the bitumen matrix, delaying oxidation.