Microstructure and rheological response of laboratory-aged SBS-modified bitumens

Abstract

Polymer additives are widely used to improve the performance of road bitumens including their resistance to hardening during oxidation, although their oxidative inhibitor effect has not been well documented. This study aims to investigate the effect of laboratory-simulated ageing on the microstructure, and rheological properties of Polymer Modified Bitumens (PMBs) prepared with a Styrene-Butadiene-Styrene (SBS) copolymer and sulphur as a cross-linker. The laboratory ageing was conducted through the Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV) procedures. The unaged and aged binders were characterised using the Multiple Stress Creep and Recovery (MSCR) test, Gel Permeation Chromatography (GPC) and fluorescence microscopy. The MSCR test showed that the cross-linked polymer had a higher capability of mitigating the effect of bitumen hardening on the rheological response, while for the PMBs without cross-linking, the polymer effects decreased significantly after RTFOT ageing. The GPC results showed that the aromatics, resins and asphaltenes fractions of the unmodified bitumens shifted towards heavier molecules after one cycle of PAV ageing but showed limited variation with further ageing. Similar behaviour was observed for the uncross-linked polymer binders, while for the cross-linked polymer binder, the behaviour depended on the polymer concentration.

Effects of ageing on the damage tolerance of polymer modified bitumens investigated through the LAS test and fluorescence microscopy

“…On one hand, polymers undergo thermo-oxidative degradation and reduce their dispersion in the bitumen-rich phase. This conclusion is supported by rheological findings and by measurements of molecular weight distribution (Cuciniello et al, 2018(Cuciniello et al, , 2019. The alternative hypothesis is represented by the de-swelling of polymer (Mouillet et al, 2019).…”

“…The microscope is connected to a camera to gather pictures of the various samples. Details about sample preparation are given in (Cuciniello et al, 2018(Cuciniello et al, , 2019.…”

“…Polymers capable of maintaining their structure during swelling positively influence the rheological response of PMBs, providing higher stiffness at high temperatures, lower stiffness at low temperatures, between the polymer and the bitumen, which is a function of the type of polymer and the source and refining process of the bitumen (Polacco, Filippi, Merusi, & Stastna, 2015). Furthermore, the effects of cross-linking agents need to be considered (Mandal, Sylla, Bahia, & Barmand, 2015;Cuciniello et al, 2019). For these reasons, the definition of a unique aging mechanism is unclear since it is polymerdependent.…”

Evaluating the Rheological, Chemical and Morphological Properties of SBS Modified Asphalt-Binder under Multiple Aging and Rejuvenation Cycles

“…These effects usually result in the degradation of the SBS polymer and oxidation along with the volatilization of light components and the polycondensation of the asphalt-binder, consequently causing a decay in the physico-rheological properties [6][7][8]. Many researchers have observed an increase in the complex modulus (G*), elastic modulus (G ) and creep recovery (R), but a reduction in phase angle (δ) and non-recoverable creep compliance (J nr ) with the deepening of the aging by DSR, which means that the viscous behavior of the asphalt-binder has partly moved to elastic behavior [9][10][11].…”

“…During the aging and rejuvenation processes, the change in the physico-rheological properties of the SBSMA can be attributed to the chemical composition and microstructures. Fourier transform infrared (FTIR), atomic force microscopy (AFM), environmental scanning electron microscope (ESEM), and other new technologies have been successfully applied to analyze the aging mechanism and rejuvenating process of SBSMA at a micro scale [11,[15][16][17][18][19][20][21][22][23][24][25]. FTIR was used to investigate the aging and rejuvenation mechanism of SBSMA as well as the relationship between the chemical and rheological characteristics by identifying the differences between the absorption peaks which represent the functional groups and contents in the asphalt-binder based on Lambert-Beer's Law [15][16][17][18].…”