Sustainable production of eco-friendly rubberized asphalt binders through chemically crosslinking with polymer modifier

The incorporation of waste tire rubber into asphalt pavement can facilitate the development of sustainable transportation infrastructure. Recently, terminal blend (TB) rubberized asphalt incorporating polymers has gained popularity due to its improved performance and eco-friendliness. However, the crosslinking mechanism between terminal blend (TB) rubberized asphalt and supplemented polymer modifier is not well understood. The present paper aims to investigate the crosslinking mechanism between degraded rubber, styrene-butadiene-styrene (SBS) polymer and crosslinking agent, and to clarify the effect of crosslinking reaction on the properties and production of eco-friendly rubberized asphalt. In this paper, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), dynamic shear rheological (DSR), multiple stress creep recovery (MSCR) and bending beam rheometer (BBR) tests were employed to investigate the chemical and physical properties of TB rubberized asphalt after incorporating various contents of SBS and crosslinking agent. FTIR test indicates that the conjugated olefins released from crumb rubber have the possibility to react with sulfur. However, sulfur alone fails to greatly improve the rheological performance of TB rubberized asphalt, for the level of crosslinking reaction between sulfur and TB rubberized asphalt is weak. Therefore, it is necessary to further add SBS polymer to enhance the crosslinking reaction. Further study showed that there are two types of crosslinking reactions when involving conjugated olefins. Type I is the reaction of sulfur with conjugated olefins provided by the degraded rubber, which helps the conjugated olefins to crosslink themselves, resulting in increase of the amount of trans olefins. Type II is that sulfur bridges the SBS polymer and degraded rubber through the chemical link between the opened trans olefins double bonds located in SBS and opened conjugated olefins from degraded rubber, which leads to reduction of the amount of trans olefins. Type II crosslinking reaction can effectively improve the high temperature performance of TB rubberized asphalt. The findings of this study not only provides valuable insights into the interaction mechanism of eco-friendly rubberized asphalt, but also promote the recycling of waste tire rubber.