Rubber–bitumen interaction of plant-blended rubberized bitumen prepared under various blending conditions

Rubberized bitumen produced from waste tire rubber has been widely used as a sustainable paving material worldwide. However, different production conditions may lead to rubberized bitumens with different performances. This study aims to understand the mechanism of the physicochemical interaction between rubber particles and virgin bitumen of the rubberized bitumens prepared in the plant under various blending conditions. To achieve this objective, samples of the rubberized bitumens prepared in the plant under four conditions were first collected and then characterized through various laboratory tests. The infrared spectra and gel permeation chromatograph test results demonstrated that the main crosslinking structures of rubber remain stable and undamaged during the whole production period, although some chemical reactions—such as oxidation, decarboxylation, and devulcanization—occur. The storage stability test results implied that the plant-blended rubberized bitumen exhibits no obvious phase separation after storage at 163°C for 48 h and becomes more stable as the blending time prolongs. The rheological test results indicated that the rubber–bitumen interaction is mainly composed of early stage absorption and swelling of rubber particles, continuous emission of volatile bitumen components, and late-stage partial degradation of fully swollen rubber particles. The surface images of the rubberized bitumen confirmed that as the blending time increases, the surface of rubberized bitumen becomes smoother, as a result of the improved rubber–bitumen interaction.