To achieve warm-mix production of crumb rubber-modified asphalt (CRA), an organic warm-mix agent, a surfactant-based warm-mix agent, and a composite warm-mix agent were employed to prepare warm-mix CRA. The effects of warm-mix agents on the physical properties of CRA were evaluated using the penetration test, softening point test, viscosity test, ductility test, and elastic recovery test. The effects of warm-mix agents on the high- and low-temperature rheological properties were investigated through dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) tests. Moreover, the viscosity–temperature characteristics and the VOC emissions of different warm-mix CRAs were explored. The results show that Sasobit, an organic warm-mix agent, increases the elastic fraction and stiffness of CRA, which enhances its high-temperature resistance to permanent deformation but compromises its low-temperature cracking resistance. UWM, a surfactant-based warm-mix agent, elevates the viscous fraction and flexibility of CRA, which improves its low-temperature cracking resistance but weakens its high-temperature rutting resistance. The composite warm-mix agent, consisting of 2 wt.% Sasobit and 5 wt.% UWM, can balance the stiffness and flexibility of CRA, endowing CRA with satisfactory pavement performance. All three warm-mix agents effectively reduce the viscosity, mixing temperature, and VOC emissions of CRA. The composite warm-mix agent reduces the VOC emissions of CRA by 53.0%, exhibiting the most pronounced reduction.
Huang et al. (Mon,) studied this question.