Influence Of Warm Mix Agent On Performance Of Warm Mix Asphalt Binders

At home and abroad highway construction, the most widely used pavement material is hot mix asphalt. In the hot mix asphalt production, asphalt is heated from room temperature to140℃, aggregate and mineral powder is heated from room temperature to180℃, and then asphalt and mineral aggregate mixed in the high temperature of170℃, paving and rolling temperature reaches about150℃. Asphalt and aggregate heated to such high temperatures, not only to consume a large amount of energy, and emit large quantities of toxic gases in the construction process. Warm mix technology is by joining the warm mix agent, significantly reduce the mixing and paving temperature, mixing temperature is usually less than140℃. This method can reduce the energy consumption and harmful gas emission so as to avoid the environmental pollution in the road construction process. The key technology of WMA is the interaction of warm additive and asphalt. This process can reduce the viscosity of asphalt at high temperature, thereby increasing the fluidity of the asphalt mixture. In this paper, Rediset was used as warm mix additive to prepare warm mix asphalt cement, and its performance was evaluated.This article first characterized the thermal stability of Rediset through TG and DTG test. TG and DTG experimental results showed that the quality of the Rediset gradually reduced as the temperature increasing, but very slowly before150℃. This indicates that the thermal stability Rediset is very good when the temperature bellow150℃. Therefore, preparation of modified warm mix asphalt in the case of less than150℃will not affect the performance of Rediset.Second, two different methods were used to prepare warm mix asphalt cement. The first method is add the Rediset into hot asphalt directly and obtained through high-speed mixing. The second method is melt the Rediset before high-speed mixing.Then, the performance of warm mix asphalt cements were characterized through different methods. Dynamic shear rheometer (DSR) was used to evaluate the dynamic viscosity and rheological properties of the asphalt cement. Rolling Thin Film Oven simulated the short-term aging of warm mix asphalt cement. The dynamic viscosity results indicated that all samples with and without Rediset behaved like a Newtonian liquid at the temperature ranging of100℃-150℃. Rediset decreases the viscosity of the binders, especially at the range of100℃-150℃. The lower viscosity of the bitumen at higher temperatures results in a lower temperature for asphalt mixture during mixing and compaction. The addition of Rediset increases the complex modulus of the bitumen and decrease the phase angle of the bitumen in DSR frequency sweep test. This indicates that Rediset can improve deformation resistance at high temperatures during the service time.Last, in the RTFOT test at123℃, the softening point increment ratio of modified bitumen with Rediset is higher than that of base bitumen tested at the same temperature. This means that the reduction in viscosity by Rediset could negatively influence the short term ageing resistance of asphalt mixture. Because a lower viscosity of bitumen during mixing implies an easier contact with fresh air which may strengthen the aging on the bitumen.