Geopolymer as an additive of warm mix asphalt: Preparation and properties

Warm mix asphalt (WMA) has become a research focus in recent years, due to its benefits of saving energy and reducing CO₂ emission. The present work aims to prepare geopolymer as a novel additive for WMA. An orthogonal experiment was conducted to optimize the preparation process to attain porous geopolymer. Thermogravimetry (TG), scanning electron microscopy (SEM), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the prepared geopolymer. Conventional bitumen tests were carried out to evaluate the softening point, penetration, ductility and viscosity of bitumen with different dosages of geopolymer additives. It was proved that geopolymer is a promising additive for producing WMA with excellent performance and considerable benefits. The weight of released water could attain 11.47% at 135 °C. The SEM, XRD and FTIR results also showed that a large amount of pores were formed during the geopolymerization. In addition, the softening point of bitumen increased while the penetration and ductility decreased slightly with the addition of geopolymer. Furthermore, the prepared geopolymer could effectively decrease bitumen viscosity and thus reduce the mixing temperature. From a cost perspective the optimized dosage of geopolymer additive was 6% by weight of the bitumen and the optimum mixing temperature for WMA was around 140 °C.